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PLoS One. 2010; 5(4): e9954.
Published online 2010 April 1. doi:  10.1371/journal.pone.0009954
PMCID: PMC2848596

A Pair of Dopamine Neurons Target the D1-Like Dopamine Receptor DopR in the Central Complex to Promote Ethanol-Stimulated Locomotion in Drosophila

Mark A. Frye, Editor

Abstract

Dopamine is a mediator of the stimulant properties of drugs of abuse, including ethanol, in mammals and in the fruit fly Drosophila. The neural substrates for the stimulant actions of ethanol in flies are not known. We show that a subset of dopamine neurons and their targets, through the action of the D1-like dopamine receptor DopR, promote locomotor activation in response to acute ethanol exposure. A bilateral pair of dopaminergic neurons in the fly brain mediates the enhanced locomotor activity induced by ethanol exposure, and promotes locomotion when directly activated. These neurons project to the central complex ellipsoid body, a structure implicated in regulating motor behaviors. Ellipsoid body neurons are required for ethanol-induced locomotor activity and they express DopR. Elimination of DopR blunts the locomotor activating effects of ethanol, and this behavior can be restored by selective expression of DopR in the ellipsoid body. These data tie the activity of defined dopamine neurons to D1-like DopR-expressing neurons to form a neural circuit that governs acute responding to ethanol.

Introduction

Alcoholism is a major societal problem with great medical, financial and social costs. Environmental and genetic factors contribute to the susceptibility to alcoholism, and it is well established that the initial sensitivity of an individual to ethanol correlates with the likelihood of developing alcohol use disorders [1]. Similarly, breeding studies in rodents have identified positive correlations between the locomotor stimulant properties of acute ethanol exposure, a measure of ethanol sensitivity, and its reinforcing properties, suggesting that a genetic link for these traits may be evolutionarily conserved [2], [3]. Acute and repeated exposure to ethanol as well as to most other abused drugs increases dopamine (DA) levels in the mesolimbic region of the brain [4]; this brain region mediates many aspects of drug responding and reinforcement in a wide variety of behavioral paradigms [5]. For ethanol, mesolimbic DA is critically important for the regulation of drug sensitivity, consumption and preference [6][8]. Definition of the molecular, cellular, and neural circuit effects of acute ethanol exposure can provide a mechanistic understanding of how ethanol co-opts normal brain functions, and a foundation for understanding the complex shifts in behavior and physiology that underlie the development of addiction.

In the fruit fly Drosophila melanogaster, acute, repeated, and chronic exposure to ethanol, cocaine, or nicotine affects behavior in ways that appear similar to mammals [9]. Acute ethanol exposure stimulates locomotor activity at low doses, and promotes motor incoordination and sedation at higher doses [10], [11]. Repeated ethanol exposure results in sensitization to its locomotor activating effects and tolerance to its incoordinating and sedating effects [12][14], behavioral changes that can lead to increased ethanol intake in higher organisms. Moreover, flies show a preference for ethanol intake [15]. Importantly, DA signaling is critical for the actions of ethanol and cocaine in flies: disruption of DA signaling blunts the locomotor activating effects of ethanol, alters cocaine sensitivity, and decreases cocaine sensitization [16][18]. As in mammals, DA is also a pleiotropic modulator of behavior in flies, regulating arousal state, associative learning, and courtship behaviors [16], [19][24]. Understanding DA function at the molecular and circuit levels will help to define the relationships between these apparently distinct behaviors [25][28], and may provide insight into how drugs of abuse impinge upon natural behaviors.

The neuronal substrates for the effects of ethanol on behavior in Drosophila remain largely unknown. Defining the DA neurons that control ethanol-induced behaviors could provide a much needed entry point for future genetic and circuit analysis. In the fly brain approximately 140 DA neurons group into seven clusters in each hemisphere (Fig. 1D), and each DA neuron elaborates a complex projection that is stereotyped within a cluster [29], [30]. The connectivity and functional properties of the DA neurons are just beginning to be explored. The goal of this study was to determine if specific DA neurons and their targets in flies function in behavioral responses to acute ethanol exposure. Using genetic tools to inactivate or activate neurons, we identified a small set of DA neurons and their targets that promote locomotor stimulation by acute ethanol exposure. Additionally, we showed that the D1-like DA receptor DopR functions in the target neurons in the central complex, a brain region implicated in motor control. Our identification of specific DA and DA target neurons will allow detailed analysis, by genetic and other means, of circuit function in drug-induced and other behaviors, including those with rewarding properties. Moreover, circuit definition will help to place into context genes whose functions in drug abuse are less well understood.

Figure 1
Blockade of evoked release from dopaminergic neurons reduced ethanol-induced hyperactivity.

Results

Dopaminergic neurons promote ethanol-induced locomotor activity

Flies placed in a behavioral testing chamber acclimate within 10 min and subsequently maintain low levels of activity (see DopR mutant characterization results below for details) [11]. Upon exposure to a continuous stream of ethanol vapor, acclimated flies immediately enter into a transient olfactory-mediated startle response (Fig. 1A–B). Following a brief period of quiescence, flies then exhibit a more sustained period of enhanced locomotor activity, the hyperactive phase, achieving peak speeds at 10–12 min. As flies continue to accumulate ethanol internally, they become progressively more uncoordinated, decrease overall locomotion, and eventually become sedated. The peak of the hyperactive phase corresponds to an inebriating 15–30 mM internal ethanol concentration [11]. Sedated flies recover following the termination of ethanol exposure [12]. The magnitude of the hyperactive phase is dose-dependent, with lower concentrations of ethanol vapor resulting in higher levels of hyperactivity, due in part to reduced sedation [11].

We asked if blockade of evoked neurotransmitter release from DA neurons in the CNS affected ethanol-induced hyperactivity. To do this, we expressed in DA neurons the tetanus toxin light chain (TeTx) that cleaves and inactivates the neuronal-specific isoform of synaptobrevin, blocking synaptic transmission [31]. This was accomplished by driving expression of the UAS-TeTx transgene with TH-GAL4 that places the yeast transcriptional activator GAL4 under the control of the tyrosine hydroxylase (TH) locus [20], [31]. In TH/TeTx flies, ethanol-induced hyperactivity was reduced (Fig. 1A). Expression of catalytically inactive TeTx (IMP) had no effect, indicating that protein overexpression in TH neurons did not impinge upon neuron function. Determining the distance traveled during the onset of the hyperactive phase (2–12.5 min exposure) revealed a significant reduction in locomotor activity specifically in TH/TeTx flies (Fig. 1C). Similarly, locomotor speed achieved at 7.5 min of ethanol exposure was reduced in TH/TeTx flies (Table S1). However, using a higher resolution data analysis, we detected no change in the magnitude of the olfactory-mediated locomotor startle response of TH/TeTx flies (Fig. 1B). Additionally, locomotor coordination appeared normal in TH/TeTx flies, both by direct observation of fly movement, and in a negative geotaxis climbing assay, indicating that motor behaviors were grossly normal, and that at least one sensorimotor circuit was fully functional. Ethanol absorption was also unaffected (TH/TeTx: 38.3 mM, TH/IMP: 39.1 mM, 30 min at 47% ethanol vapor, P = 0.69, t-test, n = 3 groups of 25 flies each). Thus, blockade of evoked release from DA-producing neurons resulted in a specific decrease in the ethanol-induced stimulation of locomotor activity.

To confirm that disruption of DA neurotransmission was the basis for the observed ethanol-induced hyperactivity defect, we performed two additional experiments. First, the Drosophila DA transporter DAT is expressed in DA neurons, and flies mutant for DAT (DATfmn) have been characterized for their altered sleep-like behavior [22], [32]. Flies homozygous for DATfmn were viable, fertile, grossly normal for motor behaviors, and exhibited a normal olfactory startle response. Ethanol-induced hyperactivity, however, was markedly reduced in DATfmn flies (Fig. S1A), indicating that disruption of DA reuptake and of evoked release from DA neurons had similar effects. Second, we confirmed that DA depletion by pharmacological means in adult flies reduced ethanol-induced hyperactivity (Fig. S1B) [16]. Thus, the effects of genetic and pharmacological manipulation of DA levels are consistent with the promotion of ethanol-induced hyperactivity by DA signaling in adult animals.!

Role of PPM3 neurons in promoting ethanol-induced locomotor activity

We next asked whether DA signaling from many or a few neurons was required to promote ethanol-induced hyperactivity. As a first step, we built Dopa decarboxylase-GAL4 (Ddc-GAL4) transgenes that express GAL4 in subsets of TH- and 5-HT-positive neurons (Fig. S1C); Ddc executes the final step in DA synthesis and the locus is well characterized [33]. We then determined the behavioral effects of blocking evoked release in the patterns specified by the Ddc transgenes, and correlated the behavioral effects with expression in TH-positive neurons. Expression of TeTx with Ddc(HL7)-GAL4 resulted in decreased ethanol-induced hyperactivity, whereas expression with Ddc(HL5)-GAL4 did not (Fig. 1C, Fig. S1E,G). Previous studies demonstrated (and we confirmed) that TH-GAL4 fully labeled all TH-positive clusters in the adult brain, except for the PAMs where approximately 12 of 100 cells showed expression (Fig. 1D,E) [20], [29]. With Ddc(HL7)-GAL4, fewer TH-positive cells were labeled in the PAL, PPL1, PPL2, and PPM3 clusters (Fig. 1F, Fig. S1D). Ddc(HL5)-GAL4 expression was further restricted, with no expression detected in the PPL1 and PPM3 clusters (Fig. 1G, Fig. S1F). We also detected 1–2 fewer labeled cells in the PPL2 and PPM1/2 clusters in Ddc(HL5)-GAL4. In the thoracic ganglion, nearly all TH-positive neurons were labeled by Ddc(HL5)-GAL4 (Fig. S2A), indicating that thoracic DA neurons were not necessary to promote ethanol-induced hyperactivity. These data suggested that DA promotion of ethanol-induced hyperactivity was localized to specific subsets of DA neurons, or, alternatively, that activity in a substantial fraction of DA neurons was required for normal ethanol responses.

To test the possibility that discrete DA neurons regulated ethanol-induced hyperactivity, we searched for GAL4 transgenic lines that expressed specifically in the DA neurons present in Ddc(HL7)-GAL4 and absent in Ddc(HL5)-GAL4. One GAL4 line, c346, was expressed in two of the 6–8 TH-positive PPM3 neurons and in no other TH-positive neurons (Fig. 2A–C). c346 sparsely labeled other neurons in the adult CNS, including a subset of the mushroom body Kenyon cells, a group of cells located in the lateral protocerebrum that projected to the lobula of the optic lobe, and approximately 15–20 cells in the thoracic ganglion (Fig. S2B). The two TH-positive c346-expressing PPM3 cell bodies, located at the posterior surface of the brain, extended a fasciculated process anteriorly towards the central complex (Fig. 2B, Movie S1). The central complex includes four interconnected neuropils: the ellipsoid body, fan-shaped body, noduli, and the protocerebral bridge. Specific regions of the central complex are heavily innervated by dopaminergic processes [29], [30], [34]. The c346-labeled PPM3 processes branched at the central complex, and elaborated dense networks of processes in three regions: the central complex ellipsoid body ring and lateral triangles, and the ventral body region located ventral and lateral to the central complex.

Figure 2
TH-positive PPM3 neurons that project to the ellipsoid body promote ethanol-induced hyperactivity.

To confirm that PPM3 neurons innervated the ellipsoid body, we used the ‘flp-out’ technique to randomly label subsets of neurons in the TH-GAL4 expression pattern. All PPM3 neurons detected by this method innervated the central complex. Three distinct patterns of innervation were found: dense arborization in a discrete layer of the fan-shaped body either with or without additional arborization in the noduli (not shown), and dense arborization in the ellipsoid body ring and lateral triangles (Fig. 2D,E). This latter innervation pattern appeared identical to that observed in c346. These innervation patterns, also observed in a recent survey of DA neuron projection patterns [29], indicate that the PPM3 DA neurons make extensive connections in the central complex, and that c346 specifically labels PPM3 neurons that project to the ellipsoid body. We detected no innervation of the central complex by other TH-positive neurons. However, one PPL1 neuron has been reported to make an arborization in the fan-shaped body [29]. Ddc(HL7) but not Ddc(HL5) also showed expression in neurons that innervated the ellipsoid body, suggesting that Ddc(HL7) and c346 labeled the same subset of PPM3 neurons (Fig. S3).

Importantly, expression of TeTx but not IMP in the c346 pattern resulted in reduced ethanol-induced hyperactivity (Fig. 2F,G), indicating that evoked release from neurons in the c346 expression pattern regulated ethanol-induced hyperactivity, and suggesting that the dopaminergic PPM3 neurons may mediate this effect.

PPM3 neurons regulate locomotor activity

If DA release in a subset of DA neurons promotes ethanol-induced hyperactivity, then directly activating these neurons may also increase locomotor activity. To address this possibility, we expressed the heat-activated TrpA1 ion channel (UAS-TrpA1) in TH-GAL4 or c346 neurons, and assessed the behavioral effects of transient neuronal activation [35]. At 15°C, when TrpA1 is inactive, TH/TrpA1 flies showed low levels of locomotor activity (Fig. 2H). When the temperature was raised to 30°C, above the temperature required for TrpA1 activation, TH/TrpA1 flies increased locomotor activity levels, whereas control flies did not (Fig. 2H,I). Interestingly, returning TH/TrpA1 flies to 15°C almost immediately resulted in a cessation of locomotion. Moreover, repeated temperature cycling caused repeated cycling between states of inactivity and activity (not shown), suggesting that locomotor activity may be specified by continued signaling by DA neurons. These data indicated that acute activation of DA neurons promotes locomotor activity.

When TrpA1 was activated in c346-expressing neurons, flies also increased locomotor activity (Fig. 2I). Importantly, activation of neurons in the Ddc(HL5) pattern had no effect. Thus, the stimulation of locomotor activity by activation of either TH-GAL4 or c346 neurons was specific, and the subset of DA neurons labeled by the Ddc(HL5) transgene (PAL, PAM, PPL2, PPM1/2, Sb) could not be the sole source of a DA-dependent locomotor activation signal. To determine whether the stimulation of locomotor activity by c346 neurons was due to activation of the PPM3s, we included TH-GAL80 to block c346 GAL4 activity specifically in TH-expressing neurons. In c346;TH-GAL80/+;UAS-TrpA1/+ flies, no stimulation of locomotor activity was detected (Fig. 2I). These data indicate that the dopaminergic PPM3 neurons that project to the ellipsoid body ring and lateral triangle promote locomotor activity when stimulated.

Lastly, we asked whether increasing DAT levels in DA neurons affected locomotor activity. Overexpression of DAT in either the TH-GAL4 or the c346 pattern resulted in increased ethanol-induced hyperactivity (Fig. 2J,K), the opposite behavioral response as compared to the loss-of-function DATfmn mutants (Fig. S1A). Taken together, these data suggest that ethanol-induced stimulation of locomotor activity was due at least in part to DA signaling from PPM3 neurons that project to the ellipsoid body ring and lateral triangle region of the brain.

Central complex ellipsoid body neurons promote ethanol-induced locomotor activity

The central complex, the putative downstream target of the PPM3 DA neurons, plays multifaceted roles in the regulation of movement behaviors, including locomotion and flight (for review, see [36] and it has been implicated in the development of ethanol tolerance [14], [37]. To determine if the central complex contributes to ethanol-induced hyperactivity, we expressed TeTx in neuronal patterns dictated by a collection of 24 GAL4 driver lines that showed expression in discrete subsets of central complex neurons (CC-GAL4) (Table 1). The phenotypes of CC-GAL4/TeTx flies fell into four classes: non-viable, non-responsive (no startle or hyperactive phase), defective in ethanol-induced hyperactivity, and unaffected. There was no obvious correlation between TeTx-induced lethality and central complex expression pattern, suggesting that evoked release from the central complex is non-essential. Six of the seven non-responsive class CC-GAL4 lines expressed GAL4 either in the fan-shaped body or in small field neurons that connect different regions of the central complex. This finding is consistent with previous evidence for a role of the central complex in locomotion [38].

Table 1
Expression of TeTx in GAL4 patterns that include the central complex.

Four CC-GAL4 lines (4.67, 5.30, 11.148, and c819/c547) resulted in reduced ethanol-induced hyperactivity when crossed to TeTx (Fig. 3A, Fig. S4A–C). All four lines showed expression in the R2/R4 subset of ellipsoid body neurons (Fig. 3B–D, Fig. S4G,H). These lines also showed expression in other regions of the brain and in the thoracic ganglion (Fig. S2). However, we detected no clearly discernible overlap of expression outside of the ellipsoid body (see below). One line, 4.67, was also expressed in a subset of TH-positive neurons. Finally, eight CC-GAL4 lines showed no apparent behavioral defect when crossed to UAS-TeTx (Fig. 3A). Three of these eight lines (189Y, c232, c561) were expressed in ellipsoid body neurons belonging to the R1, R3, and R4d classes (Fig. 3E–G, Figure S4D–F). Taken together, these data demonstrate a strong correlation between blocking evoked release in ellipsoid body neurons of the R2/R4 class and reduced ethanol-induced hyperactivity.

Figure 3
Functional mapping of ellipsoid body neurons in ethanol-induced hyperactivity.

Other brain regions implicated in locomotor control or ethanol responses appear to be dispensable for the promotion of ethanol-induced hyperactivity. First, the mushroom bodies regulate overall locomotor activity levels, but not sensitivity to the incoordinating and sedating effects of ethanol [39], [40]. Similarly, we found that ethanol-induced hyperactivity was unaffected following chemical ablation of the mushroom bodies (Fig. S5). Furthermore, the GAL4 line 189Y was expressed in the mushroom bodies and showed no phenotype when crossed to TeTx (Fig. 3E) [41]. Finally, we were unable to rescue the ethanol hyperactivity phenotype of DopR mutants utilizing mushroom body GAL4 drivers (see below). These data suggest that the mushroom bodies are not involved or play a redundant role in ethanol-induced hyperactivity. Second, the thoracic ganglion contains sufficient circuitry for some motor programs, including coordinated locomotion [42], [43]. We exposed freshly decapitated flies to ethanol vapor to ask if ethanol directly stimulates thoracic ganglion locomotor circuits. Decapitated flies maintained the righting response and the ability to groom, and walked a few steps when prodded, indicating that thoracic ganglion circuitry was functional. However, ethanol exposure elicited no increase in locomotor activity (Fig. S2E). Finally, neurosecretory cells of the pars intercerebralis regulate ethanol sensitivity [44]. However, pars intercerebralis expression in the CC-GAL4 lines did not correlate with TeTx behavioral phenotypes in our experiments (Fig. 3D–F). Collectively, our findings are consistent with a model whereby evoked neuronal activity in specific regions of the central complex, most likely the R2 and/or R4 neurons of the ellipsoid body, promotes ethanol-induced hyperactivity.

D1-like DopR receptor is expressed in the ellipsoid body

The D1-like DA receptor DopR (DmDop1, dDA1) is present in the central complex and the mushroom bodies [27], [45]. To ask if DopR is present in the ellipsoid body, we first determined the expression pattern of a GAL4 enhancer trap, PL00420, that resides in the first intron of the DopR locus (see below). Brains labeled with PL00420/UAS-dHIP14tdTOM (preferentially labeling presynaptic sites of neurons [46]) showed robust expression in the central complex ellipsoid body ring, noduli, and fan shaped body (Fig. 4A,B). We also observed labeling of the mushroom bodies, subsets of antennal lobe glomeruli and other less well-defined regions of the protocerebrum. Furthermore, we stained brains of our genetic background control strain with antiserum raised against a peptide derived from the third intracellular loop of DopR (Fig. 4C–J). DopR protein was expressed in the ellipsoid body ring (Fig. 4C–E, arrowhead), fan shaped body, noduli (Fig. 4J), and mushroom bodies (Fig. 4I). These patterns were specific, as all immunostaining was dramatically reduced in DopR mutant flies that expressed very low levels of DopR transcript (see below) (Fig. 4K). Furthermore, DopR was present in both the ring and lateral triangles of the ellipsoid body, where DopR staining overlapped with neuronal processes of R2/R4 neurons labeled by 5.30-GAL4 (Fig. 4F–H). Finally, presynaptic terminals of the c346 PPM3 neurons required for ethanol-induced hyperactivity overlapped with or were closely apposed to DopR in the ellipsoid body and the lateral triangles (Fig. 4L–N). Thus, the D1-like DopR receptor is expressed in many structures throughout the adult brain, including the R2/R4 neurons of the ellipsoid body, and these neurons may be in synaptic contact with the PPM3 neurons.

Figure 4
The D1-like DA receptor DopR expression pattern in the adult brain includes the R neurons of the central complex ellipsoid body.

DopR is required for ethanol-induced hyperactivity

To ask if DopR contributes to ethanol-induced hyperactivity, we tested the effects reducing the levels of DopR. DopRf02676 is a transposon insertion allele tha thet dramatically reduces DopR protein levels [21] (Fig. 4K, 5A).5A). In agreement with this, we found that DopR transcript was reduced by 95% in the heads of flies homozygous for DopRf02676 (Fig. 5B). No compensatory changes were detected in transcript levels for the DA receptors DopR2 and D2R. Similar to the effects of blocking evoked neurotransmission from dopaminergic and ellipsoid body neurons, DopRf02676 mutants showed reduced ethanol-induced hyperactivity (Fig. 5C,D), and no change in ethanol sedation sensitivity (Fig. S6A) or ethanol absorption (DopRf02676: 35.2 mM, control: 36.3 mM, 30 min at 47% ethanol vapor, P = 0.66, t-test, n = 6). Precise excision of f02676 restored both DopR transcript levels and ethanol-induced hyperactivity levels to those of controls, indicating that the f02676 transposon insertion was responsible for the molecular and behavioral phenotypes (Fig. 5E, Fig. S6C). Flies homozygous for the PL00420 transposon insertion showed 30% reduced DopR transcript levels and reduced ethanol-induced hyperactivity (Fig. 5F, Fig. S6E). Moreover, either f02676 or the dumb1 inversion breakpoint allele of DopR placed in trans to a deficiency that deleted the DopR locus showed reduced ethanol-induced hyperactivity (Fig. 5G, Fig. S6G). Taken together, these data demonstrate that decreased levels of the DopR receptor resulted in reduced ethanol-induced hyperactivity. Because the effects of the DopR mutations on ethanol-induced locomotor activation were partial, other DA receptors may also play a role in this behavior.

Figure 5
Molecular and behavioral characterization of DopR mutants.

DopRf02676 mutants also showed increased activity prior to ethanol exposure (‘A’ in Fig. 5C). While opposite in sign, increased pre-exposure activity could influence the magnitude of the decrease in ethanol-induced hyperactivity in DopRf02676. To quantify this behavior, we recorded the locomotion of flies without an added stimulus (‘unstimulated activity’) (Fig. S6B). Immediately after being placed in the observation chamber, control flies showed moderate levels of activity (4.7 mm/sec), and they quickly acclimated to their environment, maintaining low levels of activity for at least 1 hr (1.2–2.5 mm/sec). DopRf02676 mutants showed higher initial levels of activity (8.6 mm/sec), and while DopRf02676 flies also acclimated, they maintained two-fold higher activity levels (4.9–5.3 mm/sec) (Fig. S6B). This phenotype was due to the f02676 insertion (Fig. S6D). However, unstimulated activity was unaffected in DopRPL00420 homozygotes (Fig. S6F). Moreover, we previously demonstrated a lack of correlation between pre-exposure locomotor activity and ethanol-induced hyperactivity levels [11]. Thus, flies with strongly reduced DopR levels showed increased unstimulated activity and this behavior could be dissociated from the role of DopR in ethanol-induced hyperactivity.

Ethanol tolerance is a form of acquired resistance that facilitates increased drug intake, a major risk factor for the development of alcohol use disorders [47]. The development of ethanol tolerance in flies involves central complex neurons and the ellipsoid body [14], [37]. We found that DopRf02676 mutants performed indistinguishably from genetic background controls in a rapid tolerance paradigm, showing both increased ethanol-induced hyperactivity and increased resistance to the sedating effects of ethanol during a second exposure to ethanol vapor (Fig. 5H–M). Thus, DopR is not required for rapid ethanol tolerance.

DopR functions in the ellipsoid body for ethanol-induced locomotor activity

Our data suggested that DopR may function in the ellipsoid body to promote ethanol-induced hyperactivity. To test this, we carried out genetic rescue experiments, supplying functional DopR to specific brain regions in animals otherwise lacking DopR. We took advantage of GAL4-binding sites (UAS elements) that are present in the f02676 transposon. Flies of the genotype Tub-GAL4/+; DopRf02676/+ that express GAL4 ubiquitously from the tubulin promoter showed an almost six-fold increase in DopR transcript levels. While the DopR transcript produced in these flies is expected to lack sequences encoded by the first exon, resulting in the loss of the predicted translation initiation site (Fig. 5A), in-frame methionines encoded in the second exon are likely to initiate translation [21]. Moreover, DopR lacking the long N-terminal extracellular region remains functional in cultured cells [48]. Finally, flies of the genotype 5.30-GAL4/+; DopRf02676/DopRf02676 showed selectively restored expression of DopR protein in the ellipsoid body ring and lateral triangles (Fig. 6B) indicating that DopR protein was generated and it localized to regions of the ellipsoid body where synaptic connections are likely to be made.

Figure 6
Genetic rescue of DopR mutant ethanol-induced hyperactivity by restricted expression of DopR in the ellipsoid body.

Selectively restoring expression of DopR in DopRf02676 mutants in patterns that included the R2/R4 class ellipsoid body neurons resulted in rescue of ethanol-induced hyperactivity (Fig. 6A, Fig. S7A,B), indicating that DopR expression in these neurons was sufficient for promotion of hyperactivity by ethanol. Restoring DopR expression in the R3 neurons of the ellipsoid body resulted in a modest but statistically insignificant increase in ethanol-induced hyperactivity with one driver (189Y, Fig. S6C) but not another (c232, Fig. S7D). As DopR is expressed broadly in the ellipsoid body (Fig. 4A,C), there may be an undetected overlap in expression patterns of the ellipsoid body GAL4 drivers, or there may be differences between the effects of blocking evoked neuronal output and restoring neuronal input. Importantly, restored expression of DopR in the mushroom bodies, where DopR is also normally expressed, did not rescue DopRf02676 ethanol-induced hyperactivity defects (Fig. 6A, Fig. S7E–F), demonstrating that DopR behavioral rescue in the ellipsoid body was specific. Overexpression of DopR did not increase ethanol-induced hyperactivity (Fig. S7G,H), indicating that the genetic rescue was due to restoration of normal DopR function. Thus, DopR expression in the ellipsoid body was sufficient for the promotion of ethanol-induced hyperactivity.

Discussion

DA regulates specific behavioral responses elicited by acute exposure to drugs of abuse in mammals and in flies. For low to moderate doses of ethanol, DA signaling is associated with euphoria (the subjective high), locomotor activation, and drug seeking. Our studies extend the understanding of the role of DA in ethanol responses in flies in three main ways. First, we identified specific DA (PPM3) and DA target (central complex ellipsoid body) neurons that promote locomotor activation by acute ethanol exposure. Second, we showed that the D1-like receptor DopR is required for promotion of locomotor activity elicited by acute ethanol exposure, and that its function for this role localized to the ellipsoid body. Importantly, DA signaling through DA D1 receptors also promotes locomotor activation by ethanol in mice [6], [49]. Finally, these DA and DA target neurons were dispensable for the olfactory startle response and negative geotaxis, indicating that the circuit regulating locomotor activation by ethanol is separable from at least some other locomotor activation circuits. Our findings allow us to propose a simple DA circuit: ethanol may act either directly or indirectly on PPM3 DA neurons, eliciting a DA locomotor activation signal that is received by DopR in the ellipsoid body, where presumably it is parsed to invoke an appropriate motor response.

Definition of specific behavioral roles for DA neurons

Silencing of nearly all DA neurons (TH-GAL4) or discrete subsets (Ddc(HL7)-GAL4 and c346) resulted in reduced ethanol-induced hyperactivity, whereas silencing of further restricted DA neuron subsets (Ddc(HL5)-GAL4) did not. Comparison of expression patterns for TH, Ddc(HL7) and Ddc(HL5) revealed a correlation between effects of TeTx and expression in the PPL1 and PPM3 DA neuron clusters, and a lack of correlation with other DA neuron clusters (Fig. 1). Assignment of promotion of ethanol-induced hyperactivity to the PPM3 neurons is based on the phenotypic effects of TeTx silencing of neurons in the c346 expression pattern, stimulation of locomotion by direct activation of DA neurons in the c346 pattern, and potentiation of ethanol-induced hyperactivity by overexpression of DAT in either TH or c346 neurons (Fig. 2). Neurons in the PPM3 cluster project to distinct yet highly stereotyped locations in the central complex and are the only DA neurons to target the ellipsoid body and lateral triangles. The c346 PPM3s project to the ellipsoid body and lateral triangles while other PPM3s project to the fan-shaped body and noduli (Fig. 2) [29]. Ddc(HL7), like c346, is expressed in a subset of PPM3 neurons (Fig. S1), that project to the ellipsoid body (Fig. S3, Movie S1). c346-negative PPM3 and the PPL1 neurons may also contribute to ethanol-induced hyperactivity and DA-dependent locomotor activation.

Specific DA-dependent behaviors may map to discrete sets of DA neurons. First, the projection patterns of DA neurons from different clusters are stereotyped and largely non-overlapping [29]. Second, associative olfactory learning is DA-dependent [21], [24], and requires a subset of DA neurons in the PPL1 cluster that project to the mushroom bodies [26]. We did not uncover a DA-dependent role for the mushroom bodies in ethanol-induced hyperactivity (Fig. 3,,6,6, Fig. S5), suggesting there exists a separation between DA-dependent locomotor activation and olfactory conditioning. Other DA-influenced behaviors in flies include courtship, arousal state, and a neural correlate of a visual perceptual response [19], [27], [50]. Identifying the DA-dependent neural circuitry for each behavior is likely to help define shared and distinct underlying mechanisms in behavioral control, and will be important for the accurate assessment of gene function in behavior.

What are the inputs and outputs for the PPM3 DA neurons that carry the ethanol locomotor activation signal? Presynaptically localized GFP in the PPM3s labeled the ellipsoid body lateral triangles and ring, suggesting that these are sites of DA release (Fig. 4L–N). Morphological analysis of ellipsoid body lateral triangle neurons suggests that this region is dense with dendrites [51], and functional localization of DopR to the ellipsoid body for ethanol-induced hyperactivity suggests that this region may be a synaptic target of the PPM3s. The neurons upstream of the PPM3s are not defined, but may include neurons in the central complex or in contact with the lateral processes that extend into the ventral body region (Fig. 2B,D). Consistent with this latter possibility, we found that postsynaptically targeted GFP expressed in the PPM3s localized primarily to these lateral processes (not shown). Neurons upstream of the PPM3s could encode information from sensory cues that elicit a locomotor response, including for example the chemical or visual perception of other flies, odors, or food. Alternatively, the PPM3s may function downstream of higher order processing circuits that encode previous experience or interoceptive cues such as satiation state [52]. Descriptions of synaptic connectivity outside of the well defined olfactory and visual circuits will be needed to better understand the dopaminergic control of locomotor activity.

Effects of DAT manipulation on ethanol behavioral responses

Reduced and increased DAT expression resulted in pronounced decreases and increases in ethanol-induced hyperactivity, respectively, helping to confirm that DA regulates ethanol-induced hyperactivity (Fig. S1A, 2K). The effect of loss of DAT on DA neurotransmission is likely to be quite complex, and may include increased dopamine tone, recruitment of extrasynaptic DA targets, depletion of readily releasable pools of DA, and compensatory changes in other dopamine signaling molecules. Similarly, increased DAT levels may affect any of these parameters. Acute ethanol exposure increases dopamine release in the nucleus accumbens that is accompanied by increased locomotor activity in mice [53]. To our knowledge, the effects of DAT knockout on ethanol stimulation of locomotion in mice is not known. However, a model in flies whereby ethanol-evoked release of dopamine in DAT mutants results in higher-than-normal extracellular DA levels does not fit in a simple manner with the reduced hyperactivity of DAT mutants seen in our experiments. A recent report showed that reuptake by the serotonin transporter was crucial for maintaining serotonin releasable pools in Drosophila, raising the possibility that a similar mechanism functions at dopaminergic synapses in flies [54]. Our finding that the maintenance of increased locomotor activity required continuous activation of TH neurons is consistent with this interpretation (Fig. 2H).

Role of the ellipsoid body in control of motor behavior and ethanol responses

The ellipsoid body is a prominent central neuropil that has been implicated in regulating unstimulated locomotor activity levels [55], the visual control of walking and flight [56][58], ethanol tolerance [37], and a persistent state of arousal induced by repeated mechanical stimulation [27]. Current findings suggest that specific motor behaviors may map to distinct neuronal classes within the ellipsoid body; for example, orientation during visually guided walking maps to the R1 or R3 neurons [57], [59], whereas ethanol-induced hyperactivity maps to the R2/R4 neurons (Fig. 3, ,6).6). While the specific inputs and outputs of the ellipsoid body are not yet known (with the exception of the DA input described here), the above findings, taken together with earlier structural and lesioning studies, have led to the hypothesis that the ellipsoid body may be involved in parsing information from various sensory modalities to engage the appropriate motor output [36]. Interestingly, DopR in the R2/R4 neurons also regulates arousal state [27]. However, while ellipsoid body-expressed DopR promotes locomotor activity induced by ethanol, it suppresses locomotor activity induced by repeated mechanical stimulation. Although alternative interpretations exist, these apparently opposite roles for DopR may suggest the integration of other sources of information to set the sign of dopamine signaling in the ellipsoid body with respect to motor output. Conceptually consistent with this idea, a previous study showed that DA neuron stimulation in low activity flies increased activity, whereas high activity flies showed the opposite response [60]. Additionally, the contribution to fly locomotor behaviors of other D1-class (DopR2/DAMB/DopR99B, DmDopEcR) and D2-class (D2R) dopamine receptors is largely unknown [61][64]. Pharmacological and gene knockout studies in rodents indicate that both D1-class and D2-class DA receptors regulate the locomotor stimulant effects of ethanol [65], [66].

The R2/R4 neurons of the ellipsoid body also regulate ethanol sedation sensitivity and sedation tolerance via a Homer protein-dependent mechanism [37]. Therefore, the ellipsoid body R2/R4 neurons regulate ethanol-induced locomotor activity in a DA-dependent fashion, and ethanol sedation sensitivity and tolerance in a Homer-dependent fashion. In mammals, DA and glutamate are thought to play distinct a roles in the nucleus accumbens for the behavioral effects of ethanol [67]. Dopaminergic neurons from the ventral tegmental area and glutamatergic neurons from cortical and other brain regions make synapses onto GABAergic medium spiny neurons in the nucleus accumbens where they regulate ethanol-induced locomotor activity (DA) and ethanol consumption and withdrawal (glutamate) [68]. It is of note that there are both GABAergic and glutamatergic neurons in the ellipsoid body [69], [70], and that a subset of R2/R4 neurons in the 5.30 and 11.148 GAL4 expression patterns are GABAergic (not shown). Thus, Drosophila may serve as a model to define some fundamental properties of neural circuit function as well as gene action that may be relevant to the actions of drugs of abuse in mammals.

Locomotor activation and reward

Selective breeding studies in rodents uncovered a positive correlation between the locomotor stimulant and reinforcing properties of ethanol [2], [3], and both properties of ethanol are mediated at least in part through the mesolimbic DA pathway [71], [72]. Moreover, human studies demonstrated a correlation between ethanol sensitivity and the propensity to develop alcohol use disorders [1]. The mesolimbic DA-dependent acute locomotor and reinforcing effects of cocaine, however, are genetically separable [73], [74], suggesting that DA can encode the acute and reward learning effects of at least some drugs of abuse in a complex manner. Our current findings show that there exists a DA circuit that mediates the locomotor stimulant properties of ethanol in flies. Application of learned reward-like behavior models for drugs of abuse and other stimuli to DA circuit analysis in flies will aid in understanding how this organism codes for complex DA-dependent behaviors.

Because DopR regulates arousal levels in a set of ellipsoid body neurons that overlap with those required for ethanol-induced hyperactivity [27], it is possible that ethanol-stimulated locomotion represents a form of arousal in flies. A proposed function for mesolimbic DA in mammals is to impart salience to increase the motivational state with regard to cues in the environment [4]. It will be important to determine whether locomotor activating stimuli other than ethanol also utilize this circuit, and to determine how ethanol interacts with other locomotor-activating cues that elicit approach and avoidance responses.

Materials and Methods

Genetics and Molecular Biology

All strains were outcrossed to the wild-type Berlin strain carrying the white (w1118) mutation (control) for 5–10 generations. DATfmn was followed molecularly during outcross by PCR with the upstream primer 5′-GCTGCTGGCCTATGCATCC and the downstream primers 5′-GCAATGCACCCATGTCGCC in the fmn lesion and 5′-ACTGGTTAACAAAGCATCC downstream of the fmn lesion. DopR locus lesions included f02676 (PBac{WH}), PL00420 (PBac{GAL4D,EYFP}), dumb1 (In(3LR)234) [21], and Df(3R)ED5634. Transposon marker genes are mini-w+ for f02676 and EYFP for PL00420. Some strains (2.70, 3.16, 4.13, 4.67, 4.69, 5.21, 5.30, 5.36, 6.61, 11.17, 11.32, 11.33, 11.113, 11.148, 12.30) were generated by mobilization of the GAL4-containing enhancer trap transposon P{GawB} to random integration sites in the genome. UAS-CD2-mCherry was a gift from Bing Ye, UAS-tdTomato-GFP-HIP14 was from Steve Stowers, and UAS-dTrpA1 was from Paul Garrity. TH-GAL4, UAS-TeTx (UAS-TeTxLC.tnt), UAS-IMP (UAS-TeTxLC.IMPTNT), and UAS-n-syb-eGFP were obtained from the Bloomington stock center. The P{GawB} strains 78Y, 189Y, c42, c107, c161, c232, c346, c561, and c819 were obtained from the Fly-trap project (www.fly-trap.org). To visualize individual neurons in the TH-GAL4 pattern, flies heterozygous for TH-GAL4, hs-Flp, and UAS >CD2, y+ >CD8-GFP were heat shocked at 37°C for 10–30 min during the first larval instar. Over 500 brains were analyzed. The transposon f02676 was excised utilizing standard genetic methods and was backcrossed for ten generations to f02676. DopR antisera was raised in rabbits against the peptide sequence CVAEKQRYKSIRRPKNQPKKFK derived from the intercellular loop region between transmembrane regions five and six, and affinity purified using the peptide (Covance, Denver, PA). Antisera specificity was verified by ELISA and immunostaining of DopRf02676 brains. The DopR open reading frame was isolated by PCR from the Berlin strain with the primers 5′-ATGTACACACCACACCCA and 5′-TCAAATCGCAGACACCTGC and cloned into pUAST to generate UAS-DopR.

Quantitative PCR was carried out according to the manufacturer's instructions (Applied Biosystems) on an ABI PRISM 7900 Sequence Detection System, using expression levels of RpL32 as a standard to normalize sample concentrations. The relative transcript expression levels were determined by comparison of mutant strains to the genetic background control. Taqman probesets (Applied Biosystems) used in this study were D2R: Dm01845573_g1, DopR: Dm02134814_m1, DopR2: Dm02151743_g1, and RpL32: Dm02151827_g1.

Construction of Ddc/GAL4 fusion genes

Numbering is relative to the Ddc transcription start site [75], and underlined letters represent Ddc exons. See Fig. S1C for diagrams of the constructs.

HL5-[DdcA/GAL4]

A fragment of Ddc from Bgl II at −2702 through a PCR-added BamHI site at +160 in exon A, was cloned upstream of GAL4 at a BamHI site of the pGaTB vector [76] to generate construct HL5 [DdcA/Gal4]. The 190 bp portion (−24 to +160) downstream of this Ddc fragment was a PCR product and isolated by digestion with NcoI and BamHI. The PCR fragment was generated using oligonucleotides: 5′-CGGTCCTGCGGAATTGGCAGCGCTGC sense primer for Ddc 5′ flanking : −67→−42, and 5′-CGCGGATCCGCGCACTTGTTGCCG antisense primer in Ddc exon A, adding BamHI at +158→146.

HL7-[DdcA/Gal4/DdcABCD]

To generate [DdcA/Gal4/DdcABC], Ddc sequences from exon A through exon D were subcloned downstream of the hsp70 polyA sequences in HL5. The Ddc HpaI fragment was isolated by restriction digestion of HpaI sites at +175 in exon A and at +3756 in exon D and, ligated downstream of hsp70 of the HL5 SpeI site. The SpeI site was immediately downstream of the Ddc/GAL4 insert. The 5′ protruding SpeI ends were blunted in order to ligate with the Ddc HpaI fragment. The [DdcAB/Gal4/Ddc3'end] and [DdcA/Gal4/DdcABCD] fragments in HL7 were subcloned into P-element transformation vector CaSpeR4 at the KpnI and SpeI sites, respectively.

The constructs in P-element CaSpeR4 vectors were purified using maxi-purification method (Qiagen Plasmid Kit). Transgenic lines were generated by microinjection of purified DNA into w1118 embryos [77], [78].

Immunohistochemistry

Brains dissected from 2–5 day old adult flies were fixed for 16 hr at 4°C in 2% paraformaldehyde in PBT (0.05% Triton X-100 in phosphate buffered saline). Primary and secondary antibodies were incubated with fixed tissue at 4°C for 48 hr each in 0.5% BSA and 5% normal goat serum in PBT, with extensive washes with PBT between steps. Images were collected on a Zeiss confocal microscope after mounting brains in Vectashield (Vector Laboratories). Confocal stacks were manipulated in ImageJ and Photoshop. Antibodies used were MAb 1D4 anti-FasII (1[ratio]40, Developmental Studies Hybridoma Bank, Iowa), rabbit anti-GFP (1[ratio]1000, Invitrogen), mouse anti-GFP (1[ratio]500, Zymed), rabbit anti-TH (1[ratio]100, Pel-Freez), and rabbit anti-DopR (1[ratio]1250).

Behavioral Analysis

Flies were maintained on a standard cornmeal/molasses/yeast media at 25°C and 70% humidity with an approximately 16hr/8hr light/dark schedule. For behavioral testing, 25 males and virgin females were mated in bottles with 50 mL standard media with a few added grains of Baker's yeast for 2 days, and groups of 23 male progeny were collected into standard food vials without yeast 11 days later. “n” indicates the number of groups of flies of a given genotype derived from independent parental crosses that were tested on separate days. Flies were allowed to recover from CO2 anesthesia for 2 days, and were tested behaviorally between 11 am and 6 pm. All behavioral tests, unless noted otherwise, were carried out at 25°C with constant illumination, utilizing the booz-o-mat, an eight-chambered manifold holding 16×125 mm cylindrical tubes [11]. Ethanol vapor was delivered to the booz-o-mat as a continuous stream by bubbling air separately through a 3L flask of 95% ethanol or water. Ethanol and humidified air streams were mixed at different ratios to a final flow rate of 5.5 L/min. Locomotor tracking analysis was as described previously [11]. Ethanol-induced hyperactivity was quantified as the area under the curve from 2–12.5 min exposure for 47% and from 2–10 min exposure for 60% ethanol vapor, corresponding to the time of hyperactivity onset to peak speed achieved for control flies at each concentration [13]. Hyperactivity was also quantified as the locomotor speed achieved at 7.5 min of ethanol exposure (Table S1). Unstimulated locomotor activity was measured in 60×90×10 mm chambers in constant light in the absence of food or humidified air, and was quantified as the area under the curve from 10–60 min. For TrpA1 activation tests, 10–20 male flies were placed in a thin-walled 30×50×2 mm Plexiglas chamber on the surface of a 96-well thermal cycler heat block (MJ Research) and were allowed to acclimate for 10 min at 15°C. They were filmed for 5 min at 15°C, 45 min at 30°C, and 5 min at 15°C. Locomotor activity was averaged over 15 sec every 2 min, and the distance traveled from 20–30 min at 30°C was calculated for statistical analysis. Statistical analyses were carried out in Minitab v.15 and Prism 4. Error bars in all figures indicate SEM.

Ethanol sedation kinetics and absorption

Groups of twenty genetically identical 2–4 day old adult male flies were exposed to 60% ethanol vapor in the booz-o-mat. At 5 min intervals the flies were agitated by rotating the tubes, and the number of flies that were unable to right themselves following a 10 sec recovery were counted. The average of 10 experiments from 5 days was determined. For ethanol tolerance, the number of flies sedated following 26 min exposure, approximately the time to 50% sedation for control flies, were counted. Ethanol absorption was measured by exposing groups of 25 flies to either ethanol vapor (47%) or humidified air for 30 min. Flies were immediately frozen on dry ice and the ethanol concentration in whole fly homogenates was measured with an alcohol dehydrogenase-based spectrophotometric assay (Diagnostic Chemicals, Ltd).

Supporting Information

Table S1

Locomotor speed achieved at 7.5 min ethanol exposure.

(0.06 MB PDF)

Figure S1

Regulation of ethanol-induced hyperactivity by dopamine (DA). A1. Reduced ethanol-induced hyperactivity in flies homozygous for the DAT DA transporter mutation fmn. A2. Distance traveled (2–12.5 min) is reduced in DATfmn (**P<0.0001, 2 sample t-test, n = 12). DATfmn was recessive for this phenotype. B. Pharmacological reduction of DA in adult flies reduced ethanol-induced hyperactivity. B1. Wild-type control (w- Berlin) flies were fed 10 mg/mL 3-iodotyrosine in 2% yeast/5% sucrose for 36–48 hr, and then exposed to 45% ethanol vapor. B2. Drug fed flies showed a reduction in distance traveled (**P = 0.0072, paired t-test. n = 10). C. Diagram depicting the Ddc-GAL4 transgenes used in this study. See Methods for construction details. D, F. Expression of Ddc(HL7)-GAL4 and Ddc(HL5)-GAL4 in TH-positive neurons. Posterior groups of TH-positive neurons (magenta) and GAL4-positive neurons expressing UAS-GFP (green) are shown. E, G. Locomotor activity profiles of flies expressing either TeTx or IMP in the Ddc(HL7) (E) and Ddc(HL5) (G) patterns and exposed to 47% ethanol vapor.

(7.19 MB TIF)

Figure S2

Role of the thoracic ganglion in ethanol-induced hyperactivity. A–D. Expression pattern of the indicated GAL4 transgenes (detected with UAS-GFP, green) in the adult thoracic ganglion, counterstained with TH antibodies (magenta). A. Ddc(HL5)-GAL4 is expressed in most TH-positive neurons in the thoracic ganglion. Positions of TH-positive cell bodies are indicated by arrowheads. No overlap was evident of GAL4 drivers c346, 5.30, and 11.148 with TH expression in the thoracic ganglion. E. Ethanol-induced locomotor activity (0–25 min) in freshly decapitated and matched unoperated controls. ‘A’ indicates locomotor speed in humidified air 1 min prior to ethanol exposure. The righting response and grooming activity were intact in decapitated flies just prior to ethanol exposure, indicating that the preparation was behaviorally responsive. n = 3.

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Figure S3

Expression of Ddc(HL7)-GAL4 and Ddc(HL5)-GAL4 (detected by UAS-GFP, green) in the ellipsoid body ring and lateral triangles, counterstained with TH antibodies (magenta).

(5.94 MB TIF)

Figure S4

A–F. Locomotor activity profiles for the functional mapping of ellipsoid body neurons in ethanol-induced hyperactivity. Flies of the indicated genotypes were exposed to 47% ethanol vapor (open box on horizontal axis). GAL4 lines are indicated on each graph. G,H. Expression of the indicated GAL4 lines in R2/R4 neurons of the ellipsoid body (arrowhead), detected by GFP expression and counterstained with anti-Bruchpilot (nc82) to highlight the synaptic neuropil. I. Higher resolution analysis of startle magnitude for the GAL4 lines expressed in the R2/R4 neurons, corrected for pre-exposure locomotor activity levels. For 5.30 and 11.148, the olfactory startle responses were unaffected by TeTx expression (5.30: P = 0.4403, 11.148: P = 0.0556, 1 way ANOVA, n≥5). For c819, c819/+;UAS-IMP/+ was reduced (P = 0.0194, 1 way ANOVA, Tukey's multiple comparison test, n≥3).

(5.76 MB TIF)

Figure S5

Mushroom body ablation. A. Ethanol-induced hyperactivity at 60% ethanol vapor with (+HU) and without (-HU) hydroxyurea treatment. Distance traveled 2–12.5 min did not differ (P = 0.0861, paired t-test, n = 4). B, C. Brains from control and HU treated flies, stained with anti-FasII to highlight the mushroom bodies (arrowheads) and the central complex ellipsoid body (arrow), which is unaffected by HU treatment.

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Figure S6

DopR mutant behavioral characterization. A. Ethanol-induced sedation was unaffected in f02676 homozygotes, measured as the loss of the ability to right. (60% ethanol vapor, P = 0.0945, 2 sample t-test, n = 10). B. Unstimulated locomotor activity, measured for 60 min immediately after flies were introduced into a 60×90×10mm Plexiglas box. DopRf02676 showed higher activity (distance traveled 10–60 min, P = 0.0009, 2 sample t-test, n = 10). C, D. Precise excision of f02676 reverts ethanol-induced hyperactivity and unstimulated activity behavioral phenotypes. C. Ethanol-induced hyperactivity for the genetic background control, f02676 homozygotes, and two independent precise excisions of f02676 (Ex1 and Ex2). D. Unstimulated activity for the same strains. Distance traveled from 10–60 min showed that f02676 is different from all other genotypes (P<0.001, 1 way ANOVA, Tukey's multiple comparison test, n = 5). E. Ethanol-induced hyperactivity in animals homozygous for PL00420. F. Unstimulated activity was unaffected in PL00420 homozygotes. G. Non-complementation for ethanol-induced hyperactivity by DfED5634, a deficiency that deletes the entire DopR locus, for f02676 and the dumb1 inversion allele.

(0.65 MB TIF)

Figure S7

A–F. Locomotor activity profiles for the genetic rescue of the DopRf02676 mutant ethanol-induced hyperactivity phenotype. G. Expression of DopR utilizing the UAS sites in f02676 or a UAS-DopR transgene has no effect on ethanol-induced hyperactivity in flies that are either wild-type or heterozygous for DopR (left group: P = 0.7842, 1 way ANOVA, n = 8, right group: P = 0.575, 1 way ANOVA, n = 5). H. Increased DopR transcript levels when UAS-DopR is combined with the pan-neuronal elav-GAL4 (**P = 0.0062, 1 way ANOVA, Tukey's multiple comparison test, n = 3).

(0.79 MB TIF)

Movie S1

PPM3 neurons labeled by c346, detected by UAS-CD8-GFP, confocal stack reconstruction.

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Acknowledgments

We thank Karen Berger for the inebriometer tolerance assay, Viktor Kharazia, Elizabeth Marin, and Liqun Luo for assistance with fly brain imaging, Willa Abrone for technical assistance, David Anderson for support and advice, Bing Ye and Steve Stowers for reagents, the Bloomington and Harvard Drosophila stock centers for strains.

Footnotes

Competing Interests: The authors have declared that no competing interests exist.

Funding: Funding for this research was provided by United States National Institutes of Health grant AA014594-04 (FWW), GM27318 (JH), DA19573 (UH), and GM081863-03 (RJB). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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