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Tricyclic antidepressant (TCA) drugs are used for the treatment of chronic depression, obsessive compulsive disorder (OCD), and anxiety-related disorders. Chronic use of TCA drugs increases the expression of α1-adrenergic receptors (α1-ARs). Yet, it is unclear whether increased α1-AR expression contributes to the antidepressant effects of these drugs or if this effect is unrelated to their therapeutic benefit. In this study, mice expressing constitutively active mutant α1A-ARs (CAM α1A-AR) or CAM α1B-ARs were used to examine the effects of α1A- and α1B-AR signaling on rodent behavioral models of depression, OCD, and anxiety. CAM α1A-AR mice, but not CAM α1B-AR mice, exhibited antidepressant-like behavior in the tail suspension test and forced swim test. This behavior was reversed by prazosin, a selective α1-AR inverse agonist, and mimicked by chronically treating wild type mice with cirazoline, an α1A-AR agonist. Marble burying behavior, commonly used to model OCD in rodents, was significantly decreased in CAM α1A-AR mice but not in CAM α1B-AR mice. In contrast, no significant differences in anxiety-related behavior were observed between wild type, CAM α1A-AR, and CAM α1B-AR animals in the elevated plus maze and light/dark box. This is the first study to demonstrate that α1A- and α1B-ARs differentially modulate antidepressant-like behavior in the mouse. These data suggest that α1A-ARs may be a useful therapeutic target for the treatment of depression.
Epinephrine and norepinephrine are important modulators of animal behavior. These catecholamines mediate the “fight or flight” response to an imminent threat, participate in the regulation of mood, regulate feeding behavior, and modulate cognitive function, (see reviews by Elhwuegi, 2004; Wellman and Davies, 1991; Lapiz and Morilak, 2006). Abnormalities in adrenergic signaling in the brain are associated with a variety of behavioral pathologies including clinical depression, motor dysfunction, loss of memory, anxiety, and post-traumatic stress disorder (Murchison et al., 2004; Rommelfanger et al., 2007; Dierks et al., 2007). Drugs that inhibit the reuptake or metabolism of norepinephrine and other catecholamines in the central nervous system are widely used in the treatment of depression, obsessive compulsive disorder (OCD), and narcolepsy.
Depression is characterized by subjective feelings of hopelessness, loss of interest in pleasurable activities, sleep disturbances, and fatigue. Evidence from both clinical studies and animal models indicates that adrenergic signaling modulates mood and depression-related behavior. For example, early research showed that the antidepressant efficacy of tricyclic antidepressants (TCA) such as imipramine correlated with inhibition of norepinephrine reuptake (Glowinski and Axelrod, 1964). In addition, selective inhibitors of the norepinephrine transporter such as desipramine and reboxetine exhibit robust antidepressant activity with similar efficacy as that reported for serotonin-selective reuptake inhibitors (SSRIs) when given to patients with major depressive disorder (Bowden et al., 1993; Roth et al., 1990; Nelson, 1999). More recent meta-analysis studies suggest that antidepressants with mixed serotonin-noradrenergic reuptake inhibitor (SNRI) activity may offer therapeutic advantages to treatment with SSRIs alone (Machado et al., 2006; Papakostas et al., 2007, reviewed by Shelton 2004). However, the roles of individual adrenergic receptor (AR) subtypes in modulating depression-related behavior are not well characterized.
The effects of epinephrine and norepinephrine are mediated by adrenergic receptors (ARs). Nine different AR subtypes (α1A-, α1B-, α1D-, α2A-, α2B-, α2C, β1-, β2-, β3-AR) have been cloned and characterized (see review by Strosberg, 1993), and they differ in their amino acid sequences, ligand binding properties, tissue distribution, and coupling to signal transduction pathways. Stone and Quartermain (1999) reported that α1-AR blockade in the central nervous system induces depression-related behavior in mouse models of depression. In addition, previous studies have reported that administration of TCA drugs increases the density of α1-ARs in the forebrain, hippocampus, and cerebral cortex of mice and rats (Deupree et al., 2007; Rehavi et al., 1980) and that α1-ARs in dorsal lateral geniculate neurons, the facial nucleus, and other brain regions become supersensitized following chronic administration of TCA drugs (Menkes and Aghajanian, 1981; Menkes et al., 1983). In contrast, α2-ARs and β-ARs are downregulated by chronic use of TCA drugs (Deupree et al., 2007; Subhash et al., 2003). However, it has been unclear whether these changes in AR expression and sensitivity actually contribute to the antidepressant effect of these drugs or are only ancillary effects that are not involved in the antidepressant action of TCA drugs. The goal of this study was to investigate the effects of α1A- and α1B-AR signaling on antidepressant-like behavior of the mouse.
The currently available α1-AR ligands are not sufficiently selective for individual α1-AR subtypes in vivo to conclusively determine which subtypes modulate behavior. Therefore, we used transgenic mice that express either constitutively active mutant (CAM) α1A- or CAM α1B-ARs (Rorabaugh et al., 2005a) in addition to the endogenous α1A- and α1B-ARs. These mice selectively express CAM α1A- or CAM α1B-ARs only in tissues that normally express the respective wild type receptors (Rorabaugh et al., 2005b; Zuscik et al., 2000). Brains of CAM α1A-AR and CAM α1B-AR mice exhibit a 3-fold and 4.5-fold increase, respectively, in basal inositol-1,4,5-triphosphate production relative to wild type mouse brains, confirming their constitutive activity in vivo (Rorabaugh et al., 2005a; Zuscik et al., 2000). These mice provide a unique tool to investigate the chronic effects of signaling through the α1A- and α1B-AR receptors without the need for subtype-selective drugs.
It has been recently reported that neurogenesis is enhanced in CAM α1A-AR mice (relative to wild type mice) and that this effect can be mimicked by chronically treating wild type mice with cirazoline, an α1A-AR agonist (Gupta et al., 2009). In contrast, CAM α1B-AR signaling induces neurodegeneration (Zuscik et al., 2000). Since several different types of chronic antidepressant therapies are known to induce neurogenesis (Malberg et al., 2000), we investigated the effects of α1A- and α1B-AR signaling on depression-related behavior. Our data provide evidence that α1A-AR signaling, but not α1B-AR signaling, produces antidepressant-like behavior in the mouse.
The tail suspension test (TST) is a well established model for the characterization of antidepressant-like behavior (Cryan et al., 2005). We used the TST to determine whether chronically elevated α1A- or α1B-AR signaling promotes antidepressant-like behavior. CAM α1A-AR mice were immobile for significantly less time (44 ± 13 sec) than wild type mice (128 ± 16 sec), suggesting that α1A-AR signaling promotes antidepressant-like behavior (Fig. 1A). In contrast, immobility was slightly increased in CAM α1B-AR mice suggesting that CAM α1B-AR signaling promotes prodepressant-like behavior.
The forced swim test (FST) was used as a second measure of antidepressant-like behavior. CAM α1A-AR mice exhibited significantly less immobility than wild type mice in the FST (Fig. 1B). In contrast, CAM α1B-AR mice exhibited greater immobility than wild type animals. These data are consistent with our observations in the TST, and they further support the conclusion that signaling through α1A-ARs, but not α1B-ARs, promotes antidepressant-like behavior in the mouse.
Locomotor activity of wild type and transgenic mice was measured in an open field to determine whether the differences observed in the TST and FST represent antidepressant/prodepressant-like behavior or are caused by differences in spontaneous motor activity. The distance that CAM α1A-AR mice traveled in the open field was not significantly different from that of wild type mice (Fig. 1C). CAM α1B-AR mice exhibited significantly greater locomotor activity than wild type mice (Fig. 1C) in spite of the fact that they showed increased immobility in the TST and FST. These data suggest that differences in immobility observed between the wild type, CAM α1A-AR, and CAM α1B-AR mice in the TST and FST were not due to generalized differences in spontaneous motility.
Since an antidepressant-like phenotype was observed in mice expressing CAM α1A-ARs, we hypothesized that this behavior could be blocked by treating CAM α1A-AR mice with an inverse agonist and that this behavior could be mimicked by treating wild type mice with an α1A-AR agonist. We used prazosin, an inverse agonist at constitutively active α1-ARs (Zhu et al., 2000), to determine whether the antidepressant-like phenotype of CAM α1A-AR mice could be reversed. Intraperitoneal injection of prazosin (0.2 mg/kg) 30 min prior to the TST completely reversed the decreased immobility of CAM α1A-AR mice but had no effect on the immobility of wild type mice (Fig. 2A). We also investigated the effects of chronic cirazoline treatment of wild type mice. This agonist was used because it has 5 to 8-fold greater affinity for the α1A-AR over the α1B- and α1D-AR subtypes, respectively (Horie et al., 1995). In addition, cirazoline is a full agonist at α1A-ARs (Emax = 99% of norepinephrine’s Emax) and only a partial agonist at α1B- and α1D-ARs (Emax is approximately 50% for α1B- and α1D-ARs, relative to norepinephrine) (Horie et al., 1995). Mice treated with cirazoline exhibited significantly decreased immobility in the TST compared to control mice that were not treated with cirazoline (Fig. 2B). Thus, the antidepressant-like phenotype observed in CAM α1A-AR mice is mimicked by treating wild type mice with an α1A-AR agonist. Taken together, these data provide further evidence that the antidepressant-like behavior of CAM α1A-AR mice in the TST is the result of increased α1A-AR signaling.
Previous work has demonstrated that serotonin-norepinephrine reuptake inhibitors that are used for antidepressant pharmacotherapy are also effective in the treatment of OCD (Dell’Osso et al., 2006). Marble burying behavior is commonly used as a model of OCD in mice (see review by Witkin, 2008). Since CAM α1A-AR mice exhibited antidepressant-like behavior in the TST and FST, we next examined their behavior in the marble burying assay. CAM α1A-AR mice buried significantly fewer marbles (7.1 ± 1.4) than wild type mice (10.9 ± 0.6) (Fig. 3A). In addition, wild type mice that were chronically treated with cirazoline buried fewer marbles than age matched wild type mice that were not treated with cirazoline (Fig. 3B). Thus, the phenotype observed in the CAM α1A-AR mice can be mimicked by treating wild type mice with an α1A-AR agonist. CAM α1B-AR mice also buried fewer marbles (8.9 ± 0.5) than wild type mice (Fig. 3A), but this difference was not statistically significant. In light of previous studies demonstrating that drugs that reduce marble burying activity in mice are clinically effective in the treatment of OCD (Witkin et al., 2008), our data suggest that the α1A-AR might be a useful therapeutic target for the clinical treatment of OCD.
The comorbidity of depression and anxiety is well established, and antidepressant drugs such as tricyclic antidepressants, norepinephrine-selective reuptake inhibitors, and serotonin-selective reuptake inhibitors are clinically used for the chronic treatment of anxiety-related disorders. Therefore, we hypothesized that CAM α1A-AR mice which exhibit antidepressant-like behavior in the TST and FST, may exhibit decreased anxiety-related behavior and that CAM α1B-AR mice (which exhibit prodepressant-like behavior in the TST and FST) may exhibit increased anxiety-related behavior.
The elevated plus maze was used to determine whether α1A-AR signaling affects anxiety. Mice treated with anxiolytic drugs, such as benzodiazepines, spend more time in the open arms of the maze and less time in the closed arms (Walf and Frye, 2007). Both CAM α1A-AR mice and CAM α1B-AR mice spent slightly less time in the open arms and slightly more time in the closed arms compared to wild type mice. However, these differences were not statistically significant (Fig. 4A). Consistent with these results, cirazoline-treated wild type mice spent slightly less time in the open arms and slightly more time in the closed arms compared to age matched wild type animals that were not treated with cirazoline (Fig. 4B).
Light/dark exploration was also used to measure anxiety related behavior. This test is useful because drugs that decrease the amount of time that mice spend in the dark compartment of the box often have anxiolytic effects in humans. We found no differences between CAM α1A-AR mice, CAM α1B-AR mice, or wild type mice with regard to the amount of time that they spent in the dark compartment (Fig. 4C) or the number of entries into the dark compartment (Fig. 4D). In addition, cirazoline had no effect on the amount of time that wild type mice spent in the dark compartment (Fig. 4E) or the number of entries into the dark compartment (Fig. 4F). Taken together, the data from the elevated plus maze and the light/dark box suggest that α1A-AR and α1B-AR signaling do not significantly influence basal levels of anxiety related behavior in the mouse.
The involvement of norepinephrine in the modulation of antidepressant behavior is well established, and drugs that increase synaptic norepinephrine concentrations by inhibiting norepinephrine reuptake from the synaptic cleft have become important in the treatment of clinical depression. Previous work has demonstrated that α1-ARs are involved in the antidepressant effects of norepinephrine (Stone and Quartermain, 1999), but the ability of individual α1-AR subtypes to mediate this antidepressant effect is not well understood. In the present study, we used a unique transgenic mouse model to determine how α1A- and α1B-AR signaling influences antidepressant-like behavior in the mouse. This is the first study to demonstrate that α1A- and α1B-ARs differentially modulate antidepressant-like behavior.
The therapeutic benefit of TCA drugs is typically delayed several weeks following the initiation of drug therapy. This delay is thought to result from changes in the expression of adrenergic and serotonergic receptors in the brain. Previous studies have demonstrated that chronic use of the TCA, imipramine, increases expression of α1-ARs in the forebrain, hippocampus, and cerebral cortex (Rehavi et al., 1980; Deupree et al., 2007). Nalepa et al. (2002) reported that imipramine or electroconvulsive shock therapy increased the presence of mRNA encoding α1A-ARs, but not α1B-ARs, in the cerebral cortex. However, it has been unclear whether upregulation of α1A-AR expression is directly involved in the antidepressant effect of norepinephrine reuptake inhibitors or is only an ancillary effect that has no role in mediating antidepressant behavior. Our discovery that α1A-AR signaling promotes antidepressant-like behavior in the TST and FST suggests that increased α1A-AR expression following chronic use of norepinephrine-related antidepressants or electroconvulsive shock may play an important role in mediating the antidepressant effects of these therapies.
Previous work has demonstrated that chronic antidepressant therapies including electroconvulsant shock, fluoxetine, tranylcypromine, and reboxetine induce hippocampal neurogenesis (Malberg et al., 2000). Although the mechanism by which α1A-AR signaling promotes antidepressant-like behavior was not characterized in this investigation, recent studies have demonstrated that CAM α1A-AR expression promotes neurogenesis in the mouse (Gupta et al., 2009) and that neurogenesis is also enhanced by chronically treating wild type mice with the α1A-AR agonist, cirazoline (Gupta et al., 2009). In contrast, α1B-AR signaling causes neurodegeneration (Zuscik et al., 2000). Thus, it is quite possible that the antidepressant-like behavior in CAM α1A-AR mice is associated with enhanced neurogenesis, while the prodepressant-like behavior of CAM α1B-AR mice is caused by neurodegeneration. Further work is needed to determine whether there is a causal relationship between neurogenesis and α1A-AR-induced antidepressant-like behavior in these animals as well as the mechanisms involved.
Tricyclic antidepressants and serotonin-norepinephrine reuptake inhibitors that are used clinically to treat depression are also efficacious in the treatment of some patients with OCD (Dell’Osso et al., 2006). Marble burying has been used as a rodent model of OCD (see review by Witkin et al., 2008). In the present study, we found that CAM α1A-AR mice, which exhibit antidepressant-like behavior in the TST and FST, also exhibit decreased marble burying activity. A role for α1A-ARs in the regulation of marble burying behavior is also supported by the observation that marble burying activity was decreased in wild type mice that were chronically treated with cirazoline (Fig. 4B). These data are consistent with the work of Sugimoto et al. (2007) who reported that milnacipran, a serotonin-norepinephrine reuptake inhibitor, decreased marble burying activity in mice. Sugimoto et al. (2007) proposed that the milnacipran-induced decrease in marble burying behavior was caused by enhanced serotonin signaling rather than enhanced adrenergic signaling. However, more recent work has demonstrated that obsessive compulsive-like behavior is also inhibited by reboxetine, a selective inhibitor of norepinephrine reuptake (Weber et al., 2009). Our data suggest that adrenergic signaling reduces obsessive compulsive-like behavior and that this effect is influenced by α1-ARs.
α1A – and α1B-ARs are both Gq coupled receptors, and there is significant overlap in the distribution of these receptors in the amygdala, cerebellum, hindbrain, cerebral cortex, and other brain regions (Papay et al., 2006; Day et al., 1997). Despite similarities in their signaling pathways and tissue distributions, there is mounting evidence that the functions of these receptors are not redundant. Studies using transfected cells and isolated tissues have demonstrated that α1A- and α1B-AR subtypes activate divergent signaling pathways that result in different patterns of gene expression and different physiological responses. For example, Gonzalez-Cabrera et al. (2003) found that α1A-AR signaling induces cell cycle arrest in Rat-1 fibroblasts by decreasing the expression of cyclin dependent kinase 6 and increasing the expression of cyclin dependent kinase inhibitor p27. In contrast, α1B-AR signaling induces progression of these cells through the cell cycle (Gonzalez-Cabrera et al., 2003). α1A- and α1B-ARs are also coupled to different signaling pathways in the heart where α1A-ARs, but not α1B-ARs, protect the heart from ischemic injury (Rorabaugh et al., 2005a). Cardiac α1A- and α1B-ARs also differ in their ability to activate pertussis toxin-sensitive signaling pathways that modulate cardiac inotropy (Rorabaugh et al., 2005b). The observation that α1A-AR signaling and α1B-AR signaling differentially modulate behavior in the TST and FST provides further evidence that these α1-AR subtypes have separate and distinct functions in the central nervous system despite similarities in their anatomical distribution within the brain.
α1A- and α1B–ARs are coexpressed in several brain regions that are known to modulate anxiety-like behavior including the amygdala, hippocampus, prefrontal cortex, and paraventricular nuclei of the hypothalamus (Papay et al., 2006). Several clinical studies have demonstrated that prazosin decreases psychological distress, nightmares, and other anxiety-related symptoms in patients who have post-traumatic stress disorder (PTSD) (Peskind et al., 2003; Raskind et al., 2003), and α1-AR stimulation also promotes anxiety-related behavior in rats (Handley and Mithani, 1984). These data demonstrate that the anxiety-related symptoms of PTSD are influenced by α1-ARs. Thus, we were somewhat surprised that anxiety-related behavior was not increased by genetic or pharmacological enhancement of α1-AR signaling in this study. One limitation of our work is that we only analyzed behavioral indicators of anxiety under basal conditions in which the animals were not subjected to stressful stimuli other than the minimal handling necessary to conduct the experiments. Further work is ongoing to determine whether α1A-or α1B-AR signaling influences anxiety-related behavior in mice subjected to a traumatic event or in mice that have been conditioned to anticipate stress.
In summary, this is the first study to provide direct evidence that α1A- and α1B-ARs are differentially coupled to antidepressant-like behavior in the mouse. Our data further suggest that the α1A-AR subtype may play an important role in mediating the therapeutic effects of TCA drugs that are clinically used in the treatment of depression and OCD. Furthermore, these results suggest a possible role for selective α1A-AR agonists as a novel treatment for depression.
B6/CBA mice expressing a constitutively active mutant (CAM) α1A-AR, B6/CBA mice expressing a CAM α1B-AR, and wild type B6/CBA mice were generously donated by Dr. Dianne M. Perez (Cleveland Clinic Foundation, Cleveland, OH). These transgenic mice express constitutively active forms of the α1A- or α1B-ARs in addition to the endogenous wild type α1-ARs. Generation and genotyping of these mice has been previously described (Rorabaugh et al., 2005a; Zuscik et al., 2000). Briefly, tissue-specific distribution of the CAM α1A- or CAM α1B-AR was achieved by using the mouse α1A- or α1B-AR promoters to regulate expression of cDNA that encodes a CAM form of the α1A- or α1B-AR, respectively. Approximately 200 copies of the CAM α1A-AR or CAM α1B-AR transgene were injected into the pronuclei of one cell B6/CBA mouse embryos which were implanted into pseudopregnant female mice. Founder mice were identified and subsequent generations were genotyped by southern analysis or polymerase chain reaction using genomic DNA as the template. Tissue-specific distribution of the CAM α1A- and CAM α1B-ARs was confirmed by saturation binding assays with the α1-AR selective radioligand 2-[β-(4hydroxy-3-[125-I]iodophenyl)ethylaminomethyl]tetralone ([125I]-HEAT) (Rorabaugh et al., 2005a; Zuscik et al., 2000). Constitutive activity of these receptors in the mouse brain and other tissues was determined by measuring basal levels of inositol 1,4,5-trisphosphate production (Rorabaugh et al., 2005a; Zuscik et al., 2000).
Mice were housed with a 12/12 hour light/dark cycle (lights on 0700 – 1900 hours), and all experiments were performed 1200 – 1600 hours. Age matched wild type (n = 84), CAM α1A-AR (n = 98), and CAM α1B-AR (n = 62) mice ages 2 – 6 months were used for all experiments except for mice that were chronically treated with cirazoline, an agonist with 5 to 8-fold selectivity for the α1A-AR versus the α1B- and α1D-ARs, respectively (Horie et al., 1995). Cirazoline-treated mice (n = 20) were continuously administered cirazoline in their drinking water (40 μM) for 9 months starting at the time of weaning and continuing until these experiments were performed. Chronic treatment with cirazoline has been shown to enhance neurogenesis in the mouse (Gupta et al., 2009). Age-matched wild type animals (n = 20) that were not treated with cirazoline were used as a control group for cirazoline-treated animals. Some cirazoline-treated animals were used for multiple experiments.
Approximately equal numbers of male and female mice were used in each experimental group, and no behavioral differences were observed between the two sexes. Food and water were available ad libitum. Animal procedures were approved by the Institutional Animal Care and Use Committee of Ohio Northern University and the University of North Dakota. All experiments using cirazoline treated mice and their age-matched nontreated controls were performed at the University of North Dakota. All other experiments (except elevated plus maze) were performed at Ohio Northern University.
The tail suspension test was used to measure antidepressant-like behavior. Mice were individually suspended by the tail from a horizontal bar located 42 cm above the bench top using adhesive tape. Each mouse was suspended for 6 min and recorded with a digital video camera. The amount of time that each mouse remained immobile was later measured by an observer who was blinded to the experimental treatment and mouse genotype.
The forced swim test was used as an additional measure of antidepressant-like behavior. Mice were given a 15 min pre-swim in a glass cylinder (diameter = 14 cm) containing 15 cm of water (25 °C). Twenty-four hours later, each mouse was placed in the cylinder for 5 min while swimming activity was monitored with a video camera located above the cylinder. The total time that each mouse remained immobile in the water was later measured by an observer who was blinded to the mouse genotype.
Mice were individually placed in the center of a 44 × 44 cm open field for 15 min under ambient light conditions. Locomotor activity was measured using an Opto-M4 Auto-Track System (Columbus Instruments, Columbus, OH) equipped with 16 lasers (spaced 2.5 cm apart) on each axis. The apparatus was cleaned with ethanol and dried between each mouse.
The marble burying assay is commonly used as a rodent model of OCD (see review by Witkin, 2008). Each mouse was individually placed in a clear polycarbonate box (18 cm × 28 cm × 13 cm)containing 5 cm of corncob bedding and 15 marbles (3 rows of 5 marbles). The number of buried marbles was counted after 30 min. Marbles were considered buried if they were at least two-thirds covered.
The elevated plus maze was used to measure anxiety. The maze consisted of four Plexiglas arms (30 cm × 5 cm) extending from a common center (5 cm × 5 cm). Two enclosed arms had 13 cm opaque walls, while the center and two open arms had no walls. The maze was positioned 53 cm above the floor. Mice were placed in the center of the maze facing an open arm, and their location (center, open arms, or enclosed arms) was recorded in the absence of investigators by a video camera positioned above the maze. The time spent in each portion of the maze was later measured by an observer who was blinded to the mouse genotype. An entry was defined as having all four paws within the same arm.
The light/dark box was used as an additional measure of anxiety-related behavior. Mice were individually placed in a Plexiglas box (41cm × 33 cm) containing two chambers of equal size (20.5 cm × 16.5 cm). The light chamber had white walls 13 cm high with an open top and was illuminated by a 150 W white light bulb placed 75 cm above the box. The dark chamber had black walls and was enclosed by a lid. A 9 cm × 5 cm opening in the divider between the chambers enabled mice to move between the light and dark chambers. Mice were initially placed in the center of the light chamber facing the opening into the dark chamber and video recorded for 5 min in the absence of investigators using a camera located above the apparatus. The number of entries into the light chamber, number of entries into the dark chamber, and the time spent in each chamber were later measured by an observer who was blinded to the mouse genotype.
Data are reported as mean ± S.E.M. One-way analysis of variance followed by the Newman-Keuls posthoc test was used for statistical analysis of all experiments except for comparisons between cirazoline treated animals and their age matched controls. The student’s t-test was used to analyze cirazoline data because these experiments involved only two groups (cirazoline-treated wild type mice vs. age-matched nontreated wild type mice). Two way analysis of variance was used to compare the effects of water and prazosin in wild type and CAMα1A-AR mice in the tail suspension test since this experiment included two variables (mouse genotype and drug treatment). A value of p < 0.05 was considered significant for all analyses.
The authors thank Dr. Dianne Perez (Cleveland Clinic Foundation) for generously donating CAM α1A-AR and CAM α1B-AR mice for this study. This work was supported by the Bower, Bennet, and Bennet Endowed Research Chair Award to Boyd Rorabaugh, an American Association of Colleges of Pharmacy New Investigator Program Award to Jeff Talbot, and a National Science Foundation CAREER award 0347259 to Van Doze. Additional student support was provided by the Ronald E. McNair Achievement Program and National Institutes of Health grant P20RR016741 from the INBRE Program of the National Center for Research Resources.
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