The endogenous hippocampal opioid systems are implicated in learning associated with drug use. Recently, we showed that ovarian hormones regulate enkephalin levels in the mossy fiber pathway. This pathway overlaps with parvalbumin (PARV)-basket interneurons that contain the enkephalin-activated mu opioid receptors (MORs) and are important for controlling the “temporal timing” of granule cells. Here, we evaluated the influence of ovarian steroid on the trafficking of MORs in PARV interneurons. Two groups of female rats were analyzed: cycling rats in proestrus (relatively high estrogens) or diestrus; and ovariectomized rats euthanized 6, 24 or 72 hr after estradiol benzoate (10μg, s.c.) administration. Dorsal hippocampal sections were dually immunolabeled for MORs and PARV and examined by light and electron microscopy. As in males, in females MOR-immunoreactivity (-ir) was in numerous PARV-labeled perikarya, dendrites and terminals in the dentate hilar region. Variation in ovarian steroid levels altered the subcellular distribution of MORs in PARV-labeled dendrites but not terminals. In normal cycling rats, MOR-gold particles on the plasma membrane of small PARV-labeled dendrites (area < 1μm2) had higher density in proestrus rats than in diestrus rats. Likewise, in ovariectomized rats MORs showed higher density on the plasma membrane of small PARV-labeled dendrites 72 hrs after estradiol exposure. The number of PARV-labeled cells was not affected by estrous cycle phase or estrogen levels. These results demonstrate that estrogen levels positively regulate the availability of MORs on GABAergic interneurons in the dentate gyrus, suggesting cooperative interaction between opioids and estrogens in modulating principal cell excitability.
estrogen; estrous cycle; ovariectomy; hippocampus; endogenous opioids
Severe traumatic brain injury (TBI) is associated with a high incidence of acute mortality followed by chronic alteration of homeostatic network activity that includes the emergence of posttraumatic seizures. We hypothesized that acute and chronic outcome after severe TBI critically depends on disrupted bioenergetic network homeostasis, which is governed by the availability of the brain’s endogenous neuroprotectant adenosine. We used a rat lateral fluid percussion injury (FPI) model of severe TBI with an acute mortality rate of 46.7%. A subset of rats was treated with 25 mg/kg caffeine intraperitoneally within 1 minute of the injury. We assessed neuromotor function at 24 hours and 4 weeks, and video-EEG activity and histology at 4 weeks following injury. We first demonstrate that acute mortality is related to prolonged apnea and that a single acute injection of the adenosine receptor antagonist caffeine can completely prevent TBI-induced mortality when given immediately following the TBI. Second, we demonstrate that neuromotor function is not affected by caffeine treatment at either 24 hours or 4 weeks following injury. Third, we demonstrate development of epileptiform EEG bursts as early as 4 weeks post-injury that are significantly reduced in duration in the rats that received caffeine. Our data demonstrate that acute treatment with caffeine can prevent lethal apnea following fluid percussion injury, with no negative influence on motor function or histological outcome. Further, we show epileptiform bursting is reduced after caffeine treatment, suggesting a potential role in the modulation of epilepsy development after severe injury.
FPI; caffeine; traumatic brain injury; apnea; EEG; neuroprotection
Dysfunctional γ-aminobutyric acid (GABA)-ergic inhibitory neurotransmission is hypothesized to underlie chronic neuropathic pain. Intraspinal transplantation of GABAergic neural progenitor cells (NPCs) may reduce neuropathic pain by restoring dorsal horn inhibition. Rat NPCs pre-differentiated to a GABAergic phenotype were transplanted into the dorsal horn of rats with unilateral chronic constriction injury (CCI) of the sciatic nerve. GABA signaling in antinociceptive effects of NPC grafts was tested with the GABAA receptor antagonist bicuculline (BIC), GABAB receptor antagonist CGP35348 (CGP) and GABA reuptake inhibitor SKF 89976A (SKF). NPC-treated animals showed decreased hyperalgesia and allodynia 1-3 week post-transplantation; vehicle-injected CCI rats continued displaying pain behaviors. Intrathecal application of BIC or CGP attenuated the antinociceptive effects of the NPC transplants while SKF injection induced analgesia in control rats. Electrophysiological recordings in NPC treated rats showed reduced responses of wide dynamic range (WDR) neurons to peripheral stimulation compared to controls. A spinal application of BIC or CGP increased wind-up response and post-discharges of WDR neurons in NPC treated animals. Results suggest that transplantation of GABAergic NPCs attenuate pain behaviors and reduce exaggerated dorsal horn neuronal firing induced by CCI. The effects of GABA receptor inhibitors suggest participation of continuously released GABA in the grafted animals.
neuropathic pain; GABAergic progenitors; GABA receptors; wind-up; post-discharges
Diabetic neuropathy is a common complication of diabetes mellitus with over half of all patients developing neuropathy symptoms due to sensory nerve damage. Diabetes-induced hyperglycemia leads to the accelerated production of advanced glycation end products (AGEs) that alter proteins, thereby leading to neuronal dysfunction. The glyoxalase enzyme system, specifically glyoxalase I (GLO1), is responsible for detoxifying precursors of AGEs, such as methylglyoxal and other reactive dicarbonyls. The purpose of our studies was to determine if expression differences of GLO1 may play a role in the development of diabetic sensory neuropathy. BALB/cJ mice naturally express low levels of GLO1, while BALB/cByJ express approximately 10-fold higher levels on a similar genetic background due to increased copy numbers of GLO1. Five weeks following STZ injection, diabetic BALB/cJ mice developed a 68% increase in mechanical thresholds, characteristic of insensate neuropathy or loss of mechanical sensitivity. This behavior change correlated with a 38% reduction in intraepidermal nerve fiber density (IENFD). Diabetic BALB/cJ mice also had reduced expression of mitochondrial oxidative phosphorylation proteins in Complex I and V by 83% and 47%, respectively. Conversely, diabetic BALB/cByJ mice did not develop signs of neuropathy, changes in IENFD, or alterations in mitochondrial protein expression. Reduced expression of GLO1 paired with diabetes-induced hyperglycemia may lead to neuronal mitochondrial damage and symptoms of diabetic neuropathy. Therefore, AGEs, the glyoxalase system, and mitochondrial dysfunction may play a role in the development and modulation of diabetic peripheral neuropathy.
mice; diabetes; neuropathy; skin innervation; epidermis; glyoxalase I; dorsal root ganglion; peripheral nerve; mechanical sensitivity
Dementia and parkinsonism are late-onset symptoms associated with repetitive head injury, as documented in multiple contact-sport athletes. Clinical symptomatology is the likely phenotype of chronic degeneration and circuit disruption in the substantia nigra (SN). To investigate the initiating neuropathology, we hypothesize that a single diffuse brain injury is sufficient to initiate SN neuropathology including neuronal loss, vascular disruption and microglial activation, contributing to neurodegeneration and altered dopamine regulation. Adult, male Sprague-Dawley rats were subjected to sham or moderate midline fluid percussion brain injury. Stereological estimates indicated a significant 44% loss of the estimated total neuron number in the SN at 28-days post-injury, without atrophy of neuronal nuclear volumes, including 25% loss of tyrosine hydroxylase positive neurons by 28-days post-injury. Multi-focal vascular compromise occurred 1–2 days post-injury, with ensuing microglial activation (significant 40% increase at 4-days). Neurodegeneration (silver-stain technique) encompassed on average 21% of the SN by 7-days post-injury and increased to 29% by 28-days compared to sham (1%). Whole tissue SN, but not striatum, dopamine metabolism was altered at 28-days post-injury, without appreciable gene or protein changes in dopamine synthesis or regulation elements. Together, single moderate diffuse brain injury resulted in SN neurovascular pathology potentially associated with neuroinflammation or dopamine dysregulation. Compensatory mechanisms may preserve dopamine signaling acutely, but subsequent SN damage with aging or additional injury may expose clinical symptomatology of motor ataxias and dementia.
substantia nigra; PCR; concussion; Parkinsons; brain injury
Following cervical spinal cord injury at C2 (SH hemisection model) there is progressive recovery of phrenic activity. Neuroplasticity in the postsynaptic expression of neurotransmitter receptors may contribute to functional recovery. Phrenic motoneurons express multiple serotonergic (5-HTR) and glutamatergic (GluR) receptors, but the timing and possible role of these different neurotransmitter receptor subtypes in the neuroplasticity following SH are not clear. The current study was designed to test the hypothesis that there is an increased expression of serotonergic and glutamatergic neurotransmitter receptors within phrenic motoneurons after SH. In adult male rats, phrenic motoneurons were labeled retrogradely by intrapleural injection of Alexa 488-conjugated cholera toxin B. In thin (10 μm) frozen sections of the spinal cord, fluorescently-labeled phrenic motoneurons were visualized for laser capture microdissection (LCM). Using quantitative real-time RT-PCR in LCM samples, the time course of changes in 5-HTR and GluR mRNA expression was determined in phrenic motoneurons up to 21 days post-SH. Expression of 5-HTR subtypes 1b, 2a and 2c and GluR subtypes AMPA, NMDA, mGluR1 and mGluR5 was evident in phrenic motoneurons from control and SH rats. Phrenic motoneuron expression of 5-HTR2a increased ~8-fold (relative to control) at 14 days post-SH, whereas NMDA expression increased ~16-fold by 21-days post-SH. There were no other significant changes in receptor expression at any time post-SH. This is the first study to systematically document changes in motoneuron expression of multiple neurotransmitter receptors involved in regulation of motoneuron excitability. By providing information on the neuroplasticity of receptors expressed in a motoneuron pool that is inactivated by a higher-level spinal cord injury, appropriate pharmacological targets can be identified to alter motoneuron excitability.
Neuroplasticity; Neurotransmitter; Laser capture microdissection; Quantitative real-time RT-PCR; AMPA; NMDA; 5-HTR2a; Spinal hemisection; Motor neuron
Freezing of gait (FOG) is a debilitating feature of Parkinson’s disease (PD) and other forms of parkinsonism. The anatomical or pathophysiological correlates are poorly understood largely due to the lack of a well-established animal model. Here we studied whether FOG is reproduced in the non-human primate (NHP) model of PD. 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys (Genus Macaca, n=29) were examined for the development of FOG, and the leg movements were recorded with accelerometry. The relationships between developing FOG and the animals’ characteristics, the MPTP treatments, and the modeled outcomes were determined. In parkinsonian monkeys FOG developed frequently (48%) manifesting similar characteristics to those seen in PD patients. In addition, FOG episodes in the monkey were accompanied by leg trembling with the typical duration (2–10 s) and frequency (~7 Hz). The development of NHP FOG was significantly associated with the severity of parkinsonism, as shown by high motor disability scores (≥20) and levodopa-induced dyskinesia scores (p=0.01 and p=0.04, respectively). Differences in demographics and MPTP treatments (doses, treatment duration, etc.) had no influence on NHP FOG occurrence, with the exception of gender that showed FOG predominance in males (p=0.03). The unique features of FOG in PD can be replicated in severely parkinsonian macaques, and this represents the first description of a FOG animal model.
Freezing of gait; MPTP; Animal model; Non-human primate; Dopamine
This study was initiated due to an NIH “Facilities of Research - Spinal Cord Injury” contract to support independent replication of published studies. Transient blockage of the CD11d/CD18 integrin has been reported to reduce secondary neuronal damage as well as to improve functional recovery after spinal cord injury (SCI) in rats. The purpose of this study was to determine whether treatment with an anti-CD11d monoclonal antibody (mAb) would improve motor performance, reduce pain and histopathological damage in animals following clip-compression injury as reported. Adult male Wistar rats (250 g) were anesthetized with isoflurane, and the T12 spinal cord exposed by T10 and T11 dorsal laminectomies followed by a 60 second period of clip compression utilizing a 35 gram clip. Control animals received an isotype-matched irrelevant antibody (1B7) while the treated group received the anti-CD11d mAb (217L; 1.0 mg/kg) systemically. Open-field locomotion and sensory function were assessed and animals were perfusion-fixed at twelve weeks after injury for quantitative histopathological analysis. As compared to 1B7, 217L treated animals showed an overall non-significant trend to better motor recovery. All animals showed chronic mechanical allodynia and anti-CD11d mAb treatment did not significantly prevent its development. Histopathological analysis demonstrated severe injury to gray and white matter after compression with a non-significant trend in anti-CD11d protection compared to control animals for preserved myelin. Although positive effects with the anti-CD11d mAb treatment have been reported after compressive SCI, it is suggested that this potential treatment requires further investigation before clinical trials in spinal cord injured patients are implemented.
inflammation; integrin; locomotor; spinal cord injury; rat
The function of populations of nociceptors in muscle pain syndromes remain poorly understood. We compared the contribution of two major classes, isolectin B4-positive (IB4(+)) and IB4-negative (IB4(−)) nociceptors, in acute and chronic inflammatory and ergonomic muscle pain. Baseline mechanical nociceptive threshold was assessed in the gastrocnemius muscle of rats treated with IB4-saporin, which selectively destroys IB4(+) nociceptors. Rats were then submitted to models of acute inflammatory (intramuscular carrageenan)- or ergonomic intervention (eccentric exercise or vibration)-induced muscle pain, and each of the three models also evaluated for the transition from acute to chronic pain, manifest as prolongation of prostaglandin E2 (PGE2)-induced hyperalgesia, after recovery from the hyperalgesia induced by acute inflammation or ergonomic interventions. IB4-saporin treatment did not affect baseline mechanical nociceptive threshold. However, compared to controls, IB4-saporin treated rats exhibited shorter duration mechanical hyperalgesia in all three models and attenuated peak hyperalgesia in the ergonomic pain models. And, IB4-saporin treatment completely prevented prolongation of PGE2-induced mechanical hyperalgesia. Thus, IB4(+) and IB4(−) neurons contribute to acute muscle hyperalgesia induced by diverse insults. However, only IB4+ nociceptors participate in the long term consequence of acute hyperalgesia. Finally, using retrograde labelling we found that approximately 70% of sensory neurons innervating the gastrocnemius muscle are IB4(+).
Myalgia; nociceptor; isolectin B4; chronic muscle pain
Previous studies have demonstrated that moderate hypothermia reduces histopathological damage and improves behavioral outcome after experimental traumatic brain injury (TBI). Further investigations have clarified the mechanisms underlying the beneficial effects of hypothermia by showing that cooling reduces multiple cell injury cascades. The purpose of this study was to determine whether hypothermia could also enhance endogenous reparative processes following TBI such as neurogenesis and the replacement of lost neurons. Male Sprague-Dawley rats underwent moderate fluid-percussion brain injury and then were randomized into normothermia (37°C) or hypothermia (33°C) treatment. Animals received injections of 5-bromo-2′-deoxyuridine (BrdU) to detect mitotic cells after brain injury. After 3 or 7 days, animals were perfusion-fixed and processed for immunocytochemistry and confocal analysis. Sections were stained for markers selective for cell proliferation (BrdU), neuroblasts and immature neurons (doublecortin), and mature neurons (NeuN) and then analyzed using non-biased stereology to quantify neurogenesis in the dentate gyrus (DG). At 7 days after TBI, both normothermic and hypothermic TBI animals demonstrated a significant increase in the number of BrdU-immunoreactive cells in the DG as compared to sham-operated controls. At 7 days post-injury, hypothermia animals had a greater number of BrdU (ipsilateral cortex) and doublecortin (ipsilateral and contralateral cortex) immunoreactive cells in the DG as compared to normothermia animals. Because adult neurogenesis following injury may be associated with enhanced functional recovery, these data demonstrate that therapeutic hypothermia sustains the increase in neurogenesis induced by TBI and this may one of the mechanisms by which hypothermia promotes reparative strategies in the injured nervous system.
Dentate gyrus; Doublecortin; Fluid-percussion; Hypothermia; Neurogenesis; Traumatic brain injury
These experiments were completed as part of an NIH-NINDS contract entitled “Facilities of Research Excellence – Spinal Cord Injury (FORE-SCI) – Replication”. Our goal was to replicate pre-clinical data from Simard et al. (2007) showing that glibenclamide, an FDA approved anti-diabetic drug that targets sulfonylurea receptor 1 (SUR1)-regulated Ca2+ activated, [ATP]i-sensitive nonspecific cation channels, attenuates secondary intraspinal hemorrhage and secondary neurodegeneration caused by hemicontusion injury in rat cervical spinal cord. In an initial replication attempt, the Infinite Horizons impactor was used to deliver a standard unilateral contusion injury near the spinal cord midline. Glibenclamide was administered continuously via osmotic pump beginning immediately post-SCI. The ability of glibenclamide to limit intraspinal hemorrhage was analyzed at 6, 12 and 24 hours using a colorimetric assay. Acute recovery (24 hours) of forelimb function also was assessed. Analysis of data from these initial studies revealed no difference between glibenclamide and vehicle-treated SCI rats. Later, it was determined that differences in primary trauma affect the efficacy of glibenclamide. Indeed, the magnitude and distribution of primary intraspinal hemorrhage was greater when the impact was directed to the dorsomedial region of the cervical hemicord (as in our initial replication experiment), as compared to the dorsolateral spinal cord (as in the Simard et al. experiment). In three subsequent experiments, injury was directed to the dorsolateral spinal cord. In each case, glibenclamide reduced post-traumatic hemorrhage 24-48 hours post-injury. In the third experiment, we also assessed function and found that acute reduction of hemorrhage led to improved functional recovery. Thus, independent replication of the Simard et al. data was achieved. These data illustrate that the injury model and type of trauma can determine the efficacy of pre-clinical pharmacological treatments after SCI.
cervical spinal cord injury; hemorrhage; secondary injury; sulfonylurea receptor; glibenclamide; injury models
Although astrocytes are involved in the production of an inhibitory glial scar following injury, they are also capable of providing neuroprotection and supporting axonal growth. There is growing appreciation for a diverse and dynamic population of astrocytes, specified by a variety of glial precursors, whose function is regulated regionally and temporally. Consequently, the therapeutic application of glial precursors and astrocytes by effective transplantation protocols requires a better understanding of their phenotypic and functional properties and effective protocols for their preparation. We present a systematic analysis of astrocyte differentiation using multiple preparations of glial-restricted precursors (GRP), evaluating their morphological and phenotypic properties following treatment with fetal bovine serum (FBS), bone morphogenetic protein 4 (BMP-4), or ciliary neurotrophic factor (CNTF) in comparison to controls treated with basic fibroblast growth factor (bFGF), which maintains undifferentiated GRP. We found that treatments with FBS or BMP-4 generated similar profiles of highly differentiated astrocytes that were A2B5−/GFAP+. Treatment with FBS generated the most mature astrocytes, with a distinct and nearhomogeneous morphology of fibroblast-like flat cells, whereas BMP-4 derived astrocytes had a stellate, but heterogeneous morphology. Treatment with CNTF induced differentiation of GRP to an intermediate state of GFAP+ cells that maintained immature markers and had relatively long processes. Furthermore, astrocytes generated by BMP-4 or CNTF showed considerable experimental plasticity, and their morphology and phenotypes could be reversed with complementary treatments along a wide range of mature-immature states. Importantly, when GRP or GRP treated with BMP-4 or CNTF were transplanted acutely into a dorsal column lesion of the spinal cord, cells from all 3 groups survived and generated permissive astrocytes that supported axon growth and regeneration of host sensory axons into, but not out of the lesion. Our study underscores the dynamic nature of astrocytes prepared from GRP and their permissive properties, and suggest that future therapeutic applications in restoring connectivity following CNS injury are likely to require a combination of treatments.
bone morphogenetic protein (BMP); ciliary neurotrophic factor (CNTF); astrocyte differentiation; astrocyte transplantation; spinal cord injury; axon regeneration
Frontotemporal lobar degeneration (FTLD) is a neurodegenerative disease that involves cognitive decline and dementia. To model the hippocampal neurodegeneration and memory-related behavioral impairment that occurs in FTLD and other tau and TDP-43 proteinopathy diseases, we used an adeno-associated virus serotype 9 (AAV9) vector to induce bilateral expression of either microtubule-associated protein tau or transactive response DNA binding protein 43 kDa (TDP-43) in adult rat dorsal hippocampus. Human wild-type forms of tau or TDP-43 were expressed. The vectors/doses were designed for moderate expression levels within neurons. Rats were evaluated for acquisition and retention in the Morris water task over 12 weeks after gene transfer. Neither vector altered acquisition performance compared to controls. In measurements of retention, there was impairment in the TDP-43 group. Histological examination revealed specific loss of dentate gyrus granule cells and concomitant gliosis proximal to the injection site in the TDP-43 group, with shrinkage of the dorsal hippocampus. Despite specific tau pathology, the tau gene transfer surprisingly did not cause obvious neuronal loss or behavioral impairment. The data demonstrate that TDP-43 produced mild behavioral impairment and hippocampal neurodegeneration in rats, whereas tau did not. The models could be of value for studying mechanisms of FTLD and other diseases with tau and TDP-43 pathology in the hippocampus including Alzheimer's disease, with relevance to early stage mild impairment.
These experiments were completed as part of an NIH “Facilities of Research Excellence in Spinal Cord Injury” contract to support independent replication of published studies that could be considered for eventual clinical testing. Recent studies have reported that selective inhibition of the P2X7 receptor improves both the functional and histopathological consequences of a contusive spinal cord injury (SCI) in rats. We repeated two published studies reporting the beneficial effects of pyridoxal-5′-phosphate-6-azophenyl-2′-4′-disulphonic acid (PPADS) or Brilliant blue G (BBG) treatment after SCI (Wang et al., 2004 and Peng et al., 2009). Mild thoracic SCI was first produced in Experiment 1 by means of the MASCIS impactor at T10 (height 6.25 mm, weight 10 gm) followed by intraspinal administration of a P2X7 antagonist (2 μl/10mM) after injury. Treatment with PPADS or another highly selective P2X7R antagonist Brilliant Blue G (BBG) (2 μl/02mM) did not improve locomotive (BBB rating scale) over a 7 week period compared to vehicle treated rats. Also, secondary histopathological changes in terms of overall lesion and cavity volume were not significantly different between the PPADS, BBG, and vehicle treated animals. In the second experiment, the systemic administration of BBG (10 or 50 mg/kg, iv) 15 min, 24 and 72 hours after moderate (12.5 mm) SCI failed to significantly improve motor recovery or histopathological outcome over the 6 week observational period. Although we cannot conclude that there will be no long-term beneficial effects in other spinal cord injury models using selective P2X7 receptor antagonists at different doses or treatment durations, we caution researchers that this potentially exciting therapy requires further preclinical investigations before the implementation of clinical trials targeting severe SCI patients.
inflammation; purinergic signaling; neuroprotection; spinal cord injury
These experiments were completed as part of an NIH-NINDS contract entitled “Facilities of Research Excellence-Spinal Cord Injury (FORE-SCI)—Replication”. Our goal was to replicate data from a paper published by Dr. Lloyd Guth and colleagues in which combined injections of lipopolysaccharide, indomethacin and pregnenolone (referred to herein as LIP therapy) conferred marked neuroprotection in a pre-clinical model of spinal cord injury (SCI). Specifically, post-injury injection of the combination LIP therapy was found to significantly reduce tissue damage at/nearby the site of injury and significantly improve recovery of locomotor function. In this report, we confirm the primary observations made by Guth et al., however, the effects of LIP treatment were modest. Specifically, LIP treatment improved myelin and axon sparing, axonal sprouting while reducing lesion cavitation. However, spontaneous recovery of locomotion, as assessed using historical (Tarlov scoring) and more current rating scales (i.e., BBB scoring), was not affected by LIP treatment. Instead, more refined parameters of functional recovery (paw placement accuracy during grid walk) revealed a significant effect of treatment. Possible explanations for the neuroprotective effects of LIP therapy are described along with reasons why the magnitude of neuroprotection may have differed between this study and that of Guth and colleagues.
Neuroinflammation; LPS; Steroids; Spinal cord injury; Replication
The pedunculopontine tegmental nucleus (PPN) is being explored as a site for deep brain stimulation (DBS) for the treatment of patients with medically refractory gait and postural abnormalities (MRGPA) associated with Parkinson's disease (PD). The PPN is involved in initiation and modulation of gait and other stereotyped motor behaviors and is inter-connected with the pallido-thalamo-cortical circuit. GPi DBS is effective at treating the motor signs associated with PD, however its impact on MRGPA is limited and its effect on PPN neuronal activity is unknown. The current work characterizes the effect of therapeutically-effective GPi DBS on PPN neuronal activity in a single rhesus monkey made parkinsonian using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). A scaled-down, quadripolar DBS lead was implanted into sensorimotor GPi under electrophysiological and stereotactic guidance. Single neuron activity was recorded from PPN before, during and after DBS. GPi DBS reduced the mean discharge rate of PPN neurons from 16.8 Hz to 12.8Hz, with 34 (66.7%) neurons showing a decreased mean rate, 3 (6.7%) increased and 12 (26.7%) unchanged. Consistent with known GABAergic projections from GPi to PPN, and with previous observations that stimulation increases output from the stimulated structure, GPi DBS suppressed activity in PPN. The present observations, together with previous reports of improvement in MRGPA during low frequency stimulation in PPN, suggest that activation of PPN output may be required to improve MRGPA and may account for the lack of improvement in MRGPA typically observed with GPi or STN DBS.
deep brain stimulation; pedunculopontine tegmental nucleus; globus pallidus; MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine); monkey; Parkinsonism
Deep brain stimulation (DBS) of the internal segment of the globus pallidus (GPi) and the subthalamic nucleus (STN) are effective for the treatment of advanced Parkinson’s disease (PD). We have shown previously that DBS of the external segment of the globus pallidus (GPe) is associated with improvements in parkinsonian motor signs; however, the mechanism of this effect is not known. In this study, we extend our findings on the effect of STN and GPi DBS on neuronal activity in the basal ganglia thalamic network to include GPe DBS using the MPTP monkey model. Stimulation parameters that improved bradykinesia were associated with changes in the pattern and mean discharge rate of neuronal activity in the GPi, STN, and the pallidal [ventralis lateralis pars oralis (VLo) and ventralis anterior (VA)] and cerebellar [ventralis lateralis posterior pars oralis (VPLo)] receiving areas of the motor thalamus. Population post-stimulation time histograms revealed a complex pattern of stimulation-related inhibition and excitation for GPi and VA/VLo, with a more consistent pattern of inhibition in STN and excitation in VPLo. Mean discharge rate was reduced in GPi and STN and increased in VPLo. Effective GPe DBS also reduced bursting in STN and GPi. These data support the hypothesis that therapeutic DBS activates output from the stimulated structure and changes the temporal pattern of neuronal activity throughout the basal ganglia thalamic network and provide further support for GPe as a potential therapeutic target for DBS in the treatment of PD.
deep brain stimulation; globus pallidus; monkey; MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine); parkinsonism
Deep brain stimulation (DBS) of the subthalamic nucleus (STN) can be an effective treatment for the motor symptoms of Parkinson’s disease. The therapeutic benefits are voltage dependent and, in many cases, limited by the appearance of side effects, including muscle contractions. We have observed a number of clinical cases where improvements in rigidity were accompanied by a worsening of bradykinesia. Considering the anatomic position of STN and current approaches to implantation of the DBS lead, we hypothesized that this dissociation of motor symptoms arises from activation of pyramidal tract fibers in the adjacent internal capsule. The objective of this study was to assess the physiological basis for this dissociation and to test our hypothesis that the underlying etiology of this paradox is activation of fibers of the internal capsule. The effect of STN DBS at 80% of motor threshold for each of the four contacts was evaluated for its effect on rigidity, bradykinesia and akinesia in a single primate made parkinsonian with MPTP. Consistent with our observations in humans, this near-threshold stimulation was found to improve rigidity while bradykinesia and akinesia worsened. Worsening bradykinesia in the face of improvement of other motor signs in PD patients is suggestive of activation of pyramidal tract fibers during stimulation. This phenomenon may occur without overt muscle contraction and in the face of improved rigidity.
Deep Brain Stimulation; Parkinson’s disease; Subthalamic Nucleus; Internal Capsule
Deep brain stimulation (DBS) involves the delivery of continuous, fixed-frequency electrical pulses to specific brain regions; however the reliance of therapeutic benefit on the fixed-frequency nature of the stimulation pattern is currently unknown. To address this, we investigated the effect of changes in the pattern and frequency of DBS in the internal segment of the globus pallidus (GPi) on bradykinesia in a single, hemi-parkinsonian monkey. Therapeutic parameters (i.e., contacts, pulse width, amplitude) were established for fixed-frequency stimulation at 135 Hz based on improved movement times during a reach and retrieval task. Thereafter, the pattern and frequency of stimulation was varied to assess the effect of variability, bursting and oscillatory patterns of stimulation on bradykinesia. During fixed-frequency stimulation, performance improved as a function of increasing pulse rate (p < 0.01). Using a temporally irregular pattern at the same average frequency failed to alter therapeutic benefit relative to the fixed-frequency condition. Introducing an 80 Hz burst pattern (20 bursts/second at 4 pulses/burst) improved bradykinesia (p < 0.01) relative to both “OFF” and 80 Hz fixed-frequency conditions, yielding results comparable to fixed-frequency stimulation at 135 Hz with 40% less current drain. Compared to burst and fixed-frequency stimulation, oscillatory patterns at 4 and 8 Hz were less effective. These results suggest that lower frequency stimulation delivered in a regular bursting pattern may be equally effective and require lower energy than higher frequency continuous patterns of stimulation, thereby prolonging battery life and call into question the role of bursting activity in the pathogenesis of bradykinesia.
deep brain stimulation; globus pallidus, MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine); monkey; Parkinsonism
Communication between neurons and microglia is essential for maintaining homeostasis in the central nervous system (CNS) during both physiological and inflammatory conditions. While microglial activation is necessary and beneficial in response to injury or disease, excessive or prolonged activation can have deleterious effects on brain function and behavior. To prevent inflammation-associated damage, microglia reactivity is actively modulated by neurons in the healthy brain. Age or stress-induced disruption of normal neuronal-microglial communication could lead to an aberrant central immune response when additional stressors are applied. Recent work suggests that both aging and stress shift the CNS microenvironment to a pro-inflammatory state characterized by increased microglial reactivity and a reduction in anti-inflammatory and immunoregulatory factors. This review will discuss how heightened neuroinflammation associated with aging and stress may be compounded by the concomitant loss of neuronally derived factors that control microglial activation, leaving the brain vulnerable to excessive inflammation and neurobehavioral complications upon subsequent immune challenge.
Diabetes mellitus is an endocrine disorder resulting from inadequate insulin release and/or reduced insulin sensitivity. The complications of diabetes are well characterized in peripheral tissues, but there is a growing appreciation that the complications of diabetes extend to the central nervous system (CNS). One of the potential neurological complications of diabetes is cognitive deficits. Interestingly, the structural, electrophysiological, neurochemical and anatomical underpinnings responsible for cognitive deficits in diabetes are strikingly similar to those observed in animals subjected to chronic stress, as well as in patients with stress-related psychiatric illnesses such as major depressive disorder. Since diabetes is a chronic metabolic stressor, this has lead to the suggestion that common mechanistic mediators are responsible for neuroplasticity deficits in both diabetes and depression. Moreover, these common mechanistic mediators may be responsible for the increase the risk of depressive illness in diabetes patients. In view of these observations, the aims of this review are: 1) to describe the neuroplasticity deficits observed in diabetic rodents and patients; 2) to summarize the similarities in the clinical and preclinical studies of depression and diabetes; and 3) to highlight the diabetes-induced neuroplasticity deficits in those brain regions that have been implicated as important pathological centers in depressive illness, namely, the hippocampus, the amygdala and the prefrontal cortex.
Depressive illness; glucocorticoids; hypothalamic-pituitary-adrenal axis; insulin; glucose; hyperglycemia; hypoglycemia; hippocampus; prefrontal cortex; amygdala
Epilepsy and depression share an unusually high coincidence suggestive of a common etiology. Disrupted production of adult-born hippocampal granule cells in both disorders may contribute to this high coincidence. Chronic stress and depression are associated with decreased granule cell neurogenesis. Epilepsy is associated with increased production – but aberrant integration – of new cells early in the disease and decreased production late in the disease. In both cases, the literature suggests these changes in neurogenesis play important roles in their respective diseases. Aberrant integration of adult-generated cells during the development of epilepsy may impair the ability of the dentate gyrus to prevent excess excitatory activity from reaching hippocampal pyramidal cells, thereby promoting seizures. Effective treatment of a subset of depressive symptoms, on the other hand, may require increased granule cell neurogenesis, indicating that adult-generated granule cells can modulate mood and affect. Given the robust changes in adult neurogenesis evident in both disorders, competing effects on brain structure are likely. Changes in relative risk, disease course or response to treatment seem probable, but complex and changing patterns of neurogenesis in both conditions will require sophisticated experimental designs to test these ideas. Despite the challenges, this area of research is critical for understanding and improving treatment for patients suffering from these disorders.
epilepsy; dentate gyrus; basal dendrite; neuronal migration; neuronal plasticity
Epidemiological studies have implicated stress (psychosocial and physical) as a trigger of first onset or exacerbation of irritable bowel syndrome (IBS) symptoms of which visceral pain is an integrant landmark. A number of experimental acute or chronic exteroceptive or interoceptive stressors induce visceral hyperalgesia in rodents although recent evidence also points to stress-related visceral analgesia as established in the somatic pain field. Underlying mechanisms of stress-related visceral hypersensitivity may involve a combination of sensitization of primary afferents, central sensitization in response to input from the viscera and dysregulation of descending pathways that modulate spinal nociceptive transmission or analgesic response. Biochemical coding of stress involves the recruitment of corticotropin releasing factor (CRF) signaling pathways. Experimental studies established that activation of brain and peripheral CRF receptor subtype 1 plays a primary role in the development of stress-related delayed visceral hyperalgesia while subtype 2 activation induces analgesic response. In line with stress pathways playing a role in IBS, non-pharmacologic and pharmacologic treatment modalities aimed at reducing stress perception using a broad range of evidence-based mind-body interventions and centrally-targeted medications to reduce anxiety impact on brain patterns activated by visceral stimuli and dampen visceral pain.
colorectal distension; CRF receptor; irritable bowel syndrome; mast cells; stress; visceral pain
Factors that enhance the intrinsic growth potential of adult neurons are key players in the successful repair and regeneration of neurons following injury. Injury-induced activation of transcription factors has a central role in this process because they regulate expression of regeneration-associated genes. Sox11 is a developmentally expressed transcription factor that is significantly induced in adult neurons in response to injury. Its function in injured neurons is however undefined. Here, we report studies that use herpes simplex virus (HSV)-vector-mediated expression of Sox11 in adult sensory neurons to assess the effect of Sox11 overexpression on neuron regeneration. Cultured mouse dorsal root ganglia (DRG) neurons transfected with HSV-Sox11 exhibited increased neurite elongation and branching relative to naïve and HSV-vector control treated neurons. Neurons from mice injected in foot skin with HSV-Sox11 exhibited accelerated regeneration of crushed saphenous nerves as indicated by faster regrowth of axons and nerve fibers to the skin, increased myelin thickness and faster return of nerve and skin sensitivity. Downstream targets of HSV-Sox11 were examined by analyzing changes in gene expression of known regeneration-associated genes. This analysis in combination with mutational and chromatin immunoprecipitation assays indicates that the ability of Sox11 to accelerate in vivo nerve regeneration is dependent on its transcriptional activation of the regeneration-associated gene, small proline rich protein 1a (Sprr1a). This finding reveals a new functional linkage between Sox11 and Sprr1a in adult peripheral neuron regeneration.
transcriptional control; sry; skin delivery; saphenous nerve injury; HSV vector