Renu Sah

γ-Aminobutyric acidA neurotransmission and cerebral ischemia

In this review, we present evidence for the role of γ‐aminobutyric acid (GABA) neurotransmission in cerebral ischemia‐induced neuronal death. While glutamate neurotransmission has received widespread attention in this area of study, relatively few investigators have focused on the ischemia‐induced alterations in inhibitory neurotransmission. We present a review of the effects of cerebral ischemia on pre and postsynaptic targets within the GABAergic synapse. Both in vitro and in vivo models of ischemia have been used to measure changes in GABA synthesis, release, reuptake, GABAA receptor expression and activity. Cellular events generated by ischemia that have been shown to alter GABA neurotransmission include changes in the Cl− gradient, reduction in ATP, increase in intracellular Ca2+, generation of reactive oxygen species, and accumulation of arachidonic acid and eicosanoids. Neuroprotective strategies to increase GABA neurotransmission target both sides of the synapse as well, by preventing GABA reuptake and metabolism and increasing GABAA receptor activity with agonists and allosteric modulators. Some of these strategies are quite efficacious in animal models of cerebral ischemia, with sedation as the only unwanted side‐effect. Based on promising animal data, clinical trials with GABAergic drugs are in progress for specific types of stroke. This review attempts to provide an understanding of the mechanisms by which GABA neurotransmission is sensitive to cerebral ischemia. Furthermore, we discuss how dysfunction of GABA neurotransmission may contribute to neuronal death and how neuronal death can be prevented by GABAergic drugs.

Low Cerebrospinal Fluid Neuropeptide Y Concentrations in Posttraumatic Stress Disorder

BACKGROUND Neuropeptide Y (NPY), a peptide neurotransmitter that regulates stress and anxiety, has been proposed to be a stress resilience factor in humans. Posttraumatic stress disorder (PTSD) is a stress-related anxiety disorder. We hypothesized that central nervous system NPY is dysregulated in PTSD and sought to redress the absence of central NPY data in the disorder. METHODS We determined morning NPY concentrations in cerebrospinal fluid (CSF) from 10 male subjects with chronic combat-related PTSD and from 13 healthy men. Neuropeptide Y-like immunoreactivity was measured by enzyme immunoassay (EIA). RESULTS As compared with the normal comparison subjects, PTSD patients had significantly lower concentrations of CSF neuropeptide Y (mean CSF NPY was 360.0 +/- 17.7 pg/mL in control subjects but only 233.6 +/- 28.7 pg/mL in PTSD patients [p = .0008]). Adjustments for age and body mass index (BMI) still revealed a highly significant reduction in CSF NPY in the PTSD group (p = .003). CONCLUSIONS Men with combat-related PTSD have low CSF concentrations of the putative resiliency hormone NPY, possibly related to the disorder or to extreme stress exposure per se.

Relevance of Neuropeptide Y (NPY) in Psychiatry

Extensive preclinical studies suggest neuropeptide Y (NPY) to be involved in stress regulation and coping. NPY counteracts the behavioral consequences of stress and anxiety to maintain emotional homeostasis. NPY is also involved in learning, memory, and cognition, all of which are dysregulated in many psychiatric states. Dense localization of NPY and NPY receptors is found in brain areas implicated in psychopathology such as the amygdala, hippocampus, neocortex, septum, caudate-putamen, hypothalamus and locus coeruleus. Impaired central NPY signaling may therefore be involved in the pathophysiology of depression, anxiety, schizophrenia, alcoholism, and trauma-induced disorders like PTSD. Studies on the readily accessible plasma from psychiatric patients have provided some information on the relevance of NPY as a marker for sympathetic tone in certain conditions. Reports on cerebrospinal fluid (CSF) NPY in subjects with depression indicate a dysregulation of central NPY in this disorder, however, other conditions still need to be investigated.

Changes in Intracellular Chloride after Oxygen–Glucose Deprivation of the Adult Hippocampal Slice: Effect of Diazepam

Ischemic injury to the CNS results in loss of ionic homeostasis and the development of neuronal death. An increase in intracellular Ca2+ is well established, but there are few studies of changes in intracellular Cl– ([Cl–]i) after ischemia. We used an in vitro model of cerebral ischemia (oxygen–glucose deprivation) to examine changes in [Cl–]i and GABAA receptor-mediated responses in hippocampal slices from adult rats. Changes in [Cl–]i were measured in area CA1 pyramidal neurons using optical imaging of 6-methoxy-N-ethylquinolinium chloride, a Cl–-sensitive fluorescent indicator. Oxygen–glucose deprivation induced an immediate rise in [Cl–]i, which recovered within 20 min. A second and more prolonged rise in [Cl–]i occurred within the next hour, during which postsynaptic field potentials failed to recover. The sustained increase in [Cl–]i was not blocked by GABAA receptor antagonists. However, oxygen–glucose deprivation caused a progressive downregulation of the K+–Cl– cotransporter (KCC2), which may have contributed to the Cl– accumulation. The rise in [Cl–]i was accompanied by an inability of the GABAA agonist muscimol to cause Cl– influx. In vivo, diazepam is neuroprotective when given early after ischemia, although the mechanism by which this occurs is not well understood. Here, we added diazepam early after oxygen–glucose deprivation and prevented the downregulation of KCC2 and the accumulation of [Cl–]i. Consequently, both GABAA responses and synaptic transmission within the hippocampus were restored. Thus, after oxygen–glucose deprivation, diazepam may decrease neuronal excitability, thereby reducing the energy demands of the neuron. This may prevent the activation of downstream cell death mechanisms and restore Cl– homeostasis and neuronal function.

Neuropeptide Y and posttraumatic stress disorder

Resiliency to the adverse effects of extraordinary emotional trauma on the brain varies within the human population. Accordingly, some people cope better than others with traumatic stress. Neuropeptide Y (NPY) is a 36-amino-acid peptide transmitter abundantly expressed in forebrain limbic and brain stem areas that regulate stress and emotional behaviors. Studies largely in rodents demonstrate a role for NPY in promoting coping with stress. Moreover, accruing data from the genetic to the physiological implicate NPY as a potential ‘resilience-to-stress’ factor in humans. Here, we consolidate findings from preclinical and clinical studies of NPY that are of relevance to stress-associated syndromes, most prototypically posttraumatic stress disorder (PTSD). Collectively, these data suggest that reduced central nervous system (CNS) NPY concentrations or function may be associated with PTSD. We also link specific symptoms of human PTSD with extant findings in the NPY field to reveal potential physiological contributions of the neuropeptide to the disorder. In pursuit of understanding the physiological basis and treatment of PTSD, the NPY system is an attractive target.

Abnormal neurodevelopment, neurosignaling and behaviour in Npas3-deficient mice

Npas3 is a member of the bHLH‐PAS superfamily of transcription factors that is expressed broadly in the developing neuroepithelium. To study the function of this gene, mice deficient in Npas3 were generated and characterized. Npas3–/– mice were growth‐retarded and exhibited developmental brain abnormalities that included a reduction in size of the anterior hippocampus, hypoplasia of the corpus callosum and enlargement of the ventricles. A number of behavioural abnormalities were identified in Npas3–/– mice including locomotor hyperactivity, subtle gait defects, impairment of prepulse inhibition of acoustic startle, deficit in recognition memory and altered anxiety‐related responses. Characterization of neurosignaling pathways using several pharmacological agents revealed dysfunctional glutamate, dopamine and serotonin neurotransmitter signaling. Consistent with these findings, we identified a significant alteration in cortical PSD‐95 expression, a PDZ‐containing protein that has been shown to be involved in postsynaptic signal transduction. Together, our observations indicate an important role for Npas3 in controlling normal brain development and neurosignaling pathways.

Enhanced fear recall and emotional arousal in rats recovering from chronic variable stress

Emergence of posttraumatic-like behaviors following chronic trauma is of interest given the rising prevalence of combat-related posttraumatic stress disorder (PTSD). Stress associated with combat usually involves chronic traumatization, composed of multiple, single episode events occurring in an unpredictable fashion. In this study, we investigated whether rats recovering from repeated trauma in the form of chronic variable stress (CVS) express posttraumatic stress-like behaviors and dysregulated neuroendocrine responses. Cohorts of Long-Evans rats underwent a 7 day CVS paradigm followed by behavioral and neuroendocrine testing during early (16 h post CVS) and delayed (7 day) recovery time points. A fear conditioning-extinction-reminder shock paradigm revealed that CVS induces exaggerated fear recall to reminder shock, suggestive of potentiated fear memory. Rats with CVS experience also expressed a delayed expression of fearful arousal under aversive context, however, social anxiety was not affected during post-CVS recovery. Persistent sensitization of the hypothalamic-pituitary-adrenocorticotropic response to a novel acute stressor was observed in CVS exposed rats. Collectively, our data are consistent with the constellation of symptoms associated with posttraumatic stress syndrome, such as re-experiencing, and arousal to fearful contexts. The CVS-recovery paradigm may be useful to simulate trauma outcomes following chronic traumatization that is often associated with repeated combat stress.

Cerebrospinal fluid neuropeptide Y in combat veterans with and without posttraumatic stress disorder

Accruing evidence indicates that neuropeptide Y (NPY), a peptide neurotransmitter, is a resilience-to-stress factor in humans. We previously reported reduced cerebrospinal fluid (CSF) NPY concentrations in combat-related posttraumatic stress disorder (PTSD) subjects as compared with healthy, non-combat-exposed volunteers. Here we report CSF NPY in combat-exposed veterans with and without PTSD. We quantified NPY concentrations in morning CSF from 11 male subjects with PTSD from combat in Iraq and/or Afghanistan and from 14 combat-exposed subjects without PTSD. NPY-like immunoreactivity (NPY-LI) was measured by EIA. The relationship between CSF NPY and clinical symptoms, as measured by the Clinician-Administered PTSD Scale (CAPS) and Beck Depression Inventory (BDI), was assessed, as was the relationship between combat exposure scale (CES) scores and CSF NPY. As compared with the combat-exposed comparison subjects without PTSD, individuals with PTSD had significantly lower concentrations of CSF NPY [mean CSF NPY was 258. 6 ± 21.64 pg/mL in the combat trauma-no PTSD group but only 180.5 ± 12.62 pg/mL in PTSD patients (p=0.008)]. After adjusting for CES and BDI scores the two groups were still significantly different with respect to NPY. Importantly, CSF NPY was negatively correlated with composite CAPS score and intrusive (re-experiencing) subscale scores, but did not significantly correlate with CES or BDI scores. Our current findings further suggest that NPY may regulate the manifestation of PTSD symptomatology, and extend previous observations of low CSF NPY concentrations in the disorder. Central nervous system NPY may be a clinically important pharmacotherapeutic target, and/or diagnostic measure, for PTSD.

The orphan receptor Gpr83 regulates systemic energy metabolism via ghrelin-dependent and ghrelin-independent mechanisms

The G protein-coupled receptor 83 (Gpr83) is widely expressed in brain regions regulating energy metabolism. Here we report that hypothalamic expression of Gpr83 is regulated in response to nutrient availability and is decreased in obese mice compared with lean mice. In the arcuate nucleus, Gpr83 colocalizes with the ghrelin receptor (Ghsr1a) and the agouti-related protein. In vitro analyses show heterodimerization of Gpr83 with Ghsr1a diminishes activation of Ghsr1a by acyl-ghrelin. The orexigenic and adipogenic effect of ghrelin is accordingly potentiated in Gpr83-deficient mice. Interestingly, Gpr83 knock-out mice have normal body weight and glucose tolerance when fed a regular chow diet, but are protected from obesity and glucose intolerance when challenged with a high-fat diet, despite hyperphagia and increased hypothalamic expression of agouti-related protein, Npy, Hcrt and Ghsr1a. Together, our data suggest that Gpr83 modulates ghrelin action but also indicate that Gpr83 regulates systemic metabolism through other ghrelin-independent pathways.

3,4-Methylenedioxymethamphetamine administration on postnatal day 11 in rats increases pituitary-adrenal output and reduces striatal and hippocampal serotonin without altering SERT activity

We have previously shown that +/-3,4-methylenedioxymethamphetamine (MDMA) treatment from P11 to P20 in rats produces deficits in cognitive ability when these animals are tested in adulthood. The purpose of this experiment was to explore the neuroendocrine and neurochemical changes produced by MDMA treatment on P11. We examined monoamines in the hippocampus and striatum and the serotonin transporter in the hippocampus as well as pituitary and adrenal output following administration of MDMA (10 mg/kg, 4 times) on postnatal day 11. Significant depletions in serotonin were evident in the hippocampus 1 h and in the striatum 24 h after the first dose and remained reduced 78 h later. No changes in serotonin transporter were observed following MDMA treatment, although females had lower levels than males. No changes in dopamine were detected. The metabolites of serotonin and dopamine had different profiles than the parent compounds after MDMA administration. Plasmatic ACTH was elevated immediately following MDMA and remained elevated for at least 1 h after the last dose and returned to baseline by 24 h. Corticosterone was increased after the first dose and remained increased for at least 24 h, and returned to baseline by 30 h. The decreases in serotonin in regions important for learning and memory in conjunction with elevated levels of corticosterone during a period of stress hyporesponsiveness suggest that these initial responses to MDMA may contribute to the long-term learning and memory deficits following neonatal MDMA exposure.