The Pathological Significance Of GABA And NO In Depressive Patients And Stress Models

Part â… :Dysregulation of GABAergic neurotransmission and the hyperactivated HPA axis in depressionObjectives:Activation of corticotropin-releasing hormone (CRH) neurons in the hypothalamic paraventricular nucleus (PVN) is crucial in the pathogenesis of mood disorder. Gamma-aminobutyric acid (GABA) is one of the major inhibitory neurotransmitters. We hypothesized that dysregulation of GABAergic neurotransmission contributes to the hyperactivity of CRH-immunoreactive (IR) neurons in depression.Methods:Glutamic acid decarboxylase (GAD)65/67-IR boutons were quantified in the postmortem PVN by image analysis in14mood disorder patients (9major depressive disorder, MDD,5bipolar disorder, BD) and12controls. For some of these subjects the total number of CRH-IR neurons in the PVN was also analyzed.Results:The density of GAD65/67-positive structures decreased in mood disorder patients (P=0.080), especially in MDD group (P=0.028), compared to the matched controls. The reduction in GAD65/67-IR was accompanied by significantly increased numbers of CRH-IR neurons. In addition, a negative correlation between PVN-GAD65/67-IR density and CRH-IR neuron numbers was found in the mood disorder group (rho=-0.527, P=0.032, n=13), but not in the control group.Conclusions:A diminished GABAergic input to the PVN may contribute to the activation of CRH-IR neurons in depression, most prominently in MDD. This is an important factor that leads to the overeactivity of HPA axis in depression. Part â…¡:A preliminary study on the alteration of NOS-NO system in stress animal modelsObjective: The gaseous neurotransmitter nitric oxide (NO) and neuronal NO synthase (nNOS) were reported to be altered in the brain and plasma in depression, but the underlying mechanism remains unknown. Therefore, we investigated in stress models the changes of NOS-NO pathway in the rat hypothalamus and plasma so as to search for an ideal model and provide scientific evidence for future research.Methods:Adult male rats were used to establish chronic unpredicted stress (CUS) model and acute stress model induced by foot shock, none of any stimuli was subjected to control rats. Open field test and sucrose preference test were performed on CUS rats. Plasma NO metabolites, plasma corticosterone (CORT) levels, and hypothalamic NOS activity were determined by respective commercial kits. The density of CRH-and nNOS-expressing cells was quantified in the hypothalamic paraventricular nucleus (PVN) by image analysis. Co-localization between nNOS and the neuropeptides, i.e. CRH, vasopressin and oxytocin in the PVN was observed by double immunofluorescence.Results:Significant increases of plasma CORT were observed after foot shock at0,5,15and30min (P<0.038), and for levels of NO metabolites at0and30min (P<0.005). The density of CRH-immunoreactivity (IR) increased at15min (P=0.024) and30min (P=0.022), while nNOS-IR deceased at15min (P=0.030) in the hypothalamic PVN after foot shock. The total NOS activity decreased at15min in the hypothalamus after foot shock (P=0.028). CUS rats showed depression-and anxiety-like behaviors in open field test and sucrose preference test. CUS rats had higher CORT (P=0.001) and NOX (P=0.001) levels in plasma than control rats. In the CUS model, nNOS-IR cell density significantly decreased in the hypothalamic PVN (P=0.019), and this reduction was based upon both strongly and weakly stained neurons. The total NOS activity significantly decreased in the hypothalamus of CUS rats (P=0.025). nNOS-IR was mainly expressed in oxytocin-positive neurons, but hardly colocalized with CRH-IR neurons.Conclusion:The present study showed a decrease of cNOS activity and PVN-nNOS expression in the hypothalamus, but an increase of NO levels in plasma both in foot shock-induced acute stress and CUS-caused depression models. In addition, nNOS did not express in CRH-IR neurons, but in oxytocin-IR neurons after foot shock. The interaction between nNOS and oxytocin will thus be a promising clue to reveal the role of nNOS in stress responses. Part â…¢:NOS-NO system is involved in the regulation of prefrontal cortex function by affecting GABAergic neurotransmission in depression Objective: Alterations in prefrontal cortex (PFC) are crucially involved in the etiology and symptoms of depression. A key role of the gaseous neurotransmitter nitric oxide (NO) has also been proposed, but whether and how NO affect the PFC activity are largely unknown in depression. The present study, therefore, aimed to determine the putative changes of brain NO production, and the transcriptional and/or protein level of the isoforms of the NO synthase (NOS), i.e. neuronal NOS (nNOS), endothelial NOS (eNOS) and inducible NOS (iNOS) in the PFC in depression. Meanwhile, we investigated the effects of NO on GABAergic neuronal activity by selectively blocking the nNOS activity.Methods:The levels of NO, as determined by its metabolites nitrate and nitrite (NOx), were measured in the postmortem ventricular cerebrospinal fluid (CSF) of depressed patients and matched controls. The mRNA levels of nNOS, eNOS and iNOS were measured by real-time PCR in the dorsolateral PFC (DLPFC) and in the anterior cingulate cortex (ACC) of depressed patients. ACC-nNOS immunoreactivity (IR) was assessed by immunocytochemistry and image analysis, and the colocalization between nNOS and GAD65/67was observed by double immunofluorescence. Moreover,7-nitroindazole, the selective nNOS inhibitor, was applied to ACC slices and observed the effects of nNOS-derived NO on the electrophysiological activity GABAergic neurons.Results:We found a significant decrease of CSF-NOx levels in the depressed patients compared to controls (P=0.007). There was a trend toward a lower nNOS mRNA levels in depression in ACC (P=0.083), but not in DLPFC (P=0.939). nNOS-IR was observed to be mainly distributed in the layer â…¡/â…¢ of the human ACC, and a remarkable decrease of nNOS-IR in the grey matter of ACC (P=0.083), especially in layer II/III (P=0.043), was found in depressed patients. A significant positive correlation between the CSF-NOx levels and the ACC-nNOS-IR cell numbers was found in the control group (rho=0.667, P=0.050, n=9). Co-localization between nNOS and GAD65/67, the marker of GABAergic neurons, was found in the human ACC. Furthermore, bath application of7-NI in ACC slices significantly enhanced the frequency of GABAergic mIPSCs (P<0.05; n=11), but did not significantly alter mIPSC amplitude.Conclusion:A diminished ACC-nNOS expression and a decreased CSF-NOX level were found in depression. Selectively inhibiting nNOS activity had a significant effect on GABAergic neurotransmission in mouse ACC slices.