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A discrete GABAergic relay mediates medial prefrontal cortical inhibition of the neuroendocrine stress response.

ABSTRACT: Complementing its roles in cognitive and affective information processing, the medial prefrontal cortex (mPFC) is a nodal point of a limbic forebrain circuit that modulates stress-related homeostatic mechanisms, including the hypothalamic-pituitary-adrenal (HPA) axis. mPFC influences on HPA output are predominantly inhibitory and emanate from the prelimbic and/or dorsal anterior cingulate cortical fields (PL and ACd, respectively). mPFC projections do not target HPA effector neurons in the paraventricular hypothalamic nucleus (PVH) directly, distributing instead to nearby forebrain regions, including some that house GABAergic neurons implicated in inhibitory PVH control. To identify pathway(s) subserving HPA-inhibitory mPFC influences, an initial screen for sources of GABAergic input to PVH whose sensitivity to an acute emotional (restraint) stress was diminished by PL/ACd lesions identified a discrete region of the anterior bed nucleus of the stria terminalis (aBST) as a candidate for fulfilling this role. Anatomical tracing experiments confirmed projections from PL (but not ACd) to implicated aBST cell groups, and from these to PVH. Finally, selective immunotoxin-mediated ablation of GABAergic aBST neurons recapitulated the effects of PL/ACd lesions on acute stress-induced activation of HPA output. The identification of a proximate mediator of HPA-inhibitory limbic influences provides a framework for clarifying how inhibitory neural and hormonal controls of HPA output are integrated, adaptations of the axis to chronic stress are effected, and how endocrine abnormalities may contribute to stress-related psychiatric illnesses in which mPFC dysfunction is implicated.

SUBMITTER: Radley JJ

PROVIDER: S-EPMC2743123 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Clinical and experimental data suggest that fronto-cortical GABAergic deficits contribute to the pathophysiology of major depressive disorder (MDD). To further test this hypothesis, we used a well characterized rat model for depression and examined the effect of stress on GABAergic neuron numbers and GABA-mediated synaptic transmission in the medial prefrontal cortex (mPFC) of rats. Adult male Wistar rats were subjected to 9-weeks of chronic mild stress (CMS) and based on their hedonic-anhedonic behavior they were behaviorally phenotyped as being stress-susceptible (anhedonic) or stress-resilient. Post mortem quantitative histopathology was used to examine the effect of stress on parvalbumin (PV)-, calretinin- (CR), calbindin- (CB), cholecystokinin- (CCK), somatostatin-(SST) and neuropeptide Y-positive (NPY+) GABAergic neuron numbers in all cortical subareas of the mPFC (anterior cingulate (Cg1), prelimbic (PrL) and infralimbic (IL) cortexes). In vitro, whole-cell patch-clamp recordings from layer II-III pyramidal neurons of the ventral mPFC was used to examine GABAergic neurotransmission. The cognitive performance of the animals was assessed in a hippocampal-prefrontal-cortical circuit dependent learning task. Stress exposure reduced the number of CCK-, CR- and PV-positive GABAergic neurons in the mPFC, most prominently in the IL cortex. Interestingly, in the stress-resilient animals, we found higher number of neuropeptide Y-positive neurons in the entire mPFC. The electrophysiological analysis revealed reduced frequencies of spontaneous and miniature IPSCs in the anhedonic rats and decreased release probability of perisomatic-targeting GABAergic synapses and alterations in GABAB receptor mediated signaling. In turn, pyramidal neurons showed higher excitability. Anhedonic rats were also significantly impaired in the object-place paired-associate learning task. These data demonstrate that long-term stress results in functional and structural deficits of prefrontal GABAergic networks. Our findings support the concept that fronto-limbic GABAergic dysfunctions may contribute to emotional and cognitive symptoms of MDD.

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A discrete GABAergic relay mediates medial prefrontal cortical inhibition of the neuroendocrine stress response.

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