Yonggang Gao1,2, Jing-Jing Zhou1, Yun Zhu3, Li Wang1, Therese A Kosten4, Xiangjian Zhang5,6, De-Pei Li1. 1. Department of Critical Care and Anesthesiology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA. 2. Department of Preventive Medicine, Hebei University of Chinese Medicine, Shijiazhuang, HeBei, China. 3. Department of Otorhinolaryngology, Union Hospital of Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China. 4. Department of Psychology, University of Houston, Houston, TX, USA. 5. Department of Neurology, Second Hospital of Hebei Medical University, Shijiazhuang, Hebei, China. 6. Hebei Collaborative Innovation Center for Cardiocerebrovascular Disease, Shijiazhuang, Hebei, China.
Abstract
BACKGROUND AND PURPOSE: Chronic stress impairs GABAA (GABA type A) receptor-mediated inhibition in the hypothalamic paraventricular nucleus (PVN). It is not clear whether GABAB receptor function is also altered. We hypothesize that chronic stress alters GABAB receptor function in PVN corticotrophin-releasing hormone (CRH) neurons to control hypothalamus-pituitary-adrenal axis activity. EXPERIMENTAL APPROACH: Whole-cell patch clamp recordings were made of PVN-CRH neurons expressing eGFP driven by CRH promoter in brain slices from unstressed rats and rats exposed to chronic unpredictable mild stress (CUMS). KEY RESULTS: CUMS elevated the basal circulating corticosterone levels and increased the basal firing activity of PVN-CRH neurons. Microinjection of GABAB receptor agonist baclofen into the PVN suppressed the increased corticosterone levels in CUMS rats compared with unstressed rats. CUMS blunted the baclofen-induced inhibition on PVN-CRH neurons and outward currents in these neurons. Furthermore, CUMS reduced expression of GABAB1 (GABAB R1) protein in the PVN. Blocking NMDA receptors with AP5 restored the reduced baclofen-induced currents in CUMS rats but had no effect on GABAB1 expression. Furthermore, CUMS treatment augmented the baclofen-induced decrease in the frequency of glutamatergic excitatory postsynaptic currents (EPSCs) and GABAergic inhibitor postsynaptic currents in PVN-CRH neurons. The GABAB receptor antagonist CGP55845 increased the firing activity of PVN-CRH neurons only in CUMS-treated rats and not in unstressed rats. CONCLUSIONS AND IMPLICATIONS: These findings suggest that chronic stress impairs postsynaptic GABAB receptor function but augments presynaptic GABAB receptor function in controlling glutamatergic and GABAergic synaptic inputs in PVN-CRH neurons.
BACKGROUND AND PURPOSE: Chronic stress impairs GABAA (GABA type A) receptor-mediated inhibition in the hypothalamic paraventricular nucleus (PVN). It is not clear whether GABAB receptor function is also altered. We hypothesize that chronic stress alters GABAB receptor function in PVN corticotrophin-releasing hormone (CRH) neurons to control hypothalamus-pituitary-adrenal axis activity. EXPERIMENTAL APPROACH: Whole-cell patch clamp recordings were made of PVN-CRH neurons expressing eGFP driven by CRH promoter in brain slices from unstressed rats and rats exposed to chronic unpredictable mild stress (CUMS). KEY RESULTS:CUMS elevated the basal circulating corticosterone levels and increased the basal firing activity of PVN-CRH neurons. Microinjection of GABAB receptor agonist baclofen into the PVN suppressed the increased corticosterone levels in CUMSrats compared with unstressed rats. CUMS blunted the baclofen-induced inhibition on PVN-CRH neurons and outward currents in these neurons. Furthermore, CUMS reduced expression of GABAB1 (GABAB R1) protein in the PVN. Blocking NMDA receptors with AP5 restored the reduced baclofen-induced currents in CUMSrats but had no effect on GABAB1 expression. Furthermore, CUMS treatment augmented the baclofen-induced decrease in the frequency of glutamatergic excitatory postsynaptic currents (EPSCs) and GABAergic inhibitor postsynaptic currents in PVN-CRH neurons. The GABAB receptor antagonist CGP55845 increased the firing activity of PVN-CRH neurons only in CUMS-treated rats and not in unstressed rats. CONCLUSIONS AND IMPLICATIONS: These findings suggest that chronic stress impairs postsynaptic GABAB receptor function but augments presynaptic GABAB receptor function in controlling glutamatergic and GABAergic synaptic inputs in PVN-CRH neurons.
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