Alcohol addiction is a chronic relapsing disorder characterized by compulsive alcohol-seeking and the emergence of a negative emotional state (allostasis) that leads to dependence on alcohol. Alcohol use disorders are associated with a persistent dysregulation of the hypothalamic pituitary adrenal (HPA) axis and corticotropin- releasing factor (CRF) signaling that leads to inappropriate responses to stress, thereby increasing relapse susceptibility in abstinent alcoholics. Although research has progressed to better understand the detrimental relationship between the allostatic HPA axis response to stress and alcohol relapse, the cellular mechanisms underlying the HPA axis allostatic response to stress in EtOH-dependence remain unclear and warrant further investigation in order to develop the much needed novel therapies to treat alcoholism and the consequent alcohol-related diseases. Stress information is processed in higher brain regions and converged onto parvocellular neurosecretory cells (PNCs) within the paraventricular nucleus of the hypothalamus (PVN) which represents the final central integrative and output step of HPA axis response. Stress induces multiple distinct forms of glutamatergic and GABAergic synaptic plasticity of PNCs which depend on different mediators of the stress-induced HPA axis response such as CRF, NMDAR, cortisol/corticosterone (CORT) and norepinephrine (NE) within the PVN. These different forms of stress-induced synaptic plasticity provide a cellular mechanism by which stress induces neuroadaptive responses of the HPA axis. Chronic intermittent ethanol (CIE) treatment alters CORT-mediated negative feedback, NE, glutamatergic, and GABAergic neurotransmissions leading to a dysregulated HPA axis function. Preliminary results show that CIE exposure increases NMDAR function and prevents CRF-induced depression of NMDAR function in PNCs. Moreover, stress-induced CRF/NMDAR- dependent glutamatergic short-term synaptic plasticity (STP) is impaired in PNCs of CIE rats but is restored after inhibition of NMDAR function. We also related the impairment of STP in PNCs to dysregulated HPA axis hormonal (CORT and ACTH) and grooming (behavioral) responses to repeated stressors. Thus, the main hypothesis of this proposal is that CIE exposure leads to the alteration of CRF-mediated NMDAR- dependent synaptic plasticity, which together with alterations in NE, CORT, and GABA signaling in the PVN is responsible for the HPA axis allostatic response to stress in EtOH dependence. To test this hypothesis we will use a combination of behavioral, electrophysiological, biochemical and pharmacological techniques to determine: 1) the role of NMDAR, 2) CORT, and 3) NE in CIE-induced neuroadaptive changes in PNCs and the maladaptive behavioral and hormonal HPA responses to repeated stress, and 4) the intra-PVN role of NMDAR, CORT, and NE signaling in excessive EtOH intake, decreased stress-induced grooming, and stress-induced increases in EtOH intake of CIE rats.
Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, a highly regulated system that mediates neuroendocrine response to stress, plays an important role in the inability of alcoholics to effectively cope with relapse-inducing stressors. This project will identify the cellular mechanisms underlying the maladaptive responses of the HPA axis to stress in alcohol dependence. These studies will help unravel the intricate mechanism involved in the dysregulated HPA axis in alcohol dependence, which is critical in the discovery of new effective therapies for stress-induced compulsive alcohol seeking.
