Background: Individuals with alcohol use disorder (AUD) exhibit maladaptive responses of the hypothalamic-pituitary-adrenal (HPA) axis to stress, which has been linked to high rates of relapse to drinking among abstinent individuals. Corticotropin-releasing factor (CRF) parvocellular neuroendocrine cells (PNCs) within the paraventricular nucleus of the hypothalamus (PVN) are critical to stress-induced HPA axis activation. Here, we investigate sex differences in synaptic transmission and plasticity in PNCs following the application of the stress-associated neurotransmitter norepinephrine (NE) in a rat model of AUD.
Methods: Adult Sprague-Dawley rats were exposed to 40 days of chronic intermittent ethanol (CIE) vapor and 30 to 108 days of protracted withdrawal. We measured changes in holding current, evoked synaptic currents, and short-term glutamatergic plasticity (STP) in putative PNCs following the application of NE (10 μM) with and without the selective α1 adrenergic receptor (AR) antagonist prazosin (10 μM) or the α2AR antagonist atipamezole (10 μM). The experiments were performed using whole-cell patch clamp recordings in slices from CIE rats and air-exposed controls.
Results: NE application caused two distinct effects: a depolarizing, inward, postsynaptic current and a reduction in amplitude of an evoked glutamatergic excitatory postsynaptic current (eEPSC). Both effects were sex- and CIE-specific. Prazosin blocked the postsynaptic inward current, while atipamezole blocked the NE-mediated suppression of eEPSCs. Additionally, STP formation was facilitated following NE application only in stress-naïve males and this response was lost in stressed animals exposed to a 30-min restraint stress following CIE exposure. Furthermore, NE + prazosin restored STP formation in stressed CIE males.
Conclusions: NE exerts excitatory and inhibitory effects on CRF PVN PNCs, and both effects are influenced by sex and CIE. Behavioral and hormonal responses to stress are influenced by STP formation within the PVN, which is lost following CIE and restored with the preapplication of prazosin. The selective blockade of α1AR may, therefore, ameliorate CIE-induced deficits in HPA responses to stress in a sex-specific manner.
Keywords: chronic intermittent ethanol; hypothalamus; metaplasticity; norepinephrine; sex differences.
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