A Microdialysis Profile of Dynorphin A1–8 Release in the Rat Nucleus Accumbens Following Alcohol Administration.

Background: Pharmacological studies have implicated the endogenous opioid system in mediating alcohol intake. Other evidence has shown that alcohol administration can influence endorphinergic and enkephalinergic activity, while very few studies have examined its effect on dynorphinergic systems. The aim of the present study was to investigate the effect of alcohol administration or a mechanical stressor on extracellular levels of dynorphin A_1–8 in the rat nucleus accumbens—a brain region that plays a significant role in the processes underlying reinforcement and stress. Methods: Male Sprague–Dawley rats were implanted with a microdialysis probe aimed at the shell region of the nucleus accumbens. Artificial cerebrospinal fluid was pumped at a rate of 1.5 μL/min in awake and freely moving animals and the dialysate was collected at 30-minute intervals. In one experiment, following a baseline period, rats were injected intraperitoneally with either physiological saline or 1 of 3 doses of alcohol, 0.8, 1.6, or 3.2 g ethanol/kg body weight. In a second experiment, following a baseline period, rats were applied a clothespin to the base of their tail for 20 minutes. The levels of dynorphin A_1–8 in the dialysate were analyzed with solid-phase radioimmunoassay. Results: Relative to saline-treated controls, an alcohol dose of 1.6 and 3.2 g/kg caused a transient increase in the extracellular levels of dynorphin A_1–8 in the first 30 minutes of alcohol administration. However, the effect resulting from the high 3.2 g/kg dose was far more pronounced and more significant than with the moderate dose. There was no effect of tail pinch on dynorphin A_1–8 levels in the nucleus accumbens. Conclusions: In this experiment, a very high dose of alcohol was especially capable of stimulating dynorphin A_1–8 release in the nucleus accumbens. Dynorphin release in the accumbens has been previously associated with aversive stimuli and may thus reflect a system underlying the aversive properties of high-dose alcohol administration. However, the lack of effect of tail-pinch stress in the present study suggests that dynorphin A_1–8 is not released in response to all forms of stressful/aversive stimuli. [ABSTRACT FROM AUTHOR]