Alcohol intake and ethanol intoxication in the rat: Effect of a 6-OHDA-induced lesion of the ascending noradrenaline pathways

Abstract

The ascending noradrenaline (NA) pathways were lesioned by injecting 6-hydroxydopamine (6-OHDA) 16 μg/ 4 μl bilaterally into the posterior mesencephalon in male Long Evans rats. Another group of rats was pretreated with protriptyline (25 mg/kg), a NA uptake blocking agent, 15 min before they received the intracerebral injections of 6-OHDA. The controls received the vehicle only. Spectrofluorimetric determination of the catecholamine concentrations in various parts of the brain revealed a marked degeneration of the ascending NA systems in the group receiving 6-OHDA. Unexpectedly, the DA systems were also affected by the 6-OHDA treatments. Three weeks after the operation the 6-OHDA group showed a transient increase in ethanol intake. In the tilting-plane test, ethanol (2 g/kg, i.p.) impaired the performance of the 6-OHDA-treated rats significantly more than that of the controls. In contrast, the hypothermic effect of ethanol (4 g/kg, i.p.) was significantly smaller in the lesioned rats. Furthermore, the catecholamine levels in various parts of the brain could be significantly correlated with both the extent of ethanol intoxication and the hypothermia. However, the duration of ethanol-induced narcosis (4 g/kg, i.p.) was not affected by the present treatments. These results give further support for the view that the central NA neurons are important in the control of ethanol intake, and that they are also involved in the expression of the acute effects of ethanol administration.