Action of intracerebroventricular epinephrine on gross behavior, locomotor activity and hexobarbital sleeping times in rats

Abstract

l-Epinephrine administered via the lateral cerebral ventricle was found to decrease exploratory locomotor activity and potentiate hexobarbital sleeping time in rats. Both effects were dose-dependent and occurred with microgram quantities (3·3–125 μg) of epinephrine. Additional signs of a central depressant effect were noted in gross behavior. Although subcutaneous injections of l-epinephrine (0·025 and 1·0 mg/kg) also depressed locomotor activity, intraventricular injections proved much more effective. Lethality of l-epinephrine was enhanced by the intraventricular route, but the observed depressant effects occurred at doses well below the ld₅₀ and were observed to be completely reversible. The importance of the catechol moiety for the central depressant effects of epinephrine was emphasized by the results obtained from studying the effect on locomotor activity of a series of sympathomimetic amines. The parent compound, phenylethylamine, which is devoid of hydroxyl groups on the benzene ring and aliphatic side chain, was found to be excitant rather than depressant. Rank order of potency studies indicated that the depressant effect of catecholamines on locomotor activity might be mediated through central adrenergic receptors of the β-type. Studies with adrenergic blocking agents did not support this idea, however, and suggested that the central receptors involved are not identical to either the classical α or β adrenergic receptor.