Effects of α-adrenoceptor agonists and antagonists on histamine-induced impairment of memory retention of passive avoidance learning in rats

Abstract

The effect of α-adrenoceptor agents on the impairment induced by histamine was measured for memory retention of passive avoidance learning in rats. Post-training intracerebroventricular (i.c.v.) injection was carried out in all the experiments. Histamine (5, 10 and 20 μg/rat) reduced, while a histamine H 1 receptor antagonist, chlorpheniramine (0.1, 1 and 10 μg/rat), increased memory retention. The histamine H 2 receptor antagonist, ranitidine (0.1, 1, 10 and 20 μg/rat), did not elicit any response in this respect. Different doses of chlorpheniramine but not ranitidine reversed the histamine-induced impairment of memory. Clonidine and prazosin decreased, but yohimbine and phenylephrine increased, memory retention. Yohimbine decreased the inhibitory response to histamine. Phenylephrine, clonidine and prazosin did not alter the histamine effect. It is concluded that a histamine-induced impairment of memory retention through histamine H 1 receptors and an α 2-adrenoceptor mechanism may be involved in the histamine response.