Subchronic treatment with prazosin improves passive avoidance learning in aged mice: possible relationships to alpha1-receptor up-regulation.

While many evidences indicate that deficits of central noradrenergic neurotransmission are involved in the age-related decline of cognitive functions in animals and man, very little is known about the specific role of central alpha1-adrenergic receptors. Therefore, this problem was specifically addressed in the present communication using the alpha1-adrenoceptor antagonist prazosin as pharmacological tool. While the acute administration of prazosin did not affect passive avoidance learning of young or aged mice, an improvement of learning capabilities was seen after subchronic treatment, but for the aged animals only. An U-shaped dose response curve was seen. 0.3 mg/kg prazosin was most effective. Very interestingly, only for this dose a significant up-regulation of the density of alpha1-adrenoceptors in the mouse brain was found in the aged animals only. The data suggest a possible causal relationship between effects of prazosin on passive avoidance learning and central alpha1-receptor density.