Verapamil enhances the impairing effects of stress on retrieval of long-term memory in rats

This study investigated an interaction between acute restraint stress and verapamil, as a blocker of L-type voltage sensitive channels on retrieval of long-term memory. Young adult male rats were trained in one trial inhibitory avoidance task (1mA, 1.5s footshock). On retention test given 48 hr after training, the latency to re-enter dark compartment and time spent in light chamber of the apparatus were recorded. Thirty min before retention test, the rats were exposed to a 10 min of restraint stress in a Plexiglass with or without prior treatment of verapamil (5, 10, 20 mg/kg). The results showed verapamil pretreatment enhanced the impairing effect of stress on memory retrieval. The applied stress increased circulating corticosterone levels as assessed immediately after the retention test, indicating that stress–induced impairment of memory retrieval is mediated, in part, by increased plasma levels of glucocorticoids. Verapamil did not affect on this response. These findings indicate that acute restraint stress impair retrieval of long-term memory, and provide evidence for the existence of an interaction between stress and L-type voltage calcium channels on this process.