Stress-dependent impairment of passive-avoidance memory by propranolol or naloxone

Abstract

Previous work has shown that the effect of opioid-receptor blockade on memory modulation is critically dependent upon the intensity of stress. The current study determined the effect of adrenergic-receptor blockade on memory modulation under varied levels of stress and then compared the effect of adrenergic-receptor blockade under intense stress to that of a) opioid-receptor blockade and b) concurrent opioid- and adrenergic-receptor blockade. In the first experiment, the β-adrenergic-receptor blocker propranolol impaired retention in the passive-avoidance procedure when administered immediately after exposure to intense stress (passive-avoidance training followed by swim stress) but not mild stress (passive-avoidance training alone). In the second experiment, while separate administration of either propranolol or the opioid-receptor blocker naloxone immediately after exposure to intense stress impaired retention, the combined administration of propranolol and naloxone failed to do so. These findings demonstrate that the effect of β-adrenergic-receptor blockade or opioid-receptor blockade on memory modulation in the passive-avoidance procedure is dependent upon the intensity of stress, and suggest that concurrent inactivation of endogenous adrenergic- and opioid-based memory modulation systems under stressful conditions is protective of memory.

Fig. 1

Propranolol impairs retention in the presence but not in the absence of swim stress. Step-through latency (mean ± SEM) in seconds on the test trial for the No Swim-Vehicle group (n = 8), No Swim-Pro group (n = 9), Swim-Vehicle group (n = 7), and Swim-Pro group (n = 9). *p<0.05 compared with the corresponding vehicle group. P-values shown are for significant protected-t tests following one-way ANOVA; F(3, 29) = 2.89, p = 0.05. Pro—propranolol and Veh—vehicle.

Fig. 2

Propranolol and naloxone each impair retention in the presence of swim stress but not when administered in combination. Step-through latency (mean ± SEM) in seconds on the test trial for the Swim-Vehicle group (n = 8), Swim-Pro group (n = 10), Swim-Nal group (n = 10), and Swim-Pro + Nal group (n = 8). *p<0.01 compared with the corresponding Swim-Vehicle group and p<0.05 compared to the Swim-Pro + Nal group. P-values shown are for significant protected-t tests following one-way ANOVA; F (3, 32) = 6.80, p<0.01. Pro—propranolol, Nal—naloxone and Veh—vehicle.