Task-dependent effects of intra-amygdala morphine injections: attenuation by intra-amygdala glucose injections

Intraseptal injections of morphine impair learning and memory in rats, and these impairments are reversed by intraseptal injections of glucose. With evidence that injections of morphine into the amygdala also impair memory for some tasks, the present experiment determined whether (1) intra-amygdala morphine injections impair performance in inhibitory avoidance and spontaneous alternation tasks, and (2) intra-amygdala glucose injections attenuate the effects of intra-amygdala morphine injections. Rats receiving bilateral injections of morphine (4.0 nmol) into the amygdala, 30 min prior to training in inhibitory avoidance, had retention latencies significantly lower than those of unoperated and CSF controls when tested 24 hr later. Bilateral morphine injections (4.0 or 8.0 nmol) 30 min prior to testing in a spontaneous alternation task did not alter performance. The morphine-induced impairment observed in inhibitory avoidance was not due to diffusion up the cannulas, altered sensitivity to shock, or seizure activity. A glucose dose of 16.67 nmol, but not 8.33 nmol, injected into the amygdala attenuated the morphine-induced deficit in inhibitory avoidance. Rats receiving CSF into the amygdala exhibited decreased retention latencies in inhibitory avoidance compared to those of unoperated controls. This decrease was not attenuated by glucose at doses of 8.33 and 16.67 nmol. Therefore, these findings suggest that the amygdala is another brain region in which glucose affects brain functions, possibly by interacting with the opioid system and/or other neurotransmitter systems.