Journal of Neuroscience, Vol 14, 7478-7485, Copyright © 1994 by Society for Neuroscience
Task-dependent effects of intra-amygdala morphine injections: attenuation by intra-amygdala glucose injections
ME Ragozzino and PE Gold
Department of Psychology, University of Virginia, Charlottesville 22903.
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.