Memory-enhancing effects of posttraining naloxone: involvement of beta-noradrenergic influences in the amygdaloid complex.
Rats (220-250 g) were bilaterally implanted with cannulae in the amygdala, trained on an inhibitory avoidance response and two weeks later, on a Y-maze discrimination response. Immediately following the training on each task, they were injected intraperitoneally (i.p.) or intra-amygdally. Retention was tested one week after training for each task. Retention of the Y-maze task was assessed by discrimination reversal training. Naloxone administered i.p. (3.0 mg/kg) significantly facilitated retention of both tasks in unoperated control rats as well as in rats implanted bilaterally with amygdala cannulae. The memory-enhancing effect of naloxone i.p. was blocked by propranolol (0.3 or 1.0 microgram) injected in the amygdala, but not when this beta-noradrenergic antagonist was injected (0.3 micrograms) into either the caudate or the cortex dorsal to the amygdala. Further, intra-amygdala injections of the beta 1-adrenoceptor blocker atenolol (0.3 or 1.0 microgram) and the beta 2-adrenoceptor blocker zinterol (0.3 or 1.0 microgram), in doses which were ineffective when administered alone, blocked naloxone-induced (3.0 mg/kg, i.p.) memory facilitation. In contrast, posttraining intra-amygdala administration (1.0 micrograms) of the alpha-antagonists prazosin (alpha 1) or yohimbine (alpha 2) did not attenuate the memory-enhancing effects of systemically administered naloxone. These findings support the view that naloxone-induced enhancement of memory is mediated by the activation of beta- but not alpha-noradrenergic receptors located within the amygdaloid complex.
McGaugh
J L
JL
Center for the Neurobiology of Learning and Memory, University of California, Irvine 92717.
Introini-Collison
I B
IB
Nagahara
A H
AH
D000679:Amygdala / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects; D002421:Caudate Nucleus / Q000502:physiology; D002540:Cerebral Cortex / Q000502:physiology; D004192:Discrimination, Psychological; D007858:Learning / Q000187:drug effects; D008297:Male; D008568:Memory / Q000187:drug effects*; D009270:Naloxone / Q000494:pharmacology*; D011433:Propranolol / Q000494:pharmacology*; D011699:Putamen / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology*
D011943:Receptors, Adrenergic, beta; D009270:Naloxone; D011433:Propranolol