Role of the central amygdala GABA-A receptors in morphine state-dependent memory.
OBJECTIVE
In the present experiments, the effects of bilateral microinjections of the GABA-A receptor agonist and/or antagonist into the central amygdala (CeA) on morphine state-dependent memory were examined.


METHODS
In order to assess memory retrieval, a step-through passive avoidance task was used in adult male Wistar rats.


RESULTS
Subcutaneous (s.c.) administration of morphine (5 and 7.5mg/kg) immediately after training (post-training) decreased the memory retrieval. Pre-test administration of the opioid (7.5mg/kg) also induced amnesia. The response induced by post-training morphine (7.5mg/kg) was significantly reversed by pre-test administration of the drug (5 and 7.5mg/kg), indicating morphine state-dependent memory. Pre-test intra-CeA microinjection of muscimol, a GABA-A receptor agonist (0.01, 0.02 and 0.03microg/rat) reduced morphine state-dependent memory. However, the same doses of muscimol by itself had no effect on memory retrieval. Furthermore, pre-test intra-CeA microinjection of bicuculline, a GABA-A receptor antagonist by itself did not alter memory retrieval. The antagonist also did not change post-training morphine (7.5mg/kg)-induced amnesia, but in combination with a lower dose of morphine (0.5mg/kg), improved memory performance. Moreover, muscimol's ability to interfere with morphine state-dependent memory was reversed by co-injection of bicuculline.


CONCLUSIONS
The results suggest that GABA-A receptor mechanism of the CeA may influence morphine state-dependent memory.
Rassouli
Yassaman
Y
Institute for Cognitive Science Studies, Tehran, Iran.
Rezayof
Ameneh
A
Zarrindast
Mohammad-Reza
MR
D000679:Amygdala / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects / Q000502:physiology; D001640:Bicuculline / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D058785:GABA-A Receptor Agonists; D058787:GABA-A Receptor Antagonists; D008297:Male; D008568:Memory / Q000187:drug effects / Q000502:physiology*; D009020:Morphine / Q000494:pharmacology; D009021:Morphine Dependence / Q000503:physiopathology*; D009118:Muscimol / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000187:drug effects / Q000502:physiology*; D012153:Retention, Psychology / Q000187:drug effects / Q000502:physiology
D058785:GABA-A Receptor Agonists; D058787:GABA-A Receptor Antagonists; D011963:Receptors, GABA-A; D009118:Muscimol; D009020:Morphine; D001640:Bicuculline