Selective, naloxone-reversible morphine depression of learned behavioral and hippocampal responses

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Science  23 Apr 1982:
Vol. 216, Issue 4544, pp. 434-436
DOI: 10.1126/science.7071592


Morphine administered intravenously causes immediate and complete abolition of a simple learned response (classically conditioned nictitating membrane extension in rabbit) and of the associated learning-induced increase in hippocampal neuron activity. Both effects are completely reversed by low doses of naloxone. Morphine has no effect at all on behavioral performance of the unconditioned reflex response.