Inhibition of acetylcholine turnover in rat hippocampus by intraseptal injections of beta-endorphin and morphine.

Intraseptal administration of morphine (70 nmol) or beta-endorphin (0.7 nmol) reduced the rate of acetylcholine (ACh) turnover (TRACh) in rat hippocampus but not in striatum or cortex. These intraseptal injections failed to modify the ACh content and did not elicit analgesia. Naltrexone (15 mumol/kg, i.p.) completely antagonized the decrease of hippocampal TRACh elicited by the two opiate receptor agonists. Furthermore, intraseptal injections of naltrexone partially blocked the decrease in hippocampal TRACh induced by intraperitoneal administration of morphine (70 mumol/kg, i.p.). These data suggest that opiate agonists decrease hippocampal TRACh by regulating septal cholinergic neurons, and that this effect is not associated with analgesia.