EFFECTS OF POSTTRAINING ADMINISTRATION OF GLUCOSE ON RETENTION OF A HABITUATION RESPONSE IN MICE - PARTICIPATION OF A CENTRAL CHOLINERGIC MECHANISM

Male Swiss mice were allowed to explore a novel environment, provided by an open-field activity chamber, for 10 min. The procedure was repea ted twice with a 24-h interval. The difference in the exploratory acti vity between the first (training) and the second (testing) exposures t o the chamber was taken as an index of retention of this habituation t ask. Posttraining intraperitoneal administration of glucose (10-300 mg /kg) enhanced retention in a dose-related manner, although only the do se of 30 mg/kg of glucose produced significant effects. Thus, the dose -response curve adopted an inverted U-shaped form. Glucose (30 mg/kg) given to untrained mice did not modify their exploratory performance w hen recorded 24 h later. The effects of glucose on retention were time -dependent, suggesting an action on memory storage. The memory-improvi ng actions of glucose were prevented by the simultaneous administratio n of both the central acting muscarinic cholinergic antagonist atropin e (0.5 mg/kg) and by the central acting nicotinic cholinergic antagoni st mecamylamine (5 mg/kg). In contrast, neither methylatropine (0.5 mg /kg), a peripherally acting muscarinic receptor blocker, nor hexametho nium (5 mg/kg), a peripherally acting nicotinic receptor blocker, prev ented the effects of glucose on retention. Low subeffective doses of g lucose (10 mg/kg) and the central anticholinesterase physostigmine (35 mu g/kg), but not neostigmine (35 mu g/kg), given together, act syner gistically and facilitated retention. We suggest that glucose modulate s memory storage of one form of learning elicited by stimuli repeatedl y presented without reinforcement, probably through an enhancement of brain acetylcholine synthesis and/or its release. (C) 1996 Academic Pr ess, Inc.