Memory-improving actions of glucose: involvement of a central cholinergic muscarinic mechanism

Post-training intraperitoneal administration of alpha-D[+]-glucose (10-300 mg/kg) facilitated 24-h retention, in male Swiss mice, of a one-trial step-through inhibitory avoidance task. The dose-response curve was an inverted U. Glucose did not increase the retention latencies of mice that had not received a footshock during training. The effect of glucose (30 mg/kg, ip) on retention was time-dependent, which suggests that the drug facilitated memory storage. The memory facilitation induced by glucose (30 mg/kg, ip) was prevented by atropine (0.5 mg/kg, ip) administered after training, but 10 min prior to glucose treatment. In contrast, neither methylatropine (0.5 mg/kg, ip), a peripherally acting muscarinic receptor blocker, nor mecamylamine (5 mg/kg, ip) or hexamethonium (5 mg/kg, ip), two cholinergic nicotinic receptor antagonists, prevented the effects of post-training glucose on retention. Low subeffective doses of the central acting anticholinesterase physostigmine (35 micrograms/kg, ip), administered immediately after training, and glucose (10 mg/kg, ip), given 10 min after training, acted synergistically to improve retention. The effects of glucose (10 mg/kg, ip) were not influenced by the peripherally acting anticholinesterase neostigmine (35 micrograms/kg, ip). Considered together, these findings suggest that the memory facilitation induced by post-training administration of glucose could result from an enhancement of brain acetylcholine synthesis and/or its release that, in turn, might modulate the activity of muscarinic cholinergic mechanisms that are critically involved in memory storage.