Time-dependent effects of hippocampo-entorhinal atropine on passive avoidance learning in the young rat.

Young rats 20 and 16 days of age received bilateral micro-injections of saline or atropine (115 micrograms/kg) into the posteroventral hippocampo-subiculo-entorhinal area, and were trained on a cool-draft-stimulus passive avoidance task thereafter. The delay between injection and training was variable: 17 min, 4 h and 6 h at 20 days; 17 min, 6 h and 12 h at 16 days. Atropine-induced learning deficits were observed after the short and intermediate intervals, but not after the longer ones, indicating that the action of atropine injected intracerebrally lasted for several hours (at least 4 h at 20 days, and 6 h at 16 days) and was over after 6 h and 12 h respectively.