Abstract: Scopolamine (M-cholinergic receptor antagonist), GABA and Picrotoxin(GABA receptor antagonist) were injected into the hippocampal area CA_3 ofrabbits with chronically embedded cannula. Rabbits were trained to performthe consolidatory operant conditioning. The influences of such injectionon the conditioned response were investigated. Injection of Scopolamine (45 ug/ul) caused a temporary depressionin the conditioned response with a time course of 5.4±0.5 min. (M±SE,n=10), while the animals' general motor activities and food intakewere not significantly affected. Application of GABA (3 mg/ul) alsocaused suppression for 58.2±5.6 min. (n=9). However, after a prior inje-ction of Picrotoxin (0.2 ug or 0.5 ug/ul) the depression of the conditionedresponse by application of GABA was relevantly reduced, in which casethe time course of depression was 38.7±4.6 min. (n=5, P 0.001) or 13.7±3.8 min. (n=6, P 0.001). As a control, when aline was injected into thesame loci no detectable effect on the conditioned response was observed. It seems that M-cholinergic receptor and GABA receptor in hipp-ocampal areaCA_3 are involved in the retention of long-term memory.

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