ENHANCED SUPPRESSIVE EFFECTS OF AVERSIVE EVENTS INDUCED IN RATS BY PICROTOXIN - POSSIBILITY OF A GABA CONTROL ON BEHAVIORAL-INHIBITION

The effects of a GABA receptor blocking agent, picrotoxin (0.5 and 1 mg kg-1 IP 30 min before testing) on the behavioral inhibition induced in rats by (1) novelty, (2) punishment or (3) non-reward were studied. Picrotoxin was found to enhance (1a) inhibition of water drinking in rats placed for the first time in an unfamiliar box, (1b) inhibition of milk drinking in rats faced with milk for the second time and (1c) inhibition of chocolate intake in rats faced with chocolate for the third time. This drug failed to further reduce milk drinking or chocolate intake in rats faced for the first time with milk or chocolate. Picrotoxin has no effect on drinking of rats habituated to the test box or familiarized with chocolate. Picrotoxin was found to enhance (2) the inhibition of lever presses for food induced in separate groups of rats by the delivery of an electric shock at each 25th or 10th press. This drug failed to further reduce depressed pressing induced by the delivery of a shock at each 5th press. Picrotoxin did not modify responding in non-punished rats. Picrotoxin was found (3a) to impair recovery from reward depression induced in rats by shift from a CRF to a FR 4 schedule but was ineffective on rats well adapted to a FR 4 schedule and (3b) to further depress reduced responding during the first extinction sessions but not during the last extinction session. It is proposed that picrotoxin only increases the inhibitory control of aversive events on behavior. Since we found this drug to be ineffective on very strong inhibition, one can suggest that GABA may be critically implicated in the release of behavior from mild inhibitory control exerted by novelty, punishment or non-reward. © 1979.