EFFECTS OF INHIBITION OF THE GABAERGIC SYSTEMS BY PICROTOXIN ON RETENTION OF A NOCICEPTIVE EXPERIENCE IN THE RAT, WITH SPECIAL REFERENCE TOTHE INFLUENCE OF CEREBELLAR CORTEX OUTPUT

Adult cerebellectomized and noncerebellectomized DA/HAN strain (pigmen ted) female rats were submitted to a one-trial passive avoidance condi tioning procedure consisting in associating darkness with a nociceptiv e stimulus. Seven days later, they were tested again to assess the ret ention stage. The results demonstrate that in noncerebellectomized rat s, picrotoxin, whatever the dose, administered prior to the retention test, does not significantly impair retrieval. On the contrary, when a dministered just prior to the initial conditioning, impairments of the initial single nociceptive experience were evident (the greater the p icrotoxin dose, the greater the impairments). In animals that were cer ebellectomized 1 week before the experiment, picrotoxin administered a t a low dose before the initial experience elicited memory impairments that were similar to those induced in noncerebellectomized rats but t hat were greater than those elicited in cerebellectomized, nontreated animals. However, in cerebellectomized rats, picrotoxin administered a t a low dose elicited memory impairments that were weaker than in nonc erebellectomized animals injected with a high dose of the drug. Consid ering that a low dose of picrotoxin administered to cerebellectomized animals had effects that were similar to those of a high dose injected to noncerebellectomized rats, and given that it has previously been d emonstrated that a cerebellectomy performed after a single nociceptive experience impairs its memory, it is tempting to suggest that the two different doses of the drug administered to cerebellectomized and non cerebellectomized rats have similar effects on memory. If such an inte rpretation is valid, the information would have to leave the cerebella r cortex to be stored for long.