Abstract

Stimulating monopolar electrodes were chronically implanted in the lateral reticular nucleus(LRN) of three groups of male rabbits, and lesioning monopolar electrodes were also chronically implanted in the interpositus region of the cerebellum. After one week recovery period, conditioning was carried out by pairing a LRN stimulation as CS with a 100msec peri-orbitai electrical shock as US. The three groups were given either 200, 350, or 550msec trains of electric! stimulation CS that coterminated with the 100msec peri orbital electricl shock US, thus producing a 100, 250 or 450msec interstimulus interval(ISI). Varing the ISI in the present study produced differences in the percentage of CRs in the three groups of rabbits. Relatively robust rapid conditioning was observed with ISI of 250msec, moderate degree of conditioning with IS] of 450msec and little conditioning with ISI of 100msec. However, the last group of rabbits demonstrated robust rapid conditioned response after they were switched to the 250msec ISI. Finally, lesion of the interpositus region abolished the conditioned response but left unconditioned response intact. The data indicated that the charaterislic ISI function which was observed for classically conditioned responses, was established with LRN electrical stimulation as a CS, and that these classically conditioned responses depended on the cerebellum.