Effects of neuroleptics on rate and duration of operant versus reflexive licking in rats

Operant conditioning techniques were used to train one group of nine rats to lick a dry horizontal metal disk on a fixed ratio 15 schedule with water reinforcement delivered at a different location. Another group of seven rats licked reflexively from a water reservoir positioned with the same spatial arrangements as the metal disk. The distance the rats' rongues traversed (10 mm) to contact the licking surface was the same in both the operant and reflexive lick conditions. The effects of three neuroleptics, haloperidol (0.06, 0.12, 0.24, 1.0, 2.0 mg/kg), chlorpromazine (0.5, 1.0, 2.0 mg/kg) and clozapine (2.5, 5.0, 7.5 mg/kg) on average lick rate and median lick duration were assessed for both groups. Dose related decreases in average lick rate were observed in both groups of rats as a function of dose of each of these neuroleptics. Moreover, operant lick rates were proportionately more affected by neuroleptic treatment than were reflexive lick rates. The dose-response effect for the duration variable was different for the two lick conditions in that reflexive lick duration was lengthened as dose increased, whereas operant lick duration was lengthened only at the lower doses of these drugs. The differential effect of these neuroleptics on operant vs. reflexive licking suggests that neuroleptics attenuate selectively those responses that require relatively more conditioning to acquire. These results may be analogous to the initiation deficit that has been suggested to account for neuroleptics' selective attenuation of avoidance, while leaving relatively intact the escape response in escape/avoidance procedures.