Similarity of clozapine's and olanzapine's acute effects on rats' lapping behavior.

As a way of further comparing the behavioral effects of clozapine and olanzapine, dose ranges of these drugs were studied in a task emphasizing fine motor detail of rats' tongue movements during lapping behavior. Rats lapped drops of tap water from a force-sensing disk. From this behavior four variables were derived: peak-force of tongue strikes, duration of tongue contact, number of separate tongue contacts in 2 min, and the rhythm of the lapping behavior as quantified by Fourier analysis. Both clozapine (0.5-4.0 mg/kg, IP, 45 min) and olanzapine (0.25-2.0 mg/kg, IP, 45 min) dose dependently reduced all four measures of behavior. With respect to lick rhythm, a behavioral marker which clearly distinguishes haloperidol from clozapine in this behavioral paradigm, olanzapine was about twice as potent as clozapine, with the two drugs having parallel dose-effect functions. Within-session decrements in behavior previously reported for haloperidol in the lick task were not produced by clozapine nor by olanzapine. Taken together, these data strengthen the idea that the behavioral effects of clozapine and olanzapine are strikingly similar, and thereby emphasize the potential of olanzapine as an atypical anti-psychotic agent.