Effects of ketamine and apomorphine on inferior colliculus and caudal pontine reticular nucleus evoked potentials during prepulse inhibition of the startle reflex in rats.

Prepulse inhibition (PPI) of the startle reaction to a strong sound is the reduction of this reaction elicited by a weak stimulus, a tone for example, when it precedes the startling sound. Its pharmacological sensitivity has been used to characterize antipsychotic drugs. Not much is known about the level of action of such drugs in the neuronal network involved in PPI. In the present study, evoked potentials from two key structures, the inferior colliculus (IC) and the caudal pontine reticular nucleus (PnC), were obtained in freely moving rats during standard startle and PPI tests, under ketamine (5 mg/kg) or apomorphine (0.5 mg/kg). In the IC, the potential evoked by the noise did not vary whether tested in basic or PPI conditions. Only minor changes were elicited by the drugs. In the PnC, the noise elicited an evoked potential that was reduced under PPI conditions. This alteration of the evoked potential was reversed by ketamine. The results obtained with apomorphine were not homogeneous either when considering the behavioral or the electrophysiological results.