PREPULSE INHIBITION OF THE ACOUSTIC STARTLE REFLEX USING VISUAL AND AUDITORY PREPULSES - DISRUPTION BY APOMORPHINE

The amplitude of the acoustic startle reflex can be reduced reliably w hen preceded at short intervals by a weak stimulus (prepulse) which it self does not elicit startle. The magnitude of this prepulse inhibitio n effect is attenuated by several dopamine agonists, such as apomorphi ne, especially when there is a relatively small difference between the intensity of the prepulse and the intensity of the background noise o ver which the prepulse is superimposed. One goal of the present experi ment was to test the generality of this disruptive effect of apomorphi ne on prepulse inhibition by using either an auditory prepulse that in cluded both a change in intensity and a change in frequency relative t o the background noise or a visual prepulse stimulus. Apomorphine redu ced auditory prepulse inhibition when induced by a small change in sti mulus intensity, but not when induced by a change in both intensity an d frequency. Apomorphine consistently reduced visual prepulse inhibiti on with a complete blockade at 100-ms test interval. However, it did n ot fully block the usual reduction in startle onset latency or even at tenuate the increase in startle amplitude when a visual prepulse was p resented 5, 10 or 15 ms before the startle stimulus. Consistent with c onclusions from other laboratories using auditory prepulse inhibition, these data suggest that apomorphine did not prevent the animal from d etecting prepulse presentation under conditions where the drug complet ely blocked prepulse inhibition. Moreover, they indicate that the bloc kade of prepulse inhibition by apomorphine was independent of prepulse modality, adding generality to the original finding. Visual prepulse inhibition may be a useful alternative procedure for evaluating the ef fects of drugs on this attentional process.