Dopamine receptor agonists alter gap prestimulus modulation.
An innocuous sensory event (a prestimulus) that briefly precedes a startle-eliciting stimulus (SES) will reduce the amplitude of the subsequently elicited reflex. In three experiments brief silent periods in otherwise continuous noise (gaps) were used as prestimuli to investigate the effects of the D1 dopamine receptor agonist (+/-)-SKF-38393 (SKF) and the dopamine D2 receptor group agonist (-)-quinpirole hydrochloride on gap inhibition of the rat's acoustic startle reflex. Gap durations of 4 and 50 ms were analyzed. Quinpirole (0-1.6 mg/kg) had a biphasic effect on gap inhibition. Lower doses increased gap inhibition, an effect that peaked at the 0.4 mg/kg dose. For higher doses, inhibition returned to control levels for the 4-ms long gap, but remained elevated for the 50-ms long gap. SKF had no effect on gap inhibition, and haloperidol (0.2 mg/kg) reversed the quinpirole-induced increase of gap inhibition. These data implicate the D2 dopamine receptor group in gap inhibition of startle modulation. The results are discussed in terms of the effects of catecholamine agonists on attention.