The role of the dopaminergic system in the modulation of the acoustic startle response in the rat

The (+) and (-) isomers of 3-(3-hydroxyphenyl)-N-propylpiperidine (3-PPP) (2-32 mg/kg) were tested for their effects on the acoustic startle response in the rat and these effects were compared with those of apomorphine and haloperidol. Both startle amplitude and startle latency were recorded. (+)-3-PPP produced a dose-dependent prolongation of startle latency. No other significant effects of the 3-PPP isomers were observed. Apomorphine (0.75-3 mg/kg) produced a dose-dependent increase in startle amplitude concurrent with a dose-dependent prolongation of startle latency. Both these effects were blocked by haloperidol. Haloperidol by itself produced a significant decrease in startle amplitude at the highest dose used (1.6 mg/kg). These and other data suggest that activation of both dopamine D-1 and dopamine D-2 receptors is essential for the stimulatory effects of dopamine receptor agonists on the acoustic startle response in the rat.