Effects of microinjections of apomorphine and haloperidol into the inferior colliculus on prepulse inhibition of the acoustic startle reflex in rat

Prepulse inhibition (PPI) is the reduction in the startle response caused by a low intensity non-startling stimulus (prepulse) which is presented shortly before the startle stimulus and is an operational measure of sensorimotor gating. PPI is impaired in schizophrenia patients and in rats with central dopamine (DA) activation. The inferior colliculus (IC) is a critical part of the auditory pathway mediating acoustic PPI. The activation of the IC by the acoustic prepulse reduces startle magnitude. The aim of this study was to elucidate the role of DA transmission of the IC on the development of acoustic PPI. Bilateral microinjections of apomorphine (9.0 μg/0.5 μL), an agonist of D(2) receptors, into the IC disrupted PPI while microinjections of haloperidol (0.5 μg/0.5 μL), an antagonist of D(2) receptors, into this structure did not alter PPI. These results suggest that dopamine-mediated mechanisms of the IC are involved in the expression of PPI in rodents.