DOI disrupts prepulse inhibition of startle in rats via 5-HT2A receptors in the ventral pallidum

Serotonin (5-HT)(2A) receptors are known to be involved in prepulse inhibition of the startle response (PPI), a measure of sensorimotor inhibition that is deficient in schizophrenia, Huntington's disease, and obsessive compulsive disorder. In the present studies, the localization of the 5-HT2A receptors responsible for modulating PPI was investigated using central injections of the hallucinogenic 5-HT2 agonist DOI and the novel 5-HT2A antagonist MDL 100,907. 5-HT2A receptors are densely localized in the nucleus accumbens (NAG) and the ventral pallidum (VP), areas known to be important components of neural circuitry that mediates the ventral forebrain modulation of PPI. In the present studies, it was found that the infusion of DOI (0.0-5.0 mu g/0.5 mu l) into the VP disrupted PPI without having effects on startle reactivity. In contrast, similar infusions into the NAC had no effect on PPI or startle reactivity. The infusion of MDL 100,907 into the VP was found to increase PPI by itself and to attenuate the PPI-disruptive effects of systemically administered DOI. It is concluded that 5-HT2A receptors within the VP are important for the modulation of PPI, presumably through interactions at intrinsic GABAergic or cholinergic interneurons.