Prefrontal D1 systems have been implicated in the regulation of working memory and in the pathophysiology of schizophrenia. D1 hypofunction might contribute to reduced sensorimotor gating in schizophrenia patients since D1 activity in the medial prefrontal cortex (MPFC) regulates prepulse inhibition of startle (PPI) in animal models. We studied the neurochemical basis for the D1 regulation of PPI in rats.