Ventral Pallidum Mediates Amygdala-evoked Deficits in Prepulse Inhibition

Prepulse inhibition (PPI) is an operational measure of sensorimotor gating. It is defined as a reduction in magnitude of a startle response when a startling stimulus is preceded by a weaker "prepulse." PPI has been found to be altered in patients with schizophrenia, autism spectrum disorders, and other neuropsychiatric illnesses. As such, the neural substrates regulating PPI are of particular interest. Previous studies using lesions, selective blockade of N-methyl-d-aspartate (NMDA) receptors, and pharmacological disinhibition have demonstrated that impairment of the function of the basolateral and lateral nuclei of the amygdala (BLA) disrupts PPI. However, transient gamma aminobutyric acid-mediated (GABA-mediated) inactivation of BLA has not been evaluated for effects on PPI. Furthermore, the downstream projection targets that mediate BLA-evoked disruptions of PPI have not been elucidated. Thus, in the present study, we evaluated the effect on PPI of bilateral and unilateral inactivation of BLA, by microinfusion of the GABA-A receptor agonist, muscimol. We found that either bilateral or unilateral inactivation impaired PPI. Because unilateral inactivation was sufficient to impair PPI, we hypothesized that this was due to an indirect activation of a downstream target of BLA, the ventral pallidum (VP). Because VP inhibition normalizes PPI deficits evoked from nucleus accumbens (Kodsi & Swerdlow, 1994), we next tested the degree to which VP inhibition would normalize PPI deficits evoked from BLA. We unilaterally inactivated BLA with concurrent inactivation of VP and found that VP inactivation blocked BLA-evoked deficits in PPI. We suggest that BLA inactivation disrupts PPI through disinhibition of VP.