Effects of bilateral electrical stimulation of the ventral pallidum on acoustic startle

The ventral pallidum (VP) is believed to occupy a critical position between the limbic and the motor systems, for transferring motive information into motor commands. To estimate the time course of signaling from the VP to motor outputs, in the present study we examined the effects of bilateral electrical stimulation of the VP on the acoustic startle reflex in awake rats. When the interstimulus interval (ISI) between VP stimulation and acoustic stimulation was shorter than 5 ms, VP stimulation potentiated acoustic startle. When the ISI was longer than 5 ms, VP stimulation inhibited acoustic startle over a large range of ISIs with the maximum inhibition at ISIs between 15 and 25 ms. In contrast, bilateral electrical stimulation of the amygdala did not have a significant inhibitory effect on acoustic startle, but strongly augmented acoustic startle at shorter ISIs (0–10 ms). Compared to unilateral electrical stimulation of the inferior colliculus (IC), bilateral stimulation of the VP gave rise to a rightward shift of the ISI curve, indicating that the neural pathways conveying the inhibitory influence from the VP to the acoustic startle circuit are longer than those from the IC.