The superior olivary complex is necessary for the full expression of the acoustic but not tactile startle response in rats.

The acoustic startle response (ASR) in rats is mediated by an oligosynaptic pathway from the cochlea via the brainstem to spinal and cranial motoneurons. The present study tested whether the superior olivary complex (SOC) plays a role in the mediation of the ASR. The SOC receives auditory information from the ventral cochlear nuclei and projects to the caudal pontine reticular nucleus (PnC), the sensorimotor interface of the ASR. Axon-sparing excitotoxic lesions of the SOC strongly reduced the ASR amplitude and slightly prolonged ASR onset and peak latencies. The integrity of PnC which is adjacent to the SOC was confirmed by testing the tactile startle response which was not affected by SOC lesions. We suggest that the SOC is necessary for a full expression of the ASR and discuss possible auditory input structures involved in the mediation of the ASR.