Glutamate antagonists in the reticular formation reduce the acoustic startle response

A previous study has shown that the acoustic responsiveness of reticulospinal neurones in the caudal pontine reticular nucleus (PnC) is reduced by glutamate antagonists. It was postulated that the acoustic startle response is mediated by glutamate receptors on PnC-neurones. In the present study, we tested this hypothesis by local microinjections of different glutamate antagonists into the PnC of unrestrained awake rats. In order to differentiate the drug effects on the head and body startle responses, we measured the head startle response electromyographically, and the body startle response in a ballistic chamber. Both the AMPA/kainate and the NMDA receptor antagonists reduced both components of the startle response dose-dependently. We conclude that both subtypes of ionotropic glutamate receptors in the PnC are relevant for the acoustic startle response in rats.