Collision and latency data suggest location of reticular formation synapses that mediate electrically-evoked startle in rat

This investigation sought to determine the location of reticularis pontis caudalis (RPC) synapses that mediate electrically-evoked startle in chloral hydrate anaesthetized rats.; Collision data indicate that electrically-evoked startle is mediated by synapses located in mid to caudal RPC. Symmetric collision effects between electrodes in medial longitudinal fasciculus (MLF) and rostral medulla suggest that fast axons mediating electrically-evoked startle pass longitudinally through medulla. Asymmetric collision-like effects were observed between electrodes in MLF and RPC. The 0.3 ms shift suggests that electrically-evoked startle is mediated by fast, unidirectional and reliable synapses in caudal RPC.; Latency data within animals lent qualitative support to the collision data. Firstly, the latency of electrically-evoked startle following MLF stimulation was always shorter than the following RPC stimulation. Secondly, the latency differential between pairs of electrodes supporting asymmetric collision was always greater than that for symmetric pairs. However, the size of this difference in latency differentials cannot account for a predicted synaptic delay of 0.3 ms. Possible factors that influence the measurement of latency following electrical stimulation are discussed. (Abstract shortened by UMI.)...