Decrease in occurrence of fast startle responses after selective Mauthner cell ablation in gold®sh (Carassius auratus )

A single action potential in one of a pair of reticulospinal neurons, the Mauthner cells, precedes a short-latency electromyographic response of the trunk and tail musculature on the opposite side of the body and a fast startle response in gold®sh. It has been postulated that not only the Mauthner cell, but also an array of neurons can trigger or participate in fast startle responses (Eaton et al. 1991). We have selectively ablated the Mauthner cells in gold®sh to study how neurons of the brainstem fast startle response network interact. The probability of eliciting a fast startle response was signi®cantly less in ®sh with double Mauthner cell ablations, as compared to the responsiveness of control ®sh. The ®nding that there is a signi®cant decrease in the occurrence of fast startle responses in animals with no Mauthner cells, implies that the Mauthner cell may play a role in triggering the involvement of the other network elements in fast startle responses. We hypothesize that Mauthner cell activation may be important in bringing those reticulospinal neurons that are ``primed'' by the behavioral context to threshold and provides the basis for studies focused on the interactive nature of the brainstem startle response network.