INTERACTIONS BETWEEN THE NEURAL NETWORKS FOR ESCAPE AND SWIMMING IN GOLDFISH

Interactions between neural networks for different motor behaviors occ ur frequently in nature; however, there are few vertebrate models for studying these interactions. One potentially useful model involves the interactions between escape and swimming behaviors in fish. Fish can produce escape bends while swimming, using some of the same axial musc les for both behaviors. Here we study the interactions between escape and swimming in a paralyzed goldfish preparation in which we can activ ate the networks for both behaviors. Fictive swimming was elicited by electrical stimulation in the midbrain locomotor region. During the sw imming, we fired a single action potential in the reticulospinal Mauth ner (M) cell, which initiates the escape behavior (Zottoli, 1977). Fir ing the M cell overrode the swimming motor output to produce an output appropriate for escape regardless of the phase of swimming at which i t was fired. The M cell also could reset the swimming rhythm dramatica lly in a way that led to a smooth transition from an escape bend to on e side into subsequent swimming. Both the override and reset supported predictions based on previous studies of the organization of the M-ce ll network. They apparently allow for a well coordinated motor output when a fish must produce an escape while swimming. The potent effects of one action potential in a single, identifiable reticulospinal neuro n make this an attractive model system for future studies of the cellu lar basis of interactions between descending pathways and spinal rhyth m-generating networks.