Meeting Abstract
An effective mechanosensory system mitigates sensory overload by discriminating between mechanical signals emanating from the environment and those created by the organism’s movements. We study this regulation, termed corollary discharge, in the fish lateral line. We backfill and optogenetically record calcium activity from cholinergic and dopaminergic efferent neurons (transgenic GCaMP6s). Cholinergic efferent activity was tightly synchronised with calcium activity of identified spinal motoneurons but dopaminergic activity was not. This suggests cholinergic neurons are the source of the corollary discharge, and dopaminergic activity has other modulatory actions. This conclusion was supported by photoablation of the cholinergic cell bodies: spontaneous afferent activity is typically partially or completely suppressed during swim bouts, but this effect is greatly diminished with photoablated cholinergic efferents. From a simple model of the function of the hair cell complex, in which efferents act on hair cells to mediate spontaneous afferent excitation, we predict that the information content of an afferent connected to one hair cell in a neuromast should be the same as for an afferent making multiple connections. Intriguingly, optogenetic recording of calcium activity in individual hair cells (GCaMP6s) indicates that in a given neuromast, only a few hair cells are active at a time, and the majority of hair cells may instead act as a reserve pool in case of damage. Thus despite fairly complex wiring patterns and multiple innervating cell types, we propose that the hair cell complex is functionally a relatively straightforward linear microcircuit.
