Yokogawa, T., Hannan, M.C., and Burgess, H.A. (2012) The Dorsal Raphe Modulates Sensory Responsiveness during Arousal in Zebrafish. The Journal of neuroscience : the official journal of the Society for Neuroscience. 32(43):15205-15215.
During waking behavior, animals adapt their state of arousal in response to environmental pressures. Sensory processing is
regulated in aroused states, and several lines of evidence imply that this is mediated at least partly by the serotonergic
system. However, there is little information directly showing that serotonergic function is required for state-dependent modulation
of sensory processing. Here we find that zebrafish larvae can maintain a short-term state of arousal during which neurons
in the dorsal raphe modulate sensory responsiveness to behaviorally relevant visual cues. After a brief exposure to water
flow, larvae show elevated activity and heightened sensitivity to perceived motion. Calcium imaging of neuronal activity after
flow revealed increased activity in serotonergic neurons of the dorsal raphe. Genetic ablation of these neurons abolished
the increase in visual sensitivity during arousal without affecting baseline visual function or locomotor activity. We traced
projections from the dorsal raphe to a major visual area, the optic tectum. Laser ablation of the tectum demonstrated that
this structure, like the dorsal raphe, is required for improved visual sensitivity during arousal. These findings reveal that
serotonergic neurons of the dorsal raphe have a state-dependent role in matching sensory responsiveness to behavioral context.