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Contributed by Nancy Pierce on 07/11/2013
Animals modulate arousal state to ensure that their sensory responsiveness and locomotor activity match environmental demands. Neuropeptides have been implicated in arousal, but studies of their roles in vertebrates have been constrained by the vast array of neuropeptides, their pleiotropic effects, and behavioral complexity. To overcome these limitations, we systematically dissected the neuropeptidergic modulation of arousal in larval zebrafish. We genetically overexpressed evolutionarily-conserved neuropeptides (adcyap1b, cart, cck, cgrp, galanin, hcrt, and pnoc) and quantified spontaneous and stimulus-evoked locomotor behaviors. Our study reveals that arousal behaviors are dissociable. For example, neuropeptide expression uncoupled spontaneous locomotor activity, a measure of endogenous arousal, from responsiveness to sensory stimuli, a measure of exogenous arousal. Both endogenous and exogenous arousal behaviors could be further partitioned into discrete parameters, including modality-specific changes in sensory responsiveness and distinct characteristics of voluntary locomotion. Principal components analysis and phenotypic clustering revealed both shared and divergent features of neuropeptidergic functions: hcrt and cgrp stimulated voluntary locomotion, whereas galanin and pnoc attenuated these behaviors. In contrast, cart and adcyap1b increased sensory responsiveness yet had minimal impacts on voluntary locomotor activity, while cck expression induced the opposite effects. Furthermore, hcrt and pnoc induced modality-specific differences in responsiveness to changes in illumination. Our study provides the first systematic high-throughput analysis of neuropeptidergic modulation of arousal, demonstrates that arousal is partitioned into independent behavioral components, and indicates ancestral and conserved functions of neuropeptides in regulating arousal.