Relaxin-3 neurons of the zebrafish periaqueductal gray mediate behavioral responses evoked by darkness
Ambient illumination influences many aspects of brain function, including responses to threats. One brain region proposed to mediate these effects is the periaqueductal gray (PAG), an evolutionarily conserved midbrain structure that contains multiple subpopulations of peptidergic neurons. Here we ask which cell types in the larval zebrafish PAG respond to changes in ambient illumination. By…
Environmental light levels play a significant role in brain function, including responses to potential dangers. A brain region known as the periaqueductal gray (PAG) in the midbrain is thought to mediate these effects. This study investigates which cell types within the larval zebrafish PAG react to alterations in ambient illumination.
Using a method to match gene expression data with recorded neurons under various sensory stimuli, the researchers discovered that GABAergic PAG neurons that produce the neuropeptide Relaxin-3 (rln3a+) remain active when exposed to darkness. However, a nearby GABAergic PAG neuron group that releases the peptide penka does not demonstrate the same reaction.
Zebrafish lacking the rln3a gene showed a decrease in movement during periods of darkness. The study suggests that darkness triggers the activity of Relaxin-3-releasing PAG neurons, which helps increase vigilance and strengthen defense circuits. These findings identify a specific peptidergic population of PAG neurons that could be important in understanding behavioral state imbalances linked to prolonged periods of darkness.
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