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bioRxiv · 10.1101/2023.04.24.538092

An single oscillating proto-hypothalamic neuron gates taxis behavior in the primitive chordate Ciona

Smith, W.·Chung, J.·Newman-Smith, E.·Kourakis, M. J.·Miao, Y.·Borba, C.·Medina, J.·Laurent, T.·Gallean, B.·Faure, E.
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Abstract

Ciona larvae display a number of behaviors, including negative phototaxis. In negative phototaxis, the larvae first perform short spontaneous rhythmic casting swims. As larvae cast in a light field, their photoreceptors are directionally shaded by an associated pigment cell, providing a phototactic cue. This then evokes an extended negative taxis swim. We report here that the larval forebrain of Ciona has a previously uncharacterized single slow-oscillating inhibitory neuron (neuron cor-assBVIN78) that projects to the midbrain, where it targets key interneurons of the phototaxis circuit known as the photoreceptor relay neurons. The anatomical location, gene expression and oscillation of cor-assBVIN78 suggest homology to oscillating neurons of the vertebrate hypothalamus. Ablation of cor-assBVIN78 results in larvae showing extended phototaxis-like swims, but which occur in the absence of phototactic cues. These results indicate that cor-assBVIN78 has a gating activity on phototaxis by projecting temporally-oscillating inhibition to the photoreceptor relay neurons. However, in intact larvae the frequency of cor-assBVIN78 oscillation does not match that of the rhythmic spontaneous swims, indicating that the troughs in oscillations do not themselves initiate swims, but rather that cor-assBVIN78 may modulate the phototaxis circuit by filtering out low level inputs while restricting them temporally to the troughs in inhibition.

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Smith, W., Chung, J., Newman-Smith, E., Kourakis, M. J., Miao, Y., Borba, C., Medina, J., Laurent, T., Gallean, B., Faure, E.. 2023-04-24. An single oscillating proto-hypothalamic neuron gates taxis behavior in the primitive chordate Ciona. https://doi.org/10.1101/2023.04.24.538092

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