Abstract

In many animals, the daily cycling of light is a key environmental cue, encoded in part by specialized light-sensitive neurons without visual functions. We serendipitously discovered innate light-responsiveness while imaging the extensively studied stomatogastric ganglion (STG) of the crab, Cancer borealis. The STG houses a motor circuit that controls the rhythmic contractions of the foregut, and the system has facilitated deep understanding of circuit function and neuromodulation. We illuminated the crab STG invitro with different wavelengths and amplitudes of light and found a dose-dependent increase in neuronal activity upon exposure to blue light (λ460-500nm). The response was elevated in the absence of neuromodulatory inputs to the STG. The pacemaker kernel that drives the network rhythm was responsive to light when synaptically isolated, and light shifted the threshold for slow wave and spike activity in the hyperpolarized direction, accounting for the increased activity patterns. Cryptochromes are evolutionarily conserved blue-light photoreceptors that are involved in circadian behaviors.1 Their activation by light can lead to enhanced neuronal activity.2 We identified cryptochrome sequences in the C.borealis transcriptome as potential mediators of this response and confirmed their expression in pyloric dilator (PD) neurons, which are part of the pacemaker kernel, by single-cell RNA-seq analysis.

Highlights

  • stomatogastric ganglion (STG) neurons are identifiable across animals, and the pyloric network has a pacemaker kernel composed of a single oscillating anterior burster (AB) neuron and two pyloric dilator (PD) neurons that serve to dilate the pylorus.[3]

  • The C. borealis stomatogastric ganglion (STG) is composed of 25–26 neurons that produce rhythmic contractions of the foregut.[3]. These are organized into two central pattern generating circuits, of which the pyloric circuit controls the movements of the filtering apparatus, the pylorus

  • STG neurons are identifiable across animals, and the pyloric network has a pacemaker kernel composed of a single oscillating anterior burster (AB) neuron and two pyloric dilator (PD) neurons that serve to dilate the pylorus.[3]

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Summary

Introduction

STG neurons are identifiable across animals, and the pyloric network has a pacemaker kernel composed of a single oscillating anterior burster (AB) neuron and two pyloric dilator (PD) neurons that serve to dilate the pylorus.[3] Inhibitory synapses connect these to a lateral pyloric (LP) and several pyloric (PY) neurons that constrict the pylorus. These neurons fire in tight coordination in a characteristic triphasic pattern to generate rhythmic pyloric contractions. The stable activity pattern of the pyloric rhythm in vitro allowed us to observe a marked increase in network activity in response to focused LED illumination

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