Investigation of hindbrain activity during active locomotion reveals inhibitory neurons involved in sensorimotor processing

Kristen E Severi,Claire Wyart,Urs L Böhm

doi:10.1038/s41598-018-31968-4

Abstract

Locomotion in vertebrates relies on motor circuits in the spinal cord receiving inputs from the hindbrain to execute motor commands while dynamically integrating proprioceptive sensory feedback. The spatial organization of the neuronal networks driving locomotion in the hindbrain and role of inhibition has not been extensively investigated. Here, we mapped neuronal activity with single-cell resolution in the hindbrain of restrained transgenic Tg(HuC:GCaMP5G) zebrafish larvae swimming in response to whole-field visual motion. We combined large-scale population calcium imaging in the hindbrain with simultaneous high-speed recording of the moving tail in animals where specific markers label glycinergic inhibitory neurons. We identified cells whose activity preferentially correlates with the visual stimulus or motor activity and used brain registration to compare data across individual larvae. We then morphed calcium imaging data onto the zebrafish brain atlas to compare with known transgenic markers. We report cells localized in the cerebellum whose activity is shut off by the onset of the visual stimulus, suggesting these cells may be constitutively active and silenced during sensorimotor processing. Finally, we discover that the activity of a medial stripe of glycinergic neurons in the domain of expression of the transcription factor engrailed1b is highly correlated with the onset of locomotion. Our efforts provide a high-resolution, open-access dataset for the community by comparing our functional map of the hindbrain to existing open-access atlases and enabling further investigation of this population’s role in locomotion.

Highlights

When exploring their environments, animals constantly perform updates based on their motor actions and available sensory information
GABAergic neurons were not investigated in that work, we know they are found in large numbers in the hindbrain and cerebellum, previously identified by transgenic lines and in situ staining[7,8,9]
In order to investigate the role of glycinergic neurons in the hindbrain, we utilized Tg(HuC:GCaMP5G; glyt2a:mCherry) double transgenic animals, expressing pan-neuronally the GCaMP5G calcium indicator[15] with mCherry expressed in glycinergic neurons[9], homozygous for the mifta mutation (Fig. 1b, Methods)

Summary

Introduction

Animals constantly perform updates based on their motor actions and available sensory information. By taking advantage of these existing transgenic lines, and with open-access larval zebrafish brain atlases, we have an opportunity to look at the activity of large populations of neurons and place that functional activity in the context of known markers, without the painstaking process of fixing and staining. Kinkhabwala et al, revealed an intricate organization of the hindbrain in alternating stripes of neurons based on glutamatergic and glycinergic neurotransmitter expression[5,6,7]. These stripes reflect an underlying organization of the hindbrain, and are stacked according to www.nature.com/scientificreports/.

Methods

Results

Conclusion