The spinal cord (SC) contains neural networks that are capable of producing organized locomotor activity autonomously from the brain. Locomotor activity can be induced in spinally transected (spinalized) animals by adding a source of tonic excitation to activate spinal networks. This is commonly accomplished by activating N-methyl-D-aspartate (NMDA) glutamate receptors through bath application of NMDA. More recently, optogenetic approaches have enabled both activation and inactivation of neuronal cell populations to control the activity of locomotor networks. Larval zebrafish are exceptionally amenable to optogenetic techniques due to their transparency, which permits noninvasive light delivery. In this study, we induced locomotor activity in spinalized transgenic zebrafish larvae that expressed channelrhodopsin-2 in all subtypes of spinal vesicular glutamate transporter 2a (vglut2a)-expressing neurons by applying 10 s of constant blue light to the preparations. The resultant locomotor activity possessed all of the characteristics of swimming: bilateral alternation, rostrocaudal progression, and organization into discrete swimming episodes. Spatially restricted light application revealed that illumination of the rostral SC produced more robust activity than illumination of the caudal SC. Moreover, illumination of only three body segments was sufficient to produce fictive swimming. Intriguingly, organized swimming activity persisted during NMDA receptor antagonism but was disrupted by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonism. Hence, AMPA receptor signaling is required for episodically-organized swimming, whereas NMDA receptor signaling is not necessary. NEW & NOTEWORTHY Spinal locomotor networks have the intrinsic capacity to transform unpatterned excitatory input into patterned output. Conventionally, spinally mediated fictive locomotor activity is experimentally elicited by N-methyl-D-aspartate (NMDA) application to bias the network toward activation. We present a novel experimental paradigm that permits spatially and temporally controllable activation of spinal vesicular glutamate transporter 2a-express-ing neurons in larval zebrafish, eliciting patterned locomotor activity that is not dependent on NMDA receptor signaling.
Bibliographical noteFunding Information:
This work was supported by National Institutes of Health (https:// www.nih.gov/) Grant R01 NS094176 (to M. A. Masino) and Regenerative Medicine Minnesota (to J. E. Montgomery).
We appreciate insightful suggestions from Dr. Matthew Beckman. We are grateful to Dr. Shin-Ichi Higashijima for kindly sharing the Tg(vglut2a: Gal4ff)nns20 line and to Marc Tye and the University of Minnesota Zebrafish Core facility staff for outstanding animal care. We thank Andor Technology and Kenneth Kilby (Olympus) for technical assistance. This work was supported by National Institutes of Health (https://www.nih.gov/) Grant R01 NS094176 (to M. A. Masino) and Regenerative Medicine Minnesota (to J. E. Montgomery).
© 2019 the American Physiological Society
- Spinal cord
PubMed: MeSH publication types
- Journal Article
- Research Support, Non-U.S. Gov't
- Research Support, N.I.H., Extramural