Functional Diversity of Glycinergic Commissural Inhibitory Neurons in Larval Zebrafish

Summary: Commissural inhibitory neurons in the spinal cord of aquatic vertebrates coordinate left-right body alternation during swimming. Their developmental origin, however, has been elusive. We investigate this by comparing the anatomy and function of two commissural inhibitory neuron types, dI6dmrt3a and V0d, derived from the pd6 and p0 progenitor domains, respectively. We find that both of these commissural neuron types have monosynaptic, inhibitory connections to neuronal populations active during fictive swimming, supporting their role in providing inhibition to the contralateral side. V0d neurons tend to fire during faster and stronger movements, while dI6dmrt3a neurons tend to fire more consistently during normal fictive swimming. Ablation of dI6dmrt3a neurons leads to an impairment of left-right alternating activity through abnormal co-activation of ventral root neurons on both sides of the spinal cord. Our results suggest that dI6dmrt3a and V0d commissural inhibitory neurons synergistically provide inhibition to the opposite side across different swimming behaviors. : Satou et al. explore the functional properties dI6dmrt3a and V0d neurons in the spinal cord of larval zebrafish. Both populations provide inhibition to the swimming CPG and motor neurons on the contralateral side when the ipsilateral side is active. Ablation of dI6dmrt3a neurons confirms their contribution to left-right alternation. Keywords: zebrafish, mid cycle inhibition, commissural inhibitory neurons, spinal cord circuit, dI6 dmrt3a neurons, V0d neurons, dbx1, glycinergic interneuons