Fig. 6: Pretectal V2a neurons drive brainstem steering circuit and generate steering turn movement.
From: Separate brainstem circuits for fast steering and slow exploratory turns
a Upper: Soma distribution of V2a neurons in Tg(Chx10:GCaMP6s). Lower: Statistical analysis of V2a soma distribution in the pretectum. b, c, Statistical analysis of soma distribution and response strength of recruited pretectal V2a neurons during steering (left upper; n = 526, N = 6) and explorative turns (left lower; n = 286, N = 6). Right upper: Ipsilateral pretectal V2a response significantly larger than contralateral during steering. Right lower: No significant difference during explorative turns. Population data (Unpaired t test, 21 trials from 6 fish for steering, 11 trials from 6 fish for explorative; circles = individual trials). d Calcium response (ΔF/F) and percentage of recruited ipsilateral V2a neurons showed a linear relationship with increasing tail bending amplitude during steering (21 trials, 6 fish; circles = individual trials). e, f ChR2-mCherry expression in pretectal V2a neurons. Optogenetic activation in Tg(Chx10:Gal4; UAS:ChR2-mCherry) in a light-intensity-dependent manner. g–j Experimental setup for optogenetic stimulation and high-speed recording (g). Stimulation of pretectal V2a neurons activated steering V2a and V0d neurons, inducing a steering turn. Neuronal firing persisted in high Ca²+/Mg²+ but was blocked by NBQX/AP5 (h). Tail angle amplitude increased with blue light intensity until plateau (i, j; one-way ANOVA, N = 6 fish; circles = individual preparations). k–m Stacked images of pretectal V2a neuron ablation in Tg(Chx10:GFP; k). Unilateral ablation reduced cumulative heading direction changes and tail angle during ipsilateral steering but not contralateral turns (l). Steering turn occurrence significantly decreased post-ablation (Paired t test, N = 14 fish). Fish failed to generate ipsilateral steering turns, producing only swim-related turns after ablation (m; N = 14 fish; circles = individual preparations). All data: mean ± SEM. Two-tailed t tests: ****P < 0.0001, ***P < 0.001, **P < 0.01, ns not significant.
