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. 2021 May 5;41(18):4006–4022. doi: 10.1523/JNEUROSCI.1556-20.2021

Figure 8.

Figure 8.

Stimulation of RMTg neurons innervated by the contralateral SC inhibit DA-like neurons in the VTA and SNc. A, Scheme of the experiment. SC was unilaterally injected with the transsynaptic viral vector (AAV1-hSyn-Cre-hGH) carrying the gene for Cre recombinase and contralateral RMTg was injected with AAV2-EF1α-DIO-ChR2(H134R)-mCherry carrying Cre-dependent genes for ChR2 and mCherry fluorescent protein. At least 2 weeks later, extracellular recordings of the activity of midbrain DA-like neurons was conducted while RMTg neurons, monosynaptically innervated by the contralateral SC, were optogenetically stimulated. The shape of a typical action potential of a DA-like neuron is shown in the inset on the left side. B, C, Top panels, Heatmaps of peristimulus firing rates (normalized to baseline) showing the responses of all recorded DA-like neurons to RMTg stimulation with trains of laser light pulses (473 nm, <20 mW, 5 ms pulses at 40 Hz over 1 s; B) or single laser light pulses (473 nm, 100 ms, <20 mW; C). Responses of individual neurons are shown in rows and are sorted by the amplitude of the response during the stimulation time (marked by vertical dashed line). Bottom panels, Peristimulus mean firing rate (normalized to baseline; ±SEM marked with gray color) and peristimulus mean change in firing rate (±SEM marked with gray color). The stimulation time is marked with a blue vertical bar. D, Localization of all recorded DA-like neurons with color-coded type of response to the optogenetic stimulation of RMTg neurons monosynaptically innervated by the contralateral SC. E, G, Pie charts showing the proportions of response types (inhibition, no effect, excitation) of VTA (marked by green outer ring) and SNc (marked by purple outer ring) DA-like neurons elicited by train (5 ms at 40 Hz; E) or single-pulse (100 ms; G) optogenetic stimulation of RMTg neurons innervated by the contralateral SC. F, H, Mean firing rates before, during, and after the train (5 ms at 40 Hz; F) or single-pulse (100 ms; H) optogenetic stimulation of RMTg neurons innervated by the contralateral SC (100 ms bins). I, J, From left to right: percentage change in firing rate, duration, and latency to the minimum of the response of DA-like neurons both in VTA (green bars) and SNc (purple bars) caused by train (5 ms at 40 Hz; I) or single-pulse (100 ms; J) optogenetic stimulation of RMTg neurons innervated by the contralateral SC. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001. ns, Nonsignificant.