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5 Feb 2022
Michiaki Suzuki, Yukio Nishimura(Neural Prosthetics Project) and colleagues published an article, ”A multisynaptic pathway from the ventral midbrain to spinal motoneurons in monkeys” in The Journal of Physiology.

Japanese Page

Motivation related region in the midbrain generates muscle activity
〜Neural substrate for motivational modulation of motor outputs〜

<Title of the paper>
A multisynaptic pathway from the ventral midbrain to spinal motoneurons in monkeys
The Journal of Physiology
DOI: 10.1113/JP282429

Outline of Research

Motivation boosts motor performance. The activity of the ventral midbrain (VM), consisting of the ventral tegmental area (VTA), the substantia nigra pars compacta (SNc), and the retrorubral field (RRF), plays an important role in processing motivation. However, little is known about a neural substrate bridging the VM and the spinal motor output. Here, the research group hypothesized that the VM might exert a modulatory influence over the descending motor pathways. Employing retrograde transneuronal labeling with rabies virus, the research group demonstrated the existence of multisynaptic projections from the VM to the cervical enlargement in an animal model. To investigate the functional significance of the anatomically-identified multisynaptic VM–spinal projections, electrical stimulation was delivered to the VM. Results showed that the VM induced muscle responses in the contralateral forelimb with a few milliseconds delay following the responses of the ipsilateral primary motor cortex (M1). The magnitude of evoked muscle responses was associated with stimulus intensity and pulse number. The muscle responses were diminished during M1 inactivation. Their findings suggest that a multisynaptic VM–M1–spinal pathway may play a pivotal role in modulatory control of the spinal motor output.

Abstract Figure
Abstract Figure
Using retrograde transsynaptic tracer, a multisynaptic projection from the ventral midbrain (VM) to the spinal cord was found. There was a certain caudo-rostral gradient, in that the caudal VM (i.e., the caudal part of the SNc and RRF) contained more neurons projecting to the spinal cord indirectly than the rostral VM (i.e., the rostral part of the SNc and VTA). The VM activation induced responses in the primary motor cortex (M1) and multiple forelimb muscles. The VM may have modulatory action on the descending motor pathways.

 Major funding for this research 

This study was supported by the Japan Society for the Promotion of Science (KAKENHI), the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan (a Grant-in-Aid for Scientific Research on Innovative Areas “Brain Information Dynamics”, “Hyper adaptability” and “Adaptive Circuit Shift”:), the Japan Science and Technology Agency (Moonshot R&D), the Cooperative Research Program of Primate Research Institute, Kyoto University and the Cooperative Study Program of National Institute for Physiological Sciences.

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