# The mesencephalic trigeminal neuron: electrophysiological insights into function and dysfunction

## TL;DR

This paper explores the role of mesencephalic trigeminal neurons in jaw movement and how their dysfunction can lead to disorders like bruxism and neurodegenerative diseases.

## Contribution

The paper provides new electrophysiological insights into MTN function and identifies novel therapeutic targets for related disorders.

## Key findings

- MTNs use specific ion channels like Nav1.6 to regulate jaw movement and reflex timing.
- Neurotransmitters like serotonin and norepinephrine modulate MTN activity for sensorimotor integration.
- Dysfunction in MTNs is linked to bruxism, temporomandibular disorders, and cognitive decline.

## Abstract

Mesencephalic trigeminal neurons (MTNs) are the sole primary afferent neurons with cell bodies located within the central nervous system. MTNs convey proprioceptive inputs from masticatory muscles and periodontal ligaments, thereby contributing to the precise regulation of jaw–oral motor functions. Through ionic mechanisms such as currents generated by the voltage-dependent sodium (Nav) channel isoform Nav1.6, hyperpolarization-activated currents, and persistent inward currents, MTNs generate sustained and burst firing that regulate masticatory rhythm and jaw-jerk reflex timing. Their activity is further modulated by neurotransmitters, including serotonin and norepinephrine, which provide flexibility in sensorimotor integration. Pathological conditions such as chronic stress and sodium channel dysfunction induce MTN hyperexcitability or irregular firing, contributing to bruxism, temporomandibular disorders, and feeding impairment in amyotrophic lateral sclerosis models. In addition, aging and tooth loss lead to Piezo2 downregulation and neuronal death, potentially resulting in masticatory dysfunction and cognitive decline. Recent findings suggest that interventions targeting vesicular glutamate transporter 1 projections, melanocortin 4 receptor signaling, and nitric oxide pathways represent novel therapeutic approaches. Taken together, MTNs have emerged as promising targets for treating conditions ranging from masticatory motor disorders to neurodegenerative diseases.

Graphical abstractInfographic detailing mesencephalic trigeminal neuron (MTN) system neurophysiology, highlighting anatomical and molecular basis, electrophysiological mechanisms, neuromodulation, sensorimotor integration, pathophysiology, therapeutic targets, and novel intervention nodes within the Vines circuit, using labeled icons and arrows to illustrate relationships and key processes.

Graphical abstract