[Functional plasticity of trigeminal motor nucleus in unilateral mastication model rats]

To observe the plasticity changes of trigeminal motor nucleus (Mo5) and masseter H-reflex in unilateral mastication model rats and explore the possible mechanism of functional plasticity in motor center involved in unilateral mastication, 54 adult male Wistar rats were randomly divided into 1-month (n = 10), 3-month (n = 10), and 16-month (n = 7) model groups and their corresponding control groups, respectively. Unilateral mastication model rats were prepared by intermittent removal of clinical crowns of left teeth (model side). Rats were anesthetized (20% urethane, i.p.), and bilateral Mo5 were chosen to conduct extracellular recordings, while bilateral electromyography (EMG) of masseter muscle and its H-reflex were simultaneously recorded by a polygraph. It was observed that the firing rate of Mo5 neurons in model sides was significantly lower than that of right sides in 3 model groups, and that of left sides in their control groups. The response latency of Mo5, which was evoked by electrical stimulation of masseter nerve in model sides of 1-month and 3-month model groups, was significantly longer than that of left sides in their control groups. Moreover, the amplitude of H-wave in model sides of 3-month and 16-month model groups was lower than that of left sides in their control groups when H-reflex was evoked by electrical stimulation of left masseter nerve. These results suggest that unilateral mastication in model rats decreases the Mo5 neuron excitability, and this may be one of the functional plasticity mechanisms in motor center involved in unilateral mastication.