Electron microscopy studies of the effect of interception of snout sensory input on the masticatory system

Abstract

In order to obtain neuroanatomical evidences as to how the interception of the sensory input affects the masticatory system, the unilateral or bilateral transection of the infraorbital nerve was made on the Japanese shrew-moles and rats. The animals were sacrificed postoperatively for electron microscopy at intervals of 14 to 450 days. The masseter and temporal muscles, trigeminal ganglion with the proximal and distal stumps and the brain stem with the upper cervical cord segments were examined electron microscopically.The results obtained are summarized as follows:1. The preganglionic and postganglionic parts of the trigeminal nerve showed definitely degenerated changes, that is, the degenerated fibers disappeared completely in the former but the majority of the degenerated fibers were retained as debris in the latter. The ganglion cells underwent typical chromatolysis with lipidosis.2. In the trigeminal spinal tract nucleus, many of the transganglionically degenerated synapses were in contact with the degenerated dendrites of the secondary neurons. There were also degenerated sencondary neuron soma (lipidosis) .3. The alpha motor end-plates and muscle spindles of the masticatory muscles showed definitely degenerated features.From the results obtained it can be emphasized that the snout sensory input plays a great role in the performance of the masticatory activities in the animals.