Effects of interception of snout sensory input on murine neck muscles: an electron microscopic study

To examine whether the interference of the snout sensory input causes neuromuscular dysfunction in the murine neck muscles, the fine structure of the dorsal neck muscles was studied by electron microscopy. The infraorbital nerves were bilaterally transected in the adult ICR mice (one-month-old), and the animals were sacrificed after postoperative periods ranging from six to 18 months. Alpha motor end-plates showed remarkable changes characterized by shrunken synaptic boutons containing abundant lysosomes and/or disappearance of the synaptic boutons. The changes in the muscle spindles were characterized by the sarcolemmal undulation of the intrafusal muscle fibers and the frequent appearance of lysosomes in their sensory terminals. These degenerative changes were observed between nine months and 18 months after neurotomy and intensified with the length of the postoperative period. From the results of the present study, it was concluded that a reflex pathway exists between the snout receptor organs and the dorsal neck muscles.