Immunoreactive Changes in the Hypoglossal Nucleus after Nerve Injury

Abstract : Choline acetyltransferase (ChAT) and calcitonin gene-related peptide (CGRP) are synthesized in the hypoglossal motoneuron. This study examines changes in ChAT and CGRP immunoreactivity (IR) after three types of hypoglossal nerve injury (resection, transection and crush) at 1, 3, 7, 20 and 50 days postoperative (dpo). Maximal reduction of ChAT immunostaining occurred at 7 dpo, and by 50 dpo had returned to normal for all injuries. CGRP immunostaining increased maximally at 1-3 dpo and at 50 dpo was normal for nerve crush, yet decreased for transection and resection. Cellular levels of ChAT and CGRP respond in diametric fashion, temporally and in regard to type of injury. Correlative data of reinnervation of tongue musculature were supplied by HRP labeling of hypoglossal motoneurons after nerve injury. These data provide a more complete picture of the role that a neurotransmitter-related protein, ChAT, and a putative trophic neuropeptide, CGRP,may play in nerve regeneration.