Expression of Glutamate Receptor Subunit 1 and Nitric Oxide Synthase in the Hypoglossal Nucleus and Dorsal Vagal Nucleus in the Rat After Neurectomy

Abstract

Using nitric oxide synthase (NOS) and glutamate receptor subunit 1 (GluRl) immunohistochemistry. the present study demonstrated changes in the expression of NOS and GluR 1 in the hypoglossal (HN) and dorsal vagal nucleus (DVN) after neurectomy. Two and 7 days after sectioning the left hypoglossal nerve, NOS expression was seen in a few neurons but GluRl immunoreactivity was drastically reduced in the ipsilateral HN. The upregulation of NOS immunoreactivity in the HN appeared to peak at 14 days postoperation (dpo). At this period, however, the GluRl immunoreactivity almost completely disappeared. Twenty-one, 35 and 56 days after neurectomy, NOS immunoreactivity was still expressed in the ipsilateral HN; at the same time, GluRl immunoreactivity reappeared in a few neurons of the nucleus. Ninety days after operation, NOS immunoreactivity completely disappeared on the operated side of the nucleus, but GluRl immunoreactivity was re-expressed in many hypoglossal neurons. The number of such neurons was obviously less than that on the unoperated side. After sectioning the left vagus nerve in the same animals, the expression of NOS immunoreactivity in the ipsilateral DVN resembled that in the HN. on the unoperated side, NOS immunoreactivity was demonstrated in some neurons in the DVN, like that in the normal. In both normal and operated rats, only a few neurons expressed GluRl immunoreactive products on both the operated and unoperated sides of the DVN. Combining with previous results on protein synthesis observed at 14 dpo, the present investigation suggested that in the early stages after neurectomy, the expression of NOS immunoreactivity and loss of GluRl expression in the HN may indicate the organism's double protective mechanism. Lastly, the reappearance of GluRl in the same nucleus from 21 to 90 days after operation may reflect functional recovery of the hypoglossal neurons.