Distribution of glutamic acid decarboxylase and gamma-aminobutyric acid in the hypoglossal nucleus in the rat.

Immunocytochemistry was used to investigate the distribution of glutamic acid decarboxylase (GAD) and gamma-aminobutyric acid (GABA) in the hypoglossal nucleus (XII) of the adult rat. The distribution of GAD and GABA was found to be co-extensive throughout XII. Although immunoreactivity was moderately dense in all regions, the intensity of staining was greatest in the ventral district of XII particularly ventromedially in the caudal half of the nucleus. Immunoreactive terminal-like profiles were observed around motoneuron somata and dendrites. There also was evidence of sparse mediolaterally-oriented densities of immunoreactivity at the junction of XII and the dorsal vagal nucleus and between dorsal and ventral districts of XII. In addition, neurons staining positive for GABA were found scattered within XII laterally and immediately outside of XII in and around the Nucleus of Roller. These observations suggest a complex, differential distribution of GABA in XII and are discussed in relation to tongue motor behavior.