Distribution of aspartate and glutamate in the nucleus of the solitary tract of the lamb

Excitatory amino acids have been implicated in several nucleus of the solitary tract (NST)-mediated functions. The distribution of the excitatory amino acids aspartate and glutamate has been described in both cat and rat. However, the distribution of these amino acids has not been described for the lamb, a species frequently used in the investigation of NST-mediated behaviors. Thus, this study was designed to investigate the distribution of aspartate-like (ASP) and glutamate-like (GLU) immunoreactivity in the lamb NST using pre- and post-embedding immunohistochemistry. Both ASP- and GLU-immunoreactive cells and puncta were observed throughout the rostral to caudal extent of the lamb NST. The most intense ASP- and GLU-immunoreactive cell and puncta staining was found ventromedial, ventral and ventrolateral to the solitary tract at intermediate and caudal levels of the lamb NST. The relative numbers of both cells and puncta stained were lower at rostral levels of the NST corresponding to the gustatory NST. The intense ASP and GLU immunoreactivity observed in areas of the lamb intermediate and caudal NST that are involved in respiration, deglutition and cardiovascular functions suggests excitatory amino acids play an important role in NST neural processing that underlies these behaviors in lamb.