GLUTAMATE-RECEPTOR SUBUNITS IN THE NUCLEUS OF THE TRACTUS-SOLITARIUS AND OTHER REGIONS OF THE MEDULLA-OBLONGATA IN THE CAT

The nucleus of the tractus solitarius (NTS) is a primary termination z one for laryngeal, gustatory, cardiovascular, respiratory, gastrointes tinal, and other visceral afferents. Although considerable information is available on the neurochemical aspects of the NTS in general, very little is known about glutamate receptors that may underlie many of t he different functions mediated by the NTS. In addition, most previous glutamate receptor distribution studies were performed in the rat, wh ereas the cat, the subject of many physiological experiments involving the NTS, has received little attention. In the present study, the imm unohistochemical distribution of pha-amino-3-hydroxy-5-methyl-4-isoxaz olepropionate (AMPA)-selective glutamate receptor subunits (GluR1, Glu R2/3, GluR4) and the N-methyl-D-aspartate (NMDA) receptor subunit NR1 in the cat caudal brainstem was investigated by using subunit-specific antibodies. In the NTS, statistically significant differences were se en in the distribution of each antibody. Highest labeling was seen for GluR2/3 in most subnuclei, whereas GluR1-immunoreactive neurons were found more frequently than were NR1- or GluR4-immunoreactive neurons. GluR1 immunolabeling was particularly high in the interstitial subnucl eus, whereas GluR2/3 immunolabeling was particularly high in the inter mediate subnucleus. Qualitatively, labeling for GluR4 was most common in glia. The present results indicate that glutamate receptors show di fferent subunit distributions in the subnuclei of the NTS and in other adjacent structures. This finding suggests that neurons in these stru ctures are designed to respond differently to excitatory input. J. Com p. Neurol. 402.75-92, 1998. (C) 1998 Wiley-Liss, Inc.dagger.