Elevated NADH-dehydrogenase activity characterizes the rostral gustatory zone of the solitary nucleus in rat.

The regional distribution of NADH-dehydrogenase (NADH-DH; EC 1.6.99.3) activity was examined in the nucleus of the solitary tract (NST) in the rat, with specific emphasis given to the rostral gustatory zone. Activity of NADH-DH in the rostral gustatory zone was compared to intermediate and caudal divisions of the NST which receive projections from the glossopharyngeal and vagus nerves. Animals received injections of horseradish peroxidase (HRP) in the anterior tongue, or applications of HRP crystals to the cut chorda tympani nerve to visualize chorda tympani terminal fields in the rostral NST. Tissue was subsequently reacted for NADH-dehydrogenase and transported HRP using sequential histochemical procedures. Results show that relative activity of NADH-DH is highest in areas of the NST that receive projections from the chorda tympani nerve. Lateral divisions of the NST, which receive projections from the lingual-trigeminal nerve, show moderate enzymatic activity, but such activity is quantitatively lower than that observed in the chorda tympani terminal field. Intermediate and caudal portions of the NST show the lowest NADH-DH activity of all NST regions examined. These results confirm that histochemistry for NADH-dehydrogenase can serve as an endogenous marker for chorda tympani terminal fields in the rostral NST.