Organization of the nucleus of the solitary tract in the hamster: acetylcholinesterase, NADH dehydrogenase, and cytochrome oxidase histochemistry.

The distribution of acetylcholinesterase (AChE), NADH dehydrogenase (NADHd), and cytochrome oxidase (CO) was determined in the nucleus of the solitary tract (NST) in the golden hamster. Histochemical staining was compared to cytoarchitectonic subdivisions of the NST (Whitehead: J. Comp. Neurol. 276:547-572, 1988) and to terminal fields of primary afferents of the nerves that innervate the tongue. These three histochemical methods resulted in differential staining patterns within the NST that were related to certain subdivisions. Transganglionic transport of horseradish peroxidase (HRP) was used to determine the central projections of the chorda tympani (CT), the lingual branch of the trigeminal (L-V), and the lingual-tonsilar branch of the glossopharyngeal nerves (L-IX). Alternate or the same brain sections were processed to reveal transported HRP, and NADHd or AChE levels. Increased staining of the neuropil with NADHd and AChE was coincident with the dense part of the afferent terminal fields of all three nerves in the NST and the laterally adjacent dorsomedial part of the spinal trigeminal nucleus. CO showed this pattern only for the most rostral part of the CT field. The densest AChE staining coincided with gustatory afferent terminal fields. The histochemical staining facilitated the interpretation of the organization of the NST. For example, at caudal levels of the gustatory NST, it is suggested that taste processing is localized predominantly in the medial part of the rostral central, and somatosensory processing in the rostral lateral subdivision. AChE or NADHd staining should facilitate studies of connections, topography, and neuroplastic changes of the gustatory NST.