TOPOGRAPHIC ORGANIZATION OF FOS-LIKE IMMUNOREACTIVITY IN THE ROSTRAL NUCLEUS OF THE SOLITARY TRACT EVOKED BY GUSTATORY STIMULATION WITH SUCROSE AND QUININE

Fos immunohistochemistry was used to elucidate the pattern of activati on elicited by two qualitatively and hedonically distinct taste stimul i, sucrose and quinine, within the first-order gustatory relay, the ro stral division of the nucleus of the solitary tract. Compared to unsti mulated controls, both sucrose and quinine elicited significant increa ses in Fos-like immunoreactivity in the rostral central subnucleus, th e region of the rostral solitary nucleus that receives the densest pri mary afferent input. Within the rostral central subnucleus, neurons th at exhibited Fos-like immunoreactivity following quinine stimulation w ere concentrated medially, but neurons that exhibited Fos-like immunor eactivity following sucrose stimulation were distributed more evenly a long the mediolateral axis. Despite their differential distribution, s ucrose- and quinine-activated neurons also demonstrated notable interm ingling. Further, the chemotopic arrangement was only partially consis tent with what would be predicted if chemotopy was merely an outcome o f orotopy. Our results suggest that a rough chemotopy characterizes th e organization of taste responses in the nucleus of the solitary tract , and that the topographic pattern of taste afferent terminations in t his nucleus is related to their chemosensitivity as well as to their p eripheral spatial distribution.