Diverse Bitter Stimuli Elicit Highly Similar Patterns of Fos-like Immunoreactivity in the Nucleus of the Solitary Tract

Abstract

Previous studies have demonstrated that oral stimulation with quinine elicits Fos-like immunoreactivity in the first-order gustatory nucleus, the NST, with a different topographic distribution than sucrose or citric acid. However, it is unknown whether the quinine pattern is unique to this alkaloid or common across bitter stimuli with different chemical structures. Indeed, recent physiological experiments suggest that taste receptor cells and primary afferent neurons may exhibit selectivity for various bitter tastants. The present investigation compared the distribution of FLI in NST following stimulation with three bitter chemicals: QHCl, denatonium and propylthiouracil, stimuli that evoked Ca(2+) currents in almost entirely different sets of receptor cells. The results demonstrate that the quinine pattern is not idiosyncratic but instead generalizes to the other two tastants. Although it remains possible that intermingled but different NST neurons are activated by these stimuli, these data suggest that a specialized region in the NST is preferentially involved in processing a common aspect of bitter tastants. In contrast to citric acid, quinine, denatonium and propylthiouracil all elicited vigorous oromotor rejection responses, consistent with our earlier hypothesis that the medial third of the NST may be an afferent trigger zone for oromotor rejection.

Taste Receptor Genes

“…Coexpression of multiple T2Rs in the same TRCs (6,124) is consistent with behavioral discrimination and generalization data in primates and rats suggesting an identical taste quality perception of different bitter compounds (10,154) and with neurophysiological data showing that responses to different bitter taste stimuli activate similar groups of neurons in the rat nucleus of the solitary tract (37) and in the primate cortex (152). On the other hand, expression of different T2Rs in different TRCs (118) is consistent with neurophysiological data showing that different bitter taste stimuli activate different TRCs (35) and afferent peripheral gustatory neurons (45) in rats and with the lack of conditioned taste aversion generalization between some bitter taste stimuli in hamsters (56).…”

Topographical representations of taste response characteristics in the rostral nucleus of the solitary tract in the rat

“…These bitter-best neurons were located in a more medial and dorsal region than other neurons, but no distinct pattern was found along the RC axis. The medial-dorsal trend of the bitter-taste neurons corresponded to the patterns of c-Fos expression that were elicited by quinine and other bitter-taste stimulations of the oral cavity (Chan et al 2004;Harrer and Travers 1996). The afferent inputs were mainly transmitted by the IX, because the quinine-elicited c-Fos expressions were largely decreased in IX-transected rats compared with CT-transected rats (King et al 1999).…”

A Behavioral and Anatomical Analysis of Conditioned Taste Aversion in C57BL/6J and DBA/2J Mice

“…For example, there have been a number of taste studies that have used c-Fos activation as a marker to determine where neurons are responding to a stimulus (Yamamoto, T. 1993;Yamamoto, T. et al 1993;Houpt, T. A. et al 1994;Swank, M. W. et al 1994;Yamamoto, T. et al 1994;Houpt, T. A. et al 1996;Streefland, C. et al 1996;Chan, C. Y. et al 2004;Koh, M. T. et al 2005;St Andre, J. et al 2007;Yamamoto, T. et al 2009;Haino, T. et al 2010). In the studies presented here, we used immunohistochemical techniques to label the immediate early gene, c-Fos, as a method of identifying neurons responding to either a visceral stimulus, or a stimulus presented in a lickometer.…”

“…Following taste stimulation (defined as direct chemical stimulation of taste buds in the oral cavity) or i.p. injection of LiCl, other studies vary perfusion times including 30 minutes (including unpublished findings by Boughter and Tokita) (Rinaman, L. et al 1997), 45 minutes (Chan, C. Y. et al 2004;, 75 minutes ), 90 minutes (Yasoshima, Y. et al 2006;St Andre, J. et al 2007), and 2 hours post-stimulation (Swank, M. W. et al 1995;Navarro, M. et al 2000;Spray, K. J. et al 2000;Grancha, M. L. et al 2002;Chan, C. Y. et al 2004;Yasoshima, Y. et al 2006;St Andre, J. et al 2007;). Even though the literature varies on wait time before perfusion, a majority of studies wait 2 h before perfusion.…”

“…Following taste stimulation, other studies vary perfusion times from 30 minutes to 2 hours poststimulation (Swank, M. W. et al 1995;Navarro, M. et al 2000;Spray, K. J. et al 2000;Swank, M. W. 2000;Grancha, M. L. et al 2002;Chan, C. Y. et al 2004;Yasoshima, Y. et al 2006;St Andre, J. et al 2007;). As previously described in Figures 2-1 and 2-2, results from our own lab confirm an optimal time for PBN c-Fos being 2 hr post stimulus.…”