C-Fos-like immunoreactivity in the brainstem following gastric loads of various chemical solutions in rats

Abstract

The distribution of c-Fos-like immunoreactivity (c-FLI) in the lower brainstem especially in the area postrema (AP), nucleus of the tractus solitarius (NTS) and parabrachial nucleus (PBN) was examined following gastric loads of various chemical solutions in rats. An aliquot of 7.5 ml of each stimulus was intragastrically infused, and c-FLI was detected. The most remarkable c-FLI was induced by LiCl, lactose and ethanol which are known to be effective unconditioned stimuli in conditioned taste aversions. Polycose and disaccharides such as sucrose and maltose induced more c-FLI than monosaccharides such as glucose, fructose and galactose. Relatively low levels of c-FLI were observed for other sweeteners such as saccharin, glycine and alanine, and other basic taste stimuli such as NaCl, HCl, quinine and umami substances. Each stimulus induced a similar proportion of c-FLI among the subnuclei of the NTS, but not in the PBN, where chemicals effective in inducing conditioned taste aversions elicited stronger c-FLI in the external lateral subnucleus, and those in inducing conditioned taste preferences such as Polycose and glucose elicited stronger c-FLI in the dorsal lateral subnucleus. Vagotomy reduced c-FLI to about 50% for LiCl stimulation and to about 30% for sucrose stimulation, suggesting that LiCl has a larger proportion of extravagal inputs than sucrose.