The present study examined whether the area postrema and adjacent nucleus of the solitary tract (AP/NTS) is necessary for the expression of
anorexia to two classes of
anorectic agent. The first agent is the
serotonergic agonist,
dexfenfluramine (DFEN) and the second is the pancreatic
peptide,
amylin. Rats were prepared with either aspiration lesions of the AP/NTS or a
sham operation. Rats with such lesions (APX) displayed normal
anorexia following administration of DFEN, but the
anorectic effect of
amylin was completely eliminated. The magnitude of a conditioned flavor aversion to DEN was similar in APX and
sham operated controls but, unlike controls, APX rats did not reduce total intake in the two-bottle preference test. Finally, the induction of Fos-like immunoreactivity (Fos-ir) following either DFEN or
amylin was examined in both APX and
sham operated groups. Both agents induced Fos-ir in the AP and/or NTS of
sham operated rats, and this region was entirely absent in the APX rats. DFEN-induced Fos-ir was reduced greatly in the PVN of APX rats, but appeared normal in several other regions surveyed, including the central nucleus of the amygdala and the dorsal striatum. In contrast,
amylin-induced Fos-ir was reduced in many rostral brain regions of APX rats. These data indicate that neither the
anorexia nor the flavor aversion that are produced by DFEN are dependent upon the AP, and in particular that Fos-ir induced by DFEN in the LPBE is not due to afferents from the AP/NTS. In contrast, the
anorectic effect of
amylin seems to be due principally to its direct action at the AP/NTS.