Differential effects of dorsomedial medulla lesion size on ingestive behavior in rats

Previous studies indicate that rats with lesions centered on the area postrema (AP) drink more saline and consume abnormally large amounts of water after treatment with subcutaneous isoproterenol (Iso) angiotensin II. In addition, lesioned rats lose a significant amount of body weight immediately after surgery. Nonetheless, there are disparate reports on the effects of lesions of the AP on fluid intake and body weight. These reports suggest that the adjacent nucleus of the solitary tract (NTS) may play a role in the effects observed subsequent to the lesion. In this study we evaluated the effects of varying lesion size on body weight, fluid intake, and the baroreflex. As the lesion included more of the NTS, the effect on body weight was reduced. Moreover, water intake induced by Iso increased as more NTS was involved in the lesion. Conversely, 3-h ad libitum saline intake and saline intake after sodium depletion decreased with more involvement of the NTS in the lesion. These data suggest that the neural population in the NTS bordering the AP may play a critical role in the control of water and saline intake as well as the regulation of body weight.