DIFFERENTIAL-EFFECTS OF DORSOMEDIAL MEDULLA LESION SIZE AN 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 o f water after treatment with subcutaneous isoproterenol (Iso) or angio tensin II. In addition, lesioned rats lose a significant amount of bod y weight immediately after surgery. Nonetheless, there are disparate r eports on the effects of lesions of the AP on fluid intake and body we ight. 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 includ ed more of the NTS, the effect on body weight was reduced. Moreover, w ater intake induced by Iso increased as more NTS was involved in the l esion. Conversely, 3-h ad Libitum saline intake and saline intake afte r sodium depletion decreased with more involvement of the NTS in the l esion. These data suggest that the neural population in the NTS border ing the AP may play a critical role in the control of water and saline intake as well as the regulation of body weight.