Localization of hindbrain glucoreceptive sites controlling food intake andblood glucose

Feeding and blood glucose responses to local injection of nanoliter volumes of 5-thio-D-glucose (5TG), a potent antimetabolic glucose analogue, were s tudied at 142 hindbrain and 61 hypothalamic cannula sites. A site was consi dered positive if 5TG elicited at least 1.5 g more food intake or a hypergl ycemic response at least 25 mg/dl greater than the respective responses eli cited by vehicle injection in the same rat. Of 61 hypothalamic cannula site s tested, none were positive for blood glucose and only one was positive fo r feeding. Increasing the 5TG dose to 48 ug did not produce additional posi tive results at hypothalamic sites. In contrast, 66 hindbrain sites were po sitive for feeding and 49 were positive for blood glucose, with 33 of these being positive for both responses. The distribution of positive sites for feeding and hyperglycemia overlapped almost completely. Positive sites were concentrated in two distinct zones: one in the ventrolateral and one in th e dorsomedial medulla. In both locations, the glucoreceptive areas extended approximately from the level of the area postrema (AP) to the pontomedulla ry junction. Glucoreceptive zones were co-distributed with epinephrine cell groups C1-C3, suggesting that epinephrine neurons may be important compone nts of the neural circuitry for glucoregulation. Localization of glucorecep tive sites will facilitate positive identification of glucoreceptor cells a nd the direct analysis of the neural mechanisms through which they influenc e food intake and metabolic responses. (C) 2000 Published by Elsevier Scien ce B.V. All rights reserved.