Gastric infusion of nutritional supplement in fasted rats increases splanchnic sympathetic nerve activity (sSNA) and activates RVLM‐projecting neurons of the paraventricular hypothalamus (PVH)

Abstract

The hypothesis that refeeding of fasted rats would stimulate SNA via activity of sympathetic regulatory neurons in the PVH was tested. In one study, immunohistochemistry was used to determine PVH neurons stimulated by “refeeding” (Ensure, 10 ml, intragastric) in 3 day fasted rats previously injected with the retrograde tracer cholera toxin subunit B (CTB) into the rostral ventrolateral medulla (RVLM). Sympathetic regulatory neurons (CTB‐immunofluorescence, CTB‐IF), neurons activated by refeeding (c‐Fos‐IF) and double labeled neurons were counted in 3 rostro‐caudal anatomically matched sections from the PVH of each rat. Refeeding increased c‐Fos‐ IF in the PVH compared to control rats. Whereas CTB‐IF and c‐Fos‐IF neurons were located throughout the PVH, c‐Fos‐IF was higher in the rostral PVH, and CTB‐IF neurons were more prevalent in the medial and caudal portions of the PVH. Colocalization of CTB and c‐Fos were noted in approximately 12% of CTB‐IF neurons. In a second study, sSNA was recorded in anesthetized, 72 h fasted rats at baseline and following intragastric delivery of Ensure (10 ml). sSNA increased in a slow, linear fashion to approximately 140% of baseline at 1 hour post refeeding. Together these results suggest that sympathetic regulatory neurons in the PVH may mediate the increase in sSNA following refeeding after fasting. Support: HL088052, HL076312 (GMT)