Yuan, Pu-Qing, and Hong Yang. Neuronal activation of brain vagal-regulatory pathways and upper gut enteric plexuses by insulin hypoglycemia. Am J Physiol Endocrinol Metab 283: E436-E448, 2002;10.1152/ajpendo.00538.2001.-Neuronal activation of brain vagal-regulatory nuclei and gastric/duodenal enteric plexuses in response to insulin (2 U/kg, 2 h) hypoglycemia was studied in rats. Insulin hypoglycemia significantly induced Fos expression in the paraventricular nucleus of the hypothalamus, locus coeruleus, dorsal motor nucleus of the vagus (DMN), and nucleus tractus solitarii (NTS), as well as in the gastric/duodenal myenteric/submucosal plexuses. A substantial number of insulin hypoglycemia-activated DMN and NTS neurons were choline acetyltransferase and tyrosine hydroxylase positive, respectively, whereas the activated enteric neurons included NADPH-and vasoactive intestinal peptide neurons. The numbers of Fos-positive cells in each above-named brain nucleus or in the gastric/duodenal myenteric plexus of insulin-treated rats were negatively correlated with serum glucose levels and significantly increased when glucose levels were lower than 80 mg/dl. Acute bilateral cervical vagotomy did not influence insulin hypoglycemia-induced Fos induction in the brain vagal-regulatory nuclei but completely and partially prevented this response in the gastric and duodenal enteric plexuses, respectively. These results revealed that brain-gut neurons regulating vagal outflow to the stomach/ duodenum are sensitively responsive to insulin hypoglycemia. dorsal motor nucleus of the vagus; nucleus tractus solitarii; glucose; vagus; stomach CONVERGING EVIDENCE SUGGESTS that hyper-or hypoglycemia affects gastrointestinal (GI) functions by influencing vagal-cholinergic outflow to the viscera. The involvement of upper GI tract organs in the hyperglycemia-induced delay of gastric emptying (5) corresponds to the distribution of the vagus in the GI tract (52). GI functions that are well established to be stimulated by vagal efferent activation, such as sham feeding-induced gastric acid secretion and pancreatic polypeptide release from the pancreas, were remarkably reduced during hyperglycemia (34). In contrast to hyperglycemia, insulin hypoglycemia is well established as a central vagal stimulus on upper GI functions (63,64,67). Visceral response to insulin hypoglycemia has been widely used to test vagus nerve integrity (67), especially used postoperatively to test the result of vagotomy (45). These findings established a role of the vagus nerve in mediating the regulation of GI functions by altered glucose metabolism. However, how the neurons in the brain vagal-regulatory nuclei and GI enteric plexuses respond to hypo-or hyperglycemia is still poorly understood.The medullary dorsal vagal complex (DVC) is composed of the dorsal motor nucleus of the vagus (DMN) and the nucleus tractus solitarii (NTS), which respectively contain somata of parasympathetic efferents that project to the GI tract (4, 48, 61) and neurons receiving vagal afferent i...