Attenuated glucoprivic feeding responses are a feature of hypoglycaemic unawareness in insulin-treated diabetes. Glucose alters the activity of hypothalamic neurones involved in regulating appetite. Arcuate nucleus (ARC) Neuropeptide Y (NPY) releasing neurones stimulate feeding. The identification of glucose-sensitive NPY releasing hypothalamic neurones suggests a strong role for these neurones in mediating changes in appetite induced by alterations of glucose. To gain a better understanding of the mechanism involved in glucoprivic feeding, we investigated the changes in NPY release by the hypothalamus at different concentrations of glucose, using static incubation of hypothalamic explants.
Hypothalami from 20 male Wistar rats (mean weight 280.4±2.3 g) were incubated in artificial CSF (aCSF) for a 2-h equilibration period. The hypothalamic explants were then incubated for three 45 min periods in 600 μl aCSF containing 3, 8 (baseline) and 15 mM glucose in randomised order. Finally, the viability of the tissue was verified by 45-min incubation in aCSF containing 56 mM KCl. At the end of each incubation period, supernatants were removed and assayed for NPY release by radioimmunoassay. Only explants that showed a greater secretion of NPY with 56 mM KCl as compared to baseline were considered viable.
NPY release in aCSF containing 3 mM, 15 mM and KCl was 285.2±92.8, 130.7±25.8 and 818.8±210.7 percent of basal NPY release, respectively. There was a significant increase in NPY release with aCSF containing 3 mM glucose versus baseline glucose. This supports the presence of glucose-sensitive NPY releasing hypothalamic neurones. These findings are consistent with previous findings that suggest an important role for NPY releasing hypothalamic neurones in stimulating glucoprivic feeding. Defects in the responses of these neurones to glucose may contribute to the development of hypoglycaemia unawareness in insulin-treated diabetes. Our work also supports the use of static incubation of hypothalamic explants to study the effects of glucose on neuropeptides involved in regulating appetite.