The origins and role of efferent vagal nuclei in hyperinsulinemia in hypothalamic and genetically obese rodents.

The main brainstem parasympathetic efferent neurons that ultimately reach the pancreas and facilitate insulin secretion are located in the nucleus ambiguus (NA) and the dorsal motor nucleus of the vagus nerve (DMX). With regard to insulin secretion, hypothalamic (produced by ventromedial hypothalamic (VMH) lesions) and genetic obesities have features in common: (a) insulin oversecretion is an early abnormality in both syndromes; and (b) this abnormality is vagus nerve-mediated. VMH lesions and possible, spontaneously occurring (i.e. genetic) CNS-located abnormalities appear to result in an increased parasympathetic efferent tone together with decreased sympathetic efferent tone that is likely to be responsible for the occurrence of hyperinsulinemia, obesity and, eventually, insulin resistance.