Increases in Plasma Insulin Levels in Response to Electrical Stimulation of the Dorsal Motor Nucleus of the Vagus Nerve

In order to investigate the physiological counterpart of the anatomical finding showing that the dorsal motor nucleus of the vagus nerve (DMX) is a source of efferent vagal fibers innervating the pancreas, unilateral electrical stimulation using monopolar electrodes (50 microA, 30 Hz, 0.2 msec) at a glycemia of 150 mg/100 ml was performed in normal anesthetized rats. DMX stimulation resulted in rapid (within 1 min) rise in plasma insulin levels (greater than or equal to 200%). Stimulation of the nucleus of tractus solitarius, anatomically connected to DMX, also produced a 50% increase in insulinemia. The effect of DMX stimulation was almost completely abolished by atropine pretreatment or acute bilateral subdiaphragmatic vagotomy. The effect of DMX stimulation was not potentiated by the alpha-adrenergic blocker (infusion of phentolamine) indicating that no inhibitory fiber was recruited during DMX stimulation. It is concluded that DMX is connected to the endocrine pancreas exclusively via vagal fibers and has a role in neurally mediated insulin release.