Nucleus ambiguus stimulation increases plasma insulin levels in the rat

The ventral lateral brainstem has been explored for sites that facilitate insulin release unilaterally, using electrical stimulation techniques in male rats anesthetized with alpha-chloralose/urethane. Stimulation in the region of nucleus ambiguus (amb) produced a rapid rise (by 1 min) in plasma insulin levels, whereas stimulation of brainstem regions further than 500 micrometers from amb had no consistent effect on insulin levels. The amb-induced rise in insulin was markedly exaggerated by the alpha-adrenergic antagonist, phentolamine, and was greatly diminished by bilateral cervical vagotomy or atropine pretreatment. These results strongly suggest that the amb is one source of vagal motoneurons that facilitate insulin secretion. However, amb electrical stimulation alone also activated an apparent sympathetic efferent output whose inhibitory effect on insulin release could be blocked by phentolamine.