Insulin acting as a modulator of feeding through the hypothalamus.

To understand the functional role of insulin in the control of feeding, biochemical and physiological studies were performed in the rat. 1) Insulin content in the brain was much higher than that in the blood, and was extremely variable from animal to animal. 2) Specific binding sites of insulin in the brain were most abundant in the hypothalamus and olfactory bulb. 3) Neither insulin content nor binding sites in the brain was significantly affected by peripheral insulin concentration. 4) Activity of glucoreceptor neurons in the ventromedial hypothalamus (VMH) was facilitated by simultaneous application of insulin and glucose, but inhibited by insulin alone. 5) Activity of the glucose-sensitive neurons in the lateral hypothalamus (LHA) was facilitated by insulin in a dose-dependent manner. 6) Stimulation of the ventral part of the LHA accelerated pancreatic vagal nerve activity. Stimulation of the dorsal part of the LHA and the VMH was inhibitory. 7) Pancreatic splanchnic nerve activity during LHA stimulation tended to show inhibition, but sometimes was modulated by the stimulus frequency. Both inhibition and facilitation were observed in the activity in response to VMH stimulation.