Visceral afferents and metabolic function

The effect of glucose, 2 DG, CCK and serotonin on the firing rate of the vagal hepatic afferents and vagal pancreatic afferents was studied in rabbits, guinea pigs and rats. The hepatic and pancreatic afferents showed a decrease in activity following administration of glucose and an increase in activity after the injection of 2 DG. These afferent elements may have a mechanism to respond to blood glucose similar to that of lateral hypothalamic neurons. The results also indicate that CCK and serotonin showed the opposite effects in the vagal hepatic afferents and in the pancreatic efferents. Decrease in the discharge rate in the vagal hepatic afferents due to CCK or serotonin may cause a suppression of food intake behavior. Increase in the discharge rate in the vagal pancreatic afferents resulting from CCK or serotonin or insulin suggests the existence of a nervous information system for these substances in the circulating blood in the pancreas.