Intravenous insulin infusions in rats decrease gustatory-evoked responses to sugars.

Physiological factors that affect food intake have been shown to influence taste-evoked activity in the rat's central nervous system. Insulin appears to have a bimodal effect on feeding, inhibiting intake when its rise is within the normal physiological range, but, with further increases, causing hyperphagia. We studied the effect of low intravenous doses (0.5 U/kg) of regular insulin on taste-evoked responses in the nucleus tractus solitarius. Taste activity was elicited by application to the tongue of glucose, fructose, NaCl, HCl, and quinine. We monitored responses before and after intrajugular injections of insulin or a control vehicle. Taste responsiveness to glucose and fructose was significantly reduced for the period 7-22 min following the injection. Activity representing NaCl, HCl, and quinine was unaffected. The suppression of responsiveness to sweet stimuli could decrease the hedonic appeal of tastants and so serve as a mechanism by which physiological doses of insulin could contribute to a reduction in feeding.