The direct effect of insulin on barosensitive neurones in the nucleus tractus solitarii of rats.

The present investigation was designed to determine the direct effect of insulin on the spontaneous discharge of barosensitive neurones in the nucleus tractus solitarii (NTS) of rats anaesthetized with urethane. Microinjection of 20 nl insulin (10 IU/ml) into NTS decreased the spontaneous discharge of 38 of the 52 units studied (73.1%), and this decrease was augmented by increasing the concentration to 40 IU/ml. Microinjections of insulin vehicle, glucose, hydralazine or phenylephrine did not elicit significant changes in the spontaneous discharge of NTS barosensitive neurones. These results demonstrate that insulin inhibits the spontaneous discharge of barosensitive NTS neurones. They suggest that insulin increases sympathetic nervous activity via a central neural mechanism and may play a role in the modulation of cardiovascular information within the NTS.