Central representation of arrival of nutrient in the duodenum.

This study was carried out to assess the extent to which the appearance of a nutrient (D-glucose) in the duodenum of the anesthetized rat is signaled within the medulla. Recordings were made from single neurons in the region of the dorsal vagal nucleus and the nucleus tractus solitarius during constant single-pass perfusion of the duodenum with isotonic saline or D-glucose at 37 degrees C. In some experiments, the response of medullary neurons to acute gastric distension was also recorded. Of the 41 spontaneously firing neurons that were studied, 20 showed changes in firing rate when glucose replaced saline in the duodenal perfusate, 9 showed decreasing firing rates, and 11 showed increased firing rates. The spontaneous firing rate of glucose-sensitive neurons was significantly slower than that of glucose-insensitive neurons. In 14 neurons tested with both glucose perfusion and gastric distension, 6 responded to only one of the two stimuli, while only 2 responded to both. It is clear that the arrival of nutrient within the duodenum is rapidly signaled within the central nervous system, suggesting the possibility of neural as well as humoral modulation of the physiological changes seen on feeding.