Effect of intraduodenal lipid on parabrachial gustatory coding in awake rats

Intestinal fat differentially suppresses sham feeding of liquid diets and p referred gustatory stimuli. Although the behavioral effect is robust, no el ectrophysiological evidence exists to account for its neural basis. Therefo re, we investigated the effect of intestinal fat on gustatory coding in the pontine parabrachial nuclei (PBN) by recording from single neurons in awak e rats before, during, and after intraduodenal infusions of lipid (Intralip id; 10 ml, 5 kcal). Intraduodenal lipid did not alter the response profiles of PEN taste neurons. It did, however, produce an overall decrease in resp onse magnitude (-16.25%; n = 43), with the largest reduction to sucrose (-3 0%; n = 43). The most pronounced suppression occurred in sucrose-best neuro ns in response to sucrose (-55%; n = 19), and this effect was largest for t he sucrose-specific cells (-77%; n = 3). After lipid infusions, nonspecific neurons in both the sucrose-best and NaCl-best categories also responded l ess to their best stimulus (sucrose, -46%; n = 16; NaCl, -35%; n = 13). In contrast, no significant changes were found in NaCl-specific cells in respo nse to NaCl. All effects appeared with short latency (similar to 5 min) and were reversible within the time frame of a meal. In controls, duodenal inf usions of saline did not cause any changes in taste responsiveness. These r esults suggest that intestinal fat has specific effects on taste coding in the PEN that may contribute to the intake suppression of palatable food obs erved in behavioral studies. The similar, short latency of both the behavio ral and neural effects supports the hypothesis of a preabsorptive site of a ction.