Effect of hepatic glucose infusion on glucose intake and licking microstructure in deprived and nondeprived rats

The effects of hepatic-portal glucose or saline infusions on intake and the temporal distribution of licking (lick microstructure) were evaluated in nondeprived and in 20.5-h food-deprived rats. Rats received portal infusions of isotonic glucose or saline (0.1 ml/min) for 2 h before and then throughout a 90-min period of access to a spout that delivered 12.5% glucose. Overall, a significant treatment-related intake suppression was obtained in nondeprived but not in deprived groups. For both groups, however, there was a significant positive linear relationship between the amount individual rats consumed under the saline (baseline) infusion condition and the extent to which portal glucose infusion suppressed intake. The linear fit for the deprived group was similar in slope, but right shifted, relative to the best fit for the nondeprived group. The individual-subject and group differences in response to portal glucose infusion are discussed in relation to the inconsistent literature on this treatment's short-term intake effects. We focused analysis of the licking pattern on those rats for which a prominent portal glucose infusion effect was obtained (i.e., nondeprived rats with higher than average baseline intakes). Features of the lick pattern associated with taste evaluation (Ist min lick rate; lick burst duration) were not significantly affected by portal glucose infusion. Rather, the minute-by-minute rate of ingestion under glucose infusion declined more rapidly than under baseline tests, indicating that portal glucose infusion enhanced the inhibitory influence of the accumulating postingestive load.