INTAKE OF DIFFERENT CONCENTRATIONS OF SUCROSE AND CORN-OIL IN PREWEANLING RATS

To investigate the orosensory control of ingestion in preweanling rats, we infused one of the following liquids continuously through anterior sublingual intraoral catheters for 20 min: sucrose solutions (5, 10, 20, and 40%) and corn oil emulsions (6.25, 12.5, 25, 50, and 100%). Pups were tested at 7, 14, 21, and 28 days of age. Each pup was tested only once. Intake of sucrose and of corn oil became increasingly correlated with concentration from 7 to 21 days. Sucrose elicited more intake than water by day 7, whereas corn oil did not until day 14. Low concentrations of sucrose had differential effects on intake by day 14, but low concentrations of corn oil emulsions did not have differential effects on intake until day 21. At all ages, the peak intake of sucrose was significantly larger than the peak intake of corn oil. These differences are probably not based on prior experience because each test of ingestion represented a first exposure to the stimulus. Thus we suggest that the differences are due to the maturation of the orosensory control of ingestion by sucrose and corn oil.