Metabolic and behavioral responses in pre-weanling rats following alteration of maternal diet

In rat pups, blockade of fatty acid oxidation by administration of 2-mercaptoacetate (MA) produces an increase in independent ingestion by 12 days of age. In contrast, administration of methyl palmoxirate (MP) fails to increase intake or to alter oxidation of fatty acids in young rats due to the high proportion of medium chain triglycerides (MCT) in rat milk. In the present experiments, the composition of rat milk was altered by placing dams on a high fat (HF) diet to examine the development of ingestive responding in rat pups following administration of MP. Following delivery of MP (0.5--10 mg/kg), pups were placed in a cage inside an incubator for 1, 3, or 6 h, and then received an intake test consuming a commercial half-and-half milk diet from the floor of test containers. Blood was collected from additional groups of pups for measurement of beta-hydroxybutyrate (beta HBA) and glucose levels. The results demonstrated that administration of MP produced significant reductions in beta HBA levels after 3 h in 12- and 15-day-old pups, but behavioral responses were noted only in pups aged 15 days. Similar results were obtained following administration of MA to pups reared by dams on HF diets; physiological responses were observed at 12 and 15 days of age, but behavioral responses were not observed after administration of MA until 15 days of age. Taken together, these results suggest that (1) changes in fatty acid oxidation may represent an early metabolic signal that can influence intake in rat pups and (2) alteration of the dam's diet produces physiological and behavioral changes in the pups.