Pre‐feeding conditions alter hypophagic responses to m‐chlorophenylpiperazine (mCPP) in young, adolescent, and adult rats

5‐HT2C receptors are implicated in the inhibitory control of feeding. The present study investigates the relationship of agonist mCPP and age, on food consumption under two deprivation conditions. Weanling (18 and 23 days), adolescent (28, 30 and 40 days) and adult (51 and 60 days) Sprague‐Dawley rats were food restricted for 20 h prior to injection with mCPP or saline. Separate groups of rats were also given 1 h access to pre‐weighed food prior to injection. After 90 min access to food, the rats, water, and remaining food were removed from the cages and weighed. Agonist mCPP produced dose‐dependent decreases of food intake in all groups of rats. However, significant differences in response to mCPP were observed dependent on the age of the rats. Agonist mCPP produced profound hypophagia in weanlings at all doses. Adolescent rats were more similar to adult rats in their responses to mCPP exposure and food intake in the rats. In the prefeeding condition, however, adolescent rats exhibited significantly less hypophagia than weanling and adult rats. These results were obtained whether rats were tested in an acute or a longitudinal study design. The age‐dependent effects of mCPP on food intake suggest that: the 5‐HT2C system undergoes neurodevelopment throughout early adolescence; and effective pharmacological treatments for obesity may depend on age. (Supported by NIDA 14763 and Health Research Formula Fund, PA)