Low doses of the 5-HT1A receptor agonist 8-OH-DPAT increase ingestive behavior in late preweanling and postweanling, but not neonatal rat pups.

Late preweanling (postnatal day 17-18; P17-18) and postweanling (P28-29) Sprague-Dawley rat pups were tested in the presence of both mash and liquid diets following s.c. administration of 0, 0.03, 0.06, 0.1 or 0.5 mg/kg of the 5-HT1A receptor agonist 8-hydroxy-2(di-n-propylamino)tetralin (8-OH-DPAT). Preweanling pups exhibited both a low dose stimulatory and high dose depressant effect of 8-OH-DPAT on mash-related ingestive behaviors, whereas postweanling rat pups were less sensitive to 8-OH-DPAT, exhibiting only an increase in mash ingestion within the dose range examined. In contrast, when neonatal (P3-4) rat pups were tested with milk across a dose range of 0.001-1.0 mg/kg 8-OH-DPAT, no increases in ingestion were seen, with lower doses in this range having no detectable effects and higher doses decreasing ingestion and mouthing. To the extent that low doses of 8-OH-DPAT increase feeding via preferential stimulation of 5-HT1A autoreceptors, these data suggest that neonates may lack functional 5-HT1A autoreceptors, with these receptors maturing by the late preweanling period.