SCH23390, but not raclopride, decreases intake of intraorally infused 10% sucrose in adult rats.

When 10% sucrose is infused intraorally on postnatal days (PN) 7, 14, and 21, raclopride, a D2 dopaminergic antagonist, does not affect intake at any age and SCH23390, a D1 antagonist, does not affect intake on PN 7 but a large dose decreases intake on PN 14 and 21. To determine if this differential effect of the antagonists on PN 14 and 21 remains after further postnatal development, we studied adult rats in this intraoral intake test. Female (n = 77) and male (n = 81) adult rats, approximately 43 or 96 days old, were deprived for 4 h before intraoral infusion of 10% sucrose. Each rat was tested once and this was its first experience with sucrose. SCH23390 (133 or 267 micrograms/kg), raclopride (357 or 714 micrograms/kg), or saline vehicle was given IP at -15 min. The larger dose of SCH23390 significantly decreased intake of rats that were approximately 43 and 96 days old, but neither dose of raclopride changed intake at either age. These results suggest that D1, but not D2, receptors are necessary components of the central neural network that processes the unconditioned gustatory stimulus of 10% sucrose into mouthing and swallowing movements that maintain ingestion in late preweanling and adult rats under these conditions.