The effects of amphetamine and chlorpromazine on independent ingestion of milk in preweanling rats.

To assess the effects of catecholaminergic drugs on independent feeding during development, preweanling rats were administered amphetamine (AMPH) or chlorpromazine (CPZ) and were allowed to ingest milk through anteriorly located intra-oral cannulas. In 1-hr milk-deprived rat pups, AMPH stimulated milk intake at 3, 7 and 10 days of age and suppressed intake at 15 days. In 22-hr-deprived pups, AMPH had no effect at 3, 7 and 10 days, but reliably suppressed intake at 15 days. CPZ stimulated intake in 3-, 10- and 15-day-old milk-satiated pups. In 22-hr-deprived pups, CPZ had no effect at 3 and 10 days, but stimulated intake at 15 days. While AMPH produced pronounced nonappetitive behavioral activation in conjunction with enhanced intake in 1-hr-deprived pups, AMPH-induced activation occurred without enhanced intake in 22-hr-derived pups. Thus, there was a dissociation between AMPH's effect on milk intake and AMPH-induced nonappetitive behavioral activation. Collectively, the present results support the following conclusions. First, a catecholaminergic system(s) that enhances independent feeding is present very early in postnatal development of the rat. Second, level of food deprivation is an important state-dependent variable when assessing the effects of AMPH and CPZ on independent feeding in preweanling rats.