The ontogeny of drinking evoked by activation of brain angiotensin in the rat pup.

Renin (1 ng) was injected into the 3rd ventricle of the brain of rat pups at various ages, and their ingestion was measured by weighing them either after 40 min of oral infusion of water or milk while they were away from their dam (off-dam), or after 40 min of suckling from their dams (on-dam). Beginning at 3-5 days of age, renin increased ingestion of milk and water off-dam. After 15 days of age, milk ingestion off-dam was no longer increased by renin, but intake of water continued to be evoked. In contrast, renin did not increase intake by suckling at any age. These findings reveal that the adult characteristics of the dipsogenic action of the renin-angiotensin system in the brain emerge at 15 days, at which age the increased intake becomes entirely specific for water. This finding confirms the precocity of the neural controls of drinking in the rat and shows that, like the controls of independent feeding, they are dissociated from those of suckling. It adds support to the idea that the neonatal mammalian brain contains separate neurological systems for suckling and for independent ingestion.