Development of postglucoprivic insulin-induced suckling and feeding in rats

Increased food or milk intake in response to insulin-induced hypoglycemia cannot be demonstrated in the rat until pups reach weaning age. However, when food and suckling are withheld from insulin-treated 5- to 25-day-old rats until their altered blood glucose levels return to normal, their rate of milk intake via suckling from their anesthetized dam is increased over saline-treated control pups. This postglucoprivic action of insulin could not be demonstrated in rats consuming wet mash until pups reached 25-30 days of age. Nonnutritive oral stimulation from dry suckling during the glucoprivic episode is sufficient to disrupt postglucoprivic suckling in 20-day-old rats. In contrast consuming a small quantity of wet mash became an effective inhibitor of postglucoprivic suckling only when pups reached 25 days of age. These data demonstrate the existence of an insulin-sensitive neural system for suckling and feeding in infant rats and point to the involvement of multiple and changing oral factors during development in insulin-induced postglucoprivic feeding.