Suckling behavior in neonatal rats: psychopharmacological investigations.

The effects of various neurotransmitter antagonists on suckling behavior of 3- and 4-day-old Sprague-Dawley rat pups were examined. Peripheral administration of three serotonergic antagonist, scopolamine, were observed to markedly reduce suckling behavior of neonatal rat pups. These effects appear to be centrally mediated since intracisternal administration of small doses of all of these drugs was observed to suppress suckling. The reduction in suckling induced by these antagonists did not appear to be a result of a debilitating effect of the drugs or to be due to any alteration in body temperature. In contrast, the opiate antagonist naloxone, the dopaminergic antagonist haloperidol, the alpha-noradrenergic antagonist phentolamine, and the beta-noradrenergi antagonist propranolol did not consistently produce any alteration in suckling behavior. These results suggest that the serotonergic and cholinergic systems may be functioning much earlier in ontogeny than previously suggested and may be involved in modulating suckling behavior in the early neonatal period.