Effects of serotonergic and cholinergic antagonists on suckling behavior of neonatal, infant, and weanling rat pups.

In Experiment 1, Sprague-Dawley rat pups at postnatal days 3-4, 7-8, 10-11, 15-16, and 23-24 were tested for suckling behavior on their anesthesized multiparous dams following administration of metergoline or scopolamine. The serotonergic antagonist, metergoline, inhibited suckling in 3- to 4- and 7- to 8-day-old rat pups, but was not found to influence suckling in older pups. Scopolamine, a cholinergic antagonist, reduced suckling primarily in 3- to 4-day-old pups. In Experiment 2, parity of the maternal female was manipulated to assess whether this variable would influence suckling behavior and the effects of metergoline on suckling of weanlings. Baseline levels of suckling were reduced in 23- to 24-day-old pups of primiparous dams when compared with multiparous-derived offspring. Administration of metergoline increased the amount of time that these primiparous-derived pups spent attached to nipples, but did not influence suckling of offspring of multiparous dams, perhaps as a result of a ceiling effect on suckling behavior in these animals.