Pharmacological suppression of prolactin does not reduce paternal responsiveness but does reduce infanticidal aggression in the biparental Djungarian hamster, Phodopus campbelli

The role of prolactin in the facilitation and maintenance of maternal behaviour is well established. The mechanisms behind paternal responsiveness are less understood, however prolactin has been implicated in several species, supporting the idea of a neuroendocrine homology existing between maternal and paternal circuitry. Female Djungarian hamsters ( Phodopus campbelli) experience a late afternoon prolactin surge in the final days of gestation that is important for the onset of maternal care. Males of this species experience a similar surge, leading to the hypothesis that prolactin before the birth is also important in the paternal behaviour of this naturally biparental species. The late gestation surge of prolactin was pharmacologically suppressed through dopamine agonist treatment in male Djungarian hamsters and paternal behaviour was assessed using a pup displacement paradigm. Although prolactin was successfully suppressed, no change in paternal responsiveness was detected. Social cues may be a strong elicitor of paternal responsiveness and could have overridden any negative effects prolactin suppression may have had on paternal behaviour. In a second study, the social experiences surrounding pregnancy and parturition were manipulated in male Djungarian hamsters to rule out any influence these may have had on the paternal behaviour seen in the first study. Prolactin was suppressed and males were separated from their mates either before parturition or after mating. Males that missed the birth and postpartum pup exposure displayed levels of infanticide comparable to non-fathers. Pharmacological suppression of prolactin, however, eliminated this infanticide and caused no deficits in paternal behaviour. Taken together, the results of these studies indicate that pituitary prolactin might play an important role in the inhibition of inappropriate aggression towards pups in new fathers, rather than a facilitating role towards paternal responsiveness.