Rat pups are reinforcing to the maternal rat: Role of sensory cues

Abstract

The present studies were undertaken to investigate the involvement of sensory cues in the expression of maternal behaviors and in the reinforcing properties of pups, reflected in performance on a conditioned place preference task. Postpartum animals were either able to interact with pups in one of two novel environments or were prevented from doing so by placing pups in a perforated Plexiglas cube. On alternate days, mothers were exposed to a second environment in the absence of pups. When the mothers tested for the development of a conditioned place preference, it was found that the group permitted pup interaction preferred the pup-paired box and that the no-interaction (distal) group did not. The role of the primary olfactory system was investigated by rinsing the nares of animals with either a 5% zinc sulphate spray to render the animal hyposmic or an air control and then permitting the animals to interact with pups in one of two novel environments. There were no differences between groups in maternal responding. However, when the mothers were tested for the development of a preference for the pup- paired box, it was found that while the air control animals preferred the pup-paired box, the anosmic zinc sulphate animals did not. To investigate the involvement of somatosensory cues, the ventral or perioral surfaces of animals were treated with either an anesthetic cream or a control cream prior to exposure to pups. Testing for maternal behaviors revealed that there were no differences between anesthetized groups and their controls. However, when the animals were tested for the development of a conditioned place preference, it was found that while both the ventral and perioral control groups preferred the pup-paired box, the ventral and the perioral anesthetized groups did not. Taken together, these studies demonstrate that several modalities involved in the interaction between pups and mothers contribute to the pups’ ability to be a reinforcing stimulus to the mother. The stimulation that postpartum mothers receive via these modalities is complex, and the disruption of any of them can alter the reinforcing capabilities of pups.