Mother rats bar-press for pups: effects of lesions of the mpoa and limbic sites on maternal behavior and operant responding for pup-reinforcement (vol 100, pg 15, 1999)

This series of studies explored the operant response rates for pup-reinforc ement of female Sprague-Dawley rats that were either postpartum or cycling and sustained lesions of the medial preoptic area (mpoa), the lateral amygd ala, the nucleus accumbens, or sham lesions. The last experiment tested the effects on operant responding of preventing direct access to pups in mpoa and sham-lesioned postpartum mothers. All animals were trained prior to mat ing on an FR-1 bar-press schedule to criterion (50 presses in 30 min) for a food (Froot Loops) reward in an operant chamber. At the end of pregnancy a nimals that were to be tested postpartum were provided in their home cages with six newborn foster pups; mother-litter interactions were observed on t he last 3 days of pregnancy and throughout the postpartum period. On each o f these same days after a period of separation from pups, females were test ed in the operant box for delivery of rat pups. With each bar-press respons e, a rat pup rather than a Fruit Loop was delivered down a gentle shoot int o the hopper. Non-postpartum, but maternal, multiparous animals who were sh owing estrous cycles were tested using the same procedures. The first and s econd studies showed that animals (both postpartum and as cycling multiparo us animals) with mpoa lesions exhibited a significant reduction in bar-pres s rate for pup reinforcement in the operant box. In postpartum animals, amy gdala lesions also produced a bar-press deficit, whereas nucleus accumbens lesions did not. All lesioned groups showed deficits in maternal responding in the home cage and deficits in retrieval in the operant box. These resul ts indicate that systems associated with the mpoa mediate both the stereoty pical maternal behaviors and pup-reinforcement. In contrast, the expression of home cage maternal behavior is dependent on the integrity of both the a mygdala and nucleus accumbens, whereas operant responding need not be. Thes e results indicate a dissociation of mechanisms mediating expression of the species-typical maternal behavior and pup-reinforcement, (C) 2000 Elsevier Science B.V. All rights reserved.