Effects of unilateral suckling on nursing behavior and c-fos activity in the caudal periaqueductal gray in rats

In rats, suckling elicits kyphosis-the bilaterally symmetrical, upright, hu mp-backed nursing posture-and maximal expression of the immediate early gen e c-fos in a region of the caudal periaqueductal gray (cPAG) that mediates the sensorimotor integration of kyphosis. We determined the effects of prep artum unilateral nipple removal on nursing behavior and c-fos expression du ring a 60-min mother-litter intel action on Day 7 postpartum. Compared with dams suckled by 6 pups bilaterally, clams suckled unilaterally displayed e ssentially normal maternal behaviors, including kyphosis. Unilaterally suck led darns, however, showed an increase in the abnormal prone nursing postur e, a decrease in proportion of kyphotic nursing of total time over pups, an d a 20% higher contralateral/ipsilateral ratio of cPAG neurons expressing c -fos. These results are consistent with an incompletely lateralized neural pathway conveying suckling stimulation to the cPAG and provide a mechanism whereby kyphosis is elicited by unilateral suckling when pups initiate nurs ing from their supine dam. (C) 1999 John Wiley & Sons, Inc.