Comparison of the expression of two immediate early gene proteins, FosB and Fos in the rat preoptic area, hypothalamus and brainstem during pregnancy, parturition and lactation

Medial preoptic area (MPA), supraoptic nucleus (SON), magnocellular (MaPVN) and parvocellular (PaPVN) paraventricular hypothalamic nuclei, and mesence phalic lateral tegmentum (MLT) are involved in maternal behavior, parturiti on and lactation. This study investigated the FosB and Fos immunoreactivity in these regions of virgin, pregnant, parturient, lactating, and lactating -arrested rats. The patterns of FosB and Fos expression were compared betwe en the sections taken from the same animals. Quantitative immunohistochemis try revealed a significant increase in the numbers of FosB-positive neurons in the MPA, SON, MaPVN, and MLT of parturient and lactating females as com pared with pregnant or virgin animals. In lactating rats, the numbers of Fo sB-positive neurons in the MPA, PaPVN, and MLT were increased, but the numb ers in the SON and MaPVN were decreased as compared with parturient females . Many Fos-positive neurons were also seen in parturient and lactating rats , and the patterns of Fos expression in each region were quite similar to t hose of FosB. Moreover, double-labeling immunohistochemistry revealed that: (I) many FosB-positive nuclei were observed in oxytocin and vasopressin ne urons of the SON and PVN in parturient rats; (2) within FosB-positive neuro ns, 89.5% in the MPA, 86.8% in the MLT of parturient rats, and 92% in the M PA and 90.8% in the MLT of lactating animals were also Fos-positive. Only a small number of FosB and Fos-positive neurons were seen in females that we re killed in the early stage of parturition. Removal of the litters immedia tely after parturition completely eliminated FosB and Fos expression in eac h region in the dams. Taken together, the present results suggest that FosB expression is co-involved with Fos in the neural activation during parturi tion and lactation in rats. (C) 1998 Elsevier Science Ireland Ltd. All righ ts reserved.