Fig. 1. c-Fos expression along the thoracic (T12–T13), lumbar (L1–L6), and sacral (S1–S2) segments of the spinal cord in parturient rats, 1 h after the birth of the first pup. (  Upper part ) Individual representative microphotographs of spinal cord 40-μm sections. c-Fos immunohistochemistry was processed as described in Materials and Methods (paragraph 6).  Scale bar represents 200 μm. (  Lower part ) Histogram showing the quantification of c-Fos expression in each spinal cord segment from T12 to S2 for eight parturients as compared with six virgin rats. All the rats (parturient and virgin) received the antiprogestative treatment (see Materials and Methods, paragraph 2). For each animal and each segment, the total number (bilateral) of c-Fos neurons was counted in 8–10 nonserial 40-μm sections and averaged. For both groups, the mean numbers for each segment were averaged according to the number of rat per group. Data are expressed as mean ± SEM. Note (1) the significant increase in c-Fos expression in all the spinal cord segments of the parturient rats as compared with the virgin rats (  P < 0.001 for all segments) and (2) the peaking numbers of c-Fos neurons in L5, L6, and to a lesser extent S1 segments in the parturient rats.***  P < 0.001 when compared with all other segments for parturient rats. From M.-C. Lombard, Ph.D., 1999, poster presentation, 9th World Congress of the International Association for the Study of Pain, Vienna, Austria, abstract No. 64; used with permission.