Neuronal NOS mRNA expression measured as film grain density over the SON (A). A significant decrease in nNOS mRNA expression was observed in late-pregnant rats (day 22), but not virgin, day 16, or parturient rats. Data are means ± SEM; *p < 0.05. Film autoradiographs of sections hybridized with a ³⁵S oligonucleotide probe against rat neuronal NOS mRNA in 16 d (B) and 22 d (C) pregnant rats. Scale bar, 1 mm.