Perinatal exposures to rotating magnetic fields 'demasculinize' neuronal density in the medial preoptic nucleus of male rats.

Pregnant rats were exposed continuously for 3 days before to 3 days after birth to 0.5 rotating magnetic fields (RMF) whose intensities ranged between 1.5 and 3.0 mT or between 50 and 300 microT or to sham field conditions. When the male and female rats exposed to these perinatal conditions were about 100 days old, the numbers of neuronal soma and the numbers of nuclei for the three major types of glial cells were counted within the medial preoptic nucleus (MPO), suprachiasmatic nucleus (SCN) and ventromedial nucleus (VMH) of the hypothalamus. The male rats but not the female rats that had been exposed to either intensity of the RMF showed a significant reduction (similar to normal females) in the numbers of neurons within the MPO; the differences accommodated one-third of the variance and were not reduced significantly when the cell densities of the VMH or SCN were covaried before the analyses. The results suggest that some sexually dimorphic structures may be permanently and differentially affected when exposed perinatally to relatively weak extremely low frequency magnetic fields.