SEXUAL DIFFERENCES IN THE MAGNOCELLULAR VASOPRESSINERGIC SYSTEM IN GOLDEN-HAMSTERS

Golden hamsters, as compared to rats, lack several parvicellular vasop ressinergic cell groups, particularly sexually dimorphic populations. We decided to test the possibility that magnocellular vasopressinergic neurons are subjected to sexual differences in hamsters, as they are known to display vasopressin (AW)-dependent sexually dimorphic behavio rs. The distribution of magnocellular vasopressinergic neurons was map ped and compared between males and females. Approximately 50% more vas opressin-immunoreactive (AVP-ir) neurons were counted in males within the medial and lateral divisions of the supraoptic nucleus. Furthermor e, levels of AVP extracted from the hypothalamus and the pituitary gla nd were three to four times higher in males than in females. Finally, hypothalamic extracts from a male and a female hypothalamus were fract ionated by HPLC and assayed for AVP immunoreactivity. Immunoreactivity from each extract had the same retention time as synthetic AW standar ds; and the levels were twice as high in the male. These results suppo rt the existence of sexual differences in the magnocellular vasopressi nergic system in golden hamsters. These differences appear to be relat ed to previously reported sexual differences in AVP secretion from the neurohypophysis.