PLASTICITY OF THE INTERFACE BETWEEN OXYTOCIN NEURONS AND THE VASCULATURE IN LATE PREGNANT RATS - AN ULTRASTRUCTURAL MORPHOMETRIC STUDY

Increased numbers of oxytocin-immunoreactive perivascular neurons have been shown to occur in the preoptic region and lateral hypothalamus of female rats around parturition. In the present study, electronmicroscopical immunocytochemistry and morphometry were used to examine such perivascular oxytocinergic neurons as well as those in the classical magnocellular nuclei in late pregnant and lactating rats. In 22 d pregnant animals and in rats killed after 2 d of lactation, numerous oxytocinergic neurons were found in direct apposition to the outer basement membrane of arterioles, venules, and capillaries. The distance between immunoreactive neurons and blood vessels was significantly lower in these animals than in 9 d lactating rats and in ovariectomized controls. It is likely that, around parturition, oxytocinergic perivascular neurons are uncovered by active retraction of glial elements. This plasticity is perhaps facilitated by changing hormonal conditions around parturition. The observed changes seem to be transitory and might reflect altered secretory properties of perivascular oxytocinergic neurons.