Production of an oxytocin like substance by the subcommissural organ (SCO), related to the reproductive cycle in oviparous and viviparous reptiles.

The subcommissural organ (SCO) is a circumventricular organ of glial origin typical of all vertebrates, The SCO releases its secretion into the third ventricle to constitute Reissner's fibre (RF). Reportedly, in reptiles, SCO has cyclic secretory activity related to the reproductive cycle, In this immunocytochemical study we show that, in females of oviparous reptiles (Lacertidae: Podarcis sicula) and in a viviparous species (Scincidae: Chalcides chalcides), SCO secretion consists of hormones, in part of the oxytocin-like (OXY-like) type. The amount of OXY-like material in the cells and in the third ventricle varies according to the different stages of the reproductive cycle. In the oviparous species, OXY-like hormone secretion can be induced by FSH administration at 28 degrees C, in the period of winter reproductive stasis as well, In the viviparous skink, showing an annual single ovulatory cycle, OXY-like secretion is present in the basal region of the cells, and is released into the third ventricle only at delivery, The role of an OXY-like hormone in the SCO is here discussed in relation to the different stages of the reproductive cycle. Its influence on the hypothalamus-hypophysis-gonad axis and its role in the transport of eggs into the ducts in the oviparous species, and at delivery in the viviparous one, are also suggested.