Localization of Transforming Growth Factors, TGFβ1 and TGFβ3, in Hypothalamic Magnocellular Neurones and the Neurohypophysis

The distribution of transforming growth factor beta (TGFβ) in the rat and human hypothalamus and neurohypophysis was investigated by immunocytochemical techniques using rabbit polyclonal antisera against TGFβ 1 and TGFβ 3 . Colocalization of TGFβ 1 or TGFβ 3 and arginine vasopressin (AVP) in the rat hypothalamus was studied by double immunolabelling in light microscopy, while their subcellular localization in the rat neurohypophysis was investigated by immunoelectron microscopy. TGFβ 1 and TGFβ 3 immunoreactivity was demonstrated in the cell bodies and processes of neurones in the supraoptic nucleus (SON) and paraventricular nucleus (PVN). The TGFβ-immunoreactive cells were more numerous in the SON compared to the PVN. TGFβ/AVP double-labelled cells were seen in both nuclei, but some neurones in the SON were labelled for TGFβ 1 or TGFβ 3 , although not for AVP. In the rat and human neurohypophysis, TGFβ 3 immunolabelling was more diffuse and stronger than TGFβ 1 immunolabelling. TGFβ 1 expression was seen in axonal vesicles and in neurosecretory granules of the axonal endings, while TGFβ 3 was observed in axonal fibres. Colocalization of TGFβ 3 or TGFβ 1 and AVP was observed in some neurosecretory granules, but many were either single-labelled for TGFβ or AVP or unlabelled. Our results demonstrate, for the first time, the colocalization of TGFβ and neurohypophysial hormones in magnocellular neurones. We suggest that TGFβ secreted by the neurohypophysis regulates the proliferation and secretion of certain anterior pituitary cells.