While the hypothalamo-pituitary axis is known to contain high levels of basic FGF (FGF2) and its high affinity receptor FGFR1, the physiological role of FGF2 in this region needs elucidation. Here, we demonstrate that FGF2 and arginine vasopressin (AVP) co-localize within the cytoplasm of nearly all supraoptic and paraventricular magnocellular neurons of human hypothalamus as well as the axonal processes of the neurohypophysis. High-resolution confocal imaging indicates that FGF2 is found in small granules distributed throughout the cytoplasm. In the neurohypophysis, FGF2 is detected in axonal processes, pituicytes and Herring bodies. Using a rat model of chronic dehydration to test the hypothesis that FGF2 is involved in fluid balance, we show that in the neural lobe, the remodeling of extracellular matrix and increased number of pituicytes is accompanied by greater levels of immunoreactive FGF2 associated with basement membranes underlying blood vessels, pituicytes and other glial cells. Disrupted water intake was thus accompanied by altered distribution of FGF2 in the neurohypophysis as well as in the fluid-forming choroid plexus. Therefore FGF2 expression patterns in the neurohypophysis, AVP-containing magnocellular neurons and choroidal epithelium point to a role for centrally-synthesized FGF2, possibly coupled to that of AVP, in regulating water balance in various regions. FGF2's role in regulating fluid phenomena points to a novel role for this multifunctional peptide.
22 - 24 Mar 2004
British Endocrine Societies