SPECIFIC EXPRESSION OF SECRETOGRANIN-II IN MAGNOCELLULAR VASOPRESSIN NEURONS OF THE RAT SUPRAOPTIC AND PARAVENTRICULAR NUCLEUS IN RESPONSE TO OSMOTIC STIMULATION

As secretogranin II is considered to be a marker for the regulated sec retory pathway, its distribution in the hypothalamo-neurohypophyseal s ystem of salt-loaded Wistar rats was studied in detail by immunocytoch emistry. Although after an osmotic challenge both vasopressin and oxyt ocin neurons are stimulated, secretogranin II was exclusively expresse d in a subpopulation of vasopressinergic magnocellular neurons in the supraoptic and paraventricular nucleus of Wistar rats. Secretogranin I I was only surely visualized after a combination of osmotic challenge and blockade of axonal transport by colchicine treatment. When these p re-treatments were not performed, only punctate fibers situated around the magnocellular neurons within the paraventricular and supraoptic n ucleus were observed. Oxytocinergic magnocellular neurons never displa yed any secretogranin II immunoreactivity, not even during lactation a nd after colchicine treatment. These findings suggest that secretogran in II is of functional importance during enhanced secretory activity w ithin vasopressinergic neurons. (C) 1997 Elsevier Science B.V.