hypothalamic nucleus supraoptic nucleus A sharply defined nucleus of nerve cells in the anterior hypothalamic region, immediately above the lateral part of the optic chiasm; many of its cells are neurosecretory in function, secreting vasopressin, which is carried to the neurohypophysis (posterior pituitary) by the fibers of the supraopticohypophysial tract; other cells are osmoreceptors, which respond to increased osmotic pressure to signal the release of vasopressin by the neurohypophysis. BTO:0002697 BrendaTissueOBO nucleus supraopticus supraoptic nucleus of hypothalamus