 It is produced in the cell bodies of the paraventricular and supraoptic nuclei and transported to its site of release in the axon terminals of the posterior pituitary.Neurophysin I neurons are more prevalent in the paraventricular nuclei while Neurophysin II neurons are more prevalent in the supraoptic nuclei.Vasopressin, a hormone similar in structure to oxytocin, is analogously bound and transported by Neurophysin II.