At least four neuronal tracts arise from the supraoptic and paraventricular nuclei. The main pathway terminates in the posterior pituitary to release its peptides into the systemic circulation. Both vasopressin and oxytocin are found in the zona externa of the median eminence, and the majority of fibres to this region arise from the paraventricular nucleus. From the median eminence, the peptides are secreted into the hypothalamopituitary portal circulation. A third tract passes to the floor of the third ventricle. It is still unknown, however, if the peptide hormones are actively secreted via this tract into the cerebro-spinal fluid. The final neuronal pathway terminates in the brainstem in close proximity to the vasomotor centre, and a few fibres pass down the spinal cord.
