Supraopticohypophyseal tract

Last revised by Daniel J Bell on 5 Aug 2022

The supraopticohypophyseal tract (TA: tractus supraopticohypophysialis) is one of the two major hypothalamohypophyseal neurosecretory tracts connecting the supraoptic nucleus and the paraventricular nucleus in the hypothalamus with the posterior pituitary (neurohypophysis).

Gross anatomy

Intracranial course

The supraopticohypophyseal tract contains the efferent magnocellular neurosecretory fibers of the supraoptic and the paraventricular nuclei 1. It courses inferiorly on the superficial surface of the infundibulum and synapses with the capillary plexuses in the posterior pituitary.

In most anatomy texts, the supraopticohypophyseal tract is described as being a single tract formed by the axonal fibers from both the supraoptic nucleus and the paraventricular nucleus (the paraventriculohypophyseal tract) 2-4, whereas in some other texts, the two tracts are considered separate entities 1,5.

The paraventriculohypophyseal tract has two anatomical courses, some fibers pass through the supraoptic nucleus, where they are joined by the axonal fibers from the supraoptic nucleus, whereas the other fibers course directly inferior to join the descending supraopticohypophyseal tract 6.

The supraoptic nucleus axons only form synaptic connections with the posterior pituitary capillary plexus. However, the paraventriculohypophyseal tract is composed of axons of varying lengths, with some projecting more proximally to the median eminence and others distally to extrathalamic regions 1.

Terminal synapse

The neuroendocrine hormones carried by the supraopticohypophyseal tract are oxytocin and vasopressin (antidiuretic hormone) in a “one neuron-one neurohypophysial hormone” fashion, and these hormones are stored in specialized axon terminals termed Herring bodies 7. The neuroendocrine axons terminate on the posterior pituitary capillaries where these hormones are released, and these hormone molecules drained into the systemic circulation via the hypophyseal veins.

Clinical importance

As the supraopticohypophyseal tract is involved in the secretion of vasopressin, disruption of the tract causes neurogenic diabetes insipidus, manifested as polyuria and polydipsia.

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