Vascular organ of lamina terminalis

The vascular organ of lamina terminalis (VOLT), organum vasculosum of the lamina terminalis (OVLT), or supraoptic crest^[1] is a sensory organ, one of the circumventricular organs of the third ventricle within the lamina terminalis. It is covered with pia mater, and lined with ependyma.^[2][3] It overlies the paraventricular nucleus of hypothalamus,^[4] and is involved in the secretion of vasopressin.^[2] The VOLT monitors the presence of peptides and macromolecules in the bloodstream, and conveys the information to the hypothalamus.^[3]

It is one of the three sensory circumventricular organs of the brain.^[5] The other four are secretory.^[6]

The VOLT, median eminence, and subfornical organ are interconnected with the mid-ventral hypothalamus, and together these three structures surround the third ventricle, a complex often called the anteroventral region of the third ventricle ("AV3V" region).^[7][8] This region functions in the regulation of fluid and electrolyte balance by controlling thirst, sodium excretion, blood volume regulation, and vasopressin secretion.^[7][9]

The VOLT is one of the three sensory circumventricular organs providing information to other brain regions.^[6][10]

VOLT capillaries do not have a blood–brain barrier, and so neurons in this region can respond to circulating factors present in the systemic circulation.^[11][9]

Neurons in the VOLT are osmoreceptors sensitive to the sodium content and osmotic pressure of blood.^[7] Neurons of the lamina terminalis project to the supraoptic nucleus and paraventricular nucleus to regulate the activity of vasopressin-secreting neurons.^[9] In a situation of lowered blood volume, secretion of renin by the kidneys results in the production of angiotensin II, which stimulates receptors in the VOLT and subfornical organ to complete a positive feedback loop.^[9][12][13] These neurons also project to the median preoptic nucleus which is involved in controlling thirst.^[11][9][12]