parvocellular neuron

Parvocellular neurons are the small hypothalamic cells that govern the anterior pituitary from behind the scenes. Rather than reaching the pituitary themselves, they release their hormones into a private network of blood vessels, the portal system, which carries the signal a short distance to the anterior pituitary, where it controls which hormones that gland releases. The name means small-bodied cell.

These neurons make the releasing and inhibiting hormones: CRH, which drives the stress axis; GnRH for reproduction; GHRH and somatostatin for growth; and TRH for the thyroid. Their axons end near the top of the pituitary stalk at the median eminence, dripping their hormones into the portal capillaries in carefully timed, often pulsatile, bursts.

Parvocellular neurons sit alongside the larger magnocellular neurons in the paraventricular nucleus, and the two types divide the labor of hypothalamic command: parvocellular cells indirectly steer the anterior pituitary, while magnocellular cells directly supply the posterior pituitary. This anatomical split is the cellular foundation of the entire hypothalamic-pituitary control system.