Magnocellular neurosecretory cells are large cells within the supraoptic nucleus and paraventricular nucleus of the hypothalamus. They are neuroendocrine neurons, as they are electrically excitable, and generate action potentials in response to afferent stimulation.
Magnocellular neurosecretory cells can either be oxytocin-producing cells or vasopressin-producing cells, however a small number can produce both hormones.
Cells typically have two or three long dendrites, which contain a very high density of hormone-containing vesicles. Oxytocin and vasopressin can thus be released within the brain from these dendrites, as well as into the blood from the terminals in the posterior pituitary gland.