WordNet sense 1 (a substance produced by the hypothalamus that is capable of accelerating the secretion of a given hormone by the anterior pituitary gland):

releasing hormone, releasing factor

WordNet sense 2 (a radioactive transuranic element which has been synthesized):

rutherfordium, unnilquadium, Unq

WordNet sense 3 (a complex neural network in the central core of the brainstem; monitors the state of the body and functions in such processes as arousal and sleep and attention and muscle tone):

reticular formation