Vasopressin immunoreactive fibers and neurons in the dorsal pontine tegmentum of the rat, monkey and human

Abstract

It is now well established that extensive extrahypothalamic vasopressin (VP) systems exist in the rat, monkey and human brain. There are marked differences between species, but in each case VP nuclei provide dense afferents to the dorsal pontine tegmentum. Here VP may play a role in the mechanisms exerted by the locus coeruleus (LC) neurons, possibly both as a neurotransmitter and as a neuromodulator. Although we are aware of some properties of VP systems, e.g., gonadal steroid dependency in the rat, major gaps characterize our knowledge of its anatomy. With regard to the interaction of VP with the LC in the brainstem of mammals some of the questions which stand out are: (1) Is VP really being biosynthesized and transported by LC cells and, if not, what is its function within these cells? (2) Is there a structural difference between male and female LC neurons in the rat as a consequence of the sex-dimorphic VP innervation? (3) What is the origin of VP afferents in the dorsal pontine tegmentum of the (non)human primate and are these afferents also controlled by gonadal steroids? Research strategies to answer these questions will provide us with information to resolve some of the current inconsistencies about the anatomy and the function of the VP and LC systems in the brain.