Arginine vasopressin as a neurotransmitter in brain.

Arginine vasopressin (AVP) which exerts diverse biological effects in mammals is no more restricted to the posterior pituitary. Neurons containing AVP are seen in many other areas and in CNS vasopressinergic neurons are identified from the neocortex to the spinal cord. With the characterization of three different types of vasopressin receptor subtypes V1a, V1b and V2 responsible for its actions, their cloning and identification in different areas--especially in the brain many more hitherto unknown functions of AVP in brain has come to light. Added to this is the recently available specific vasopressin receptor antagonists. At present AVP seems to be involved in memory retrieval, learning, circadian time keeping, modulating the actions of area postrema and many other functions in brain. In the suprachiasmatic nuclei (SCN)--the biological clock--an area of the brain where the role of VP is still not very clear, VP is found to participate not only in transmitting the circadian rhythms to the rest of the brain but also serves the function of synchronizing and amplifying the pacemaker output of SCN. AVP can act not only as a neurotransmitter but also can stimulate the production of chemicals/neurotransmitters and thereby act as a mediator. It may be concluded that there is a central vasopressinergic system which participates in a variety of physiological and behavioral functions of brain.