Nitric oxide: an adequate modulatory link between biological oscillators and control systems in the mammalian brain

Nitric oxide (NO), a free radical gas, has been widely suggested as a messenger molecule in the nervous system, whose biophysical mechanisms and biochemical pathways of action are radically different from those of more traditional transmitter candidates. The intention of the present seminar is to evaluate recent evidence indicating a close anatomical and physiological relationship between NO and subsystems in the brain associated with the circadian rhythm and the sleep/waking cycle, and thus to prompt the discussion about the functional significance and the teleological advantage of a ‘nitrergic’ link between two different sorts of synaptic activity: that which is generated within cellular networks of biological oscillators and that which is a consequence of activity in systems assumed to control or reset pacemaker activity.