The ascending reticular activating system--from aminergic neurons to nitric oxide.

The cholinergic neurons of the laterodorsal and pedunculopontine tegmental neurons are thought to comprise an important portion of the ascending reticular activating system. More recent work has demonstrated that the neurons of this cell group also released a number of neruoactive peptides and can produce nitric oxide in response to increases in intracellular calcium. The release of NO from the nerve terminals of these cells within the thalamus varies with behavioural state, being much lower during slow wave sleep than during wake and paradoxical sleep states. The NO release in the thalamus appears to act via the type II cGMP-dependent protein kinase present at high levels in the thalamic neurons. Thus the NO-cGMP signal transduction system can play an important role in regulating thalamic activity across behavioural states.