Patterns of neuromodulation and the nitric oxide signaling pathway in mesopontine cholinergic neurons

Considerable evidence links the activity of mesopontine cholinergic neurons to the induction and maintenance of arousal and REM sleep through their projections to the thalamus and medial pontine reticular formation. In addition to acetylcholine, these cells synthesize neuropeptides and express high levels of the enzyme nitric oxide synthase suggesting they transmit complex chemical signals to their targets. This article reviews the physiological properties of these cells and the patterns of modulation by some putative transmitters. We also present new data which suggests that nitric oxide synthesis may be stimulated at the soma during repetitive firing and that nitric oxide plays a role in regulating the strength of excitatory synaptic input to these cells.