Fig. 2. Cholinergic and cholinoceptive regions of the medial pontine reticular formation (mPRF) contribute to the regulation of sleep and wakefulness. ( A ) Sagittal view of cat pons. For orientation, this section identifies at the caudal ( left ) margin the abducens ( 6 ) nucleus and ventral to the genu of the facial nerve ( 7G ), the sixth cranial nerve ( 6N ). The mPRF corresponds, in part, to the gigantocellular tegmental field. The mPRF contains muscarinic cholinergic receptors 99,,100,,111,and is therefore referred to as being cholinoceptive. Cells that produce acetylcholine ( black rectangle in A ) are located in the laterodorsal and pedunculopontine tegmental (LDT/PPT) nuclei. The region of the black box is enlarged ( B ) to show cells staining positively for NADPH-diaphorase ( black cells ). In the LDT/PPT, 100% of the cholinergic neurons stain positively for NADPH-diaphorase. Cholinergic LDT/PPT neurons ( C ) project to the mPRF and can be labeled by mPRF injection of fluorescent tracers ( D ) and other retrograde tracing molecules. 88,,89 Acetylcholine release from LDT/PPT neurons contributes to the brain activation characteristic of rapid eye movement sleep and wakefulness.