The Mesopontine Cholinergic System: A Dual Role in REM Sleep and Wakefulness

The mesopontine tegmentum contains cholinergic neurons that project widely to the forebrain and brainstem. These neurons are distributed in the pedunculopontine tegmental (PPT) and laterodorsal tegmental (LDT) nuclei. Cholinergic neurons in the mesopontine tegmentum have long been thought to play a critical role in the generation of rapid eye movement sleep. Tegmental cholinergic neurons have long been thought to have an important role in behavioral wakefulness and cortical arousal as part of the ascending reticular activating system. Anatomically, cholinergic neurons in the mesopontine tegmentum are distributed in a continuum encompassing the PPT and LDT. Cholinergic neurons are not the only cell type found in the PPT and LDT, as non-cholinergic neurons are also present intermixed with cholinergic neurons. In conclusion, it is clear that non-cholinergic neurons vary in their morphology, projection, and neurotransmitter content.