Distribution of Choline Acetyltransferase Immunoreactive Somata in the Feline Brainstem: Implications for REM Sleep Generation

In the present study we examined the distribution of cholinergic and catecholaminergic neurons, in the feline brainstem, as defined by choline acetyltransferase (ChAT) and tyrosine hydroxylase (TH) immunohistochemistry. In the dorsal tegmentum, ChAT immunoreactive neurons were distributed in the parabrachial area [the pedunculopontine group (PPG)] and along the medial adjacent central gray [the lateral dorsal tegmental group (LDT)]. The cholinergic neurons in the LDT area were larger than those in the PPG. When adjacent tissue sections were labeled with TH we noted extensive overlap between catecholamine and cholinergic neurons in the PPG, suggesting that REM sleep may occur as a result of an interaction between these transmitters in this area rather than the medial pontine reticular formation where no cholinergic or catecholamine neurons were found. Cholinergic neurons were also found in the cranial nerve nuclei and the nucleus ambiguus. The presence of cholinergic neurons in the PPG and LDT suggest that these neurons may play an important role in the generation of some of the tonic and phasic components of REM sleep, such as cortical desynchronization, pontogeniculo occipital waves, and muscle atonia.