Organization of choline acetyltransferase-containing structures in the cranial nerve motor nuclei and lamina IX of the cervical spinal cord of the rat.

The cholinergic structures in the cranial nerve motor nuclei and lamina IX of the cervical spinal cord of the rat were examined immunohistochemically with a monoclonal antibody to choline acetyltransferase (ChAT). The brainstem motor nuclei were classified into 3 groups according to the way of distribution of ChAT-positive structures in the neuropil of the nucleus. 1. The oculomotor, trochlear and abducent nuclei contained moderately ChAT-positive perikarya and dendrites. A small number of ChAT-positive bouton-like structures were found in the neuropil, but they were not in contact with ChAT-positive perikarya and dendrites. 2. Motoneurons in the facial, hypoglossal and trigeminal motor nuclei were moderately to strongly ChAT-positive. There were in the neuropil numerous ChAT-positive bouton-like structures and many of them were in contact with ChAT-positive perikarya and dendrites. The same pattern of organization of ChAT-positive structures was observed in lamina IX of the cervical spinal cord. In the nucleus ambiguus, the perikarya and proximal dendrites of about half population of motoneurons contacted with ChAT-positive bouton-like structures while the rest of motoneurons did not. ChAT-positive bouton-like structures in contact with motoneurons are interpreted as the cholinergic synaptic terminals, and this suggests that motoneurons in this group are cholinoceptive as well as cholinergic. 3. Neuronal perikarya and dendrites in the dorsal nucleus of the vagus showed weak to moderate positivity of ChAT. The neuropil of this nucleus was free from any distinctly ChAT-positive structures.