Ultrastructural and cytochemical study of neurones in the rat dorsal motor nucleus of the vagus after axon crush.

The cell populations in the dorsal motor nucleus of the vagus (DMNV) of the rat were studied by light microscopy and transmission electron microscopy, including retrograde labeling with horseradish peroxidase and histochemical demonstration of the distribution of the activity of the enzymes acetylcholinesterase (AcChE) and butyrylcholinesterase (BuChE). Two types of neurones were observed: 1) Larger Type A cells, which stain for both AcChE and BuChE and which project into the vagus nerve trunk, and 2) smaller Type B cells, which stain lightly for AcChE but not for BuChE and which do not project into the vagus nerve. Standardised vagal crush at the mid-cervical level causes loss of cholinesterase activity in Type A neurones within a few days but has no effect on Type B neurones. Changes in nuclear morphology of Type A neurones are pronounced at 10 weeks postinjury, indicating that degeneration is irreversible even by this stage. The number of Type A cells projecting to the vagus nerve reduces as a function of time, presumably as these cells die. Only a small number of Type A neurones persist at 2 years postinjury.