Morphological changes of unmyelinated nerves in the cerebral arteries after removal of the pterygopalatine ganglion--an electron microscopic study.

To investigate the participation of the pterygopalatine ganglion in the parasympathetic innervation of the cerebral arteries, Wallerian degeneration was evaluated in the unmyelinated nerves of the major cerebral arteries following the removal of the bilateral pterygopalatine ganglia in dogs. Several days after removal, transmission electron microscopy demonstrated typical features of degeneration in about one-third of the unmyelinated nerves, which are generally considered to be mostly autonomic, i.e., sympathetic and/or parasympathetic. Accordingly, removal of the pterygopalatine ganglion causes Wallerian degeneration of the sympathetic and/or parasympathetic nerves innervating the cerebral arteries. A supplementary study using monoamine fluorescence histochemistry demonstrated that there was no degeneration of the sympathetic nerves innervating the cerebral arteries. Therefore, the degenerated unmyelinated nerves are almost all parasympathetic. These experimental results support the concept that most parasympathetic nerves innervating the cerebral arteries originate in the pterygopalatine ganglion.