OBJECTIVES: The purpose of this study was to localize in cranial ganglia of man the occurrence of the putative gaseous neural messenger carbon monoxide (CO) and the biliverdin degrading enzyme biliverdin reductase (BVR).
METHODS: Immunocytochemistry with antibodies against the CO-inducing enzymes HO-1, HO-2, BVR and calcitonin gene-related peptide was used.
RESULTS: In the trigeminal ganglion about 60% of the cell bodies exhibited HO-2- and about 40% BVR-immunoreactivity. HO-2- as well as BVR-immunoreactivity was predominantly (78%) expressed in medium-sized cells (30-60 microm). In the superior cervical ganglion about 40% of the cell bodies exhibited HO-2-immunoreactivity. In the sphenopalatine and otic ganglia only a few cell bodies were HO-2 immunoreactive. HO-1, the inducible isoform of heme oxygenase, gave only very weak immunoreactivity in all ganglia examined. Double immunostaining revealed that in the human trigeminal ganglion HO-2 and BVR co-localized with calcitonin gene-related peptide.
CONCLUSIONS: The finding suggests that CO might serve as a modulator of synaptic transmission in man.