Trigeminal afferents to cerebral arteries and forehead are not divergent axon collaterals in cat

Horseradish peroxidase conjugated to wheat germ agglutinin (HRP-WGA), and bisbenzimide (a fluorescent dye) were used as retrograde axonal tracers to examine whether or not intracranial and extracranial trigeminal afferents represent divergent axon collaterals. HRP-WGA was applied to the proximal segment of the middle cerebral artery and bisbenzimide was injected into a branch of the ophthalmic nerve in 5 cats. Histologic examination of the ipsilateral trigeminal ganglion revealed HRP-labeled cell bodies located among clusters of cells exhibiting bisbenzimide fluorescence. Cells containing both labels were not observed. These results support the concept that divergent axon collaterals are probably not involved in the pathogenesis of referred pain during vascular headache.