Fine structure of normal and degenerating primary afferent boutons associated with characterized spinocervical tract neurons in the cat.

Spinocervical tract neurons in the dorsal horn of the cat spinal cord were intracellularly stained with horseradish peroxidase. The neurons came from one intact animal and from animals with dorsal rhizotomies (L3-S2) 3, 5, 10, 28 and 42 days previously. The morphology of terminals associated with spinocervical tract neurons was examined in a combined light and electron microscopical study. Some terminals containing agranular, circular vesicles degenerated as a result of deafferentation; these are therefore the terminals forming monosynaptic inputs to the neurons from primary afferent fibres. Other terminals containing agranular circular vesicles and terminals containing ovoid agranular vesicles survived deafferentation; these boutons therefore do not originate from primary afferent fibres.