Journal of Neuroscience, Vol 7, 3984-3995, Copyright © 1987 by Society for Neuroscience
Substance P and cholecystokinin-like immunoreactive varicosities in somatosensory and autonomic regions of the rat spinal cord: a quantitative study of coexistence
MM Tuchscherer, C Knox and VS Seybold
University of Minnesota Medical School, Department of Cell Biology and Neuroanatomy, Minneapolis 55455.
Substance P- and cholecystokinin-like immunoreactivities have been shown to
coexist in some, but not all, dorsal root ganglion cell bodies of the rat.
Quantitative immunofluorescence techniques were used in the present study
to describe densities of substance P- and cholecystokinin- like
immunoreactive varicosities in several spinal cord nuclei. By combining
simultaneous immunofluorescent techniques on one tissue section with
computerized image processing, coexistence of substance P- and
cholecystokinin-like immunoreactivity in varicosities was also quantified.
By comparing spinal cord regions between normal and unilateral dorsal
rhizotomy affected animals, densities of substance P- and
cholecystokinin-like immunoreactive varicosities associated with primary
afferent neurons were established. To determine the densities of
immunoreactive varicosities that were related to unmyelinated primary
afferent fibers, data were compared between normal animals and those
treated neonatally with capsaicin. Four major observations were made: (1)
Substance P- and cholecystokinin-like immunoreactivity coexist in
populations of varicosities in sensory and autonomic regions of rat spinal
segment L6. (2) Within the superficial laminae of the dorsal horn,
varicosities containing both substance P- and cholecystokinin-like
immunoreactivity and cholecystokinin-like immunoreactivity alone are of
primary afferent neuron origin, but those containing only substance P-like
immunoreactivity are most likely of spinal or descending neuronal origin.
(3) Capsaicin-insensitive cholecystokinin-like immunoreactive varicosities
were present predominantly in lamina I. These data suggest some
cholecystokinin-like immunoreactive varicosities are associated with
myelinated primary afferent neurons. (4) Primary afferent fibers containing
substance P- and cholecystokinin-like immunoreactivity project to
intermediate gray regions of the rat spinal cord. A large proportion of
these fibers are capsaicin sensitive, suggesting that they are
unmyelinated.