K. Messlinger et al., INNERVATION OF THE DURA-MATER-ENCEPHALI OF CAT AND RAT - ULTRASTRUCTURE AND CALCITONIN-GENE-RELATED PEPTIDE-LIKE AND SUBSTANCE P-LIKE IMMUNOREACTIVITY, Anatomy and embryology, 188(3), 1993, pp. 219-237
Ultrastructural, immunocytochemical, and immunoelectron microscopical
examinations are reported that describe the morphology of putative sen
sory nerve endings in the dura mater encephali of the rat and the cat.
Morphometrical measurements and reconstructions showed that in the ca
t the mean diameter of axons, the bare area of axolemma, and the conte
nt of mitochondria and vesicles are highly variable in dural nerve end
ings. Nerve fibers with a high volume density of mitochondria are thou
ght to be sensory, while nerve fibers containing many small vesicles a
re considered autonomic. There is, however, a broad overlap of mitocho
ndria-rich and vesicle-rich nerve fibers in the dura, so that discrimi
nation between sensory and autonomic endings by these characteristics
frequently fails. Whole-mount preparations treated cytochemically for
detection of substance P- and calcitonin gene-related peptide-like imm
unoreactivity in the rat and the cat showed a network of immunopositiv
e nerve fibers in the vicinity of dural blood vessels. Most of these p
eptidergic and probably sensory nerve fibers were found terminating in
the dural connective tissue far from vessels. Calcitonin gene-related
peptide-positive nerve fibers were much more abundant than substance
P-positive fibers. Immunoelectron microscopic preparations revealed th
at calcitonin gene-related peptide- and substance P-like immunoreactiv
ity is found in a small proportion of generally thin unmyelinated nerv
e fibers. These proportions were very similar in the rat and the cat.
Summarizing the recent literature, the morphological characteristics o
f putative sensory nerve fibers in the dura mater are discussed in rel
ation to their possible functional significance for neurogenic inflamm
ation and nociception.