Calcitonin gene-related peptide (CGRP) in the human spinal cord: a light and electron microscopic analysis.

The distribution of CGRP immunoreactivity in the cervical, thoracic, lumbar, and sacral levels of the human spinal cord was mapped at the light microscopic level with the aid of a rabbit-generated antiserum against human calcitonin gene-related peptide (CGRP). CGRP-positive fibers formed a dense plexus in lamina I, II, the reticulated region of lamina V, and the tract of Lissauer at all spinal cord levels. The distribution of fibers showed some variations dependent on the cord level analyzed. At the light microscopic level, intervaricose fiber diameters consistently measured 1.0 micron or less, and two types of CGRP varicosities were observed: a small (1 to 2 microns in diameter), relatively round profile and a larger, (3 to 4 microns in diameter) oval or oblong profile. At the electron microscopic level, immunostained varicosities contained a mixture of round clear vesicles and vesicles that contained dense cores. The CGRP immunoreaction product was often associated with vesicles containing dense cores. The reaction product was also seen associated with clear round vesicles or in the cytoplasmic matrix. Postsynaptic elements included dendritic spines, small and large diameter dendritic shafts and vesicle containing profiles. The presence of CGRP in the superficial dorsal horn of human spinal cord is highly suggestive of a role in primary afferent transmission as postulated in lower vertebrates. This study establishes the distribution of CGRP at four different spinal levels in human cord and will serve as a basis for future studies related to the pathologic conditions affecting sensory systems.

Collaterals of spinothalamic tract cells to the periaqueductal gray: a fluorescent double-labeling study in the rat.

Spinothalamic tract (STT) cells were investigated in the rat to determine the distribution of STT cells with terminals in both the ventrobasal (VB) thalamus and the lateral periaqueductal gray (PAG). Two retrogradely transported fluorescent dyes (Diamidino yellow and Granular blue) were injected into each animal. The distribution of single- and double-labeled cells was mapped in the cervical, thoracic, lumbar and sacral spinal cord. An average of 1.4% of all STT cells and 6.2% of PAG cells projected to both VB thalamus and PAG. Double-labeled cells were observed only in cervical and lumbar levels of the spinal cord, with the greatest number found in the cervical enlargement. The double-labeled cells were located in laminae I and V and also in the lateral spinal nucleus (LSN). The number of double-labeled cells found in each of these 3 areas varied depending on the spinal cord level. This population of neurons exhibiting collaterals provide an anatomical mechanism by which noxious stimuli activate neurons not only in the thalamus but also in the PAG, which is an area involved in stimulation-produced analgesia (SPA).