Abstract
In the rodents spinal cord, the synthesis and/or action of several compounds mediating nociception (e.g. substance P [SP], neurokinin receptors, met-enkephalin [met-ENK], γ-aminobutyric acid) are altered by estrogens. We recently demonstrated the presence of a local estrogen production (active aromatase) in the spinal dorsal horns of Japanese quail. Nociception may thus be modulated in the spinal cord, at least in part, by locally produced estrogens. We analyzed by immunocytochemistry the distribution of SP, met-ENK, glutamate receptors and estrogen receptors alpha (ER) in the quail spinal cord in relation with aromatase-immunoreactive (ARO-ir) neurons. Few ER-containing nuclei were found in the dorsal horns, mostly at the boundary between laminae II and III whereas ARO-ir neurons are mostly located along the external border of these laminae. This apparent lack of colocalization raises questions concerning the mode of action of locally produced estrogens. SP, met-ENK and glutamate receptors were broadly distributed in the dorsal horns. Stained fibers and punctate structures immunoreactive for met-ENK and SP cover the areas containing ARO-ir neurons. In double labeled sections, SP-ir punctate structures are in close apposition to ARO-ir fibers and perikarya suggesting synaptic contacts and functional interactions. AMPA receptors (GluR2-3)-ir cells were scattered in laminae I-V, overlapping with areas containing ARO-ir cells. These data indicate that the spinal aromatase activity may be influenced by nociceptive inputs and/or, conversely, that locally produced estrogens could modulate nociception by processes that would be independent of ER.
