Immunohistochemical demonstration of the calcium channel α2 subunit in the chicken dorsal root ganglion and spinal cord: A special reference to colocalization with calbindin-D28k in dorsal root ganglion neurons

We used immunohistochemical methods to examine the distribution of the calcium channel α2 (CCα2) subunit in the chicken spinal cord and dorsal root ganglion (DRG) neurons and determine its relationship with calbindin-D28k (CB) in the DRG neurons. In the spinal cord, CCα2 subunit was detected in nerve terminals, which were observed as dot-like structures, and in laminae I, II, III and Lissauer's tract in the dorsal horn. In the DRG neurons, approximately 65% of the total neurons were CCα2 subunit positive, and most (86%) of these neurons were small to medium sized, suggesting that the CCα2 subunit and/or a complex of the CCα2 and δ subunits is possibly localized in a number of nociceptive neurons. A majority (77%) of the positive neurons showed CB immunoreactivity and most (88%) of these neurons were small to medium sized. This may indicate a close correlation between the CCα2 subunit and CB in the nociceptive neurons. Thus, it is postulated that the mode of nociceptive transmission may involve a cellular Ca2+-regulating system that consists of both Ca2+ entry via calcium channels with the α2δ subunit and intracellular Ca2+-binding activity of CB in the nociceptive neurons of the DRG.