Osteocalcin-immunoreactive primary sensory neurons in the rat spinal and trigeminal nervous systems

Osteocalcin-immunoreactivity (OC-ir) was examined in spinal and trigeminal primacy sensory neurons of the adult rat. Sixteen percent of dorsal root ganglion (DRG) neurons were immunoreactive (ir) for this protein. These neurons were mostly large and measured 594-4583 mu m(2) (mean +/- S.D. = 2243 +/- 748 mu m(2)) Thirty-four percent of DRG neurons > 1200 mu m(2) and 4% of those in the range 600-1200 mu m(2) showed the ir. Virtually all DRG neurons < 600 mu m(2) were devoid of OC-ir. In the trigeminal ganglion (TG), 25% of neurons exhibited the ir. Such neurons were of various sizes (range = 156-2825 mu m(2), mean +/- S.D. = 1234 +/- 543 mu m(2)). Forty-five percent of TG neurons > 800 mu m(2) and 6% of those < 400 mu m(2) were immunoreactive for this protein. Twelve percent of TG neurons in the range 400-800 mu m(2) showed the ir. In the mesencephalic trigeminal tract nucleus (Mes5), 63% of primary sensory neurons contained OC-ir. Virtually all OC-ir DRG and Mes5 neurons co-expressed parvalbumin-ir but not CGRP-ir. On the other hand, only 31% of OC-ir neurons co-expressed parvalbumin-ir and 10% co-expressed CGRP-ir in the TG. The present study indicates that DRG and Mes5 primary sensory neurons co-expressing OC- and parvalbumin-irs are spinal and trigeminal proprioceptors. OC-ir TG neurons which co-express parvalbumin- and CGRP-irs appear to include low-threshold mechanoreceptors and nociceptors, respectively. (C) 1999 Elsevier Science B.V. All rights reserved.