Stereological analysis of Ca²⁺/calmodulin-dependent protein kinase IIα-containing dorsal root ganglion neurons in the rat: Colocalization with isolectin Griffonia Simplicifolia, calcitonin gene-related peptide, or vanilloid receptor 1

The enzyme Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) is widely distributed in the nervous system. A previous report describes immunostaining for CaMKIIα in dorsal root ganglion (DRG) neurons. In this study, CaMKIIα is colocalized in the rat with three putative markers of nociceptive DRG neurons, isolectin Griffonia simplicifolia (I-B4), identifying small-diameter, "peptide-poor" neurons; calcitonin gene-related peptide (CGRP), identifying "peptide-rich" neurons; or the vanilloid receptor 1 (VR1), identifying neurons activated by heat, acid, and capsaicin. Lumbar 4 and 5 DRG sections were labeled using immunofluorescence or lectin binding histochemistry, and percentages of single and double-labeled CaMKIIα neurons were determined. Stereological estimates of total neuron number in the L4 DRG were 13,815 ± 2,798 and in the L5 DRG were 14,111 ± 4,043. Percentages of single-labeled L4 DRG neurons were 41% ± 2% CaMKIIα 38% ± 3% I-B4, 44% ± 3% CGRP, and 32% ± 6% VR1. Percentages of single-labeled L5 DRG neurons were 44% ± 5% CaMKIIα, 48% ± 2% I-B4, 41% ± 7% CGRP, and 39% ± 14% VR1. For L4 and L5, respectively, estimates of double-labeled CaMKIIα neurons showed 34% ± 2% and 38% ± 17% labeled for I-B4, 25% ± 14% and 19% ± 10% labeled for CGRP, and 37% ± 7% and 38% ± 5% labeled for VR1. Conversely, for L4 and L5, respectively, 39% ± 14% and 38% ± 7% I-B4 binding neurons, 24% ± 12% and 23% ± 10% CGRP neurons, and 42% ± 7% and 35% ± 7% VR1 neurons labeled for CaMKIIα. The mean diameter of CaMKIIα-labeled neurons was approximately 27 μm, confirming that this enzyme was preferentially localized in small DRG neurons. The results indicate that subpopulations of DRG neurons containing CaMKIIα are likely to be involved in the processing of nociceptive information. Thus, this enzyme may play a critical role in the modulation of nociceptor activity and plasticity of primary sensory neurons.