Co-Existence of Protein Kinase C γ and Calcium-Binding Proteins in Neurons of the Medullary Dorsal Horn of the Rat

Abstract

Protein kinase C γ isoform (PKCγ) is present at high levels in the spinal and medullary dorsal horns and is thought to play a role in the sensitization of dorsal horn neurons in certain pain states. Calbindin-D28k (CB), calretinin (CR) and parvalbumin (PV) are the most commonly expressed calcium-binding proteins and are located abundantly in the medullary dorsal horn (also called the caudal subnucleus of the spinal trigeminal nucleus). In the present study, immunofluorescence histochemical double staining for PKCγ and CB, CR or PV was performed in the rat medullary dorsal horn. Most of the PKCγ-, CB-, CR- and PV-immunoreactive neurons were observed in lamina II; some were also encountered in lamina I and lamina III of the medullary dorsal horn. Neurons co-expressing CB/PKCγ, CR/PKCγ and PV/PKCγ were also mainly found in lamina II, while in lamina I and lamina III, only a few neurons co-expressing CB/PKCγ, CR/PKCγ and PV/PKCγ were encountered. The percentages of neurons co-expressing CB/PKCγ in the total numbers of CB- and PKCγ-immunoreactive neurons were 6.7 and 5.9%, respectively. Of the total numbers of CR- and PKCγ-immunoreactive neurons, 5.0 and 5.6%, respectively, showed both CR and PKCγ immunoreactivities. The percentages of neurons co-expressing PV/PKCγ in the total numbers of PV- and PKCγ-immunoreactive neurons were 25.7 and 4.1%, respectively. Most of these neurons co-expressing CB/PKCγ, CR/PKCγ and PV/PKCγ were small (≤15 µm) and medium-sized (16–35 µm) neurons and had round, triangular or fusiform-shaped cell bodies; large (≧36 µm) multipolar neurons were infrequently seen. The present results indicate that there are some neurons co-expressing CB/PKCγ, CR/PKCγ and PV/PKCγ in the medullary dorsal horn. These neurons might play important roles in the nociceptive modulation from the oro-facial region.