Localisation of cannabinoid receptor 1 in rat dorsal root ganglion using in situ hybridisation and immunohistochemistry

In this study we used in situ hybridisation and double-label ing immunohistochemistry to characterise cannabinoid receptor 1 (CB1) expression in rat lumbar dorsal root ganglion (DRG) neurons. Approximately 25% of DRG neurons expressed CB1 mRNA and displayed immunoreactivity for CB1. Sixty-nine percent to 82% of CB1-expressing cells were also immunoreactive for neurofilament 200, indicative of myelinated A-fibre neurons, which tend to be large- and medium-sized DRG neurons (>600 mum(2)). Approximately 10% of CB1-expressing cells also expressed transient receptor potential vanilloid family ion channel 2 (TRPV2), the noxious heat-transducing channel found in medium to large lightly myelinated Adelta-fibre DRG neurons. Seventeen percent to 26% of CB1-expressing cells co-stained using Isolectin B4, 9-10% for calcitonin gene-related peptide and 11-20% for transient receptor potential vanilloid family ion channel 1 (TRPV1), predominantly markers of small non-myelinated C-fibre DRG neurons (<600 mum(2)). These findings suggest that whilst a wide range of DRG neuron phenotypes express CB1, it is predominantly associated with myelinated fibres. (C) 2003 IBRO. Published by Elsevier Science Ltd. All rights reserved.