Cannabinoid 1 receptors are expressed in nociceptive primary sensory neurons

Expression of cannabinoid 1 (CB1) and vanilloid 1 (VR1) receptor proteins w as studied in adult, cultured rat dorsal root ganglion neurons. Immunostain ing of CB1 receptors alone produced labelling in 57 +/- 2% of the cultured dorsal root ganglion neurons (n = 3 cultures). The area of the labelled cel ls was between 200 and 800 mum(2) with an average of 527 +/- 68 mum(2). VR1 immunolabelling revealed immunopositivity in 42 +/- 6% of the total popula tion of dorsal root ganglion neurons. Cells showing VR1-like immunopositivi ty had an area between 200 and 600 mum(2). The mean area of the VR1-like im munopositive neurons was 376 +/- 61 mum(2). Double immunostaining with anti sera raised against the CB1 and VR1 receptor proteins, showed a high degree of co-expression between CB1 and VR1 receptors, An average of 82 +/- 3% of the CB1-like immunopositive cells also showed VR1-like immunoreactivity (n = 3 cultures) while 98 +/- 2% of the VR1-like immunolabelled neurons showe d CB1 receptor-like immunostaining (n = 3 cultures). Our data suggests that nociceptive primary sensory neurons co-express CB1 and VR1 receptors to a very high degree. We propose that this may provide an anatomical basis for a powerful combination of VR1 mediated excitation and CB1-mediated inhibiti on of nociceptive responses at central and peripheral terminals of nocicept ive primary afferents. (C) 2000 IBRO. Published by Elsevier Science Ltd. Al l rights reserved.