Neuroscience Letters 499 (2011) 124–126 Contents lists available at ScienceDirect Neuroscience Letters j our nal ho me p ag e: www.elsevier.com/locate/neulet Xenon fails to inhibit capsaicin-evoked CGRP release by nociceptors in culture Guy Calcott 1 , John P.M. White 1 , Istvan Nagy ∗ Section of Anaesthetics, Pain Medicine and Intensive Care, Department of Surgery and Cancer, Faculty of Medicine, Imperial College London, Chelsea and Westminster Hospital, 369, Fulham Road, London SW10 9NH, United Kingdom a r t i c l e i n f o Article history: Received 22 February 2011 Received in revised form 26 April 2011 Accepted 19 May 2011 Keywords: Analgesia CGRP Nociceptors Pain Xenon a b s t r a c t To investigate whether the xenon-induced inhibition of the transient receptor potential vanilloid type 1 (TRPV1) ion channel in rat dorsal root ganglion (DRG) neurons reduces nociceptive processing, we examined the effect of xenon in reducing the release of calcitonin gene-related peptide (CGRP) from those neurons. We found that exposure to xenon failed to effect a reduction of capsaicin-evoked CGRP release from cultured primary sensory neurons when stimulated by capsaicin. This finding suggests that xenon acts on several molecular targets on nociceptive primary sensory neurons, and that xenon’s action on one, or more, of those targets serves to offset the inhibitory, pro-analgesic, effect of xenon on TRPV1. It is concluded that xenon may not produce any analgesic effect through peripheral nociceptors. © 2011 Elsevier Ireland Ltd. All rights reserved. Xenon is an inert gas which binds to a remarkable range of proteins, including ion channels, such as the ionotropic N-methyl- d-aspartate (NMDA) receptor for glutamate, as well as certain non-NMDA receptors [6,8,20]. In addition to its anaesthetic effect, xenon, at sub-anaesthetic doses, has been reported to provide anal- gesia in certain, but not all, pain states in human subjects [13,15,21]. Xenon also reduces certain pain-related behaviour in laboratory animals, including that which is evoked by formalin injection, which induces an inflammatory reaction in tissues [9]. This for- malin injection-evoked pain-related behaviour is also reduced by antagonists of the transient receptor potential vanilloid type 1 ion channel (TRPV1) [10]. TRPV1 is a non-selective cationic channel, which is expressed by the great majority of nociceptive primary sensory neurons, as well as by some neurons in the central nervous system and certain non- neuronal cells at the periphery [14,19]. Activation of TRPV1 results in the release of neurotransmitters, including neuropeptides, such as calcitonin gene-related peptide (CGRP) both from the peripheral and central terminals of primary sensory neurons [1,17]. CGRP is a significant contributor to nociceptive processing both in the spinal cord and in peripheral nociceptors [3]. While acute activation of TRPV1 in primary sensory neurons results in a short-lasting burning ∗ Corresponding author at: Section of Anaesthetics, Pain Medicine and Inten- sive Care, Department of Surgery and Cancer, Imperial College London, Faculty of Medicine, Chelsea and Westminster Hospital, Room G3.45, 369 Fulham Road, Lon- don SW10 9NH, United Kingdom. Tel.: +44 0 20 8746 8897; fax: +44 0 20 8237 5109. E-mail address: i.nagy@imperial.ac.uk (I. Nagy). 1 John White and Guy Calcott contributed equally to this article. pain sensation, sustained TRPV1 activation in these neurons, result- ing, for example, from inflammation of peripheral tissues, leads to the development of heat hyperalgesia and visceral hyper-reflexia [22,23]. We have recently shown that when rat primary sensory neu- rons and heterologously expressed human TRPV1 are exposed to the archetypical TRPV1 agonist, capsaicin, in the presence of xenon, the capsaicin-induced activation of TRPV1 is greatly reduced [24]. These findings suggested that xenon might be used as an adjunct analgesic where TRPV1 is a significant contributor to the develop- ment and maintenance of the pain sensation. Here, we examined whether CGRP release from rat cultured dorsal root ganglion (DRG) neurons in response to capsaicin application is reduced in the pres- ence of xenon. All procedures were performed in accordance with the require- ments of the UK. Animals (Scientific Procedures) Act, 1986. Altogether, 3 female Sprague Dawley rats (each ∼100 g in weight) were used in this study. The animals were kept at 12 h light–dark cycles at controlled temperature and humidity, with food and water ad libitum Rats were terminally anaesthetised by Enflourane (Abbott, Maidenhead, UK) and their DRG from the first cervical to the first sacral segments were dissected out and maintained in culture medium (Ham’s nutrient F12 (Invitrogen, UK), supplemented with 1 ml l-glutamine (Invitrogen, UK); 50 IU/ml penicillin (Invitrogen, UK); 50 g/ml streptomycin (Invitrogen, UK); and 4% Ultroser G (Pall BioPharmaceuticals, France)). Ganglia were incubated in colla- genase (2000 U/ml, Sigma) for 3 h at 37 ◦ C in an atmosphere of 95% air and 5% CO 2 . Following washes in the supplemented medium, the ganglia were triturated through a fire-polished Pasteur pipette, before being re-suspended and plated on poly-dl-ornithine-coated 0304-3940/$ – see front matter © 2011 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2011.05.051