| pA2 online © Copyright 2004 The British Pharmacological Society |
036P
University of Newcastle Winter Meeting December 2004 |
Effects of JWF-133 on somatosensory processing in neuropathic and sham-operated rats D.R. Sagar1, P.J.Millns1, C.T. O’ Shaughnessy2, D.A.Kendall1, V.Chapman1. 1IoN, University of Nottingham, UK, 2Neurology & GI CEDD , GSK, Harlow, UK. |
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Print abstractCannabinoid CB2 receptor agonists have anti-nociceptive effects in animal models of inflammatory and neuropathic pain, in the absence of CNS mediated side-effects (Malan et al., 2001). CB2 receptor mRNA is increased in the spinal cord of neuropathic rats (Zhang et al., 2003).
The present study reports effects of the selective receptor CB2 agonist JWH-133 on capsaicin-evoked calcium responses in dorsal root ganglion (DRG) neurones in primary culture and on mechanically-evoked responses in dorsal horn neurones of the spinal cord in vivo in sham-operated and neuropathic rats.
Tight ligation of spinal nerves was performed in male Sprague Dawley rats (110-140g) A control group of rats received sham surgery. 14-17 days post-surgery DRG neurones were isolated and grown 24 hours prior to incubation with Fura-2AM (5µM, 30min, 37°C Intracellular Ca2+ concentrations ([Ca2+]i) in individual neurones in fields of 30-40 cells were estimated as the ratios of peak fluorescence intensities (measured at 500 nm) at excitation wavelengths of 340 and 380 nm respectively Cells were superfused with the TRPV1 receptor agonist capsaicin (100nm, 60s), the CB2 receptor agonist JWH-133 (1µM, 60s) and the CB2 receptor antagonist SR144528 (10µM, 4min) alone, or in combination.
In a separate group of anaesthetised neuropathic and sham rats, extracellular recordings of wide dynamic range neurones in the dorsal horn of the spinal cord were made. Peripheral mechanically-evoked responses of neurones were measured (bending forces 10-100g) and effects of spinal administration of JWH-133 (8, 78, 156 and 468ng/50µl) or vehicle (0.005-0.3% ethanol in distilled water) on evoked responses were studied.
Capsaicin (100nM) increased [Ca2+]i in DRG neurones from sham and neuropathic rats. JWH-133 (1µM) significantly (p<0.001) attenuated capsaicin-evoked calcium responses in DRG neurones in neuropathic and sham-operated rats. JWH-133 (1µM) alone did not increase [Ca2+]i in either group. JWH-133-evoked attenuations were significantly larger in neuropathic rats (59.93±4.58% of control response to 6mM KCl) compared to sham-operated (77.36±3.89 % of control response to 60mM KCL) rats. Pre-incubation (40min) with the CB2 receptor antagonist SR144528 (10µM) significantly inhibited the effects of JWH-133.
Spinal application of JWH-133 (8-486ng/50µl) attenuated mechanically-evoked responses of dorsal horn neurones in neuropathic rats, but not sham-operated rats. The highest dose of JWH-133 (486ng/50µl) attenuated innocuous (10g) and noxious (60g) mechanically-evoked responses of wide dynamic range neurons by 50 ± 23.56% and 38 ± 6.63% (of pre-drug control values, p<0.05 and p<0.001) respectively. Vehicle did not alter mechanically-evoked responses of spinal neurones. SR144528 (0.001µg/50µl) attenuated the effects of JWH-133.
These data support previous behavioural studies and provide evidence for a functional role of CB2 receptors on DRG neurones in sham and neuropathic rats and for a role of spinal CB2 receptors in neuropathic rats.
Malan et al., 2001, Pain, 93, 293-245.
Zhang et al., 2003, Eur J Neurosci., 17, 2750-2754.
This study was supported by GlaxoSmithKline and BBSRC.