| pA2 online © Copyright 2004 The British Pharmacological Society |
037P
University of Newcastle Winter Meeting December 2004 |
Noxious-evoked changes in levels of endocannabinoids in the central nervous system D. Richardson* †, D.A. Kendall †, S.R.G. Beckett †, D.A. Barrett*, V. Chapman † . School of Pharmacy*, School of Biomedical Sciences †, University of Nottingham, UK. |
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Print abstractThe endocannabinoid (EC) receptor system produces analgesic effects in animal models of pain. Previous studies suggest that EC release following noxious stimulation modulates nociceptive responses (Walker et al., 1999). The aim of this study was to investigate the effects of noxious stimulation on regional levels of ECs in rat brain using a liquid chromatography-mass spectrometry method.
Male Sprague-Dawley rats (150-180g) received an intraplantar injection of formalin (2.5%, 50 µl) or saline (n=4 per group). Behavioural responses (licking and flinching) of rats were measured for 60 minutes. Rats were killed and brain regions and spinal cord dissected rapidly on ice. A lipid extraction method (Kingsley et al., 2003) with liquid chromatograpy-mass spectrometry was used to quantify levels of anandamide (AEA), 2-arachidonyl glycerol (2-AG), noladin ether, virodhamine, N-arachidonyl dopamine (NADA) and oleoyl ethanolamine (OEA).
AEA, 2-AG and OEA were detected in the midbrain, hypothalamus and thalamus of saline-treated rats (Table 1). Following injection of formalin, levels of 2-AG and OEA were significantly lower in the midbrain, compared to saline treated rats. There were no significant changes in the levels of AEA, 2-AG or OEA in the hypothalamus. AEA levels were significantly lower, and 2-AG higher in the thalamus of formalin-treated rats. Levels of AEA and OEA were significantly decreased in the ipsilateral spinal cord of formalin-treated rats. There were no significant changes in levels of AEA, 2-AG and OEA in the ipsilateral spinal cord after formalin treatment.
AEA (pmol/g) |
2-AG (nmol/g) |
OEA (nmol/g) |
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| Midbrain | Saline |
43.3 ±18 |
13.1 ±0.7 |
1.08 ±0.14 |
Formalin |
10.8 ±1.0 |
10.0 ±0.9* |
0.46 ±0.03* |
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| Hypothalamus | Saline |
18.7 ±1.7 |
12.0 ±0.9 |
0.59 ±0.08 |
Formalin |
19.6 ±0.9 |
17.3 ±2.6 |
0.50 ±0.03 |
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| Thalamus | Saline |
21.3 ±1.4 |
10.6 ±0.9 |
0.57 ±0.02 |
Formalin |
13.7 ±1.2* |
13.9 ±0.4* |
0.47 ±0.05 |
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| Ipsilateral spinal cord | Saline |
38.8 ±3 |
35.9 ±11 |
1.78 ±0.14 |
Formalin |
17.5 ±3.1* |
14.4 ±1.9 |
1.02 ±0.14* |
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| Contralateral spinal cord | Saline |
27.0 ±4.8 |
13.8 ±0.3 |
1.56 ±0.3 |
Formalin |
22.3 ±4.2 |
17.4 ±2.1 |
1.24 ±0.1 |
Table 1: Levels of endocannabinoids (mean ± s. e. mean) in formalin and saline treated rats (wet weight tissue). Statistical comparisons with Students’ t-test: *p=0.05.
This study demonstrates that AEA, 2-AG and OEA are present in the brain and spinal cord, and are quantifiable using this analytical methodology. The physiological importance of the reported pattern of changes in levels of ECs following peripheral noxious stimulation requires further investigation.
Walker, J.M. et al. (1999) Proc. Natl.Acad. Sci. USA. 96, 12198-12203.
Kingsley, P.J. et al. (2003) Anal. Biochem. 314, 8-15.