Research ReportChanges in CB1 receptors in motor-related brain structures of chronic relapsing experimental allergic encephalomyelitis mice
Introduction
Recent pharmacological evidence (see Pryce and Baker, 2005, for review) has provided strong experimental support to the previous anecdotal, uncontrolled or preclinical data which indicated that multiple sclerosis (MS) patients self-medicate with marijuana to alleviate symptoms, such as spasticity, dystonia, tremor, ataxia, pain and others (for review, see Consroe et al., 1997, British Medical Association Report, 1997, Pertwee, 2002). This pharmacological evidence mainly comes from a series of studies conducted with different cannabinoid-based compounds in animal models that reproduce specific pathological aspects of this autoimmune disease (Baker et al., 2000, Baker et al., 2001, Arévalo-Martin et al., 2003, de Lago et al., 2004, de Lago et al., 2006, Cabranes et al., 2005), but it also comes from recent clinical trials developed according to standard criteria (randomization, double-blind, placebo-controlled) with different types of cannabinoid-based medicines (Zajicek et al., 2003, Zajicek et al., 2005, Rog et al., 2005). Thus, a clinical trial developed in the UK using oral administration of placebo, cannabis extract or Δ9-tetrahydrocannabinol (Δ9-THC) in a population of 667 patients with stable MS and muscle spasticity, suggested that cannabinoids do not have a beneficial effect on spasticity in MS patients, when this is measured with the Ashworth Scale over the short term, but definitively increased the patient's perception of an improvement of motor performance and pain (Zajicek et al., 2003). In addition, Δ9-THC also affected the Ashworth Score following long-term treatment (Zajicek et al., 2005). Also in the UK and using the oromucosal spray Sativex®, which contains Δ9-THC and cannabidiol, another plant-derived cannabinoid, Rog et al. (2005) just reported benefits in reducing pain and sleep disturbances in a population of 66 patients with MS and central pain states.
The studies in laboratory animals lead to similar findings. For instance, we have demonstrated that plant-derived, synthetic and endogenous cannabinoid agonists reduced some signs (spasticity and tremor) in mice with chronic relapsing experimental allergic encephalomyelitis (CREAE), a mouse model of MS (Baker et al., 2000, Baker et al., 2001). These effects were mediated by cannabinoid CB1 receptors (Baker et al., 2000). Using this mouse model, we have also described anti-spastic effects of compounds that are able to inhibit the process of termination of the biological action of endocannabinoids, such as the endocannabinoid reuptake inhibitors AM404 (Baker et al., 2001), arvanil (Brooks et al., 2002), UCM707 (de Lago et al., 2006) and OMDM2 (de Lago et al., 2004), and the fatty acid amide hydrolase (FAAH) inhibitor AM374 (Baker et al., 2001). Beneficial effects for cannabinoid-related compounds have been also reported in other models of MS in mice (Arévalo-Martin et al., 2003) or rats (Cabranes et al., 2005). In these studies, cannabinoids were effective against disease progression, which is concordant with the data obtained after the induction of CREAE in CB1 receptor deficient mice (Pryce et al., 2003).
Despite the progress in the pharmacological evaluation of cannabinoid-based medicines in MS both in patients and animal models, there are still no data on the possible changes in cannabinoid CB1 and CB2 receptors, the main molecular targets for the action of cannabinoids, in the post-mortem brain of patients with MS, while only a few studies have examined the status of the cannabinoid signaling system in animal models of this disease (Baker et al., 2001, Berrendero et al., 2001, Cabranes et al., 2005, Witting et al., 2006). Thus, we reported a decrease of CB1 receptors in the monophasic model of EAE in rats that was restricted to the basal ganglia and cortical structures (Berrendero et al., 2001) and accompanied by reduced levels of endocannabinoid ligands in these and other brain regions (Cabranes et al., 2005). By contrast, anandamide has been reported to be elevated in active MS lesions (Eljaschewitsch et al., 2006) and endocannabinoid levels are increased in the spinal cord and to a lesser extent the brain, which shows lower lesion load, of CREAE mice during the spastic phase of disease (Baker et al., 2001). This has been interpreted to indicate an endocannabinoid influence in the control of some of the signs of MS in an environment of existing neurological damage (see Baker and Pryce, 2003, for review). However, no data exist on the status of CB1 receptors in the brain of CREAE mice. This has been the objective of the present study, where we have examined the density, mRNA expression and activation of GTP-binding proteins for the cannabinoid CB1 receptor subtype in several brain structures of CREAE, at different phases of the progression of this disease (acute, remission and chronic), and control mice. These data might be important in terms of re-evaluating the reported efficacy of those cannabinoid compounds that activate CB1 receptors in this murine model of MS.
Section snippets
Results
We found a moderate decrease in the density of CB1 receptors in the acute phase of CREAE in some motor-related regions compared to normal animals. These decreases disappeared during the remission phase, but were again observed to a more marked extent in the chronic phase of EAE (Table 1; Fig. 1). This was the case in some basal ganglia areas, such as the lateral [F(3,31) = 4.372, P < 0.05] and medial (only as a trend: P = 0.137) caudate–putamen, and the cerebellum [F(3,27) = 3.105, P < 0.05] (
Discussion
Multiple sclerosis is the neurological disease that represents the most frequent cause of chronic disability in young adults (for review, see Polman and Uitdehaag, 2000). As yet, no treatment can completely halt the accumulation of disability and substantial efforts are being made to find new therapeutic molecules in this disease. As mentioned in Introduction, cannabinoid-based compounds have been proposed as potentially useful in the treatment of some symptoms of this disease (for review, see
Animals, treatments and sampling
Male Biozzi ABH mice were from stock bred at the Institute of Neurology and housed in a room with controlled photoperiod (12 h light/dark cycle), temperature (20 ± 1 °C) and relative humidity (40–60%). They had free access to standard food and water. They were used at adult age (6–8 week old) for all the experiments, which were performed according to European regulations for experimental work with animals (directive 86/609/EEC) and the UK Animals (Scientific Procedures) Act (1986). CREAE was
Acknowledgments
This work has been supported by grants from MEC (SAF2003-08269), Red CIEN (C03/06) and SANTANDER/COMPLUTENSE (PR27/05-13975) to JFR, and The Multiple Sclerosis Society of Great Britain and Northern Ireland and Aims2Cure to DB. Ana Cabranes is a predoctoral fellow supported by the Complutense University.
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