Anti-inflammatory property of the cannabinoid agonist WIN-55212-2 in a rodent model of chronic brain inflammation

Abstract

Cannabinoid receptors (CBr) stimulation induces numerous central and peripheral effects. A growing interest in the beneficial properties of manipulating the endocannabinoid system has led to the possible involvement of CBr in the control of brain inflammation. In the present study we examined the effect of the CBr agonist, (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)-pyrrolo[1,2,3-de]-1,4benzoxazin-6-yl]-1-naphthalenyl-methanone mesylate (WIN-55212-2), on microglial activation and spatial memory performance, using a well-characterized animal model of chronic brain inflammation produced by the infusion of lipopolysaccharide (LPS, 250 ng/h for 3 weeks) into the fourth ventricle of young rats. WIN-55212-2 (0.5 or 1.0 mg/kg/day, i.p.) was administered for 3 weeks. During the third week of treatment, spatial memory ability was examined using the Morris water-maze task. We found that 0.5 and 1 mg/kg WIN-55212-2 reduced the number of LPS-activated microglia, while 1 mg/kg WIN-55212-2 potentiated the LPS-induced impairment of performance in the water maze task. Cannabinoid receptors 1 were not expressed by microglia and astrocytes, suggesting an indirect effect of WIN-55212-2 on microglia activation and memory impairment. Our results emphasize the potential use of CBr agonists in the regulation of inflammatory processes within the brain; this knowledge may lead to the use of CBr agonists in the treatment of neurodegenerative diseases associated with chronic neuroinflammation, such as Alzheimer disease.

Figure 1

Water maze performance. On days 2 and 3, all LPS-infused animals (closed triangles, squares and circles) were significantly impaired (*p<0.0033, Bonferroni/Dunn post hoc test) compared to their control groups. On days 2 and 3, LPS+WIN 1 rats were significantly impaired († p<0.0033, Bonferroni/Dunn post hoc test) compared to the LPS+vehicle rats. WIN 55212-2 did not impair performance (open squares and circles) of aCSF-infused rats and did not attenuate the impairment due to the LPS infusion (closed squares and circles)

Figure 2

(A.) Activated microglia in the dentate gyrus. Note the diminution of activated microglia cells in the dentate gyrus of animals treated with either doses of WIN 55212-2 (e,f) compare to the LPS+vehicle group (d) (B.) Density of activated microglial cells in different areas of interest. Similar results were obtained for the two doses of WIN-55212-2 used in the dentate gyrus and CA3 areas. For both of them, LPS infused animal were significantly different from their control group (*p<0.0033, Bonferroni/Dunn post hoc test). The injection of both doses (0.5 and 1 mg/kg) reversed partially the LPS induction of activated microglia († p<0.0033, Bonferroni/Dunn post hoc test). No significant effect of the treatment was found for either CA1 or the entorhinal cortex.

Figure 3

Immunoreactivity (IR) of CBr in the CA3 region of the hippocampus. (a) CB1-IR (DAB stain) is seen in the cytoplasm of all CA3 neuronal cell bodies (counterstaining with cresyl violet). (b) CB1-IR (red) and MCH-II-IR (green) do no co-localize, as indicated by white arrows. (c) CB1-IR (red) and GFAP-IR (green) do no co-localize as indicated by white arrows. CB1-IR thus seem to be located only within neurons in the hippocampus. These photomicrographs were obtained from only LPS-infused rats that are representative of the staining observed in aroups.