Cannabinoid receptor stimulation is anti-inflammatory and improves memory in old rats

Abstract

The number of activated microglia increase during normal aging. Stimulation of endocannabinoid receptors can reduce the number of activated microglia, particularly in the hippocampus, of young rats infused chronically with lipopolysaccharide (LPS). In the current study we demonstrate that endocannabinoid receptor stimulation by administration of WIN-55212-2 (2mg/kg day) can reduce the number of activated microglia in hippocampus of aged rats and attenuate the spatial memory impairment in the water pool task. Our results suggest that the action of WIN-55212-2 does not depend upon a direct effect upon microglia or astrocytes but is dependent upon stimulation of neuronal cannabinoid receptors. Aging significantly reduced cannabinoid type 1 receptor binding but had no effect on cannabinoid receptor protein levels. Stimulation of cannabinoid receptors may provide clinical benefits in age-related diseases that are associated with brain inflammation, such as Alzheimer's disease.

Figure 1

Water maze performance. During day 2 and 3, young rats receiving the 0.5 mg/kg WIN dose (open circle) performed significantly worse than rats in the other two young groups (open triangle and open square) († p<0.05). On day 4, the young rats receiving the 2 mg/kg WIN dose (open square) performed significantly better than the other two groups of young rats (open triangle and circle, † p<0.05). As previously described (Hauss-wegrzyniak et al., 2000), old rats were significantly impaired as compared to young rats (* p<0.05). WIN 55212-2 2 mg/kg (closed square) improved performance of age rats (closed triangle, † p<0.05 ).

Figure 2

(A.) Activated microglia in the CA3 region. Note the diminution of activated microglia cells in this region of rats treated with 2 mg/kg/day of WIN 55212-2 (f), as compared to the normal aged rats (d). Scale bar: 100µm (B.) Density of activated microglial cells in different areas of interest. Microglia density in the dentate gyrus and CA3 of aged animal were significantly different from their young control group (*p<0.05). The infusion of the highest dose (2 mg/kg/day) of WIN 55212-2 reversed partially the aged induction of activated microglia († p<0.05). No significant effect of aging or treatment was found for either CA1 or the entorhinal cortex.

Figure 3

Protein expression of CB1 receptors in the hippocampus. No changes in protein expression were found between groups for CB1 receptors in the hippocampus of rats.

Figure 4

Immunoreactivity (IR) of CB1 in the CA3 region of the hippocampus. All scale bars: 50 µm. (A) CB1-IR (red) do not co-localized with OX-6-IR (green), as magnified in (a). (B) CB1-IR (green) and NeuN-IR (red) do co-localize, as magnified in (b). (C) CB1-IR (green) and GFAP-IR (red) do not co-localize as magnified in (c). (D) CB1-IR (green) and NMDA-R1-IR (red) do co-localize as magnified in (d). (E) CB1-IR (green) and cd11b-IR (red) do not co-localize as magnified in (e). CB1-IR thus seems to be located only within neurons in the hippocampus, particularly with neurons expressing NMDA receptors. These photomicrographs are representative of the staining observed in all groups.