Microglial activation underlies cerebellar deficits produced by repeated cannabis exposure
Laura Cutando, … , Rafael Maldonado, Andrés Ozaita
Laura Cutando, … , Rafael Maldonado, Andrés Ozaita
Published June 24, 2013
Citation Information: J Clin Invest. 2013;123(7):2816-2831. https://doi.org/10.1172/JCI67569.
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Microglial activation underlies cerebellar deficits produced by repeated cannabis exposure

Abstract

Chronic cannabis exposure can lead to cerebellar dysfunction in humans, but the neurobiological mechanisms involved remain incompletely understood. Here, we found that in mice, subchronic administration of the psychoactive component of cannabis, delta9-tetrahydrocannabinol (THC), activated cerebellar microglia and increased the expression of neuroinflammatory markers, including IL-1β. This neuroinflammatory phenotype correlated with deficits in cerebellar conditioned learning and fine motor coordination. The neuroinflammatory phenotype was readily detectable in the cerebellum of mice with global loss of the CB1 cannabinoid receptor (CB1R, Cb1–/– mice) and in mice lacking CB1R in the cerebellar parallel fibers, suggesting that CB1R downregulation in the cerebellar molecular layer plays a key role in THC-induced cerebellar deficits. Expression of CB2 cannabinoid receptor (CB2R) and Il1b mRNA was increased under neuroinflammatory conditions in activated CD11b-positive microglial cells. Furthermore, administration of the immunosuppressant minocycline or an inhibitor of IL-1β receptor signaling prevented the deficits in cerebellar function in Cb1–/– and THC-withdrawn mice. Our results suggest that cerebellar microglial activation plays a crucial role in the cerebellar deficits induced by repeated cannabis exposure.

Authors

Laura Cutando, Arnau Busquets-Garcia, Emma Puighermanal, Maria Gomis-González, José María Delgado-García, Agnès Gruart, Rafael Maldonado, Andrés Ozaita

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Figure 2

Cerebellar responses 5 days after THC treatment cessation.

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Cerebellar responses 5 days after THC treatment cessation. (A) Immunoblo...
(A) Immunoblot and quantification of CD11b and CB1R in cerebellar homogenates from mice processed 5 days after subchronic treatment (n = 5–6 mice per group). The optical density of CD11b and CB1R was normalized to GAPDH in the same samples. (B) Immunofluorescence and quantification of CB1R intensity in the granular and molecular layers of the cerebellum from mice processed 5 days after subchronic treatment (n = 3 mice per group, 5 images per mouse). Scale bar: 75 μm. (C) Immunolocalization and ICQ of IBA1 (red) and CD11b (green) in the molecular and granular layers of the cerebellum after treatment (n = 3 mice per group, 3 images per mouse). Scale bars: 100 μm. (D) Morphological analysis of IBA1+ microglial cells in the molecular layer of the cerebellum (n = 4 mice per group, 4 cells per mouse). See Supplemental Figure 17 for details. Scale bar: 25 μm. (E) Analysis of Cb2r mRNA expression and inflammation-related genes in cerebellar samples (n = 7–8 mice per group). (F) Flow cytometric analysis of CD11b expression and qRT-PCR analysis of acutely dissociated cerebellar cells from VEH-, THC-5–, and THC-20–treated mice (n = 3 per group). Sorted CD11b+ population (P4) and CD11b– population (P5) in THC-treated mice showed a differential expression of Cb1r, Cb2r, and Il1b. *P < 0.05; **P < 0.01; ***P < 0.001 versus subchronic VEH plus SAL (5 days).