Attenuation of Novelty-Induced Hyperactivity of Gria1-/- Mice by Cannabidiol and Hippocampal Inhibitory Chemogenetics

Abstract

Gene-targeted mice with deficient AMPA receptor GluA1 subunits (Gria1-/- mice) show robust hyperlocomotion in a novel environment, suggesting them to constitute a model for hyperactivity disorders such as mania, schizophrenia and attention deficit hyperactivity disorder. This behavioral alteration has been associated with increased neuronal activation in the hippocampus, and it can be attenuated by chronic treatment with antimanic drugs, such as lithium, valproic acid, and lamotrigine. Now we found that systemic cannabidiol strongly blunted the hyperactivity and the hippocampal c-Fos expression of the Gria1-/- mice, while not affecting the wild-type littermate controls. Acute bilateral intra-dorsal hippocampal infusion of cannabidiol partially blocked the hyperactivity of the Gria1-/- mice, but had no effect on wild-types. The activation of the inhibitory DREADD receptor hM4Gi in the dorsal hippocampus by clozapine-N-oxide robustly inhibited the hyperactivity of the Gria1-/- mice, but had no effect on the locomotion of wild-type mice. Our results show that enhanced neuronal excitability in the hippocampus is associated with pronounced novelty-induced hyperactivity of GluA1 subunit-deficient mice. When this enhanced response of hippocampal neurons to novel stimuli is specifically reduced in the hippocampus by pharmacological treatment or by chemogenetic inhibition, Gria1-/- mice recover from behavioral hyperactivity, suggesting a hippocampal dysfunction in hyperactive behaviors that can be treated with cannabidiol.

Keywords: AMPA receptors; DREADD; c-Fos; cannabidiol; hM4Gi; hippocampus; hyperactivity; novelty.

FIGURE 1

Dose–response analysis of cannabidiol on novelty-induced hyperlocomotion of Gria1-/- mice. (A,B) Distance traveled in a novel environment in 5-min periods after treatment with vehicle and doses of cannabidiol (mg/kg, i.p.). (C) Distance traveled from the beginning of the trial until 30 min. (D) Total distance traveled during the whole 2 h test trial. Means ± SEMs are shown for 5–6 mice per group. ^∗∗∗P < 0.001 for the significances of the differences between WT and Gria1-/- mice after vehicle treatment; ^#P < 0.05, ^##P < 0.01, and ^###P < 0.001 between vehicle and CBD within the same genotype (Bonferroni post-test). Veh, vehicle; CBD, cannabidiol.

FIGURE 2

Expression of c-Fos protein in hippocampal subregions of the Gria1-/- and WT mice after a 2-h exposure to a novel environment with pre-treatment with vehicle or cannabidiol (15 mg/kg). (A) Representative images of the dorsal hippocampus. (B) Counts of c-Fos+ cells in the subregions of the dorsal hippocampus. Open bars for the vehicle- (VEH) treated and closed bars for cannabidiol- (CBD) treated groups. (C) Representative images of the ventral hippocampus. (D) Counts of c-Fos+ cells in the subregions of the ventral hippocampus. Means ± SEMs are shown for 4–6 mice per group. ^∗P < 0.5, ^∗∗P < 0.01 for the significances of the differences between genotypes after the same treatment, ^#P < 0.05, ^##P < 0.01 for the difference from the vehicle within the same genotype (Bonferroni post-test). Scale bar: 100 μm.

FIGURE 3

Intrahippocampal infusion of cannabidiol decreases novelty-induced hyperlocomotion of Gria1-/- mice. Animals were given an infusion with vehicle or cannabidiol (5 μg/side) followed by recording of distance moved for 30 min. (A) Injector tip placements within the dorsal hippocampus for all experimental groups. The brain images were modified with permission from Paxinos and Franklin (2001). (B) Distance traveled in a novel environment in 5-min periods. (C) Total distance traveled during 30-min trials. ^∗∗P < 0.01 and ^∗∗∗P < 0.001 for the significances of the differences between the genotypes after vehicle; ^#P < 0.05 between vehicle and CBD within the same genotype (Bonferroni post-test). N = 10 for both genotypes. Veh, vehicle; CBD, cannabidiol.

FIGURE 4

Chemogenetic inhibition of novelty-induced hyperlocomotion in Gria1-/- mice. (A) Virus injection resulted in hM4Gi-mCherry expression in the dorsal hippocampus. Hb, habenula; fi, fimbria; scale bar: 1 mm. (B) A close-up photograph displaying transduced neurons and neurites in the dentate gyrus. No transduced neurites were observed outside the hippocampus (not shown). Gr, granule cell layer; Mol, molecular layer; scale bar: 50 μm. (C) Distance traveled in a novel environment in 5-min periods in mice transduced with DREADDs. (D) Total distance traveled during the 30-min trial in mice transduced with DREADDs. ^∗∗P < 0.01 and ^∗∗∗P < 0.001 for the significances of the differences between the genotypes after vehicle; ^#P < 0.05 and ^##P < 0.01 between vehicle and CNO treatments within the same genotype (Bonferroni post-test), n = 10 for both genotypes. (E) Distance traveled in a novel environment in 5-min periods in non-DREADD expressing WT and Gria1-/- control mice. ^∗∗∗P < 0.001 for the significances within drug treatment and between genotypes (ANOVA). (F) Total distance traveled during the 30-min trial in non-DREADD-expressing control mice. ^∗P < 0.05 between genotypes and within drug treatment (Bonferroni post-test). n = 11–14. Veh, vehicle; CNO, clozapine-N-oxide.