Cannabidiol ameliorates cognitive and motor impairments in bile-duct ligated mice via 5-HT1A receptor activation

Abstract

Background and purpose: We aimed to demonstrate the involvement of 5-HT(1A) receptors in the therapeutic effect of cannabidiol, a non-psychoactive constituent of Cannabis sativa, in a model of hepatic encephalopathy induced by bile-duct ligation (BDL) in mice.

Experimental approach: Cannabidiol (5 mg x kg(-1); i.p.) was administered over 4 weeks to BDL mice. Cognition and locomotion were evaluated using the eight-arm maze and the open field tests respectively. Hippocampi were analysed by RT-PCR for expression of the genes for tumour necrosis factor-alpha receptor 1, brain-derived neurotrophic factor (BDNF) and 5-HT(1A) receptor. N-(2-(4-(2-methoxy-phenyl)-1-piperazin-1-yl)ethyl)-N-(2-pyridyl) cyclohexanecarboxamide (WAY-100635), a 5-HT(1A) receptor antagonist (0.5 mg x kg(-1)), was co-administered with cannabidiol. Liver function was evaluated by measuring plasma liver enzymes and bilirubin.

Key results: Cannabidiol improved cognition and locomotion, which were impaired by BDL, and restored hippocampal expression of the tumour necrosis factor-alpha receptor 1 and the BDNF genes, which increased and decreased, respectively, following BDL. It did not affect reduced 5-HT(1A) expression in BDL mice. All the effects of cannabidiol, except for that on BDNF expression, were blocked by WAY-100635, indicating 5-HT(1A) receptor involvement in cannabidiol's effects. Cannabidiol did not affect the impaired liver function in BDL.

Conclusions and implications: The behavioural outcomes of BDL result from both 5-HT(1A) receptor down-regulation and neuroinflammation. Cannabidiol reverses these effects through a combination of anti-inflammatory activity and activation of this receptor, leading to improvement of the neurological deficits without affecting 5-HT(1A) receptor expression or liver function. BDNF up-regulation by cannabidiol does not seem to account for the cognitive improvement.

Figure 1

Cognitive function of the mice 3 weeks post surgery. Performance in the eight-arm maze test that was impaired in BDL mice was improved by 5 mg·kg⁻¹ CBD, and this effect was blocked by WAY-100635. **P < 0.01 versus sham; #P < 0.01 versus BDL; +P < 0.01 versus BDL + 5 mg·kg⁻¹ CBD. AUC, area under the curve; BDL, bile-duct ligation; CBD, cannabidiol; WAY-100635, N-(2-(4-(2-methoxy-phenyl)-1-piperazin-1-yl)ethyl)-N-(2-pyridyl) cyclohexanecarboxamide.

Figure 2

Motor activity of the mice 3 weeks post-surgery. The number of crossings that occurred in 1 min in the open field test decreased in bile-duct ligation (BDL) mice and was restored by 5 mg·kg⁻¹ cannabidiol (CBD). The effect of CBD was blocked by N-(2-(4-(2-methoxy-phenyl)-1-piperazin-1-yl)ethyl)-N-(2-pyridyl) cyclohexanecarboxamide (WAY-100635). ***P < 0.001 versus sham; #P < 0.001 versus BDL; +P < 0.001 versus BDL + 5 mg·kg⁻¹ CBD.

Figure 3

Hippocampal gene expression 4 weeks after bile-duct ligation (BDL) was altered. (A) Tumour necrosis factor (TNF)-α receptor 1 expression increased in the hippocampus of BDL mice; this was normalized after cannabidiol (CBD) administration, and this effect was reversed by N-(2-(4-(2-methoxy-phenyl)-1-piperazin-1-yl)ethyl)-N-(2-pyridyl) cyclohexanecarboxamide (WAY-100635). *P < 0.05 versus sham; #P < 0.01 versus BDL; +++P < 0.01 versus BDL + 5 mg·kg⁻¹ CBD. (B) Brain-derived neurotrophic factor (BDNF) expression decreased and was normalized by CBD. ***P < 0.01 versus sham; #P < 0.01 versus BDL.

Figure 4

Hippocampal 5-HT_1A receptor expression decreased following cannabidiol (CBD) treatment and bile-duct ligation (BDL) and was not restored by CBD. *P < 0.05 versus sham; **P < 0.01 versus sham.

Figure 5

(A) Plasma liver enzymes were elevated in BDL mice but were not restored by CBD. (B) Plasma bilirubin was elevated in BDL mice but was not restored by CBD. ***P < 0.001 versus sham. ALT, alanine aminotransferase; AST, aspartate aminotransferase; BDL, bile-duct ligation; CBD, cannabidiol.