Interrelated involvement of the endocannabinoid/endovanilloid (TRPV1) systems and epigenetic processes in anxiety- and working memory impairment-related behavioural effects of nicotine as a stressor

Abstract

The addictive use of nicotine contained in tobacco is associated with stressor-like emotional and cognitive effects such as anxiety and working memory impairment, and the involvement of epigenetic mechanisms such as histone acetylation has recently been reported. Although the precise nature of behavioural plasticity remains unclear, both anxiogenic- and working memory impairment-like effects were observed in the present experimental model of mice treated with repeated subcutaneous nicotine and/or immobilization stress, and these effects were commonly attenuated by the histone deacetylase (HDAC) inhibitors that induce histone acetylation. Such HDAC inhibitor-induced resilience was mimicked by ligands for the endocannabinoid (ECB) system, a neurotransmitter system that is closely associated with nicotine-induced addiction-related behaviours: the anxiogenic-like effects were mitigated by the cannabinoid type 1 (CB1) agonist arachidonylcyclopropylamide (ACPA), whereas the working memory impairment-like effects were mitigated by the CB1 antagonist SR 141716A. Moreover, the effects of the HDAC inhibitors were also mimicked by ligands for the endovanilloid (transient receptor potential vanilloid 1 [TRPV1]) system, a system that shares common characteristics with the ECB system: the anxiogenic-like effects were mitigated by the TRPV1 antagonist capsazepine, whereas the working memory impairment-like effects were mitigated by the TRPV1 agonist olvanil. Notably, the HDAC inhibitor-induced anxiolytic-like effects were attenuated by SR 141716A, which were further counteracted by capsazepine, whereas the working memory improvement-like effects were attenuated by capsazepine, which were further counteracted by SR 141716A. These results suggest the contribution of interrelated control of the ECB/TRPV1 systems and epigenetic processes such as histone acetylation to novel therapeutic approaches.

Keywords: anxiety/working memory; endocannabinoid; endovanilloid (TRPV1); epigenetic histone acetylation; nicotine; stress.

FIGURE 1

Mitigating effects of the HDAC inhibitors, CB1 agonist, or TRPV1 antagonist against anxiety‐like behaviours. The parameter values of the EPM test (percentages of entries into open arms and time spent on open arms) at the 2‐h time point after the last NC (0.8 mg/kg, sc) and/or IM (10 min) treatment are shown as means with standard deviation (SD) bars (n = 10) for each HDAC inhibitor (SB or VA), CB1 agonist (AC), or TRPV1 antagonist (CZ) cotreatment group (with each ip dose [mg/kg]), and statistical significance in posthoc tests is denoted using the symbols as defined below. The detailed data and statistical results have been included in Table S1. (A) SB (100 mg/kg, ip) cotreatment groups (SB groups); (B) VA (300 mg/kg, ip) cotreatment groups (VA groups); (C) AC (0.2 mg/kg, ip) cotreatment groups (AC groups); (D) CZ (1 mg/kg, ip) cotreatment groups (CZ groups). **P < 0.01: significant attenuation as compared with the control group; ++P < 0.01: significant increase as compared with the NC, IM, or NC‐IM group without any cotreatments; $$P < 0.01: significant attenuation as compared with the IM group without any cotreatments.

FIGURE 2

Mitigating effects of the HDAC inhibitors, TRPV1 agonist, or CB1 antagonist against working memory impairment‐like behaviours. The parameter values of the Y‐maze test (SAP rates) at the 2‐h time point after the last NC (0.8 mg/kg, sc) and/or IM (10 min) treatment are shown as means with SD bars (n = 10) for each HDAC inhibitor (SB or VA), TRPV1 agonist (OL), or CB1 antagonist (SR) cotreatment group (with each ip dose [mg/kg]), and statistical significance in post hoc tests is denoted using the symbols as defined below. The detailed data and statistical results have been included in Table S2. (A) SB (100 mg/kg, ip) cotreatment groups (SB groups); (B) VA (300 mg/kg, ip) cotreatment groups (VA groups); (C) OL (1 mg/kg, ip) cotreatment groups (OL groups); (D) SR (1 mg/kg, ip) cotreatment groups (SR groups). **P < 0.01: significant attenuation as compared with the control group; ++P < 0.01: significant increase as compared with the NC, IM, or NC‐IM group without any cotreatments; @@P < 0.01: significant attenuation as compared with the NC group without any cotreatments; $$P < 0.01: significant attenuation as compared with the IM group without any cotreatments.

FIGURE 3

Interacting effects between the CB1 antagonist and mitigating (anxiolytic‐like) drug (i.e., HDAC inhibitor, CB1 agonist, or TRPV1 antagonist) against anxiety‐like behavioural alterations caused by NC and/or IM. The parameter values of the EPM test at the 2‐h time point after the last NC (0.8 mg/kg, sc) or IM (10 min) treatment are shown as means with SD bars (n = 10) for each mitigating drug plus CB1 antagonist group (with each ip dose [mg/kg]), and statistical significance in post hoc tests is denoted using the symbols as defined below. The detailed data and statistical results have been included in Table S3. (A) SB (100 mg/kg, ip) plus SR (1 mg/kg, ip) groups (SB + SR groups); (B) VA (300 mg/kg, ip) plus SR (1 mg/kg, ip) groups (VA + SR groups); (C) AC (0.2 mg/kg, ip) plus SR (1 mg/kg, ip) groups (AC + SR groups); (D) CZ (1 mg/kg, ip) plus SR (1 mg/kg, ip) groups (CZ + SR groups). **P < 0.01: significant attenuation as compared with the control group; ++P < 0.01: significant increase as compared with the NC, IM, or NC‐IM group without any cotreatments; $$P < 0.01: significant attenuation as compared with the IM group without any cotreatments; ##P < 0.01: significant attenuation as compared with the NC, IM, or NC‐IM group cotreated with the efficacious HDAC inhibitor, CB1 agonist, or TRPV1 antagonist.

FIGURE 4

Counteraction caused by the TRPV1 antagonist against attenuating effects of the CB1 antagonist on HDAC inhibitor‐ or CB1 agonist‐induced anxiolytic‐like behavioural alterations in the NC and/or IM treatment groups. The parameter values of the EPM test at the 2‐h time point after the last NC (0.8 mg/kg, sc) and/or IM (10 min) treatment are shown as means with SD bars (n = 10) for each anxiolytic‐like drug (HDAC inhibitor or CB1 agonist) plus CB1 antagonist cotreatment group with or without additional TRPV1 antagonist (with each ip dose [mg/kg]), and statistical significance in post hoc tests is denoted using the symbols as defined below. The detailed data and statistical results have been included in Table S4. (A) SB (100 mg/kg, ip) plus SR (1 mg/kg, ip) cotreatment groups with (or without) additional CZ (1 mg/kg, ip) (SB + SR + CZ groups); (B) VA (300 mg/kg, ip) plus SR (1 mg/kg, ip) cotreatment groups with (or without) additional CZ (1 mg/kg, ip) (VA + SR + CZ groups); (C) AC (0.2 mg/kg, ip) plus SR (1 mg/kg, ip) cotreatment groups with (or without) additional CZ (1 mg/kg, ip) (AC + SR + CZ groups). **P < 0.01: significant attenuation as compared with the control group; ++P < 0.01: significant increase as compared with the NC, IM, or NC‐IM group without any cotreatments; $$P < 0.01: significant attenuation as compared with the IM group without any cotreatments; ##P < 0.01: significant attenuation as compared with the NC, IM, or NC‐IM group cotreated with the efficacious (anxiolytic‐like) HDAC inhibitor or CB1 agonist; &&P < 0.01: significant increase as compared with the NC, IM, or NC‐IM group cotreated with the mitigating drug (HDAC inhibitor or CB1 agonist) plus SR.

FIGURE 5

Interacting effects between the TRPV1 antagonist and mitigating (working memory improving‐like) drug (i.e., HDAC inhibitor, TRPV1 agonist, or CB1 antagonist) against working memory impairment‐like behavioural alterations caused by NC and/or IM. The parameter values of the Y‐maze test at the 2‐h time point after the last NC (0.8 mg/kg, sc) or IM (10 min) treatment are shown as means with SD bars (n = 10) for each mitigating drug plus TRPV1 antagonist group (with each ip dose [mg/kg]), and statistical significance in post hoc tests is denoted using the symbols as defined below. The detailed data and statistical results have been included in Table S5. (A) SB (100 mg/kg, ip) plus CZ (1 mg/kg, ip) groups (SB + CZ groups); (B) VA (300 mg/kg, ip) plus CZ (1 mg/kg, ip) groups (VA + CZ groups); (C) OL (1 mg/kg, ip) plus CZ (1 mg/kg, ip) groups (OL + CZ groups); (D) SR (1 mg/kg, ip) plus CZ (1 mg/kg, ip) groups (SR + CZ groups). **P < 0.01: significant attenuation as compared with the control group; ++P < 0.01: significant increase as compared with the NC, IM, or NC‐IM group without any cotreatments; @@P < 0.01: significant attenuation as compared with the NC group without any cotreatments; $$P < 0.01: significant attenuation as compared with the IM group without any cotreatments; ##P < 0.01: significant attenuation as compared with the NC, IM, or NC‐IM group cotreated with the efficacious HDAC inhibitor, TRPV1 agonist, or CB1 antagonist.

FIGURE 6

Counteraction caused by the CB1 antagonist against attenuating effects of the TRPV1 antagonist on HDAC inhibitor‐ or TRPV1 agonist‐induced working memory improving‐like behavioural alterations in the NC and/or IM treatment groups. The parameter values of the Y‐maze test at the 2‐h time point after the last NC (0.8 mg/kg, sc) and/or IM (10 min) treatment are shown as means with SD bars (n = 10) for each working memory improving‐like drug (HDAC inhibitor or TRPV1 agonist) plus TRPV1 antagonist cotreatment group with or without additional CB1 antagonist (with each ip dose [mg/kg]), and statistical significance in post hoc tests is denoted using the symbols as defined below. The detailed data and statistical results have been included in Table S6. (A) SB (100 mg/kg, ip) plus CZ (1 mg/kg, ip) cotreatment groups with (or without) additional SR (1 mg/kg, ip) (SB + CZ + SR groups); (B) VA (300 mg/kg, ip) plus CZ (1 mg/kg, ip) cotreatment groups with (or without) additional SR (1 mg/kg, ip) (VA + CZ + SR groups); (C) OL (1 mg/kg, ip) plus CZ (1 mg/kg, ip) cotreatment groups with (or without) additional SR (1 mg/kg, ip) (OL + CZ + SR groups). **P < 0.01: significant attenuation as compared with the control group; ++P < 0.01: significant increase as compared with the NC, IM, or NC‐IM group without any cotreatments; @@P < 0.01: significant attenuation as compared with the NC group without any cotreatments; $$P < 0.01: significant attenuation as compared with the IM group without any cotreatments; ##P < 0.01: significant attenuation as compared with the NC, IM, or NC‐IM group cotreated with the efficacious (working memory improving‐like) HDAC inhibitor or TRPV1 agonist; &&P < 0.01: significant increase as compared with the NC, IM, or NC‐IM group cotreated with the mitigating drug (HDAC inhibitor or TRPV1 agonist) plus CZ.