Chronic exposure to a synthetic cannabinoid improves cognition and increases locomotor activity in Tg4-42 Alzheimer's disease mice

Abstract

Background: Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cognitive decline and behavior impairments. Despite recent approvals of anti-amyloid antibodies, there remains a need for disease modifying and easily accessible therapies. Emerging evidence suggests that targeting the endocannabinoid system may hold promise for AD therapy as it plays a crucial role in different physiological processes, including learning, memory and anxiety, as well as inflammatory and immune responses.

Objective: In this study, we investigated the therapeutic potential of the synthetic cannabinoid WIN 55,212-2 on memory deficits in Tg4-42 transgenic mice.

Methods: Tg4-42 mice were assigned to two treatment groups to investigate the preventive effects of WIN 55,212-2 after a prolonged washout period, as well as the therapeutic effects of WIN 55,212-2 on behavior. Furthermore, the effects of WIN 55,212-2 treatment on AD pathology, including inflammation, amyloid-β load, neurogenesis, and brain glucose metabolism, were evaluated.

Results: Therapeutic WIN 55,212-2 treatment rescued recognition memory and spatial reference deficits in Tg4-42 mice. Furthermore, therapeutic WIN 55,212-2 administration improved motor performance. In addition, preventative WIN 55,212-2 treatment rescued spatial learning and reference memory deficits. Importantly, WIN 55,212-2 treatment did not affect anxiety-like behavior. However, therapeutic and preventative WIN 55,212-2 treatment resulted in an increase locomotor activity and swimming speed in Tg4-42 mice. WIN-treatment reduced microgliosis in the hippocampus of preventively treated mice and rescued brain glucose metabolism in therapeutically treated Tg4-42 mice.

Conclusions: Our findings emphasize the therapeutic promise of the synthetic cannabinoid WIN 55,212-2 in alleviating behavioral and cognitive deficits linked to AD.

Keywords: Alzheimer's disease; WIN 55,212-2; anxiety; behavior testing; cannabis; medical marijuana.

Figure 1.

Schematic illustration of the experimental setup. Tg4-42 mice received treatment with WIN 55,212-2 or a vehicle solution for 42 consecutive days, starting at 3 months (preventive) or 5 months (therapeutic), respectively. Behavioral assessments started at 6 months.

Figure 2.

Influence of prolonged WIN treatment on motor performance of Tg4-42 mice. (a) Tg4-42 mice that received preventive WIN 55,212-2 performed worse than control mice on day 7. (c) In contrast, preventively with WIN 55,212-2 treated mice displayed a significantly improved motor performance in the rotarod task. (b,d) The administration of WIN 55,212-2 did not impact the body weight of Tg4-42 mice. Two-way ANOVA followed by Bonferroni multiple comparisons; n = 13-16. Data presented as mean ± S.E.M; *p < 0.05.

Figure 3.

Influence of prolonged WIN treatment on novel object recognition memory in Tg4-42 mice. (a,e) All mice spent an equal amount of time interacting with the two identical objects (O1, O2) during the training phase. During the testing phase, only (g) therapeutically treated Tg4-42 displayed a significant preference for the novel object (N). Control Tg4-42 and (c) preventive WIN-treated Tg4-42 were unable to differentiate between the novel (N) and the familiar object (F). Distance traveled, regardless of treatment start, was not affected by WIN treatment during the (b,f) training and testing phase (d,e). The dashed line represents the 50% chance level. Two-way ANOVA followed by Bonferroni multiple comparisons; n = 11-16. Blue dots represent male mice, while red dots represent female mice. Data presented as mean ± S.E.M; ***p < 0.001.

Figure 4.

Influence of prolonged WIN 55,212-2-treatment on spatial reference memory in Tg4-42 mice. (a) Preventive and (e) therapeutic WIN-treated mice exhibited significantly shorter latencies to reach the goal platform compared to control mice in the acquisition training. (b) Preventive and (f) therapeutic WIN-treated mice demonstrated significantly higher swimming speeds than vehicle-treated animals throughout the acquisition training and probe trial (d,h). During the probe trial, WIN-treated mice demonstrated a significant preference for the target quadrant (c,g), while vehicle-treated Tg4-42 mice displayed no preference for the target quadrant. The dashed line signifies the chance level. Two-way (a,b,e,f) and one-way (c,g,d,h) ANOVA followed by Bonferroni multiple comparisons; n = 12-15. Blue dots represent male mice, while red dots represent female mice. Data presented as mean ± S.E.M; * p < 0.05, ** p < 0.01, *** p < 0.001.

Figure 5.

Influence of prolonged WIN 55,212-2-treatment on exploratory behavior and anxiety-related behavior in the elevated plus maze and open field in Tg4-42 mice. (a,e) The duration spent in the open arms of the EPM remained unchanged after WIN treatment, irrespective of the treatment start. (b,f) Preventive and therapeutic WIN-treated mice covered a significantly greater distance in the EPM compared to control mice. The time spent in the central area of the open field (c, g) did not exhibit a significant difference between WIN-treated and control mice, regardless of treatment initiation. (d,h) Both groups treated with WIN 55,212-2 travelled a similar distance in the OF as the control mice. One-way ANOVA followed by Bonferroni multiple comparisons, n = 13-16. Blue dots represent male mice, while red dots represent female mice. Data presented as mean ± S.E.M; *p < 0.05, **p < 0.01.

Figure 6.

Influence of prolonged WIN 55,212-2-treatment on anxiety-related behavior in the Dark-Light Box in Tg4-42 mice. (a) Preventive WIN-treated Tg4-42 mice spent significantly more time in the light area than control mice. (d) No significant distinction in the duration spent in the illuminated area between mice treated therapeutically with WIN and the control group. (b,e) The time taken to enter the dark area was comparable between WIN- and vehicle-treated mice, irrespective of the treatment start. (c,f) The number of light/dark transitions, serving as an indicator of mobility, did not exhibit any significant differences between the treatment groups. One-way ANOVA followed by Bonferroni multiple comparisons, n = 13-16. Blue dots represent male mice, while red dots represent female mice. Data presented as mean ± S.E.M.

Figure 7.

Effects of prolonged WIN 55,212-2 treatment on AD pathology in Tg4-42 mice. (a) Preventive WIN treatment reduced microgliosis, while (f) therapeutic treatment had no effect on IBA1 expression in Tg4-42 mice. (b,g) GFAP expression remained unaltered after WIN treatment. (e,j) WIN had no impact on Aβ load in the hippocampus of Tg4-42 mice. Additionally, (c,h) WIN treatment did not affect neurogenesis in the hippocampus or the (d,i) number of neurons in the CA1 region. (k) Therapeutic WIN treatment resulted in increased ¹⁸F-FDG uptake in the hippocampus. (a-d; f-i) One-way ANOVA followed by Bonferroni multiple comparisons and (e,j,k) unpaired t-test. Blue dots represent male mice, while red dots represent female mice. Data presented as mean ± S.E.M.