Antidepressant effects of novel positive allosteric modulators of Trk-receptor mediated signaling - a potential therapeutic concept?

Abstract

Background: Major depressive disorder (MDD) is defined as a complex mental disorder which is characterized by a pervasive low mood and aversion to activity. Several types of neurotransmitter systems e.g. serotonergic, glutamatergic and noradrenergic systems have been suggested to play an important role in the origination of depression, but neurotrophins such as brain derived neurotrophic factor (BDNF) have also been implicated in the disease process.

Objectives: The purpose of this study was to examine the effects of a newly developed class of molecules, characterized as positive allosteric modulators of neurotrophin/Trk receptor mediated signaling (Trk-PAM), on neurotransmitter release and depression-like behavior in vivo.

Methods: The effect of and possible interaction of neurotrophin/Trk signaling pathways with serotonergic and glutamatergic systems in the modulation of depression-related responses was studied using newly developed Trk-PAM compounds (ACD855, ACD856 and AC26845), as well as ketamine and fluoxetine in the forced swim test (FST) in rodents. Moreover, in vivo microdialysis in freely moving rats was used to assess changes in neurotransmitter levels in the rat.

Results: The results from the study show that several different compounds, which all potentiate Trk-receptor mediated signaling, display antidepressant-like activity in the FST. Moreover, the data also indicate that the effects of both fluoxetine and ketamine in the FST, both used in clinical practice, are mediated via BDNF/TrkB signaling, which could have implications for novel therapies in MDD.

Conclusions: Trk-PAMs could provide an interesting avenue for the development of novel therapeutics in this area.

Keywords: BDNF; Fluoxetine; Ketamine; MDD; Mice; Positive allosteric modulator; TrkB.

Fig. 1

Antidepressant-like effects in the forced swim test after ACD855 administration. The forced swim test was conducted using a 10 min pre-test (day 1) followed 24 h later (day 2) by a 6 min test session where the immobility was recorded. Mice were injected either with a single dose of ACD855 (3 mg/kg, s.c.; panel a) on day 2 prior to behavioral test or repeated administration (once daily; 3 mg/kg/day, s.c.) for 4 or 28 consecutive days (panel b and c respectively) before behavioral testing, and were compared with mice receiving vehicle or mice treated with a single dose of 20 mg/kg fluoxetine on day 2 prior to behavioral test. Both fluoxetine and ACD855 (p < 0.01; p < 0.001; p < 0.0001) significantly reduced the immobility time in the forced swim test compared with vehicle treated mice. The bars represent the immobility time (seconds), mean ± SEM (n = 6–8 mice per group). The statistical analysis was performed using one-way ANOVA followed by Tukey's test (panel A and B), or unpaired t-test (C). **p < 0.01; ***p < 0.001; ****p < 0.0001 vs control group

Fig. 2

Antidepressant-like effects in the forced swim test after ACD856 administration. The forced swim test was conducted using a 10 min pre-test (day 1) followed 24 h later (day 2) by a 6 min test session where the immobility was recorded. Mice were injected either with a single dose of ACD856 (0.1, 0.3 and 1 mg/kg, s.c.; panel a) on day 2 prior to behavioral test or repeated administration (once daily; 1 mg/kg/day, s.c.) for 4 and 28 days (panel b and c respectively) before behavioral testing, and were compared with vehicle treated mice or mice treated with a single dose of 20 mg/kg fluoxetine on day 2 prior to behavioral test. Both fluoxetine (p < 0.0001) and ACD856 (p < 0.001; 0.0001) significantly reduced the immobility time in the forced swim test compared with vehicle treated mice. The bars represent the immobility time (seconds), mean ± SEM (n = 6–8 mice per group). The statistical analysis was performed using one-way ANOVA followed by Tukey's test (panel A and B), or unpaired t-test (panel C). ***p < 0.001; ****p < 0.0001 vs control group

Fig. 3

Antidepressant-like effects in the forced swim test after administration of ACD855, ACD856 and fluoxetine. The forced swim test was conducted using a 10 min pre-test (day 1) followed 24 h later (day 2) by a 6 min test session where the immobility was recorded. FSL rats were repeatedly (4 days) administered a dose of ACD856 (1 mg/kg/day, s.c.), ACD855 (3 mg/kg/day, s.c.) before behavioral testing, or a single dose of fluoxetine (20 mg/kg, i.p.) on day 2 prior to behavioral test and were compared with vehicle treated animals. ACD855 and ACD856 significantly reduced (p < 0.05) the immobility time in the forced swim test compared with control rats. The bars represent the immobility time (seconds), mean ± SEM (n = 7–8 rats per group). The statistical analysis was performed using one-way ANOVA followed by Tukey's test. *p < 0.05 vs control group

Fig. 4

Antidepressant-like effects of AC-0026845 and ANA-12 in the forced swim test. The forced swim test was conducted using a 10 min pre-test (day 1) followed 24 h later (day 2) by a 6 min test session where the immobility was recorded. Mice were injected day 2 prior to behavioral test either with a single dose of AC-0026845 (0.3 and 1 mg/kg, s.c.) or AC-0026845 (1 mg/kg, s.c.) and ANA-12 (0.5 mg/kg, s.c., panel a) or with different doses of ANA-12 (0.5 and 1 mg/kg, s.c., panel b) and were compared with control mice or mice treated with a single dose of 1 mg/kg of AC-0026845. AC-0026845 induced a significant decrease in immobility time at 0.3 and 1 mg/kg (p < 0.05; 0.01, respectively) compared with control mice. Administration of ANA-12 (0.5 mg/kg) 30 min prior to AC-0026845 (1 mg/kg) completely blocked its antidepressant-like activity (P < 0.05). ANA-12 at the above mentioned doses, failed to induce any significant decrease in immobility time (p = 0.139, ns). The bars represent the immobility time (seconds), mean ± SEM (n = 8 mice per group). The statistical analysis was performed using a two-way ANOVA (Fig. 4a) and one-way ANOVA (Fig. 4b) respectively, followed by Tukey's test. *P < 0.05 and **p < 0.01vs control; #p < 0.05 vs AC-0026845-treated mice

Fig. 5

Antidepressant-like effects of different doses of fluoxetine in the forced swim test. The forced swim test was conducted using a 10 min pre-test (day 1) followed 24 h later (day 2) by a 6 min test session where the immobility was recorded. Mice were injected day 2 prior to behavioral test either with acute single doses of fluoxetine (5, 10 and 20 mg/kg, i.p.) or administered both fluoxetine (10 mg/kg, i.p.) and AC-0026845 (0.1 mg/kg, s.c.) and were compared with vehicle treated mice or mice given a single dose of fluoxetine (10 mg/kg) or AC-0026845 (0.1 mg/kg). Fluoxetine at doses 5, 10 and 20 mg/kg induced a significant decrease in immobility time at 10 and 20 mg/kg (Fig. 5a, p < 0.05; p < 0.0001, respectively) compared with control mice. Administration of a subthreshold dose of AC-0026845 (0.1 mg/kg) in combination with fluoxetine (10 mg/kg) induced a significant decrease in immobility time as compared to control, AC-0026845 (0.1 mg/kg) or fluoxetine (10 mg/kg) alone (Fig. 5b, p < 0.01, p < 0.05; p < 0.05, respectively). The bars represent the immobility time (seconds), mean ± SEM (n = 6 mice per group). The statistical analysis was performed using one-way ANOVA (Fig. 5a) and two-way ANOVA (Fig. 5b) respectively, followed by Tukey's test. *p < 0.05; ****p < 0.001vs control; #p < 0.05 vs fluoxetine treated mice; §p < 0.05vs AC-0026845 treated mice

Fig. 6

Antidepressant-like effects of different doses of Ketamine in the forced swim test. The forced swim test was conducted using a 10 min pre-test (day 1) followed 24 h later (day 2) by a 6 min test session where the immobility was recorded. Mice were injected day 2 prior to behavioral test either with acute single doses of ketamine (2.5, 5, and 10 mg/kg, i.p.) or administered both a sub-threshold dose of ketamine (5 mg/kg, i.p.) and AC-0026845 (0.1 mg/kg, s.c.) and were compared with vehicle treated mice and mice treated with a single dose of ketamine (5 mg/kg) or AC-0026845 (0.1 mg/kg). Ketamine at doses 2.5, 5, and 10 mg/kg induced a significant decrease in immobility time at 10 mg/kg (Fig. 6a, p < 0.01) compared with control mice. Administration of AC-0026845 (0.1 mg/kg) in combination with ketamine (5 mg/kg) induced a significant decrease in immobility time as compared to control and AC-0026845 treated mice (Fig. 6b, P < 0.05; p < 0.05, respectively). The bars represent the immobility time (seconds), mean ± SEM (n = 7–8 mice per group). The statistical analysis was performed using one-way ANOVA (Fig. 6a) and two-way ANOVA (Fig. 6b) respectively, followed by Tukey's test. *p < 0.05 vs control; #p < 0.05 vs AC-0026845 treated mice

Fig. 7

Effect of ANA-12 on Antidepressant-like activity of Ketamine and fluoxetine in the forced swim test. The forced swim test was conducted using a 10 min pre-test (day 1) followed 24 h later (day 2) by a 6 min test session where the immobility was recorded. Mice were injected day 2 prior to behavioral test with a single dose of ketamine (10 mg/kg, i.p.) or fluoxetine (20 mg/kg, i.p.), or in combination with ANA-12 (0.5 mg/kg, s.c.) and were compared with vehicle treated mice or mice treated with a single dose of ketamine (10 mg/kg) or fluoxetine (20 mg/kg) alone. Ketamine induced a significant decrease in immobility time at 10 mg/kg (Fig. 7a, p < 0.01) compared with control mice. Administration of ANA-12 (0.5 mg/kg) 30 min prior to ketamine (10 mg/kg) completely blocked its antidepressant-like activity (Fig. 7a, P < 0.05). Fluoxetine (20 mg/kg) induced a significant decrease in immobility time as compared to control mice (Fig. 7b, p < 0.01). Similarly, administration of ANA-12 (0.5 mg/kg) 30 min prior to fluoxetine, completely blocked its antidepressant like activity (Fig. 7b, p < 0.05). The bars represent the immobility time (seconds), mean ± SEM (n = 7–8 mice per group). The statistical analysis was performed using one-way ANOVA followed by Tukey's test. **p < 0.01vs control; #p < 0.05 vs ketamine- or fluoxetine-treated mice

Fig. 8

Effects of ACD856 on neurotransmitter release in the hippocampus. Rats were injected with a single dose of ACD856 (10 mg/kg) s.c. and serotonin (5-HT), noradrenaline (NA), dopamine (DA), acetylcholine (ACh) and glutamate (Glu) release were continuously measured by microdialysis. There was a significant increase in the amount of serotonin as measured by a) AUC(0-120 min) values, while a more detailed analysis in b) showed a rapid and transient effect. Noradrenaline and dopamine did not reach significance in AUC (a) but showed significant increases at the 60-90 min timepoint (b). No significant effects of ACD856 on the extracellular levels of acetylcholine or glutamate were seen (data not shown). The statistical analysis was performed using a one-way (Fig. 8a) and two-way repeated measures ANOVA (Fig. 8b) respectively, followed by Bonferroni’s multiple comparison test.