Effects of Unpredictable Chronic Mild Stress on the Effects of Antidepressants in the Forced Swimming Test

Validation of the forced swim test in Drosophila, and its use to demonstrate psilocybin has long-lasting antidepressant-like effects in flies

Psilocybin has been shown to be a powerful, long-lasting antidepressant in human clinical trials and in rodent models. Although rodents have commonly been used to model psychiatric disorders, Drosophila have neurotransmitter systems similar to mammals and many comparable brain structures involved in similar behaviors. The forced swim test (FST), which has been used extensively to evaluate compounds for antidepressant efficacy, has recently been adapted for Drosophila. The fly FST has potential to be a cost-effective, high-throughput assay for evaluating potential antidepressants. For this study we pharmacologically validated the fly FST using methamphetamine, DL-α-methyltyrosine, and the antidepressant citalopram. While methamphetamine and DL-α-methyltyrosine altered overall locomotor activity in the Drosophila Activity Monitor System (DAMS), they had no significant impact on measures of immobility in the FST. Conversely, chronic citalopram decreased measures of immobility in the FST in both sexes without increasing DAMS activity. We used the validated FST to evaluate the antidepressant-like effects of high (3.5 mM) and low (0.03 mM) doses of psilocybin. Both doses of psilocybin significantly reduced measures of immobility in male flies, but not females. 0.03 mM had an effect size comparable to chronic citalopram, and 3.5 mM had an effect size approximately twice that of chronic citalopram.

Anxiolytic and antidepressant effects of Ziziphus mucronata hydromethanolic extract in male rats exposed to unpredictable chronic mild stress: Possible mechanisms of actions

ETHNOPHARMACOLOGICAL RELEVANCE

Ziziphus mucronata (ZM) is used traditionally in the treatment of mood and depression. However, no existing scientific data is confirming this traditional claim.

AIM OF THE STUDY

The present study was planned to investigate the anxiolytic and antidepressant-like effects of this plant in a stressed-induced depression model in rats.

MATERIALS AND METHODS

Depressive-like behaviors were induced by exposing rats to different stress paradigms daily for 30 days. A sucrose preference test was performed to assess anhedonia in rats. Anxiety and depression-related behavior were assessed. The oxidative parameters (lipid peroxidation, SOD and catalase activities) were evaluated. Pindolol and Flumazenil were also used to assess the mechanism of action of ZM extract.

RESULTS

The results showed that chronic administration of ZM (150, 300, and 600 mg/kg, p.o., 30 days) and imipramine treatment (20 mg/kg, p.o, 30 days) remarkably (P < 0.05) reversed the UCMS-induced behavioral changes observed in stress vehicle treated rats by reducing sucrose preference, decreased the immobility period in the FST and latency in NSF. Besides, ZM (300 and 600 mg/kg, p.o., 30 days) raised the percentages of time spent and number of open arms entries as well as the number of transitions. Also, ZM (300 mg/kg, (P < 0.05) decreased lipid peroxidation and increased both SOD and catalase activities (300 and 600 mg/kg, (P < 0.05)). These aforementioned behavioral indices were also completely nullified by pindolol a β-adrenoceptors blocker and 5-HT 1A/1B receptor antagonist but not by flumazenil, a benzodiazepine receptors antagonist.

CONCLUSION

ZM improved symptoms of anxiety and depression in behavioral despair paradigm in chronically stressed rats. The observed effects could be due to its capacities to restore the antioxidant status, and probably the modulation of monoamines transmissions.

Chronic retinoic acid treatment induces affective disorders by impairing the synaptic plasticity of the hippocampus

BACKGROUND

More and more people are suffering from depression in modern society. It is believed that the development of depression results from alterations in synaptic transmission, especially in the hippocampus. Animal experiments and clinical studies have demonstrated that retinoids are essential components in hippocampal synaptic plasticity, and they have a close relationship with depression. However, it is still unclear how excessive retinoic acid (RA) causes depression and what synaptic and molecular mechanisms underlie it.

METHODS

Behavioral, electrophysiological, and molecular approaches were employed to characterize the effects of RA on depression and synaptic plasticity. RA was continuously administered intracerebroventricularly through an osmotic pump.

RESULTS

RA treatment induced depression-like behaviors, as evidenced by decreased sucrose preference and increased immobile duration in both the forced swim test and the tail suspension test. RA administration also induced anxiety-like behaviors, indicated by decreased duration in the open arms of the elevated plus maze and the central of the open field. RA treatment decreased the neuronal excitability of the hippocampus either by changing the excitatory/inhibitory receptor balance or by promoting the synthesis of inhibitory neurotransmitters. Moreover, long-term potentiation was decreased in both the excitatory postsynaptic potential and the population spike in RA-treated rats, presumably a consequence of the reduced glur1 transcript level.

LIMITATIONS

The mechanism of how excess RA affects the hippocampal gene expression and synaptic plasticity requires further study.

CONCLUSIONS

RA treatment can induce depression-like behavior in rats and impair hippocampal plasticity. Thus, improving synaptic plasticity in the hippocampus may ameliorate the affective disorders caused by excessive RA.

Antidepressant-like effect of fluoxetine may depend on translocator protein activity and pretest session duration in forced swimming test in mice

The antidepressant-like effect of fluoxetine (20 mg/kg i.p.) has been assessed using the forced swimming test (FST) in IRC (CD-1) mice exposed or not to a pretest session of different duration (5 or 20 min). The influence of the mitochondrial translocator protein (TSPO) activity on the antidepressant-like effect of fluoxetine (20 mg/kg i.p.) in the FST was also studied. The antidepressant-like effect of fluoxetine was observed only in mice subjected to a 5-min pretest session 24 h before the FST. The TSPO antagonist PK11195 [1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide; 1 or 3 mg/kg i.p.] inhibited the antidepressant activity of fluoxetine in the FST. In the present study, fluoxetine or PK11195 was administered for a short duration. We suppose that the functional activity of TSPO may depend on a pretest session and that using this procedure is necessary to detect antidepressant activity of fluoxetine-like drugs.