Comparative evaluation of anti-depressant effects of Citalopram, Ketamine and their combination in animal models of depression: A potential anti-depressant?

Author(s): Salim Sheikh, Pankaj Sonone, Veena Verma, Chakra Dhar Tripathi, Bushra Ahmed Karim* and Girish Gulab Meshram Background: The prevalence of depression is highest amongst the mood disorders. Nearly one third of the patients suffer from major depression, characterized by increased rate of relapse, residual symptoms and impairment of functionality, along with increased tendency for suicide related behaviour. Therefore, it’s very important to acquire and explore in depth knowledg ... Abstract View Full Article View DOI: 10.17352/ojpp.000016

The neurotransmitters serotonin (5-HT), norepinephrine and dopamine are the major targets for the currently available treatment [5]. Most preferable drugs are SNRI and SSRI drugs due to decreased incidence of side effects and better safety [6,7]. Treatment refractory depression still remains a major cause of concern in spite of a plethora of anti-depressant drugs because of the effi cacy variations in the individuals [8]. Safety wise also there is increased incidence of early withdrawl from the treatment due to serious adverse effects [9]. In addition, there is higher rate of suicidal behavior during the initial phase of treatment owing to the therapeutic lag, which is around [3][4] weeks. The vulnerability of patient to suicide is highest during this period [10]. Therefore, testing of potential new agents with better effi cacy and reduced toxicity which offers treatment option over the traditional therapy, need to be done.
The N-Methyl-D-Aspartate receptor family is a potential new target for treatment of depression. Several preclinical studies have shown drugs targeting NMDA receptor have enhanced antidepressant effect and decreased therapeutic lag [11][12][13]. Ketamine is a non-competitive NMDA antagonist and a derivative of phencyclidine (PCP) which was found to produce rapid, robust and persistent antidepressant effects in clinical studies [14]. Our study targeted the NMDA receptor to elaborate and demonstrate the potential activity of ketamine in animal models of depression.

Ethical considerations
The approval for the experimentation of animals was obtained from the Institutional Animals Ethics Committee.
The study was conducted in accordance with the guidelines of the Committee for the Purpose of Control and Supervision of Experiments on Animals (CPCSEA). Testing of the animals was done for a single procedure only.

Study design and setting
The site for the study was the animal laboratory in the Pharmacology department of a medical college in New Delhi. The utilization of Swiss Albino male mice having weight of 22-25g was done for this study. The laboratory conditions for housing of the animals were light/dark cycle of 12 hours, temperature was maintained around 21±1°C and relative humidity was kept at 55±5% with 24 hour accessibility to food and water prior to the experiments. The allocation of housed animlas were done after acclimatization of 7 days into 8 random groups (Table   1) comprising of six mice per group. Concurrently, the control groups were also studied.

Experimental drugs
The procurement of Normal saline and Ketamine was from the hospital drug pharmacy. department of the hospital and Sigma Aldrich, India provided Citalopram. The drugs were given as per treatment schedule ( Table 2). The test sessions were conducted 60 minutes after intraperitoneal injections.
Normal saline was administered in the Control group. The doses of ketamine and citalopram were determined as per the previous studies and there was reduction of the drug doses in the combination group [15,16].

Animal models of depression
Experimental animals (1 mice for a single test only) were assessed with the Forced swim test (FST) and Tail suspension test (TST), both being valid animal models for depression [17][18][19][20][21]. Both models evaluate the behavior of the treated mice tests for antidepressant effects.
In FST, after placing the mice in an inescapable transparent water fi lled tank, its behavior in relation to mobility for

Statistical analysis
Calculation of the mean+SEM of the immobility time was done and one way analysis of variance (ANOVA) was performed for the analysis of the results, supplemented by Tukey's

Results
In the TST, on comparison with the control group, the groups treated with citalopram, ketamine and their combination demonstrated a signifi cant (p <0.05) reduction in the immobility time and increase in the time spent in struggle ( Figure 1). However, the decrease in immobility time was more pronounced with the groups treated with ketamine and its combination with citalopram than with citalopram itself

Discussion
Delay in the therapy responsiveness and unsatisfactory control along with not so good patient compliance owing to adverse effects are the major challenges in modern day anti-depressant therapy [8]. This necessitate the need of potential new drugs with faster onset of action and sustained prolonged effects. Ketamine has fast acting and sustainable antidepressant effect, making it a valuable next generation of rapidly acting antidepressants [13,14,22]. In our study, we  did not decreased the immobility time signifi cantly [25,26].
Interestingly, when citalopram and fl uoxetine are administered chronically they cause signifi cant reduction in the immobility time [25][26][27], probably explaining the therapeutic lag seen in SSRIs.
In our study, mice treated with Ketamine reduction of immobility time both in FST & TST models, which was signifi cant.
This result was consistent with previous studies demonstrating reduction of immobility time in a dose dependent by MK-801, ketamine & imipramine, but not by fl uoxamine [28]. Ketamine acting as a NMDA receptor antagonist, explains this effect. In addition, the increased Brain Derived Neurotropic Factor levels and activated mammalian target of rapamycin (mTOR), may explain this reduction due to more synaptic signaling protein in the pre frontal cortex [29][30][31].
In present study, ketamine with citalopram combination reduced the immobility time and increased the struggle time signifi cantly in both the models as compared to control group.
This is attributed to synergistic activity of citalopram with ketamine as seen in earlier studies [28,32,33]. Additionally, ketamine affect mood due to its interaction with monoamine and opiate systems [34][35][36].
Limitation of the study is the assessment of an acute effect of the drugs. Acute administration might be suffi cient for ketamine' mechanism of action but not for citalopram's effect onset.

Conclusion
Ketamine, an NMDA receptor antagonist has antidepressant effect as evident in both TST & FST models. Not only it has antidepressant effect of its own, it also potentiates the antidepressant effect of citalopram, suggesting possible involvement of NMDA receptors and its interaction with the monoaminergic system in depression.