Ketamine; A better anti-depressant? An animal study evaluating the efficacy of citalopram, ketamine and their combination in animal models of depression

Author(s): Salim Sheikh, Pankaj Sonone, Veena Verma, Chakar Dhar Tripathi, Bushra Ahmed Karim* and Girish Gulab Meshram Background: Despite the availability of vast group of drugs, treatment of depression still remains unsatisfactory, largely due to differential efficacy of antidepressants at adequate doses resulting in treatment refractive depression. In addition, serious adverse effects of anti-depressants also lead to early withdrawal from treatment. One more important concern is th ... Abstract View Full Article View DOI: 10.17352/jnnsd.000043

Despite the availability of vast group of drugs, treatment of depression still remains unsatisfactory, largely due to differential effi cacy of antidepressants at adequate doses resulting in treatment refractive depression [8]. In addition, serious adverse effects of anti-depressants also leads to early withdrawl from treatment [9]. One more important concern is the therapeutic lag of nearly 3-4 weeks, before some appreciable clinical effect. This is the period when there is high risk of suicide [10]. Therefore, newer agents with good safety profi le, rapid onset of action and with substantial benefi ts in treating patients who are either refractory or resistant to conventional therapy, need to be explored.
In this pursuit, focus has now shifted to drugs targeting the N-Methyl-D-Aspartate receptor family. 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 study [14]. Therefore, the present study was carried out to elucidate the role of ketamine in animal models of depression.

Ethical considerations
All experimental procedures were carried out after being approved by 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). Each animal was used only once in the experimental procedures.

Study design and setting
The study was conducted in the department of Pharmacology of a tertiary care teaching hospital in New Delhi. Swiss Albino male mice weighing between 22-25g were utilized for this study. The animals were kept under standard laboratory conditions. The animals were housed in standard laboratory conditions (12-h light/dark cycle, 21 ± 1°C, and relative humidity of 55±5%) with free access to food and water prior to the experiments. After 7 days of acclimatization to laboratory conditions, the animals were randomly allocated into the different (08) groups (Table 1), each group comprising of six mice. The control groups were studied concurrently with the experimental groups.

Experimental drugs
The normal saline and ketamine were procured from the drug store department of the hospital, whereas Citalopram was provided by Sigma Aldrich, India. The treatment was given as per treatment design ( Table 2). The drugs were injected intraperitonealy (ip) 60 min before conducting the test session.
Control group received appropriate vehicle (normal saline). The dose of ketamine and citalopram for present study was based on doses used in previous studies from literature [15,16]. While giving drugs in combination, doses of drugs were reduced ( Figure 1).
The FST is a rodent behavioral test used for evaluation of antidepressant drugs. Mice were placed in an inescapable transparent tank that is fi lled with water and their escape related mobility behavior was measured. The cylindrical tanks of transparent Plexiglas (30 cm height x 20 cm diameters) were

Statistical analysis
The mean+SEM of the immobility time was calculated and the data were analysed using one way analysis of variance (ANOVA) followed by Tukey"s multiple range test, wherever applicable. P values less than 0.05 were considered signifi cant.

Results
In the TST, on comparison with the control group, However, the decrease in immobility time was more pronounced with the groups treated with ketamine and its combination with citalopram than with citalopram itself (Figure 2).
In the FST, the group treated with citalopram alone showed a non-signifi cant (P >0.05) decrease in the immobility time as compared to the control group. Whereas, other groups treated with ketamine alone and its combination with citalopram showed a signifi cant reduction of the immobility time and increase in the duration of struggle (Figures 3,4). However, when the combination was compared with citalopram group, not much change in immobility time was observed, and the effect was not signifi cant.

Discussion
Major challenges in modern day anti-depressant therapy are delay in the therapeutic response and inadequate improvement along with poor patient compliance due to adverse effects [8].
Therefore, newer drugs with rapid onset and longer sustainable effect are the need of the hour. Ketamine has fast acting and sustainable antidepressant effect, making it a valuable next generation of rapidly acting antidepressants [13,14,22]. of new substances in these tests allow a simple assessment of their potential antidepressant activity by the measurement of their effect on immobility time [23].
In our study citalopram caused signifi cant reduction in the immobility time and increased the struggle period in TST, further strengthening its anti-depressant effect [24].  [29][30][31].
In our study, combination of ketamine with citalopram showed signifi cant reduction in the immobility time and increase in struggle time 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].

Conclusion
Ketamine have an antidepressant activity of its own, as shown in both TST & FST models. Moreover, it also potentiated the antidepressant effect of citalopram, which could be attributed to possible involvement of NMDA receptors and its interaction with the monoaminergic system.

Author contributions
All authors have accepted responsibility for the entire content of this manuscript and approved its submission.

Availability of data
The data that support the fi ndings of this study are available from the corresponding author upon reasonable request. Some data may not be made available because of privacy or ethical restrictions.