P Rataboli, A Garg, K Muchandi
animal model, ccb calcium channel blockers, depression., forced swim test
P Rataboli, A Garg, K Muchandi. Antidepressant effect of low dose nimodipine in the mouse behaviour despair model. The Internet Journal of Pharmacology. 2009 Volume 8 Number 1.
Dihydropyridine Calcium Channel Blockers (DHP-CCB) have been reported to exert conflicting effects in various experimental models of depression. We observed the effect of centrally acting DHP-CCB, nimodipine at various doses in behaviour despair model using Porsolt’s Forced Swim Test in mice. Nimodipine showed significant antidepressant activity only at 2.5 mg/kg given intraperitoneally. A possible therapeutic window phenomenon is thought to come to play at lower doses of the drug. Thus nimodipine can be developed as a strong weapon and added to the armamentarium used especially against cerebrovascular diseases where the possibility of depression setting in can not be ruled out.
Calcium channel blockers of the dihydropyridine class (DHP-CCB) like nifedipine, nitrendipine, and nimodipine have been reported to reduce immobility in the mouse behavioural despair model of depression in the dose of 0.1, 1.0, and 10 mg/kg i.p., and co-administration of antidepressant potentiates the effect of nifedipine (Mogilnicka et al., 1987). In another study, in a dose of 5 mg/kg i.p., nimodipine did not affect the immobility but nifedipine or nitrendipine reduced the immobility time in the same dose (Czyrak et al., 1989). It was further reported that there was no significant decrease in immobility time of rats in the forced swim test treated with nimodipine in the dose of 10 mg/kg i.p. or compared to tricyclic antidepressants (Czyrak et al., 1990).
Although nifedipine and nitrendipine seemed to consistently decrease the immobility time in rats and mice, nimodipine seemed to have variable actions at different doses and in different animal species. Nimodipine, unlike other CCB-DHP is centrally acting approved for its use in ischemic stroke and sub-arachnoid haemorrhage (Tettenborn et al., 1985). Apart from these, there are other roles which have been attributed to nimodipine including as an analgesic (Filos et al., 1993), anti-platelet agent (Feinberg and Bruck, 1993), as a cognition enhancer, and to prevent migraine attacks. A potential role as an antidepressant is still questionable.
Considering this diversity of reports, we examined the effect of nimodipine in various doses (1.25, 2.5, 5, 10, and 20 mg/kg i.p.) in the behaviour despair model in mice and compared it with standard antidepressant amitriptyline for its potential antidepressant action.
Materials and methods
Swiss albino mice weighing 23-28 g were selected for the procedure. Animals were housed in our laboratory with 12 hour light and dark cycle along with adequate food and water for at least 1 week prior to the study. The experiment was performed between 10 a.m.-4 p.m. i.e. during the light phase of the day.
The drugs used in the study were; nimodipine as a test drug and amitriptyline as positive control. As both the drugs are insoluble in water, 1% tween-20 was used to make their suspension. The suspension was freshly prepared and was protected from direct sun light. Mother solution of nimodipine was later titrated down to attain various calculated doses (1.25, 2.5, 5, 10, and 20 mg/kg).
Apparatus and test procedure
Water tub of 60 cm (inner diameter) and 35 cm (height) was used. It was filled with water (27-29 °C) up to a height of 15 cm. For the evaluation of drugs, we used Porsolt’s Forced Swim Test (Porsolt et al., 1977). It was a 2 day procedure. On day 1, each animal was dropped in water and was forced to swim for 6 min. It was then wiped dry and returned to home cage. On day 2, mice were injected (intraperitoneal; i.p.) with various doses of the test and control drug. After a gap of 1 hour they were subjected to the swim test. In accordance with Porsolt et al, mice were kept in water for 6 min. First, animals make vigorous attempt to climb and come out of water. Later, realizing the futility of the attempts, they give up. In between, the animals stops making any attempts to swim or come out of water and it only moves that much, what is required of them to stay afloat. These are called the “immobility spells” and forms the basis of the data collected.
Individual immobility spells were counted with the help of a stopwatch and later added together to get a total out of 240 s (evaluated only during last 4 min). This procedure was repeated with all mice and mean immobility time was obtained in all sets of experiments.
Keeping in mind the variability of the results published in literature so far, a well planned study design was sought for. Our study was split in 2 stages. In the first stage, we compared the control mice with those who received vehicle (tween-20), positive control (amitriptyline 10 mg/kg i.p.) and the test drug (nimodipine 1.25, 2.5, 5, 10, and 20 mg/kg i.p.). For this, sample size of 6 was chosen with α and β error set at 0.05 and 0.20 respectively. The aim of this stage was to:
Collect data to calculate the adequate sample size for the final stage of the study
Decrease α and β errors in the second stage to increase power of the study, and
Apply Student’s paired
After covering a wide range of doses, in stage 2, we further split the dose around significant results. Here, validity of the results generated was increased by making the design for two tailed, paired Student’s
Sample size and the power calculation were done using software-PS version 2.1.30. All the means were compared to the mean of control animal group using two-tailed, paired and unpaired Student’s
In the first stage of the study, the mean immobilization time of control group differed significantly only with the positive control i.e. amitriptyline 10 mg/kg i.p. (
After these preliminary findings, we observed the effect of nimodipine more closely in the second stage. With the paired design also, nimodipine showed significant antidepressant activity only at 2.5 mg/kg i.p. (
Behavioural effects of calcium channel antagonists in experimental animals have been highlighted in a few studies (Renwart et al., 1986). A report also significantly points to the role of calcium and calcium channels in depression (Dubovsky et al., 1989). A few preliminary non double blind clinical studies also indicate the possible role of CCBs as antidepressant agents (Jacques and Cox, 1991). Although DHP-CCB nifedipine and nitrendipine are reported to act as antidepressant consistently in various models of depression, nimodipine has been an exception with different results at different doses. In a controlled EEG study in humans, nimodipine has been showed to have an EEG profile closely resembling part of anti depressants imipramine and fluvoxamine (Itil et al., 1984). To set aside these contradicting reports, nimodipine was tested in various dose range varying from 1.25 to 20 mg/kg i.p. The main finding of our study is that nimodipine showed significant antidepressant activity only at 2.5 mg/kg i.p. there was no response at higher or lower doses used.
The exact mechanism of antidepressant action of DHP-CCB is unclear. Interestingly so is the present understanding of neurochemistry of depression. A lot of research workers have proposed several theories regarding the aetiology of depression. All theories point out to a malfunctioning in central aminergic mechanisms. Willner (1990) opined that involvement of a particular amine may translate into specific clinical symptomatology and this can give birth to multifactorial nature of depression. Nimodipine may thus act through either of these actions: increase in nor adrenergic release, decrease in dopamine release, potentiation of cholinergic action and α1 blocking action. It is also possible that the antidepressant effect of nimodipine is due to calcium influx blockade in the brain. Tricyclic antidepressants (TCA) appear to inhibit Ca++ activated K+ channels following inhibition of voltage sensitive Ca++ channels (Kamatachi and Ticku, 1991). This could be due to calmodulin blockade property (Lamers et al., 1985).
There is no study involving nimodipine at a dose of 2.5 mg/kg i.p., where we have obtained significant results. This dose correlates clinically to sub-therapeutic levels of nimodipine. Nimodipine did not show the dose dependent effect. There was no antidepressant effect at either very low or high doses. This could be an example of “therapeutic window”, where the optimal therapeutic effects are exerted only over a narrow range of plasma drug concentrations or drug doses. Tricyclic antidepressants like imipramine, antihypertensives like clonidine and antidiabetics like glipizide are well known to behave this way. The pharmacological basis of this phenomenon is not known but is thought to be a consequence of complexity of action of a drug; different mechanisms coming into play at different doses. The reason why the range of effect was not caught in our study is probably that the effect varies in much smaller concentration increments than what we had anticipated and evaluated. Further studies are required to identify the exact site and mechanism of action of nimodipine using radio-ligands studies.