Differential Sensitivities of Three Strains of Drosophila melanogaster (Diptera: Drosophilidae) to Imipramine as an Antidepressant Drug

MATERIALS AND METHODS

Imipramine hydrochloride, the material used for this study manufactured by Sarabhai Pirmal Ltd. India, has the following structural formula:

To assess the effect of imipramine, three strains of D. melanogaster, including one wild type (Oregan-K) and two mutant strains (Muller-5 and bw/st) have been used. Larval feeding technique was employed for assessing the differential sensitivity. This investigation was done on the base of procedure of Delcour (1969) and explanations of Nichols (2006) on life cycle of D. melanogaster. Eggs of the same age were collected and equal numbers of eggs were placed in vials containing either wheat cream agar media or media with different concentrations of drug. Twenty replicates of each set were maintained. The LC₅₀ was calculated for wild type and then three concentrations below this (1, 2 and 4 g L^-1) were selected and used for comparison of sensitivity of these strains. For preparing different concentrations of treated series, imipramine was mixed with distilled water then added to standard wheat cream agar media after cooking. The number of flies emerged and their sexes were recorded every day from the first to the last day of eclosion. All the experiments were conducted at constant temperature of 20±1°C.

Statistical analysis: Viability and developmental time of three strains were analyzed by using of one way analysis of variance (ANOVA) with DMRT (Duncan’s Multiple Range Test) whereas sex ratio was analyzed by chi-square (χ²).

RESULTS

Table 1 shows the effect of different concentrations of imipramine on viability of three strains. Observation reveals that the viability decreases with increasing dose of test chemical. This parameter is significant for all of concentrations (p<0.01). It also represents that in all concentrations of imipramine there is significant difference between three strains but in the 1 and 4 g L^-1 concentrations, this value is not significant between two mutant strains (p<0.01).

In the highest concentration (4 g L^-1), viability of Oregan-K is 57.20 % while, for bw/st and Muller-5 it is zero. It means these two mutant strains could not tolerate this high concentration and they are more sensitive to imipramine compared to the wild type.

The effect of imipramine on developmental time of three strains could be seen in Table 2. It reveals that developmental time significantly increased in all treated series compared to the control (p<0.01). There is linear relationship between the concentrations employed in treated series and increase in developmental time. Such results have also been reported by Mahmood et al. (1990) in Drosophila while assessing toxicity of a pesticide, furadan and also by Choudhary (2004) who used fenvalerate as a contact poison against larval development and viability.

Table 1:	Viability of three strains of Drosophila melanogaster in different concentrations of imipramine
Valves significant (p<0.01), *The viability with the same letter in the parenthesis are not significant at 5% level according to DMRT

Table 2:	Comparison of effects of imipramine on developmental time of three strains of Drosophila melanogaster
Value significant by ANOVA test (p value 0<0.01), *The developmental time with the same letter in the parenthesis are not significant at 5 % level according to DMRT

DISCUSSION

The genotoxic and carcinogenic effects of antipsychotics and antidepressant drugs have been reported by most of researches (Brambilla et al., 2009). In this review of Brambilla et al. (2009) there was not any test system on effects of imipramine on dominant lethal and life cycle test on D. melanogaster. So this study was done to increase knowledge of effects of imipramine that was applied long term in several countries.

The rate of development time and viability are two factors for evaluating the toxicity of chemicals (Luning, 1966). Bonnier (1961) has demonstrated that change in rate of development is due to compound effects of genotype and environment. Uysal et al. (2007) have reported recovering effects of some plant extracts on the teratogenic effects during the development of D. melanogaster. Smith et al. (2011) have also investigated sexual dimorphism in the effect of a Taurine supplemented diet on biology of adult D. melanogaster. The present study also revealed significant difference in developmental time and viability that must be due to the drug employed and also different genetic system of the three strains. In this investigation, Oregan-K is more resistant to imipramine compared to other two mutant strains, perhaps because it is a wild strain which is having certain advantage of being in man made as well as in natural environments. Sex ratio is one of the adaptive traits of any population which identifies the rate of changes of a sexual population in an environment.

Statistical analysis of the data in the present investigation on the effect of imipramine on sex ratio of three strains revealed that, the female to male ratio of Oregan-K (wild type) has significantly increased in concentrations 1 and 2 g L^-1 (Table 3). It means female germ cells compared to male are more resistant to exposure to this drug. In contrast to this, among mutants, sex ratio deviation was significant only in 2 g L^-1 concentration for bw/st and in 1 g L^-1 for Muller-5 (p<0.05). This difference is perhaps due to absence of flies at the highest concentration of 4 g L^-1. Thus, this research shows that imipramine has toxic effect on Drosophila and different strains have different sensitivity. Although, no enough data on the effect of imipramine on viability ,developmental time and sex ratio is available until now, changes in these biological data due to incorporation of other chemicals have been demonstrated by earlier workers in D. melanogaster (Sorsa and Pfeifer, 1973; Chinnici et al., 1976; Vasudev and Krishnamurthy, 1979; Rajasekarasetty et al., 1979; Lopez-Fanjul and Villaverde, 1989; Basheer et al., 1999). This study also agrees with the most work of them in some aspects. Finally, the scrutiny of the overall results of this investigation on D. melanogaster reveals that imipramine has toxicity and genotoxicity.

Table 3:	Effect of imipramine on sex ratio of three strains of Drosophila melanogaster
No. of eggs for each concentration = 500, *Differences are statistically significant (p<0.05)

CONCLUSION

With respect to overall picture of data of this investigation on D. melanogaster, it is clear that imipramine is genotoxic both in larval and adult feeding in dominant lethal test. Also according to the report of pervious workers, this drug is mutagenic in somatic cells of Drosophila. On the other hand this antidepressant drug associates with development of breast cancer. So, it was suggested that, due to possible genotoxic and carcinogenic potential of imipramine as antidepressant drug, prescription in medicine should be done with more caution especially in pediatric age group , during pregnancy and lactation.

ACKNOWLEDGMENTS

The authors thanks to emeritus Professor S.N. Hegde, Dept. of Zoology, for consulting on testing D. melanogaster .We also appreciate the deputy of research affairs of SUMS and , Kazerun Branch, Islamic Azad University for providing a part of facilities.