The effects of the simultaneous administration of Methylphenidate and Nicotine on the structure and function of testicular tissue in adult rats

 Exposure to different xenobiotics can affect the male reproductive system by making structural and functional changes in testicular tissue (Aitken and Roman 2008). The changes in the cellular structure of testicular tissue are associated with varying degrees of infertility (Aitken and Roman 2008). Methylphenidate is an amphetamine derivative which used for treatment of ADHD syndrome (Kraus and Burch 1992 and Levin and Kleber 1995 and Doskoch 2002 and Cansu et al 2010). Long-term administration of methylphenidate has been associated with changes in testicular tissue and sperm population. Nicotine is a toxic alkaloid that available in a wide range of population through different forms (Miranda-Spooner et al 2016). The negative effects of nicotine on spermatogenesis and decreased sperm quality have been reported (Mosadegh et al 2017). Experimental studies in humans and laboratory animals have shown that the use of stimulant compounds such as methylphenidate and amphetamine derivatives increases the tendency to consume nicotine-containing products (Wooters et al 2008). Given the importance of above mentioned subject and the negative effects of nicotine (as a gonadotoxic composition) and methylphenidate on the reproductive system, in this study the effects and the complications of the long-term exposure to methylphenidate and nicotine in the form of simultaneous administration were evaluated on the structure and the function of testicular tissue in animal model of adult rats.

 Methylphenidate (10 mg/kg b.w.) (Geha et al 2000) and Nicotine (4 mg/kg b.w.) (Nesseim et al 2010) were administrated intraperitoneally once a day for eight weeks in adult rats. The animals were divided into control and three treatment groups: 1) methylphenidate administrated group; 2) nicotine administrated group and 3) methylphenidate+nicotine administrated group. At the end of the eight weeks, the blood sampling was performed for measurement of the blood levels of pituitary gonadotropins (follicle stimulating hormone and luteinizing hormone) and testosterone. Plasma lipid peroxidation (malondialdehyde) assay was performed on the blood samples Briefly, testicular tissues were homogenized in KCl. Measurement of tissue and plasma malondialdehyde (MDA) levels were quantitatively carried out base on the MDA-TBA (thiobarbituric acid) complex formation (Katoh et al 2002). The animals were euthanized and the body and testicular weight were recorded. Testicular tissue samples were fixed in 10% formaldehyde solution and paraffin embedded tissue were prepared for histomorphometrical study and evaluation of microscopic indices of spermatogenesis. For morphometric assessment of seminiferous tubules, the slides were studied at 200× magnification. To get extra precise results, only the seminiferous tubules (STs) that sectioned transversely were studied and the shortest diameter of seminiferous tubules was considered for measurement. For every one animal, three microscopic slides from different parts of testicular tissue were prepared and 200 tubules were studied. For estimation of spermatogenesis in testicular tissue, three different indices were used. Tubular differentiation index (TDI), repopulation index (RI) and spermiogenesis index (SPI). To determine the tubular differentiation index, the number of seminiferous tubules with more than three layers of germinal cells derived from type A of spermatogonia was calculated. To find out the repopulation index, the ratio of active spermatogonia (with euchromatic nucleus) to inactive ones (with dense heterochromatic nucleus) was evaluated. The ratio of the number of seminiferous tubules with spermatozoids to the empty tubules, were calculated for spermiogenesis index (Miskowiak et al 1998 and Shetty et al 2000). The sperm analysis was performed on the epididymal tissue. For analyses of sperm, the cauda epididymis was separated from testis and cut into small pieces into one milliliter of Ham’s F10 culture medium. The epididymal sperm count was evaluated by hemocytometer with light microscope at ×400 magnification. Sperm motility was assessed with a phase contrast microscope at ×400 magnification. In average 10 microscopic fields were observed and the mean of counted sperms was considered as sperm motility for each rat (Wyrobek et al 1983). The results were analyzed using the GraphPad PRISM®</sup> software version 5.04 (GraphPad Software, Inc. USA). All data were reported as mean (SD). The comparison of the means between experimental groups was evaluated by one way-ANOVA method followed by Tukey’s multiple comparison tests. Differences were considered to be statistically significant if P< 0.05.

 The results showed that, the administration of methylphenidate and nicotine separately or simultaneously induce various structural and functional changes in testicular tissue compared to control group. There was no significant difference in body weight between experimental groups (P<0.05). The mean of testicular weight was reduced in all treated groups in comparison to control group. The ratio of testicular/body weight was decreased in treated groups compared to control group. The separate administration of methylphenidate and nicotine was led to elevation of the blood FSH levels (P=0.002) and decrement of the blood LH levels (P=0.008). Whereas, the coadministration of these compounds led to increase of the blood LH levels. The mean of the blood testosterone levels was increased in all treated groups in comparison to control group (P=0.0002). This elevation of the blood testosterone levels was observed in separately treated groups. The mean of the serum malondialdehyde was increased in treated groups compared to control group (P=0.25). The most elevation of serum malondialdehyde levels was observed in nicotine treated animals.  Histomorphometrical studies indicate various structural changes in testicular tissue such as increasing of the capsule thickness, reduction of tubular diameter, decrease of the height of germinal epithelium. All microscopic indices of spermatogenesis were reduced in treated groups in comparison to control group (P<0.0001). Accordingly, the lowest indices of spermatogenesis were observed in nicotine administrated group. All sperm analysis indices were reduced in treated groups in comparison to control group. The lowest mean of epididymal sperm population and sperm motility and viability was observed in nicotine treated group and methylphenidate+nicotine administrated group consequently (P<0.0001).

 In conclusion, nicotine and methylphenidate induces testicular tissue damage with different mechanisms. However, the results of this study showed that the simultaneous administration of methylphenidate and nicotine could exacerbate the structural and functional alterations of testicular tissue. Moreover, the comparison of the results between treated groups expresses the greater and stronger portion of nicotine in inducing of alterations in testicular tissue structure and function.