formaldehyde is an environmental pollutant that is extensively soluble in water and has a sharp odor ( 1 ) . the liquid form of formaldehyde , which usually is a 37% solution of formaldehyde in distilled water , is called formaldehyde , whereas the solid form is known as paraformaldehyde ( 2 ) . as estimated by the national institute for occupational safety and health ( niosh ) , the permissible exposure limit for formaldehyde in all workplaces is in the range of 1.53 mg / m ( 3,4 ) . however , many studies have demonstrated that the formaldehyde levels in occupational sites are higher than this limit . formaldehyde has a high propensity for reacting with rna , dna , and protein , which leads to health problems ( 5 , 6 ) . many people are exposed to formaldehyde in industrial laboratories , such as those in which wood , plaster , textiles , paper , ink , and leather are utilized . in addition , anatomists and pathologists are affected by formaldehyde as a fixative ( 2 ) . formaldehyde also is found in cigarette smoke , domestic air , deodorants , home cleaning agents , toothpaste , and cosmetic products . thus , exposure to formaldehyde for everyone is possible at any time ( 2 ) . formaldehyde has toxic effects on the skin , eyes , respiratory tract , urogenital system , and the nervous system ( 2 , 7 9 ) . some studies have been shown that formaldehyde can cause a high level of reactive oxygen species ( ros ) . however , there are very few studies concerning the effect of antioxidant treatment on histopathological changes of the cerebellum caused by formaldehyde toxicity . therefore , this study was designed to assess the protective effects of selenium against the neuronal damage caused by formaldehyde . experiments were conducted using adult male naval medical research institute ( nmri ) mice . regarding our current state of knowledge , there is very little information in the literature concerning the effects of formaldehyde on the cerebellum or the protective effects of antioxidants . also , females hormones have an effect on the results , so adult male mice were used for this study . they were kept in polypropylene cages at the temperature 24c , 45% relative humidity , and 12-h light and dark cycles with free access to drinking water and food . possible confounding factors in this study were the weight , age , environment , water , and food of the mice . however , these conditions were identical for all of the mice , and we controlled any confounding factors . the mice in group ii received 10 mg / kg of formaldehyde intraperitoneally ( ip ) once daily for 14 days . groups iii  vi were injected ip with selenium ( 0.1 , 0.2 , 0.4 and 0.8 mg / kg ) plus formaldehyde . at the end of the two - week experimental period , all of the mice were killed , and their brains were obtained for histological examination . the cerebellum specimens were embedded in paraffin wax , sectioned with 5- thicknesses , and stained with haematoxylin the images were captured by an olympus ( japan ) light microscope under a 40x objective lens . the software was used to investigate the following parameters , i.e. , the thickness of the granular , molecular , and purkinje layers , the number cells in the gray matter of the cerebellum , the thickness of the white matter , and comparative information concerning the gray matter and white matter in the mice s cerebellums . , and all data were analyzed using spps software version 20.0 and one - way analysis of variance ( anova ) . a value of p < 0.05 was considered to be significant . the morphology of the neurons in the cerebellum tissue of the control group had a normal appearance ( figure 1a ) . after formaldehyde treatment , the number of purkinje cells , the number of granular cells , and the thickness of the granular layer were less than those of the control mice ( p < 0.05 ) . in addition , the mice in the group treated with formaldehyde had dissociation of the purkinje cells from the granular layer , which was not observed in the control mice . in selenium treatment group ( 0.1 mg / kg ) , the thickness of the molecular layers was significantly greater than those of the control mice , i.e. , 642.75  198.25  vs. 528.59  111.45 . also , the thickness of granular layer of cerebellum was higher in this group than in the control group ( 556.24  187.92  vs. 452.71  127.35  ) . treatments with selenium at dose of 0.1 mg / kg resulted in a greater number of purkinje cells than existed in the controls ( fig . however , selenium at the dose of 0.1 mg / kg resulted in a decrease in the height of the purkinje cells . our results indicated that treatment with selenium at the optimum dose ( 0.1 mg / kg ) can protect against the neuronal damage induced by formaldehyde in the cerebellum tissue . formaldehyde has adverse effects on several different systems , and this is especially true for the central nervous system . various reports have indicated that exposure to formaldehyde can cause headaches as well as mental , memory , and sleep disorders . also , it has been shown to cause sensory - emotional and balance disorders in exposed employees in industries and hospitals ( 13 ) . it has been shown that formaldehyde is a substrate for the cytochrome p-450 monooxygenase system s 2e1 isozyme , which can activate such enzymes as peroxidase , aldehyde oxidase , and xanthine oxidase , resulting in increased formation of reactive oxygen species . antioxidants have a critical role in scavenging free oxygen radicals in the tissues of the body . for example , zararsiz et al . reported that the daily treatment of rats with 400 mg / kg of omega -3 fatty acids decreased cellular damage in the hippocampus and prefrontal tissue . in addition , the administration of omega-3 fatty acids increased superoxide dismutase and reduced malondealdehyde levels ( 13 ) . several studies have shown that low concentration of formaldehyde can stimulate neurons , whereas high levels act as a depressant on the nervous system ( 13 ) . in a study by kabuto and colleagues , it was found that the administration of melatonin , a well - known antioxidant , reversed the negative effects that were observed in rats that were exposed to formaldehyde ( 14 ) . also , gurelet et al . reported that 300 mg / kg of vitamin e significantly reduced the neuronal damage caused by exposure to formaldehyde ( 15 ) . degenerative damage and dark neurons were observed in the mice that were exposed to formaldehyde . these damages were significantly less in the antioxidant - treated group than those in the formaldehyde group . in addition , the number of the neurons was greater in the antioxidant - treated group than in the formaldehyde group ( 15 ) . in our study , the formaldehyde - induced changes in the cerebellum were reversed by selenium treatment as an antioxidant . the administration of selenium in the amount of 0.1 mg / kg resulted in a significant increase in the number of neurons in the molecular layer and increased the thicknesses of the granular and molecular layers . one limitation of this was study was that we did not have sufficient financial support to acquire biochemical findings in parallel with the histopathological evaluations . the results of this study showed that formaldehyde caused a reduction in the numbers and sizes of purkinje cells and granular cells ; in addition , the thickness of the granular layer was thinner than that in the control mice . the administration of selenium at a level of 0.1 mg / kg resulted in an increases number of purkinje cells and an increase in the area of the gray matter . this means that there was a protective effect of n - acetyle cysteine against formaldehyde - induced damage , which demonstrated its potential for clinical use . our results indicated that the administration of selenium at the level of 0.1 mg / kg for 14 days prevented formaldehyde - induced neural damage in mice . also , we recommend that the mechanisms by which n - acetyle cysteine prevents neuronal damage be assessed in a future study .
background : formaldehyde is used in medicine and industry , and it is known to have detrimental effects on various systems including the nervous system , by increasing oxidative stress . 
 however , data are scarce related to substances that can protect against the neurotoxicity induced by formaldehyde . 
 therefore , this study was designed to assess the protective effects of selenium against the toxic effect of this compound.methods:a total of 48 adult male mice were divided randomly into six groups , i.e. , ( 1 ) control , ( 2 ) treated with formaldehyde , ( 3 ) treated with formaldehyde plus 0.1 mg / kg selenium , ( 4 ) treated with formaldehyde plus 0.2 mg / kg selenium , ( 5 ) treated with formaldehyde plus 0.4 mg / kg selenium , and ( 6 ) treated with formaldehyde plus 0.8 mg / kg selenium . at the end of 14 days , the cerebellums were removed for histological evaluation . 
 morphological changes were examined using image j software . 
 the data were analyzed using spss software version 20.0 and analysis of variance ( anova).results : formaldehyde caused a reduction in the numbers and sizes of purkinje cells and granular cells ; in addition , the thickness of the granular layer was thinner than that in the control mice ( p < 0.05 ) . 
 treatment with 0.1 mg / kg selenium resulted in an increase in the number of purkinje cells as well as the area of the gray matter compared to those of the control mice.conclusion:formaldehyde-induced neuronal damage was prevented by the administration of 0.1 mg / kg selenium , hence this treatment shows therapeutic potential for the treatment of neurotoxicity