Spontaneous and benzo[a]pyrene-induced micronuclei in the embryos of the black-headed gull (Larus ridibundus L.)

The spontaneous levels of micronuclei in erythrocytes were established in embryos of the black-headed gull of two natural populations. In total 216 blood samples from the same number of individuals were examined. A statistically significant decrease in the number of spontaneous micronucleated erythrocytes was found after 13 days of incubation. We found no statistically significant difference in the spontaneous frequencies of micronucleated erythrocytes in the embryos of the two colonies studied, although they differed in anthropogenic load. Results of analysis of variance indicated that egg incubation time was the only variable significantly (P=0.0001) affecting spontaneous frequency of micronucleated erythrocytes in the embryos of black-headed gulls. We also took 78 eggs of different developmental stages from both colonies and exposed them for a further 24h to a dose of benzo[a]pyrene (30 microg per egg). After exposure to benzo[a]pyrene, the frequency of micronucleated erythrocytes was not increased in the embryos incubated for a total period of 13 days. A statistically significant increase in the number of micronucleated erythrocytes was recorded in the benzo[a]pyrene-treated embryos incubated for a total period of 14 days. Decrease in numbers of spontaneous micronucleated erythrocytes after the 13 day of incubation and increased levels of benzo[a]pyrene-induced micronuclei after the 13 day of incubation were discussed to be caused by changes in spleen and liver function in advanced developmental stages of the embryo.     

The micronucleus test with mouse spleen cells

The results of this study show that the micronucleus test can be carried out with mouse spleen cells as well as with cells from bone marrow. Polychromatic erythrocytes occurred in the spleen at a frequency of about 9% of the whole spleen cells compared with about 13% in the bone marrow. 3 test compounds were used to compare the frequency of micronuclei in cells from the 2 tissues. Mitomycin C and cyclophosphamide induced micronucleated polychromatic erythrocytes in both spleen and bone marrow. Fosfomycin, an antibiotic having a broad spectrum of antimicrobial activities, did not induce micronucleated erythrocytes in either organ.     

Computerized automated morphometric assay including frequency estimation of pentachlorophenol induced nuclear anomalies (micronucleus) in catfish Heteropneustes fossilis

An in vivo study of the effects of pentachlorophenol was carried out with a pre-acclimatized fish species, Heteropneustes fossilis, using four sub-lethal concentrations, 0.1, 0.2, 0.3 and 0.4 ppm, and three sampling times, 48, 72 and 96 h. Cytogenetic preparations were stained by the haematoxylin-eosin technique. The incidence of micronuclei was scored by a manual and an automated method. Small-sized micronuclei appeared in the cytoplasm in addition to the main nucleus. The frequency of micronucleated erythrocytes peaked at 4 days (96 h) exposure. The percentage of single micronuclei increased with longer exposures. The Mann-Whitney U test showed all micronuclei frequencies were significantly different from control (P<0.05). No statistical difference was observed between scores obtained by the manual and automated methods. A linear relationship between the percentage of micronucleated erythrocytes and dose was confirmed at all levels. Computer image analysis of morphological variations of erythrocytes indicated a 1:5 ratio of micronuclei and main nucleus accompanied by a reduction in cell volume by 600 dot units. Pentachlorophenol-mediated genotoxicity was confirmed in this fish for the first time. Possible consequences of genotoxicity and cytotoxicity are discussed.     

In vivo cytogenetic effects of cooked food mutagens

Using a variety of in vivo cytogenetic endpoints, we have investigated the effects of several compounds formed during the cooking of meat. C57Bl/6 mice were used to test for an increase in the frequency of sister-chromatid exchanges (SCEs), chromosomal aberrations, and micronucleated erythrocytes by 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx). 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx), and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). MeIQx and DiMeIQx did not induce SCEs in mouse bone marrow cells. PhIP induced sister-chromatid exchanges, but not chromosomal aberrations in bone marrow. In peripheral blood lymphocytes, PhIP did induce aberrations at 100 mg/kg, the highest dose tested. PhIP induced a low but significantly increased frequency of micronuclei in normochromatic but not polychromatic erythrocytes in bone marrow and peripheral blood. However, dose responses were not observed. With the exception of the SCEs induced by PhIP, these results contrast with observations made in vitro, where these compounds were found to have significant genotoxicity in mammalian cells and a very high mutation frequency in prokaryotic systems.     

Induction of micronuclei in BALB/c-3T3 cells by selected chemicals and complex mixtures.

The genotoxicity of benzo[a]pyrene, cyclophosphamide, 2-aminoanthracene, 2-nitrofluorene, nitrosated coal-dust extracts, and cigarette-smoke condensate were tested with the micronucleus assay using an established mammalian cell line. The results showed that all chemicals and complex mixtures studied induced micronuclei in BALB/c-3T3 cells. These results indicate that BALB/c-3T3 cells are capable of activating certain promutagens and procarcinogens. It seems, therefore, that in addition to cell transformation, the micronucleus assay in BALB/c-3T3 cells without an exogenous activation system may be useful for in vitro studies to detect genotoxic chemicals and complex mixtures.     

Genotoxicity of paraquat: micronuclei induced in bone marrow and peripheral blood are inhibited by melatonin

The ability of melatonin to influence paraquat-induced genotoxicity was tested using micronucleated polychromatic erythrocytes as an index of damage in both bone marrow and peripheral blood cells of mice. Melatonin (10 mg/kg) or an equal volume of saline were administered intraperitoneally (ip) to mice 30 min prior to an ip injection of paraquat (20 mg/kgx2), and thereafter at 6-h intervals until the conclusion of the study (72 h). The number of the micronucleated polychromatic erythrocytes increased after paraquat administration both in peripheral blood and bone marrow cells. Melatonin administration to paraquat-treated mice significantly reduced micronuclei formation in both peripheral blood and bone marrow cells; these differences were apparent at 24, 48 and 72 h after paraquat administration. The induction of micronuclei was time-dependent with peak values occurring at 24 and 48 h. The reduction in paraquat-related genotoxicity by melatonin is likely due in part to the antioxidant activity of the indole. We did not observe effects of melatonin over paraquat in paraquat+melatonin groups incubated at 0, 60 and 120 min. Mitomycin C, which was used as a positive control, also caused the expected large rises in micronuclei in both bone marrow and peripheral blood cells at 24, 48 and 72 h after its administration.     

Extended exposure of adult and fetal mice to 50 Hz magnetic field does not increase the incidence of micronuclei in erythrocytes.

The flow cytometer-based micronucleus assay was used to study the effects on chromosomes in erythroid cells of CBA/Ca mice after extended exposure to 50 Hz magnetic field (MF), 14 microT, peak-to-peak (p-p). The study included two different experiments: (a) mice exposed in utero during 18 days of their prenatal stage, and (b) adult mice exposed for 18 days. In experiment (a) 35 days after exposure was terminated, peripheral blood was drawn from the mice exposed in utero to determine whether the exposure had a genotoxic effect on the pluripotent erythroid stem cells. About 200000 polychromatic erythrocytes (PCE) and 200000 normochromatic erythrocytes (NCE) were analysed from each of 20 exposed mice. The EMF exposure did not significantly change the frequency of micronucleated PCE or NCE in comparison with 20 sham-irradiated mice. There was no difference in the proportion of PCE between exposed and unexposed animals. Similarly, in experiment (b) no differences were seen between EMF exposed and unexposed adult mice when samples of peripheral blood were taken at the end of exposure and analyzed for micronuclei in PCE and NCE. The proportion of PCE was the same in both groups. The results indicate that exposure to EMF does not induce direct or indirect effects on chromosomes in erythroid cells expressed as increased levels of micronucleated erythrocytes of mice. No indications of delayed genetic effects were found.     

Detection of micronuclei in peripheral blood of mitomycin C-treated mice using supravital staining with acridine orange.

The induction of micronuclei in peripheral blood from mitomycin C (MMC)-treated mice was examined using a supravital acridine orange staining method. Male ICR mice were intraperitoneally given MMC at a single dose of 0.25, 0.5, 1, or 2 mg/kg. Blood was sampled from the tail 24, 48, 72, and 96 h after treatment, and the frequency of micronucleated reticulocytes (MNRETs) was examined. The induction of MNRETs peaked at 48 h after treatment with MMC; there was a clear, dose-related increase in MNRETs. In a multiple-treatment study, mice were treated with 4 consecutive daily injections of MMC at a dose of 0.13, 0.25, 0.5, or 1 mg/kg. The frequency of MNRETs increased markedly 24 h after the second treatment as compared with the first treatment, and did not change significantly until 24 h after the fourth treatment. The frequency of MNRETs decreased to approximately control values 96 h after the last treatment. In addition, a slight but statistically significant increase in the number of micronucleated normochromatic erythrocytes in peripheral blood was detected by means of Giemsa staining 7 days after the last treatment. These results confirm the usefulness of the supravital acridine orange staining method to evaluate micronucleus induction in mouse peripheral blood.     

The role of short-lived lesions in the induction of micronuclei in rat liver by ethylnitrosourea and methyl methanesulphonate: the importance of experimental design

Rats received single injections of ethylnitrosourea (ENU) or methyl methanesulphonate (MMS) at the peak of DNA synthesis after partial hepatectomy. Hepatocytes were isolated 1–4 days later, and analysed for presence of micronuclei. With both chemicals, frequencies of micronucleated hepatocytes were increased in a dose-dependent manner, but ENU proved to be both more effective (6 times; based on molar dose) and more efficient (18 times; based on total DNA alkylation) than MMS.

In general, the micronucleus frequency was relatively low at 1 day after injection, then increased to reach a maximum at days 2 or 3 (depending on the dose), after which it decreased strongly in the case of MMS or remained stable in the case of ENU. The result with ENU is interpreted as a balance between loss and/or dilution of micronucleated hepatocytes and simultaneous formation of new ones. The present observations are in line with our earlier conclusion that ENU, in contrast with MMS, is able to induce persistent preclastogenic lesions in rat hepatocytes.

ENU also proved to be more effective and efficient than MMS with respect to the formation of micronuclei in bone marrow cells. Our results with ENU and MMS indicate that administration of the genotoxin at the peak of DNA synthesis after partial hepatectomy, instead of before hepatectomy, increases the sensitivity of the liver micronucleus assay at least in the case of directly acting chemicals.     

Density-gradient enrichment of newly-formed mouse erythrocytes. Application to the micronucleus test

To facilitate scoring micronuclei in peripheral blood erythrocytes, we have developed a centrifugation method to concentrate polychromatic and newly-formed normochromatic erythrocytes from microliter quantities of blood in a Percoll density gradient. Erythrocytes were separated into two discrete bands in a continuous gradient generated in situ in a microhematocrit capillary tube. The upper band contained white blood cells and a mixture of polychromatic and young normochromatic erythrocytes with a density of 1.080-1.082 g/ml. More than 75% of the polychromatic erythrocytes in samples of normal blood were recovered in the upper band. Older normochromatic erythrocytes migrated to the lower band. The frequency of polychromatic erythrocytes was increased from approximately 2% in whole blood to 60-80% in the upper band. After clastogen treatments, the elevated frequencies of micronuclei in the upper band polychromatic erythrocytes were similar to those in unfractionated blood. The frequencies of micronucleated normochromatic erythrocytes in the upper band were higher than those in whole blood at 48, 72 and 96 h after clastogen treatment, consistent with the expectation that the low-density normochromatic cells are newly derived from polychromatic erythrocytes. This density-gradient centrifugation technique enhances the efficiency of scoring micronuclei in the acute peripheral blood micronucleus test.     

The persistence of micronucleated erythrocytes in the peripheral circulation of normal and splenectomized Fischer 344 rats: implications for cytogenetic screening

Micronucleated erythrocytes are selectively removed from the peripheral circulation of normal rats. Splenectomy prevents this selective removal. In normal rats treated daily for 20 days with 0.2 mg/kg triethylenemelamine (TEM), micronucleated normochromatic (mature) erythrocytes did not accumulate in peripheral blood. In these same animals, the frequencies of micronucleated cells among polychromatic (newly formed) erythrocytes increased from 0.21 to 5.25 per thousand in peripheral blood and from 1.75 to 31.5 per thousand in bone marrow. Since both control and induced frequencies in peripheral blood were approximately 15% of those in bone marrow, the removal appears to be equally efficient for cells containing either spontaneously occurring or clastogen-induced micronuclei. In splenectomized rats treated daily for 11 days with 0.2 mg/kg TEM, the frequency of micronucleated normochromatic erythrocytes (NCEs) in the peripheral blood rose rapidly to 9 times the control value and remained elevated for 50-55 days, indicating a life span approximately equivalent to that of normal erythrocytes. Among splenectomized rats exposed to either 0.15 mg/kg triethylenemelamine, 6.5 mg/kg cyclophosphamide, or 300 mg/kg urethane for periods exceeding the erythrocyte life span, the incidences of micronucleated NCEs in the peripheral blood rose steadily from a control value of 1.0 per thousand to maximum values of 15.0, 12.7 and 8.9 per thousand, respectively. During these extended exposures, the mean frequencies of micronucleated polychromatic erythrocytes (PCEs) in peripheral blood increased from a spontaneous value of 0.9 per thousand to 23.0, 13.0 and 6.6 per thousand, respectively, reflecting the frequencies among PCEs in the bone marrow and approximating the maximum values among NCEs in the peripheral blood. Thus, the frequency of micronucleated erythrocytes in the peripheral blood of splenectomized rats can be used as an index of both acute and cumulative chromosomal damage, while in normal rats the use of peripheral blood for cytogenetic monitoring is restricted by the selective removal of these micronucleated cells.     

Radioprotective effects of Dragon's blood and its extract against gamma irradiation in mouse bone marrow cells

PurposeThe radioprotective effects of Dragon's blood (DB) and its extracts (DBE) were investigated using the chromosomal aberrant test, micronucleus and oxidative stress assay for anti-clastogenic and anti-oxidative activity.Materials and methodsAdult BALB/C mice were exposed to the whole body irradiation with 4 Gy ⁶⁰Co γ-rays. DB and DBE were administered orally once a day from 5 days prior to irradiation treatment to 1 day after irradiation. The mice were sacrificed on 24 h after irradiation. The cells of bone marrow were measured by counting different types of chromosomal aberrations and the frequency of micronuclei. Oxidative stress response was carried out by analysis of serum from blood.ResultsDB and DBE significantly decreased the number of bone marrow cells with chromosome aberrations after irradiation with respect to irradiated alone group. The administration of DB and DBE also significantly reduced the frequencies of micronucleated polychromatic erythrocytes (MPCE) and micronucleated normochromatic erythrocytes (MNCE). In addition, DB and DBE markedly increased the activity of antioxidant enzymes and the level of antioxidant molecular. Malondialdehyde (MDA) and nitric oxide (NO) levels in serum were significantly reduced by DB and DBE treatment.ConclusionsOur data suggested that DB and DBE have potential radioprotective properties in mouse bone marrow after ⁶⁰Co γ-ray exposure, which support their candidature as a potential radioprotective agent.     

Comparison of single-, double- or triple-exposure protocols for the rodent bone marrow/peripheral blood micronucleus assay using 4-aminobiphenyl and treosulphan

Two human carcinogens, 4-aminobiphenyl (4AB) and treosulphan (Treo), were tested in male B6C3F1 mice for the induction of micronuclei in bone marrow and peripheral blood cells by 1-, 2- and 3-exposure protocols. Both compounds tested positive. The magnitude of response with respect to the incidence of micronucleated polychromatic erythrocytes by 2- and 3-exposure protocols was considerably higher than by the single-exposure protocol. The peripheral blood results for Treo were as typically seen with a 24-h delay when compared to the bone marrow. The peripheral blood results for 4AB, however, differed from those expected. The incidence of MN-PCE in peripheral blood of animals exposed to 4AB was significantly greater than seen in the bone marrow in 2- and 3-exposure protocols. There was also an increase in the % PCE at the 60 mg/kg dose level as a function of time. Based on these studies, it is concluded that a step-wise scoring scheme may be the best protocol for rodent micronucleus assay, involving a 3-exposure protocol with single sampling of bone marrow (24 h after the last treatment) and two samplings of peripheral blood (24 h and 48 h after the first treatment). This approach is cost-effective, it limits the number of animals required and provides maximum sensitivity.     

The evaluation of a multiple dosing protocol for the mouse bone-marrow micronucleus assay using benzidine and 2,6-xylidine

Male ICR mice were treated with 1, 2 or 3 daily doses of either benzidine or 2,6-xylidine. Groups of 5 animals were sacrificed 24 h after the last dose and the bone marrow examined for micronuclei. Benzidine was given at dose levels of 40 and 200 mg/kg and 2,6-xylidine was given at dose levels of 75 and 375 mg/kg. These doses represent 10 and 50% of the respective median lethal doses. Benzidine produced a significant (p less than 0.001) dose related increase in the incidence of micronucleated polychromatic erythrocytes (MPE), while 2,6-xylidine had no effect on the frequency of micronucleated cells. Statistical analyses of the data indicated that the incidence of MPE was independent of the number of doses administered prior to bone marrow harvest.     

Evaluation of nongenotoxic and genotoxic factors modulating the frequency of micronucleated erythrocytes in the peripheral blood of mice

The hematological micronucleus test is regarded as an indicator of the clastogenic effect of chemicals and acute cytogenetic damage. The test can be carried out in red blood cells of the bone marrow and of the spleen, as well as in peripheral erythrocytes. We have determined the precise background values of micronucleated red blood cells for the peripheral blood of BALB/c, DBA/2, and NMRI mice. Bleeding, phenylhydrazine-induced hemolysis, and splenectomy generated an increase of micronucleated erythrocytes in the peripheral blood of mice. Our data thus demonstrate that such factors should be taken into consideration when the micronucleus test is used for screening the genotoxic potential of chemicals. Furthermore, the micronucleus-inducing effect of cyclophosphamide was studied in normal and splenectomized mice and, in addition, a comparison of the sensitivity of the micronucleus test was carried out in peripheral blood and bone marrow after cyclophosphamide treatment. Our data demonstrate that the kinetics of micronucleus formation were similar in normal and in splenectomized mice in which the micronucleus levels had returned to normal. The comparison of micronucleus formation in bone marrow and peripheral blood after cyclophosphamide treatment revealed the generation of similar quantities of micronucleated red blood cells in both tissues. The physiological mechanisms of micronucleus formation and removal and the potential role of chemically induced spleen damage during this process are discussed; the usefulness of the peripheral micronucleus test as a simple, rapid, and animal-saving modification of the standard bone marrow test is evaluated.Abbreviations CP cyclophosphamide - MN micronuclei - MNCE micronucleated normochromatic erythrocytes - MNPCE micronucleated polychromatic erythrocytes - MNRBC micronucleated red blood cells - NCE normochromatic erythrocytes - PCE polychromatic erythrocytes     

Evaluation of nongenotoxic and genotoxic factors modulating the frequency of micronucleated erythrocytes in the peripheral blood of mice

The hematological micronucleus test is regarded as an indicator of the clastogenic effect of chemicals and acute cytogenetic damage. The test can be carried out in red blood cells of the bone marrow and of the spleen, as well as in peripheral erythrocytes. We have determined the precise background values of micronucleated red blood cells for the peripheral blood of BALB/c DBA/2, and NMRI mice. Bleeding, phenylhydrazine-induced hemolysis, and splenectomy generated an increase of micronucleated erythrocytes in the peripheral blood of mice. Our data thus demonstrate that such factors should be taken into consideration when the micronucleus test is used for screening the genotoxic potential of chemicals. Furthermore, the micronucleus-inducing effect of cyclophosphamide was studied in normal and splenectomized mice and, in addition, a comparison of the sensitivity of the micronucleus test was carried out in peripheral blood and bone marrow after cyclophosphamide treatment. Our data demonstrate that the kinetics of micronucleus formation were similar in normal and in splenectomized mice in which the micronucleus levels had returned to normal. The comparison of micronucleus formation in bone marrow and peripheral blood after cyclophosphamide treatment revealed the generation of similar quantities of micronucleated red blood cells in both tissues. The physiological mechanisms of micronucleus formation and removal and the potential role of chemically induced spleen damage during this process are discussed; the usefulness of the peripheral micronucleus test as a simple, rapid, and animal-saving modification of the standard bone marrow test is evaluated.Abbreviations CP cyclophosphamide - MN micronuclei - MNCE micronucleated normochromatic erythrocytes - MNPCE micronucleated polychromatic erythrocytes - MNRBC micronucleated red blood cells - NCE normochromatic erythrocytes - PCE polychromatic erythrocytes     

Induction of micronuclei by vinyl acetate in mouse bone marrow cells and cultured human lymphocytes

A dose-dependent increase in micronucleated polychromatic erythrocytes was observed in the bone marrow of male C57B1/6 mice 30 h after a single intraperitoneal injection of vinyl acetate (250, 500, 1000 or 2000 mg/kg b.wt.; (9-14 animals per group). The effect was statistically significant at 1000 mg/kg (1.33 +/- 0.29% vs. 0.6 +/- 0.10% in olive oil-treated controls) and at 2000 mg/kg (1.57 +/- 0.19%) of vinyl acetate. These doses were fatal to 6 (1000 mg/kg) and 8 (2000 mg/kg) out of 14 animals in both groups. The ratio of polychromatic to normochromatic cells decreased as a function of vinyl acetate dose. Cyclophosphamide (20 mg/kg), used as a positive control chemical, induced a clear increase in micronucleated polychromatic erythrocytes (2.07 +/- 0.20%). None of the treatments affected the number of micronuclei in normochromatic erythrocytes. In human whole-blood lymphocyte cultures, micronucleus induction by a 48-h treatment with vinyl acetate (0.125, 0.25, 0.5, 1 and 2 mM; 24 h after culture initiation) was studied in lymphocytes with preserved cytoplasm from smear slides prepared by a method involving the removal of erythrocytes at harvest by sodium cyanide treatment to improve preparation quality. The frequency of micronucleated lymphocytes reached a peak at 0.5 mM (3.2 +/- 1.0% vs. 0.9 +/- 0.1% in control cultures) and 1 mM (3.1 +/- 0.7%), with a decline at 2 mM probably because of a toxic effect resulting in mitotic inhibition.     

The induction of chromosomal damage in rat hepatocytes and lymphocytes I. Time-dependent changes of the clastogenic effects of diethylnitrosamine,dimethylnitrosamine and ethyl methanesulfonate

Male Wistar rats received a single injection of diethylnitrosamine (DEN), dimethylnitrosamine (DMN) or ethyl methanesulfonate (EMS). After a number of time intervals (up to 56 days) liver cells were assayed for the presence of possible preclastogenic damage by performing partial hepatectomy and subsequent analysis of chromosomal damage (micronucleus formation) in isolated hepatocytes. Peripheral blood lymphocytes from the same animals were collected, stimulated to proliferate and assayed for the frequency of sister-chromatid exchanges (SCEs). Whereas all agents significantly increased frequencies of SCEs in lymphocytes up to at least 28 days (EMS) or 56 days (DMN, DEN) after injection, only the latter 2 compounds gave rise to significantly increased incidences of micronucleated hepatocytes. DMN-induced preclastogenic damage in hepatocytes was lost between 28 and 56 days after injection. After DEN, this type of damage was persistent over the entire experimental period (56 days).When rats treated with DEN did not undergo partial hepatectomy, the frequencies of micronuclei at different time intervals after treatment were at control level. This result, together with those from hepatectomized DEN-treated rats, suggests that it is the persistent character of the preclastogenic damage that is responsible for the occurrence of micronucleated hepatocytes at later time intervals after treatment with DEN, rather than the stability of micronuclei which might eventually have been formed soon after injection.     

Cytogenetic effects of acrylamide in the bone marrow of mice

A single i.p. injection of 100 mg/kg acrylamide monomer elevated the frequency of chromosome aberrations and micronucleated polychromatic erythrocytes in the bone marrow of male ICR mice. A positive relationship between frequency of micronuclei and dose of acrylamide was obtained in the dose range of 2 x 25, 2 x 50 and 2 x 100 mg/kg.     

Effects of long term low dose acrylamide exposure on rat bone marrow polychromatic erythrocytes

Abstract

I investigated whether long term low dose exposure to acrylamide increased micronucleus frequency in rat bone marrow polychromatic erythrocytes (PCEs). Twenty-five male and 25 female Wistar rats were used. Animals of each sex were segregated into two treatment groups and one control group. Each treatment group consisted of ten animals and each control group consisted of five animals. Acrylamide, 2 or 5 mg/kg/day, was administered to the treatment groups in their drinking water for 90 days. Twenty-four hours after the last treatment, bone marrow samples were obtained and analyzed for the frequency of micronucleated polychromatic erythrocytes (MNPCEs). The cytotoxic effect of acrylamide on bone marrow also was tested by assessing the polychromatic erythrocyte/normochromatic erythrocyte (PCE/NCE) ratio. Both doses of acrylamide significantly increased the frequency of MNPCEs in both male and female rats. Acrylamide also decreased the PCE/NCE ratio in both sexes compared to the control group. My study showed that chronic low dose exposure to acrylamide increased the formation of micronuclei in PCEs of male and female rat bone marrow.