Fetal programming of adult hypertension in female rat offspring exposed to androgens in utero

Aims

The influence of prenatal factors on the development of arterial hypertension has gained considerable interest in recent years. We examined the effects of prenatal testosterone treatment on blood pressure in adult female rats. Further, to define the mechanisms whereby blood pressure may be raised, we examined vascular endothelial function and nitric oxide synthesis.

Methods and Results

Testosterone propionate (0.5 mg/kg/day; SC) or vehicle was administered to pregnant Sprague-Dawley rats from gestational day 15-19. Maternal feed intake and plasma levels of steroid hormones were measured in the dams. In the female offspring, birth weight, growth rate, blood pressure, vascular reactivity, eNOS expression, and nitric oxide production were examined. In the pregnant rats, testosterone-treatment increased plasma testosterone levels by 2-fold without any significant changes in 17β-estradiol, progesterone and corticosterone levels. Testosterone-treatment did not affect maternal feed intake. The pups born to testosterone mothers were smaller in size but exhibited catch-up growth. The blood pressure in the testosterone offspring at 6 months of age was significantly higher compared to controls. Endothelium-intact mesenteric arteries from testosterone group exhibited increased contractile responses to phenylephrine, decreased vasodilation to acetylcholine and unaltered responses to sodium nitroprusside in comparison to control rats. Testosterone rats demonstrated decreased expression for eNOS, and reduced nitric oxide production.

Conclusions

Our data show that elevated plasma maternal testosterone levels: (1) causes low birth weight followed by catch-up growth and hypertension in female offspring and (2) alters endothelium-dependent vascular responses. The endothelial dysfunction is associated with decreased activity/expression of eNOS.     

Disruption of brain development in male rats exposed prenatally to 5-bromo-2'-deoxyuridine

ABSTRACT  Sprague-Dawley rats were treated intraperitoneally with 5-bromo-2'-deoxyuridine (BrdU) at 0,12.5 or 50 mg/kg/day on days 9 through 15 of gestation to evaluate the effects on development of the brain of offspring. Prenatal exposure to BrdU induced abnormal development of the brain; dilatation of the lateral ventricles in male offspring in the postnatal period. The ratio of the length of the longitudinal fissure to that of the cerebral cortex decreased in a dose-dependent manner in the embryonic period and thereafter. In 14-week-old male offspring exposed prenatally to BrdU at 50 mg/kg, the cortex layer of the cerebrum was thinner than that of the controls. Masculine sexual behavior was markedly impaired and the volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) was decreased in the 50 mg/kg group as compared with the controls. These results demonstrate that prenatal exposure to BrdU affected the development of the brain hi the prenatal and postnatal stages and reduced the volume of SDN-POA after puberty, resulting in a disruption of reproductive ability in male rats.     

Cardiovascular malformations induced by prenatal exposure to phenobarbital in rats

The effects of prenatal exposure to phenobarbital (PB) on the cardiovascular system were examined in rat fetuses and pups. PB was administered at a dose of 80 or 120 mg/kg/day by gavage to Sprague Dawley (SD) rats on two consecutive gestational days (GD): 7-8, 8-9, 9-10, or 10-11. Fetuses were examined for cardiovascular malformations on GD 20. In addition, pups were examined for PB-induced cardiovascular malformations. Incidences of ventricular septal defect (VSD), overriding aorta, double outlet right ventricle and transposition of great arteries were significantly increased in the fetuses whose dams were administered PB at 120 mg/kg on GD 8-9, 9-10 or 10-11. GD 8-11 was the critical period for the cardiovascular malformations associated with administration of PB in rats. Various types of cardiovascular malformations were detected in pups from the PB-administered dam. Severe cardiovascular malformations induced by PB caused deaths on early postnatal days. However, slight malformations such as isolated VSD persisted until weaning, and did not affect postnatal viability.     

Growth hormone and insulin-like growth factor-I therapy promote protein deposition and growth in dexamethasone-treated piglets

BACKGROUND: Dexamethasone treatment facilitates the weaning of premature infants from mechanical ventilation but impairs protein homeostasis, lean tissue deposition, and growth. The current study was conducted to investigate whether dexamethasone mediates these effects by reducing protein synthesis or elevating protein breakdown, and whether adjuvant growth hormone+/-insulin-like growth factor-I therapy can attenuate such effects. METHODS: Piglets (n = 24) were randomized to placebo, a tapered course of dexamethasone (0.5, 0.3, 0.2 mg/kg per day for 5, 5 and 4 days each, respectively), dexamethasone + growth hormone 0.1 mg/kg per day, or dexamethasone + growth hormone + insulin-like growth factor-I 0.1 mg/kg per day for 14 days. On day 13, 15N-glycine was administered as a single oral dose, and urine was collected at timed intervals during the subsequent 48 hours. RESULTS: Total urinary N and cumulative 15N excretion were higher in all dexamethasone groups than in control subjects. Protein synthesis was suppressed, whereas protein breakdown was unaltered by dexamethasone. Adjunctive growth hormone+/-insulin-like growth factor-I therapy enhanced protein synthesis, but only combined therapy improved net protein gain compared with dexamethasone alone. Higher circulating insulin-like growth factor-I may have mediated the greater net protein gain. Blood urea nitrogen was elevated in all dexamethasone-treated groups at days 6 and 11 but was normalized by day 15 with adjunctive growth hormone+/-insulin-like growth factor-I. From a functional perspective, both adjunctive growth hormone and growth hormone+/-insulin-like growth factor-I partially attenuated the dexamethasone-induced reduction in weight and length gain but not in whole body lean and fat mass. Conclusion: Adjunctive growth hormone+/-insulin-like growth factor-I therapy partially reverses the dexamethasone-induced reduction in protein synthesis, resulting in improved growth when given concurrently with a low tapering dose of dexamethasone.     

Effects of in utero exposure to 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) on somatic growth and endocrine status in rat offspring

Exposure to polychlorobiphenyl (PCB) mixtures at an early stage of development has been reported to affect endocrine glands; however, little is known about the precise toxicological properties of individual PCB. The present study was undertaken to determine whether prenatal exposure to 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153), a di-ortho-substituted non-coplanar congener, affects postnatal development in rat offspring. Pregnant Sprague-Dawley rats (Crj: CD (SD) IGS) were given PCB 153 (0, 16, or 64 mg/kg/day) orally from gestational day (GD) 10 through GD 16, and developmental parameters in the male and female offspring were examined. We found no dose-dependent changes in body weight, body length (nose-anus length), tail length, or the weights of kidneys, testes, ovaries and uterus in offspring at 1 or 3 weeks of age. Liver weights were increased in the PCB 153-treated groups, although we observed a significant difference only in males. Anogenital distance was unaffected in the PCB 153-treated groups. We observed a significant dose-dependent decrease in the plasma concentrations of thyroxine and tri-iodothyronine, whereas those of thyroid-stimulating hormone were not significantly changed. In addition, there were no dose-dependent changes in plasma concentrations of growth hormone and insulin-like growth factor-I in any dose group. These findings suggest that prenatal exposure to PCB 153 (GD 10-16, 16-64 mg/kg/day) may alter the thyroid status in rat offspring to some extent without affecting somatic growth or its related hormonal parameters.     

Effects of oral administration of insulin-like growth factor-I on circulating concentration of insulin-like growth factor-I and growth of internal organs in weanling mice

Insulin-like growth factor (IGF)-I is a polypeptide that mediates the growth-promoting action of growth hormone in postnatal animals. The present study was conducted to examine whether orally administered IGF-I would be absorbed into the general circulation and also whether ingested IGF-I would enhance the growth of whole body as well as internal organs, and tissues in 3-week-old ICR-strain female weanling mice. In experiment (Exp) 1, a total of 70 mice received IGF-I orally at 1 microg.g-1 in 0.2-ml PBS or the vehicle alone. Concentrations of IGF-I and glucose in heart blood were measured after killing 5 animals in each group every fourth hour during a 24-hour period. In Exp 2, a total of 40 mice received oral IGF-I administration at 1 microg.g-1 or vehicle every third day beginning from day 0 for a 13-day period. Half the animals were killed at day 7 and the other half at day 13. Weights of whole body and organs/tissues (small intestine, liver, thigh muscle, and brain) were measured every day and at slaughter, respectively. In Exp 1, following the oral IGF-I administration, serum IGF-I concentration increased at hour 4 (p<0.01) and returned to the hour 0 level by hour 8, whereas glucose concentration was lowest at hour 4 and returned to the hour 0 level by hour 16. In the PBS-fed group, neither IGF-I nor glucose concentration changed during the 24-hour period. In Exp 2, weight of small intestine increased (p<0.05) in response to the oral IGF-I, whereas weights of liver and thigh muscle of the IGF-I-fed group were greater (p<0.01) and tended to be greater (p=0.06), respectively, than those of the PBS-fed only at day 13. However, brain weight and serum concentrations of IGF-I and IGF-II were not affected by oral IGF-I administration. Results suggest that although orally administered IGF-I mainly acts at the intestine, a portion of ingested IGF-I is absorbed into the general circulation to enhance the growth of selective organs/tissues in weanling mice.     

Cleft lip and palate in mice treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin: a morphological in vivo study

It is well-known that TCDD (2,3,7,8, tetrachloridedibenzo-p-dioxin) induces cleft palates (CPs) in pregnant C57BL mice. However, it is unclear if TCDD is a possible teratogen for cleft lip. We examined maxillofacial malformations including cleft lip in three animal strains: A/J mice, C57BL/6J mice and ICR mice. The A/J mouse develops cleft lip and palate spontaneously at a 5-10% rate. TCDD was administered in olive oil on gestation day (GD) 12.5 with gastric tubes at 10 microg/kg, 20 microg/kg, or 40 microg/kg to examine the dose-response, and on a single day from GD 8.5-14.5 to examine the timing effects of TCDD administration on lip and palate formation. Furthermore, the palatal shelf movements during GD 8.5-14.5 were observed with a stereoscopic microscope. All embryos had cleft palates when the TCDD was administered just before palatogenesis (GD11.5-GD12.5). With respect to the TCDD effects, there were large differences among the strains. In the A/J mice, the difference between a lethal dose and a dose that could induce a cleft palate was close. Cleft lips were not induced, even when the TCDD was given just before labiogenesis. Morphologically, both palatal shelves contacted perfectly along their lengths, but separated and formed cleft palates. In conclusion, TCDD is a strong inducer of cleft palates, and interferes with the fusion phase of the secondary palate, but has no effect on the lip.     

Developmental toxicity of N,N1-bis(dichloroacetyl)-1,8-octamethylene diamine: effects of in utero exposure on the postnatal murine immune system

Oral gavage of pregnant C57BL/6J mice with N,N1-bis(dichloroacetyl)-1,8-octamethylene diamine on day 10 of gestation alters the morphology of a primary lymphoid organ, i.e., thymus, of the offspring when observed at 36 days of postnatal life. Thymuses obtained from the experimental offspring exhibited an overall reduction in size and cortical hypoplasia. Morphology of the spleen, a secondary lymphoid organ, is also affected in the offspring obtained from dams treated with this compound on day 10 of gestation. Spleens exhibited diffusely distributed white pulp areas compared to the distinctly nodular appearance in control spleens. Furthermore, it has been shown for the first time that prenatal administration of N,N1-bis(dichloroacetyl)-1,8-octamethylene diamine on day 12 of gestation alters the functional responsiveness of splenocytes obtained from the offspring of treated dams to a variety of mitogens when examined at 3, 5, 9 and 16 weeks of postnatal life. Administration of the compound prenatally on day 12 of gestation did not alter the postnatal morphological appearance of either thymus or spleen.     

Plasma concentrations of phenobarbital in the treatment of seizures in newborns.

The plasma concentration of phenobarbital given as anticonvulsive treatment in the newborn period has been followed in 18 infants. With constant daily doses, the drug accummulated for at least 5 days. After intramuscular injection of a single dose, 90% of the peak concentration was reached within 4 hours in 8 of the 10 infants. The peak concentration (in mug/ml) approximately equalled 1.3 x the dose (in mg/kg). Absorption after oral administration was less reliable. In 12 of the infants the clinical course allowed attempts to evaluate the anticonvulsive effect of phenobarbital. In 4 cases the convulsions continued. In those 8 infants where phenobarbital seemed to be effective, the approximate range of phenobarbital concentration when convulsions ceased was 12-30 mug/ml. Phenobarbital half-life ranged between 59 and 182 hours. In some infants the rate of phenobarbital disappearance from the plasma varied considerably from day to day. The pathological conditions causing seizures probably influence the distribution, metabolism and excretion of the drug. For the often seriously ill infants with convulsions it is therefore difficult to construct rational maintenance dose schedules, and optimal dosage must be based on repeated determinations of the plasma concentration.     

Increased constriction of the ductus arteriosus with combined administration of indomethacin and L-NAME in fetal rats

We studied age-related changes and the caliber of the ductus arteriosus (DA) after two-pathway inhibition of prostaglandin E(2) and nitric oxide (NO) by the combined administration of indomethacin, a cyclooxygenase inhibitor, and N(G)-nitro-L-arginine methyl ester (L-NAME), an NO synthase inhibitor, in fetal rats. Pregnant rats from day 18 to 21 of gestation were used. They were administered indomethacin orally (3 mg/kg) 3 h before cesarean section, and then L-NAME (50 mg/kg) was injected intraperitoneally 3 h before the rats were killed. Using rapid-freezing and shaving methods, the caliber of the DA in fetal rats was measured. Compared with the indomethacin alone group, indomethacin plus L-NAME further constricted the DA after indomethacin and L-NAME were simultaneously administered 3 h before the rats were sacrificed. The extent of the final DA constriction was almost equal to the addition of each effect of indomethacin and L-NAME. We concluded that the magnitude of DA constriction following indomethacin plus L-NAME was due to the additive effects of these agents, suggesting a possible method to treat patent DA in premature infants.     

Phenobarbital in prophylaxis of neonatal jaundice. A control trial of two regimens.

The prevention of neonatal hyperbilirubinemia by phenobarbital is widely used in many countries. However, dose and period of administration vary according to authors, as the dose-effect relation is not known and since little research in pharmacokinetics of phenobarbital has been done so far. In the present study we compared the effect on serum bilirubin of a single injection of 10 mg/kg body weight and of a prolonged administration of 10 mg/kg/day during 3 days in premature and full-term newborn infants. The single injection had the same effect as the prolonged administration, provided it was given within 12 h after birth.     

Pharmacokinetics of paraldehyde disposition in the neonate

The pharmacokinetic parameters controlling paraldehyde elimination were determined in nine infants infused with paraldehyde at the rate of 150 mg/kg/hr in a 5% solution in 5% dextrose for the treatment of status epilepticus. The mean +/- SEM values for the observed parameters were as follows: rate constant for the disposition of paraldehyde 0.0680 +/- 0.0071 hr,-1 half-life 10.2 +/- 1.0 hr; volume of distribution 1.73 +/- 0.20 L/kg; clearance 0.121 +/- 0.023 L/hr/kg. Phenobarbital administration prior to or within 24 hours of the cessation of paraldehyde infusion decreased both paraldehyde clearance and volume of distribution in a manner linearly related to the logarithm of the phenobarbital dose. The rate constant for paraldehyde elimination was decreased as a linear function of the logarithm of the combined dose of administered phenobarbital and phenytoin. No acetaldehyde was detected in any blood samples. Paraldehyde administration was not correlated with any adverse reactions or toxicities.     

Effect of nicotine on the development of fetal and suckling rats.

Nicotine, administered at a dose of 100 micrograms/kg/day from day 14 of gestation, did not affect maternal food intake, weight gain, length of gestation, litter size or fetal development; however, a daily dose of 1 mg/kg led to smaller litter size and higher incidence of stillbirth. Continued maternal administration of nicotine (100 micrograms/kg/day) until 12 days post partum did not affect newborn growth (body weight and length and size of heart and lung) during the first week after birth; during the second week, however, the nicotine-treated group lagged behind the controls. The stomachs of pups of nicotine-treated rats contained less food than those of controls; this difference increased with age, becoming more than 40% at 12 days. We suggest that lower milk production of nicotine-treated rats interferes with the normal development of the offspring during periods of rapid growth.     

汉防己甲素对先天性膈疝大鼠的保护作用

目的：探讨汉防己甲素（TET）产前干预对先天性膈疝（CDH）大鼠的保护作用及机制。方法：将妊娠Sprague-Dawley大鼠随机分为对照组、除草醚组与TET治疗组。后两组孕 9.5 d 时采用除草醚灌胃法建立 CDH 大鼠模型;治疗组自孕18.5 d 起给予 TET 灌胃（每日30 mg/kg,连续3 d）;21 d 对部分孕鼠行剖腹并抽取羊水,观察胎鼠膈疝形成情况。采用 ELISA 法、免疫组化染色法检测羊水和胎肺中 TNF-α 的表达情况。余孕鼠自然分娩,观察各组仔鼠出生后情况。结果：除草醚组胎鼠无论有无膈疝形成均存在肺发育不良,肺及羊水中 TNF-α 的表达均明显升高;TET治疗组胎鼠巨大膈疝的发生率低于除草醚组,肺与羊水中 TNF-α的含量明显较除草醚组少（P＜0.01）。在自然分娩的仔鼠中,TET治疗组仔鼠的 24 h存活率明显高于除草醚组（P＜0.01）。结论：产前应用 TET 能降低CDH大鼠模型胎肺与羊水中 TNF-α 的含量,改善因除草醚诱导的胎鼠肺发育不良,减少巨大膈疝的发生,提高仔鼠的存活率。     

Antiandrogenic effects of dibutyl phthalate and its metabolite,monobutyl phthalate,in rats

ABSTRACT  Developmental toxicity following administration of dibutyl phthalate (DBF) and its major metabolite, monobutyl phthalate (MBuP), by gavage was determined in Wistar rats. DBF on days 0–8 of pregnancy induced an increase in the incidence of preimplantation loss at 1250 mg/kg and higher and postimplantation loss at 750 mg/kg and higher. MBuP on days 0–8 of pregnancy produced an increase in the incidence of pre-and postimplantation loss at 1000 mg/kg. DBF on days 7–15 of pregnancy caused an increase in the incidence of fetuses with malformations at 750 mg/kg. MBuP on days 7–15 of pregnancy produced an increased incidence of fetuses with malformations at 500 mg/kg and higher. DBF on days 15–17 of pregnancy resulted in a decrease in the anogenital distance (AGD) of male fetuses and increase in the incidence of fetuses with undescended testes at 500 mg/kg and higher. MBuP on days 15–17 of pregnancy caused a decreased male AGD and increased incidence of fetuses with undescended testes at 250 mg/kg and higher. No effect of DBF and MBuP on the AGD was found in female offspring. The spectrum of fetal malformations, dependence of gestational days of treatment on the manifestation of teratogenicity, and alterations in development of the male reproductive system observed after administration of DBF were in good agreement with those observed after administration of MBuP. These findings suggest that MBuP may be responsible for the induction of developmental toxic effects of DBP. The doses that produced a decrease in the AGD and undescended testes in male offspring were lower than those producing maternal toxicity, fetal malformations after administration during major organogenesis, and embryonic loss. The male reproductive system may be more susceptible than other organ systems to DBP and MBuP toxicity after maternal exposure.     

Effect of Prenatal Methylazoxymethanol Acetate Exposure on the Motor Behavior of the Rat Offspring

Abstract Crj:CD (Sprague-Dawley) rats were treated intraperitoneally with methylazoxymethanol acetate (MAM) at 0 and 30 mg/kg on day 13 of gestation and were allowed to deliver. On day 4 postpartum, the litter size was adjusted to 8 with an equal sex distribution. Two males and females from each litter were tested between 3 and 5 weeks of age for open field activity and rotorod performance. At week 7 postpartum, all offspring were sacrificed and examined for brain anomalies.
The open field activity of MAM treated offspring tended to increase; number of ambulations and rearings were significantly increased at 3 weeks of age in male offspring treated with MAM when compared to those of male controls. At 3 weeks of age, the male offspring in the MAM treated group showed significantly reduced rotorod performance when compared to that in the control. Severe reductions of the cerebral hemispheres were observed at 7 weeks of age in the male and female offspring treated with MAM.
These results indicate that the motor behavior of offspring is significantly impaired at weaning when they were exposed to MAM prenatally. The effects were more severe for males than females.     

Acipimox, a nicotinic acid analog, stimulates growth hormone secretion in short healthy prepubertal children

Recent studies in adult volunteers have demonstrated that the free fatty acid reduction induced by acipimox, a nicotinic acid analog, stimulated GH secretion per se and enhanced in an additive manner the GH secretion elicited by such different stimuli as pyridostigmine, GHRH and GHRP-6. In order to evaluate whether acipimox administration stimulates GH secretion in prepubertal children, we administered a single oral dose of acipimox (100 mg for children weighing <30 kg and 200 mg for those >30 kg) to 14 healthy prepubertal children with a mean age of 8.2 +/- 1.9 years, a mean bone age of 6.2 +/- 3.0 years, growing along the 5-10th percentiles, and with normal thyroid function and IGF-I levels. Acipimox administration elicited a sustained increase in GH from a mean baseline level of 0.6 +/- 0.4 to 6.7 +/- 2.4 microg/l at the end of the test (p<0.05), with a mean GH peak of 10.5 +/- 3.5 microg/l. GH release was delayed so that peak GH levels were achieved 180 minutes after acipimox administration. In order to determine whether acipimox was capable of enhancing the GH secretion elicited by levodopa (L-Dopa), we administered either oral L-Dopa (250 mg for children weighing <30 kg and 500 mg for those >30 kg) or oral acipimox plus L-Dopa to the same children on different days. GH concentrations increased in a similar fashion following either of these tests (from a baseline level of 1.2 +/- 0.4 and 0.7 +/- 0.4 microg/l to 8.4 +/- 2.7 and 9.3 +/- 2.9 microg/l at the end of the test (p<0.001), with peak GH concentrations of 13.1 +/- 4.1 and 11.8 +/- 3.3 microg/l after L-Dopa or acipimox plus L-Dopa, respectively). Although the peak GH concentrations obtained after the combined administration of acipimox plus L-Dopa were similar to those obtained after either acipimox or L-Dopa administration, a larger number of our patients reached a GH cut-off point of >7 microg/l following combined therapy than with either stimulus alone (13/14 patients with combined therapy and 10/14 with acipimox alone). No side effects other than mild facial flushing were noted after acipimox administration. These results indicate that: 1) following the administration of a single oral dose of acipimox, significant GH secretion was elicited in healthy short prepubertal children; 2) the combined administration of acipimox plus L-Dopa did not, however, enhance the GH secretion of this group of children; 3) acipimox was well tolerated with minimal side effects; and 4) further studies in both GH sufficient and GH deficient children are necessary to evaluate acipimox's usefulness in assessing GH reserve.     

The effect of captopril on urinary protein excretion in puromycin aminonucleoside nephrosis in rats

We investigated the effect of captopril, an orally active angiotensin converting enzyme inhibitor, on urinary protein excretion in puromycin aminonucleoside nephrotic rats. The administration of captopril (10 mg/100 g body weight) decreased proteinuria on days 10-14 following the administration of puromycin aminonucleoside (73.0 versus 125.0 mg, p less than 0.01), without affecting glomerular filtration rate. The beneficial effect of captopril was not abolished by the continuous intravenous infusion of angiotensin II (10 micrograms/kg/h for 9 days) or subcutaneous injections of aprotinin (50,000 KIU/day for 3 days). Indomethacin, in moderate (5 mg/kg/day for 3 days) or high (10 mg/kg/day) doses, abolished the captopril attenuation in urinary protein excretion. The salutory effect of captopril was characterized by a reduction in the fractional excretion of protein without compromising the glomerular filtration rate. No difference in renal ultrastructure was noted in captopril-treated versus control animals. Captopril was ineffective in reducing urinary protein excretion in rats with adriamycin-induced glomerulopathy. We conclude that captopril acts to reduce proteinuria in renal disease states arising from depletion of the glomerular basement membrane polyanion. The mechanism of action is postulated to be an alteration in renal hemodynamics, namely increased blood flow and a decrease in the ultrafiltration coefficient, that are the consequence of increased intrarenal prostaglandin production.     

Neuropathological examination of fetal rat brain in the 5-bromo-2'-deoxyuridine-induced neurodevelopmental disorder model

The majority of prior developmental neurotoxicity studies focused on postnatal subjects rather than on the fetus. In the present paper, we demonstrate the use of histological examination of fetal rat (embryonic day 16.5) brain serial sections, employing Nissl staining and microtubule-associated protein 2 (MAP2) immunohistochemistry, in evaluating a chemical-induced neurodevelopmental disorder. Since prenatal treatment with 5-bromo-2'-deoxyuridine (BrdU) is known to induce behavioral abnormalities such as locomotor hyperactivity in offspring, pregnant rats were administered 50 mg/kg on gestation days 9.5 through 15.5. The fetal brains at embryonic day 16.5 were collected and processed for neuropathological study. Cell death, including DNA strand breaks, was observed in specific areas of the fetal brain such as the neuroepithelium, intermediate zone and/or differentiating zones (e.g. neocortex and striatum) in exposed fetuses. In addition, the neocortex had an abnormal appearance cortical plate, which was also detected by MAP2 immunohistochemistry. The abnormal cortical plate was observed consistently, while the grade of cell death was generally very mild and variable. No significant alteration was detected in the brainstem. The present study reveals that histological observation of the fetal brain includes sensitive endpoints in developmental neurotoxicity, and that BrdU, at a dose generally administered to label proliferating cells, affects the development of the fetal neocortex.