Exposure to Aroclor 1254 persistently suppresses the functions of pancreatic β-cells and deteriorates glucose homeostasis in male mice

Polychlorinated biphenyls (PCBs) are a class of persistent organic pollutants that have been shown to be related to the occurrence of type 2 diabetes mellitus (T2DM). Nevertheless, it is necessary to further explore the development of T2DM caused by PCBs and its underlying mechanisms. In the present study, 21-day-old C57BL/6 male mice were orally treated with Aroclor 1254 (0.5, 5, 50 or 500 μg kg^-1) once every three days. After exposure for 66 d, the mice showed impaired glucose tolerance, 13% and 14% increased fasting serum insulin levels (FSIL), and 63% and 69% increases of the pancreatic β-cell mass in the 50 and 500 μg kg^-1 groups, respectively. After stopping exposure for 90 d, treated mice returned to normoglycemia and normal FSIL. After re-exposure of these recovered mice to Aroclor 1254 for 30 d, fasting plasma glucose showed 15%, 28% and 16% increase in the 5, 50 and 500 μg kg^-1 treatments, FSIL exhibited 35%, 27%, 30% and 32% decrease in the 0.5, 5, 50 or 500 μg kg^-1 groups respectively, and there was no change in pancreatic β-cell mass. Transcription of the pancreatic insulin gene (Ins2) was significantly down-regulated in the 50 and 500 μg kg^-1 groups, while DNA-methylation levels were simultaneously increased in the Ins2 promoter during the course of exposure, recovery and re-exposure. Reduced insulin levels were initially rescued by a compensative increase in β-cell mass. However, β-cell mass eventually failed to make sufficient levels of insulin, resulting in significant increases in fasting blood glucose, and indicating the development of T2DM.

Developmental Exposure to Aroclor 1254 Alters Migratory Behavior in Juvenile European Starlings (Sturnus vulgaris)

Birds exposed to endocrine disrupting chemicals during development could be susceptible to neurological and other physiological changes affecting migratory behaviors. We investigated the effects of ecologically relevant levels of Aroclor 1254, a polychlorinated biphenyl (PCB) mixture, on moult, fattening, migratory activity, and orientation in juvenile European starlings (Sturnus vulgaris). Birds were orally administered 0 (control), 0.35 (low), 0.70 (intermediate), or 1.05 (high) μg Aroclor 1254/g-body weight by gavage from 1 through 18 days posthatch and later exposed in captivity to a photoperiod shift simulating an autumn migration. Migratory activity and orientation were examined using Emlen funnel trials. Across treatments, we found significant increases in mass, fat, and moulting and decreasing plasma thyroid hormones over time. We observed a significant increase in activity as photoperiod was shifted from 13L:11D (light:dark) to 12L:12D, demonstrating that migratory condition was induced in captivity. At 12L:12D, control birds oriented to 155.95° (South-Southeast), while high-dosed birds did not. High-dosed birds showed a delayed orientation to 197.48° (South-Southwest) under 10L:14D, concomitant with apparent delays in moult. These findings demonstrate how subtle contaminant-induced alterations during development could lead to longer-scale effects, including changes in migratory activity and orientation, which could potentially result in deleterious effects on fitness and survival.

Disruption of the thyroid system by the thyroid-disrupting compound Aroclor 1254 in juvenile Japanese flounder (Paralichthys olivaceus)

Polychlorinated biphenyls (PCBs) are a group of persistent organochlorine compounds that have the potential to disrupt the homeostasis of thyroid hormones (THs) in fish, particularly juveniles. In this study, thyroid histology, plasma TH levels, and iodothyronine deiodinase (IDs, including ID₁, ID₂, and ID₃) gene expression patterns were examined in juvenile Japanese flounder (Paralichthys olivaceus) following 25- and 50- day waterborne exposure to environmentally relevant concentrations of a commercial PCB mixture, Aroclor 1254 (10, 100, and 1000 ng/L) with two-thirds of the test solutions renewed daily. The results showed that exposure to Aroclor 1254 for 50 d increased follicular cell height, colloid depletion, and hyperplasia. In particular, hypothyroidism, which was induced by the administration of 1000 ng/L Aroclor 1254, significantly decreased plasma TT₄, TT₃, and FT₃ levels. Profiles of the changes in mRNA expression levels of IDs were observed in the liver and kidney after 25 and 50 d PCB exposure, which might be associated with a reduction in plasma THs levels. The expression level of ID₂ mRNA in the liver exhibited a dose-dependent increase, indicating that this ID isotype might serve as sensitive and stable indicator for thyroid-disrupting chemical (TDC) exposure. Overall, our study confirmed that environmentally relevant concentrations of Aroclor 1254 cause significant thyroid disruption, with juvenile Japanese flounder being suitable candidates for use in TDC studies.

Aroclor 1254 inhibits the chemiluminescence response of peritoneal cavity cells from sharpsnout sea bream (Diplodus puntazzo)

Chronic exposure to polychlorinated biphenyls (PCBs) affect the immune system of fish and could lead to a decreased disease resistance. The effects of Aroclor 1254, PCB mixtures, on the Diplodus puntazzo innate immunity were examined by assaying the zymosan stimulated chemiluminescence response (CL) of peritoneal cavity cells (PCCs) at various times (1, 24, 48 h and 1-4 weeks) from intraperitoneal injection of the xenobiotic (1 mg kg(-1) body weight). Controls were performed by assaying cells from medium-treated fish. Since the kinetic of the chemiluminescence response showed the highest peak at 25 min after the zymosan stimulation of the cells, the values found at that time were considered. The CL enhancement observed at 1 h after the treatment with xenobiotic was followed by a decreased response at 24 h and appeared to be lower at 1-4 weeks when compared to the CL response of the control, suggesting a protracted effect of PCBs on the peritoneal cavity. Since PCCs incubated in vitro for 1 h with 0.05 and 0.1 μg ml(-1) Aroclor showed an enhanced CL, the effect of the xenobiotic could be exerted on the cell responsiveness to zymosan. It is known that fish CL response of PCCs can be imputed to phagocyte (macrophages and neutrophils) activation, these cells and their responsiveness to zymosan can be used in immunotoxicology assay to monitor the fish health in polluted environment.

Enhanced hepatotoxicity induced by repeated exposure to polychlorinated biphenyls and 2,3,7,8-tetrachlorodibenzo-p-dioxin in combination in male rats

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and polychlorinated biphenyls (PCBs) are among persistent polyhalogenated aromatic hydrocarbons that exist as complex mixtures in the environment worldwide. The present study was attempted to investigate the hepatotoxicity following repeated exposure to TCDD and PCBs in combination in male rats, and to reveal the involvement of potential mechanisms. Male Sprague-Dawley rats were exposed to TCDD (10 microg/kg) and Aroclor 1254 (10 mg/kg, a representative mixture of PCBs) alone or in combination by intragastric administration. After 12-day exposure, all treatments produced significant hepatotoxicity as characterized by changes of plasma biochemistry and histopathological changes. These effects were more prominent in the combined group. Furthermore, all treatments induced hepatic cytochrome P450 1A1 (CYP1A1) expression, and the maximal level of CYP1A1 expression was observed in the combined group, as in the case of the most severe hepatotoxicity evoked by the combined exposure. These findings indicated that the hepatotoxicity induced by TCDD and Aroclor 1254 might be ascribed to the high expression of hepatic CYP1A1. The present study demonstrates the enhanced hepatotoxicity after exposure to TCDD and PCBs in combination in rats.

Simultaneous extraction and clean-up of polychlorinated biphenyls and their metabolites from small tissue samples using pressurized liquid extraction

A pressurized liquid extraction-based method for the simultaneous extraction and in situ clean-up of polychlorinated biphenyls (PCBs), hydroxylated (OH)-PCBs and methylsulfonyl (MeSO(2))-PCBs from small (<0.5 g) tissue samples was developed and validated. Extraction of a laboratory reference material with hexane-dichloromethane-methanol (48:43:9, v/v) and Florisil as fat retainer allowed an efficient recovery of PCBs (78-112%; RSD: 13-37%), OH-PCBs (46+/-2%; RSD: 4%) and MeSO(2)-PCBs (89+/-21%; RSD: 24%). Comparable results were obtained with an established analysis method for PCBs, OH-PCBs and MeSO(2)-PCBs.

Prenatal Aroclor 1254 exposure and brain sexual differentiation: Effect on the expression of testosterone metabolizing enzymes and androgen receptors in the hypothalamus of male and female rats

Polychlorinated biphenyls (PCBs) are industrial pollutants detected in human milk, serum and tissues. They readily cross the placenta to accumulate in fetal tissues, particularly the brain. These compounds affect normal brain sexual differentiation by mechanisms that are incompletely understood. The aim of this study was to verify whether a technical mixture of PCBs (Aroclor 1254) would interfere with the normal pattern of expression of hypothalamic aromatase and 5-alpha reductase(s), the two main enzymatic pathways involved in testosterone activation and of androgen receptor (AR). Aroclor 1254 was administered to pregnant rats at a daily dose of 25 mg/kg by gavage from days 15 to 19 of gestation (GD15-19). At GD20 the expression of aromatase, 5-alpha reductase types 1 and 2 and androgen receptor (AR) and aromatase activity were evaluated in the hypothalamus of male and female embryos. The direct effect of Aroclor was also evaluated on aromatase activity adding the PCB mixture to hypothalamic homogenates or to primary hypothalamic neuronal cultures. The data indicate that aromatase expression and activity is not altered by prenatal PCB treatment; 5-alpha reductase type 1 is similarly unaffected while 5-alpha reductase type 2 is markedly stimulated by the PCB exposure in females. Aroclor also decreases the expression of the AR in females. The observed in vivo effects are indicative of a possible adverse effect of PCBs on the important metabolic pathways by which testosterone produces its brain effects. In particular the changes of 5-alpha reductase type 2 and AR in females might be one of the mechanisms by which Aroclor exposure during fetal development affects adult sexual behavior in female rats.

Aroclor 1254 impairs the hearing ability of Xenopus laevis

In this study we assessed the effects of chronic, dietary exposure of Aroclor 1254 (A1254) on the hearing of Xenopus frogs. We used the auditory brainstem response (ABR) to assay changes in hearing physiology; ABR thresholds, as well as latency-intensity and amplitude-intensity profiles of the initial positive (P1) and negative (N1) peaks were measured. Two groups of animals that received 50 ppm and 100 ppm of A1254 in their diet from 5 days post-fertilization through metamorphosis were compared to a control group that received untreated chow. The results showed significant threshold elevations in the 3-4 kHz range and significantly delayed peak latencies and reduced amplitudes at these frequencies in A1254 treated animals as compared to control animals. These findings indicate that A1254 selectively damages the high-frequency sensorineural hearing system associated with the basilar papilla of frogs. This preferential damage may be related to inherent differences in the vulnerability of the basilar versus amphibian papilla in the frog. The overall results of this study are also consistent with the reported A1254-induced auditory deficits in mammals indicating that the basilar papilla of the Xenopus frog may serve as an effective model for studying the effects of A1254 on the auditory system.

Polychlorinated biphenyls, sex steroid hormones and liver retinoids in adult male European common frogs Rana temporaria

Declines in amphibian populations and species biodiversity during the last decades has called for an assessment of possible threats to these animals. Polychlorinated biphenyls (PCBs) are known endocrine disrupting contaminants and are found in high levels in some populations of wild living amphibians. To evaluate the endocrine disrupting potential of PCBs in adult frogs, Aroclor 1,254 were subcutaneously injected into male European common frogs Rana temporaria. The injected doses ranged from 0.01 to 100 mg/kg body mass, resulting in liver concentrations between 74 and 133,619 microg/kg ww. After 14 days, serum testosterone (T), estradiol (E) and hepatic retinol (R) and retinylpalmitate (RP) were easured. No dose dependent effects were found on levels of hormones or retinoids. However, a significantly higher within-group variation in the E-T ratio in the exposed groups may indicate that the sex-hormone homeostasis of male R. temporaria is affected by PCBs shortly after arousal from hibernation, but that the effects are subtle and that several different mechanisms are involved. The lack of direct effect on T, E, R and RP may be due to the timing of exposure (shortly after arousal from hibernation), or due to a relatively short exposure time to Aroclor 1,254. Based on the results, we propose that future research should focus on effects of PCBs in relation to the different physiological phases frogs experience throughout the year (hibernation, reproduction etc.).

Ontogenetic alterations in prototypical transcription factors in the rat cerebellum and hippocampus following perinatal exposure to a commercial PCB mixture

Polychlorinated biphenyls (PCBs) are prevalent in the environment despite the ban of their use for decades and offer a model system to understand developmental neurotoxicity of persistent pollutants. Disturbances in brain development and cognition are among the neurotoxic manifestations of PCBs. The cellular and molecular basis for PCB-induced developmental neurotoxicity is still unclear; however, a series of in vitro and some in vivo studies have revealed that the disruption of Ca(2+) homeostasis and Ca(2+)-mediated signal transduction play a significant role. The culminating event in a variety of signal transduction pathways is the regulation of gene expression. Therefore, we examined the DNA-binding of prototypical transcription factors in order to identify those that are involved in signal transduction-transcription coupling in the cerebellum and hippocampus of developing rat brains following exposure to a commercial PCB mixture Aroclor 1254. Pregnant rats (Long Evans) were exposed perinatally to 0 or 6 mg/kg/day of Aroclor 1254 (Accu Standard Inc., Lot # 124-191) from gestational day 6 through postnatal day (PND) 21. On specific time points such as days 7, 14, 21, and 60, the DNA-binding of various transcription factors (Sp1, AP-1, NF-kappaB and CREB) was monitored in the cerebellum and hippocampus by a gel mobility shift assay. The induction of DNA-binding of transcription factors was more pronounced during the first 2 weeks after birth than at later periods. Sp1, AP1, and NF-kappaB exhibited a significant increase in DNA-binding following PCB exposure and peaked between 7 and 14 days after birth. However, the DNA-binding activity of CREB remained unchanged. These distinct changes delineate the involvement of specific transduction-transcription coupling pathways that may mediate PCB-induced perturbations in developmental gene expression.

Ontogenetic development, sexual differentiation, and effects of Aroclor 1254 exposure on expression of the arylhydrocarbon receptor and of the arylhydrocarbon receptor nuclear translocator in the rat hypothalamus

Interaction of polychlorinated biphenyls (PCBs) with the aryl hydrocarbon receptor (AhR)/nuclear translocator (ARNT) system might interfere with the mechanisms controlling the sexual differentiation of the developing hypothalamus. The aim of this study was to evaluate the presence of AhR/ARNT in brain cells and the developmental profile of their expression in the hypothalamus of male and female rats during the perinatal period. Brain accumulation of the main PCB congeners after prenatal exposure to Aroclor 1254 and its influence on hypothalamic expression of AhR/ARNT was also assessed. The results show that: (a) AhR and ARNT are expressed both in neurons and in glia; (b) AhR expression progressively increases in the developing hypothalamus particularly in males, while ARNT is relatively constant in both sexes; (c) the prenatal administration of Aroclor to dams produces a differential accumulation of PCBs, depending on the chlorine atom number, and stimulates AhR expression only in the male hypothalamus. In conclusion, the developing male hypothalamus might be more sensitive to disrupting potential of PCBs.

Circulating thyroid hormone levels and iodothyronine deiodinase activities in Nile tilapia (Oreochromis niloticus) following dietary exposure to Endosulfan and Aroclor 1254

We evaluated the effects of two organochlorinated environmental contaminants, Endosulfan and Aroclor 1254 on peripheral thyroid hormone metabolism and thyroid hormone plasma levels in Nile tilapia (Oreochromis niloticus). Tilapia were exposed through diet to 0.1 and 0.5 microg g(-1) of Endosulfan and 0.5 microg g(-1) of Aroclor 1254 for 21 and 35 days. Decreased plasma T4 and rT3 levels were observed in tilapia exposed to the lower dose of Endosulfan, while treatment with a higher dose and Aroclor 1254 produced no changes. Plasma T3 levels were not affected by these compounds. Hepatic type I deiodinase (D1) activity was depressed by a lower dose of Endosulfan and hepatic type III (D3) activity was increased following 35 days of exposure to the lower dose of Endosulfan and following 21 and 35 days of exposure to Aroclor 1254; while type II (D2) remained unchanged in liver as well as in all other organs analysed. Apart from hepatic D3 activity, Endosulfan and Aroclor 1254 also increased D3 activity in gill, but not in other tested organs. It is concluded that dietary exposure of tilapia to Endosulfan or Aroclor 1254 can lead to changes in circulating thyroid hormone levels and/or in peripheral thyroid hormone metabolism. The changes in hormone metabolism differ between tissues, eventually reflecting tissue-specific differences in adaptation.

Early Developmental Exposure to BDE 99 or Aroclor 1254 Affects Neurobehavioural Profile: Interference from the Administration Route

Among the most persistent and bio-accumulative environmental pollutants are the polybrominated diphenyl ethers (PBDEs), a class of chemicals widely used as flame retardants in plastics and textile coating, and the polychlorinated biphenyls (PCBs), previously used as coolants and lubricants in electrical equipment. Monitoring programs revealed high levels of both these classes of compounds in human breast milk, raising concerns for their potential noxious effects on infants. The aim of the present study was to investigate the neurotoxic effects of 2,2',4,4',5-penta BDE (BDE 99: 18mg/kg/day) or Aroclor 1254 (A1254, a PCB mixture: 10mg/kg/day) administration, from gestational day (GD) 6 to postnatal day (PND) 21, on neurobehavioral development in the CD-1 Swiss mouse. In addition, we investigated whether the administration route affects the emergence or the magnitude of the toxic effects of BDE 99 or A1254. In particular, we compared self-administration, consisting in letting the mouse drink spontaneously the compound dissolved in oil from a syringe, with gavage, consisting in force-feeding a substance by a tube inserted in the mouth and then into the stomach, a procedure reported to be stress-inducing. Both compounds induced hyperactivity, though BDE 99 affected activity profile only during adolescence and A1254 mainly at adulthood. Levels of total circulating thyroxine were decreased by both BDE 99 and A1254 administration, though only in the latter group the decrease was statistically significant. These findings suggest a different neurotoxic action exerted by PBDEs and PCBs. An effect of the administration route, independent from the compound administered, was found on thigmotactic behavior and gavage administration affected pup body weight gain only in the A1254 group, suggesting that the stress induced by gavage procedure may either affect results per se or modulate the detrimental action of selected compounds.

Effects of Vitamin C and E on PCB (Aroclor 1254) induced oxidative stress, androgen binding protein and lactate in rat Sertoli cells

The effect of Aroclor 1254 and the ameliorative effect of Vitamin C and E on Sertoli cell function were studied in adult male rats. The rats were administered Aroclor 1254 at a dose of 2 mg/kg bw/day intraperitoneally for 30 days. One group of rats received Vitamin C (100 mg/kg bw/day) while the other group received Vitamin E (50 mg/kg bw/day) orally simultaneously with Aroclor 1254 for 30 days. Necropsy was performed at 24 h after the last injection. Sertoli cells were isolated for the estimation of enzymatic antioxidants superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GST), and gamma-glutamyl transpeptidase (gamma-GT). Lipid peroxidation (LPO), hydrogen peroxide and hydroxyl radical were estimated. Sertoli cellular androgen binding protein (ABP) and lactate were also quantified. Whereas body weight, testis weight, relative weight of testis, ABP, lactate and specific activities of SOD, CAT, GPx, GR, GST, gamma-GT were all decreased, the levels of hydrogen peroxide, hydroxyl radical and LPO were significantly increased in the Sertoli cells of Aroclor 1254 treated rats. Simultaneous administration of Vitamin C or E restored these parameters to a normal range. Thus, the present study suggests that Aroclor 1254 exposure induces oxidative stress in rat Sertoli cells and furthermore that simultaneous administration of Vitamin C or E ameliorated these effects.

Accumulation of methylmercury or polychlorinated biphenyls in in vitro models of rat neuronal tissue

In vivo exposure levels for neurotoxicants are often reported in parts per million (ppm) concentration in tissue, whereas exposure levels in experiments utilizing in vitro models are most commonly reported in micromolar (muM) concentration in the exposure solution. The present experiments sought to determine whether or not in vitro solution concentration was an appropriate dose-metric for comparison to in vivo tissue levels for lipophilic compounds. To do so, the accumulation of the polychlorinated biphenyl (PCB) mixture Aroclor 1254 (A1254) or methylmercury (MeHg) was examined in three commonly utilized in vitro neuronal tissue models: nerve growth factor differentiated pheochromocytoma (PC12) cells, primary cultures of rat neocortical cells, and adult rat hippocampal slices. Tissues were exposed to A1254 (0.65 ppm) or to MeHg (0.0033-0.33 ppm) in serum-free media for 1 or 24 h. Total PCB or mercury accumulation was measured by dual column gas chromatography with electron capture detection or by cold vapor atomic absorption, respectively. PC12 cells accumulated 66.7 and 103.8 ppm PCBs after 1 and 24 h exposure to A1254. Neocortical neurons also accumulated significant concentrations of PCBs, but less so than PC12 cells. After 1 h exposure to 0.65 ppm A1254, slices contained 3.46 and 0.81 ppm PCBs when exposed in a static and perfused system, respectively. After 1 h exposure to 0.0033, 0.033, and 0.33 ppm MeHg, PC12 cells contained 0.3, 2.2, and 17.7 ppm mercury, respectively; after 24 h, PC12 cells contained 0.4, 2.8, and 21.9 ppm. Hippocampal slices accumulated 1.7 and 4.8 ppm mercury after 1 and 3 h exposure to 0.33 ppm MeHg. For comparison, mercury accumulation in rat fetal and pup brain tissue after maternal exposure [0, 0.1, 1.0, or 2.0 mg/kg/day MeHg from gestational day (GD) 6-15] ranged from 0.05 to 7.89 ppm in 0.1 mg/kg dose animals on postnatal day 10 and 2.0 mg/kg dose animals on GD16, respectively. These results demonstrate that accumulation of PCBs and MeHg in vitro is tissue-, time-, and concentration-dependent and indicates that tissue levels rather than exposure concentrations are a more appropriate metric for comparison of in vitro to in vivo effects.

Early Developmental Neurotoxicity of a PCB/Organochlorine Mixture in Rodents after Gestational and Lactational Exposure

The developmental and neurobehavioral effects of gestational and lactational exposure to a mixture of 14 polychlorinated biphenyls (PCBs) and 11 organochlorine pesticides was examined and compared against the commercial PCB mixture Aroclor 1254. The mixture was based on blood levels reported in Canadian populations living in the Great Lakes/St. Lawrence basin. Pregnant Sprague-Dawley rats were dosed orally with 0.013, 0.13, 1.3, or 13 mg/kg of the chemical mixture or 15 mg/kg of Aroclor 1254 from gestation day (GD) 1 to postnatal day (PND) 23. The highest mixture dose decreased maternal gestation and lactation body weight, and produced high mortality rates (80% overall) and reductions in offspring weight that persisted to adulthood. Aroclor 1254 produced smaller but persistent decreases in offspring weight without affecting maternal weight or offspring mortality. Aroclor 1254 and 13 mg/kg of the mixture produced comparable decreases in maternal and offspring serum T4 levels and comparable alterations to maternal thyroid morphology. Aroclor 1254 delayed the righting reflex and ear opening, accelerated eye opening, and reduced grip strength at PNDs 10-14. The mixture at 13 mg/kg delayed negative geotaxis in addition to delaying righting reflex and ear opening and reducing grip strength but had no effect on eye opening. Lower mixture doses (0.13 and 1.3 mg/kg) also delayed ear opening but affected no other parameters. Developmental exposure to the chemical mixture was found to be more toxic than exposure to Aroclor 1254 and produced a different profile of effects on early neurodevelopment. This PCB/organochlorine pesticide mixture affects mortality, growth, thyroid function, and neurobehavioral development in rodents.

Testicular histopathology in deer mice (Peromyscus maniculatus) following exposure to polychlorinated biphenyl

Adult deer mice testes were subjected to routine histopathology following exposure to Aroclor 1254 supplemented diet (5 ppm), for 30 days. Body and testicular weight revealed no statistical significance between the control and treated animals. From a histological standpoint the testes of the controls were similar to normal murids and other animals. In contrast, the testes from treated animals displayed seminiferous tubules with significant degenerative alterations. These alterations included fewer layers of seminiferous epithelium exaggerated intercellular spaces and appearance of pyknotic nuclei. Most tubules displayed subluminal nuclei that morphologically could be identified as part of spermatozoa heads and these usually lacked tails, indicating that the treatment interfered with spermiogenesis. Therefore, we concluded that Aroclor 1254 as an environmental contaminant is highly destructive to seminiferous tubules, and that these histological alterations undoubtedly are responsible for the depressed fertility in Peromyscus following chronic exposure to PCBs, that has been reported in the literature.

Biological effects of gestational and lactational PCB exposure in neonatal and juvenile C57BL/6 mice

The purpose of this study was to obtain a better understanding of polychlorinated biphenyl (PCB) immunotoxicity in the developing mouse. Adult female mice were dosed with three subcutaneous injections per week of 50 mg/kg Aroclor 1242 (A1242), Aroclor 1254 (A1254), or corn oil for 2 weeks and then mated with nondosed males. First-litter pups were sacrificed at 7 or 28 days of age. At both ages, the tissue concentration of PCB was significantly higher in both the A1242 and A1254 pups than in oil-treated controls. Seven-day-old pups exposed to A1242 or A1254 had significantly decreased splenic IL-2 production. Alterations in the percentages of T cell subsets compared to controls were observed in A1242-exposed pups; an increased spleen somatic index was noted only in A1254-exposed pups. Twenty-eight-day-old pups exposed to A1254 demonstrated a significant decrease in thymus somatic index, an increase in liver somatic index, a 25% decrease in total circulating T(4), and decreased B cell percentages relative to their controls. Alteration in the percentages of CD3(int) T cells was observed in A1254-exposed 28-day-old pups. A significant increase in 7-ethoxyresorufin- O-deethylase (EROD) and 7-benzoxyresorufin-O-dearylase (BROD) activity was measured at both ages in A1254-exposed pups and in A1242-exposed 28-day-old pups. These data confirm that during gestation and lactation A1242 and A1254 are transferred from dams to pups and that such exposure results in immune-related effects in neonatal (7-day-old) and juvenile (28-day-old) mice. Furthermore, A1254 exposure produces more frequent and pronounced effects than exposure to A1242.

Neurobehavioral assessments of rats perinatally exposed to a commercial mixture of polychlorinated biphenyls

Because of behavioral deficits associated with gestational exposure to PCBs in children, we sought to quantify neurobehavioral effects of perinatal exposure to Aroclor 1254(R) (A1254), a commercial mixture of PCBs, in rats. Pregnant Long-Evans rats were fed A1254 at doses of 0, 1.0, or 6.0 mg/kg/day throughout gestation and nursing. The growth and behavior of their male and female offspring were assessed both during development and as adults, using a variety of behavioral tests that included a neurobehavioral screening battery (functional observational battery [FOB] and automated tests of locomotor activity), habituation of motor activity, acquisition of a visual discrimination, and performance of a visual signal-detection task. During the suckling period, A1254 at 6 mg/kg reduced survival and body weight gain of offspring of both sexes; however, locomotor activity was unaffected, and only small and transient changes in other measures were evident. In adulthood, perinatal exposure to A1254 did not affect habituation of locomotor activity, acquisition of the visual discrimination, or sustained attention. Rats performing the signal-detection task were challenged with cocaine (0, 1.25, 2.5, 5.0 mg/kg) and haloperidol (0, 0.003, 0.010, 0.030 mg/kg) to probe the integrity of dopaminergic systems in the central nervous system (CNS). A1254 did not alter the impairment of attention caused by haloperidol. Cocaine reduced false alarms more in controls than in rats exposed to A1254, but the effect was not clearly related to the dose of A1254. Perinatal exposure to this commercial PCB mixture had very little effect on these tests of behavior during development and in adulthood.

Gestational-lactational exposure to Aroclor 1254 impairs radial-arm maze performance in male rats

Developmental exposure to polychlorinated biphenyls (PCBs) has been associated with cognitive deficits in children. The current study assessed effects of gestational and lactational exposure to a commercial PCB mixture, Aroclor 1254 (A1254), on spatial learning and memory in rats, using the radial-arm maze (RAM). Pregnant Long-Evans females (10/dose group) were exposed to 0 or 6-mg/kg/day A1254 (po in corn oil) from gestation day (GD) 6 to weaning at postnatal day (PND) 21. After they reached adulthood, 1 male and 1 female from each litter were tested on a working/reference memory task using a 12-arm RAM. Eight of the 12 arms were baited, with the pattern of baited arms remaining the same on every trial for each rat. Compared to control males, the A1254-exposed males made significantly more working memory errors (2.15 +/- 0.13 and 3.20 +/- 0.18 errors +/- SEM for control and A1254 males, respectively) and reference memory errors (3.17 +/- 0.10 and 4.13+/-0.14 errors +/- SEM for control and A1254 males, respectively) on the RAM. In contrast, A1254-exposed females were not impaired relative to control females on the RAM. Drug challenges with dizocilpine (MK-801) and scopolamine did not differentially affect working or reference memory of control and exposed rats. These data suggest that perinatal exposure to A1254 may cause sex-specific deficits in spatial learning and memory, and that NMDA-mediated and muscarinic neurotransmission, as assessed with the drug challenges, were not markedly impaired in the A1254-exposed animals.

Dosing via gavage or diet for reproduction studies: a pilot study using two fat-soluble compounds-hexachlorobenzene and aroclor 1254

The choice of a dosing route for in vivo toxicological tests is often dictated by practical constraints. Reproduction studies are particularly challenging in this regard since the determination of no-effect levels and allowable daily intakes from reproduction data encompasses exposure of the dam to the test xenobiotic prior to pregnancy, during gestation and during lactation. The fetus/infant can be exposed to the xenobiotic as well as the dam's metabolic products of the test xenobiotic during gestation and lactation. We initiated a series of two-litter, pilot reproduction studies with Sprague-Dawley and Fischer 344 rats to specifically ascertain the amount of xenobiotic and its metabolites ingested by the nursing neonate on lactation days 4, 7, 12, 17 and 21, when its dam received the xenobiotic via its diet or by gavage. The xenobiotics studied in this initial series of experiments were hexachlorobenzene (HCB) and Aroclor(R) 1254 (polychlorinated biphenyls; PCBs). The dams were dosed for 28 days, mated to untreated males and then remated approximately 2 weeks after weaning their first litter to a second untreated male. Dietary levels of 10 ppm HCB or 10 ppm PCBs, and gavage doses of 0.9 mg HCB or 0.8 mg PCBs/kg body weight/day were chosen and resulted in similar doses of HCB and PCBs per unit of the body weight of the dam during the premating period. There were no apparent toxicological effects regarding the dam nor were any of the reproduction parameters (feed consumption, dam weight, litter size, pup weight, external anomalies and day 4 viability index) significantly different from control values. Following impregnation, the body weight of the dam increased appreciably during gestation, but its feed consumption increased only slightly. During lactation, the dam's feed consumption increased markedly while its body weight increased slightly. Consequently, when dams received the xenobiotic in their diet they consumed slightly less xenobiotic per unit of body weight during gestation when compared to the gavaged dams, whereas the situation was dramatically reversed during lactation. While the greater consumption of xenobiotic by the dietary-dosed dams during lactation did result in more HCB (P</=0.0001 for both litters) and PCBs/metabolites (litter one: P=0.05; litter two: P</=0.0001) in the suckling neonate's stomach contents in both generations, there was no evidence of any differences between the two litters when each sampling date was assessed separately, except for the day 4-HCB results when the litter one pups had more HCB in their stomachs (P=0.018). For the PCBs, the F344 neonates were found to have more PCBs in their stomachs (litter one P=0.0015; litter two P=0.002) than the Sprague-Dawley neonates. In addition, the amount of HCB, PCBs and fat in the neonates' stomachs decreased during lactation, as the pups age increased (P</=0.035). These preliminary results suggest that analogous amounts of HCB and PCBs given via diet or gavage may not result in similar lactational exposure by the suckling neonate.