Perinatal Tetrahydrocannabinol Compromises Maternal Care and Increases Litter Attrition in the Long-Evans Rat.

The marijuana legalization trend in the U.S. will likely lead to increased use by younger adults during gestation and postpartum. The current study examined the hypothesis that delta-9-tetrahydrocannabinol (THC) would disrupt voluntary maternal care behaviors and negatively impact offspring development. Rat dams were gavaged with 0, 2, 5, or 10 mg/kg THC from the 1st day of gestation through the 21st postnatal day. Somatic growth and developmental milestones were measured in the offspring, and maternal pup retrieval tests were conducted on postnatal days 1, 3, and 5. THC did not affect body growth but produced transient delays in the righting reflex and eye opening in offspring. However, there was significant pup mortality due to impaired maternal care. Dams in all THC groups took significantly longer to retrieve their pups to the nest and often failed to retrieve any pups. Serum levels of THC and metabolites measured at this time were comparable to those in breastfeeding women who are chronic users. Benchmark doses associated with a 10% reduction of pup retrieval or increased pup mortality were 0.383 (BMDL 0.228) and 0.794 (BMDL 0.442) mg/kg THC, respectively. The current findings indicate that maternal care is an important and heretofore overlooked index of THC behavioral toxicity and should be included in future assessments of THC's health risks.

Sex-specific behavioral impairments produced by neonatal exposure to MK-801 are partially reversed by adolescent CDPPB treatment.

Psychomimetic behaviors manifest in adult rodents long after neonatal exposure to the noncompetitive NMDA receptor antagonist MK-801. In the present study, we used this neurodevelopmental model of schizophrenia to evaluate the therapeutic potential of positive allosteric modulation of metabotropic glutamate receptor 5 (mGluR5) during adolescence. To this end, we randomly assigned male and female C57BL6 mouse littermates to one of three treatment groups: (i) neonatal and adolescent saline, (ii) neonatal MK-801 (0.25 mg/kg) and adolescent saline, and (iii) neonatal MK-801 and adolescent CDPPB (10 mg/kg), a positive allosteric modulator of mGluR5. When animals reached adulthood, a wide range of behavioral tests were conducted including sucrose preference, anxiety assessment in the elevated plus maze, and a series of food-reinforced operant procedures meant to assess motor activity, motivation, learning, and attention. Neonatal MK-801 exposure produced profound motor hyperactivity in both sexes and attenuated sucrose preference in males, effects that were reversed by CDPPB. MK-801 produced other deficits such as impaired set shifting or response inhibition deficits that were not reversed by CDPPB. Overall, female mice were more susceptible to MK-801's behavioral effects than males. These findings further support the use of neonatal MK-801 exposure as an animal model of schizophrenia and suggest that CDPPB can reverse the neurodevelopmental progression of some schizophrenia-like behaviors.

Early postnatal decabromodiphenyl ether exposure reduces thyroid hormone and astrocyte density in the juvenile mouse dentate gyrus.

Decabromodiphenyl ether (decaBDE) is a flame retardant that was widely-applied to many consumer products for decades. Consequently, decaBDE and other members of its class have become globally-distributed environmental contaminants. Epidemiological and animal studies indicate that decaBDE exposure during critical periods of brain development produces long-term behavioral impairments. The current study was designed to identify potential neuroendocrine mechanisms for learning and response inhibition deficits observed by our lab in a previous study. C57BL6/J mouse pups were given a single daily oral dose of 0 or 20 mg/kg decaBDE from day 1 to 21. Serum thyroid hormone levels and astrocyte-specific staining in three regions of the hippocampus were measured on day 22. DecaBDE exposure significantly reduced serum triiodothyronine, thyroxine, and astrocyte density in the subgranular zone but not the hilus or granular layer in both male and female mice. The reduction of thyroid hormone and/or glia activity could impair hippocampal development, leading to behavior dysfunction.

Motor deficits, impaired response inhibition, and blunted response to methylphenidate following neonatal exposure to decabromodiphenyl ether.

Decabromodiphenyl ether (decaBDE) is an applied brominated flame retardant that is widely-used in electronic equipment. After decades of use, decaBDE and other members of its polybrominated diphenyl ether class have become globally-distributed environmental contaminants that can be measured in the atmosphere, water bodies, wildlife, food staples and human breastmilk. Although it has been banned in Europe and voluntarily withdrawn from the U.S. market, it is still used in Asian countries. Evidence from epidemiological and animal studies indicate that decaBDE exposure targets brain development and produces behavioral impairments. The current study examined an array of motor and learning behaviors in a C57BL6/J mouse model to determine the breadth of the developmental neurotoxicity produced by decaBDE. Mouse pups were given a single daily oral dose of 0 or 20mg/kg decaBDE from postnatal day 1 to 21 and were tested in adulthood. Exposed male mice had impaired forelimb grip strength, altered motor output in a circadian wheel-running procedure, increased response errors during an operant differential reinforcement of low rates (DRL) procedure and a blunted response to an acute methylphenidate challenge administered before DRL testing. With the exception of altered wheel-running output, exposed females were not affected. Neither sex had altered somatic growth, motor coordination impairments on the Rotarod, gross learning deficits during operant lever-press acquisition, or impaired food motivation. The overall pattern of effects suggests that males are more sensitive to developmental decaBDE exposure, especially when performing behaviors that require effortful motor output or when learning tasks that require sufficient response inhibition for their successful completion.

Prenatal exposure to the brominated flame retardant hexabromocyclododecane (HBCD) impairs measures of sustained attention and increases age-related morbidity in the Long-Evans rat.

Hexabromocyclododecane (HBCD) is a brominated flame retardant that is widely-used in foam building materials and to a lesser extent, furniture and electronic equipment. After decades of use, HBCD and its metabolites have become globally-distributed environmental contaminants that can be measured in the atmosphere, water bodies, wildlife, food staples and human breastmilk. Emerging evidence suggests that HBCD can affect early brain development and produce behavioral consequences for exposed organisms. The current study examined some of the developmental and lifelong neurobehavioral effects of prenatal HBCD exposure in a rat model. Pregnant rats were gavaged with 0, 3, 10, or 30mg/kg HBCD from gestation day 1 to parturition. A functional observation battery was used to assess sensorimotor behaviors in neonates. Locomotor and operant responding under random ratio and Go/no-go schedules of food reinforcement were examined in cohorts of young adult and aged rats. HBCD exposure was associated with increased reactivity to a tailpinch in neonates, decreased forelimb grip strength in juveniles, and impaired sustained attention indicated by Go/no-go responding in aged rats. In addition, HBCD exposure was associated with a significant increase in morbidity in the aged cohort. One health complication, a progressive loss of hindleg function, was observed only in the aged, 3mg/kg HBCD animals. These effects suggest that HBCD is a developmental neurotoxicant that can produce long-term behavioral impairments that emerge at different points in the lifespan following prenatal exposure.

Effects of prenatal exposure to sodium arsenite on motor and food-motivated behaviors from birth to adulthood in C57BL6/J mice.

Consumption of arsenic-contaminated drinking water is associated with numerous cancers and dermal and vascular diseases. Arsenic is also a potent nervous system toxicant and epidemiological studies indicate that intellectual functions in children are compromised following early developmental exposure. This study was designed to examine the effects of arsenic on a broad range of age-specific behaviors including basic sensory-motor responses in neonates, locomotor activity and grip strength in juveniles, and operant measures of learning and attention in adults. Pregnant C57BL6/J mice consumed drinking water containing 0, 8, 25, or 80 ppm sodium arsenite from the fourth day of gestation until birth. Arsenic produced a range of behavioral impairments in male and female offspring at each of the test ages. The most striking effects of arsenic were on the development of gait and other motor responses including acoustic startle, righting reflexes, and forelimb grip. These results suggest that developmental arsenic exposure can produce other behavioral impairments in children in addition to cognitive impairment.

Tissue-specific and dose-related accumulation of arsenic in mouse offspring following maternal consumption of arsenic-contaminated water.

The developmental toxicity of arsenic is not as well characterized as other metals such as lead or mercury. Many previous animal studies have used an acute exposure paradigm, which does not model chronic, low-level human exposure. The following study administered 10, 20, 40, 80 or 100 ppm sodium arsenite in drinking water to pregnant C57BL6/J mice. Adipose, blood, brain, breastmilk in stomach, kidney and liver tissues were collected from male and female offspring on postnatal day (PND) 1 and 21 to allow for disposition comparisons between tissues, sexes and across time. The 100 ppm dose was foetotoxic. Significantly fewer female pups were born in litters exposed to 80 ppm, while significantly more male pups were born in litters exposed to 20 ppm. Total arsenic levels differed between tissues with the highest levels in the brain and kidney in PND1 offspring. Levels were higher on PND1 than PND21, and there were few sex differences. The dose-response relationships in PND1 tissues were curvilinear, but in PND21 liver and kidney tissues, arsenic levels in control animals were significantly higher than levels in exposed animals. The tissue and age-specific disposition suggests that common biomarkers such as blood and urinary arsenic are not accurate predictors of levels in sensitive organs such as the brain.

Behavioral changes in aging but not young mice after neonatal exposure to the polybrominated flame retardant decaBDE.

BACKGROUND: After several decades of commercial use, the flame-retardant chemicals polybrominated diphenyl ethers (PBDEs) and their metabolites are pervasive environmental contaminants and are detected in the human body. Decabrominated diphenyl ether (decaBDE) is currently the only PBDE in production in the United States. OBJECTIVES: Little is known about the health effects of decaBDE. In the present study we examined the effects of neonatal decaBDE exposure on behavior in mice at two ages. METHODS: Neonatal male and female C57BL6/J mice were exposed to a daily oral dose of 0, 6, or 20 mg/kg decaBDE from postnatal days 2 through 15. Two age groups were examined: a cohort that began training during young adulthood and an aging cohort of littermates that began training at 16 months of age. Both cohorts were tested on a series of operant procedures that included a fixed-ratio 1 schedule of reinforcement, a fixed-interval (FI) 2-min schedule, and a light-dark visual discrimination. RESULTS: We observed minimal effects on the light-dark discrimination in the young cohort, with no effects on the other tasks. The performance of the aging cohort was significantly affected by decaBDE. On the FI schedule, decaBDE exposure increased the overall response rate. On the light-dark discrimination, older treated mice learned the task more slowly, made fewer errors on the first-response choice of a trial but more perseverative errors after an initial error, and had lower latencies to respond compared with controls. Effects were observed in both dose groups and sexes on various measures. CONCLUSIONS: These findings suggest that neonatal decaBDE exposure produces effects on behavioral tasks in older but not younger animals. The behavioral mechanisms responsible for the pattern of observed effects may include increased impulsivity, although further research is required.

Developmental delays and locomotor activity in the C57BL6/J mouse following neonatal exposure to the fully-brominated PBDE, decabromodiphenyl ether.

After several decades of commercial use, the flame retardant chemicals polybrominated diphenyl ethers (PBDEs) and their metabolites have become pervasive environmental contaminants with a global distribution. PBDEs have entered the food chain and increasing levels can be detected in the human body. Decabrominated diphenyl ether (decaBDE) is currently the most widely used of the PBDEs in the United States. Despite its widespread use, little is known about the health effects of decaBDE. The current study examined the effects of neonatal exposure to decaBDE in the inbred C57BL6/J mouse. Neonatal male and female mice were exposed to a daily oral dose of 0, 6, or 20 mg/kg decaBDE from postnatal day 2 to 15. Three groups of endpoints were examined: the ontogeny of sensorimotor responses and serum thyroxine levels in immature animals, and locomotor activity in adult animals. In immature animals, 20 mg/kg/day produced developmental delays in the acquisition of the palpebral reflex. At this age, exposed males also showed a dose-related reduction of serum thyroxine levels. As adults, decaBDE exposure altered the normal sex- and age-specific characteristics of spontaneous locomotor activity. The most striking effect was an increase of activity during the first 1.5 h of the 2 h assessment in males exposed to 20 mg/kg/day decaBDE. These effects suggest that decaBDE is a developmental neurotoxicant that can produce long-term behavioral changes following a discrete period of neonatal exposure.

Learning deficits expressed as delayed extinction of a conditioned running response following perinatal exposure to vinclozolin.

Vinclozolin (Vz) is one member of a group of fungicides whose metabolites are androgen receptor antagonists. These fungicides have been shown to block androgen-driven development and compromise reproductive function. The current study sought to determine if Vz also affects learning following exposure to low doses during the perinatal period. To test this, an androgen-dependent behavior was examined, the extinction of a previously reinforced running response. Pregnant Long-Evans rats were administered a daily oral dose of 0, 1.5, 3, 6 or 12 mg/kg Vz from the 14th day of gestation through postnatal day 3. After reaching adulthood, male and female offspring were trained to run through a short alleyway for food reinforcement. Acquisition of the response was not affected by Vz exposure. However, males required more trials than females for response extinction once food was no longer available in the apparatus. Males exposed to 6 or 12 mg/kg Vz failed to show any extinction by the end of the procedure, while the lowest dose of Vz appeared to facilitate extinction in both male and female offspring. These results demonstrate that endocrine disrupting antiandrogens can alter nervous system development in addition to the reproductive system.

Perinatal exposure to low levels of the environmental antiandrogen vinclozolin alters sex-differentiated social play and sexual behaviors in the rat.

In this study we examined the effects of exposure to the antiandrogenic fungicide vinclozolin (Vz) on the development of two sex-differentiated behaviors that are organized by the perinatal actions of androgens. Pregnant Long-Evans rats were administered a daily oral dose of 0, 1.5, 3, 6, or 12 mg/kg Vz from the 14th day of gestation through postnatal day (PND)3. The social play behavior of juvenile offspring was examined on PND22 and again on PND34 during play sessions with a same-sex littermate. After they reached adulthood, the male offspring were examined with the ex copula penile reflex procedure to assess erectile function. Vz did not produce any gross maternal or neonatal toxicity, nor did it reduce the anogenital distance in male pups. We observed no effects of Vz on play behavior on PND22. However, the 12-mg/kg Vz dose significantly increased play behavior in the male offspring on PND34 compared with controls. The most dramatic increases were seen with the nape contact and pounce behavior components of play. The Vz effect was more pronounced in male than in female offspring. As adults, male offspring showed a significant reduction of erections at all dose levels during the ex copula penile reflex tests. The 12-mg/kg dose was also associated with an increase in seminal emissions. These effects demonstrate that perinatal Vz disrupts the development of androgen-mediated behavioral functions at exposure levels that do not produce obvious structural changes or weight reductions in androgen-sensitive reproductive organs.

Impaired cued delayed alternation behavior in adult rat offspring following exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin on gestation day 15.

This investigation used random ratio (RR) and cued delayed alternation procedures to examine the operant behavior of adult male and female rats following prenatal 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Offspring were exposed to a single maternal dose of 0.0, 0.06, 0.18 or 0.54 microg/kg po of TCDD on gestation day (GD) 15. For RR, adult subjects were trained to respond on one lever in a two-lever chamber for food reinforcement. The response requirement was increased across sessions. Male offspring responded at higher rates than females regardless of RR value and prenatal exposure history. For delayed alternation, animals were required to alternate responses on both apparatus levers and to inhibit responding during randomly interpolated delay intervals. The performance of male and female offspring exposed to 0.18-microg/kg TCDD was significantly less accurate and this group committed more errors by responding during the delay intervals than the other exposure groups. A similar trend was observed in the 0.54- microg/kg group. Overall, response accuracy during the delayed alternation procedure was inversely related to delay length and tended to improve with experience. Interpretations of these outcomes include the possibility that TCDD interfered with the development of attentional processes, impaired response inhibition or promoted response perseveration despite the presence of cues, indicating changes in reinforcement contingencies.

Sexually dimorphic alterations of brain cortical dominance in rats prenatally exposed to TCDD.

Sexually dimorphic patterns of cortical lateralization are documented extensively in both human and animal brains. Male rats tend to exhibit pronounced right hemisphere dominance compared with females, whereas females typically exhibit more diffuse lateralization patterns and greater left hemisphere bias compared with males. Prenatal TCDD (2,3,7,8 tetrachlorodibenzo-p-dioxin) exposure produces demasculinization of male offspring sexual behavior. In previous studies, we showed a reversal of cortical dominance in rats after prenatal TCDD exposure on gestational day 18 (GD 18). The current study aimed to determine the nature of changes observed in rats exposed to TCDD on GD 8. In addition, locomotor activity was measured in male and female offspring on postnatal day (PND) 30, 60 and 90. Pregnant females were given, via gavage, a single dose of 0, 20, 60 or 180 ng kg(-1) TCDD on GD 8. Cortical depth measurements were taken in selected brain regions in offspring 3 months old that had been exposed to the 180 ng kg(-1) dose. Areas 2, 3, 17, 18a and 39 at bregmas -1.8, -3.8 and -5.8 were analyzed by quantifying digitized, enhanced images produced by a photomicroscope fitted with a special color camera. In both male and female offspring, cortical thicknesses in control brains exceeded those of exposed brains. In several brain areas of male offspring exposed to TCDD, right hemispheric dominance reversed to left hemispheric dominance. Female offspring brains showed a contrary move towards right hemisphere dominance. Motor activity in juvenile and mature animals did not differ among dose groups. These data demonstrate that prenatal exposure to TCDD reduces cortical thickness and alters the normal pattern of cortical asymmetry, a finding consistent with the sexually dimorphic behavioral effects induced by this agent.

Sexually dimorphic behavioral responses to prenatal dioxin exposure.

Pregnant Sprague-Dawley rats received a single oral dose of 0, 20, 60, or 180 ng/kg 2,3,7,8-tetrachlorodibenzo-p-dioxin on day 8 of gestation. Each litter contributed a single male-female pair trained to press a lever to obtain food pellets under two operant behavior procedures. Initially, each lever press was reinforced. The fixed-ratio (FR) requirement was then increased every four sessions from the initial setting of 1 to values between 6 and 71. We then studied responses for 30 days under a multiple schedule combining FR 11 and another schedule requiring a pause of at least 10 sec between responses (DRL 10-sec). TCDD evoked a sexually dimorphic response pattern. Generally, TCDD-exposed males responded at lower rates than control males. In contrast, exposed females responded at higher rates than controls. Each response measure from the mult-FR DRL schedule yielded a male-female difference score. We used the differences in response rate to calculate benchmark doses based on the relative displacement from modeled zero-dose performance of the effective dose at 1% (ED(01)) and 10% (ED(10)), as determined by a second-order polynomial fit to the dose-effect function. For the male-female difference in FR rate of responding, the mean ED(10) was 2.77 ng/kg with a 95% lower bound of 1.81 ng/kg. The corresponding ED(01) was 0.27 ng/kg with a 95% lower bound of 0.18 ng/kg. For the male-female difference in DRL rate, the mean ED(10) was 2.97 ng/kg with a 95% lower bound of 2.02 ng/kg. The corresponding ED(01) was 0.30 ng/kg with a 95% lower bound of 0.20 ng/kg. These values fall close to, but below, current estimates of human body burdens of 13 ng/kg, based on TCDD toxic equivalents.