Differential Susceptibility to Benzo[a]pyrene Exposure during Gestation and Lactation in Mice with Genetic Variations in the Aryl Hydrocarbon Receptor and Cyp1 Genes.

Polycyclic aromatic hydrocarbons are ubiquitous air pollutants, with additional widespread exposure in the diet. PAH exposure has been linked to adverse birth outcomes and long-term neurological consequences. To understand genetic differences that could affect susceptibility following developmental exposure to polycyclic aromatic hydrocarbons, we exposed mice with variations in the aryl hydrocarbon receptor and the three CYP1 enzymes from gestational day 10 (G10) to weaning at postnatal day 25 (P25). We found unexpectedly high neonatal lethality in high-affinity AhrbCyp1b1(-/-) knockout mice compared with all other genotypes. Over 60% of BaP-exposed pups died within their first 5 days of life. There was a significant effect of BaP on growth rates in surviving pups, with lower weights observed from P7 to P21. Again, AhrbCyp1b1(-/-) knockout mice were the most susceptible to growth retardation. Independent of treatment, this line of mice also had impaired development of the surface righting reflex. We used high-resolution mass spectrometry to measure BaP and metabolites in tissues from both dams and pups. We found the highest BaP levels in adipose from poor-affinity AhrdCyp1a2(-/-) dams and identified three major BaP metabolites (BaP-7-OH, BaP-9-OH, and BaP-4,5-diol), but our measurements were limited to a single time point. Future work is needed to understand BaP pharmacokinetics in the contexts of gestation and lactation and how differential metabolism leads to adverse developmental outcomes.

The behavioral effects of gestational and lactational benzo[a]pyrene exposure vary by sex and genotype in mice with differences at the Ahr and Cyp1a2 loci.

Benzo[a]pyrene (BaP) is a polycyclic aromatic hydrocarbon (PAH) and known carcinogen in the Top 10 on the United States' list of priority pollutants. Humans are exposed through a variety of sources including tobacco smoke, grilled foods and fossil fuel combustion. Recent studies of children exposed to higher levels of PAHs during pregnancy and early life have identified numerous adverse effects on the brain and behavior that persist into school age and adolescence. Our studies were designed to look for genotype and sex differences in susceptibility to gestational and lactational exposure to BaP using a mouse model with allelic differences in the aryl hydrocarbon receptor and the xenobiotic metabolizing enzyme CYP1A2. Pregnant dams were exposed to 10 mg/kg/day of BaP in corn oil-soaked cereal or the corn oil vehicle alone from gestational day 10 until weaning at postnatal day 25. Neurobehavioral testing began at P60 using one male and one female per litter. We found main effects of sex, genotype and treatment as well as significant gene x treatment and sex x treatment interactions. BaP-treated female mice had shorter latencies to fall in the Rotarod test. BaP-treated high-affinity AhrbCyp1a2(-/-) mice had greater impairments in Morris water maze. Interestingly, poor-affinity AhrdCyp1a2(-/-) mice also had deficits in spatial learning and memory regardless of treatment. We believe our findings provide future directions in identifying human populations at highest risk of early life BaP exposure, because our model mimics known human variation in our genes of interest. Our studies also highlight the value of testing both males and females in all neurobehavioral studies.

Supplemental taurine during adolescence and early adulthood has sex-specific effects on cognition, behavior and neurotransmitter levels in C57BL/6J mice dependent on exposure window.

The mammalian brain goes through final maturation during late adolescence and early adulthood with sex differences in timing. The key cellular processes, including changes in neurotransmitter receptor density and synaptic pruning, make this age uniquely vulnerable to neurotoxic insults. Teenagers and young adults are the major consumers of energy drinks, which contain high levels of taurine and caffeine. Taurine is one of the most abundant amino acids in the central nervous system, but the effects of supplemental taurine consumption during adolescence has not been well studied. We conducted an initial short-term exposure study with 0.12% taurine in drinking water and a long-term exposure dose-response study using 0.06 and 0.12% taurine in male and female C57BL/6J mice. We examined a broad range of cognitive functions and behaviors and measured neurotransmitter levels. We found no significant differences in anxiety, open field locomotor activity, or sensorimotor gating. However, we found impairments in novel object recognition and sex differences in Morris water maze. When taurine treatment stopped before behavioral experiments began, male mice had significant impairments in spatial learning and memory. In the dose-response study when taurine treatment continued throughout behavioral experiments, females had significant impairments. We also found sex differences in neurotransmitter levels with females having higher levels of glutamate, DOPAC and 5-HIAA. We conclude that both females and males are at risk from excess taurine consumption during final brain maturation.

Ahr and Cyp1a2 genotypes both affect susceptibility to motor deficits following gestational and lactational exposure to polychlorinated biphenyls.

Polychlorinated biphenyls (PCBs) are persistent organic pollutants known to cause adverse health effects and linked to neurological deficits in both human and animal studies. Children born to exposed mothers are at highest risk of learning and memory and motor deficits. We developed a mouse model that mimics human variation in the aryl hydrocarbon receptor and cytochrome P450 1A2 (CYP1A2) to determine if genetic variation increases susceptibility to developmental PCB exposure. In our previous studies, we found that high-affinity AhrbCyp1a2(-/-) and poor-affinity AhrdCyp1a2(-/-) knockout mice were most susceptible to learning and memory deficits following developmental PCB exposure compared with AhrbCyp1a2(+/+) wild type mice (C57BL/6J strain). Our follow-up studies focused on motor deficits, because human studies have identified PCBs as a potential risk factor for Parkinson's disease. Dams were treated with an environmentally relevant PCB mixture at gestational day 10 and postnatal day 5. We used a motor battery that included tests of nigrostriatal function as well as cerebellar function, because PCBs deplete thyroid hormone, which is essential to normal cerebellar development. There was a significant effect of PCB treatment in the rotarod test with impaired performance in all three genotypes, but decreased motor learning as well in the two Cyp1a2(-/-) knockout lines. Interestingly, we found a main effect of genotype with corn oil-treated control Cyp1a2(-/-) mice performing significantly worse than Cyp1a2(+/+) wild type mice. In contrast, we found that PCB-treated high-affinity Ahrb mice were most susceptible to disruption of nigrostriatal function with the greatest deficits in AhrbCyp1a2(-/-) mice. We conclude that differences in AHR affinity combined with the absence of CYP1A2 protein affect susceptibility to motor deficits following developmental PCB exposure.

Genetic differences in the aryl hydrocarbon receptor and CYP1A2 affect sensitivity to developmental polychlorinated biphenyl exposure in mice: relevance to studies of human neurological disorders.

Polychlorinated biphenyls (PCBs) are persistent organic pollutants that remain a human health concern with newly discovered sources of contamination and ongoing bioaccumulation and biomagnification. Children exposed during early brain development are at highest risk of neurological deficits, but highly exposed adults reportedly have an increased risk of Parkinson's disease. Our previous studies found allelic differences in the aryl hydrocarbon receptor and cytochrome P450 1A2 (CYP1A2) affect sensitivity to developmental PCB exposure, resulting in cognitive deficits and motor dysfunction. High-affinity Ahr b Cyp1a2(-/-) mice were most sensitive compared with poor-affinity Ahr d Cyp1a2(-/-) and wild-type Ahr b Cyp1a2(+/+) mice. Our follow-up studies assessed biochemical, histological, and gene expression changes to identify the brain regions and pathways affected. We also measured PCB and metabolite levels in tissues to determine if genotype altered toxicokinetics. We found evidence of AHR-mediated toxicity with reduced thymus and spleen weights and significantly reduced thyroxine at P14 in PCB-exposed pups. In the brain, the greatest changes were seen in the cerebellum where a foliation defect was over-represented in Cyp1a2(-/-) mice. In contrast, we found no difference in tyrosine hydroxylase immunostaining in the striatum. Gene expression patterns varied across the three genotypes, but there was clear evidence of AHR activation. Distribution of parent PCB congeners also varied by genotype with strikingly high levels of PCB 77 in poor-affinity Ahr d Cyp1a2(-/-) while Ahr b Cyp1a2(+/+) mice effectively sequestered coplanar PCBs in the liver. Together, our data suggest that the AHR pathway plays a role in developmental PCB neurotoxicity, but we found little evidence that developmental exposure is a risk factor for Parkinson's disease.

Taurine, caffeine, and energy drinks: Reviewing the risks to the adolescent brain.

Energy drinks are emerging as a major component of the beverage market with sales projected to top $60 billion globally in the next five years. Energy drinks contain a variety of ingredients, but many of the top-selling brands include high doses of caffeine and the amino acid taurine. Energy drink consumption by children has raised concerns, due to potential caffeine toxicity. An additional risk has been noted among college-aged consumers of energy drinks who appear at higher risk of over-consumption of alcohol when the two drinks are consumed together. The differential and combinatorial effects of caffeine and taurine on the developing brain are reviewed here with an emphasis on the adolescent brain, which is still maturing. Key data from animal studies are summarized to highlight both reported benefits and adverse effects reported following acute and chronic exposures. The data suggest that age is an important factor in both caffeine and taurine toxicity. Although the aged or diseased brain might benefit from taurine or caffeine supplementation, it appears that adolescents are not likely to benefit from supplementation and may, in fact, suffer ill effects from chronic ingestion of high doses. Additional work is needed though to address gaps in our understanding of how taurine affects females, since the majority of animal studies focused exclusively on male subjects.

Comparison of Neurological Function in Males and Females from Two Substrains of C57BL/6 Mice.

The C57BL/6 (B6) mouse is the background strain most frequently used for genetically-modified mice. Previous studies have found significant behavioral and genetic differences between the B6J (The Jackson Laboratory) and B6N substrains (National Institutes of Health); however, most studies employed only male mice. We performed a comprehensive battery of motor function and learning and memory tests on male and female mice from both substrains. The B6N male mice had greater improvement in the rotarod test. In contrast, B6J female mice had longer latencies to falling from the rotarod. In the Morris water maze (MWM), B6J males had significantly shorter latencies to finding the hidden platform. However, B6N females had significantly shorter path lengths in the reversal and shifted-reduced phases. In open field locomotor activity, B6J males had higher activity levels, whereas B6N females took longer to habituate. In the fear conditioning test, B6N males had a significantly longer time freezing in the new context compared with B6J males, but no significant differences were found in contextual or cued tests. In summary, our findings demonstrate the importance of testing both males and females in neurobehavioral studies. Both factors (sex and substrain) must be taken into account when designing developmental neurotoxicology studies.

The teratology society 2012-2017 strategic plan: pushing the boundaries.

The Teratology Society held its fourth strategic planning session in Albuquerque, NM, April 10-12, 2012, and launched the 2012-2017 Strategic Plan in conjunction with the 2012 annual meeting in Baltimore, MD. Building on the energy of the successful implementation of prior strategic plans (San Diego, 2007; Nashville,TN 2002; Cincinnati, OH 1998), session participants worked to identify barriers to success as a scientific society, as well as impending challenges and opportunities to which the Society needs to respond. The following report provides an overview of the Strategic Planning process, objectives, activities, and conclusions. A total of 23 members were present at the session, and the group included representation from Council, various committees, and different member constituencies. This plan, Pushing the Boundaries, and its three strategic intents: Broaden Our Identity, Expand Our Membership, and Increase Our Influence, will drive the direction of the Teratology Society for the next five years.

Ahrd Cyp1a2(-/-) mice show increased susceptibility to PCB-induced developmental neurotoxicity.

Polychlorinated biphenyls (PCBs) are developmental neurotoxicants that produce cognitive and behavioral changes in children exposed during gestation and lactation. Coplanar PCBs bind the aryl hydrocarbon receptor (AHR) and can be sequestered in liver by cytochrome P450 1A2 (CYP1A2). The AHR is a ligand-activated transcription factor which increases expression of the CYP1 family, including CYP1A2. Our previous work examining genetic susceptibility to developmental PCB neurotoxicity showed that Ahr(b)Cyp1a2(-/-) mice with the high-affinity Ahr(b) allele and lacking CYP1A2 were most susceptible while Ahr(b)Cyp1a2(+/+) and poor-affinity Ahr(d)Cyp1a2(+/+) mice were resistant. To follow up, a fourth line of mice was generated with the Ahr(d)Cyp1a2(-/-) genotype and compared with the background strain Ahr(b)Cyp1a2(+/+). Dams received a PCB mixture or the corn oil vehicle at gestational Day 10 (GD10) and postnatal Day 5 (PND5). Offspring were tested at PND60 in open field locomotor, acoustic startle with pre-pulse inhibition (PPI), novel object recognition and Morris water maze. Locomotor activity was increased in PCB-treated Ahr(b)Cyp1a2(+/+) mice, but no differences were seen in control vs. PCB-treated Ahr(d)Cyp1a2(-/-) mice. PCB-treated Ahr(d)Cyp1a2(-/-) mice had a higher baseline startle response and significantly reduced pre-pulse inhibition at the 74dB level compared with corn oil-treated controls (P<0.05). PCB-treated Ahr(d)Cyp1a2(-/-) mice had impairments in novel objective recognition (P<0.05) and during all three hidden platform phases of Morris water maze (P<0.01). Combined with our previous findings, these results indicate Cyp1a2 genotype is more important in susceptibility to PCB-induced deficits in learning and memory, but Ahr genotype appears more important when assessing acoustic startle-PPI and locomotor activity.