Environmental Toxins And Autism Link

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(CNN) Autism and environmental health experts called for greater scrutiny of chemicals found in the environment, which could potentially lead to autism and other neurodevelopmental disorders, in a conference call Tuesday.

"We live, breathe and start our families in the presence of toxic chemical mixtures and constant low-level toxic exposures, in stark contrast to the way chemicals are tested for safety," said Donna Ferullo, Director of Program Research at The Autism Society.

"Lead, mercury, and other neurotoxic chemicals have a profound effect on the developing brain at levels that were once thought to be safe," she said.

Autism spectrum disorders are being diagnosed at unprecedented rates, partly because of improved diagnostic tools and criteria, but also a host of other factors including what mothers-to-be are exposed and consequently their unborn children too, said Irva Hertz-Piccotto, Chief of the Division of Environmental Health at the University of California, Davis, and a faculty member at the Mind Institute.

About 1 in 110 children in the United States has autism, a group of developmental disorders that lead to impairments in behavior, communication and socialization. The cost of autism is staggering: $3.2 million for the care of a person with autism throughout his or her life; behavioral therapy can be hard to come by and be very limited,  and most medications don't help much.
Studies have strongly suggested a genetic component in the cause of autism, but it's becoming clear that genetics alone isn't the whole story; there could be interactions between susceptibility genes and environmental chemicals.

Recent research from her group, appearing in the journal Epidemiology, showed that prenatal vitamins taken prior to conception seem to interact with certain metabolizing genes that are inherited.  Those women who did not take the vitamins, and had the high-risk genotypes, were more likely to have a child with autism.  Still, this was a small study limited in scope, and more research should be done to confirm these findings.

The central nervous system of the fetus is sensitive to a wide range of chemicals, Hertz-Piccotto said.  Hormones, such as estrogens and androgens, are essential for proper brain development. Endocrine-disrupting compounds need more research, she said. Flame-retardant chemicals called PBDEs interfere with the body's hormones.  Even though many of them are no longer used in manufacturing, they can hang around in the environment and the human body for a long time.  The Environmental Protection Agency (EPA) is aware of concerns about these chemicals and is working on accessing substitutions (see the action plan).

Bisphenol A, present in plastic food packaging and water bottles, among other products, is another big concern, she said, because it could interfere with the body's natural estrogen system; antimicrobials added to soaps, toothpaste and other products can artificially enhance androgenic activity.

"That means that they could potentially play a role in autism or other neurodevelopmental disorders," Hertz-Piccotto said.

Moreover, many children with autism spectrum disorders have abnormal immune responses. The chemical messengers in the immune system interact with the receptors in the brain, so chemicals that affect immunity could also be implicated in autism.

Thyroid dysfunction is common in children with autism that psychiatrist Dr. Suruchi Chandra sees, even though that's not part of the classical symptoms of the condition.  She believes the abnormalities are due to the thyroid hormone disruptors such as BPA and flame retardants.
"Thyroid hormone is critical for brain development in early life, and even small alterations in hormone levels can have serious consequences; long-lasting and perhaps irreversible consequences in terms of brain function," she said.

Air pollution from traffic and certain pesticides have also been shown to have associations with autism, studies have shown.  Maternal conditions could partially result from chemicals in the environment.

Andy Igrejas, National Campaign Director of Safer Chemicals, Healthy Families, called for an update of the 1976 Toxic Substances Control Act. Sen. Frank Lautenberg (D-NJ) has proposed a stricter version that would require all industrial chemicals to be tested for safety.

Can Too Much Exercise Cause Anxiety?

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By GRETCHEN REYNOLDS

There exists a large and soothing body of scientific literature suggesting that regular exercise can improve someone’s mood and fight anxiety. And then there is this experiment from Germany, in which researchers placed running wheels in the cages of a group of laboratory mice and let them exercise at will.

Mice generally love to run, and these rodents spent almost every waking hour on their wheels, skittering through more miles than most animals are allowed to complete during exercise studies, averaging about seven miles per mouse per day. The scientists, from the Central Institute of Mental Health Mannheim, then placed these avid runners in unfamiliar situations. What they found was surprising, in part because it contradicted earlier experiments by other researchers. The mice froze or quickly fled to dark corners, behaviors considered by some researchers to signify anxiety. It was as if the marathon runners in this experiment had become more anxious and neurotic than the nonrunners, presumably because of the volume of their running.

The apparent implication of that finding — that too much running makes an animal a nervous wreck — might seem disconcerting. But as this study, published in the journal Hippocampus, and additional new research makes clear, a great deal still needs to be understood about just how exercise affects mood.

To date, most research into the interplay of exercise and anxiety has focused on the actions of various neurotransmitters or chemical messengers within the brain, like serotonin and dopamine. But the German researchers weren’t looking at neurotransmitters. Their interest was in a different brain mechanism. They were trying to determine whether the formation of new brain cells, a process called neurogenesis, was making their lab animals nervous.

Exercise spurs neurogenesis, a finding confirmed by seminal research completed a few years ago. This neurogenesis would seem to be completely laudable, since it occurs mostly in the hippocampus, a portion of the brain associated with memory and thinking. Rodents that have exercised and that have brains fizzing with new neurons tend to score well on tests of memory and cognition.

But the effects of neurogenesis on mood are murkier. A number of neurological case studies have reported that people and animals with lesions in the hippocampus — meaning fewer brain cells in that region — are less prone to anxiety than other people.

So could high volumes of running and the commensurately large amounts of neurogenesis in the hippocampus produce anxiety? The German work seemed to say yes, particularly a follow-up experiment by the same scientists published in September in the online journal PLoS One. In that study, the researchers radiated the brains of mice to prevent neurogenesis, and then let them run. The treated mice eagerly took to their wheels, but grew almost no new neurons.

Afterward, placed in stressful situations, they remained calm, reacting much like sedentary mice.
It seemed that neurogenesis had been the culprit behind the earlier runners’ excessive anxiety.
But the scientists are quick to point out that these findings do not mean that human marathon and ultramarathon runners are necessarily at risk of developing mood problems. The “exercise schedule of mice is not comparable to human fitness training,” wrote Dr. Johannes Fuss and Dr. Peter Gass, the primary authors of the two studies, in a shared e-mail response to questions. With very rare exceptions, humans will not spend their entire waking hours running.

More important, it’s not clear whether the behavior of the nervous mice was necessarily anxiety as we might experience it. The exercised mice did frequently freeze and hide, but they are prey animals, a situation that does not reward insouciance. To be less anxious, if you are a mouse, Dr. Fuss and Dr. Gass wrote, “might not always be the best survival strategy.”

The German scientists, in focusing narrowly on neurogenesis, may also have underestimated the intricate and broad ways in which exercise affects the brain’s mood centers. A fascinating series of experiments conducted at Princeton University and presented at the 2010 annual meeting of the Society for Neuroscience in November showed that neurons born from running actually behave differently from other neurons. They are not as physiologically excitable, even in stressful situations.

The Princeton scientists showed that after a rodent stress test, the hippocampi of running mice contained fewer proteins associated with neuron activity than the brains of sedentary mice, even though the runners had more neurons over all. The runners’ brain cells had remained, it seemed, more calm in the face of stress. Similarly, the scientists found, areas of the brain that would normally shoot stimulating messages to the hippocampus during and after stress were quieter in exercised mice.

“Thus,” the Princeton researchers concluded, “running may reduce anxiety-like behavior” despite increasing the number of new brain cells. Exercise had recalibrated the animals’ brains so that they were more serene.

What this emerging science means for those of us who regularly exercise is, admittedly, still being teased out by researchers. But other recent studies are encouraging. A review article published last year in The Archives of Internal Medicine, for instance, concluded that compared with sloth, “exercise training significantly reduced anxiety symptoms” in a group of people at risk for mood problems. And in a beguiling experiment also presented at the 2010 Society for
Neuroscience meeting, scientists from Oklahoma State University found that female rats allowed to run at a moderate pace for 10 to 60 minutes several times a week — my exercise regimen, in fact — behaved with robust mental health in stress tests. So whether you run on two legs or four, the message may be: relax.

Corrections: An earlier version of this post misidentified the affiliation of Dr. Fuss and Dr. Gass; they are with the Central institute of Mental Health Mannheim and the University of Heidelberg. The earlier version also misidentified the affiliation of the scientists whose experiment was presented at the 2010 Society for Neuroscience meeting; it is Oklahoma State University.