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March 25, 2015
Digest

Eye Cells May Use Math to Detect Motion

Our eyes constantly send bits of information about the world around us to our brains where the information is assembled into objects we recognize. Along the way, a series of neurons in the eye uses electrical and chemical signals to relay the information.

Eye cells multiply. NIH scientists uncovered how neurons in the eye may use math to distinguish moving objects.
Eye cells multiply. NIH scientists uncovered how neurons in the eye may use math to distinguish moving objects.

PHOTO: DIAMOND LAB, NINDS

In a study of mice, NIH scientists showed how one type of neuron may do this to distinguish moving objects. The study suggests that the NMDA receptor, a protein normally associated with learning and memory, may help neurons in the eye and the brain relay that information.

“The eye is a window onto the outside world and the inner workings of the brain,” said Dr. Jeffrey Diamond, NINDS senior scientist and senior author of the study published in Neuron. “Our results show how neurons in the eye and the brain may use NMDA receptors to help them detect motion in a complex visual world.”

Vision begins when light enters the eye and hits the retina, which lines the back of the eyeball. Neurons in the retina convert light into nerve signals that are then sent to the brain.

Using retinas isolated from mice, Dr. Alon Poleg-Polsky, a postdoctoral fellow in Diamond’s lab, studied neurons called directionally selective retinal ganglion cells (DSGCs), which are known to fire and send signals to the brain in response to objects moving in specific directions across the eye.

Electrical recordings showed that some of these cells fired when a bar of light passed across the retina from left to right, whereas others responded to light crossing in the opposite direction. Previous studies suggested these unique responses are controlled by incoming signals sent from neighboring cells at chemical communication points called synapses.

In this study, Poleg-Polsky discovered that the activity of NMDA receptors at one set of synapses may regulate whether DSGCs sent direction-sensitive information to the brain.

“Cells in the eye can multiply,” said Poleg-Polsky. “The process may help these cells determine whether a tiger is sauntering by, or fast approaching as it’s looking for dinner.”

Marijuana Use Disorder Is Common, Often Untreated

Marijuana use disorder is common in the United States, is often associated with other substance use disorders, behavioral problems and disability and goes largely untreated, according to a new study conducted by NIAAA. The analysis found that 2.5 percent of adults—nearly 6 million people—experienced marijuana use disorder in the past year, while 6.3 percent had met the diagnostic criteria for the disorder at some point in their lives.

A report of the study, led by Dr. Bridget Grant of NIAAA’s Laboratory of Epidemiology and Biometry, appeared online Mar. 4 in the American Journal of Psychiatry.

Grant and her team found that the percentage of Americans who reported using marijuana in the past year more than doubled between 2001-2002 and 2012-2013, and the increase in marijuana use disorders during that time was nearly as large.

The researchers interviewed more than 36,000 U.S. adults about alcohol use, drug use and related psychiatric conditions. To be diagnosed with the disorder, individuals must meet at least two of 11 symptoms that assess craving, withdrawal, lack of control and negative effects on personal and professional responsibilities. Severity of the disorder is rated as mild, moderate or severe depending on the number of symptoms met.

Marijuana use disorder is about twice as common among men than women; younger age groups are much more likely to experience the disorder than people age 45 and over. The risk for onset of the disorder was found to peak during late adolescence and among people in their early 20s, with remission occurring within 3 to 4 years. The study also found that past-year and lifetime marijuana use disorders were strongly and consistently associated with other substance use and mental health disorders.

“These findings demonstrate that people with marijuana use disorder are vulnerable to other mental health disorders,” said Dr. Nora Volkow, director of NIDA, which contributed funding to the study. “The study emphasizes the need for such individuals to receive help through evidence-based treatments that address these co-occurring conditions.”

Prevention Strategy Benefits Persist After 1-Year Peanut Avoidance

Findings suggest that children who have regularly consumed peanut-containing foods from infancy to age 5 as a peanut allergy prevention strategy can safely switch to consuming peanut as part of a normal diet.
Findings suggest that children who have regularly consumed peanut-containing foods from infancy to age 5 as a peanut allergy prevention strategy can safely switch to consuming peanut as part of a normal diet.

The benefits of regularly consuming peanut-containing foods early in life to prevent the development of peanut allergy persist even after stopping peanut consumption for 1 year, new clinical trial findings show. The results were published online Mar. 4 in the New England Journal of Medicine.

NIAID’s LEAP-On study is an extension of the Learning Early About Peanut Allergy (LEAP) study. LEAP showed that regular peanut consumption begun in infancy and continued until 5 years of age led to an 81 percent reduction in development of peanut allergy in infants deemed at high risk because they already had severe eczema, egg allergy or both.

At the end of LEAP, participants who enrolled in LEAP-On were instructed to avoid peanut consumption for 1 year to help investigators determine whether continuous peanut consumption is required to maintain protection against development of peanut allergy. After the avoidance period, peanut allergy prevalence was determined, as it was in LEAP, by an oral food challenge. Only 4.8 percent of the children who had regularly consumed peanut-containing foods during LEAP were allergic to peanut following the year of peanut avoidance. In comparison, the prevalence of peanut allergy was 18.6 percent among those who had avoided peanut throughout LEAP and LEAP-On.

“The findings suggest that children who have regularly consumed peanut-containing foods from infancy to age 5 as a peanut allergy prevention strategy can safely switch to consuming peanut as desired as part of a normal diet,” said Dr. Daniel Rotrosen, director of NIAID’s Division of Allergy, Immunology and Transplantation. “We expect that many will continue to enjoy peanut-containing foods consumed regularly and others will maintain their non-allergic status with moderate intervals of diminished or no peanut consumption.”

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