Journal Digest

Children and adolescents who use marijuana may have more difficulty controlling their behavior and maintaining focus than nonusers, a new study suggests.

Research presented at the Society for Neuroscience annual meeting last November in San Diego also found that marijuana users who begin using the drug at an early age may suffer cognitive consequences of their behavior.

The study's senior author, Staci Gruber, Ph.D., of Harvard Medical School at McLean Hospital, and colleagues hypothesized that individuals who use marijuana would have lower scores on tests that assess cognitive skills. The researchers compared responses from 33 chronic marijuana users with those of 26 healthy controls who were nonusers of the drug. The researchers also performed a subgroup analysis of the marijuana users according to “early” or “late” use to see if there was any relationship to the drug's effects on cognition and executive function in the participants who reported using the drug before or after age 16.

Study participants were asked to complete verbal IQ and memory tests and were also assessed on the amount of time taken to complete short “visual scanning tasks.”

Compared with “late” users and nonusers, investigators found that those who began using marijuana at an earlier age were not able to respond as well to tasks that required “cognitive flexibility,” indicating that the use of marijuana can alter cognitive processing skills, and especially when the use starts at a younger age.

Overall, the researchers observed that nonusers made significantly fewer errors on the tests designed to evaluate executive function and ability to adapt in the context of a situation while performing small tasks.

This study “underscores the importance of establishing effective strategies to decrease marijuana use, especially in younger populations,” Gruber said.

The study was funded by the National Institute on Drug Abuse.

Research presented in December at the annual meeting of the Radiological Society of North America (RSNA) showed that moderate walking—just five miles a week—may decrease a person's risk of developing Alzheimer's disease.

“Because a cure for Alzheimer's is not yet a reality, we hope to find ways of alleviating disease progression or symptoms in people who are already cognitively impaired,” said Cyrus Raji, Ph.D., of the University of Pittsburgh who presented the study at the conference.

The researchers analyzed data from 426 individuals who are also part of a larger 20-year cohort study, the Cardiovascular Health Study, which is in its 13th year. The researchers evaluated the association between physical activity and brain structure as measured by three-dimensional magnetic resonance images of patients upon enrolling in the study and at its 10-year mark. Patients were also given the Mini-Mental State Exam (MMSE) to assess cognitive function over a five-year period. MMSE results for patients who had signs of cognitive impairment and reported less physical activity decreased an average of five points more over the five-year period than those of patients who engaged in more physical activity, whose MMSE score decreased by just one point.

Results of this ongoing study showed that even in people who had a small decline in cognitive impairment when beginning the study, walking slowed the rate of memory loss and decreased loss of brain volume, according to Raji and colleagues.

The study was funded by the National Institute on Aging, American Heart Association, and RSNA Research and Education Foundation.

Mechanisms that affect the circadian rhythm of a person with depression may be the result of altered gene expression.

Prior studies have suggested that changes in the expression of circadian genes and/or polymorphisms may make a person more susceptible to developing depression. Thus, alterations in these genes can interrupt normal fluctuations in messenger RNA (mRNA) and the expression of gene proteins.

A small cross-sectional study of 60 adults, approximately half of whom had a history of depression and four of whom were considered currently clinically depressed, was conducted. Data from a control group of demographically matched adults without a history of depression were used for comparison.

The purpose of the study was to determine if the association between chronic stress seen in animal studies is reproducible in humans who are caregivers for a person with dementia. However, in this case, study results showed that the history of depression, not the stress resulting from dementia caregiving, was associated with changes in the genes involved in regulating a caregiver's circadian rhythm.

The study, led by Jean-Philippe Gouin, a graduate student in psychology at Ohio State University, and colleagues examined blood samples of 25 participants with depression aged 45 to 85 who provided care for at least five hours a week to a family member with dementia. They then compared those samples with blood samples from 35 control subjects. To control for the diurnal variations in the expression of circadian-rhythm genes, blood samples of study participants that were taken between 9 a.m. and 11 a.m. were analyzed by real-time, quantitative polymerase chain reaction tests.

The investigators measured the levels of four genes—the CLOCK, Brain, and muscle Arnt-like protein 1 (BMAL1), Period1, and Period2-mRNA levels—in peripheral white blood cells. They found that individuals with a history of depression had increased levels of four genes compared with patients without a history of depression. In particular, the levels of the CLOCK gene were significantly increased. “The over-expression of circadian genes mRNA may represent a biomarker of vulnerability to unipolar affective disorder,” the authors wrote.

The study was funded by a grant from the National Institutes of Health, a General Clinical Research Center Grant, a Comprehensive Cancer Center Grant, and a Fonds de la Recherche en Santé du Québec Doctoral Training Award.

An abstract of “Altered Expression of Circadian Rhythm Genes Among Individuals With a History of Depression” is posted at <www.jad-journal.com/article/S0165-0327(10)00338-1/abstract>.