Posts tagged neuroscience
Articles and news from the latest research reports.
Scientists peek at the early evolution of sex chromosomes
Two new studies offer insight into sex chromosome evolution by focusing on papaya, a multimillion dollar crop plant with a sexual problem (as far as growers are concerned) and a complicated past.
The research reveals that the papaya sex chromosomes have undergone dramatic changes in their short evolutionary histories (they are about 7 million years old; by comparison, human sex chromosomes began their evolution more than 167 million years ago). One of the two studies compares the papaya X chromosome with that of a closely related non-sex chromosome (called an autosome) in a sister species. The other looks at differences between the X and Y chromosomes.
Pupil Dilation Reveals Sexual Orientation
There is a popular belief that sexual orientation can be revealed by pupil dilation to attractive people, yet until now there was no scientific evidence. For the first time, researchers at Cornell University used a specialized infrared lens to measure pupillary changes to participants watching erotic videos. Pupils were highly telling: they widened most to videos of people who participants found attractive, thereby revealing where they were on the sexual spectrum from heterosexual to homosexual.
The findings were published August 3 in the scientific journal PLoS ONE.
Brain signal ID’s responders to fast-acting antidepressant
August 3, 2012
Scientists have discovered a biological marker that may help to identify which depressed patients will respond to an experimental, rapid-acting antidepressant. The brain signal, detectable by noninvasive imaging, also holds clues to the agent’s underlying mechanism, which are vital for drug development, say National Institutes of Health researchers.
Dr. Zarate views subject in MEG scanner from scanner control room.
The signal is among the latest of several such markers, including factors detectable in blood, genetic markers, and a sleep-specific brain wave, recently uncovered by the NIH team and grantee collaborators. They illuminate the workings of the agent, called ketamine, and may hold promise for more personalized treatment.
"These clues help focus the search for the molecular targets of a future generation of medications that will lift depression within hours instead of weeks," explained Carlos Zarate, M.D., of the NIH’s National Institute of Mental Health (NIMH). "The more precisely we understand how this mechanism works, the more narrowly treatment can be targeted to achieve rapid antidepressant effects and avoid undesirable side effects."
Zarate, Brian Cornwell, Ph.D., and NIMH colleagues report on their brain imaging study online in the journal Biological Psychiatry.
Previous research had shown that ketamine can lift symptoms of depression within hours in many patients. But side effects hamper its use as a first-line medication. So researchers are studying its mechanism of action in hopes of developing a safer agent that works similarly.
Ketamine works through a different brain chemical system than conventional antidepressants. It initially blocks a protein on brain neurons, called the NMDA receptor, to which the chemical messenger glutamate binds. However, it is not known if the drug’s rapid antidepressant effects are a direct result of this blockage or of downstream effects triggered by the blockage, as suggested by animal studies.
To tease apart ketamine’s workings, the NIMH team imaged depressed patients’ brain electrical activity with magnetoencephalography (MEG). They monitored spontaneous activity while subjects were at rest, and activity evoked by gentle stimulation of a finger, before and 6.5 hours after an infusion of ketamine.
It was known that by blocking NMDA receptors, ketamine causes an increase in spontaneous electrical signals, or waves, in a particular frequency range in the brain’s cortex, or outer mantle. Hours after ketamine administration— in the timeframe in which ketamine relieves depression — spontaneous electrical activity in people at rest was the same whether or not the drug lifted their depression.
Electrical activity evoked by stimulating a finger, however, was different in the two groups. MEG imaging made it possible to monitor excitability of the somatosensory cortex, the part of the cortex that registers sensory stimulation. Those who responded to ketamine showed an increased response to the finger stimulation, a greater excitability of the neurons in this part of the cortex.
Such a change in excitability is likely to result, not from the immediate effects of blocking the receptor, but from other processes downstream, in the cascade of effects set in motion by NMDA blockade, say the researchers. Evidence points to changes in another type of glutamate receptor, the AMPA receptor, raising questions about whether the blocking of NMDA receptors is even necessary for ketamine’s antidepressant effect. If NMDA blockade is just a trigger, then targeting AMPA receptors may prove a more direct way to effect a lifting of depression.
While antipsychotic drugs alleviate the symptoms of many people with schizophrenia, around a third of patients resist such treatments. A new study, led by Javier Gonzalez-Maeso of the Mount Sinai School of Medicine, suggests that this frustrating intractability depends on how DNA is packaged.
Gonzalez-Maeso and his colleagues found that antipsychotic drugs can suppress the expression of glutamate receptors in the brain, stunting their effectiveness as treatments for schizophrenia. But the researchers also found a way of boosting the effects of antipsychotics—by pairing them with drugs that block the gene suppression pathway.
Schizophrenia
Credit: JOHN BAVOSI/SCIENCE PHOTO LIBRARY
Caption: Schizophrenia. Artwork of a man hearing non- existent women’s voices. Auditory hallucinations are one of the most common symptoms of schizophrenia. One explanation for this disease is known as the dopamine hypothesis. Dopamine (the molecules at lower left & right) is a type of neurotransmitter. This chemical (tiny red spheres) is released from the ends (synapses) of nerve cells (neurons, upper left & right) when they pass on nerve impulses to other neurons. In schizophr- enia, however, the dopamine-producing neurons of the brain are overactive. This causes the sufferer to lose contact with reality, suffering from confused thoughts and emotional responses.
Guinea pig hearts beat with human cells
Damaged skin and liver can often repair themselves, but the heart rarely heals well and heart disease is the world’s leading cause of death. Research published today raises hopes for cell therapies, showing that heart muscle cells differentiated from human embryonic stem cells can integrate into existing heart muscle.
“What we have done is prove that these cells do what working heart muscles do, which is beat in sync with the rest of the heart,” says Chuck Murry, a cardiovascular biologist at the University of Washington in Seattle, who co-led the research.
It’s a longstanding question in biology: How do cells know when to progress through the cell cycle? In simple organisms such as yeast, cells divide once they reach a specific size. However, determining if this holds true for mammalian cells has been difficult, in part because there has been no good way to measure mammalian cell growth over time.
A team of MIT and Harvard Medical School (HMS) researchers has precisely measured the growth rates of single cells, allowing them to answer that fundamental question. In the Aug. 5 online edition of Nature Methods, the researchers report that mammalian cells divide not when they reach a critical size, but when their growth rate hits a specific threshold.
3D reconstruction of Phineas Gage’s skull, showing the passage of the tamping iron. Read about Gage’s connectome here
The World’s Most Famous Brain
In the summer of 1953, Henry Gustav Molaison (1926-2008) underwent brain surgery to contain epileptic seizures that had become critically debilitating. The intervention brought some relief from convulsions, but these positive results were overshadowed by an astonishing and indelible side effect. Soon after the operation, it became apparent that he could no longer recognize hospital staff, he did not remember the way home, he did not remember newspaper articles he had just read, nor the crossword puzzles he had solved; otherwise, he was completely normal. Since the time of the surgery, more than five decades of scrupulous neuropsychological research examined the nature of patient H.M.’s amnesia which proved to be both persistent and remarkably selective.
The goal of our project is to provide a window into the brain of the man who helped establish the scientific study of memory and unfailingly forgot the enormously generous contribution he made to medical research.
Earth’s Fractal Brain From Above
Photography by Hector Garrido