Neuronal Support Cells Get the Message

During motor neuron development in zebrafish, a class of glial (support) cells, called perineurial glia, migrates out of the spinal cord based on signals that have been unknown until now.  Sarah Kucenas and colleagues at the University of Virginia showed in new work, published this week in the Journal of Neuroscience, that the Notch signaling pathway plays a role in correct migration of perineurial glia and in the differentiation of Schwann cells, the cells that ensheath nerve axons. Using the zebrafish embryo, which is optically clear, the researchers visualized Notch signaling and cell migration in real time, generating convincing and beautiful evidence that perineurial glia rely on Notch signaling to move the long distances necessary for their function.

Too Much Salt

The landscape of taste receptors consists of cells responsive to sweet, sour, bitter, sodium salt, and umami tastes. Sweet and umami tastes attract animals, while sour and bitter tastes generally repulse them. Sodium salt tastes straddle the fence, in that low salt doses are attractive and high doses are aversive. Before work published online this week in Nature, how salty tastes elicit different responses was still a mystery. Charles S. Zuker and colleagues at Columbia University and the NIH showed in mice that bitter and sour taste receptors respond to highly salty tastes and then communicate to the brain that the salty taste is repulsive. Mice without functioning bitter and sour taste receptors still find salty tastes attractive, but do not find highly salty tastes repulsive.

BRAINS OF MOMS AND NON-MOMS ARE DIFFERENT

Healthy new moms are less focused on non-baby stresses than women that are not mothers.

“We were interested in trying to understand why new mothers seem less stressed out,” says neuroscientist Heather A. Rupp of the Kinsey Institute for Research in Sex, Gender, and Reproduction. Rupp and her colleagues from the Kinsey Institute and the University of Zurich published the results of their study September 6 online in Social Cognitive and Affective Neuroscience.

Rupp and colleagues guessed that the hormone oxytocin might regulate the decreased response to stress in new mothers’ brains. They used functional MRI, an imaging technique that correlates activation in different brain areas to changes in blood flow, and compared the brains of non-mothers to mothers while the groups of women looked at emotionally-evocative negative images. They also exposed a subset of both groups to oxytocin via nasal spray.

One part of the brain, the right amygdala, was less responsive to the negative images in the moms than the non-moms, but only in the women that did not receive oxytocin. When the women received oxytocin, the brains of both moms and non-moms showed no difference in the right amygdala, with both groups showing fairly low activation.

When the team initially designed the study, Rupp “had high hopes that the oxytocin nasal spray would have really strong effects,” thus a lack of activation difference in the moms and non-moms who received the hormone raises questions worth investigating. According to Rupp, the effects of oxytocin turn out to be “more interesting and complex” than previously believed.

Most hormones are thought to function immediately and with predictable outcomes. Rupp notes, “With this study and some other work since then, it becomes a lot more clear that oxytocin’s role is very much modulated by the social context and the environment of the individual.” Understanding the window of time during which oxytocin functions as well as its social and environmental influences are obvious future directions for study.

In the case of the brains of the new mothers, their amygdalae might not have responded to the oxytocin because the hormonal environment had already been altered through the processes of carrying, birthing, and caring for their babies. Perhaps their brains were already saturated with oxytocin. Alternatively, the amygdala’s ability to respond might have shifted because the landscape of proteins responsible for recognizing the hormone changed.

The take home message, though, is that healthy women who have recently given birth have a buffered response to stress as compared to non-mothers. “This reduction in stress in healthy moms might have implications for women who have postpartum depression or anxiety disorders, which could help in treating them,” Rupp says.

Rupp predicts that the brains of women with postpartum depression would react to stress similarly to the brains of non-moms. Therefore, increasing oxytocin, either synthetically or in natural ways like getting a massage, may turn out to be an effective treatment for postpartum depression.

Understanding Habits

Researchers at MIT have shown that habits, long believed to be automatic, are actively controlled in rats by the part of the brain called the infralimbic (IL) cortex. In the study, published in the journal PNAS, the group trained rats to follow a T-maze automatically to receive a chocolate milk or sugar water reward, creating a well-ingrained habit. Then, using animals with a molecular channel called halorhodopsin expressed by cells in the IL cortex, the researchers directed light to the area with a fiber optic cable. When the light shone on the halorhodopsin-expressing neurons, it prevented them from firing, which abolished the habitual behavior. The results of the research provide new insight into how quickly habits are formed and replaced and into the parts of the brain that mediate habitual behavior.

Click for video or written explanations of their technique, called optogenetics.