Posts Tagged ‘hypothalamus’

A research team at University of Copenhagen including a researcher from the Faculty of Health and Medical Sciences has discovered a circuit in the brains of mice connecting circadian rhythm to aggressive behaviour. The discovery is particularly interesting to Alzheimer’s patients who experience increased aggression at night. The researchers have developed special protein tools capable of turning off the cells in the brain causing the behaviour.

Each year around 8,000 Danes are diagnosed with a form of dementia. Alzheimer’s disease is one of them. The disease manifests itself in memory difficulties in particular, but can also result in personality changes and mood swings.

When the sun sets 20 per cent of all Alzheimer’s patients experience increased bewilderment, anxiety, unease, disorientation, irritation and aggression. This phenomenon is called ‘sundowning’ or sundown syndrome. At worst, the condition can mean that the patient must be left in professional care, as it can be difficult for family members to handle. The cause of the condition is unknown, but previous research has suggested that it is connected to the circadian rhythm.

A research team including a researcher from the Department of Drug Design and Pharmacology at the University of Copenhagen is now able to confirm this connection. The researchers have identified and mapped a circuit between the part of the brain containing the circadian clock or circadian rhythm and a part of the brain controlling aggression.

’We have shown that the circadian clock in mice is closely linked to an aggression centre in the mouse brain by a cell circuit. The human brain has those same groups of cells that the circuit goes through. With this knowledge, we are now enabled to target this circuit pharmacologically and target cells that make people aggressive at the end of the day’, says Assistant Professor Timothy Lynagh from the Department of Drug Design and Pharmacology at the University of Copenhagen.

Turn off the Aggression
The inner clock or circadian rhythm is located in the part of the brain called suprachiasmatic nucleus. One of the parts of the brain that control aggressive behaviour is called the ventromedial hypothalamus. Researchers have previously observed a connection between the two parts of the brain, though none have had knowledge of the specific circuit connecting them.

Using electrophysiology and microscopy, the researchers measured the activity of the brain cells at main author Clifford Saper’s laboratory in Boston. They also turned off parts of the cell circuit in the brains of mice to map the circuit and to identify the cells connecting the two parts of the brain. To map circuits in the brain you need a protein tool that can turn off the various cells to determine their function. Assistant Professor Timothy Lynagh has designed precisely such a tool.

‘We take a receptor and mutate it, so that it is not sensitive to anything in the brain, but very sensitive to a particular drug. The tool works like an on/off switch. When you put the protein tool in the mouse brain, under normal circumstances, nothing will happen. But when you give the animal the drug, the cells that have the receptor on them will be turned off’, Timothy Lynagh explains.

Using this tool, the researchers can thus in theory turn off the cells that cause people suffering from sundown syndrome to become more aggressive at night.

May Be Used on Humans 20 Years into the Future
The tool can also be used in other contexts than sundown syndrome. In other studies, Tim Lynagh’s tool has been used to turn off cells in rats linked to anxiety and fear.

‘If you can start understanding which cells in the brain lead to which problems, you can then put this tool into any of those parts of the brain. The person who takes the drug will then have the cells causing the problem turned off’, Timothy Lynagh says.

Even though the study was conducted on mice, the tool and the knowledge the research has generated can potentially be used in the treatment of humans.

‘Because of the huge advances that are coming along with CRISPR, I would be tempted to say that based on a recent demonstration of gene therapy for brain disease, potentially, it could be used in the human brain in 20 years’ time. Of course it needs a lot more research’, he says.

Todd, W. D., Fenselau, H., Wang, J. L., Zhang, R., Machado, N. L., Venner, A., … & Lowell, B. B. (2018). A hypothalamic circuit for the circadian control of aggression. Nature neuroscience, 1.


By Ashley P. Taylor

During adulthood, the mouse brain manufactures new neurons in several locations, including the hippocampus and the subventricular zone of the forebrain. The hypothalamus, previously identified as an area with an important role in aging, also generates new neurons from neural stem cells. In a study published July 26 in Nature, Dongsheng Cai and his team at the Albert Einstein College of Medicine in New York connect the dots between these two observations, reporting that hypothalamic neural stem cells have widespread effects on the rate of aging in mice.

In what David Sinclair, who studies aging at Harvard Medical School and who was not involved in the work, calls a “Herculean effort,” the researchers “discovered that stem cells in the hypothalamus of the mouse play a role in overall health and life span,” he tells The Scientist.

Cai and his team found that killing hypothalamic neural stem cells accelerates aging, and transplantation of additional neural stem cells into the same brain region slows it down. Further, the stem cells’ anti-aging effects could be reproduced simply by administering the cells’ secreted vesicles, called exosomes, containing microRNAs (miRNAs).

“If this is true for humans, one could imagine a day when we are treated with these small RNAs injected into our bodies or even implanted with new hypothalamic stem cells to keep us younger for longer,” Sinclair adds.

Researchers who study aging have long been searching for a central location that controls the process system-wide. In a 2013 paper, Cai and his team reported aging-associated inflammation in the hypothalamus of the mouse, which they could experimentally manipulate to speed up or slow down various types of aging-related decline, from muscle endurance to cognitive skills.

This study, Cai says, suggested the hypothalamus might be that central locus in control of aging. The researchers wanted to understand more about how this region of the brain drives aging and what role hypothalamic neural stem cells might play in that process, so they undertook a series of experiments.

Age-defying stem cells

The researchers first confirmed that cells bearing protein markers of neural stem cells (Sox2 and Bmi1) were present in the hypothalamus of early-to-middle-aged mice (11 to 16 months old) and that the number of those cells decreased in older mice.

Next, they destroyed neuronal stem cells in the hypothalamus by injecting the third ventricle, adjacent to the hypothalamic region where the stem cells are found, with a lentivirus that converted an administered compound into a toxin in cells expressing the stem-cell marker Sox2. Three or four months later, the researchers compared a variety of aging-related measures, including muscle endurance, coordination, social behaviors, novel object recognition, and cognitive performance, between mice injected with the virus and various control groups of mice that received a brain injection of some sort but in which the toxin could not be produced and the hypothalamic stem cells were consequently not ablated.

The mice in the experimental group lost 70 percent of their hypothalamic stem cells and, based on results of the physiological tests, had accelerated aging. Mice with ablated hypothalamic stem cells also died earlier than control mice.

Next, the researchers implanted middle-aged mice with neural stem cells derived from newborn mice to see if the additional stem cells would slow aging. But the implanted stem cells almost all died, which the researchers believe was a result of the inflammatory environment of the aging hypothalamus. Newborn neuronal stem cells genetically engineered to withstand that environment, on the other hand, did survive, and mice implanted with those cells lived longer and performed better on aging-related measures than control mice.

“What’s cool about this study is that they specifically delete a population of cells in the hypothalamus of the brain . . . and they show pretty striking alterations in whole-body aging,” says Anna Molofsky, a psychiatrist at the University of California, San Francisco, who studies glial cells and whose graduate work focused on neuronal stem cells and aging. “That’s really showing that there’s a mechanism within the brain that’s regulating whole-body organismal aging,” she adds. Molofsky, who was not involved in the work, says that these results support the idea of the hypothalamus as a central regulator of aging.

Anti-aging mechanism

Although neural stem cells are known for their ability to produce new neurons, that doesn’t seem to be their primary method for protecting against aging. The anti-aging effects of these hypothalamic stem cells were visible at around four months—not long enough, the authors write, for significant adult neurogenesis to have taken place.

The authors looked instead for some other factor that might be responsible for the stem cells’ effects. In the hypothalamic neural stem cells, the researchers detected exosomes—secreted vesicles that can contain RNA and proteins—containing a variety of miRNAs, short RNA molecules that inhibit the expression of targeted genes. These exosomes were not present in non-stem cells of the hypothalamus.

To test the effects of the exosomes alone on aging, the researchers purified the vesicles from cultured hypothalamic neural stem cells and transplanted them into middle-aged mice, finding that the exosome-treated mice aged more slowly than vehicle-treated controls. They also found that the exosomes could ameliorate the aging symptoms of mice whose hypothalamic neurons had been ablated.

Cai says microRNAs could be a potential mechanism by which hypothalamic neural stem cells have such wide-ranging effects on aging, yet he believes that neurogenesis may also be involved.

Regardless of the mechanism, Molofsky says, “the medical applications could be pretty profound.” The phenotypes, such as muscle mass and skin thickness, affected by these stem cells are the same ones that cause age-related disease, she notes. “The fact that you can reverse that with a brain-specific modulation, potentially, in a cell type that one could pharmacologically target, I think potentially that could be very profound, assuming that the mouse work translates to humans.”

Y. Zhang et al., “Hypothalamic stem cells control ageing speed partly through exosomal miRNAs,” Nature, doi:10.1038/nature23282, 2017.