|
The idea that the brain is still forming new nerve cells, orneurons, into adulthood has become well-established over the pastseveral decades, says study leader Seth Blackshaw, Ph.D., anassociate professor in the Solomon H. Snyder Department ofNeuroscience at the Johns Hopkins University School of Medicine.However, he adds, researchers had previously thought that thisprocess, called neurogenesis, only occurs in two brain areas: thehippocampus, involved in memory, and the olfactory bulb, involvedin smell. More recent research suggests that a third area, the hypothalamus-- associated with a variety of bodily functions, including sleep,body temperature, hunger and thirst -- also produces new neurons.However, the precise source of this neurogenesis and the functionof these newborn neurons remained a mystery. To answer these questions, Blackshaw and his colleagues used miceas a model system. The researchers started by investigating whetherany particular part of the hypothalamus had a high level of cellgrowth, suggesting that neurogenesis was occurring. They injectedthe animals with a compound called bromodeoxyuridine (BrdU), whichselectively incorporates itself into newly replicating DNA ofdividing cells, where it's readily detectable. Within a few days,the researchers found high levels of BrdU in an area of thehypothalamus called the median eminence, which lies on the base ofthe brain's fluid-filled third ventricle. Further tests showed that these rapidly proliferating cells weretanycytes, a good candidate for producing new neurons since theyhave many characteristics in common with cells involved inneurogenesis during early development. To confirm that tanycyteswere indeed producing new neurons and not other types of cells,Blackshaw and his colleagues selectively bred mice that produced afluorescent protein only in their tanycytes. Within a few weeks,they found neurons that also fluoresced, proof that these cellscame from tanycyte progenitors. With the source of hypothalamic neurogenesis settled, theresearchers turned to the question of function. Knowing that manyprevious studies have suggested that animals raised on a high-fatdiet are at significantly greater risk of obesity and metabolicsyndrome as adults, Blackshaw's team wondered whether hypothalamicneurogenesis might play a role in this phenomenon. The researchers fed mice a diet of high-fat chow starting atweaning and looked for evidence of neurogenesis at severaldifferent time points. While very young animals showed nodifference compared with mice fed normal chow, neurogenesisquadrupled in adults that had consistently eaten the high-fat chowsince weaning. These animals gained more weight and had higher fatmass than animals raised on normal chow. When Blackshaw and his colleagues killed off new neurons in thehigh-fat eaters by irradiating just their median eminences withprecise X-ray beams, the mice gained significantly less weight andfat than animals who had eaten the same diet and were considerablymore active, suggesting that these new neurons play a critical rolein regulating weight, fat storage and energy expenditure. "People typically think growing new neurons in the brain is agood thing -- but it's really just another way for the brain tomodify behavior," Blackshaw explains. He adds thathypothalamic neurogenesis is probably a mechanism that evolved tohelp wild animals survive and helped our ancestors do the same inthe past. Wild animals that encounter a rich and abundant foodsource would be well-served to eat as much as possible, since sucha resource is typically scarce in nature. Being exposed to such a resource during youth, and consequentlyencouraging the growth of neurons that would promote more foodintake and energy storage in the future, would be advantageous.However, Blackshaw explains, for lab animals as well as people indeveloped countries, who have nearly unlimited access to abundantfood, such neurogenesis isn't necessarily beneficial -- it couldencourage excessive weight gain and fat storage when they're notnecessary. If the team's work is confirmed in future studies, he adds,researchers might eventually use these findings as a basis to treatobesity by inhibiting hypothalamic neurogenesis, either byirradiating the median eminence or developing drugs that inhibitthis process. Other Hopkins researchers involved in this study include Daniel A.Lee, Joseph L. Bedont, Thomas Pak, Hong Wang, Juan Song, AnaMiranda-Angulo, Vani Takiar, Vanessa Charubhumi, Susan Aja and EricFord. This research was supported by the National Institutes of Health,the National Science Foundation, a Basil O'Connor Starter ScholarAward, the Klingenstein Fund and NARSAD. Seth Blackshaw is a W.M.Keck Distinguished Young Scholar in Medical Research. We are high quality suppliers, our products such as Turbo Journal bearing Manufacturer , China Turbo Compressor Wheels for oversee buyer. To know more, please visits Turbine wheels.
Related Articles -
Turbo Journal bearing Manufacturer, China Turbo Compressor Wheels,
|
