New nerve cells formed in a select part of the brain could hold considerable sway over how much you eat and consequently weigh, new animal research by Johns Hopkins scientists suggests in a study published in the May issue of Nature Neuroscience.
The idea that the brain is still forming new nerve cells, or neurons, into adulthood has become well-established over the past several decades, says study leader Seth Blackshaw, Ph.D., an associate professor in the Solomon H. Snyder Department of Neuroscience at the Johns Hopkins University School of Medicine. However, he adds, researchers had previously thought that this process, called neurogenesis, only occurs in two brain areas: the hippocampus, involved in memory, and the olfactory bulb, involved in 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 function of these newborn neurons remained a mystery.
To answer these questions, Blackshaw and his colleagues used mice as a model system. The researchers started by investigating whether any particular part of the hypothalamus had a high level of cell growth, suggesting that neurogenesis was occurring. They injected the animals with a compound called bromodeoxyuridine (BrdU), which selectively incorporates itself into newly replicating DNA of dividing cells, where it’s readily detectable. Within a few days, the researchers found high levels of BrdU in an area of the hypothalamus called the median eminence, which lies on the base of the brain’s fluid-filled third ventricle.
Further tests showed that these rapidly proliferating cells were tanycytes, a good candidate for producing new neurons since they have many characteristics in common with cells involved in neurogenesis during early development. To confirm that tanycytes were indeed producing new neurons and not other types of cells, Blackshaw and his colleagues selectively bred mice that produced a fluorescent protein only in their tanycytes. Within a few weeks, they found neurons that also fluoresced, proof that these cells came from tanycyte progenitors.