A neuron in the hypothalamus affects both hunger and bone mass. (Source: Wikimedia Commons)
For many years, neurologists and other scientists have been concerned with the functions of brain and the purpose of each group of neurons within it. A recent study conducted at the Yale School of Medicine announced that a group of neurons previously thought to control appetite also affects bone density (1).
The studied cells, known as agouti-related peptide (AgRP) neurons, are found within the hypothalamus, the area of the brain that regulates homeostasis, which is the process by which organisms stabilize inner conditions (1).
While the AgRP neurons were known to affect hunger, Tamas Horyath, a neurobiology professor at Yale and the author of the study, hypothesized that these same neurons might also have an effect upon the structure of our bones. To test his hypothesis, Horyath and his team genetically modified groups of mice in order to either inhibit or enhance AgRP neural pathways (1). The genetic modifications controlled for the other variables involved with hunger and isolated the effects of AgRP neurons activity.
The researchers found that mice whose AgRP pathways were inhibited, which made them less likely to be used, experienced a reduction in bone mass. In the mice whose pathways were enhanced, or made more usable, the opposite occurred. With this information, Horyath and his team were able to conclude that AgRP neurons are involved with both hunger and bone density (1).
The bone used to measure a change in bone mass was the trabecular bone, the spongy tissue underneath the harder, outer bone. The total volume of trabecular bone in the AgRP enhanced mice was 29.05% of the usable space within the bones (2). This was nearly 10% higher than the trabecular bone volume in AgRP inhibited mice, which was only 19.85 % (2).
According to Karl Insogna, a co-author of the study, more research needs to be done on the wide variety of mechanisms by which AgRP pathways could generate changes in bone density. The researchers/scientists believe that many of the hormone-producing organs, such as the adrenal glands, thyroid, and gonads, could possibly be involved (1).
References:
1) ScienceDaily. (2015, September 24). Of brains to bones: how hunger neurons control bone mass.ScienceDaily. Retrieved September 27, 2015 from http://www.sciencedaily.com/releases/2015/09/150924142703.htm
2) Kim, J.G., Sun, B.H., Dietrich, M.O., Koch, M., Y, G.Q., Diano, S.,…Horvath, T.L. (2015) AgRP neurons regulate bone mass. CellReports, 13, 1-7. doi: 10.1016/j.celrep.2015.08.070