PhysOrg reveals a new discovery (using old tools) of a single brain protein that does two very different things to help us think:
Details of the observation in lab mice, published Dec. 24 in Nature, reveal that semaphorin, a protein found in the developing nervous system that guides filament-like processes, called axons, from nerve cells to their appropriate targets during embryonic life, apparently assumes an entirely different role later on, once axons reach their targets. In postnatal development and adulthood, semaphorins appear to be regulating the creation of synapses — those connections that chemically link nerve cells.
Using two lines of mice — one missing semaphorin and another missing neuropilin, its receptor — postdoctoral fellow Tracy Tran used a classic staining method called the Golgi technique to look at the anatomy of nerve cells from mouse brains. (The Golgi technique involves soaking nerve tissue in silver chromate to make cells’ inner structures visible under the light microscope; it allowed neuroanatomists in 1891 to determine that the nervous system is interconnected by discrete cells called neurons.)
Tran saw unusually pronounced “spines” sprouting willy-nilly in peculiar places and in greater numbers on the dendrites in the neurons of semaphorin-lacking and neuropilin-lacking mice compared to the normal wild-type animals. It’s at the tips of these specialized spines that a lot of synapses occur and neuron-to-neuron communication happens, so Tran suspected there might be more synapses and more electrical activity in the neurons of the mutant mice.