Around February 14 every year, millions of people think about how their hearts and minds are intertwined with those of their loved ones. Neuroscientists are also talking about newly discovered links between the blood and brain at the molecular level.

Although nerve fibers and blood vessels are closely associated throughout the human body, how this shadowlike pairing becomes established has not been clear. But a report from the recent Society for Neuroscience Meeting in Atlanta announced that a protein familiar to scientists as a powerful stimulant for sprouting blood vessel growth—VEGF (vascular endothelial growth factor)—has the same potent effect on nerves.

Peter Carmeliet of the Flanders Interuniversity Institute for Biotechnology in Belgium reported that VEGF released by nerve cells and glia provides a navigation signal guiding the direction of growing nerve fibers, much the same way blood vessels are stimulated to grow toward the same protein. In addition to engendering new neurons, VEGF protects neurons from lack of oxygen after a stroke.

This factor can also guard mice against a form of amyotrophic lateral sclerosis (ALS), a degenerative neuron disease famous for killing legendary baseball player Lou Gehrig and crippling renowned physicist Stephen Hawking. Restoring normal levels of VEGF in these animals rescues them from death and stimulates new nerve sprouts to form synapses on muscle fibers. The finding could lead to new treatments for many neurodegenerative diseases, including Parkinson's disease, Alzheimer's disease, multiple sclerosis and epilepsy.

Perhaps it should not come as a surprise to find the same growth-promoting protein in blood vessels at work in nerves. Simple animals, such as microscopic nematode worms, need a nervous system to sense food and pursue it, but because they are so small they get all the oxygen they need without a circulatory system. Scientists may have discovered VEGF's circulatory role first, but Carmeliet concludes that VEGF must have originated in nerves and only later in evolution was it adapted to control the growth of blood vessels.