Pound for pound, the brain consumes vastly more energy than other organs, and, puzzlingly, it remains a fuel-guzzler even when its neurons are not firing signals called neurotransmitters to each other. Now researchers at Weill Cornell Medicine have found that the process of packaging neurotransmitters may be responsible for this energy drain.
In their study, reported Dec. 3 in Science Advances, they identified tiny capsules called synaptic vesicles as a major source of energy consumption in inactive neurons. Neurons use these vesicles as containers for their neurotransmitter molecules, which they fire from communications ports called synaptic terminals to signal to other neurons. Packing neurotransmitters into vesicles is a process that consumes chemical energy, and the researchers found that this process, energy-wise, is inherently leaky—so leaky that it continues to consume significant energy even when the vesicles are filled and synaptic terminals are inactive.
“These findings help us understand better why the human brain is so vulnerable to the interruption or weakening of its fuel supply,” said senior author Dr. Timothy Ryan, a professor of biochemistry and of biochemistry in anesthesiology at Weill Cornell Medicine.
The observation that the brain consumes a high amount of energy, even when relatively at rest, dates back several decades to studies of the brain’s fuel use in comatose and vegetative states. Those studies found that even in these profoundly inactive states, the brain’s consumption of glucose typically drops from normal by only about half—which still leaves the brain as a high energy consumer relative to other organs. The sources of that resting energy drain have never been fully understood.