Researchers have published a three-dimensional map of the fats in the mouse brain and found that it divides into 539 chemically distinct territories, which they call lipizones. The work was carried out at the Ecole Polytechnique Federale de Lausanne, whose account of it was carried by ScienceDaily.
The atlas was built from 172 lipid types measured across 109 brain slices taken from 11 mice, some 7 million measurements in total, assembled into a 3D reconstruction with machine learning tools. The lipids were read by mass spectrometry imaging, in which a laser scans a tissue section one location at a time.
The study appears in Nature under the title "The lipidomic architecture of the mouse brain". It was co-led by Giovanni D'Angelo, Luca Fusar Bassini and Gioele La Manno.
Lipids turn out to be arranged in organised patterns, with some boundaries that earlier approaches missed. White matter, long treated as uniform, contains many distinct lipid zones, and previously unrecognised chemical boundaries appeared in the choroid plexus and in the tissues lining the brain's internal cavities.
"In effect, lipids work like postal codes, giving distant but related parts of the brain the same chemical address," D'Angelo said.
In pregnant mice, lipid composition shifted across many regions, more than typical differences between males and females did. The cortex changed most, and galactosyl ceramide, a component of myelin, rose sharply through much of the white matter. "Together, these shifts suggest the brain retunes its own wiring to meet the demands of pregnancy," La Manno said.
The authors are careful about the limits. The atlas maps mouse brains and cannot be applied directly to people. "What transfers to humans isn't the map, it's the method," Fusar Bassini said. The Lipid Brain Atlas is freely available online.
The number is the part that repays attention. The brain was found to have 539 regions because 172 lipids were measured, and the regions are the combinations those measurements can distinguish.
This newspaper notes the implication for anatomy, which is that the region count is a property of the instrument. A laser that reads 172 compounds finds 539 territories; a laser that reads twice as many would find more, and none of them would be new.
The Department of Unnecessary Research has followed the method to its conclusion. At sufficient chemical resolution every cell becomes its own territory, at which point the brain has as many regions as it has cells and the atlas becomes a census.
The postal metaphor holds up to the end. Give an instrument enough sensitivity and every address in the brain is distinct, which is also true of every address in Lausanne.