The visit by Cursor, on the day before obtaining his PhD, makes the wheel come full circle for Rémy Kusters. After all, it was a report in this newspaper in 2012 that alerted him to an interesting project for which Kees Storm from the Theory of Polymers and Soft Matter group (Applied Physics) had received a subsidy. A couple of months later he could get started for Storm as a PhD candidate within the Barriers in the brain project.
In cooperation with groups from Leiden, Utrecht and Amsterdam (VU University) Kusters researched the genesis of so-called ‘dendritic spines’, the mushroom-shaped protrusions on branched extensions (dendrites) of brain cells, which fulfil an important role in conveying signals in the brain. “When we learn things, or store information, then that is the level at which you see changes in the brain”, Kusters explains. “The shape of the brain, the weight, and the superficial structure stay the same, and even the network of connections between neurons is laid down at an early age.” It is only at the level of the synapse - the connection between the extensions of two nerve cells, or neurons – that essential changes take place.
Although a great many things about the way in which we store memories in our brain exactly are still not clear, we do know that the strength of the connection between brain cells plays an important role. At the synapse an electric signal that is carried via an axon (the transmitting extension of a nerve cell), is converted into a chemical signal. After the transfer the reverse conversion takes place, and the signal travels further via a dendrite (the receiving branch of the neighboring nerve cell). The chemical step is made by means of so-called neurotransmitters, which are absorbed on the exterior membrane of the dendrite by special receptor molecules.
Fewer spines in Alzheimer patients
“The more of these receptors, the stronger the connection”, Kusters explains. “It appears that dendrites can spontaneously form mushroom-like extrusions, causing more receptors to gather on the synapse.” While a portion of the receptor molecules is actively transported to the ‘head’ of the mushroom by the cell, most of the receptors end up there through diffusion - a random, unfocused movement. “The shape of the spine, with a big head and a narrow neck, turns out to have a big impact on the receptor molecules in the head. Although that can already be understood intuitively, I have calculated exactly how the receptors move across the membrane, and then the effect turns out to be even greater than you would think at first sight.” Hence the shape of the dendritic spines is by no means accidental, as he concludes, but has everything to do with their function. This is in line with the observation that in Alzheimer patients, among others, fewer of these spines are found.
Kusters will continue his scientific career in Paris, as postdoc at the renowned Institut Curie. After nine years in Eindhoven the Belgian who grew up between Liège and Maastricht gets to speak his mother tongue again, he says. “Paris may be an international city alright, but that I speak French is definitely a bonus there.”