Mechanisms Underlying Dendritic Spine Dynamics Elucidated

Researchers at CHU Sainte-Justine Hospital and Université de Montréal report that they have determined the structural organization of dendritic spines and the rules that control the induction of synaptic plasticity, which are important for learning and memory formation. Their research is described in a paper published today in Nature Communications.

Led by Professor Roberto Araya, the team studied the function and morphological transformation of dendritic spines, which serve as a contact zone between neurons by receiving inputs (information) of varying strength. If an input is persistent, a mechanism by which neurons amplify the "volume" is triggered so that it can better "hear" that particular piece of information. Otherwise, information of a low "volume" will be further turned down so that it goes unnoticed. This phenomenon corresponds to synaptic plasticity, which involves the potentiation or depression of synaptic input strength.

"This is the fundamental law of time-dependent plasticity, or spike-timing-dependent plasticity (STDP), which adjusts the strength of connections between neurons in the brain and is believed to contribute to learning and memory," said Sabrina Tazerart, co-author of the study. While the scientific literature shows this phenomenon and how neurons connect, the precise structural organization of dendritic spines and the rules that control the induction of synaptic plasticity have remained unknown. Araya's team has succeeded in shedding light onto the mechanisms underlying STDP.

"Until now, no one knew how synaptic inputs (incoming information) were arranged in the 'neural tree' and what precisely causes a dendritic spine to increase or decrease the strength, or loudness, of information it passes on," the professor said. "Our goal was to extract "laws of synaptic connectivity" responsible for building memories in the brain.'"

For their study, his team employed preclinical models at a juvenile stage. Using advanced techniques in two-photon microscopy that mimic synaptic contacts between two neurons, the researchers discovered an important law related to the arrangement of information received by dendritic spines. Their work shows that depending on the number of inputs received (synapses) and their proximity, the information will be taken into account and stored differently.

"We found that if more than one input occurs within a small piece of tree branch, the cell will always consider this information important and will increase its volume," said co-first author Diana E. Mitchell.