Synapses in the brain are approached by perisynaptic astrocyte processes, which are important for the clearance of the neurotransmitter glutamate, for instance. But the coverage of synapses by theses astrocytic processes varies considerably from synapse to synapse. In a first recent study, we could demonstrate that stronger synapses are covered less, relative to their size, and uptake of glutamate is less efficient at these synapses, which increases the probability of synaptic crosstalk. In a second recent study, we could reveal that induction of synaptic long-term potentiation, a cellular mechanism underlying learning, but not depression can trigger the withdrawal of astrocytic processes from synapses and increase synaptic crosstalk. Together, both studies show that the geometrical arrangement of synapses and persisynaptic astrocyte processes is dynamically regulated and defines the spatial precision of synaptic transmission.
Herde K, Bohmbach K, Domingos C, Vana N, Komorowska-Müller JA, Passlick S, Schwarz I, Jackson CJ, Dietrich D, Schwarz MK, Henneberger C (2020) Local efficacy of glutamate uptake decreases with synapse size. Cell Rep. 32(12):108182 (link)
Henneberger C, Bard L, Panatier A, Reynolds J, Kopach O, Medvedev NI, Minge D, Herde MK, Anders S, Kraev I, Heller JP, Rama S, Zheng K, Jensen TP, Sanchez-Romero I, Jackson C, Janovjak H, Ottersen OP, Nagelhus EA, Oliet SHR, Stewart MG, Nägerl UV, Rusakov DA (2020) LTP induction boosts glutamate spillover by driving withdrawal of perisynaptic astroglia. Neuron (in press) (link)