Which cell type primarily clears neurotransmitters from the extracellular space?

Which cell type primarily clears neurotransmitters from the extracellular space?

• A. Oligodendrocytes
• B. Neurons
• C. Astrocytes
• D. Microglia

Answer: (C)

Astrocytes are primarily responsible for clearing neurotransmitters from the extracellular space. They express high-affinity transporters for key neurotransmitters such as glutamate and GABA, allowing rapid uptake from the synaptic cleft after release. Inside astrocytes, the neurotransmitter glutamate is converted to glutamine by glutamine synthetase, a step that helps terminate signaling and prevents accumulation that could excessively stimulate neurons. The glutamine is then shuttled back to neurons, where it is converted again to glutamate for future neurotransmission. This coordinated uptake and recycling is part of the glutamate–glutamine cycle and is essential for maintaining synaptic efficiency and protecting neurons from excitotoxicity. Astrocytes also help regulate extracellular potassium, supporting overall synaptic function in tandem with their neurotransmitter clearance role, which is why they are central to the concept of the tripartite synapse. Oligodendrocytes mainly insulate axons with myelin and don’t participate in clearing synaptic neurotransmitters. Neurons have their own receptors and transporters but do not serve as the primary cleanup crew for the extracellular neurotransmitter pool. Microglia act as immune watchdogs and can prune synapses or respond to injury, not primarily to remove neurotransmitters from the synaptic space.

Astrocytes are primarily responsible for clearing neurotransmitters from the extracellular space. They express high-affinity transporters for key neurotransmitters such as glutamate and GABA, allowing rapid uptake from the synaptic cleft after release. Inside astrocytes, the neurotransmitter glutamate is converted to glutamine by glutamine synthetase, a step that helps terminate signaling and prevents accumulation that could excessively stimulate neurons. The glutamine is then shuttled back to neurons, where it is converted again to glutamate for future neurotransmission. This coordinated uptake and recycling is part of the glutamate–glutamine cycle and is essential for maintaining synaptic efficiency and protecting neurons from excitotoxicity. Astrocytes also help regulate extracellular potassium, supporting overall synaptic function in tandem with their neurotransmitter clearance role, which is why they are central to the concept of the tripartite synapse.

Oligodendrocytes mainly insulate axons with myelin and don’t participate in clearing synaptic neurotransmitters. Neurons have their own receptors and transporters but do not serve as the primary cleanup crew for the extracellular neurotransmitter pool. Microglia act as immune watchdogs and can prune synapses or respond to injury, not primarily to remove neurotransmitters from the synaptic space.