synaptosome

A synaptosome is a subcellular particle enriched from brain tissue that represents a pinched-off nerve terminal. It is formed during gentle tissue homogenization followed by differential and density-gradient centrifugation. Each synaptosome is a sealed, resealed presynaptic bouton containing synaptic vesicles, cytoplasm, and portions of the presynaptic membrane, and it may retain a fragment of the postsynaptic membrane with receptors.

Synaptosomes are typically prepared from mammalian brain regions such as cortex or hippocampus and are enriched in presynaptic terminals in the P2 fraction; further purification can be achieved with Percoll or Ficoll gradients. They preserve many biochemical and functional features of the presynaptic terminal, including transmitter storage, uptake, and Ca2+-dependent exocytosis, and they may respond to depolarization with transmitter release. They also retain components of the membrane machinery involved in vesicle cycling and can contain postsynaptic surface elements in varying degrees.

Applications of synaptosomes are widespread in neurochemistry and pharmacology. They are used to study neurotransmitter transporters and vesicle dynamics, receptor–ligand interactions, enzyme activities, and drug effects on presynaptic function. Radiolabeled substrates enable measurements of uptake and release, while biochemical assays can monitor metabolic processes and signaling pathways within the terminal.

Limitations include the loss of intact neuronal circuits and postsynaptic signaling, potential heterogeneity in preparations, and reduced viability over time. As a simplified model of the synapse, synaptosomes provide valuable insights but require cautious interpretation within the context of intact neural networks.

See also: synaptoneurosome, synaptic vesicle, postsynaptic density.