Active and inactive central synapses in cell culture.

Area of Science:

• Neuroscience
• Cell Biology
• Synaptic Plasticity

Background:

• Understanding synaptic transmission is crucial for comprehending neural circuit function.
• The relationship between the number of synaptic boutons and active neurotransmitter release sites is not fully understood.

Purpose of the Study:

• To investigate the morphological and physiological properties of synaptic connections between spinal cord (SC) neurons and between dorsal root ganglion (DRG) neurons and SC neurons.
• To determine the number of release elements (n) at synaptic connections and compare it to the number of boutons.

Main Methods:

• Dissociated cell cultures from fetal mouse spinal cord and dorsal root ganglia.
• Combined horseradish peroxidase (HRP) and Lucifer yellow injections for morphological and physiological correlation.
• Statistical analysis of excitatory postsynaptic potentials (EPSPs) to determine the number of release elements (n).

Main Results:

• In 80% of studied synaptic connections, the number of boutons was equal to or greater than the number of physiological release elements (n).
• In some cases, bouton counts exceeded n by more than fivefold.
• This suggests that a single bouton may release at most one quantum of transmitter, and many boutons may not participate in release.

Conclusions:

• A significant proportion of synaptic boutons may remain inactive during neurotransmitter release.
• Variations in release probability (p) likely contribute to the observed disparity between bouton number and release elements.
• Dendritic location of synaptic inputs does not appear to significantly influence these findings.