Do sympathetic nerves release noradrenaline in "quanta"?

Area of Science:

• Neuroscience
• Neuropharmacology
• Cell Biology

Background:

• The discovery of excitatory junction potentials (EJPs) in guinea-pig vas deferens demonstrated sympathetic transmitter secretion in
• Initial research assumed EJPs were triggered by noradrenaline, prompting studies on noradrenaline overflow to estimate
• Early findings suggested each pulse released a small fraction of tissue noradrenaline, leading to two models of quantal release.

Purpose of the Study:

• To investigate the release probability and quantal size of sympathetic neurotransmitters at individual release sites.
• To explore the intermittent nature of transmitter exocytosis in sympathetic varicosities.
• To reconcile findings with existing models of noradrenaline release.

Main Methods:

• Optical methods: Labeling of synaptic vesicle proteins SV2 and synaptotagmin.
• Electrophysiological methods: Recording of excitatory junction currents (EJCs) at single visualized varicosities.
• Amperometric methods: Measuring noradrenaline oxidation current using carbon fiber electrodes.

Main Results:

• Transmitter exocytosis in sympathetic varicosities was found to be intermittent.
• Excitatory junction currents and noradrenaline oxidation currents showed similar intermittency and amplitude fluctuations.
• Responses suggest exocytosis of single or few

Conclusions:

• Findings support the
• The exact size of the noradrenaline "quantum" (subfraction or whole vesicle content) remains an open question.
• Further research is needed to definitively prove the intermittent model of noradrenaline release.