The neurotransmitter cycle and quantal size

Neuron. 2007 Sep 20;55(6):835-58. doi: 10.1016/j.neuron.2007.09.001.


Changes in the response to release of a single synaptic vesicle have generally been attributed to postsynaptic modification of receptor sensitivity, but considerable evidence now demonstrates that alterations in vesicle filling also contribute to changes in quantal size. Receptors are not saturated at many synapses, and changes in the amount of transmitter per vesicle contribute to the physiological regulation of release. On the other hand, the presynaptic factors that determine quantal size remain poorly understood. Aside from regulation of the fusion pore, these mechanisms fall into two general categories: those that affect the accumulation of transmitter inside a vesicle and those that affect vesicle size. This review will summarize current understanding of the neurotransmitter cycle and indicate basic, unanswered questions about the presynaptic regulation of quantal size.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Animals
  • Cell Membrane / metabolism
  • Chlorides / physiology
  • Glutamic Acid / metabolism
  • Glutamic Acid / physiology
  • Glutamine / metabolism
  • Glutamine / physiology
  • Humans
  • Hydrogen-Ion Concentration
  • Membrane Potentials / physiology
  • Neurotransmitter Agents / biosynthesis
  • Neurotransmitter Agents / metabolism
  • Neurotransmitter Agents / physiology*
  • Neurotransmitter Transport Proteins / metabolism
  • Proton Pumps / physiology
  • Receptors, Neurotransmitter / physiology
  • Synaptic Transmission / physiology*
  • Synaptic Vesicles / physiology*


  • Chlorides
  • Neurotransmitter Agents
  • Neurotransmitter Transport Proteins
  • Proton Pumps
  • Receptors, Neurotransmitter
  • Glutamine
  • Glutamic Acid