Quantal analysis of synaptic processes in the neocortex.
The application of fluctuation analysis to studies of synaptic function in the neocortex is discussed. Analysis of failures of transmission has been valuable in indicating whether a presynaptic or a postsynaptic site is responsible for a change in synaptic efficacy. When combined with detailed ultrastructural verification of all synapses involved in an individual cell to cell connection, a reasonable estimate of quantal size and release probability under conditions of low frequency activity can be obtained. However, both the number of available release sites in functional terms and the probability that an action potential (AP) will release transmitter from any given site can vary from AP to AP at higher frequencies. A variety of presynaptic mechanisms that modulate release are now apparent. For example, one mechanism dominates release patterns at one class of connection which is insensitive to absolute firing frequency, but responsive to changes in frequency. At another class of connection, a different mechanism dominates, resulting in high sensitivity to frequency.
Department of Physiology, Royal Free Hospital School of Medicine, London, UK.
A M
AM
Thomson
D000818:Animals; D019706:Excitatory Postsynaptic Potentials; D019579:Neocortex / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology; D011789:Quantum Theory; D009435:Synaptic Transmission / Q000502:physiology*