Synaptic dendritic activity modulates the single synaptic event

The Origins of Variability in The Responses of The Glutamatergic Synapse

“…This point is not negligible because it means that a small current can produce a high value of V m . [38][39][40][41][42]. From the above equations if follows that the synaptic response, for a given number of active receptors depends on the value of V m .…”

“…The membrane potential (V m ) depends on several factors. The input resistance R i is particularly high since the spine represents a separate electrical compartment with a high input impedance [10,[38][39][40][41][42]. This point is not negligible because it means that a small current can produce a high value of V m .…”

“…For example, the fast activation of AMPA receptors following the release of a single vesicle, thanks to the high input resistance of the PSD, can depolarize the PSD sufficiently to activate few NMDA receptors even if the starting value of V m is close to the resing potential (-65mV) [38][39]. In the real neuron, where many synapses can be active at the same time, a very strong contribution to the variability of V m , and consequently of the EPSP, is given by the activity of pool of synapses active in the same time window (coincidence) positioned at a distance such to modify the membrane potential under the synapse [40][41][42].…”

“…The degree of modulatation by these the external synaptic pool depends on the number of active synapses and on their firing frequency [40][41]. For each size of the pool (number of active synapse) and for each mean firing frequency of the synapses of the pool, it is possible to identify a band of voltage, considered as a subset of values of membrane potential at which the synaptic response can occur [40][41][42]. The amplitude of each response for a given band of potential depends on the level of V m at the time of occurrence [41][42] of the synaptic vesicle release.…”

“…For each size of the pool (number of active synapse) and for each mean firing frequency of the synapses of the pool, it is possible to identify a band of voltage, considered as a subset of values of membrane potential at which the synaptic response can occur [40][41][42]. The amplitude of each response for a given band of potential depends on the level of V m at the time of occurrence [41][42] of the synaptic vesicle release. In the dendritic tree, positioned on the dendritic shaft, there are also inhibitory GABA A synapses.…”