This observation agrees with the well known fact that conditions in which there is an increase in probability of neurotransmitter release i.e. higher [Ca]o, entail a larger synaptic depression [15], [31], probably as a result of the faster depletion of a readily releasable vesicle pool that occurs with repetitive presynaptic activation [32] [34].
Consistent with the changes in AMPA receptor-mediated EPSCs described above, paired-pulse ratios of NMDA receptor-mediated EPSCs were lower in TASTPM than wild-type mice, consistent with a presynaptic change in probability of glutamate release (Fig. 2I).
Activation of CB1R, in the presynaptic terminals of CCK-positive interneurons, leads to a reduction in probability of synaptic release from CCK neurons to principal cells and interneurons (Freund, 2003; Armstrong and Soltesz, 2012).
On the other hand, lower Ca2+ in the solution and the subsequent decrease in the probability of release typically reduces synaptic depression [35], [36].
Because the number of excitatory synapses was unchanged, these results suggest that a reduction in the probability of release (Pr) may occur at Q555X-hSynI excitatory synapses.
Thus strong synaptic synchronization requires large, coordinated increases in the probability of release (a notion supported by the electrically compact nature of the RBC, Protti and Llano, 1998) and low intrinsic variability at individual synaptic connections (see 'Discussion').
Changes in probability of presynaptic vesicle release are usually accompanied by broad impairments in PPF.
DOI: http://dx.doi.org/10.7554/eLife.03581.005 Increased mEPSC frequency could be due to an increase in synapse number or increase in probability of presynaptic neurotransmitter release.
The variable u+ therefore describes the effective use of the synaptic resources of the synapses, which is analogous to the probability of release in the model described in (Markram et al. 1998).
Hence, our data suggest that putative synapses with larger contact zones at strengthened local excitatory connections in L2/3 of spared cortex have a higher probability of release, resulting in more reliable neurotransmission.
