7 - 130 see comments section vesicles
||Zucker RS, Regehr WG. Short-term synaptic plasticity. Annu Rev Physiol. 2002 64: 355-405. p.371 bottom paragraphPubMed ID11826273
|| von Gersdorff H, Vardi E, Matthews G, Sterling P. 1996. Evidence that vesicles on the synaptic ribbon of retinal bipolar neurons can be rapidly released. Neuron 16:1221–27  Lenzi D, Runyeon JW, Crum J, Ellisman MH, Roberts WM. 1999. Synaptic vesicle populations in saccular hair cells reconstructed by electron tomography. J. Neurosci. 19:119–32  Rao-Mirotznik R, Harkins AB, Buchsbaum G, Sterling P. 1995. Mammalian rod terminal: architecture of a binary synapse. Neuron 14: 561–69  Harris KM, Sultan P. 1995. Variation in the number, location and size of synaptic vesicles provides an anatomical basis for the nonuniform probability of release at hippocampal CA1 synapses. Neuropharmacology 34: 1387–95  Schikorski T, Stevens CF. 1997. Quantitative ultrastructural analysis of hippocampal excitatory synapses. J. Neurosci. 17: 5858–67  Schikorski T, Stevens CF. 1999. Quantitative fine-structural analysis of olfactory cortical synapses. Proc. Natl. Acad. Sci. USA 96: 4107–12PubMed ID8663998, 9870944, 7695902, 8606788, 9221783, 10097171
||P.371 bottom paragraph: "How big is the readily releasable pool at individual release sites? A number of approaches have been taken to measure the size of this pool of vesicles, including a large depolarizing pulse in the presynaptic terminal, caged Ca2+ in the presynaptic terminal, application of high-osmolarity solution, and integration of fully depressing responses to brief stimulus trains (refs 13, 14, 107, 171). The challenge with all of these approaches is to measure the full size of the release-ready pool without it being replenished from the reserve pool. Failure to release all of the vesicles will lead to an underestimation of the size of the pool, whereas contributions from the reserve pool can lead to an overestimation (ref 192). Serial electron microcopy has also been used to determine the number of morphologically docked vesicles, which may correspond to the readily releasable pool. Estimates of the functional size of the readily releasable pool per active zone are 7–8 at the parallel fiber and climbing fiber synapses, 22 in goldfish bipolar neurons (primary source 193), 32 in frog saccular hair cells (primary source 194), 130 in cat rod photoreceptors (primary source 195), an average of about 10 for the CA1 region of the hippocampus (primary sources 196, 197), and in layers 1a and 1b of pyriform cortex, the average number of docked vesicles is 16 and 27, respectively (primary source 198). There is considerable variability in the number of docked vesicles at individual synapses, even for the same type of synapse." Primary source  studied goldfishes,  studied frogs,  studied cats,  studied rats, & [197, 198] studied mice.