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. 2018 Apr 20;27(14):2425–2442. doi: 10.1093/hmg/ddy142

Figure 4.

Figure 4.

Reduced probability of transmitter release underlies enhanced short-term synaptic facilitation in pre-symptomatic AR97Q NMJs. (A) Synapses in pre-symptomatic AR97Q males exhibit a significant increase in facilitation (based on average EPP responses to trains of five pulses at 100 Hz) compared with junctions from WT males of the same age, suggesting a reduced probability of transmitter release. (B) Representative traces of evoked EPP (average of 10–20 individual EPPs) from WT and pre-symptomatic AR97Q NMJs showing the enhanced size of EPPs with repeated stimulation for Tg junctions. (C and D) The size of the RRP for pre-symptomatic AR97Q males is unaffected (C). The same x-intercept extrapolated from the initial phase of rapid decline in QC for Tg and WT synapses indicates that the maximum number of immediately releasable quanta (RRP size) without replenishment is comparable, with mean (± SEM) values in (D). (E) Pr, on the other hand, is significantly decreased in motor nerve terminals of pre-symptomatic AR97Q males, indicating that early deficits in QC reflect deficits in Pr with the size of the RRP eventually also reduced as disease progresses. Pr was calculated as initial QC/RRP. Values plotted are group means ± SEM (WT: n/N = 42/4 and pre-symptomatic AR97Q: n/N = 42/4). n is the number of endplates per experimental group and N is the number of mice per experimental group. *P < 0.05 from WT.