Figure 3

Electrophysiological assessment shows normal synaptic transmission at transforming growth factor (TGF)-β2 knock-out (KO) neuromuscular junctions (NMJs). (a-h) Bar graphs display the group mean values ± standard error of the mean (n = 3 and 5 embryos for the TGF-β2 KO and control (CON) groups, respectively; data from 3–20 NMJs sampled per muscle). (a) Amplitude, (b) rise-time and (c) frequency of miniature endplate potentials (MEPPs) are unchanged (P = 0.52, 0.23 and 0.11, respectively). (d) MEPP frequency evoked by 2.5 nM α-latrotoxin (α-LTx) is normal (P = 0.48). (e) Similar delay between nerve stimulation and start of the recorded postsynaptic response, either an action potential or an endplate potential (EPP; P = 0.49). (f) Rise time and (g) amplitude of EPPs are normal, as well as (h) the calculated quantal content, that is, the number of transmitter quanta released upon one nerve impulse. (i) Example traces of MEPP recordings in normal Ringer's medium (left panel, showing all MEPPs encountered during a 5 minute recording period) and in the presence of 2.5 nM α-LTx (right panel, 1 s recorded). (j) Examples of recorded muscle fiber action potentials following from a single nerve stimulation. The ensuing contraction of the impaled fiber (and neighboring fibers) leads to the contraction artifact visible in the recording trace just after the action potential. (k) At fibers that were allowed to depolarize to around -30 mV by waiting for some time, a single nerve stimulation evoked an EPP. Example traces of EPPs with similar characteristics recorded in TGF-β2 KO and control fibers. Contraction of neighboring fibers is visible as an artifact on the signal, starting just after the EPP.