Figure 4. Muscle DICR induces a negative feedback on ACh release.

(A) In order to trigger the DICR signal in absence of nicotinic Ca²⁺ influx in Xenopus, postsynaptic APs were directly induced in the muscle cell with brief current steps, without presynaptic stimulation, in presence or absence of external Ca²⁺ (upper right scheme) and with ryanodine that blocks the DICR (bottom right scheme). (B) Effect of selective postsynaptic firing on synaptic currents. Same layout as in Figure 3B. The middle trace shows the muscle APs firing in response to positive current steps injection. (C) In Xenopus, mean ePSC relative change 45 min after control chronic bursting synaptic activity ('chronic activity', n = 5, see 1E), direct triggering of the muscle APs shown in B ('Direct AP', n = 5), APs triggered in a Ca²⁺-free medium ('Direct AP Ca²⁺-free', n = 6, illustrated in Figure 4—figure supplement 1), APs triggered in muscle cells loaded with ryanodine ('Direct AP Ryanodine', n = 3, illustrated in Figure 4—figure supplement 2). (D), Relative change in sPSCs amplitude and frequency in Xenopus after potentiation (red) or depression (green). (E), In FDB mouse muscles, voltage reached by ePSPs in externally stimulated preparations (15 bursts of 120 events at 30 Hz, 10 min) in presence (black dots, n = 75 fibers, 2 mice) and in absence of external Ca²⁺ (green dots, n = 120 fibers, 2 mice). (F), Mean ePSP amplitude in control ('no stim') and high frequency nerve stimulation ('Pre stim') shown in Figure 1D, in externally stimulated preparations shown in E in presence ('External stim-Ca²⁺') and absence of external Ca²⁺ ('External stim-0Ca²⁺'). ***, p<0.001.

DOI: http://dx.doi.org/10.7554/eLife.12190.012

Figure 4—figure supplement 1. External calcium-independent LTD and blockade by postsynaptic ryanodine.

(A) LTD induction in a Ca²⁺ free medium. For the conditioning bursts, postsynaptic APs were triggered by postsynaptic injection of positive current steps, without presynaptic stimulation. (B). ePSC depression via muscle firing is prevented when DICR is blocked with 100 µM ryanodine pre-loaded into the muscle cell.

DOI: http://dx.doi.org/10.7554/eLife.12190.013

Figure 4—figure supplement 2. Recovery from LTD.

In adult mice preparations, external stimulation in a Ca²⁺ free medium is a situation comparable to direct stimulation of the Xenopus muscle cells, and induces a depression of the ePSPs. Here, after a depression induced by 3 bursts of external stimulations in a Ca²⁺ free medium, subsequent bursts of nerve-stimulations (arrow) induced a partial recovery of the ePSPs amplitude. We transiently increased further the external Ca²⁺ concentration to 8mM (which increases the nicotinic Ca²⁺ influx), and this resulted in an increase of the potentiating effect of the bursting nerve stimulations (arrow).

DOI: http://dx.doi.org/10.7554/eLife.12190.014