Figure 1.

Parallel fiber transmission generates an E/I sequence mediated by AMPA receptors.

A) DCN circuit and experimental set-up. Projection neurons (fusiform cells; FC) integrate excitatory synapses from auditory nerve and granule cell parallel fibers. The latter also contact the stellate interneurons that are electrically coupled to fusiform cells. A bipolar stimulating electrode is placed in the molecular layer to activate parallel fibers.

B) A single parallel fiber shock generates an E/I sequence in stellate cells that is blocked by the AMPA receptor antagonist NBQX (10 μM; red trace). Black trace is an average of events that had an initial rapidly rising component, whereas the gray trace is an average of events lacking the fast component. The right panel shows the two types of events on a faster time base to highlight the drastic difference in rise times.

C) Parallel fiber EPSCs in cx36 −/− mice lack the slow inward and outward components. Black and gray traces represent averages of trials in which the fast component either succeeded or failed, respectively.

D) Quantification of EPSCs from wild-type and cx36 −/− mice. Left panel: The total inward charge transfer of parallel fiber EPSCs in wild-type mice was on average −734±164 pA*ms (n=11), whereas it was only −62±6 pA*ms in the KO mice (n=12). Middle and right panels: The inward charge transfer and peak amplitude of the fast rising AMPA EPSC from parallel fiber synapses directly on stellate cells was not significantly different between wild-type and KO mice (WT charge and peak amplitude: −65±8 pA*ms, −29±3 pA. KO charge and peak amplitude: −60±6 pA*ms, −32±3 pA. p=0.67 and 0.39, respectively; unpaired t-test). The fast rising AMPA EPSC was isolated by subtracting the average of slowly-rising events from the average of fast rising events (e.g., black trace minus gray trace).