Figure 7. Convergence of SGNs onto bushy and T stellate cells tends to be lower in Npr2 mutants.

(A) Voltage-clamp recordings (−65 mV) from individual bushy cells showed that in wild-type and heterozygote controls, gradual increase in the strength of shocks applied to auditory nerve fiber bundles evoked first one or two small jumps in current, presumably from bringing to threshold one or two fibers that contacted the recorded bushy cells, and then a large jump likely from bringing to threshold a fiber that contacted the bushy cell with an endbulb of Held. In the mutant, the response was all-or-none, increasing in a single step. In all genotypes, at least one of the steps was >1 nA. There was no obvious difference in the amplitudes of steps between mutant, heterozygote and wild type mice (P17–19). Five out of seven mutant bushy cells likely received one input through an endbulb. (B) Recordings from individual control T stellate cells showed that the synaptic current grew in 8 or 9 small steps, but that in a T stellate cell recorded anteriorly in an Npr2 mutant, the response grew in only 4, larger steps. Small numbers of steps were recorded in 4 of 10 mutant T stellate cells, all of which lay anteriorly; the remaining 6 cells were located posteriorly. This difference is statistically significant (P<0.001, Student's t-test). (C) Recordings from individual octopus cells grew in more steps that were too numerous to count both in the wild type and in mutants. There was no discernible difference between them.