Characterization of GABA(A) and glycine receptors in neurons of the developing rat inferior colliculus.

GABA(A) receptors (GABA(A)Rs) and glycine receptors (GlyRs) expressed in developing neurons (P3-8) of the rat inferior colliculus (IC) were investigated using fast application of transmitters on nucleated patches and whole-cell patch-clamp recordings. At a holding potential of -60 mV and an E(Cl) close to 0 mV GABA and glycine activated inward currents with a half-maximal activation concentration of 127 microM and 353 microM, respectively. GABA(A)Rs activated and deactivated significantly faster than GlyRs (20-80% rise-time: 0.71 ms for GABA(A)Rs and 1.31 ms for GlyRs; amplitude-weighted decay time constant, tau(w), 22.4+/-1.3 ms for GABA(A)Rs and 108.7+/-32.9 ms for GlyRs). The tau(w) values for receptor desensitization were 26.8+/-1.9 ms for GABA(A)Rs and 177.9+/-47.2 ms for GlyRs. Recovery from desensitization was significantly faster for GlyRs (tau=334 ms) than for GABA(A)Rs (tau1=82 ms; tau2=3783 ms). The tau(w) values of GABA(A)R-mediated spontaneous and miniature inhibitory postsynaptic currents were not significantly different from those of GABA(A)Rs activated by fast application, but significantly different to the tau(w) of GlyRs activated by fast application. The different properties of GABA(A)Rs and GlyRs expressed in the same IC neuron suggest a distinct functional contribution to the development of inhibitory synapses in the IC.