Characterization of GABAA and glycine receptors in neurons of the developing rat inferior colliculus
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GABAA receptors (GABAARs) 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 ECl close to 0 mV GABA and glycine activated inward currents with a half-maximal activation concentration of 127 µM and 353 µM, respectively. GABAARs activated and deactivated significantly faster than GlyRs (20–80% rise-time: 0.71 ms for GABAARs and 1.31 ms for GlyRs; amplitude-weighted decay time constant, τw, 22.4±1.3 ms for GABAARs and 108.7±32.9 ms for GlyRs). The τw values for receptor desensitization were 26.8±1.9 ms for GABAARs and 177.9±47.2 ms for GlyRs. Recovery from desensitization was significantly faster for GlyRs (τ=334 ms) than for GABAARs (τ1=82 ms; τ2=3783 ms). The τw values of GABAAR-mediated spontaneous and miniature inhibitory postsynaptic currents were not significantly different from those of GABAARs activated by fast application, but significantly different to the τw of GlyRs activated by fast application. The different properties of GABAARs and GlyRs expressed in the same IC neuron suggest a distinct functional contribution to the development of inhibitory synapses in the IC.
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