Developmental inhibitory transmitter switching for GANA to glycine

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In order to elucidate the functional implication of inhibitory transmitter switching occurring at auditory relay nucleus of brain stem, we employed electrophysiological and immunohistochemical approach of GABA_B receptor expression over the developmental period. There was a concomitant developmental reduction in the density of expression of the GABAB receptor subunits, R1 and R2, and we also observed a developmental change in the expression pattern of R1 from neurons to astroglia. The GABAB receptor mediated increase in postsynaptic K^+ conductance showed a dramatic reduction over the same period. We have therefore shown that, around the onset of hearing in rats (about 10 days after birth) there is a dramatic reduction in both GABAB receptor expressions in LSO neurons and in the functional effects of GABA_B receptor activation i.e. increased membrane K^+ conductance. It is known that inhibitory input into the LSO changes from being GABAergic to being glycinergic around the onset of hearing ; our results indicate that GABA_B receptor mediated inhibition also shows developmental plasticity. In addition to the well-described developmental change of GABA_A receptor mediated responses from depolarizing to hyperpolarizing, the current data provides a novel and additional example of developmental changes in GABAergic neurobiology.