Activation of metabotropic GABAB receptors inhibited glutamate responses in spiral ganglion neurons of mice.

The lateral olivocochlear efferent (LOC) fibers form axodendritic synapses with auditory nerve dendrites synapsing on inner hair cells to affect postsynaptic responses GABA is one of the primary transmitters used by the LOC efferent. However, the molecular nature and developmental expression of the GABA receptors in spiral ganglion (SG) neurons are poorly understood. We have identified the GABAB receptors in SG neurons of mice by pharmacological criteria and polymerase chain reaction (PCR) detection. Applications of GABA or baclofen increased intracellular Ca2+ concentrations and inhibited glutamate responses. The responses were blocked by saclofen, but not by bicuculline. Relative-quantitative PCR showed that GABAB receptors were expressed prenatally, and their levels did not change significantly during the maturation of SG neurons.