Neuronal discriminator formed by metabotropic gamma-aminobutyric acid receptors

Neurotransmitters function in one of two modes, promoting either inhibition or excitation. However, the metabotropic gamma-aminobutyric acid receptor (GABA(B)R) system can switch between these modes. Ln the presence of a smal l excitatory stimulus, the GABA(B)R mediates a shunting inhibition that sup presses excitation. However, in the presence of a strong excitatory stimulu s, the GABA(B)R potentiates the response. This bipartite action is accompli shed by linking the GABA(B)R to two electrogenic mechanisms; one activates an outward current and another reduces an outward current. As a consequence , the GABA(B)R serves as a discriminator that reduces the influence of weak signals while augmenting responses to strong signals. in retinal ganglion cells, this mechanism acts to promote the communication of phasic informati on.