GABA_B receptor-mediated modulation in the developing dorsal nucleus of the lateral lemniscus

The dorsal nucleus of the lateral lemniscus (DNLL) is a GABAergic, reciprocally connected auditory brainstem structure that continues to develop postnatally in rodents. One key feature of the DNLL is the generation of a strong, prolonged, ionotropic, GABA_A receptor-mediated inhibition. Possible GABA_B receptor-mediated signalling is unexplored in the DNLL. Here, we used Mongolian gerbils of either sex to describe GABA_B receptor-mediated modulation of postsynaptic potassium currents and synaptic inputs in postnatal (P) animals of days 10/11 and 23-28. Throughout development, we observed the presence of a Baclofen-activated GABA_B receptor-enhanced potassium outward conductance that is capable of suppressing action potential generation. In P10/11, old gerbils GABA_B receptor activation enhances glutamatergic and suppresses ionotropic GABAergic synaptic transmission. During development, this differential modulation becomes less distinct, because in P22-28, old animals Baclofen-activated GABA_B receptors rather enhance ionotropic GABAergic synaptic transmission, whereas glutamatergic transmission is both enhanced and suppressed. Blocking GABA_B receptors causes an increase in ionotropic GABAergic transmission in P10/11 old gerbils that was independent on stimulation frequency but depended on the type of short-term plasticity. Together with the lack of Baclofen-induced changes in the synaptic paired-pulse ratio of either input type, we suggest that GABA_B receptor-mediated modulation is predominantly postsynaptic and activates different signalling cascades. Thus, we argue that in DNLL neurons, the GABA_B receptor is a post-synaptically located signalling hub that alters signalling cascades during development for distinct targets.