Figure 7.

Summary diagram of the circuitry in the DCN. The GABA/GABA_BR/PKCγ triple-labeled neurons are distributed in the molecular layer and fusiform cell layer. Most of these neurons are presumed to be cartwheel cells, which receive input from parallel fibers. As inhibitory interneurons, their GABAergic terminals were attached to the other cartwheel cells and fusiform cells. The glutamatergic fusiform cells, which might also express GABA_BRs, receiving inputs from parallel fibers and auditory nerve afferents, finally project to the inferior colliculus (IC). The noise stimulation could activate both cartwheel cells and fusiform cells. The activation of cartwheel cells could be attributed to the decreased GABA_BRs, leading to the disinhibition among the GABA-containing cartwheel cells. The noise injury also increases PKCγ in these activated cartwheel cells. In the glutamatergic fusiform cells expressing GABA_BRs, because of the reduction of GABA_BRs, the loss of presynaptic and postsynaptic inhibition of glutamate activation might promote glutamate neurotransmission in NIHL.