Accommodation enhances depolarizing inhibition in central neurons

Neurons in the avian cochlear nucleus are depolarized by GABAergic synaptic input. We recorded GABAergic synaptic currents using the gramicid in-perfo rated-patch method and found their reversal potential (V-rev) to be depolar ized relative to spike threshold, which is surprising given that these inpu ts are inhibitory. Depolarizing IPSPs (dIPSPs) are kept below spike generat ion threshold by the activation of a dendrotoxin-I-sensitive, voltage-gated K+ conductance. We show experimentally that the polarity of IPSPs contribu tes to their efficacy; dIPSPs induce accommodation, the positive shift in s pike threshold, and are therefore more strongly inhibitory than conventiona l, hyperpolarizing IPSPs in the same neurons. A similar inhibitory mechanis m has been described in invertebrate sensory fibers and axons of dorsal roo t ganglion cells and may be a general means of amplifying the strength of i nhibition in cases where the size of excitatory conductances greatly exceed s that of inhibitory conductances.