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 gramicidin-perforated-patch method and found their reversal potential (V(rev)) to be depolarized relative to spike threshold, which is surprising given that these inputs are inhibitory. Depolarizing IPSPs (dIPSPs) are kept below spike generation threshold by the activation of a dendrotoxin-I-sensitive, voltage-gated K(+) conductance. We show experimentally that the polarity of IPSPs contributes to their efficacy; dIPSPs induce accommodation, the positive shift in spike threshold, and are therefore more strongly inhibitory than conventional, hyperpolarizing IPSPs in the same neurons. A similar inhibitory mechanism has been described in invertebrate sensory fibers and axons of dorsal root ganglion cells and may be a general means of amplifying the strength of inhibition in cases where the size of excitatory conductances greatly exceeds that of inhibitory conductances.