The Journal of Neuroscience, October 1, 2001, 21(19):7823-7830
Graduate Program in Neurobiology and Behavior and Virginia Merrill
Bloedel Hearing Research Center, University of Washington, Seattle,
Washington 98195
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
(Vrev) 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.
Key words: inhibition; GABA; magnocellularis; dynamic clamp; PAD; accommodation; auditory