Martin LJ, Zurek AA, MacDonald JF, Roder JC, Jackson MF, Orser BA. (2010) J Neurosci. 30(15):5269-82.
Synaptic plasticity, which is the neuronal substrate for many forms of hippocampus-dependent learning, is attenuated by GABA type A receptor (GABAAR)-mediated inhibition. The prevailing notion is that a synaptic or phasic form of GABAergic inhibition regulates synaptic plasticity; however, little is known about the role of GABAAR subtypes that generate a tonic or persistent inhibitory conductance. We studied the regulation of synaptic plasticity by α5 subunit-containing GABAARs (α5GABAARs), which generate a tonic inhibitory conductance in CA1 pyramidal neurons using electrophysiological recordings of field and whole-cell potentials in hippocampal slices from both wild-type and null mutant mice for the α5 subunit of the GABAAR (Gabra5-/- mice). In addition, the strength of fear-associated memory was studied. The results showed that α5GABAAR activity raises the threshold for induction of long-term potentiation in a highly specific band of stimulation frequencies (10-20 Hz) through mechanisms that are predominantly independent of inhibitory synaptic transmission. The deletion or pharmacological inhibition of α5GABAARs caused no change in baseline membrane potential or input resistance but increased depolarization during 10 Hz stimulation. The encoding of hippocampus-dependent memory was regulated by α5GABAARs but only under specific conditions that generate moderate but not robust forms of fear-associated learning. Thus, under specific conditions, α5GABAAR activity predominates over synaptic inhibition in modifying the strength of both synaptic plasticity in vitro and certain forms of memory in vivo.
Click on link to Pubmed