Postsynaptically different inhibitory postsynaptic currents in Cajal–Retzius cells in the developing neocortex

Fast and slowly rising inhibitory postsynaptic currents (IPSCs, IPSCF and IPSCS) in neocortical Cajal–Retzius cells are observed. In this study, zolpidem, a benzodiazepine agonist that specifically modulates γ-aminobutyric acid type A receptors (GABAARs) containing γ2 subunit, was used to characterize GABAARs mediating IPSCF and IPSCS. One-hundred-nanomolar zolpidem prolonged IPSCS, increased evoked IPSCS (eIPSCS) amplitude, and decreased paired-pulse ratio (PPR) of eIPSCS. Two micromolar zolpidem prolonged both IPSCF and IPSCS, increased miniature IPSCF and eIPSCF amplitudes, increased eIPSCS amplitude but not miniature IPSCS amplitude, decreased PPR of eIPSCS, but failed to affect PPR of eIPSCF. We conclude that IPSCF are mediated by α2/3-containing GABAARs, which are not saturated by synaptic GABA release, whereas IPSCS are mediated by α1-containing and α2/3-containing GABAARs, which are saturated by quantal GABA release.