Recruitment of Perisomatic Inhibition during Spontaneous Hippocampal Activity In Vitro
Figure 1
Extracellular recording of spontaneous inhibitory post-synaptic potentials (eIPSPs) in CA3.
A. Simultaneous extracellular recording (guinea pig) from CA3 strata pyramidale (e1, pyr) and radiatum (e2, rad) of spontaneous eIPSPs in vitro. Note eIPSP reversed polarity in radiatum. B. Simultaneous intracellular (from a pyramidal neuron, intra-pyr) and extracellular (extra) recording of an inhibitory synaptic event (guinea pig). C. Simultaneous extracellular recording (e1 and e2, separated by about 150 µm) of eIPSPs evoked by the spontaneous firing of a single action potential from an intracellularly recorded interneuron (intra-iNn), which soma was located at the oriens/pyramidale border (guinea pig). D. Spontaneous extracellular activity in the pyramidal layer (guinea pig): eIPSPs, of positive polarity (upper trace, *), are easily distinguishable from multi-unit activity (arrows). Upper trace, control. Lower trace, in presence of the NMDA and AMPA/KA glutamatergic receptor blockers APV+NBQX. E. Spontaneous activity (control) simultaneously recorded in extracellular (extra) and patch clamp (w/c, whole cell voltage clamp at −50 mV from an individual nearby pyramidal neuron) in a P21 rat. Due to ECl-, GABA-A currents are outward while glutamatergic currents (triangles) are inward. Note that in presence of bicuculine (bicu), eIPSPs and IPSPs are no longer observed, in spite of intense neuronal activity visible as multi-unit discharge (upper trace, extra) and high-frequency glutamatergic synaptic events (lower trace, w/c, triangles). F. Comparison of eIPSP decay (left, average trace normalized on amplitude, right, histogram distribution of eIPSPs decay times) in control (black) and in presence of diazepam (red) in a guinea pig. Note prolonged eIPSP decay under diazepam.