Unitary inhibitory synaptic potentials in the guinea‐pig hippocampus in vitro.

Abstract

Mechanisms involved in the generation of synaptic inhibition have been investigated by making simultaneous intracellular recordings from pairs of neurones in the CA3 pyramidal cell field of guinea‐pig hippocampal slices. Inhibitory post‐synaptic potentials dependent on single presynaptic action potentials (i.p.s.p.s) and mediated through monosynaptic and disynaptic connexions have been identified. The recurrent nature of some hippocampal inhibition has been demonstrated by showing that activity in a single cell may initiate feed‐back i.p.s.p.s onto itself. The observation of synchronous i.p.s.p.s in recordings from two cells illustrates the divergence of synaptic contacts made by inhibitory neurones. The peak conductance change associated with an i.p.s.p. was in the range 5‐9 nS and it reversed uniformly throughout its time course at membrane potentials between ‐73 and ‐80 mV. The shortest time‐to‐peak of synaptic potentials was approximately 3 ms and in this case the i.p.s.p. decayed with a time constant comparable to the passive membrane time constant of the post‐synaptic neurone. The peak amplitude of i.p.s.p.s fluctuated in a way consistent with the quantal release of inhibitory neurotransmitter. Inhibitory neurones could fire bursts of action potentials not unlike those generated by pyramidal cells in this area. A comparison of the conductance change associated with identified i.p.s.p.s with that associated with the maximal inhibitory post‐synaptic potential resulting from electrical stimulation of fibre pathways suggested that, in the slice, a pyramidal cell is innervated by up to fifteen inhibitory neurones.

Stratum lacunosum-moleculare interneurons of hippocampal CA1 region. II. Intrasomatic and intradendritic recordings of local circuit synaptic interactions

“…However, basket cell-and O/A interneuron-induced IPSPs decay more rapidly (25-40 msec) than L-M interneuron-induced IPSPs (40-l 50 msec; mean, 90 msec). The slow kinetics of CA1 pyramidal cell IPSPs evoked by interneuron stimulation are in contrast to CA3 pyramidal cell unitary IPSPs, which have a more rapid rise time (3-5 msec) and decay (15-40 msec) (MacVicar and Dudek, 1980;Miles and Wong, 1984).…”

A thin slice preparation for patch clamp recordings from neurones of the mammalian central nervous system

“…Pairs of neurones can be filled with fluorescent dyes during simultaneous whole-cell recording. If such a pair of neurones were synaptically connected, stimulated or spontaneous action potentials recorded in the presynaptic cell would result in synaptic responses which could be measured in the postsynaptic cell (Miles and Wong 1984). Together with recent development of confocal microscopy and its application to neurones (A, slund et al 1987;Wall6n et al 1988) this would allow detailed investigation of the location and nature of synapses involved.…”

Distinct nonuniform cable properties optimize rapid and efficient activation of fast-spiking GABAergic interneurons

“…Although inhibition comprises several steps, including activation of excitatory input synapses on BCs, dendritic integration of excitatory postsynaptic potentials (EPSPs), action potential initiation and propagation, and GABA release from output synapses, the kinetics of disynaptic inhibition can be very rapid, with ≈2 ms total onset time at physiologic temperature (3,7). Several synaptic specializations contribute to the remarkable speed of feedforward and feedback inhibition.…”