S. Bertrand et Jc. Lacaille, Unitary synaptic currents between lacunosum-moleculare interneurones and pyramidal cells in rat hippocampus, J PHYSL LON, 532(2), 2001, pp. 369-384
1. Unitary inhibitory postsynaptic currents (uIPSCs) were characterised bet
ween 23 synaptically coupled interneurones at the border of stratum radiatu
m and lacunosum-moleclare (LM) and CA1 pyramidal cells (PYR) using dual who
le-cell recordings and morphological identification in rat hippocampal slic
es.
2. LM interneurones presented a morphology typical of stellate cells, with
a fusiform soma as well as dendritic and axonal arborisations in stratum ra
diatum and lacunosum-moleculare.
3. Single spikes in interneurones triggered uIPSCs in pyramidal cells that
were blocked by the GABAA antagonist bicuculline and mediated by a chloride
conductance. The latency, rise time, duration and decay time constant of u
IPSCs were a function of amplitude in all pairs, suggesting a homogeneity i
n the population sampled.
4. During paired pulse stimulation, individual LM-PYR connections exhibited
facilitation or depression. The paired pulse ratio was inversely related t
o the amplitude of the first response. The transition from facilitation to
depression occurred at 26 % of the maximal amplitude of the first uIPSC. Pa
ired pulse depression was not modified by CGP 55845 and thus was GABA(B) re
ceptor independent.
5. CGP 55845 failed to modify the amplitude of uIPSCs, suggesting an absenc
e of tonic presynaptic GABA(B) inhibition at LM-PYR connections. B. Increas
ing G;ABA release by repetitive activation of interneurones failed to induc
e GABAB IPSCs. With extracellular minimal stimulation, increasing stimulati
on intensity above threshold, or repetitive activation, evoked GABA(B) IPSC
s, probably as a result of coactivation of several GABAergic fibres. 7. Thu
s, dendritic inhibition by LM interneurones involves GABA(A) uIPSCs with ki
netics dependent on response amplitude and subject to GABA(B)-independent p
aired pulse plasticity.