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Post‐tetanic potentiation of GABAergic IPSCs in cultured rat hippocampal neurones
Author(s) -
Jensen Kimmo,
Jensen Morten Skovgaard,
Lambert John D. C.
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.0071o.x
Subject(s) - tetanic stimulation , egta , chemistry , post tetanic potentiation , long term potentiation , stimulation , neuroscience , postsynaptic potential , inhibitory postsynaptic potential , biophysics , excitatory postsynaptic potential , biology , calcium , receptor , biochemistry , organic chemistry
1 Dual whole‐cell patch‐clamp recording was used to investigate post‐tetanic potentiation (PTP) of GABAergic IPSCs evoked between pairs of cultured rat hippocampal neurones. Tetanization of the presynaptic neurone at frequencies ( f ) ranging from 5 to 100 Hz resulted in PTP of the IPSCs. Maximum PTP had a magnitude of 51.6 % just after the stimulus train, and lasted up to 1 min. PTP was shown to be dependent on the number of stimuli in the train, but independent of f at frequencies ≥ 5 Hz. 2 Blocking postsynaptic GABA A receptors with bicuculline during the tetanus did not affect the expression of PTP, showing that it is a presynaptic phenomenon. PTP was strongly affected by changing [Ca 2+ ] o during the tetanus: PTP was reduced by lowering [Ca 2+ ] o , and increased by high [Ca 2+ ] o . 3 PTP was still present after presynaptic injection of BAPTA or EGTA, or following perfusion of the membrane‐permeable ester EGTA‐tetraacetoxymethyl ester (EGTA AM, 50 μM). On the other hand, EGTA AM blocked spontaneous, asynchronous IPSCs (asIPSCs), which were often associated with tetanic stimulation. 4 Tetanic stimulation in the presence of 4‐aminopyridine (4‐AP), which promotes presynaptic Ca 2+ influx, evoked sustained PTP of IPSCs in half of the neurones tested. 5 The results indicate that PTP at inhibitory GABAergic synapses is related to the magnitude of presynaptic Ca 2+ influx during the tetanic stimulation, leading to an enhanced probability of vesicle release in the post‐tetanic period. The increase in [Ca 2+ ] i occurs despite the presence of high‐affinity exogenous and endogenous intracellular Ca 2+ buffers. That PTP of IPSCs depends on the number, and not the frequency, of spikes in the GABAergic neurone is in accordance with a slow clearing of intracellular Ca 2+ from the presynaptic terminals.