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Bicuculline‐ and Phaclofen‐Resistant Hyperpolarizations Evoked by Glutamate Applications to Stratum Lacunosum‐Moleculare in CA1 Pyramidal Cells of the Rat Hippocampus In Vitro
Author(s) -
Williams Sylvain,
Lacaille JeanClaude
Publication year - 1990
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/j.1460-9568.1990.tb00012.x
Subject(s) - inhibitory postsynaptic potential , glutamate receptor , bicuculline , neuroscience , cnqx , interneuron , reversal potential , chemistry , neurotransmission , excitatory postsynaptic potential , biology , biophysics , electrophysiology , gabaa receptor , ampa receptor , biochemistry , patch clamp , receptor
In the hippocampus, different types of interneurons may mediate distinct gamma‐aminobutyric acid (GABA) responses, i.e. the early and late inhibitory postsynaptic potentials (IPSPs). To verify this hypothesis, intracellular recordings were obtained from CA1 pyramidal cells ( n = 63) in rat hippocampal slices. Glutamate (1 mM) was locally ejected in stratum lacunosum‐moleculare to activate interneurons in this region. Glutamate‐evoked hyperpolarizing responses were characterized in pyramidal cells and compared to the early IPSP and the late IPSP elicited by stratum radiatum electrical stimulation. Several characteristics were similar for the glutamate‐evoked IPSPs and late IPSPs: their amplitude was small (−3.4 versus −4.9 mV, respectively), each was associated with a small conductance increase (5.0 versus 9.3 nS, respectively), their peak latency was slow (124.4 versus 129.8 ms, respectively) and in the majority of cells, each displayed little response reversal. However, the equilibrium potential of the glutamate IPSP (−76.5 mV) was similar to that of the early IPSP (−73.8 mV). Perfusion with a low Ca 2+ (0.5 mM)/high Mg 2+ (8 mM) medium or with tetrodotoxin (1 μM), which blocked synaptic transmission, also reduced the glutamate IPSP. Therefore the glutamate IPSP may be mediated indirectly by inhibitory interneurons. The GABA A antagonist bicuculline (10 μM), or picrotoxin (10–20 μM), blocked the early IPSP, but not the glutamate IPSP. The GABA B antagonist phaclofen (1 mM) attenuated the late IPSP, but did not affect the glutamate IPSP. The results of these experiments suggest that glutamate stimulation of interneurons in stratum lacunosum‐moleculare evokes a slow IPSP different from the GABA‐mediated early and late IPSPs in CA1 pyramidal cells of the hippocampus.

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