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The conductance underlying the parallel fibre slow EPSP in rat cerebellar Purkinje neurones studied with photolytic release of L‐glutamate
Author(s) -
Canepari Marco,
Papageorgiou George,
Corrie John E. T.,
Watkins Chris,
Ogden David
Publication year - 2001
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.1469-7793.2001.00765.x
Subject(s) - metabotropic glutamate receptor , glutamate receptor , metabotropic glutamate receptor 1 , ionotropic effect , biophysics , chemistry , metabotropic receptor , kainic acid , excitatory postsynaptic potential , biochemistry , receptor , biology
1 Tetanic stimulation of parallel fibres (PFs) produces a slow EPSP (sEPSP) or slow EPSC (sEPSC) in Purkinje neurones (PNs), mediated by type 1 metabotropic glutamate receptors (mGluR1). The conductance change underlying the sEPSP was investigated with rapid photolytic release of L‐glutamate from nitroindolinyl (NI)‐caged glutamate with ionotropic glutamate receptors blocked, and showed a slow mGluR1‐activated cation channel. 2 In cerebellar slices rapid photolytic release ( t 1/2 < 0.7 ms) of 7‐70 μM L‐glutamate on PNs voltage clamped at −65 mV activated first a transient inward current, peaking in 8 ms, followed by a slow inward current with time course similar to the PF sEPSP, peaking at −1 nA in 700 ms. 3 The initial current was inhibited by 300 μM threo‐hydroxyaspartate (THA) and did not reverse as the potential was made positive up to +50 mV, suggesting activation of electrogenic glutamate uptake. 4 The slow current was inhibited reversibly by 1 mM ( R,S) ‐MCPG or the non‐competitive mGluR1 antagonist CPCCOEt (20 μM), indicating activation of metabotropic type 1 glutamate receptors. The mGluR current was associated with increases of input conductance and membrane current noise, and reversed close to 0 mV, indicating activation of channels permeant to Na + and K + . 5 The sEPSC was not blocked by Cd 2+ , Co 2+ , Mg 2+ or Gd 3+ ions, by the inhibitor of hyperpolarisation‐activated current ( I H ) ZD7288, or by the purinoceptor inhibitor PPADS. Activation was not affected by inhibitors of phospholipase C (PLC) or protein kinase C (PKC), nor mimicked by photorelease of Ins P 3 or Ca 2+ . The results show that mGluR1 in PNs produces a slow activation of cation‐permeable ion channels which is not mediated by PLC activation, Ca 2+ release from stores, or via the activation of PKC.