Receptors and Second Messengers Involved in Long‐term Depression in Rat Cerebellar Slices In Vitro: a Reappraisal

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Abstract
In patch-clamped Purkinje cells (PCs), bath application of the ionotropic glutamate receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) prevents induction of long-term depression (LTD) of parallel fibre (PF)-mediated EPSPs by a pairing protocol between Ca2+ spike firing and PF stimulation whereas bath application of (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG), a metabotropic glutamate (mGLU) receptor antagonist, does not. On the other hand, LTD can be also induced by pairing direct depolarization of PCs with activation of mGLU receptors by 1S,3R-aminocyclopentyl-dicarboxylate (1S,3R-ACPD), even in the presence of CNQX. In this case, LTD induction is not consistently blocked by bath application of the nitric oxide synthase inhibitor, NG-methyl-L-arginine (L-NMMA), whereas it is strongly blocked when the protein kinase C inhibitor peptide 19-36 is dialysed into PCs. These results are at variance with LTD induced by a pairing protocol between Ca2+ spikes and PF-mediated EPSPs which depends to the same extent on both cascades. Finally, thapsigargin, which depletes most intracellular Ca2+ pools, does not block induction of LTD by a pairing protocol between Ca2+ spikes and PF-mediated EPSPs whereas it prevents the induction of LTD depending on strong mGLU receptor activation.