Related Experiment Videos
Receptors and second messengers involved in long-term depression in rat cerebellar slices in vitro: a reappraisal
N Hémart1, H Daniel, D Jaillard
1ERS CNRS F0100, Bâtiment 440, Université Paris-Sud, Orsay, France.
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.
Insights
Long-term depression (LTD) in Purkinje cells involves distinct pathways. Ionotropic glutamate receptors are crucial for LTD induced by parallel fiber stimulation, while metabotropic glutamate receptors mediate LTD via direct depolarization.
Area of Science:
- Neuroscience
- Cellular Neuroscience
- Synaptic Plasticity
Background:
- Purkinje cells (PCs) in the cerebellum are critical for motor control.
- Long-term depression (LTD) is a key form of synaptic plasticity in PCs, influencing motor learning.
- Understanding the molecular mechanisms of LTD induction is essential for deciphering cerebellar function.
Purpose of the Study:
- To elucidate the distinct signaling pathways involved in different forms of LTD in Purkinje cells.
- To investigate the roles of ionotropic and metabotropic glutamate receptors in LTD induction.
- To differentiate the downstream molecular cascades, including nitric oxide synthase and protein kinase C, in LTD.
Main Methods:
- Patch-clamp recordings were performed on Purkinje cells.
- Pharmacological agents including CNQX, MCPG, 1S,3R-ACPD, L-NMMA, and protein kinase C inhibitor peptide 19-36 were used.
- Specific pairing protocols were employed to induce LTD by combining Ca2+ spike firing and parallel fiber stimulation or direct PC depolarization.
Main Results:
- Induction of LTD by parallel fiber stimulation requires ionotropic glutamate receptors (blocked by CNQX) but not metabotropic glutamate receptors.
- LTD induced by direct PC depolarization and metabotropic glutamate receptor activation is independent of ionotropic receptors.
- Nitric oxide synthase inhibition did not consistently block LTD, whereas protein kinase C inhibition did, for mGLU receptor-dependent LTD.
- Thapsigargin differentially affected LTD induction, blocking mGLU receptor-dependent LTD but not LTD induced by Ca2+ spikes and PF stimulation.
Conclusions:
- Distinct molecular mechanisms underlie different forms of LTD in Purkinje cells.
- Ionotropic and metabotropic glutamate receptors activate separate downstream pathways for LTD induction.
- Protein kinase C and intracellular calcium stores play differential roles in mediating cerebellar LTD.