Inositol-1,4,5-Trisphosphate Receptor-Mediated Ca Mobilization Is Not Required for Cerebellar Long-Term Depression in Reduced Preparations

Abstract

Inositol-1,4,5-trisphosphate receptor-mediated Ca mobilization is not required for cerebellar long-term depression in reduced preparations. J. Neurophysiol. 80: 2963-2974, 1998. Cerebellar long-term depression (LTD) is a cellular model system of information storage in which coincident parallel fiber and climbing fiber activation of a Purkinje neuron (PN) gives rise to a sustained attenuation of parallel fiber-PN synaptic strength. Climbing fiber and parallel fiber inputs may be replaced by direct depolarization of the PN and exogenous glutamate pulses, respectively. The parallel fiber-PN synapse has a high-density of mGluR1 receptors that are coupled to phosphoinositide turnover. Several lines of evidence indicated that activation of mGluR1 by parallel fiber stimulation is necessary for the induction of cerebellar LTD. Because phosphoinositide hydrolysis has two initial products, 1, 2-diacylglycerol and inositol-1,4,5-trisphosphate (IP3), we wished to determine whether IP3 signaling via IP3 receptors and consequent Ca mobilization were necessary for the induction of cerebellar LTD. First, ratiometric imaging of free cytosolic Ca was performed on both acutely dissociated and cultured PNs. It was determined that the threshold for glutamate pulses to contribute to LTD induction was below the threshold for producing a Ca transient. Furthermore, the Ca transients produced by depolarization alone and glutamate plus depolarization were not significantly different. Second, the potent and selective IP3 receptor channel blocker xestospongin C was not found to affect the induction of LTD in either acutely dissociated or cultured PNs at a concentration that was sufficient to block mGluR1-evoked Ca mobilization. Third, replacement of mGluR activation by exogenous synthetic diacylglycerol in an LTD induction protocol was successful. Taken together, these results suggest that activation of an IP3 signaling cascade is not required for induction of cerebellar LTD in reduced preparations.

Protein phosphatase 2A inhibition induces cerebellar long-term depression and declustering of synaptic AMPA receptor

“…It should be noted that the period between the second and third postnatal week in vivo corresponds to an extensive synaptic remodeling (disappearance of functional N-methyl-Daspartate receptors and of multiple climbing fiber innervation) and changes in electrical properties resulting from alteration of voltage-dependent channel populations (45,46). The signaling cascade underlying cerebellar LTD also appears to undergo considerable maturation during this period, with neither IP 3 nor NO required in immature PCs (47,48), whereas these signals are necessary in the mature cerebellum (5). Furthermore, this period also corresponds to a drastic inversion of the relative abundance of PP-2A B ␤ and PP-2A B ␥ in the brain, two PP-2A regulatory subunits highly expressed in PCs and involved in PP-2A targeting (21).…”

Sindbis Virus-Induced Neuronal Death Is both Necrotic and Apoptotic and Is Ameliorated by N -Methyl- d -Aspartate Receptor Antagonists

“…The cells were washed twice with a solution containing (in mM) NaCl, 140; KCl, 5; CaCl 2 , 2; MgCl 2 , 0.8; HEPES, 10; and glucose, 10. Imaging was performed at room temperature as previously described (29,44). Fura-2 AM ratio imaging of intracellular free Ca 2ϩ was accomplished by measuring the background-corrected fluorescence ratio at 340-and 380-nm excitation with a cooled chargecoupled device camera system.…”

Type-1 metabotropic glutamate receptor in cerebellar Purkinje cells: a key molecule responsible for long-term depression, endocannabinoid signalling and synapse elimination

“…IP 3 -induced Ca 2C release is also shown to be required for LTD induction in cerebellar slices (Hemart et al 1995;Khodakhah & Armstrong 1997;Inoue et al 1998;Daniel et al 1999;Miyata et al 2000), although it is not required for LTD of glutamate responsiveness in certain cultured Purkinje cell preparations ( Narasimhan et al 1998). Several studies indicate that pharmacological blockade of IP 3 receptors or depletion of Ca 2C stores blocks LTD or LTD-like synaptic depression in cerebellar slices (Hemart et al 1995;Khodakhah & Armstrong 1997;Inoue et al 1998).…”