Disassembly of Shank and Homer Synaptic Clusters Is Driven by Soluble β-Amyloid1-40 through Divergent NMDAR-Dependent Signalling Pathways

Disruption of the postsynaptic density (PSD), a network of scaffold proteins located in dendritic spines, is thought to be responsible for synaptic dysfunction and loss in early-stage Alzheimer''s disease (AD). Extending our previous demonstration that derangement of the PSD by soluble amyloid-β (Aβ) involves proteasomal degradation of PSD-95, a protein important for ionotropic glutamate receptor trafficking, we now show that Aβ also disrupts two other scaffold proteins, Homer1b and Shank1, that couple PSD-95 with ionotropic and metabotropic glutamate receptors. Treatment of fronto-cortical neurons with soluble Aβ results in rapid (within 1 h) and significant thinning of the PSD, decreased synaptic levels of Homer1b and Shank1, and reduced synaptic mGluR1 levels. We show that de novo protein synthesis is required for the declustering effects of Aβ on Homer1b (but not Shank1) and that, in contrast to PSD-95, Aβ-induced Homer1b and Shank1 cluster disassembly does not depend on proteasome activity. The regulation of Homer1b and Shank1 by Aβ diverges in two other respects: i) whereas the activity of both NMDAR and VDCC is required for Aβ-induced declustering of Homer1b, Aβ-induced declustering of Shank1 only requires NMDAR activity; and ii) whereas the effects of Aβ on Homer1b involve engagement of the PI-3K pathway and calcineurin phosphatase (PP2B) activity, those on Shank1 involve activation of the ERK pathway. In summary, soluble Aβ recruits discrete signalling pathways to rapidly reduce the synaptic localization of major components of the PSD and to regulate the availability of mGluR1 in the synapse.     

Regional difference of glutamate-induced swelling in cultured rat brain astrocytes

L-glutamate (glutamate) is an important neurotoxin as well as the major excitatory neurotransmitter. Extracellular glutamate levels are elevated following ischemia, hypoglycemia, and trauma. One consequence of elevated glutamate levels is cell swelling. Such swelling occurs primarily in astroglial cells. We characterized the regional difference in glutamate-induced swelling response of cultured astrocytes from rat cerebral cortex, hippocampus and cerebellum. Glutamate produced dose-dependent astrocytic swelling in both cerebral cortex and hippocampus, showing a maximal effect in 0.5 mM concentration, as measured by 3-O-methyl-D-[1-3H]glucose uptake. However, in cerebellum, glutamate did not produce astrocytic swelling. It has been suggested that Na+ -dependent glutamate uptake is a possible mechanism of glutamate-induced swelling. The Vmax for glutamate uptake into cerebellum astrocytes was significantly lower (6.7 nmol/mg protein/min) than those for cerebral cortex and hippocampus astrocytes (13.0 and 12.0 nmol/mg protein/min, respectively). In three regions, more than 90% of the cultured cells showed glial fibrillary acidic protein (GFAP) immunoreactivity. Immunoreactivity of GLT, one of the markers of glutamate transporters, which is expressed at low levels in cultured astrocytes, did not show any differences in three regions. However, immunoreactivities of GLAST, the other astroglial glutamate transporter, and aquaporin4 (APQ4), a water transporter, were significantly higher in cerebral cortex and hippocampus than in cerebellum. These results may explain the regional difference of glutamate-induced astrocytic swelling.     

Negative regulation of neurotransmitter release by calpain: a possible involvement of specific SNAP-25 cleavage

Synaptic transmission is conducted by neurotransmitters released from presynaptic nerve terminals by means of Ca2+-dependent exocytosis of synaptic vesicles. Formation of a complex of soluble N-ethylmaleimide-sensitive fusion protein receptor (SNARE) proteins, including vesicle-associated membrane protein-2 (VAMP-2) in the synaptic vesicle membrane, and syntaxin 1 and synaptosomal-associated protein of 25 kDa (SNAP-25) in the plasma membrane, is essential for exocytosis. Ionomycin treatment of cultured rat cerebellar granule cells led to cleavage of SNAP-25, but not syntaxin 1 and VAMP-2, that was dependent on extracellular Ca2+. Cleavage was also induced by N-methyl-D-aspartate (NMDA) treatment, but not by depolarization. The use of various site-specific antibodies to SNAP-25, suggested that the cleavage site was in the N-terminal domain of SNAP-25. Calpain inhibitors abolished the Ca2+-dependent cleavage of SNAP-25 and markedly facilitated Ca2+-dependent glutamate (Glu) release from cerebellar granule cells. These results suggest that calpain may play an important role in the long-lasting regulation of synaptic transmission by suppressing neurotransmitter release, possibly through the proteolytic cleavage of SNAP-25.     

Drebrin contains a cryptic F-actin–bundling activity regulated by Cdk5 phosphorylation

Drebrin is an actin filament (F-actin)–binding protein with crucial roles in neuritogenesis and synaptic plasticity. Drebrin couples dynamic microtubules to F-actin in growth cone filopodia via binding to the microtubule-binding +TIP protein EB3 and organizes F-actin in dendritic spines. Precisely how drebrin interacts with F-actin and how this is regulated is unknown. We used cellular and in vitro assays with a library of drebrin deletion constructs to map F-actin binding sites. We discovered two domains in the N-terminal half of drebrin—a coiled-coil domain and a helical domain—that independently bound to F-actin and cooperatively bundled F-actin. However, this activity was repressed by an intramolecular interaction relieved by Cdk5 phosphorylation of serine 142 located in the coiled-coil domain. Phospho-mimetic and phospho-dead mutants of serine 142 interfered with neuritogenesis and coupling of microtubules to F-actin in growth cone filopodia. These findings show that drebrin contains a cryptic F-actin–bundling activity regulated by phosphorylation and provide a mechanistic model for microtubule–F-actin coupling.     

Glutamate-mediated extrasynaptic inhibition: direct coupling of NMDA receptors to Ca(2+)-activated K+ channels

NMDA receptors (NMDARs) typically contribute to excitatory synaptic transmission in the CNS. While Ca(2+) influx through NMDARs plays a critical role in synaptic plasticity, direct actions of NMDAR-mediated Ca(2+) influx on neuronal excitability have not been well established. Here we show that Ca(2+) influx through NMDARs is directly coupled to activation of BK-type Ca(2+)-activated K+ channels in outside-out membrane patches from rat olfactory bulb granule cells. Repetitive stimulation of glutamatergic synapses in olfactory bulb slices evokes a slow inhibitory postsynaptic current (IPSC) in granule cells that requires both NMDARs and BK channels. The slow IPSC is enhanced by glutamate uptake blockers, suggesting that extrasynaptic NMDARs underlie the response. These findings reveal a novel inhibitory action of extrasynaptic NMDARs in the brain.     

Down-regulation of Homer1b/c attenuates glutamate-mediated excitotoxicity through endoplasmic reticulum and mitochondria pathways in rat cortical neurons

Glutamate-mediated excitotoxicity is involved in many acute and chronic brain diseases. Homer proteins, a new member of the postsynaptic scaffolding proteins, regulate glutamatergic signaling and intracellular calcium mobilization in the central nervous system. Here we investigated the effects of down-regulating Homer1b/c, a constitutively expressed long form of Homer proteins, on glutamate excitotoxicity-induced neuronal injury. In our in vitro excitotoxic models, we demonstrated that glutamate insults led to a dose-dependent neuronal injury, which was mediated by the intracellular calcium-dependent reactive oxygen species (ROS) production. We found that down-regulation of Homer1b/c with specific small interfering RNA (siRNA) improved neuronal survival, inhibited intracellular ROS production, and reduced apoptotic cell death after neurotoxicity. Homer1b/c knockdown decreased the intracellular calcium overload through inhibition of the group I metabotropic glutamate receptor (mGluR)/inositol 1,4,5-trisphosphate receptor (IP3R)-mediated Ca2+ release from the endoplasmic reticulum (ER) in injured neurons. In addition, Homer1b/c siRNA transfection attenuated the activation of eukaryotic initiation factor 2α (eIF2α), RNA-dependent protein kinase-like ER kinase (PERK) and caspase-12, and inhibited the up-regulation of glucose-regulated protein 78 (GRP78) and C/EBP homologous protein (CHOP) after glutamate treatment. Homer1b/c knockdown also preserved the mitochondrial membrane potential (MMP), reduced cytochrome c (Cyt. c) release, and partly blocked the increase of capase-9 activity and Bax/Bcl-2 ratio. Taken together, these results suggest that down-regulation of Homer1b/c protects cortical neurons against glutamate-induced excitatory damage, and this neuroprotection may be dependent at least in part on the inhibition of calcium-dependent ROS production and the preservation of the ER and mitochondrial function.     

Determinants of postsynaptic Ca2+ signaling in Purkinje neurons

Neuronal integration in Purkinje neurons involves many forms of Ca2+ signaling. Two afferent synaptic inputs, the parallel and the climbing fibers, provide a major drive for these signals. These two excitatory synaptic inputs are both glutamatergic. Postsynaptically they activate alpha-amino-3-hydroxy-5-methyl-4-propionic acid (AMPA) receptors (AMPARs) and metabotropic glutamate receptors (mGluRs). Unlike most other types of central neurons, Purkinje neurons do not express NMDA (N-methyl-D-aspartate) receptors (NMDARs). AMPARs in Purkinje neurons are characterized by a low permeability for Ca2+ ions. AMPAR-mediated synaptic depolarization may activate voltage-gated Ca2+ channels, mostly of the P/Q-type. The resulting intracellular Ca2+ signals are shaped by the Ca2+ buffers calbindin and parvalbumin. Ca2+ clearance from the cytosol is brought about by Ca2+-ATPases in the plasma membrane and the endoplasmic reticulum, as well as the Na+-Ca2+-exchanger. Binding of glutamate to mGluRs induces postsynaptic Ca2+-transients through two G protein-dependent pathways: involving (1) the release of Ca2+ ions from intracellular Ca2+ stores and (2) the opening of the cation channel TRPC1. Homer proteins appear to play an important role in postsynaptic Ca2+ signaling by providing a direct link between the plasma membrane-resident elements (mGluRs and TRPC1) and their intracellular partners, including the IP3Rs.     

Excitotoxic injury to mitochondria isolated from cultured neurons

Neuronal death in response to excitotoxic levels of glutamate is dependent upon mitochondrial Ca2+ accumulation and is associated with a drop in ATP levels and a loss in ionic homeostasis. Yet the mapping of temporal events in mitochondria subsequent to Ca2+ sequestration is incomplete. By isolating mitochondria from primary cultures, we discovered that glutamate treatment of cortical neurons for 10 min caused 44% inhibition of ADP-stimulated respiration, whereas the maximal rate of electron transport (uncoupler-stimulated respiration) was inhibited by approximately 10%. The Ca2+ load in mitochondria from glutamate-treated neurons was estimated to be 167 +/- 19 nmol/mg protein. The glutamate-induced Ca2+ load was less than the maximal Ca2+ uptake capacity of the mitochondria determined in vitro (363 +/- 35 nmol/mg protein). Comparatively, mitochondria isolated from cerebellar granule cells demonstrated a higher Ca2+ uptake capacity (686 +/- 71 nmol/mg protein) than the cortical mitochondria, and the glutamate-induced load of Ca2+ was a smaller percentage of the maximal Ca2+ uptake capacity. Thus, this study indicated that Ca(2+)-induced impairment of mitochondrial ATP production is an early event in the excitotoxic cascade that may contribute to decreased cellular ATP and loss of ionic homeostasis that precede commitment to neuronal death.     

Oxidative stress, mitochondrial function, and acute glutamate excitotoxicity in cultured cerebellar granule cells

On exposure to glutamate, cultured rat cerebellar granule cells undergo a delayed Ca2+ deregulation (DCD), which precedes and predicts cell death. We have previously shown that mitochondria control the sensitivity of the neurons to DCD. Mitochondrial depolarization by rotenone/oligomycin before glutamate addition is strongly neuroprotective, and the indication is therefore that mitochondrial Ca2+ loading leads to a delayed loss of bioenergetic function culminating in DCD and cell death. In this report it is shown that superoxide (O2.-) generation in intact cells, monitored by oxidation of hydroethidine to ethidium, was enhanced by glutamate only when mitochondria were polarized. Production of superoxide was higher in the subset of cells undergoing DCD. In the presence of rotenone and oligomycin, addition of glutamate did not result in increased superoxide generation. Menadione-generated superoxide enhances the DCD of cells exposed to glutamate; in contrast, glutamate-induced DCD was potently inhibited by the presence of the cell-permeant antioxidant manganese(III) tetrakis(4-benzoic acid) porphyrin. An inverse correlation is observed between the cytoplasmic free Ca2+ maintained in individual cells in the presence of glutamate and the ability of these cells to restore basal Ca2+ when NMDA receptors are inhibited and mitochondrial Ca2+ is released. It is concluded that mitochondrial Ca2+ accumulation and reactive oxygen species each contribute to DCD, probably related to damage to a process controlling Ca2+ efflux from the cell.     

Synaptic targeting of PSD-Zip45 (Homer 1c) and its involvement in the synaptic accumulation of F-actin

PSD-Zip45/Homer1c, which contains an enabled/VASP homology 1 (EVH1) domain and leucine zipper motifs, is a postsynaptic density (PSD) scaffold protein that interacts with metabotropic glutamate receptors and the shank family. We studied the molecular mechanism underlying the synaptic targeting of PSD-Zip45 in cultured hippocampal neurons. The EVH1 domain and the extreme C-terminal leucine zipper motif were molecular determinants for its synaptic targeting. The overexpression of the mutant of the EVH1 domain or deletion of the extreme C-terminal leucine zipper motif markedly suppressed the synaptic localization of endogenous shank but not PSD-95 or GKAP. In contrast, an overexpressed GKAP mutant lacking shank binding activity had no effect on the synaptic localization of shank. Actin depolymerization by latrunculin A reduced the synaptic localization of PSD-Zip45, shank, and F-actin but not of PSD-95 or GKAP. Overexpression of PSD-Zip45 enhanced the accumulation of synaptic F-actin. Additionally, overexpression of PSD-Zip45 and an isoform of shank induced synaptic enlargement in association with the further accumulation of synaptic F-actin. The EVH1 domain and extreme C-terminal leucine zipper motif of PSD-Zip45 were also critical for these events. Thus, these data suggest that the PSD-Zip45-shank and PSD-95-GKAP complexes form different synaptic compartments, and PSD-Zip45 alone or PSD-Zip45-shank is involved in the synaptic accumulation of F-actin.     

Histone deacetylase mediates the decrease in drebrin cluster density induced by amyloid beta oligomers

Dendritic spine defects are found in a number of cognitive disorders, including Alzheimer’s disease (AD). Amyloid beta (Aβ) toxicity is mediated not only by the fibrillar form of the protein, but also by the soluble oligomers (Aβ-derived diffusible ligands, ADDLs). Drebrin is an actin-binding protein that is located at mature dendritic spines. Because drebrin expression is decreased in AD brains and in cultured neurons exposed to Aβ, it is thought that drebrin is closely associated with cognitive functions. Recent studies show that histone deacetylase (HDAC) activity is elevated in the AD mouse model, and that memory impairments in these animals can be ameliorated by HDAC inhibitors. In addition, spine loss and memory impairment in HDAC2 over-expressing mice are ameliorated by chronic HDAC inhibitor treatment. Therefore, we hypothesized that the regulation of histone acetylation/deacetylation is critical to synaptic functioning. In this study, we examined the relationship between HDAC activity and synaptic defects induced by ADDLs using an HDAC inhibitor, suberoylanilide hydroxamic acid (SAHA). We show that ADDLs reduce the cluster density of drebrin along dendrites without reducing drebrin expression. SAHA markedly increased the acetylation of histone proteins, and it simultaneously attenuated the ADDL-induced decrease in drebrin cluster density. In comparison, SAHA treatment did not affect the density of drebrin clusters or dendritic protrusions in control neurons. Therefore, SAHA likely inhibits ADDL-induced drebrin loss from dendritic spines by stabilizing drebrin in these structures, rather than by increasing drebrin clusters or dendritic protrusions. Taken together, our findings suggest that HDAC is involved in ADDL-induced synaptic defects, and that the regulation of histone acetylation plays an important role in modulating actin cytoskeletal dynamics in dendritic spines under cellular stress conditions, such as ADDL exposure.     

The Homer-1 protein Ania-3 interacts with the plasma membrane calcium pump

The Homer family of scaffold proteins couples NMDA receptors to metabotropic glutamate receptors and links extracellular signals to calcium release from intracellular stores. Ania-3 is a member of the Homer family and is rapidly inducible in brain in response to diverse stimuli. Here, we report the identification of the plasma membrane Ca2+ ATPase (PMCA) as a novel Ania-3/Homer-associated protein. Ania-3/Homer interacts with the b-splice forms of all PMCAs (PMCA1b, 2b, 3b, and 4b) via their PDZ domain-binding COOH-terminal tail. Ectopically expressed Ania-3 colocalized with the PMCA at the plasma membrane of polarized MDCK epithelial cells, and endogenous Ania-3/Homer and PMCA2 are co-expressed in the soma and dendrites of primary rat hippocampal neurons. The interaction between Ania-3/Homer and PMCAs may represent a novel mechanism by which local calcium signaling and hence synaptic function can be modulated in neurons.     

Spinophilin is phosphorylated by Ca2+/calmodulin-dependent protein kinase II resulting in regulation of its binding to F-actin

Spinophilin is a protein phosphatase-1- and actin-binding protein that modulates excitatory synaptic transmission and dendritic spine morphology. We have recently shown that the interaction of spinophilin with the actin cytoskeleton depends upon phosphorylation by protein kinase A. We have now found that spinophilin is phosphorylated by Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) in neurons. Ca(2+)/calmodulin-dependent protein kinase II, located within the post-synaptic density of dendritic spines, is known to play a role in synaptic plasticity and is ideally positioned to regulate spinophilin. Using tryptic phosphopeptide mapping, site-directed mutagenesis and microsequencing analysis, we identified two sites of CaMKII phosphorylation (Ser-100 and Ser-116) within the actin-binding domain of spinophilin. Phosphorylation by CaMKII reduced the affinity of spinophilin for F-actin. In neurons, phosphorylation at Ser-100 by CaMKII was Ca(2+) dependent and was associated with an enrichment of spinophilin in the synaptic plasma membrane fraction. These results indicate that spinophilin is phosphorylated by multiple kinases in vivo and that differential phosphorylation may target spinophilin to specific locations within dendritic spines.     

Homer protein increases activation of Ca2+ sparks in permeabilized skeletal muscle

Members of the Homer family of proteins are known to form multimeric complexes capable of cross-linking plasma membrane channels (e.g. metabotropic glutamate receptor) and intracellular Ca2+ release channels (e.g. inositol trisphosphate receptor) in neurons, which potentiates Ca2+ release. Recent work has demonstrated direct interaction of Homer proteins with type 1 and type 2 ryanodine receptor (RyR) isoforms. Moreover, Homer proteins have been shown to modulate RyR-dependent Ca2+ release in isolated channels as well as in whole cell preparations. We now show that long and short forms of Homer H1 (H1c and H1-EVH1) are potent activators of Ca2+ release via RyR in skeletal muscle fibers (e.g. Ca2+ sparks) and potent modulators of ryanodine binding to membranes enriched with RyR, with H1c being significantly more potent than H1-EVH1. Homer did not significantly alter the spatio-temporal properties of the sparks, demonstrating that Homer increases the rate of opening of RyRs, with no change in the overall RyR channel open time and amount of Ca2+ released during a spark. No changes in Ca2+ spark frequency or properties were observed using a full-length H1c with mutation in the EVH1 binding domain (H1c-G89N). One novel finding with each Homer agonist (H1c and H1-EVH1) was that in combination their actions on [3H]ryanodine binding was additive, an effect also observed for these Homer agonists in the Ca2+ spark studies. Finally, in Ca2+ spark studies, excess H1c-G89N prevented the effects of H1c in a dominant negative manner. Taken together our results suggest that the EVH1 domain is critical for the agonist behavior on Ca2+ sparks and ryanodine binding, and that the coiled-coil domain, present in long but not short form Homer, confers an increase in agonist potential apparently through the multimeric association of Homer ligand.     

Functional and immunocytochemical evidence for the expression and localization of the secretory pathway Ca2+-ATPase isoform 1 (SPCA1) in cerebellum relative to other Ca2+ pumps

Membrane fractions of pig cerebellum show Ca2+-ATPase activity and Ca2+ transport due to the presence of the secretory pathway Ca2+-ATPase (SPCA). The SPCA1 isoform shows a wide distribution in the neurons of pig cerebellum, where it is found in the Golgi complex of the soma of Purkinje, stellate, basket and granule cells, and also in more distal components of the secretory pathway associated with a synaptic localization such as in cerebellar glomeruli. The SPCA1 may be involved in loading the Golgi complex and the secretory vesicles of these specific neuronal cell types with Ca2+ and also Mn2+. This study of the cellular and subcellular localization of SPCA1 pumps relative to the sarco(endo) plasmic reticulum Ca2+-ATPase and plasma membrane Ca2+-ATPase pumps hints to a possible specific role of SPCA1 in controlling the luminal secretory pathway Ca2+ (or Mn2+) levels as well as the local cytosolic Ca2+ levels. In addition, it helps to specify the zones that are most vulnerable to Ca2+ and/or Mn2+ dyshomeostasis, a condition that is held responsible of an increasing number of neurological disorders.     

Mechanisms of destabilization of Ca2+-homeostasis of brain neurons caused by toxic glutamate challenge

The long-term stimulation of mammalian central neurons with an excitatory neuromediator, glutamate, results in destabilization of Ca2+-homeostasis caused mainly by an impairment of the systems of excessive Ca2+ extrusion from the cytoplasm both into the environment (Na+/Ca2+-exchanger, Ca2+/H+ pump) and mitochondria. The data available suggest that inhibition of the mitochondrial Ca2+ uptake following the glutamate action is due to the strong depolarization of inner mitochondrial membrane caused by opening of the "large pore" in response to the Ca2+ overload and overproduction of free oxygen radicals and NO. The mechanism of deterioration of Ca2+ extrusion from the neuron into extracellular medium following the glutamate challenge has not been yet fully clarified. It is only known that some factors inhibiting or irreversibly altering the functions of Na+/Ca2+-exchanger and Ca2+/H+ pump are accumulated in the cell during the prolonged action of glutamate. They include lowering of ATP concentration and pHi, as well as overproduction of free oxygen radicals and products of lipid peroxidation. The exact contribution of these factors to the final destabilization of Ca2+ homeostasis is under study. A good correlation between the glutamate-induced mitochondrial depolarization and the failure of neurons to extrude excessive Ca2+ from the cytoplasm during the post-glutamate period indicates that at this period the mitochondrial dysfunction is critical for the destabilization of Ca2+ homeostasis.     

Excitotoxic loss of post-synaptic sites is distinct temporally and mechanistically from neuronal death

Dendritic degeneration and loss of synaptic proteins are early events correlated with functional decline in neurodegenerative disease. The temporal and mechanistic relationship between synapse loss and cell death, however, remains unclear. We used confocal microscopy and image processing to count post-synaptic sites on rat hippocampal neurons by expressing post-synaptic density protein 95 fused to green fluorescent protein. Fluorescent puncta co-localized with neurotransmitter release sites, NMDA-induced Ca²⁺ increases and NMDA receptor immunoreactivity. During excitotoxic neurodegeneration, synaptic sites were lost and synaptic transmission impaired. These changes were mediated by NMDA receptors and required Ca²⁺-dependent activation of the proteasome pathway. Tracking synapses from the same cell following brief neurotoxic insult revealed transient loss followed by recovery. The time-course, concentration-dependence and mechanism for loss of post-synaptic sites were distinct from those leading to cell death. Cells expressing p14ARF, which inhibits ubiquitination of post-synaptic density protein 95 and prevents loss of synaptic sites, displayed an increased sensitivity to glutamate-induced cell death. Thus, excitotoxic synapse loss may be a disease-modifying process rather than an obligatory step leading to cell death. These results demonstrate the importance of assessing synaptic function independent of neuronal survival during neurodegeneration and indicate that this approach will be useful for identifying toxins that degrade synaptic connections and for screening for agents that protect synaptic function.     

Mechanisms of modification of excitatory and inhibitory inputs in various neurons of olivary-cerebellar network

It is known from the experimental data that at different cerebellar neurons there are voltage-dependent Ca2+ channels, NMDA receptors, metabotropic glutamate and GABAB receptors. This receptor arrangement ensures that activation of excitatory and inhibitory input results in changes in activity of protein kinases and phosphatases and subsequent modification of synaptic efficacy. The mechanism of synaptic plasticity is advanced that in accordance with the known experimental data concerning the modification of excitatory and inhibitory inputs to Purkinje cells, granule cells, and deep cerebellar nuclei cells. The mechanism is based on a postulate that phosphorylation/dephosphorylation of AMPA (GABAA) receptors on cerebellar cells causes the LTP/LTD of excitatory (LTD/LTP of inhibitory) transmission. It is assumed that modification rules for Purkinje cells, granule cells, and deep cerebellar nuclei cells, wherein cGMP-dependent protein kinase G is involved in synaptic plasticity, are distinct from those of hippocampal/neocortical cells, wherein cAMP-dependent protein kinase A is involved in synaptic plasticity, since cGMP (cAMP) concentration decreases (increases) with Ca2+ rise.