title: Signaling cascade regulating long-term potentiation of GABA(A) receptor responsiveness in cerebellar Purkinje neurons.
abstract: Synaptic plasticity, a cellular basis of learning and memory, has been studied extensively at excitatory synapses. Although synaptic plasticity has also been reported at inhibitory synapses, the molecular mechanism remains elusive. Here we attempted to clarify the overall signaling cascades regulating the induction of inhibitory synaptic plasticity in the cerebellum. Rebound potentiation (RP), a long-lasting increase in GABA(A) receptor (GABA(A)R) responsiveness, is induced by postsynaptic depolarization of a Purkinje neuron (PN) at synapses formed with inhibitory interneurons (stellate or basket neurons). Previously, we showed that RP is suppressed by homosynaptic activation during depolarization through activation of the postsynaptic GABA(B) receptor (GABA(B)R). Activation of GABA(B)R reduces cAMP-dependent protein kinase (PKA) activity via the G(i)/G(o)-protein. Here we examined the molecular pathway through which PKA activity affects RP induction. We confirmed that inhibition of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) or PKA suppresses RP. We also found that inhibition of protein phosphatase 1 (PP-1) or calcineurin (PP-2B) impaired suppression of RP induction. Inhibition of either PP-1 or calcineurin abolished RP impairment by PKA inhibition, but not that by CaMKII inhibition. Antisense oligonucleotide-mediated knock down of DARPP-32, which is a substrate of PKA and calcineurin and inhibits PP-1 when phosphorylated by PKA, suppressed RP. Furthermore, activation of GABA(B)R inhibited CaMKII activation through PKA inhibition and PP-1 activity. These results suggest that calcineurin activation accompanied by PKA inhibition in a PN causes dephosphorylation of DARPP-32, which releases PP-1 from inhibition. PP-1 in turn inhibits CaMKII activity, which is then directly involved in the RP induction.
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Shin-Ya
authors.initials: SY
authors.lastname: Kawaguchi
authors.forename: Tomoo
authors.initials: T
authors.lastname: Hirano
mesh_terms: D000818:Animals; D019703:Calcineurin / Q000378:metabolism; D065095:Calcineurin Inhibitors; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D051937:Dopamine and cAMP-Regulated Phosphoprotein 32; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D017774:Long-Term Potentiation / Q000187:drug effects / Q000502:physiology*; D009419:Nerve Tissue Proteins; D009433:Neural Inhibition / Q000502:physiology; D009473:Neuronal Plasticity / Q000187:drug effects / Q000502:physiology; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010750:Phosphoproteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D054645:Protein Phosphatase 1; D011689:Purkinje Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000378:metabolism*; D018080:Receptors, GABA-B / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D065095:Calcineurin Inhibitors; D051937:Dopamine and cAMP-Regulated Phosphoprotein 32; D004791:Enzyme Inhibitors; D018756:GABA Antagonists; D009419:Nerve Tissue Proteins; D016376:Oligonucleotides, Antisense; D010750:Phosphoproteins; D011963:Receptors, GABA-A; D018080:Receptors, GABA-B; D005680:gamma-Aminobutyric Acid; D017868:Cyclic AMP-Dependent Protein Kinases; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1