Motor Dysfunction and Altered Synaptic Transmission at the Parallel Fiber-Purkinje Cell Synapse in Mice Lacking Potassium Channels Kv3.1 and Kv3.3

Abstract

Micelacking both Kv3.1 and both Kv3.3 K+ channel alleles display severe motor deficits such as tremor, myoclonus, and ataxic gait. Micelacking one to three alleles at the Kv3.1 and Kv3.3 loci exhibit in an allele dose-dependent manner a modest degree of ataxia. Cerebellar granule cells coexpress Kv3.1 and Kv3.3 K+ channels and are therefore candidate neurons that might be involved in these behavioral deficits. Hence, we investigated the synaptic mechanisms of transmission in the parallel fiber-Purkinje cell system. Action potentials of parallel fibers were broader in mice lacking both Kv3.1 and both Kv3.3 alleles and in mice lacking both Kv3.1 and a single Kv3.3 allele compared with those of wild-type mice. The transmission of high-frequency trains of action potentials was only impaired at 200 Hz but not at 100 Hz in mice lacking both Kv3.1 and Kv3.3 genes. However, paired-pulse facilitation (PPF) at parallel fiber-Purkinje cell synapses was dramatically reduced in a gene dose-dependent manner in mice lacking Kv3.1 or Kv3.3 alleles. Normal PPF could be restored by reducing the extracellular Ca2+ concentration indicating that increased activity-dependent presynaptic Ca2+ influx, at least in part caused the altered PPF in mutant mice. Induction of metabotropic glutamate receptor-mediated EPSCs was facilitated, whereas longterm depression was not impaired but rather facilitated in Kv3.1/Kv3.3 double-knockout mice. These results demonstrate the importance of Kv3 potassium channels in regulating the dynamics of synaptic transmission at the parallel fiber-Purkinje cell synapse and suggest a correlation between short-term plasticity at the parallel fiber-Purkinje cell synapse and motor performance.

Purkinje-Cell-Restricted Restoration of Kv3.3 Function Restores Complex Spikes and Rescues Motor Coordination inKcnc3Mutants

“…Kcnc3-null mice (ϩ/ϩ; Ϫ/Ϫ and ϩ/Ϫ; Ϫ/Ϫ) improve their performance on the 1 cm and 0.5 cm beams just as rapidly as wild-type mice during the 5 d test, suggesting that altered simple and complex spike firing does not affect this type of motor skill learning. This is in agreement with theories of cerebellar learning stipulating a role for parallel fiberPurkinje cell long-term depression (LTD) and the previous observation that LTD is intact at these synapses in the absence of Kv3.3 (Matsukawa et al, 2003). The contribution of climbing fiber input to LTD is thought to arise from calcium influx in the dendrite, whereas the alterations here affect the sodium spikes of resulting complex spikes at the soma.…”

“…It has been reported that anxiety decreases performance in a variant of the beam test (Lepicard et al, 2003). Alternatively, parallel fiber input to Purkinje cells, which is affected when Kcnc1 and Kcnc3 alleles are absent (Matsukawa et al, 2003), is initially abnormal but undergoes plastic changes on training that compensate for the augmented glutamatergic drive.…”

“…As a primarily depressing synapse, the Purkinje cell-to-DCN synapse is considerably more sensitive to sudden changes in Purkinje cell firing rate than tonic input at a constant frequency (Telgkamp and Raman, 2002;Pedroarena and Schwarz, 2003;Telgkamp et al, 2004). Given the enhancement of parallel fiber input to Purkinje cells (Matsukawa et al, 2003), it is unclear whether the decrease in spontaneous simple spike frequency described in slices generalize to Purkinje cells in vivo with intact parallel fibers. Complex spikes, and the pauses that follow, are poised to have a greater impact on the DCN, for they involve sudden changes in input.…”

Properties and expression of Kv3 channels in cerebellar Purkinje cells

“…In addition, also Kv3.1/Kv3.3 double knockout mice are severely ataxic and have a marked broadening of action potentials in cerebellar granule cells and PCs (Espinosa et al, 2001;Matsukawa et al, 2003). Kv3.3 single mutant mice are not overtly ataxic, but they have a 100% increase of PC action potential duration and lack harmaline-induced tremor, indicating a disrupted function of the olivo-cerebellar circuit (McMahon et al, 2004).…”

Plasma Membrane Ca2+ATPase 2 Contributes to Short-Term Synapse Plasticity at the Parallel Fiber to Purkinje Neuron Synapse

“…Two-hundred seventy-micrometer-thick sagittal slices or 300-m-thick coronal slices were prepared from age-matched littermate male and female WT and homozygous (PMCA2Ϫ/Ϫ) and heterozygous (PMCA2ϩ/Ϫ) mice (on the same day), 21-26 d old, after rapid anesthesia with halothane as described previously (Matsukawa et al, 2003). Slices were maintained at 24°C, or temporarily at 35°C (TC324B; Harvard Apparatus, Hamden, CT) in a flow (3 ml/min) of artificial CSF (aCSF), equilibrated with 95% O 2 and 5% CO 2 , containing (in mM) 126 NaCl, 2.…”