1. The Battle of the LTDs in the Cerebellum
Wolfgang Mittmann and Michael Husser
Purkinje cells provide the sole output of cerebellar cortex, thus serving as the final common pathway for cerebellar synaptic integration and plasticity. The cellular plasticity associated with cerebellar motor learning is thought to arise from long-term depression (LTD) of excitatory parallel fibers (PFs) triggered by simultaneous climbing fiber (CF) activity. Mittmann and Husser show this week that its not quite so simple: plasticity at feedforward inhibitory synapses is also important. The authors recorded from spontaneously spiking Purkinje cells in rat cerebellar slices. PF EPSPs increased Purkinje cell firing, whereas interneuron inhibitory PSPs reduced spiking. When CF inputs were paired with PF EPSPs or with interneuron IPSPs, LTD occurred in both inputs, but with opposite effects on Purkinje cell spiking. The net effect of this battle of the LTDs varied with inhibitory/excitatory input ratios. Plasticity produced a reduction in Purkinje cell spike output when there was only a small inhibitory component.
2. Dynein, LIS1, and Growth Cones
Peter W. Grabham, Garrett E. Seale, Malika Bennecib, Daniel J. Goldberg, and Richard B. Vallee
The molecular motor dynein and its regulatory factors dynactin and LIS1 associate with microtubules to promote cellular migration and axonal growth. This week, Grabham et al. examined the role of these molecules in growth cone dynamics. The authors treated embryonic chick dorsal root ganglion (DRG) neurons with laminin, which caused rapid reorganization of microtubules in growth cones as well as dynein staining that was concentrated at the leading edge. Dynactin and LIS1 were colocalized with dynein. A similar staining pattern was observed in growth cones of rat hippocampal neurons. Knockdown of LIS1 by RNA interference delayed polarization of hippocampal neurons and decreased axonal lengths. Dynein
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Society for Neuroscience