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Injury of peripheral axons results in a regenerative response from the central as well as the peripheral process of a dorsal root ganglion (DRG) neuron. This conditioning effect is mediated by altered transcription of multiple genes and involves both enhanced axonal growth and reduced inhibition by myelin. Seijffers et al. concentrated on the transcription factor ATF3 as a candidate mediator of the enhanced growth because ATF3 is expressed after peripheral, but not central, axonal injury. The authors generated transgenic mice that expressed ATF3 constitutively in DRG neurons. After sciatic nerve crush, ATF3 transgenic mice displayed early nerve regeneration similar to wild-type (WT) mice after a preconditioning lesion. Preconditioned WT mice extended axons into the spinal cord after a dorsal column injury, but axons in ATF3 transgenic mice did not. Similarly, ATF3-expressing neurons were unable to overcome myelin inhibition. Thus ATF by itself did not completely recapitulate the benefits of preconditioning.

Sometimes if you want something well made, you have got to allow some time. So it goes it seems with making synapses. Ngerl et al. this week focused on the temporal requirements for the synapse formation at newly formed spines. The authors used two-photon laser-scanning microscopy to image hippocampal slice cultures. After theta-burst stimulation (TBS), CA1 pyramidal neurons generated new dendritic spines that lasted throughout a 19 h imaging period. Spines were visualized in living slices with calcein dye. Most preexisting spines had mature synapses with synaptic clefts and adjacent vesicle-filled boutons. The authors then fixed slices at differ
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