Volume 13 Issue 3, March 2010

Investigating the organization of tone representation in the rodent auditory cortex at high resolution, two new studies in this issue find that the arrangement of relative frequency responsiveness is not preserved at a fine-scale cortical level.

A new localization element in the 3′ untranslated region of the IMPA1 mRNA enables its NGF-dependent targeting to sympathetic axons, suggesting that high local inositol levels are required for axon growth and maintenance.

Axonal integrity depends on an intact myelin sheath, but the role of the axon in myelin maintenance is more mysterious. A new study reports that preservation of the myelin sheath requires neuronal expression of the enigmatic prion protein.

Synaptic long-term potentiation and depression are determined by the frequency and timing of coactivated synapses. A new model explains many experimental plasticity observations and allows new predictions about neural circuit function.

What is the minimal sensory processing time before we can make a decision about a stimulus? A study now reports that, for simple perceptual decisions, this can take as little as 30 ms.

Cannabinoid signaling is generally thought to increase food intake. Bellocchio et al. show that cannabinoids can increase or attenuate feeding after a fast, depending on whether they act on glutamatergic forebrain or GABAergic ventral striatal neurons.

The authors generated a mutant mouse with neuron-specific reductions in brain cytochrome P450 activity. These mice have attenuated morphine antinociception, which suggests that neuronal P450 epoxygenase mediates the pain-relieving properties of morphine.

After a focal demyelination of the corpus callosum in adult mice, the demyelinated axons form functional excitatory synapses onto adult-born oligodendrocyte progenitor cells. This input is lost later on.

The authors report that the mRNA for myo-inositol monophosphatase-1, an enzyme that regulates the inositol cycle and the main target of lithium in neurons, is localized to axons. They identify a novel NGF-responsive localization element within the 3′ UTR that directs this targeting and local translation.

The authors report that a dose of BDNF elicits very different signaling, morphological and synaptic responses in hippocampal neurons or slices, depending on whether it is applied all at once or gradually.

The signals ensuring maintenance of the myelin sheath on peripheral nerves are distinct from those instructing myelination and are largely unknown. Here, the authors report that neuronal expression and regulated proteolysis of the prion protein are essential for myelin maintenance.

Cuprizone causes demyelination and oligodendrocyte death in mice. Cuprizone lesions resemble a particular form of white-matter lesions that is seen in multiple sclerosis. This study reports that infiltrating neutrophils expressing the chemokine receptor CXCR2 contribute to oligodendrocyte death in the cuprizone model of demyelination.

The number of dendritic spines is reduced in the postmortem brains of individuals with schizophrenia. Revealing a potential mechanism of such change, this study finds that the schizophrenia-associated protein DISC1 regulates the Rho GTPase pathway to modulate dendritic spine size.

A-type potassium currents determine a neuron's firing characteristics. Anderson et al. find that Cav3 calcium channels complex with Kv4 potassium channels, such that Ca²⁺ influx through T-type channels via the calcium-binding protein KChIP3 enhances Kv4 function.

SNAP-23 has previously been implicated in exocytosis regulation in non-neuronal cells. Here the authors report that SNAP-23 is also important in neurons, where it is responsible for functional regulation of postsynaptic glutamate receptors.

The authors develop a model of synaptic plasticity that can account for a large body of experimental data on connection patterns in the cortex. This model uses multiple parameters, including presynaptic spike interval and postsynaptic membrane potential.

The authors use in vivo two-photon calcium imaging to examine the responses and network dynamics of layer 2/3 neurons in the primary auditory cortex of mice in response to pure tones. They find that local populations in A1 are heterogeneous, but, despite this, there was a higher than average noise correlation.

Using two-photon calcium imaging, the authors found that although tonotopy was present in mouse auditory cortex at a coarse scale, it was fractured on a fine scale. Intensity tuning appeared to have no topography at all, but subthreshold responses revealed that there was some clustering of neurons with similar response properties.

The authors measured the variability of neuronal responses across a large number of datasets and cortical areas. They found that variability decreased in response to all stimuli tested, whether the animal was awake, behaving or anesthetized, suggesting that the stabilization of cortex in response to an input is a general cortical property.

It is hard to dissociate the time taken for purely perceptual processes from motor reaction times when making responses to stimuli. Using a combination of a novel task design and computational modeling, this study dissociates these two processes and finds that monkeys can discriminate perceptual color information in as little time as 30 ms.

Channelrhodopsins such as ChR2 can drive spiking with millisecond precision. However, when ChR2 is highly expressed, a single light pulse can produce extra spikes, and ChR2 does not allow sustained spike trains above about 40 Hz. Rapid ChR2-driven spike trains can also cause plateau potentials. Here, the authors report an engineered opsin gene, ChETA, that overcomes these limitations and allows sustained spike trains up to 200 Hz.

This paper reports the first recording from brain neurons of flying Drosophila. The responses of visual interneurons to moving grate stimuli were substantially modulated by flight, as compared with the resting situation.