Volume 12 Issue 7, July 2009

How are volatile molecules entering the nose converted to odor percepts in the brain? A fMRI study finds that distributed patterns of activity in the human posterior piriform cortex code the perceived category of odorants. This categorization of odors into objects is independent of their chemical structure.

A study shows that the histone deacetylases HDAC1 and HDAC2 stimulate oligodendrocyte differentiation by antagonizing the inhibitory action of Wnt signaling, linking genetic and epigenetic control of oligodendrocyte development.

A recent study shows that GABA switches from stimulating to inhibiting interneuron motility during neocortical development. This change in response is gated by the expression of the chloride transporter KCC2.

Mitochondria are considered to be the main source of reactive oxygen species during glutamate excitotoxicity. Data now support a prominent role in this process for NADPH oxidase, the enzyme that neutrophils use to kill bacteria.

How different frontal brain regions contribute to goal-directed behavior is not fully understood. A study now suggests a parallel functional architecture in medial and lateral prefrontal cortex for motivating and selecting behavior.

Synaptic plasticity at the cerebellar parallel fiber–Purkinje cell is mediated by calcium/calmodulin kinase II. In a knockout mouse line lacking the beta subunit of CaMKII, the authors show a bidirectional inversion of synaptic plasticity accompanying movement disorders and impaired motor learning.

Mutations in LRRK2 can cause Parkinson's disease. The authors create a transgenic mouse model of LRRK2 that recapitulates several cardinal features of the disease.

Previous work has suggested that the histone deacetylase HDAC1 promotes and canonical Wnt signaling antagonizes oligodendrocyte differentiation. Here, Ye et al. show that HDAC1/2 directly interferes with canonical Wnt signaling in oligodendrocyte precursors by competing with β-catenin for interaction with the transcriptional co-factor TCF7L2. TCF7L2 itself is shown to be crucial for oligodendrocyte development.

Although the role of Notch signaling in CNS glial development is well established, its participation in peripheral glial development is still unclear. This paper shows that Notch signaling regulates the differentiation of Schwann cell precursors and the proliferation of Schwann cells, and acts as a break on myelination of peripheral nerves.

Lee and colleagues demonstrate that actin depolarizing factor (ADF)/cofilin regulates, and is required for, the insertion of acetylcholine receptors (AChRs) into the postsynaptic membrane at neuromuscular synapses. ADF/cofilin also appears to stabilize membrane AChRs; it associates with AChR clusters and disappears before the clusters themselves disassemble.

NMDA-induced superoxide production, which can lead to cell death at excessive levels, is widely believed to originate from mitochondria. Here, the authors find that, in both cultured neurons and mouse hippocampus, NADPH oxidase is actually the primary source of NMDA-induced superoxide production.

PolyQ-Htt inhibits fast axonal transport in cellular and animal Huntington's disease models. Here, the authors show that this effect is a result of the activation of JNK3. PolyQ-Htt–activated JNK3 reduces kinesin-1 binding to microtubules.

Orr and colleagues identify a molecular pathway in microglia that converts ATP-dependent process extension into process retraction during inflammation. This reversal is dependant on A_2A adenosine receptor upregulation and P2Y₁₂ downregulation.

The authors use high-resolution total reflection fluorescence microscopy to study the mechanisms of AMPA receptor synaptic delivery. They report that palmitoylation of the GluR1 subunit modulates phosphorylation by PKC. This enhances protein 4.1N binding to GluR1, thereby facilitating GluR1 insertion.

The authors examine the effect of increased synthesis of AMPAR subunits on their subcellular distribution in hippocampal neurons. Virally expressing AMPARs caused an accumulation in cell bodies with little effect on dendritic amounts. Stargazin coexpression enhanced dendritic GluR1 levels by protecting it from lysosomal degradation but didn't increase surface or synaptic GluR1 levels.

Most synapses in the mature CNS are wrapped by a dense extracellular matrix (ECM). The authors show that removing the ECM increased the lateral diffusion of AMPA receptors and affected short-term synaptic plasticity. This suggests that the ECM may modulate synaptic transmission by restricting receptor diffusion.

Memories can be reconsolidated when reactivated. However, reconsolidation does not occur under certain boundary conditions. The authors show that these boundary conditions can be transient and that strong auditory fear memories in rats that initially did not undergo reconsolidation eventually did over time. Moreover, they find that the hippocampus is necessary for preventing reconsolidation from occuring in the amygdala, and that NR2B subunits, normally required for induction of reconsolidation in the amygdala, are downregulated when strong memories do not undergo reconsolidation.

Hippocampal replay is thought to be essential for the consolidation of event memories. Sleep replay involves the reactivation of stored representations in the absence of specific sensory inputs, whereas awake replay is thought to reflect input from the current environment. Here the authors find that the hippocampus consistently replays past experiences during brief pauses in waking behavior, suggesting a role for waking replay in memory consolidation and retrieval.

During sleep, neural patterns reflecting previously acquired information are replayed in the hippocampus. Here, the authors report that there is reactivation of learning-related patterns of activity in the medial prefrontal cortex during sleep following rule acquisition that coincided with hippocampal sharp wave/ripple complexes.

Young birds rely on auditory feedback when learning to imitate the songs of adult birds. Here the authors find that, as with humans, birds use auditory feedback to correct vocal errors in adulthood. This suggests that lifelong error correction may be a general principle of learned vocal behavior.

This study reports that odorants that elicited similar fMRI activity patterns in the posterior piriform cortex were more likely to be judged as being more perceptually alike. This correlation between spatially distributed activity and perceptual judgments was not reproduced in other areas of the brain, suggesting that the posterior piriform cortex contains a spatially distributed ensemble code for odor object quality.

Using functional magnetic resonance imaging, the authors investigate how the prefrontal cortex (PFC) combines the motivation and selection processes underlying cognitive control. They find that these functions are physically separable, represented in different areas of the PFC, and that these areas may subserve the integration of motivation and cognitive control for decision making.

The mosaic analysis with repressible cell markers (MARCM) technique allows for lineage tracing in Drosophila. Here, the authors report an improvement on this technique, twin-spot MARCM, which permits high-resolution lineage tracing of both sister clones.