Volume 15 Issue 1, January 2012

Are astrocytes merely housekeeping cells that maintain constant the environment of neurons or are they important for CNS information processing? Intense debate over the function of calcium signaling in astrocytes will increase with the discovery of a previously unknown mechanism by which astrocyte [Ca²⁺]_i is regulated.

A study now identifies a protein that mediates the cellular transport of the lipophilic endocannabinoid anandamide in aqueous environments.

CRMP and ankyrin have been implicated individually in the regulation of neuronal polarity. A study now identifies an interaction between them that controls microtubule organization and thereby protein sorting into axons and dendrites.

A study finds that the voltage-gated K⁺ channel KCNQ4 is expressed in a subset of rapidly adapting, low-threshold mechanoreceptors, where it shapes the response profile to dynamic tactile stimuli.

Learned odor discrimination and generalization are reflected in patterns of ensemble activity in anterior piriform cortex, where learned discrimination between two odors reduces the correlation between their induced patterns.

Recent work in a number of species has emphasized the role of orbitofrontal cortex in value-based decision-making. However, discrepancies have arisen when comparing the findings from animal models to those from humans. In this review, the author examines several possibilities that might explain these discrepancies.

The authors conduct direct measurements of parvalbumin concentration and paired recordings in rodent hippocampus and cerebellum and show that parvalbumin affects synaptic dynamics, exerting Ca²⁺-buffering effects only when expressed at high levels.

A1 adenosine receptor is antagonized by caffeine and is highly expressed in the CA2 layer of rodent hippocampus. This study now shows that caffeine can induce CA2 synaptic potentiation in a dosage-dependent manner.

The authors report that the two main types of adult-born neurons in the mouse olfactory bulb show experience-dependent plasticity long after maturation and integration into the network.

Xenopus retinal ganglion cells show a switch in sensitivity to the guidance cue Sema3A during development. In this study, the authors show that the timing of this switch is determined by a mechanism in which miR-124 regulates the expression of Neuropilin-1 through modulation of the transcription-repressing cofactor CoREST.

This study reveals a novel function of the Rho GTPase-activating protein called α2-chimerin in cortical development, where acute knockdown of α2-chimerin caused neuronal migration deficit and cortical circuit malformation in the developing mouse brain. This developmental defect was also associated with an impairment of circuit development causing epileptic discharges in adult animals.

Polarized transport to axons and dendrites is critical for neuronal function, but the molecular mechanisms and cytoskeletal cues for asymmetry are incompletely defined. Here the authors show that Caenorhabditis elegans CRMP (UNC-33) acts early in neuronal development, together with ankyrin (UNC-44), to polarize microtubule organization and kinesin-dependent axon-dendrite sorting.

In this study, the authors identify a cell-surface leucine-rich repeat protein, DMA-1, and show that it is both necessary and sufficient to promote dendritic branching in C. elegans sensory neurons. Endogenously, DMA-1 expression is maintained only in those neurons that exhibit elaborate dendritic branching.

After its release, the endocannabinoid anandamide is taken up from the synaptic cleft by internalization by neurons and astrocytes. Although several lines of evidence suggest that the anandamide uptake itself is a carrier-mediated diffusion process, the molecular identity of the transporter was unknown until now. Here Fu et al. show that anandamide uptake is mediated by a novel protein named FAAH-like anandamide transporter (FLAT) that is generated as an alternative splicing product of the fatty acid amide hydrolase-1 (Faah) mRNA.

Using a membrane-tethered, genetically encoded Ca²⁺ indicator, the authors describe a novel Ca²⁺ signal in hippocampal astrocytes. These 'spotty' Ca²⁺ signals were found to be mediated by astrocytic TRPA1 channels. Decreasing astrocyte resting Ca²⁺, regulated by TRPA1 channels, decreased interneuron inhibitory synapse efficacy by reducing GABA transport through GAT-3.

In cultured hippocampal neurons, the authors show that postsynaptic N-cadherin is important to control the basal release probability, and that β-catenin acts via a different trans-synaptic pathway to control the gain adjustment of release probability.

The authors report that prolonged inhibition of nicotinic acetylcholine receptors in Drosophila CNS results in a homeostatic increase in the α7 receptor, which then induces an increase in the A-type K⁺ current carried by Shal/Kv4 channels. This increase in Shal activity stabilizes postsynaptic potentials.

This study demonstrates that the cytosolic helicases RIG-I and MDA5 act to negatively regulate the expansion of the encephalitogenic T_H1 and T_H17 T cells via a mechanism that induces type I interferon production specifically in dendritic cells. Activating this pathway leads to decreased pathology in response to CNS autoimmunity.

C. elegans show a dispersal behavior called nictation. The authors show that this is regulated by the ciliated neuron IL2 and requires cholinergic transmission.

The authors show that paired stimulation of thalamic and cortical auditory inputs to the lateral nucleus of the amygdala, with the interstimulus interval mimicking their activation in behaving animals during auditory fear conditioning, results in persistent potentiation of synaptic transmission in the cortico-amygdala pathway in rat brain slices.

The activity of striatal cholinergic interneurons is known to match phasic dopaminergic response to reinforcing stimuli. Here, the authors use optogenetic techniques to stimulate cholinergic interneurons and measured the response of striatal spiny projection neurons, and reveal an indirect inhibitory circuit in the striatum.

Here the authors identify NCKX4, a potassium-dependent Na⁺/Ca²⁺ exchanger as being necessary for rapid response termination and proper adaptation of vertebrate olfactory sensory neurons. They also report that Nckx4^−/− mice have a reduced ability to locate an odorous source and have lower body weights.

Heidenreich et al. show that KCNQ4—a gene encoding a K⁺ channel whose mutation is linked to progressive human deafness—is expressed in a subset of dorsal root ganglion neurons and mechanosensory touch neurons that serve tactile sensation. The authors show that KCNQ4 loss of function in mice causes a specific tactile dysfunction owing to altered touch sensitivity. The study also finds that human subjects with KCNQ4 mutations and progressive deafness are hypersensitive to tactile information and are able to discern minute high-frequency tactile vibrations.

Using a multisensory cue-conflict task, the authors report that monkeys employ the optimal strategy of weighting each cue in proportion to its reliability, and that population decoding of neural responses from area MSTd predicts behavioral cue weighting. This behavior is further linked to the specific computations by which single neurons combine their inputs, consistent with recent theories of optimal probabilistic neural computation.

The authors show that rats trained with overlapping complex odorant mixtures have improved behavioral discrimination ability and enhanced cortical ensemble pattern separation. Training to disregard normally detectable differences between overlapping mixtures impairs cortical pattern separation and behavioral discrimination. These results show that the balance between pattern separation and completion is experience dependent.

The authors describe the design of an optetrode, a device that allows for colocalized multi-tetrode electrophysiological recording and optical stimulation in freely moving mice.