Volume 15 Issue 11, November 2012

Ligands for G protein–coupled receptor 88 (GPR88) have not yet been found. A new study finds that GPR88 is important in the physiology of dorsal striatal projection neurons, as well as in behaviors involving this brain region.

A study reveals that medial entorhinal cortex layer III spiking dynamics shape the neocortical-hippocampal dialog during Up-Down state fluctuations in slow-wave sleep that may contribute to memory consolidation.

Variability in neuronal firing rates and spike timing can be modeled as doubly stochastic. A study now suggests that these phenomena could arise from a network built of deterministic neurons with balanced excitation and inhibition.

The authors review our understanding of the biological basis of resilience to stress. The review examines findings from both humans and animals and also discusses how this knowledge can help guide treatment for stress-related disorders.

Neural progenitor cells (NPCs) are known to be influenced by their local environment. However, in the current study, the authors show that NPCs can also secrete signaling proteins that regulate microglial cell function.

In this study, the authors compare the RNA binding patterns of FUS/TLS and TDP-43. Although these proteins regulate the processing of mostly distinct gene products, they do show concurrent regulation of a subset of neuronal transcripts that all have exceptionally long introns.

Excitatory connections in cortex are clustered into groups of highly connected neurons. Here the authors examine the effect this clustering has on the dynamics of neuronal networks with balanced excitation and inhibition. Their model suggests that the reported variability in spontaneous and evoked spiking activity may result from clustered cortical architecture.

Using a knock-in strategy to ablate a Cdk5-targeted serine phosphorylation site on residue 478 of the TrkB receptor, the authors demonstrate the role of this phosphorylation in activity-dependent functional and structural plasticity, as well as in learning and memory. They further show that TIAM1 and Rac1 act downstream of TrkB S478 phosphorylation during spine remodeling.

Dopamine signaling is known to influence sleep and arousal in Drosophila. Here the authors identify the circuitry underlying the effect of dopamine on arousal, which involves D1 dopamine receptors in the dorsal fan-shaped body as the target of dopaminergic projections.

The authors selectively target a population of hippocampal interneurons called oriens lacunosum-moleculare (OLM) cells with the Chrna2 promoter to demonstrate that these cells differentially modulate CA3 and entorhinal inputs to CA1 pyramidal cells. They also find that OLM cells receive fast cholinergic inputs, providing a plausible explanation for how nicotine affects hippocampal plasticity.

Persistent activity can mediate working memory during behavior. Here, the authors report persistent activity during sleep, occurring spontaneously in medial entorhinal cortex layer III (MECIII) neurons' membrane potential. This persistent activity excited hippocampal CA1 neurons. Thus, persistent activity in MECIII contributes to cortico-hippocampal interaction, which could serve several important mnemonic functions.

The authors explore how sensory maps are reshaped by experience in vivo, using chronic two-photon calcium imaging to follow whisker-evoked activity of individual layer 2/3 neurons in adult mouse barrel cortex over weeks. By first measuring activity with whiskers intact and then with continued trimming of all but one whisker, they describe how the redistribution of population activity underlies large-scale cortical remapping.

GPR88 is an orphan G protein–coupled receptor expressed in striatal medium spiny neurons (MSNs). The authors show that deletion of Gpr88 in mice leads to hyperactivity, poor motor coordination and impaired cue-based learning. MSNs lacking GPR88 show increased excitation and reduced inhibition in vitro, and enhanced firing rates in vivo.

The authors previously showed that a minority of nucleus accumbens neurons, which show strong cocaine-induced activation of the immediate early gene Fos, are necessary for cocaine-induced psychomotor sensitization. Here they find that these cocaine-activated neurons have increased numbers of silent synapses following cocaine sensitization.

This study shows that a mouse's trial-and-error learning in the Morris water maze is mediated by a stereotyped sequence of hippocampus activation along its ventral-to-dorsal axis. Using anatomical or molecular lesions and a previously validated morphological readout of mossy fiber circuit refinement, the authors show that the ventral hippocampus in mice has an early role in goal-oriented learning and searching.

The authors attempt to improve existing retinal models by incorporating measurements of the physiological properties and connectivity of only the primary excitatory circuitry of the retina. The resulting model predicts ganglion cell responses to a variety of spatial patterns and provides a direct correspondence between circuit connectivity and retinal output.

Different types of bipolar cells in the retina carry distinct visual signals to select types of amacrine cells and ganglion cells. The authors show that a single bipolar cell can evoke distinct responses in different ganglion cells and that this signal divergence is the result of interactions with amacrine cells.

The authors show, for human observers, that glossy surfaces can generate both bright specular highlights and dark specular 'lowlights' and that the presence of either is sufficient to generate compelling percepts of gloss. These results suggest that the image structure generated by specular highlights and lowlights is used to construct our experience of surface gloss.

Moving objects generate motion information at different scales, but it is not known how the brain pools all of this information to reconstruct object speed and whether pooling depends on the purpose for which the information will be used. Here the authors find task-dependent differences in pooling that can be explained by an adaptive gain control mechanism.