Volume 13 Issue 12, December 2010

Tiny gaze shifts, or microsaccades, have little function in the eye movement control system and were once thought to be suppressed during fine spatial judgements. A new study suggests that they are important for finely guided visuomotor tasks and may actively contribute to the acquisition of spatial information in the same way as do larger saccades.

A study in this issue reveals gene expression differences between neurons that do, and those that do not, show recovery-associated growth after stroke. The differentially expressed genes may provide potential therapeutic targets.

Two studies in this issue find that postsynaptic TRPV1 receptors affect AMPA receptor endocytosis to mediate anandamide-induced long-term depression in the hippocampus and nucleus accumbens.

Optogenetic stimulation of the locus coeruleus noradrenergic neurons can increase wakefulness, and high-frequency stimulation decreases noradrenaline levels and produces loss of muscle tone similar to that seen in cataplexy.

Whether the same pool of synaptic vesicles participates in both spontaneous and activity-dependent release remains controversial. Using a combination of new and established probes, the authors find cross-depletion of spontaneously and activity-dependent pools, indicating that both types of release draw from a common pool.

Synaptic vesicles release neurotransmitters both at rest and when stimulated. Wilhelm et al. use a variety of assays to show that the same vesicles participate in both active and spontaneous release.

5-hydroxytryptamine 2C receptors (5-HT2CRs) in the brain have been shown to regulate glucose homeostasis. Xu and colleagues find that 5-HT2CRs expressed specifically by hypothalamic pro-opiomelanocortin neurons are involved in the regulation of insulin sensitivity and glucose homeostasis in liver.

Liu and colleagues report that toll-like receptor 7 (TLR7), which is typically thought to be expressed in immune cells and to function to regulate innate immunity, is expressed and acts in C-fiber primary sensory neurons. In mice, they find that TLR7 is important for inducing itch, but is not necessary for eliciting pain.

The nuclei of radial glia divide and complete mitosis at the apical surface of the embryonic brain. They then migrate to the basal surface and back before dividing again. This study shows that these nuclei travel along microtubules, driven by KIF1A in the basal direction and by dynein in the apical direction.

He et al. identify the transcription factor YY1 as being critical for peripheral myelination. YY1 phosphorylation by neuregulin is required for transcriptional activation of Egr2/Krox20, a critical regulator of peripheral myelination.

This study shows that the transcriptional repressor Otx2 negatively regulates the expression of the dopamine transporter DAT in dopaminergic neurons of the ventral tegmental area (VTA). Elevated Otx2 confers resistance to the neurotoxin MPTP and may explain why a subpopulation of VTA neurons resist degeneration in Parkinson's disease.

A screen for mutations depressing AMPA receptor expression in C. elegans revealed a gene encoding a putative RNA binding protein, dubbed GRLD-1. Wang et al. find that GRLD-1 acts on the glr-1 introns to boost expression and speculate that it may excise a destabilizing intron.

The authors compare the whole-genome expression profiles of peri-infarct neurons that show axonal sprouting after stroke to their non-sprouting neighbors. They describe a 'sprouting transcriptome' and perform further gain- and loss-of-function studies, finding novel roles in sprouting for a DNA-modifying molecule, a growth factor, and inhibitory myelin receptors.

Rosenzweig and colleagues show that incomplete cervical spinal cord injury in macaques triggers substantially greater sprouting of spared corticospinal axons below the lesion. The monkeys also recovered significant locomotor ability, correlating with the extent of anatomical 'repair'.

The authors report that the cation channel TRPV1 suppresses excitatory synaptic transmission in dentate gyrus via a Ca²⁺-calcineurin and clathrin-dependent internalization of AMPA receptors. Activation of TRPV-1 triggers a form of LTD that is mediated by anandamide, but is independent of type 1 endocannabinoid receptors.

The authors show that synaptic activation of group I metabotropic glutamate receptors in indirect, but not direct, pathway nucleus accumbens medium spiny neurons causes endocannabinoid production. This in turn triggers a form of long-term depression that is dependent on postsynaptic TRPV1 cation channels and endocytosis of AMPA receptors.

Using optogenetic tools, Carter et al. find a frequency-dependent causal relationship between locus coeruleus firing, sleep-to-wake transitions and locomotor arousal in mice.

Sensory adaptation is thought to improve perceptual discriminability of sensory stimuli. Using simultaneous recordings in aligned thalamic and cortical cells in the vibrissal pathway, the authors find evidence suggesting that adaptation of cortical signals is not apparent in the firing of individual thalamic neurons, but is reflected in thalamic synchrony.

Cortical visual area V4 contains cells with diverse response properties, including preference for color, orientation, disparity and higher order features. Tanigawa et al. used intrinsic optical imaging to reveal that regions with preferential response to color or luminance are largely separate from orientation-selective regions.

It had been thought that microscopic relocations of gaze (microsaccades) were suppressed during fine spatial judgments. Ko et al. find that microsaccades move the eye to locations of interest and are influenced by task demands. This suggests that they may actively contribute to the acquisition of fine spatial detail.

Evidence suggests that covert visual attention can improve behavioral performance by modulating contrast or response gain. Herrmann et al. find that the size of the stimulus and the attention field determine which mechanism is used. These results support predictions of the normalization model of attention.