Volume 11 Issue 9, September 2008

Although the CNS has a robust innate ability to repair demyelinated axons, this capacity appears to dissipate with age. A study in this issue suggests that epigenetic processes participate in myelin repair and that the epigenetic response is less dynamic in older individuals.

The neural basis of aggression is poorly understood. A study in this issue used genetic scalpels to dissect the circuitry of the fly brain and identified a small cluster of octopaminergic neurons that can make a fly fighting mad.

Spontaneous ultra-slow oscillations in brain signals are ubiquitous, although their source and function remain unknown. A new study now reports that this activity is correlated between functionally related areas across hemispheres in humans.

Mitogen-activated Protein Kinases (MAPKs) are critical for the formation of stable long-term memories. New work shows that circadian MAPK activity cycling is important in the formation of new hippocampus-dependent memories.

Structural sexual dimorphism in the developing nervous system can lead to functional differences in physiology and behavior. Postnatal, gender-based differences in cell number were presumed to be passively maintained, but here, Ahmed et al. reveal an active mechanism modulated by sex hormones that maintains different numbers of cells in sexually dimorphic brain areas.

Neurons expressing Agouti-related protein (AgRP) and neuropeptide Y (NPY) in the hypothalamus are involved in regulation of feeding and body weight, but genetic disruption of AgRP and NPY have little effect on energy homeostasis. A new study from Tong et al. shows that the energy homeostasis function is mediated through their GABAergic transmission.

The central serotonergic system is an important modulator of neural circuitry that regulates behavior and emotion state of an animal. Current study from Lerch-Haner et al. shows that mutant female mice with defective serotonergic neurons exhibit gross maternal neglect resulting in offspring death, and that this defect can be rescued by expression of a homologous gene from human.

Repetition suppression, the reduction in neural activity with repeated stimuli, is usually thought to be a result of automatic sensory processes. This study instead finds that this reduction results from high stimulus predictability, a more 'top-down' process.

Although certain ion channels can be gated by temperature, it is currently unknown how this occurs. Here, the authors identify regions of TRPV3 that are critical for heat sensation, yet independent of other channel gating mechanisms.

The developing brain generates neurons first and glia later. This study shows that the two COUP-TF transcription factors are essential for the transition from neurogenesis to gliogenesis. COUP-TFI/II in this context appear to function as transcriptional repressors.

With aging comes a decline in remyelination efficiency, but it is currently unknown why this occurs. In this study, the authors reveal an age-dependent epigenetic mechanism that modulates the levels of oligodendrocyte differentiation inhibitors and dictates the extent of remyelination.

The shuttling of AMPA receptors to and from the synaptic membrane determines the strength of synaptic transmission. This study shows that ephrinB2 is part of the mechanism that stabilizes AMPA receptors at the synaptic surface. EphrinB2 and AMPA receptors are linked by two PDZ domains in the intracellular adaptor protein GRIP.

Dendritic protrusions have a major role in the production of glutamatergic synapses. Much less is known regarding the development of GABAergic connections. This study examined contact formation between GABAergic axons and their targets, revealing that new putative GABAergic terminals were produced through the appearance of new boutons at pre-exisiting axon/dendrite crossing points, without the participation of dendritic or axonal protrusions.

This study demonstrates that relapse in heroin-addicted rats requires endocytosis of the AMPA receptor subunit GluR2 in the medial prefrontal cortex. When endocytosis was inhibited in this specific brain structure, the addicted, but abstinent, rats were less intent on seeking heroin when re-exposed to drug-associated cues.

Invertebrates engage in complex aggressive behaviors that involve several neurotransmitters. The circuitry that regulates aggression is unknown. Zhou et al. show here that aggression in male fruit flies correlates with levels of octopamine and that a small group of octopaminergic neurons in the subesophageal is crucial for aggressive behaviors.

Ambient light can acutely modulate sleep and can be detected by the retina independently of photoreceptors. A new study from Foster and colleagues shows that photosensitive retinal ganglion cells, with their activation of sleep-promoting centers, mediate this irradiance-dependent sleep induction.

Several signaling pathways have been previously implicated in memory persistence, but new data suggests that circadian oscillations of cAMP production and protein phosphorylation in the hippocampus are important for the reactivation of a transcriptional pathway and memory consolidation.

To better understand the development of the binocular circuit and the nature of visual information processing, Ramdya and Engert examine the neuronal activity of zebrafish optic tectum when it was rewired to receive inputs from both eyes.

The response of some cortical neurons seems to exceed psychophysical sensitivity. Recording in rat barrel cortex, this study finds that neuronal sensitivity is degraded under more life-like conditions of stimulus uncertainity. However, pooled spike-timing information from the most sensitive neurons still correlates with subjects' psychophysical sensitivity.

Spontaneous cortical waves have been widely observed, although previous evidence from humans has been indirect, using functional magnetic resonance imaging. This study reports that there are slow modulations in neuronal firing rates and gamma local field potentials in human auditory cortex in the absence of sensory stimuli or task.

Using a combination of behavioral measures and transcranial magnetic stimulation (TMS), this study finds that elite basketball players are better at predicting whether a free basketball throw will land in the basket or out and that they also have higher TMS-evoked motor potentials for when the ball misses its mark.