Volume 12 Issue 12, December 2009

The pruning of unneeded axons and dendrites is crucial for circuitry maturation, but poorly understood on the molecular level. During Drosophila metamorphosis, the transcription factor Sox14 acts as a context-dependent mediator of death, axonal or dendritic pruning. Its transcriptional target Mical acts specifically in dendrite pruning.

The vascular niche-derived factor PEDF enhances Notch signaling in adult neural stem cells via an unexpected mechanism involving nuclear export of a transcriptional repressor, to promote both proliferation and multipotentiality.

The firing of most hippocampal neurons is modulated by the theta rhythm, but it's not clear how and where the rhythm is generated. A study now shows that the required machinery for theta generation lies in local circuits of the hippocampus.

Dendritic excitability is a plastic property of neurons. This study shows that exposure to an enriched environment increases propagation of dendritic sodium spikes in a subset of dendritic branches in CA1 pyramidal neurons. This effect is mediated by localized downregulation of A-type potassium channel function.

This study finds that excitatory neurons in cortical layer 2/3 can respond to their own firing with persistent hyperpolarization, termed slow self-inhibition or SSI. This process is mediated by endocannabinoids and regulates neuronal excitability.

Although numerous in vivo studies have suggested that hippocampal theta oscillations are generated by the extrinsic medial septal input, theoretical studies have suggested that the hippocampus has the minimal feedback circuitry necessary to intrinsically generate its own theta rhythm. Here, Goutagny et al. directly demonstrate such oscillation independently of external inputs.

Studying a patient with selective damage to the insular and anterior cingulate cortex, the current study finds that these regions are not necessary for interoceptive awareness of one's own heartbeat, but the primary somatosensory cortex is required for such self-awareness.

Certain Drosophila dendrites undergo major remodeling during metamorphosis. This study shows that the severing of larval dendrites, which is the first step of remodeling, depends on the upregulation of the cytoskeleton-binding protein Mical by the transcription factor Sox14.

Nardilysin (NRDc) enhances the shedding of ectodomains from neuronal membrane proteins. The null mutant described here reveals that nardilysin is necessary for myelination in both central and peripheral nervous system.

Notch signaling is essential for the maintenance of adult neural stem cells in vivo. Here, Andreu-Agulló and colleagues show that PEDF, released from endothelial cells, enhances Notch signaling in the mouse subependymal zone by inactivating a repressor of Notch target genes.

Neural stem cells in the adult mouse SVZ are thought to only generate GABAergic olfactory bulb interneurons. This study reports that a dorsal region of the adult SVZ gives rise to a glutamatergic type of olfactory bulb neurons. These newborn glutamatergic neurons can be diverted to migrate into the cortex towards an injury, possibly contributing to repair.

During development of the peripheral ganglia, 50% of neurons die by apoptosis. This study finds that satellite glial cell precursors clear these neuronal corpses in developing dorsal root ganglia and identifies some of the molecular components involved in this phagocytosis.

In Drosophila, the connections between olfactory receptor neurons and projection neurons are highly specific. Here, the authors report that two leucine-rich repeat transmembrane proteins (Capricious and Tartan) serve as a mechanism for projection neuron dendrite targeting in the olfactory map.

Major histocompatibility complex peptides function as olfactory cues for vomeronasal sensory neurons (VSNs) in the mammalian nose. Here, the authors report that individual VSNs expressing the receptor gene V2r1b have broad peptide responsiveness, but sufficient specificity to distinguish peptides differing by a single amino acid residue. Furthermore, they find that targeted disruption of V2r1b eliminates the VSN peptide response.

Severe stress in early childhood can increase an individual's vulnerability to depression later in life. This study found that early-life stress in mice resulted in persistent elevation of the stress hormone arginine vasopressin (AVP), which was caused by persistent hypomethylation of CpG islands in the Avp promoter in the hypothalamus.

Even without the symptoms of Alzheimer's disease, normal brain releases a small amount of amyloid-β peptide (Aβ). Abramov and colleagues now show that endogenous Aβ that is produced and released from presynaptic terminals can alter synaptic transmission and short-term plasticity.

The cortex is sensitive to weak stimuli, but also responds to stronger inputs without saturating. In this study, Scanziani and colleagues find some of the circuits that enable neuronal populations to respond to a wide range of input strengths.

Systematically monitoring the activities of various cortical pyramidal neurons and interneurons during different stages of locomotion, the authors characterize differential firing activities of motor cortex microcircuitry in behaving, head-restraint rats that were trained to push, pull or hold a lever for reward.

Previous work has suggested that visual attention improves behavioral performance by increasing the firing rates of individual sensory neurons. Recording from populations of neurons in monkey visual area V4, this study finds that most of the attentional improvement in the population signal results from decreases in interneuronal correlations.