Volume 12 Issue 2, February 2009

Many sensory brain areas are characterized by a specific spatial organization, with neurons being ordered according to their similarity in receptive field properties. A surprising new study provides evidence that the organization of glomeruli in the olfactory bulb violates this anatomical principle, suggesting that olfaction might work by a different set of rules.

ProBDNF has been proposed to alter synaptic plasticity, but whether it is normally released from neurons has been a matter of contention. New work suggests that proBDNF is indeed secreted from central neurons.

The floor plate can generate neurons, but does so only in the midbrain. New work shows that Shh suppresses floor plate neurogenesis, and that in the midbrain, Wnt downregulates Shh expression via canonical signaling through β-catenin.

Brain development requires precise control of progenitor proliferation and differentiation. PML appears to be a crucial regulator of cortical progenitors, limiting proliferation and promoting the generation of committed neuronal precursors.

The in vitro reconstitution of vesicular glutamate transport reveals that the transporter itself antiports chloride ions and suggests that extracellular chloride concentrations may determine neurotransmitter refilling and quantal size.

ProBDNF can have drastic effects on synaptic function that are quite different from those of mature BDNF. It is, however, controversial whether proBDNF is ever released in amounts that are sufficient to affect normal synaptic plasticity. Here, Yang and colleagues have detected the release of proBDNF from hippocampal neurons using newly developed knock-in mice and antibodies.

The authors use chronic in vivo imaging to study pyramidal neurons before and after deletion of the tumor suppressor gene Pten in mature neurons of the mouse cortex. They find that Pten/mTOR signaling only regulates growth of layer 2/3 apical dendrites.

Cheng and colleagues propose a mechanism for amyloid-β toxicity that may have relevance for Alzheimer's disease. They show that Aβ1–42 induces expression of collagen VI and that collagen VI protects against Aβ toxicity in cultured neurons.

This study finds that reducing the amount of slow-wave sleep results in worse performance on a subsequent memory test and reduced encoding-related hippocampal fMRI activation. This happens even though the total amount of sleep was unaffected, suggesting that hippocampus-dependent memory is particularly affected by shallow sleep.

The floor plate is not usually a neurogenic structure, but in the embryonic midbrain, dopaminergic neurons do develop from floor plate. This study shows that the high levels of Shh that are present in the floor plate generally suppress neurogenesis and that for neurons to be generated, Shh must be downregulated by Wnt signaling in the midbrain.

This work shows that the transcriptional modulator and tumor suppressor Pml functions in embryonic nestin-positive cortical progenitor cells to regulate protein phosphatase 1α, leading to dephosphorylation of pRb, reduction of mitosis and increased neurogenesis.

Fate-mapping the cells that express the homeodomain transcription factor Dbx1 in the developing mouse brain, this study finds that the preoptic area is a previously unknown source of inhibitory amygdala neurons. In contrast, excitatory amygdala neurons are shown to develop from Dbx1-positive cells in the ventral pallium.

In the worm, netrin and the TGFβ-related molecule UNC-129 form opposing dorsoventral gradients. Motor axons are repelled by netrin and attracted to UNC-129, but no TGFβ receptors appear to be involved in the attraction. This study shows that UNC-129 enhances repulsive signaling from the netrin receptor complex UNC-5/UNC-40, via a direct interaction with UNC-5.

Glutamate loading of synaptic vesicles requires moderate Cl⁻ concentrations, but is inhibited by high Cl⁻. Here, Schenck et al. show that the glutamate transporter VGLUT1 is itself a chloride channel. Although high extravesicular Cl⁻ inhibited glutamate import through a competitive mechanism, high intravesicular Cl⁻ concentrations enhanced glutamate import. This suggests that, in addition to the pH gradient, VGLUT1 can also utilize a steep Cl⁻ gradient to drive glutamate transport.

The function of Synaptotagmin IV (Syt IV) in vesicle exocytosis and neurotransmitter release is debated, as Syt IV does not bind calcium. Here, Zhang et al. show that Syt IV localizes to the vesicles of neuropeptide-secreting nerve terminals in the posterior pituitary and regulates the kinetics of calcium-triggered exocytosis.

The endocytosis of AMPA receptors underlies several forms of synaptic plasticity. Here, the authors show that PSD-95, via its binding to AKAP150, is important for NMDAR-triggered endocytosis of synaptic AMPARS.

The authors report that rats that were withdrawn from cocaine self-administration had an in vivo deficit in their ability to develop long-term potentiation and depression in the nucleus accumbens core following prefrontal cortex stimulation. N-acetylcysteine, a drug that prevents relapse, restored the ability to induce plasticity.

Individual prefrontal cortex neurons can exhibit persistent activity during a delay between a cue and a behavioral response. Here the authors report on an mGluR5-mediated depolarization that underlies persistent activity and is sensitive to both dopamine and cocaine.

cAMP response element–binding protein (CREB) is a key regulator of the nucleus accumbens shell function in animals' responses to emotional stimuli. The present study demonstrates that passive stress in the form of social isolation induces anhedonia and depression-like symptoms that are mediated by CREB activity and neuronal excitability.

The primary sensory areas are generally thought to be mapped according to the organizational structure of the sensory input; retinotopic, somatotopic, cochleotopic and even coarse chemotopic maps have all been identified in the brain. Optical imaging of the olfactory bulb now reveals that there is no fine-scale chemotopic map in the rodent olfactory bulb.

The authors show that individual sensorimotor neurons in freely behaving swamp sparrows exhibit categorical responses to features of their songs. The neuronal response boundary predicts the categorical perceptual boundary that was measured in field studies of the same sparrow population, but not the perceptual boundary in populations that learn different song dialects.

Transgenic expression of microbial channelrhodopsins in neurons allows direct light activation of ionic currents. Here, the authors describe a modified channelrhodopsin that remains open for seconds once it is activated by light and can be 'switched off' by a second light flash, thereby obviating the need for constant illumination during an experiment.