Articles in 2009

It has been controversial whether the ependymal cells that line cerebral ventricles can generate neurons in the adult brain. This study reports that Notch signaling keeps ependymal cells in their differentiated state under normal circumstances. After an ischemic stroke, however, these cells can de-differentiate and generate both neuroblasts and astrocytes.

The neurodevelopmental disorder Rett Syndrome (RTT) is caused by sporadic mutations in the transcriptional factor methyl CpG–binding protein 2 (MeCP2). The authors show that the loss of MeCP2 also occurs in glial cells in RTT brains. Moreover, in an in vitro coculture system, mutant astrocytes from a RTT mouse model affect the dendritic morphology of both RTT mutant and wild-type hippocampal neurons. This suggests that astrocytes may have a non–cell autonomous effect on neuronal properties in RTT.

Cones generate a finely graded voltage signal over a range of light intensities that must be translated into quantal neurotransmitter release at the synapse. Here the authors track synaptic vesicle dynamics in darkness and in light, suggesting that vesicle depletion and resupply mediate the dynamic range of cone synapses.

Explicit memory is linked to conscious awareness of memory retrieval, whereas implicit memory can guide behavior without conscious awareness of memory retrieval. Here, the authors demonstrate recognition memory without awareness of the retrieval. ERP measures differentiated between implicit and explicit recognition.

The authors use in vivo striatal recordings to study region-specific changes in activity during the different phases of skill learning. The dorsomedial striatum is preferentially engaged early in training and the dorsolateral striatum is engaged later in training.

Studying the mechanisms by which spike frequency adaptation shapes visual stimulus selectivity in the lobula giant movement detector interneuron of the locust visual system, the authors find that spike frequency adaptation selectively decreases this neuron's responses to nonpreferred stimuli.

Fast-acting neurotransmitters are usually cleared quickly from synaptic regions, making the time course of synaptic responses independent of active sites. The authors describe an exception to this rule at glycinergic synapses on granule cells of the dorsal cochlear nucleus.

Neurons in the blowfly vertical system integrate wild-field motion from an array of local motion detectors. Using calcium imaging and compartmental modeling, the authors demonstrate that these cells have two distinct receptive fields: a narrow dendritic field corresponding to feedforward input and an axon-terminal receptive field that incorporates input from neighboring cells via lateral axo-axonal gap junctions.

Bright light vision requires rapid regeneration of the photosensitive chromophore in cone photoreceptors. This study demonstrates that such rapid regeneration is accomplished via a pathway that resides in retinal Müller glia, with the final step being performed in the cones themselves.

A subset of hippocampal mossy fibers initially grow past their targets in the CA3 region and then retract. Here, this axon pruning is shown to require reverse ephrin signaling. Extracellular domains of EphBs stimulate ephrin-B3 on mossy axons to trigger pruning. The downstream intracellular signaling pathway includes the adaptor Grb4, the kinase Pak1 and the cytoskeletal regulator Rac.

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.

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.

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.

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 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.

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.

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.

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.

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.

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.