Volume 12 Issue 6, June 2009

The orientation of the mitotic spindle determines whether divisions of the polarized neural progenitors in the ventricular zone cause their expansion or lead to neurogenesis. A guanine nucleotide exchange factor for the small GTPase RhoA is now shown to tip this balance in favor of neurogenesis.

A study in this issue uses a new technique to show that synaptic vesicles released spontaneously and those released in response to action potentials are drawn from distinct, non-overlapping pools that coexist in presynaptic terminals.

The olfactory bulb is densely innervated by serotonergic fibers. A study now shows that serotonin activates periglomerular interneurons, which release GABA to reduce transmitter release from olfactory sensory neurons.

Projections from the amygdala to the ventral striatum are important for learning. A study finds that fleeting epochs of coherent gamma oscillations between these brain areas may be important for reinforcement learning.

Whereas birds can generate new auditory neurons even in adulthood, mammals cannot. This perspective suggests that factors such as increasing life span expose a deficit in cochlear self-regeneration that was irrelevant for most of mammalian evolution, resulting in hearing loss. Authors discuss various approaches aimed at regenerating hair cells to ameliorate such hearing loss.

In this perspective, the authors discuss recent advances in the development of cochlear implants and elucidate the implications of implant-induced plasticity for future technology.

This perpective offers an evolutionary perspective on the advantages of binaural hearing, and discusses the many different strategies for such hearing that animals have evolved. Authors discuss how these strategies might inform future work on auditory prosthetics.

Primary auditory cortex is usually thought to be directly analogous to primary visual cortex, with stimulus physical properties being represented at this level. This perspective argues that the auditory system has unique operating principles that make it different from the visual system, such as considerably greater subcortical processing.

This review describes how the genetic causes of the many forms of human deafness have provided insight into the molecular mechanisms of auditory transduction. In combination with mouse models, these genetic studies have elucidated the mechanisms behind the formation and functioning of the hair bundle as a mechanical transducer.

This review summarizes recent work in auditory brainstem nuclei to demonstrate that developing brain stem circuits are subject to experience-dependent synaptic refinement. This is in contrast to the traditional view, which interprets the early development of brain stem tonotopy as indicative of a 'hard-wired' mechanism.

As language is unique to humans, it is usually thought that work in other animals has made limited contributions to understanding it. Authors here review work on species-specific vocalizations in nonhuman primates to arrive at a new model for how human speech is processed.

Potassium-chloride co-transporter 2 (KCC2) activity is known to be attenuated by neural injury. Hershfinkel et al. show that KCC2 activity is inhibited by intracellular free zinc, a component of neuronal injury signaling pathways. Oxygen-glucose deprivation results in attenuation of KCC2 activity that is reversible by intracellular zinc chelation.

Lledo and colleagues report that one subset of excitatory synapses onto adult-born granule cells in the mouse olfactory bulb shows long-term potentiation. This property, however, fades as the newborn neurons mature.

Using two photon–guided stimulation, the authors demonstrate spike timing–dependent plasticity of cortical feedback inputs to olfactory bulb granule cells.

Neurogenesis requires a switch of progenitor divisions from symmetrical and self-renewing to asymmetrical. This study shows that the Rho-activating protein Lcf is required for neurogenesis in the murine cortex and that its negative regulator Tctex-1 conversely acts to allow self-renewing symmetrical progenitor division.

Budelli et al. show that a sodium-dependent potassium current is a major component of the delayed rectifier outward current in neurons. This current is carried by Slack channels encoded by the Slo2.2 gene and activated by a persistent sodium current.

The existence of physically distinct synaptic vesicle populations with different functional properties has been debated. Here, Fredj and Burrone use a new method of labeling the synaptic vesicle protein VAMP to demonstrate that vesicles labeled during spontaneous fusion are from a different population than those labeled during evoked fusion.

The authors show that spontaneous and evoked neurotransmitter release in cortical neurons use the same Ca²⁺-dependent release mechanism. Their data suggest that synaptotagmin-1 controls both evoked and spontaneous release, acting as a simultaneous Ca²⁺-dependent activator and clamp of exocytosis.

Unlike the involvement of the synaptotagmin (syt) family of proteins in calcium-triggered membrane fusion, the precise function and localization of syt-IV are not clear. Here the authors demonstrate that syt-IV is present in BDNF-containing vesicles and regulates axonal/dendritic release of BDNF, which in turn modulates long-term potentiation in hippocampal neurons.

The authors test whether experience-dependent neocortical modifications need Ube3a, an ubiquitin ligase implicated in autism and Angelman syndrome, using a mouse model of Angelman syndrome. They find that experience-dependent maturation of excitatory circuits in the visual cortex is impaired in these mice and that there are deficits in plasticity. This loss of plasticity was reversible with visual deprivation.

Petzold and colleagues show that serotonergic innervation of the olfactory bulb functions to attenuate odor-evoked transmitter release from olfactory sensory neurons (ORNs). This effect is indirect, as serotonin stimulates 5-HT2C receptors on juxtaglomerular interneurons, whose release of GABA inhibits glutamate release from ORN terminals via GABAB receptors.

During active tactile sensation in rodents, whisker movements across surfaces generate complex whisker micro-motion. Here, the authors find that these micro-motions are a tactile feature encoded by sparse, temporally precise, synchronous spiking in rodent somatosensory cortex.

It has been suggested that the basolateral amygdala mediates emotional enhancement of memory. Here, the authors suggest a potential mechanism for this process, showing that coherent gamma oscillations coordinate amgydalostriatal interactions during learning. This coupling could facilitate synaptic plasticity.

Nature Neurosciencepresents a special focus issue on hearing, which covers recent advances in genetics, clinical treatment and neuroscience which have advanced our understanding of how sounds are translated into neural signals and processed to support functions such as language.