Articles in 2009

This study reports that odorants that elicited similar fMRI activity patterns in the posterior piriform cortex were more likely to be judged as being more perceptually alike. This correlation between spatially distributed activity and perceptual judgments was not reproduced in other areas of the brain, suggesting that the posterior piriform cortex contains a spatially distributed ensemble code for odor object quality.

Most synapses in the mature CNS are wrapped by a dense extracellular matrix (ECM). The authors show that removing the ECM increased the lateral diffusion of AMPA receptors and affected short-term synaptic plasticity. This suggests that the ECM may modulate synaptic transmission by restricting receptor diffusion.

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.

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.

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.

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.

Responses of primary visual cortex neurons to optimal gratings are suppressed when a non-optimal grating is superimposed. Using intrinsic optical imaging and intracellular recordings, the authors report that this effect is mediated by divisive suppression in independent population codes for stimulus orientation and strength.

Using computational methods to model neural recordings and behavioral data, the authors find that reinforcement learning rules, combined with a standard model of decision-making, can explain a range of experimentally observed phenomena in perceptual learning.

The authors study the molecular mechanisms that discriminate axonal microtubules from somatodendritic microtubules. They report that amino acid substitutions in the beta loop region of kinsin-1 can change the compartmentalization of kinesin-1 from axons to axons and dendrites. Moreover, tyrosinated tubulins normally prevent kinesin-1 from binding to microtubules, but do not similarly inhibit kinesin-1 that is changed to allow localization to both axons and dendrites.

How proteins are targeted for dendrites versus axons remains unclear. Lewis et al. show that the dendritic localization of several transmembrane proteins is dependent on specific myosin motors and an intact actin network. They also target Channelrhodopsin-2 specifically to dendrites, demonstrating a potentially important tool for probing neuronal circuits.

Calcium influx through AMPA receptors can trigger a switch in AMPA receptor subunit composition and cause a loss of Ca²⁺ permeability at the parallel fiber–stellate cell synapse in the cerebellum. Cull-Candy and colleagues now report that mGluRs and GABAB receptors both modulate this plasticity as well.

The authors combine electrophysiology, calcium imaging and immunohistochemistry to show that L-type Ca_v channels in rat A17 amacrine cells are well placed to mediate reciprocal inhibitory feedback to rod bipolar cells. However, they find that the contribution of these channels to GABA release is diminished by large-conductance Ca²⁺-activated potassium (BK) channels, which suppress postsynaptic depolarization in A17s and limit Ca_v channel activation.

Selective attention is proposed to enhance relevant responses. Here the authors report that, paradoxically, responses in auditory cortex are suppressed when rats are engaged in a task, relative to responses that occurred while the animals were awake, but not performing any task.

Voltage-gated channels influence processing of synaptic potentials in dendrites. George et al. report the hyperpolarization-activated cation current (I_h) exerts both direct depolarizing and net inhibitory hyperpolarizing effects on subthreshold excitatory postsynaptic potentials, as a function of synaptic strength. Interaction of I_h with an M-type potassium current (I_m) underlies the inhibition.

This study shows that chronic amphetamine exposure in rats downregulates the NMDA receptor NR2B subunit on striatal neurons. This loss of NR2B has consequences for synaptic transmission and for behavior, sensitizing the rats to the stimulant.