Volume 12 Issue 8, August 2009

Quantitative immunostaining, electrophysiology and modeling show that two sodium channel isoforms are asymmetrically distributed in the axon initial segment. Their polarized distribution explains many of the unique properties of the axon initial segment, including its ability to both initiate spikes and guarantee subsequent backpropagation.

Breathing relies on a respiratory rhythm generator. A study characterizes an early emerging oscillatory group of Phox2b-expressing parafacial cells that entrain and couple with the preBötzinger Complex at the onset of fetal breathing.

In the face of uncertainty, how do we choose between maintaining our current strategy or trying new strategies? A study shows that a gene controlling prefrontal dopamine function is predictive of uncertainty-driven exploration.

Manipulation of the neurons required for a specific behavior can be difficult, but is required for proof of causality. A clever technique now allows inactivation of only the subset of neurons that have been recently active.

Current techniques are insufficient for resolving the contribution of single photoreceptors to the responses of visually responsive neurons in the brain. Here, the authors employ a new technique, which utilizes adaptive optics, to show that LGN neurons respond reliably to the stimulation of a single cone.

When learning to use a novel tool, autistic children build a stronger link between their movements and proprioceptive feedback than typically developing children. Their greater reliance on proprioception correlates with the severity of social and impairment deficits.

Defects in DNA single strand break repair (SSBR) can cause neurodegeneration. To better understand the function of SSBR in the nervous system, the authors ablated Xrcc1 in all of the neural progenitors of developing mice. This revealed that the postnatal differentiation of several types of cerebellar interneurons is particularly dependent on SSBR.

Some neurites in developing C. elegans interneurons are eventually pruned. Which exact neurites are subject to pruning appears to be random, suggesting an ongoing local competition between pro- and anti-pruning signals. Hayashi and colleagues show that Wnt signaling through the transmembrane receptor kinase CAM-1/Ror protects developing neurites from being pruned.

Ethanol activates G protein-gated inwardly rectifying K⁺ (GIRK) channels, but it is unclear how. This study identifies an alcohol-binding pocket located in the cytoplasmic domains of GIRK2. A leucine residue in this pocket was crucial for GIRK2 activation by alcohols, but was not involved in the alcohol inhibition of related, but constitutively active, K⁺ channels.

Action potentials initiate preferentially from the distal axon initial segent (AIS). Why do they not initiate from the proximal AIS? This study shows that the distal AIS is rich in low-threshold Na_v1.6, whereas the proximal AIS has a high density of high-threshold Na_v1.2 channels. Although the distal Na_v1.6 promotes action potential initiation, the proximal Na_v1.2 regulates action potential backpropagation to the soma.

Endocytosis in a number of forms (slow, bulk, rapid and excess) is necessary for maintaining synaptic transmission. Here the authors report that all of these forms are initiated by the same mechanism, which requires calcium and calmodulin, although each one has its own calcium level threshold.

This study shows that, although AMPA-type glutamate receptors are trafficked to dendrites through the normal Golgi secretory pathway, NMDA receptors bypass the somatic Golgi apparatus and instead move from the endoplasmic reticulum in endoplasmic reticulum–like vesicles to Golgi 'outposts' located in the dendrites.

Evf2 is a polyadenylated, noncoding RNA that is transcribed from the intergenic region of Dlx5 and Dlx6, which are genes for homeodomain transcriptional factors. The authors now show that the loss of Evf2 in mice results in a substantial reduction of GABAergic interneurons via interference with Dlx5/6 expression.

Breathing relies on a respiratory rhythm generator, which depends on activity of the pre-Bötzinger complex (preBötC) and the parafacial respiratory group. The authors characterize an early emerging group of Phox2b-expressing parafacial oscillatory cells that entrain and couple with the preBötC at the onset of fetal breathing.

The authors combine electrophysiology and behavioral assays to show that the duration of cocaine-induced synaptic plasticity in the VTA of mice is gated by mGluR1. The lack of mGluR1 in vivo made VTA potentiation persistent and led to synaptic plasticity in the NAc, which is important for relapse.

The role of feedforward inhibition onto Purkinje cells during learning is still not well understood. Here, the authors report that selective genetic removal of GABA_A receptor–mediated inhibition onto Purkinje cells modulates fine-scale patterns of Purkinje cell activity. These patterns may mediate the induction of downstream plasticity and, ultimately, the consolidation of cerebellar motor learning.

It is well established that monkey middle temporal area and the human middle temporal complex (MT+) mediate two-dimensional motion perception. Here, the authors use functional magnetic resonance imaging to demonstrate that MT+ carries signals that are also critical for three-dimensional motion perception.

Sensory signals for movement planning originate in multiple reference frames. Here the authors present a model in which the statistical properties of sensory signals and the transformations needed to compare them determine their effect on movement planning. Their results account for known patterns of movement planning errors and suggest that maintaining multiple reference frames is actually an optimal use of available sensory information.

The exploration/exploitation dilemma describes the choice between maintaining the current strategy, or trying new strategies, to maximize rewards. The authors show that genes controlling striatal dopamine function are associated with exploitative learning. In contrast, a gene controlling prefrontal dopamine function is predictive of exploration when the value of alternative strategies is uncertain.

Until now, no tools existed to selectively manipulate the small number of sparsely distributed neurons activated during a drug-related learned behavior. Here the authors describe a new method for selectively inactivating only those neurons activated by cocaine in an environment repeatedly paired with drug injections.