News & Views in 2005

Activation of G protein–coupled receptors can inhibit secretion of neurotransmittters and hormones. Two recent reports in Nature Neuroscience show that this inhibition is due to Gβγ binding to SNAP-25, directly blocking the vesicle fusion machinery.

Actin destabilization is an early step in specifying axon identity in young neurons. A new paper proposes a molecular mechanism for this process, but the data can also be explained by making a distinction between axon specification and axon growth.

Song learning in juvenile birds is guided by daytime sensorimotor feedback, but nighttime sleep is also integral to song learning, reports a study in Nature, setting the stage for physiological insights into sleep-dependent learning mechanisms.

Postsynaptic receptor trafficking is associated with long-term synaptic plasticity, but whether this mechanism actually mediates learning is unclear. A new study shows that fear learning drives AMPA receptors into synapses in the lateral amygdala.

In V1, neurons preferring similar orientations are grouped in columns too small to be resolved by conventional fMRI. Two studies circumvent this limitation by using algorithms to recognize patterns of activation across a large area. This new trick allows the authors to distinguish responses to different orientations in human V1 and to study its contribution to conscious perception.

A new study shows that amyloid plaques tagged with fluorinated ligand can be detected with ¹⁹F MRI in transgenic mice. The superior signal to noise of this technique is a major step toward visualizing the histopathology of Alzheimer disease in living patients.

A report in Nature describes a physiological screen used to identify a previously unknown chemical signal in mouse urine. The chemical's selective response in the olfactory bulb raises interesting questions for how socially relevant odors are encoded.

A new model by Machens et al. proposes a mechanism by which prefrontal cortex neurons can do two jobs that are normally thought to occur independently. In a stimulus comparison task, these model neurons both cast votes for a stimulus and make decisions.

The outer photoreceptors of Drosophila project to their targets in an extremely intricate pattern. Prakash et al. in this issue show that homophilic adhesion via N-cadherins is an essential part of the axon guidance mechanism in this system. The new results suggest that axons respond to the level of N-cadherins, and not to any combinatorial cadherin code, as had been postulated previously.

A new paper quantifies the dependence of synaptic transmission on transient local changes in internal calcium, examining the equilibrium dynamics of the calcium sensor for exocytosis and its contribution to short-term changes in synaptic strength.

A recent study of an Olig1 knockout mouse concludes that remyelination after injury may occur by a different mechanism from myelination during normal development, but another report suggests that this mouse model should be interpreted cautiously.

In a technical tour de force, Okhi et al. image the activity of thousands of visual cortical neurons in vivo at a single-cell resolution, and examine their orientation and direction selectivity. Their results show that cortical maps can be built with single-cell precision.

How activity-dependent synaptic plasticity shapes the development of inhibitory synapses has remained unclear. In this issue, Gillespie et al. show that in the developing rat auditory system, inhibitory synapses transiently co-release glutamate. The consequent activation of postsynaptic NMDA receptors may be critical for the plasticity mechanisms that determine tonotopic sharpening.

Having control over a stressful situation can reduce its negative physiological and cognitive consequences. In this issue, a new study in rats suggests that descending inputs from the prefrontal cortex to the serotonergic midbrain signal the controllability of stress.

Stem cells transplanted after spinal cord injury mostly generate astrocytes, which can promote aberrant sprouting of sensory neurons, leading to allodynia. Making cells produce more oligodendrocytes reduces allodynia and improves functional recovery.

Despite 20 years of study, the mechanism underlying the cochlear amplifier remains contentious. In this issue, a novel in vitro cochlear preparation implicates calcium current–driven active stereocilia motion in generating amplification.

Voltage-gated ion channels shape the integration of synaptic input in dendrites. Forebrain-restricted deletion of the hyperpolarization-activated channel HCN1 enhances spatial learning, demonstrating a behavioral role for an active dendritic conductance.

Comm downregulates the Slit receptor Robo on commissural axons, thereby enabling midline crossing. Elegant new experiments show that Comm functions by diverting Robo to the endosomal pathway, preventing its delivery to the growth cone.