Volume 11 Issue 8, August 2008

A new study identifies pikachurin, a previously-unknown dystroglycan-binding protein that is critical for the apposition of photoreceptor and bipolar cell dendrites at the ribbon synapse. This work could explain some of the visual defects seen in several muscular dystrophies.

The transcription factor hypoxia-inducible factor 1 (HIF-1) triggers multiple cellular responses to cope with hypoxia. A study in this issue suggests that elevated HIF-1 also causes axon guidance defects under hypoxic conditions.

A study uses electrophysiological recordings from primary visual cortex of the monkey to demonstrate that the effects of attention are modulated by task difficulty and that two different neuronal populations mediate this effect.

Two new studies in Science and Nature Neuroscience combine functional magnetic resonance imaging and electrical microstimulation to reveal face-selective temporal and frontal areas and their connectivity.

The physical properties of nematode neurons have led many to believe that neuronal signals in worms are passively propagated. Here, the authors present evidence for the production of regenerative action potentials in some nematode neurons, which can participate in the control of a bistable state.

Corticosterone triggers increased AMPA receptor membrane mobility and surface expression, according to a new study by Groc and colleagues. This mechanism helps to explain the observed modulation of synaptic plasticity and strength induced by this stress hormone.

Drosophila larvae maintain a very precise ability to sense small environmental temperature differences, influencing thermotactic behavior. Kwon et al. suggest a requirement for TRPA1 activation in mediating this sensitivity, but with channel responses arising from a PLC-based signaling cascade, not by direct thermal activation of the channel.

Chemosensory cues are important indicators during Drosophila courtship. This study reveals that disrupting the expression of a gustatory receptor (Gr32a) causes flies to exhibit enhanced courtship behavior towards males and equivalent reactions to mated or virgin females, establishing Gr32a as a receptor for inhibitory courtship pheromones.

Although the existence of face-selective processing in the temporal lobes is well-accepted, the existence of similar patches in frontal cortex is debated, with contradictory evidence. This study used fMRI in alert macaques to identify three face-selective regions in ventral prefrontal cortex, one of which was strongly lateralized to the right hemisphere.

People can moderate their aversive emotional reactions. Delgado and colleagues now show that people can also downregulate expectations of reward, which can at times be maladaptive (for example, drug cravings), and that this results in an attenuation of the physiological and neural correlates of reward expectation.

Trimeric P2X receptor channels are activated by ATP and function in neural signaling, pain transmission and inflammation-based pathways. Cysteine scanning analysis of the transmembrane regions revealed that the second domain lines the central ion-conductance pore and acts like a gate to limit ion flow in the closed state.

The multipotency of adult CNS stem cells has been shown in vitro, but not in vivo. Progenitors in the adult hippocampal subgranular zone normally generate only granule neurons. Retrovirus-mediated expression of the transcription factor Ascl1, however, resulted in the generation of immature and mature oligodendrocytes, demonstrating the progenitors' latent multipotency.

Perinatal lack of oxygen can impair brain development. In the worm C. elegans, this study shows that oxygen deprivation during embryogenesis caused specific axon-pathfinding errors. The defects were absent in worms lacking the hypoxia-response transcription factor HIF-1. Overexpression of HIF-1 replicated the hypoxia-induced defects. Hypoxia or HIF-1 induced the Eph receptor Vab-1, which may in part explain the pathfinding errors.

Adult neurogenesis in hippocampus yields newly born granule cells that receive synaptic inputs from existing neurons. Characterizing morphological and functional features of newborn neurons in adult mice, Toni et al. demonstrate the functional maturation of their synaptic output onto the appropriate target cells in the hippocampus.

It is currently unknown how some animals maintain such precise temperature sensation. Ramot et al. report that the thermosensory neurons in C. elegans utilize cGMP-dependent signaling machinery to alter ionic current responses and maintain a dynamic range of sensitivity.

C.elegans do not possess eyes and are believed to lack responses to light. Ward et al. report a photophobic response in these worms and map this behavior to a group of sensory neurons. Their results also suggest that there could be some conservation in phototransduction between nematodes and vertebrates.

This study identifies a dystroglycan-interacting protein, pikachurin, that is localized in the extracellular space between photoreceptors and bipolar cells. The authors also demonstrate its requirement in normal ribbon synapse development and function. Kevin Campbell and Jakob Satz discuss this paper in an accompanying News and Views article.

DARPP-32 phosphorylation is crucial to the actions of both psychostimulant and antipsychotic drugs. By using BAC transgenic mice to tag DARPP32 selectively in either striatonigral or striatopallidal neurons, the authors show that cocaine (a psychostimulant) and haloperidol (an antipsychotic) exert different effects on DARPP-32 in these two neuronal populations. This may help explain the opposing behavioral effects of these drugs.

Mice lacking the metabotropic glutamate receptor mGluR7 are hypersensitive to convulsant drugs. But how does mGluR7 act to prevent seizures? Here the authors show that interfering with the interaction between mGluR7 and the intracellular adaptor protein PICK1 causes a phenotype in mice and rats that is reminiscent of human absence epilepsy.

Pregnancy in mice is aborted if a female smells the urine of a new male up to 3 days after insemination, but not later. What changes? Dopamine increased in the female main olfactory bulb after copulation, peaking at 4 days. This diminished the mice's ability to recognize male urine. A dopamine receptor inhibitor improved recognition of male urine, and thereby increased the probability of abort.

The neural circuitry of primary auditory cortex is known to have a critical period during which the representation of sound frequency is shaped to represent the external world. De Villers-Sidani and colleagues now show that the end of this critical period is driven by local patterns of activity reflecting environmental stimuli.

In this article, the authors report that the temporal precision of the reward prediction error signal encoded by midbrain dopamine neurons declines as the delay between a reward predicting stimulus and an expected reward increases. The temporal precision of the neural signal is qualitatively similar to that of anticipatory behavior.

Spatial attention works to modulate neuronal responses as early as V1, according to this study. Using electrophysiological recordings in monkey primary visual cortex, the authors found that there are two distinct cell populations (differentiated by direction selectivity, spike width, interspike interval distribution and contrast sensitivity) whose responses are either suppressed or enhanced by attention.