Development

MicroRNA-9a ensures the precise specification of sensory organ precursors in Drosophila.Li, Y., Wang, F. & Gao, F.-B. Genes Dev. 2 October 2006 (doi:10.1101/gad.1466306)

MicroRNAs (miRNAs) have important roles in several aspects of animal development, although their specific functions in the brain are less clear. New in vivowork in the Drosophila PNS shows that miRNA-9a is crucial for the generation of the correct number of sensory organ precursor (SOP) cells during development. Deletion of this miRNA led to the ectopic expression of SOPs, whereas overexpression resulted in a marked reduction in SOPs, suggesting that the role of miRNA -9a in non-SOP cells is to prevent precursor cells from becoming neurons.

Neurotransmitter receptors

Measurement of conformational changes accompanying desensitization in an ionotropic glutamate receptor. Armstrong, N. et al. Cell 127, 85–97 (2006)

Ligand-gated ion channels undergo conformational changes in response to ligand binding, leading to activation followed by deactivation or desensitization. Although much is known about the structural alterations underlying activation and deactivation, those leading to desensitization have proven elusive. Several techniques were used to explore structural rearrangments in the GluR2 receptor, showing that desensitization involves the rupture of the interface between two glutamate-binding core subunits, resulting in closure of the ion channel.

Synaptic physiology

Clathrin-mediated endocytosis is the dominant mechanism of vesicle retrieval at hippocampal synapses. Granseth, B. et al. Neuron 51, 773–786 (2006)

Following neurotransmitter release, synaptic vesicles must be recycled to prepare them for the next release event. Retrieval of the collapsed vesicle membrane has been proposed to occur through both slow and fast mechanisms of endocytosis. Using an enhanced fluorescent reporter that consisted of pHluorin fused to synaptophysin, these authors found evidence that, after physiologically relevant levels of activity, the slow mode of endocytosis provides the principal form of retrieval at hippocampal synapses and that this depends on clathrin.

Cognitive neuroscience

Diminishing reciprocal fairness by disrupting the right prefrontal cortex. Knoch, D. et al. Science 5 October 2006 (doi: 10.1126/science.1129156)

Ignoring self interest when responding to unfair actions in a manner consistent with moral and social values is apparently a uniquely human behaviour, yet the neural substrates underlying this behaviour are unknown. In the Ultimatum Game, subjects asked to choose between accepting an 'unfair' deal proposed by a stranger or rejecting it and gaining nothing for themselves often select the latter option. Disrupting dorsolateral prefrontal cortex (DLPFC) activity using transcranial magnetic stimulation showed that the right DLPFC has a role in overriding selfish impulses to promote fairness-related behaviour.