Volume 12 Issue 3, March 2009

Rett syndrome (RTT) is caused by mutations in the X-linked gene encoding methyl CpG–binding protein (MeCP2). The loss of MeCP2 function in neurons was thought to cause the disease. A study now challenges this assumption by showing that MeCP2 is expressed in glia and that MeCP2 loss in glia causes abnormalities in neighboring neurons.

Rat models implicate epigenetic regulation of hippocampal glucocorticoid receptor expression in mediating the effects of early life experience on adult behavior. A report now suggests that the same mechanism might also be at work in humans.

The ependymal cells lining the lateral ventricles are not stem cells, but a study now shows that they can be activated to generate neuroblasts in a stroke model, and mature olfactory bulb neurons when Notch signaling is disrupted.

Previous studies have attempted to decode functional imaging data to infer the perceptual state of an observer, but the level of detail has been limited. A new decoding study reconstructs accurate pictures of what an observer has seen.

The glucocorticoid receptor is a transcription factor that mediates adaptation to stress. The authors show that selective glucocorticoid receptor deletion in postsynaptic dopamine receptor 1a–expressing neurons, but not in presynaptic neurons that release dopamine, decreases the motivation of mice to self-administer cocaine.

Many population coding models of reinforcement learning assign a single global reward signal to the entire population. As the population size increases, however, this reward signal is less and less related to the performance of a single neuron, slowing down learning. This computational modeling study shows that an additional population response term modifying synaptic plasticity speeds up learning.

One of the ongoing debates in memory research is whether the fidelity of remote memory, as it matures, requires the hippocampus. Using a contextual discrimination procedure that can test memory precision over time, this paper reveals that the hippocampus is not essential in the precise maintenance of remote memory.

Animal studies show that fear memories can change when recalled, a process known as reconsolidation. Here the authors find that administration of propranolol prior to memory reactivation erases the expression of fear memory and prevents its return.

It has been controversial whether the ependymal cells that line cerebral ventricles can generate neurons in the adult brain. This study reports that Notch signaling keeps ependymal cells in their differentiated state under normal circumstances. After an ischemic stroke, however, these cells can de-differentiate and generate both neuroblasts and astrocytes.

A subset of hippocampal mossy fibers initially grow past their targets in the CA3 region and then retract. Here, this axon pruning is shown to require reverse ephrin signaling. Extracellular domains of EphBs stimulate ephrin-B3 on mossy axons to trigger pruning. The downstream intracellular signaling pathway includes the adaptor Grb4, the kinase Pak1 and the cytoskeletal regulator Rac.

TARPs, which are associated with AMPA-type glutamate receptors and which regulate their properties and trafficking, have not been shown to specifically regulate calcium-permeable AMPARs. In this study, the authors report that the stargazin-related protein g-5, which is expressed in Bergmann glia, preferentially regulates calcium-permeable AMPARs.

Fast-acting neurotransmitters are usually cleared quickly from synaptic regions, making the time course of synaptic responses independent of active sites. The authors describe an exception to this rule at glycinergic synapses on granule cells of the dorsal cochlear nucleus.

Bright light vision requires rapid regeneration of the photosensitive chromophore in cone photoreceptors. This study demonstrates that such rapid regeneration is accomplished via a pathway that resides in retinal Müller glia, with the final step being performed in the cones themselves.

Cones generate a finely graded voltage signal over a range of light intensities that must be translated into quantal neurotransmitter release at the synapse. Here the authors track synaptic vesicle dynamics in darkness and in light, suggesting that vesicle depletion and resupply mediate the dynamic range of cone synapses.

The neurodevelopmental disorder Rett Syndrome (RTT) is caused by sporadic mutations in the transcriptional factor methyl CpG–binding protein 2 (MeCP2). The authors show that the loss of MeCP2 also occurs in glial cells in RTT brains. Moreover, in an in vitro coculture system, mutant astrocytes from a RTT mouse model affect the dendritic morphology of both RTT mutant and wild-type hippocampal neurons. This suggests that astrocytes may have a non–cell autonomous effect on neuronal properties in RTT.

Studying the mechanisms by which spike frequency adaptation shapes visual stimulus selectivity in the lobula giant movement detector interneuron of the locust visual system, the authors find that spike frequency adaptation selectively decreases this neuron's responses to nonpreferred stimuli.

Neurons in the blowfly vertical system integrate wild-field motion from an array of local motion detectors. Using calcium imaging and compartmental modeling, the authors demonstrate that these cells have two distinct receptive fields: a narrow dendritic field corresponding to feedforward input and an axon-terminal receptive field that incorporates input from neighboring cells via lateral axo-axonal gap junctions.

The authors use in vivo striatal recordings to study region-specific changes in activity during the different phases of skill learning. The dorsomedial striatum is preferentially engaged early in training and the dorsolateral striatum is engaged later in training.

Childhood abuse or neglect alters the hormonal stress response and increases the risk for suicide. Analysis of hippocampal samples from human suicide victims with a history of child abuse indicated changes in the expression of the NC3R1 gene that did not occur in suicide victims with no childhood abuse or in people who died of other causes.

Explicit memory is linked to conscious awareness of memory retrieval, whereas implicit memory can guide behavior without conscious awareness of memory retrieval. Here, the authors demonstrate recognition memory without awareness of the retrieval. ERP measures differentiated between implicit and explicit recognition.

This resource article describes a bioinformatical tool that, accessing an extensive gene expression database, allows the definition and identification of new brain structures based on gene expression patterns.