Articles in 2009

This study shows that adult neurogenesis requires canonical Wnt signaling to trigger transcription of pro-neural NeuroD1. Wnt signaling activates β-catenin, which in complex with TCF/LEF displaces the repressor Sox2 from a previously unknown combined Sox/LEF element in the Neurod1 promoter. Similar Sox/LEF elements activated by Wnt signaling were found in LINE-1 retrotransposons.

Climbing fiber input to the cerebellum is thought to control the induction of motor learning. Here, the authors use a new behavioral training procedure in which climbing fiber signals are eliminated, but learning still occurs. This suggests that other neural signals, possibly Purkinje cell simple spike activity, are sufficient to induce motor learning.

Here, Tain et al. describe the genetic interaction between 4E-BP, an inhibitor of translation, with Parkinson's disease–associated park and Pink1 in Drosophila, where the manipulation of 4E-BP reduced the pathologic phenotypes, including degeneration of dopaminergic neurons, in park and Pink1 mutant flies.

Individual performance during learning is known to be affected by stress and motivation, as well as by genetic predispositions that influence sensitivity to these factors. Here, the authors find that a reinforcement-learning model can provide an integrative framework for predicting the influence of these factors on mouse learning behavior.

In the Drosophila antennal lobe, there are several projection neurons (PNs) that are postsynaptic to each glomerulus. Here, the authors report that activity in these 'sister' PNs is correlated at a fine temporal scale. The predominant source of correlated activity is shared input from olfactory receptor neurons, with a smaller contribution from reciprocal PN-PN connections.

This paper shows that neurons in the thalamic reticular nucleus (TRN) respond strongly to unexpected sounds and convey this information to the auditory thalamus, modulating the responses of medial geniculate body (MGB) neurons in complex ways. Unexpectedly, visual stimuli via the TRN also modulated the 'auditory' MGB, suggesting a new site of cross-modal sensory integration.

In the striatum, acetylcholine modulates glutamate release via muscarinic receptors. The authors examine individual synapses in rat striatum and find that glutamatergic afferents show multivesicular release and low postsynpatic receptor saturation. Acetylcholine decreases both the probability of release and the amount of glutamate in the cleft, thereby suppressing the activation of nonlinearities in dendrites.

It has been thought that blue-yellow color opponent cells in the primate retina receive little input from rods. Here, the authors report that rod and cone signals are multiplexed in blue-yellow cells and that this may be the source of the blue hue bias in night vision.

Cells in a primate face area are sensitive to both specific face parts and the presence of the whole, upright face reports an electrophysiology study in monkeys. Cells in the middle face patch detected distinct constellations of face parts, but their tuning amplitude was modulated by the presence of a whole, upright face.

Degradation of chondroitin sulphate proteoglycans by chondroitinase ABC (ChABC) in the adult or injured rodent nervous system is known to promote local structural plasticity; however, this alone does not enable much functional recovery after a spinal cord injury. In this study, the authors coupled ChABC treatment with specific motor exercises, which resulted in substantial recovery of injured rats' grasping abilities.

The closely related Sox5 and Sox6 turn out to perform distinct functions during brain development. Maintenance of the ventricular zone neuroepithelium requires Sox6 in the dorsal and Sox5 in the ventral telencephalon. A portion of the interneurons born in ventral telencephalon then express Sox6, which is necessary for their correct migration and phenotypic differentiation.

The authors propose a mechanism of partial agonism, showing that partial agonists of both GluN1 and GluN2 NMDA receptor subunits have similar effects on the NMDA receptor activation reaction and they increase the height of all energy barriers during NMDA receptor activation. This contrasts with the localized effects observed for pentameric ligand-gated channels.

The authors report a successfully targeted reinnervation of hindlimb sensory fibers projection into the CNS following spinal cord injury in rats. Cervical level 1 lesions followed by expression of the neurotrophin NT-3 in the appropriate brainstem target led to proper targeting of regenerating axons.

Cannabis can impair memory function. This study shows that, in mice, the active component of cannabis, via CB1 receptors on GABA interneurons and a mechanism involving NMDA receptors, activates the mTOR pathway and protein synthesis. This transient activation impairs mice's performance in a memory test.

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.

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.

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.

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.

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.

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.