Volume 12 Issue 9, September 2009

No effective therapeutic interventions exist for severe spinal cord injury. A report in this issue shows that rats can recover substantial 'hand' function after complete lesion of the cervical dorsal corticospinal tract, if treated with a combination of specific reaching rehabilitation exercises and chondroitinase injections to enhance axonal sprouting.

NeuroD1 is well known for its role in development. In this issue, two papers collectively show that the Wnt pathway directly activates the transcription factor NeuroD1 to regulate adult neurogenesis and, potentially, neuron diversity.

The study by Ozaita and colleagues in this issue identifies a function of CB₁ cannabinoid receptors—THC-induced amnesia—and reveals the surprising role of GABAergic synapses in mediating this phenomenon.

Using fMRI to probe face cells in the monkey temporal lobe, a study shows that these face-responsive cells appear to be feature detectors, but only work this way in the holistic construct of a face.

This study implicates the proteosome degradation machinery in controlling axon guidance by showing that the deubiquiting enzyme USP33 is essential for controlling Slit/Robo-mediated commissural axonal guidance.

This study uses inducible ablation of NeuroD1 from adult neuronal stem cells/progenitors to show that this transcription factor is crucial for the survival and maturation of adult-born neurons in the hippocampus and olfactory bulb.

Here, the authors describe the presynaptic mechanism for the induction of cortico-amygdala LTP that involves presynaptic L-type voltage-dependent Ca²⁺ channels in the lateral amygdala.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Selective targeting of specific neuronal populations, for genetic or other manipulations, is crucial to much of neuroscience. The authors screened 536 BAC transgenic mouse lines from the GENSAT collection for specific reporter expression in the retina. Here, they describe several mouse lines selectively targeting different retinal cell types. The full dataset is accessible at http://www.gensat.org/retina.jsp.