Volume 11 Issue 7, July 2008

Although voltage-clamp recordings remain a favorite method for studying synaptic transmission, the space-clamp problems that are associated with somatic voltage-clamp recordings have never been directly measured. A study by Williams and Mitchell in this issue now measures the experimental errors associated with this technique.

Pascual et al. conditionally delete glial cell line-derived neurotrophic factor (GDNF) expression in adult mice. They report that GDNF is indispensable for the survival of adult catecholaminergic neurons.

Drugs of abuse are known to induce changes in synaptic strength in the reward neurons of the brain. Two recent studies shed some light on how drug-induced plasticity might mediate addictive behavior long after drug use.

Have facial expressions evolved randomly or do their different shapes support some adaptive purpose? New work offers evidence of a selection pressure that may have shaped fearful and disgusted expressions.

TRPC6 promotes the formation of synapses in a CaMKIV-CREB–dependent manner. TRPC6-expressing transgenic animals showed increased numbers of spines and demonstrated enhanced learning on behavioral tasks.

In synaptically connected layer 4 and 2/3 cells, NMDA receptors are required postsynaptically for the expression of LTP and presynaptically for the expression of LTD.

Sound detection in mammalian cochlear involves a mechanoelectrical sensory transduction whose signal can be amplified by the outer hair cells in the organ of Corti. By recording the mechanical responses of cochlear taken from genetically modified mice, the current study provides evidence for hair-cell somatic motility as the underlying mechanism of cochlear amplification.

Greenberg and colleagues directly compare the activity of cortical neurons in awake and subsequently anesthetized rats, finding that anesthesia modulates the relationship between firing rate and correlation, and suggesting that brain activity during wakefulness cannot be inferred from data gathered under anesthesia.

The peptide hormone ghrelin has previously been linked to the regulation of metabolism. This study in mice finds that increasing levels of ghrelin, either through subcutaneous injections or calorie restriction, has an anxiolytic and antidepressive effect. This reveals a previously unknown function for ghrelin.

The exact function of glial cell line–derived neurotrophic factor (GDNF) in catecholaminergic cell survival in adulthood is unclear. Using a conditional GDNF-null mouse that suppresses GDNF expression in adulthood, Pascual et al. show that GDNF is an essential factor whose downregulation results in massive catecholaminergic neuronal death. Carlos Ibáñez discusses this paper in an accompanying News and Views.

Diffusible axon guidance molecules can modulate membrane potential shifts in the growth cone, producing either attraction or repulsion. This is accomplished through the manipulation of Na⁺ or Cl⁻ currents by cGMP-based signaling mechanisms, producing a differential change in the Ca²⁺ influx into the growth cone.

Sanshool, the compound responsible for the tingling sensations experienced when consuming Szechuan peppercorns, excites sensory neurons through a unique mechanism, the inhibition of two-pore potassium channels.

Beuming and colleagues determined that the binding site for cocaine overlaps with that of dopamine on the dopamine transporter. Detailed modeling and mutagenesis experiments revealed that this site is deeply buried amongst several transmembrane domains.

Although the technique of somatic voltage clamp is widely used, computational models have predicted that this controls voltage in the dendritic tree poorly. Williams and Mitchell directly quantify this error using simultaneous recordings from the soma and apical dendrites of rat neocortical pyramidal neurons. Spruston and Johnston also highlight this in an associated news and views.

Grant and colleagues used comparative proteomics and genomics to examine the evolution of the postsynaptic density and MAGUK-associated signaling complexes implicated in learning and memory. They found conservation of synaptic components amidst diverse species, but also found species-specific adaptation and increased signaling complexity in vertebrates.

In vivo, synaptic receptor densities were maintained over minutes by a rapid exchange with nonsynaptic receptor pools and over hours through turnover. These changes and receptor dynamics may represent the initial phases of synaptic efficacy modulation before eventual structural modification involving spine growth or retraction.

Acidosis can stop seizures, but it is unclear how it does this. This study demonstrates that the acid-sensing channel ASIC1a is required for either spontaneous or CO₂-induced termination of convulsant-induced seizures in mice. Moreover, ASIC1a strongly activates inhibitory interneurons under acidotic conditions, which may explain the effect.

Fujisawa and colleagues report that during a working memory task, firing patterns in ensembles of rat medial prefrontal cortex neurons reflect behavioral outcomes on coarser time scales and short-term synaptic plasticity on finer time scales. These results suggest that short-term plasticity plays a role in the neural computations guiding behavior.

The fornix is the major fiber tract connecting the medial temporal lobe and the medial diencephalon. This structural imaging study of individuals with fornix atropy finds that the fornix is important for recall, but not recognition, consistent with the idea that hippocampal inputs are selectively important for recall, rather than recognition.

This behavioral study finds that when subjects pose expressions of fear, they have a subjectively larger visual field, faster eye movements, and an increase in nasal volume and air velocity during breathing in. Posing expressions of disgust, an expression objectively opposite to fear, produced opposite results. Emotional facial expressions may therefore modify preparedness for perception and action.