Volume 13 Issue 4, April 2010

Vasopressin release increases late in sleep. Suprachiasmatic clock neurons modulate osmosensory synapses onto vasopressin neurons to facilitate osmoregulated vasopressin release, reports a study in this issue. This explains the increased late-night vasopressin release, and such facilitation prevents dehydration during sleep.

A study finds that the DNA methylation enzymes Dnmt1 and Dnmt3a are needed to maintain the epigenetic landscape in nondividing, postmitotic neurons and that this process is required for normal learning and memory.

A study in this issue reports that mice can be fear conditioned through observation of other mice receiving aversive stimuli and identifies some of the brain regions involved in this observational fear learning.

Memories are continually adapted by ongoing experience. A study now suggests that the reactivation of previously stored memories during the formation of new memories is a critical mechanism for determining memory survival.

Using two-photon imaging in a transgenic mouse model of Alzheimer's disease, the authors find that microglia, the resident macrophages of the brain, surround neurons prior to nerve cell death. They also find that inactivation of the microglial chemokine receptor CX3CR1, which is critical in neuron-microglia communication, prevents neuron loss.

Rod photoreceptors contact Off cone bipolar cells, but it has been unclear what the function of this pathway is. The authors recorded from pairs of rods and Off cone bipolar cells in the ground squirrel and show that this new pathway can mediate rapid signaling in the retina.

Faces and bodies are highly familiar visual stimuli that occur in stereotypical configurations. Using fMRI, the authors find that face and body representations are strongest and most distinct in the commonly experienced combinations of visual field and side of body.

Psychopathy is a disorder that has typically been considered to result from a primary deficit in fear or empathy. Here the authors find that impulsive-antisocial psychopathic traits are correlated with hyper-reactivity of the dopaminergic reward system as measured with positron emission tomography and functional magnetic resonance imaging.

In dividing cells, the epigenetic mechanism of DNA methylation is catalyzed by enzymes that maintain DNA methylation or act as a de novo methyltransferase. In this study, the authors find that DNA methyltransferases Dnmt1 and 3a have an active role in the maintenance of DNA methylation in postmitotic excitatory neurons. Results indicate that there is a redundancy between the two enzymes in neurons and that DNA methylation is essential for normal synaptic plasticity and memory formation.

This study shows that tonically active, delta subunit–containing presynaptic GABA_A receptors facilitate excitatory synaptic transmission at hippocampal mossy fiber synapses. Presynaptic GABA_A receptors depolarize presynaptic boutons, enhance calcium entry evoked by action potentials and facilitate LTP induction in mossy fiber–CA3 synapses.

Authors present a comprehensive genetic, anatomical and electrophysiological analysis of the local interneurons in the Drosophila antennal lobe. They find an unexpected degree of complexity and individual variation in this invertebrate neural circuit.

The immediate early gene Arc has been implicated in many forms of synaptic plasticity. This report finds that in mice lacking Arc, the visual cortex remains unmodified by deprivation or experience, suggesting that Arc expression is among the mechanisms that are critical for experience-dependent plasticity.

This study defines the roles of the doublesex gene in male and female flies' courtship circuitry and behaviors.

Osmoregulated vasopressin release is facilitated during the late sleep period to prevent dehydration. This study finds that suprachiasmatic clock neurons modulate osmosensory synapses onto vasopressin neurons to enable such facilitation.

The mechanisms by which methylphenidate (MPH or Ritalin) modifies behavioral performance are poorly understood. The authors show that MPH increased learning-induced strengthening of connections between the cortex and amygdala. This modulation was dependent on specific dopamine receptor subtypes.

Primates can develop a conditioned fear response by witnessing other primates being subjected to adverse stimuli. Jeon et al. report that mice are capable of this form of observational fear conditioning and that the medial pain system underlies the neural circuits mediating socially acquired fear.

The mechanisms underlying fear extinction remain unclear. Here, the authors show that extinction enhances basolateral amygdala inputs about conditioned stimuli to intercalated cells, resulting in the inhibition of fear output central amygdala neurons. These changes required medial prefrontal activity during extinction training, but, once induced, could be expressed without prefrontal inputs.

Lateral intraparietal cortex (LIP) has been implicated in both attention and oculomotor control, but whether these functions are spatially overlapping remains unknown. Here the authors co-injected muscimol, to temporarily inactivate areas of LIP, and manganese, to enable MRI imaging of the inactivation site. They found that dorsal LIP is primarily an oculomotor planning area, whereas ventral LIP shows dissociable circuits for both attentional and oculomotor processes.

The authors find that during the encoding of new memories, responses in the human hippocampus are predictive of the retention of memories for previously experienced, overlapping events. They report that this is accomplished by reactivating the neural representation of older memories as new memories are formed.

Attention can be driven by both stimulus- and goal-based processes. In the procedure used in this study, such 'bottom-up' and 'top-down' driven attentional processes appear to converge in the lateral prefrontal cortex.

The authors devised a method for detecting the bioluminescent Ca²⁺ sensor GFP-Aequorin in freely behaving zebrafish larvae. To demonstrate the efficacy of the technique, they targeted the sensor to a genetically specified population of hypothalamic neurons. The resulting neuroluminescence reveals patterns of neuronal activity that are associated with distinct swimming behaviors.