Transformation of olfactory representations in the Drosophila antennal lobe

Molecular genetics has revealed a precise stereotypy in the projection of primary olfactory sensory neurons onto secondary neurons. A major challenge is to understand how this mapping translates into odor responses in these second-order neurons. We investigated this question in Drosophila using whole-cell recordings in vivo. We observe that monomolecular odors generally elicit responses in large ensembles of antennal lobe neurons. Comparison of odor-evoked activity from afferents and postsynaptic neurons in the same glomerulus revealed that second-order neurons display broader tuning and more complex responses than their primary afferents. This indicates a major transformation of odor representations, implicating lateral interactions within the antennal lobe.     

Coherent control of a single electron spin with electric fields

Manipulation of single spins is essential for spin-based quantum information processing. Electrical control instead of magnetic control is particularly appealing for this purpose, because electric fields are easy to generate locally on-chip. We experimentally realized coherent control of a single-electron spin in a quantum dot using an oscillating electric field generated by a local gate. The electric field induced coherent transitions (Rabi oscillations) between spin-up and spin-down with 90 degrees rotations as fast as approximately 55 nanoseconds. Our analysis indicated that the electrically induced spin transitions were mediated by the spin-orbit interaction. Taken together with the recently demonstrated coherent exchange of two neighboring spins, our results establish the feasibility of fully electrical manipulation of spin qubits.     

Insect odorant receptors are molecular targets of the insect repellent DEET

DEET (N,N-diethyl-meta-toluamide) is the world's most widely used topical insect repellent, with broad effectiveness against most insects. Its mechanism of action and molecular target remain unknown. Here, we show that DEET blocks electrophysiological responses of olfactory sensory neurons to attractive odors in Anopheles gambiae and Drosophila melanogaster. DEET inhibits behavioral attraction to food odors in Drosophila, and this inhibition requires the highly conserved olfactory co-receptor OR83b. DEET inhibits odor-evoked currents mediated by the insect odorant receptor complex, comprising a ligand-binding subunit and OR83b. We conclude that DEET masks host odor by inhibiting subsets of heteromeric insect odorant receptors that require the OR83b co-receptor. The identification of candidate molecular targets for the action of DEET may aid in the design of safer and more effective insect repellents.     

Rats smell in stereo

It has been hypothesized that rats and other mammals can use stereo cues to localize odor sources, but there is limited behavioral evidence to support this hypothesis. We found that rats trained on an odor-localization task can localize odors accurately in one or two sniffs. Bilateral sampling was essential for accurate odor localization, with internasal intensity and timing differences as directional cues. If the stimulus arrived at the correct point of the respiration cycle, internasal timing differences as short as 50 milliseconds sufficed. Neuronal recordings show that bulbar neurons responded differentially to stimuli from the left and stimuli from the right.     

Oscillations and sparsening of odor representations in the mushroom body

In the insect olfactory system, oscillatory synchronization is functionally relevant and reflects the coherent activation of dynamic neural assemblies. We examined the role of such oscillatory synchronization in information transfer between networks in this system. The antennal lobe is the obligatory relay for olfactory afferent signals and generates oscillatory output. The mushroom body is responsible for formation and retrieval of olfactory and other memories. The format of odor representations differs significantly across these structures. Whereas representations are dense, dynamic, and seemingly redundant in the antennal lobe, they are sparse and carried by more selective neurons in the mushroom body. This transformation relies on a combination of oscillatory dynamics and intrinsic and circuit properties that act together to selectively filter and synthesize the output from the antennal lobe. These results provide direct support for the functional relevance of correlation codes and shed some light on the role of oscillatory synchronization in sensory networks.     

Dynamic optimization of odor representations by slow temporal patterning of mitral cell activity

Mitral cells (MCs) in the olfactory bulb (OB) respond to odors with slow temporal firing patterns. The representation of each odor by activity patterns across the MC population thus changes continuously throughout a stimulus, in an odor-specific manner. In the zebrafish OB, we found that this distributed temporal patterning progressively reduced the similarity between ensemble representations of related odors, thereby making each odor's representation more specific over time. The tuning of individual MCs was not sharpened during this process. Hence, the individual responses of MCs did not become more specific, but the odor-coding MC assemblies changed such that their overlap decreased. This optimization of ensemble representations did not occur among olfactory afferents but resulted from OB circuit dynamics. Time can therefore gradually optimize stimulus representations in a sensory network.     

Normalization for sparse encoding of odors by a wide-field interneuron

Sparse coding presents practical advantages for sensory representations and memory storage. In the insect olfactory system, the representation of general odors is dense in the antennal lobes but sparse in the mushroom bodies, only one synapse downstream. In locusts, this transformation relies on the oscillatory structure of antennal lobe output, feed-forward inhibitory circuits, intrinsic properties of mushroom body neurons, and connectivity between antennal lobe and mushroom bodies. Here we show the existence of a normalizing negative-feedback loop within the mushroom body to maintain sparse output over a wide range of input conditions. This loop consists of an identifiable "giant" nonspiking inhibitory interneuron with ubiquitous connectivity and graded release properties.     

Phase-coherent optical pulse synthesis from separate femtosecond lasers

We generated a coherently synthesized optical pulse from two independent mode-locked femtosecond lasers, providing a route to extend the coherent bandwidth available for ultrafast science. The two separate lasers (one centered at 760 nanometers wavelength, the other at 810 nanometers) are tightly synchronized and phase-locked. Coherence between the two lasers is demonstrated via spectral interferometry and second-order field cross-correlation. Measurements reveal a coherently synthesized pulse that has a temporally narrower second-order autocorrelation width and that exhibits a larger amplitude than the individual laser outputs. This work represents a new and flexible approach to the synthesis of coherent light.     

Odor-induced membrane currents in vertebrate-olfactory receptor neurons

In olfactory receptor neurons, odor molecules cause a depolarization that leads to action potential generation. Underlying the depolarization is an ionic current that is the earliest electrical event in the transduction process. In two preparations, olfactory receptor neurons were voltage-clamped and stimulated with odors and this generator current was measured. In addition, a method was developed to estimate the time course and absolute concentration of odorants delivered to the receptor sites. With this method, olfactory neurons were found to have relatively high stimulus thresholds, steep dose-response relations, long latencies, and an apparent requirement for cooperativity at one or more steps in the pathway from odorant binding to activation of the generator current.     

Coherence and conservation

A principal aim of current conservation policy is to reduce the impact of habitat fragmentation. Conservation corridors may achieve this goal by facilitating movement among isolated patches, but there is a risk that increased connectivity could synchronize local population fluctuations (causing coherent oscillations) and thereby increase the danger of global extinction. We identify general conditions under which populations can or cannot undergo coherent oscillations, and we relate these conditions to local and global extinction probabilities. We suggest a simple method to explore the potential success of conservation corridors and, more generally, any manipulations of dispersal patterns that aim to protect threatened species or control pests.     

Neuronal oscillations in cortical networks

Clocks tick, bridges and skyscrapers vibrate, neuronal networks oscillate. Are neuronal oscillations an inevitable by-product, similar to bridge vibrations, or an essential part of the brain's design? Mammalian cortical neurons form behavior-dependent oscillating networks of various sizes, which span five orders of magnitude in frequency. These oscillations are phylogenetically preserved, suggesting that they are functionally relevant. Recent findings indicate that network oscillations bias input selection, temporally link neurons into assemblies, and facilitate synaptic plasticity, mechanisms that cooperatively support temporal representation and long-term consolidation of information.     

Intrinsic oscillations of neocortex generated by layer 5 pyramidal neurons

Rhythmic activity in the neocortex varies with different behavioral and pathological states and in some cases may encode sensory information. However, the neural mechanisms of these oscillations are largely unknown. Many pyramidal neurons in layer 5 of the neocortex showed prolonged, 5- to 12-hertz rhythmic firing patterns at threshold. Rhythmic firing was due to intrinsic membrane properties, sodium conductances were essential for rhythmicity, and calcium-dependent conductances strongly modified rhythmicity. Isolated slices of neocortex generated epochs of 4- to 10-hertz synchronized activity when N-methyl-D-aspartate receptor-mediated channels were facilitated. Layer 5 was both necessary and sufficient to produce these synchronized oscillations. Thus, synaptic networks of intrinsically rhythmic neurons in layer 5 may generate or promote certain synchronized oscillations of the neocortex.     

Host Finding by Odor in the Myrmecophilic Beetle Atemeles pubicollis Bris. (Staphylinidae)

The beetle Atemeles publicollis orients to the odor of its host ants by positive anemotaxis and osmoclinotaxis. The chemical response changes with age of the beetles. After hatching they are attracted by Myrmica odors, and, after hibernating, by Formica odors.     

Discrimination by rats of conspecific odors of reward and nonreward

The hypothesis that, after receiving reward and nonreward, rats excrete differential odors perceptible to other rats was tested by making the correct turn in a T-maze contingent on discrimination of any such odors. Clear evidence for an "odor of nonreward or frustration" was obtained, and there was the suggestion of a transistory odor after early reward trials.     

顶空固相微萃取与气质联用法分析鲢肉中风味成分

以我国重要食用的淡水鱼之一,鲢为原料。采用聚二甲基硅氧烷二乙烯苯(PDMS DVB)涂层的固相微萃取头萃取鱼肉中的挥发性成分,并通过气质联用仪分析鉴定鱼肉中的气味成分。结果表明:固相微萃取技术有效地吸附了鱼肉中的挥发性成分,经NIST质谱数据库检索和文献对照,共检出并确定48种成分,所检出物质的分子量范围大部分处于90～250MW之间,并且这些成分多是一些羰基类及醇类化合物,其总百分含量高达88.23%,其中以1 辛烯3醇的百分含量最多,为18.95%,1 辛烯3醇一般表现为土味、蘑菇味。其次是一些直链的饱和醛类,如己醛、庚醛、辛醛、壬醛、葵醛等,而这些醛类通常产生一些令人不愉快、辛辣的刺激性气味,并且普遍存在于淡水鱼中。     

Responses of vomeronasal neurons to natural stimuli

The vomeronasal organ (VNO) of mammals plays an essential role in the detection of pheromones. We obtained simultaneous recordings of action potentials from large subsets of VNO neurons. These cells responded to components of urine by increasing their firing rate. This chemosensory activation required phospholipase C function. Unlike most other sensory neurons, VNO neurons did not adapt under prolonged stimulus exposure. The full time course of the VNO spiking response is captured by a simple quantitative model of ligand binding. Many individual VNO neurons were strongly selective for either male or female mouse urine, with the effective concentrations differing as much as a thousandfold. These results establish a framework for understanding sensory coding in the vomeronasal system.     

顶空固相微萃取与气质联用法分析鲢肉中风味成分

以我国重要食用的淡水鱼之一,鲢为原料。采用聚二甲基硅氧烷二乙烯苯(PDMS DVB)涂层的固相微萃取头萃取鱼肉中的挥发性成分,并通过气质联用仪分析鉴定鱼肉中的气味成分。结果表明:固相微萃取技术有效地吸附了鱼肉中的挥发性成分,经NIST质谱数据库检索和文献对照,共检出并确定48种成分,所检出物质的分子量范围大部分处于90～250MW之间,并且这些成分多是一些羰基类及醇类化合物,其总百分含量高达88.23%,其中以1 辛烯3醇的百分含量最多,为18.95%,1 辛烯3醇一般表现为土味、蘑菇味。其次是一些直链的饱和醛类,如己醛、庚醛、辛醛、壬醛、葵醛等,而这些醛类通常产生一些令人不愉快、辛辣的刺激性气味,并且普遍存在于淡水鱼中。     

普通大蓟马子代性比对同种成虫气味的响应

为了探究同种成虫的气味对普通大蓟马(Megalurothrips usitatus)交配期间性比调节的影响,设置对照（无气味）、已交配雌虫、未交配雌虫和已交配雄虫等4种气味源,分别处理单对刚羽化成虫24 h,然后用幼嫩豇豆(Vigna unguiculata)豆荚单头饲养被测雌虫,观测每日所产子代的性别和数量,计算子代性比。结果表明：已交配雌虫气味处理的子代雌虫数（22.80头）最少,跟其他处理差异显著。同对照的子代性比（0.31）相比,已交配雌虫和未交配雌虫的气味分别导致子代性比显著提高和降低,子代性比分别为0.48和0.22,而已交配雄虫气味对子代性比无显著影响。4个处理中,仅已交配雌虫气味处理的雌虫在产卵最后1天的日性比达到1.00,即雌虫体内的精子已消耗殆尽。成虫气味源对雌虫产卵天数没有明显影响。实验结果说明,普通大蓟马在交配期间能依靠嗅觉判别周边雌虫的交配状况,然后通过调控雌虫的获精数量,实现对子代性比的自调节。     

Genetic component of bee odor in kin recognition

The primitively social sweat bee, Lasioglossum zephyrum, blocks the entry into its nest of most conspecifics from other colonies. Laboratory inbreeding of these bees produced lines which showed a positive linear relationship between the coefficient of relationship of bees tested and how often they permitted non-nestmates to pass them. The most probable mechanism is a genetically determined odor coupled with a learned component by which guard bees discriminate between odors of close kin and other bees.     

Hemodynamic signals correlate tightly with synchronized gamma oscillations

Functional imaging methods monitor neural activity by measuring hemodynamic signals. These are more closely related to local field potentials (LFPs) than to action potentials. We simultaneously recorded electrical and hemodynamic responses in the cat visual cortex. Increasing stimulus strength enhanced spiking activity, high-frequency LFP oscillations, and hemodynamic responses. With constant stimulus intensity, the hemodynamic response fluctuated; these fluctuations were only loosely related to action potential frequency but tightly correlated to the power of LFP oscillations in the gamma range. These oscillations increase with the synchrony of synaptic events, which suggests a close correlation between hemodynamic responses and neuronal synchronization.