Detection of near-atmospheric concentrations of CO2 by an olfactory subsystem in the mouse

Carbon dioxide (CO2) is an important environmental cue for many organisms but is odorless to humans. It remains unclear whether the mammalian olfactory system can detect CO2 at concentrations around the average atmospheric level (0.038%). We demonstrated the expression of carbonic anhydrase type II (CAII), an enzyme that catabolizes CO2, in a subset of mouse olfactory neurons that express guanylyl cyclase D (GC-D+ neurons) and project axons to necklace glomeruli in the olfactory bulb. Exposure to CO2 activated these GC-D+ neurons, and exposure of a mouse to CO2 activated bulbar neurons associated with necklace glomeruli. Behavioral tests revealed CO2 detection thresholds of approximately 0.066%, and this sensitive CO2 detection required CAII activity. We conclude that mice detect CO2 at near-atmospheric concentrations through the olfactory subsystem of GC-D+ neurons.     

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.     

Regulation of Drosophila life span by olfaction and food-derived odors

Smell is an ancient sensory system present in organisms from bacteria to humans. In the nematode Caenorhabditis elegans, gustatory and olfactory neurons regulate aging and longevity. Using the fruit fly, Drosophila melanogaster, we showed that exposure to nutrient-derived odorants can modulate life span and partially reverse the longevity-extending effects of dietary restriction. Furthermore, mutation of odorant receptor Or83b resulted in severe olfactory defects, altered adult metabolism, enhanced stress resistance, and extended life span. Our findings indicate that olfaction affects adult physiology and aging in Drosophila, possibly through the perceived availability of nutritional resources, and that olfactory regulation of life span is evolutionarily conserved.     

Combinatorial effects of odorant mixes in olfactory cortex

In mammals, each odorant is detected by a combination of different odorant receptors. Signals from different types of receptors are segregated in the nose and the olfactory bulb, but appear to be combined in individual neurons in the olfactory cortex. Here, we report that binary odorant mixes stimulate cortical neurons that are not stimulated by their individual component odorants. We propose that cortical neurons require combinations of receptor inputs for activation and that merging the receptor codes of two odorants provides novel combinations of receptor inputs that stimulate neurons beyond those activated by the single odorants. These findings may explain why odorant mixtures can elicit novel odor percepts in humans.     

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.     

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.     

Sexual deprivation increases ethanol intake in Drosophila

The brain's reward systems reinforce behaviors required for species survival, including sex, food consumption, and social interaction. Drugs of abuse co-opt these neural pathways, which can lead to addiction. Here, we used Drosophila melanogaster to investigate the relationship between natural and drug rewards. In males, mating increased, whereas sexual deprivation reduced, neuropeptide F (NPF) levels. Activation or inhibition of the NPF system in turn reduced or enhanced ethanol preference. These results thus link sexual experience, NPF system activity, and ethanol consumption. Artificial activation of NPF neurons was in itself rewarding and precluded the ability of ethanol to act as a reward. We propose that activity of the NPF-NPF receptor axis represents the state of the fly reward system and modifies behavior accordingly.     

Postnatal refinement of peripheral olfactory projections

Axonal projections from the olfactory epithelium to the olfactory bulb are organized into glomeruli according to the expressed odorant receptor. Using gene-targeted mice, we show that glomerular maturation proceeds along different time courses for two similar receptors and requires sensory input during distinct sensitive periods. During early development, some glomeruli are innervated by axons of neurons that do not express the same receptor. These heterogeneous glomeruli normally disappear with age, but they persist in adults deprived of sensory input by unilateral and permanent naris closure. Persistence may be due, in part, to prolonged survival of olfactory sensory neurons.     

Encoding pheromonal signals in the accessory olfactory bulb of behaving mice

Many mammalian species rely on pheromones-semiochemicals produced by other members of the same species-to communicate social status and reproductive readiness. To assess how the central nervous system integrates the complex repertoire of pheromones, we recorded from single neurons in the accessory olfactory bulb, a nucleus that processes pheromonal signals, of male mice engaged in natural behaviors. Neuronal firing was robustly modulated by physical contact with male and female conspecifics, with individual neurons activated selectively by specific combinations of the sex and strain of conspecifics. We infer that mammals encode social and reproductive information by integrating vomeronasal sensory activity specific to sex and genetic makeup.     

2个新的鳞翅目OR83b类化感蛋白基因的克隆和序列分析

【目的】分离和克隆昆虫触角中一类非常保守的嗅觉受体蛋白基因全序列。【方法】采用简并引物反转录多聚酶链式反应(RT-PCR)和cDNA末端快速扩增(RACE)技术克隆基因,用生物信息学方法对获得的cDNA全序列及推导的氨基酸序列进行分析。【结果】从甜菜夜蛾(Spodoptera exigua Hübner)和斜纹夜蛾[Spodoptera litura(Fabricius)]雄蛾触角中扩增得到2个分别为1906bp和2483bp的OR83类化感蛋白基因的cDNA,开放阅读框(ORF)编码473个氨基酸,命名为SexiOR2和SlitOR2。通过在GenBank中进行序列的同源性比较,发现这2个鳞翅目化感蛋白新序列与已知蛾类昆虫的OR83b类化感蛋白氨基酸序列具较高的同源性。【结论】明确了所获得的2个鳞翅目蛋白新序列属于OR83b类化感蛋白。     

Grueneberg ganglion cells mediate alarm pheromone detection in mice

Alarm pheromones (APs) are widely used throughout the plant and animal kingdoms. Species such as fish, insects, and mammals signal danger to conspecifics by releasing volatile alarm molecules. Thus far, neither the chemicals, their bodily source, nor the sensory system involved in their detection have been isolated or identified in mammals. We found that APs are recognized by the Grueneberg ganglion (GG), a recently discovered olfactory subsystem. We showed with electron microscopy that GG neurons bear primary cilia, with cell bodies ensheathed by glial cells. APs evoked calcium responses in GG neurons in vitro and induced freezing behavior in vivo, which completely disappeared when the GG degenerated after axotomy. We conclude that mice detect APs through the activation of olfactory GG neurons.     

Resetting the circadian clock by social experience in Drosophila melanogaster

Circadian clocks are influenced by social interactions in a variety of species, but little is known about the sensory mechanisms underlying these effects. We investigated whether social cues could reset circadian rhythms in Drosophila melanogaster by addressing two questions: Is there a social influence on circadian timing? If so, then how is that influence communicated? The experiments show that in a social context Drosophila transmit and receive cues that influence circadian time and that these cues are likely olfactory.     

Golf: an olfactory neuron specific-G protein involved in odorant signal transduction

Biochemical and electrophysiological studies suggest that odorants induce responses in olfactory sensory neurons via an adenylate cyclase cascade mediated by a G protein. An olfactory-specific guanosine triphosphate (GTP)-binding protein alpha subunit has now been characterized and evidence is presented suggesting that this G protein, termed Golf, mediates olfaction. Messenger RNA that encodes Golf alpha is expressed in olfactory neuroephithelium but not in six other tissues tested. Moreover, within the olfactory epithelium, Golf alpha appears to be expressed only by the sensory neurons. Specific antisera were used to localize Golf alpha protein to the sensory apparatus of the receptor neurons. Golf alpha shares extensive amino acid identity (88 percent) with the stimulatory G protein, Gs alpha. The expression of Golf alpha in S49 cyc- kin- cells, a line deficient in endogenous stimulatory G proteins, demonstrates its capacity to stimulate adenylate cyclase in a heterologous system.     

Impaired respiratory and body temperature control upon acute serotonergic neuron inhibition

Physiological homeostasis is essential for organism survival. Highly responsive neuronal networks are involved, but their constituent neurons are just beginning to be resolved. To query brain serotonergic neurons in homeostasis, we used a neuronal silencing tool, mouse RC::FPDi (based on the synthetic G protein-coupled receptor Di), designed for cell type-specific, ligand-inducible, and reversible suppression of action potential firing. In mice harboring Di-expressing serotonergic neurons, administration of the ligand clozapine-N-oxide (CNO) by systemic injection attenuated the chemoreflex that normally increases respiration in response to tissue carbon dioxide (CO(2)) elevation and acidosis. At the cellular level, CNO suppressed firing rate increases evoked by CO(2) acidosis. Body thermoregulation at room temperature was also disrupted after CNO triggering of Di; core temperatures plummeted, then recovered. This work establishes that serotonergic neurons regulate life-sustaining respiratory and thermoregulatory networks, and demonstrates a noninvasive tool for mapping neuron function.     

The role of Drosophila mushroom body signaling in olfactory memory

The mushroom bodies of the Drosophila brain are important for olfactory learning and memory. To investigate the requirement for mushroom body signaling during the different phases of memory processing, we transiently inactivated neurotransmission through this region of the brain by expressing a temperature-sensitive allele of the shibire dynamin guanosine triphosphatase, which is required for synaptic transmission. Inactivation of mushroom body signaling through alpha/beta neurons during different phases of memory processing revealed a requirement for mushroom body signaling during memory retrieval, but not during acquisition or consolidation.     

Loss of sex discrimination and male-male aggression in mice deficient for TRP2

The mouse vomeronasal organ (VNO) is thought to mediate social behaviors and neuroendocrine changes elicited by pheromonal cues. The molecular mechanisms underlying the sensory response to pheromones and the behavioral repertoire induced through the VNO are not fully characterized. Using the tools of mouse genetics and multielectrode recording, we demonstrate that the sensory activation of VNO neurons requires TRP2, a putative ion channel of the transient receptor potential family that is expressed exclusively in these neurons. Moreover, we show that male mice deficient in TRP2 expression fail to display male-male aggression, and they initiate sexual and courtship behaviors toward both males and females. Our study suggests that, in the mouse, sensory activation of the VNO is essential for sex discrimination of conspecifics and thus ensures gender-specific behavior.     

Functional requirement for class I MHC in CNS development and plasticity

Class I major histocompatibility complex (class I MHC) molecules, known to be important for immune responses to antigen, are expressed also by neurons that undergo activity-dependent, long-term structural and synaptic modifications. Here, we show that in mice genetically deficient for cell surface class I MHC or for a class I MHC receptor component, CD3zeta, refinement of connections between retina and central targets during development is incomplete. In the hippocampus of adult mutants, N-methyl-D-aspartate receptor-dependent long-term potentiation (LTP) is enhanced, and long-term depression (LTD) is absent. Specific class I MHC messenger RNAs are expressed by distinct mosaics of neurons, reflecting a potential for diverse neuronal functions. These results demonstrate an important role for these molecules in the activity-dependent remodeling and plasticity of connections in the developing and mature mammalian central nervous system (CNS).