Chemistry: A Molecular Approach (2nd US Edition)

This innovative text explains difficult concepts in a relevant, student-oriented manner.  Chemistry is presented visually through multi-level images—macroscopic, molecular and symbolic representations—helping you see the connections among the formulas (symbolic), the world around you (macroscopic), and the atoms and molecules that make up the world (molecular). Among other revisions, the Second Edition offers a crisp new design, adds more challenging problems, and significantly revises cove

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Insects have a highly sensitive sense of smell. Extremely low concentrations of odor molecules in the air are sufficient to be detected by receptor neurons on their antennae. Specific proteins, so-called receptor proteins, expressed in these neurons recognize the odors. The odor molecules bind to the receptors and produce chemical and electrical signals that are processed in the insect brain and eventually affect the insect's behavior.

Apart from the receptors, further proteins involved in olfaction, including enzymes and chemosensory proteins, come into play. Based on these molecular principles, all insects follow their innate and elementary survival formula: finding food, recognizing mates, and - in case of females - identifying adequate oviposition sites that guarantee nutritious and easily digestible food for their offspring.

Moths (Lepidotera) are popular research objects in addition to fruit flies. The genome of the silkworm Bombyx mori has been fully sequenced; however, this insect has been domesticated by humans for thousands of years, therefore its native conspecifics cannot be found anymore. On the other hand, the "habits" of the tobacco hornworm Manduca sexta, a moth species native to North America, have been the subject of intense physiological investigations to study the insect olfactory system, and recently also because its host plant, wild tobacco Nicotiana attenuata, has advanced to an important model plant in ecological research.

Genetic analysis of the Manduca sexta antennae closes a gap in the search after the insect's odor-directed behavior: The release of stress-induced odor molecules by tobacco plants is well studied, as is the pollination of the flowers by the moths. "But how does the plant odor – metaphorically speaking - end up in the insect's brain?" asks Bill Hansson, director of the Department of Evolutionary Neuroethology founded in 2006 at the Max Planck Institute.

The scientists identified the antennal transcriptome as an important basis for studying olfactory function of the insect and sequenced active genes in the antennae completely. Additionally, they determined the amount of individual messenger RNAs (mRNAs) that belong to each gene. Sequence information which involved more than 66 million nucleotides was analyzed. Basically, the results can be summarized as follows: i.) Manduca sexta has 18 specific odorant binding proteins (OBPs) and 21 chemosensory proteins (CSPs). ii.) Manduca males possess 68 different odorant receptors, each expressed in a specific type of neuron coupled to a corresponding glomerulus in the brain, whereas females have 70 of these "response units". Most of the receptors could be identified in the course of these studies. iii.) 69% of the transcripts could not be annotated to a specific gene function: their role in the antennae is so far unknown. Presumably there are many more neural mechanisms of stimulus processing in the antennae that are yet to be elucidated. Some mRNAs imply that there is intense enzymatic activity, esterases for instance; there is also a larger amount of transcripts that regulate gene expression, indicating that the antenna can adapt to new situations by gene regulation. iv.) Antennal genetics do not seem particularly complex: For comparison: there are almost twice as many active genes in the larval midgut as in the antennae of an adult moth. Only 348 genes are exclusively expressed in males; females, after all, claim 729 genes as their own. This may be due to their life sustaining formula to lay their fertilized eggs in ideal places, such as wild tobacco leaves, where young larvae can feed. [JWK, AO]

Source : Max Planck Institute for Chemical Ecology

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It's been a puzzle why our two closest living primate relatives, chimpanzees and bonobos, have widely different social traits, despite belonging to the same genus. Now, a comparative analysis of their brains shows neuroanatomical differences that may be responsible for these behaviors, from the aggression more typical of chimpanzees to the social tolerance of bonobos.

"What's remarkable is that the data appears to match what we know about the human brain and behavior," says Emory anthropologist James Rilling, who led the analysis. "The neural circuitry that mediates anxiety, empathy and the inhibition of aggression in humans is better developed in bonobos than in chimpanzees."

The journal of Social Cognitive and Affective Neuroscience published the results April 5, the most comprehensive comparative analysis to date of the neural systems of chimpanzees and bonobos.

"By contributing to our basic understanding of how brain anatomy relates to social behavior, this study may provide clues to the brain dysfunction underlying human social behavioral disorders like psychopathy and autism," Rilling says.

Chimpanzees and bonobos diverged from a common ancestor with humans about six million years ago, and from each other just one-to-two million years ago. Despite this relatively brief separation in evolutionary terms, the two species exhibit significant differences in social behavior. Compared with chimpanzees, bonobos are more anxious, less aggressive, more socially tolerant, more playful, more sexual and perhaps more empathic.

"Chimpanzees tend to resolve conflict by using aggression, while bonobos are more likely to use behavioral mechanisms like sex and play to diffuse tension," Rilling says. "The social behaviors of the two species mirror individual differences within the human population."

Rilling heads Emory's Laboratory for Darwinian Neuroscience, a leader in the use of non-invasive neuro-imaging technology to compare the neurobiology of humans and other primates. The lab draws on resources of Emory's Yerkes National Primate Research Center.

"In addition to exploring links between neuroanatomy and different social behaviors, we're mapping the underlying biology for how species evolve and differentiate," Rilling says.

A range of imaging and analytical techniques were used in the chimpanzee-bonobo study. Voxel-based morphometry compared the gray matter in standard structural scans of the brains. Diffusion tensor imaging (DTI) captured the white matter connections, to compare the fiber tracts that "wire" the brain.

The results showed that bonobos have more developed circuitry for key nodes within the limbic system, the so-called emotional part of the brain, including the amygdala, the hypothalamus and the anterior insula. The anterior insula and the amygdala are both implicated in human empathy.

"We also found that the pathway connecting the amygdala and the prefrontal cortex is larger in bonobos than chimpanzees," Rilling says. "When our amygdala senses that our actions are causing someone else distress, we may use that pathway to adjust our behavior in a prosocial direction."

Chimpanzees have better developed visual system pathways, according to the analysis. Previous research has suggested that those pathways are important for tool use, a skill which chimpanzees appear better at than bonobos.

Source : Emory University

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