Chemical Ecology The Chemistry of Biotic Interaction (1995) / Chapter Skim
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Analysis of Chemical Signals by Nervous Systems
Analysis of Chemical Signals by Nervous Systems
Pages 161-182
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From page 161... ...
Lobsters appear to release into the urine the products of a small cluster of glands located in the nephropore nipple some 100 ,um inside the excretory pore (231. Both the gland with its duct and surrounding muscle tissue and the muscular valve of the nephropore appear designed to give the animal control over chemical signals released into the gill current.
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From page 162... ...
In a courtship context, males accept even much smaller premolt females and cohabit with them, one at a time, each for 1-2 weeks. Although such context appears to be provided by chemical signals (33, 34)
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From page 163... ...
Chemical signals appear to be used to remember individuals and to facilitate stable dominance hierarchies. One may wonder why lobsters appear to use urine as a dispersal solvent for chemical signals, whereas terrestrial arthropods such as the well-studied insects use direct release of gland products into the air.
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From page 164... ...
Lobster chemoreceptor cells have flicker fusion frequencies of 4 Hz and can integrate stimuli over 200 ms, closely corresponding to odor sampling behavior with 4-Hz "sniffs." Using this information, spatial odor gradients can be determined from temporal analysis of odor patches typical of turbulent dispersal. Lobsters appear to use this information to locate odor sources.
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From page 165... ...
Chemical Signals in the Marine Environment /159 REFERENCES 1. Atema, J
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From page 167... ...
The importance of such chemical signals for survival and reproductive success is reflected in remarkable chemosensory capacities and specializations in diverse species of animals. After considering the evolutionary origins of the olfactory system and some basic principles of olfaction, this brief review examines one of the most extensively studied examples of neural processing of semiochemical information: the sex pheromone-specific olfactory subsystem in male moths.
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From page 168... ...
E cold possess finely "tuned" receptors for specific substances in the environment, mechanisms for transducing the stimuli and for decoding, integrating, and transmitting information about them, and means to generate appropriate behavioral responses.
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From page 169... ...
The difference between the central organization of projections of gustatory receptors and ORCs reflects basic functional differences between these two chemical senses: the numbers of receptor cells, substances that normally stimulate those receptors, and qualities or categories of stimuli that can be discriminated are smaller for taste than for olfaction. Olfactory glomeruli must have evolved early, because these characteristic structures are present in the "olfactory brains" of modern representatives of ancient marine groups including molluscs (5)
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From page 170... ...
That ability also depends on neural circuitry in the CNS through which afferent olfactory information is integrated, abstracted, and recognized. To begin to understand how chemical signals are analyzed by the olfactory system and ultimately affect behavior, we must consider the anatomical and functional organization of the olfactory pathway and the processing performed, and abstraction accomplished, by neural circuitry at each level in that pathway.
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From page 171... ...
According to this model, olfactory information processing involves generation of a sequence of activity maps, termed "molecular images," in the olfactory pathway. Most of the mechanisms involved in this sequence are adaptations of, and bear similarities to, those underlying vision, immune responses, hormonal communication, chemotaxis of motile unicellular organisms, and other biological processes.
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From page 172... ...
Moreover, mounting evidence suggests that interneuronal circuitry in other regions of the insect protocerebrum shapes descending premolar neural activity. This olfactorily influenced neural activity ultimately participates in the control of behavioral responses to odor stimuli (such as the characteristic flight patterns of male moths stimulated by female sex pheromone; ref.
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From page 173... ...
is that the response patterns the molecular images-at various levels in the central olfactory pathway are set up by the differential responses of the ORCs in the peripheral receptor epithelium. These studies also suggest that functional modules, which may correspond to recognizable structural units such as individual glomeruli with their associated cells, in the olfactory bulb or lobe participate in the analysis of olfactory information conveyed to them
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From page 174... ...
Moreover, recent investigations of the response specificities or "molecular receptive ranges" of individual uniglomerular output neurons (mitral and tufted cells) in the vertebrate olfactory bulb strongly support the idea that the glomeruli are functional units (30-331.
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From page 175... ...
sexta, give their characteristic, qualitatively and quantitatively optimal behavioral responses only when stimulated by the correct blend of sex-pheromone components and not by individual components or partial blends lacking key components (43, 441. Solvent washes of the pheromone gland of female M
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From page 176... ...
Each of these properties of the pheromonal message is important, as the male moth gives his characteristic behavioral responses only when the necessary and sufficient pheromone components A and B are present in the blend (44) , when the concentrations and blend proportions of the components fall within acceptable ranges (49)
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From page 177... ...
It is likely that these cation channels, which are permeable to Na+ and K+ as well as Ca2+ ions, play an important role in pheromone transduction. Functional Organization of Central Olfactory Pathways Axons of antenna!
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From page 178... ...
Thus first-order synaptic processing of sensory information about these key components of the sex pheromone apparently is confined to different, distinctive neuropil regions of the MGC. Stimulus Quality By means of intracellular recording and staining methods, we have examined the responses of AL neurons to stimulation of the ipsilateral antenna with each of the sex pheromone components as well as partial and complete blends (751.
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From page 179... ...
Thus these neurons can discriminate between the two inputs based upon how each affects the spiking activity of the cell. These PNs also respond uniquely to the natural pheromone blend released by the female: these pheromone specialist neurons have enhanced ability to follow intermittent pheromonal stimuli occurring at natural frequencies of '10 stimuli per sec (771.
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From page 180... ...
Because spatial discontinuity of the pheromonal signal in the environment is detected by a flying male moth as temporally intermittent stimuli, intermittent pheromonal stimuli received by a male's antenna must be registered by MGC PNs. We discovered that certain pheromone specialist PNs have greatly enhanced ability to follow pulsed pheromonal stimuli with corresponding bursts of impulses.
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From page 181... ...
Such GABAergic synaptic transmission is essential to the enhanced ability of the specialized AL PNs to follow intermittent pheromonal stimuli (77~. Synaptic Interactions Between AL Neurons We have tested the idea that this inhibition of PNs is mediated through LNs by directly recording synaptic interactions between pairs of AL neurons (701.
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From page 182... ...
In some other protocerebral neurons, pheromonal stimuli elicit brief excitations that recover to background firing rates <1 sec after stimulation. LLE is more frequently elicited by the complete sex pheromone blend or a mixture of components A and B than by either component alone.
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