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At least 253 records · Page 14Linked to original sources
PubMed1998

Perisynaptic Schwann cells at neuromuscular junctions revealed by a novel monoclonal antibody.

This study aimed to generate a probe for perisynaptic Schwann cells (PSCs) to investigate the emerging role of these synapse-associated glial cells in the formation and maintenance of the neuromuscular junction (NMJ). We have obtained a novel monoclonal antibody, 2A12, which labels the external surface of PSC membranes at the frog NMJ. The antibody reveals PSC fine processes or "fingers" that are interposed between nerve terminal and muscle membrane, interdigitating with bands of acetylcholine receptors. This antibody also labels PSCs at the avian neuromuscular junction and recognizes a 200 kDa protein in Torpedo electric organs. In frog muscles, axotomy induces sprouting of PSC processes beyond clusters of acetylcholine receptors and acetylcholinesterase at denervated junctional branches. PSC branches often extend across several muscle fibers. At some junctions, PSC sprouts join the tips of neighboring branches. The average length of PSC sprouts is approximately 156 microm at 3-week denervated NMJs. PSC sprouting is accompanied by a significant increase in the number of Schwann cell bodies per NMJ. Following nerve regeneration, nerve terminals reinnervate the junction along the PSC processes. In vivo observations of normal frog muscles also show PSC processes longer than nerve terminals at some junctional branches. The results suggest that nerve injury induces profuse PSC sprouting that may play a role in guiding nerve terminal regeneration at frog NMJs. In addition, antibody 2A12 reveals the fine morphology of PSCs in relation to other synaptic elements and is a useful probe in elucidating the function of these synapse-associated glial cells in vivo.

Animals↗
PubMed2001

Effects of predator chemical cues and behavioral biorhythms on foraging activity of terrestrial salamanders.

Red-backed salamanders, Plethodon cinereus, show a variety of alarm responses to chemical cues from eastern garter snakes, Thamnophis sirtalis. We measured the foraging activity of red-backed salamanders exposed to water soiled by a garter snake (fed P. cinereus) or to unsoiled water. Salamanders exposed to snake-soiled water showed less foraging activity than salamanders exposed to unsoiled water; therefore, predators could have nonlethal effects on salamander populations. Our results also show additional factors influenced salamander foraging activity. Salamander foraging activity and responsiveness to chemical cues do not appear to have been affected by sex or food deprivation. Salamander foraging activity does appear to have been influenced by activity biorhythms. Foraging activity of animals in both treatments showed a bimodal periodicity that is consistent with natural activity patterns controlled by internal biorhythms. Exposure to snake-soiled water significantly reduced foraging activity during periods of peak foraging activity, but had a subtler effect on foraging activity during natural lulls in activity. We suggest that both activity biorhythms and exposure to chemical cues are important factors affecting salamander foraging behavior.

Animals↗
PubMed2001

Importance of bacterial decomposition and carrion substrate to foraging brown treesnakes.

Brown treesnakes are an invasive species to the island of Guam that have caused extensive ecological and economic damage. Efforts to control the snake population have included trapping using live mouse lures, but for logistical and economic reasons a synthetic lure is needed. When searching for live food, brown treesnakes use both visual and odor cues. However, when searching for carrion, odor cues are sufficient. Attempts to develop synthetic lures based on chemical reconstruction of the complex carrion odor have not succeeded. We provide evidence that a microbial-substrate interaction is important for bait take by brown treesnakes. Microbial cultures taken from mouse carrion indicate that Enterobacter agglomerans is the predominant bacterium, and field tests suggest that this organism may be important to odor production that attracts brown treesnakes. This information may prove useful in the development of microbial-based biological reactors that could be formulated to produce a continuous stream of odor of sufficient complexity so as to be attractive to foraging snakes.

Animals↗
PubMed2001

Probing the structural diversities of long alpha-neurotoxins by fluorescence quenching studies.

Trp fluorescence of Ophiophagus hannah neurotoxins (Oh-4, Oh-6A, Oh-7, and Oh-8) and Bungarus multicinctus (alpha-bungarotoxin was quenched by acrylamide and iodide. Acrylamide quenching studies indicated that the degree of exposure of Trp residues in the neurotoxins followed the order Oh-8 > Oh-7 > Oh-6A > Oh-4 > alpha-bungarotoxin, as did the accessibility for iodide. These results reveal that the exposed degree of Trp residues and the microenvironment surrounding Trp residues in the neurotoxins differ, even though their Trp residues and positively charged residues are located at the same or homologous positions. In contrast to unfolded Oh-4, Oh-6A, Oh-7, and alpha-bungarotoxin, unfolding of Oh-8 by reduction and S-carboxymethylation caused a notable decrease in the susceptibility of their Trp residues for iodide. These observations support the view that the side chains of Trp residues and positively charged residues in their native structure do not point toward the same spatial positions. Computer models of the neurotoxins are in good agreement with this proposition. These results elucidate why the conserved Trp residues and cationic groups do not always play the same roles in the biological activities of the neurotoxins.

Acrylamide↗
PubMed2001

Pheromone trailing behavior of the brown tree snake, Boiga irregularis.

The ability of snakes to follow pheromone trails has significant consequences for survival and reproduction. Of particular importance is the ability of snakes to locate conspecifics during the breeding season via the detection of pheromone trails. In this study, the ability of male brown tree snakes (Boiga irregularis), a tropical, rear-fanged colubrid, to follow pheromone trails produced by reproductively active conspecifics was tested in the laboratory by using a Y maze. Males displayed a trailing response to both female and male pheromone trails over blank controls. As males of this species display ritualized combat behavior, these responses likely represent both direct and indirect mechanisms, respectively, for the location of potential mates in the wild. Males did not, however, discriminate between male and female trails when given a choice on the Y maze.

Aggression↗
PubMed2002

Variation in a female sexual attractiveness pheromone controls male mate choice in garter snakes.

Male red-sided garter snakes (Thamnophis sirtalis parietalis) display a courtship preference for larger females during the breeding season. Utilizing behavioral experiments and chemical analyses, we tested the hypothesis that males can discriminate among females of varying size solely by means of the sexual attractiveness pheromone, a previously characterized sex pheromone composed of a homologous series of long-chain saturated and omega-9 cis-unsaturated methyl ketones contained in the skin lipids of females. When presented with skin lipid extracts from large and small females, a greater proportion of males displayed courtship behaviors to large female extracts. This demonstrates that there is an intrinsic property of the female skin lipids that allows males to differentiate among large and small females. Analysis of the sexual attractiveness pheromone revealed that the necessary variation exists for this pheromone to function as a reliable indicator to males of female body size. Specifically, we observed a strong correlation between female snout-vent length and the relative concentration of saturated and omega-9 cis-unsaturated methyl ketones composing the pheromone; smaller females expressed pheromone profiles higher in saturated methyl ketones. while larger females expressed pheromone profiles dominated by unsaturated methyl ketones. The results of this study suggest that male red-sided garter snakes utilize compositional variation in the female sexual attractiveness pheromone to differentiate among potential mates of varying size.

Animals↗
PubMed1993

Synthesis and enhancing effect of dodecyl 2-(N,N-dimethylamino)propionate on the transepidermal delivery of indomethacin, clonidine, and hydrocortisone.

The biodegradable transdermal penetration enhancer, dodecyl 2-(N,N-dimethylamino)propionate (II; DDAIP), was prepared by reacting dodecyl 2-bromopropionate (I), obtained by reaction of n-dodecanol with 2-bromopropionyl halogenide, with dimethylamine. The penetration enhancing effects of DDAIP on the transport of indomethacin, clonidine, and hydrocortisone across shed snake skin (Elaphe obsoleta) were evaluated. Azone and lauryl alcohol, a possible decomposition product of DDAIP, were used as standard enhancers for comparison. In terms of flux, DDAIP showed 4.7 and 7.5 times the promoting effect for indomethacin compared to azone and lauryl alcohol, respectively. With clonidine this effect was 1.7 and 3.1 times, whereas with hydrocortisone it was 2.4 and 2.8 times higher, respectively. In vitro biodegradability of DDAIP was demonstrated in the presence of porcine esterase. The results indicate that DDAIP increases markedly the transepidermal delivery of several types of drug substances.

Administration, Cutaneous↗
PubMed2002

A complex, cross-taxon, chemical releaser of antipredator behavior in amphibians.

Prey species show diverse antipredator responses to chemical cues signaling predation threat. Among terrestrial vertebrates, the red-backed salamander, Plethodon cinereus, is an important species in the study of these chemical defenses. During the day and early evening, this species avoids rinses from garter snakes, Thamnophis sirtalis, independent of snake diet, but late at night. avoids only those rinses from garter snakes that have recently eaten P. cinereus. We tested whether the selective, late-night response requires the ingestion or injury of salamanders. In three experiments, we tested P. cinereus for their responses to separate or combined rinses from salamanders (undisturbed, distressed, and injured P. cinereus) and snakes (unfed, earthworm fed, and salamander-fed T. sirtalis). When paired against a water control, only rinses from salamander-fed snakes were avoided. When salamander treatments (undisturbed or distressed) were combined with the snake treatments (unfed or earthworm-fed) and tested against a water control, the combinations elicited avoidance. When selected treatments were paired against the standard rinse from salamander-fed snakes, only the combined rinses from salamanders and snakes nullified the avoidance response to the standard rinse. These data reveal a prey defense mechanism involving chemical elements fromboth the predatorand prey that does not require injury or ingestion of the prey in the formation of the cue.

Animals↗
PubMed2002

Predatory response of brown tree snakes to chemical stimuli from human skin.

The brown tree snake (Boiga irregularis) is an exotic pest species on Pacific islands, most notably on Guam where it has caused considerable ecological and economic damage. On Guam, the snake commonly associates with people and can be found near or in human habitations. Bites are common, approximately 1 of 1200 emergency room visits to Guam hospitals were reported to be the result of B. irregularis bites; 80% of these victims were attacked while sleeping. Most of the attacks occurred on fingers and hands and the attacks appeared to be predatory, rather than defensive, in nature. In order to characterize the mechanism releasing this unusual behavior, we measured the predatory response of B. irregularis to chemical stimuli from humans and controls using a lab population that originated from Guam and a wild population from the species' native range in Queensland, Australia. To quantify behavior we measured the proportion of snakes displaying predatory behavior to each of the stimuli, the latency to attack, and the number of tongue-flicks displayed. We quantified predatory behavior using the tongue-flick attack score for repeated measures [TFAS(R)], a common method for quantifying predatory behavior in squamate reptiles. Captive brown tree snakes responded to human skin stimuli with feeding behavior, including predatory attacks, at the same frequency as they did to prey stimuli derived from mice, while never responding to controls with such behavior. Captive snakes also responded to human skin stimuli and prey stimuli with significantly higher TFAS(R) scores than to controls, although there were no differences between the human and mouse stimuli. Wild-caught animals in Australia also responded with predatory attacks to human skin stimuli, while not showing predatory behavior to a blank control and with higher TFAS(R) scores to human skin stimuli than to the control. As B. irregularis is a generalized predator that relies heavily on chemical signals to recognize prey, we hypothesize that the snakes recognize compounds on human skin that may be shared with other prey.

Animals↗
PubMed2003

Pheromonally mediated sexual isolation among denning populations of red-sided garter snakes, Thamnophis sirtalis parietalis.

Utilizing behavioral experiments and chemical analyses, we examined whether pheromonally mediated sexual isolation exists between denning populations of red-sided garter snakes (Thamtnophis sirtalis parietalis) in Manitoba, Canada. Simultaneous choice tests conducted during the breeding season revealed that adult males from a hibernaculum in central Manitoba displayed a strong courtship preference for females from their own population over females from a hibernaculum in western Manitoba, whereas males from the western Manitoba hibernaculum showed no such preference. In addition. trailing experiments testing the response of males from the two hibernacula to familiar and unfamiliar female trails showed similar results, demonstrating that the observed male preference is mediated through chemical cues. Subsequent chemical analysis of the female sexual attractiveness pheromone. a homologous series of long-chain saturated and (omega-9 cis-unsaturated methyl ketones responsible for eliciting male courtship behavior and trailing behavior in garter snakes, showed significant variation in the composition of the pheromone between the two populations. Specifically, the two populations varied in the relative concentrations of individual unsaturated methyl ketones expressed by females. These results suggest that sexual isolation exists to a degree among denning populations of red-sided garter snakes due to variation in the expression of the female sexual attractiveness pheromone.

Animals↗
PubMed2004

A resistant predator and its toxic prey: persistence of newt toxin leads to poisonous (not venomous) snakes.

The common garter snake (Thamnophis sirtalis) preys upon the rough-skinned newt (Taricha granulosa), which contains the neurotoxin tetrodotoxin (TTX) in the skin. TTX is toxic, large quantities are present in a newt, and highly resistant snakes have the ability to ingest multiple newts; subsequently snakes harbor significant amounts of active toxin in their own tissues after consuming a newt. Snakes harbor TTX in the liver for 1 mo or more after consuming just one newt, and at least 7 wk after consuming a diet of newts. Three weeks after eating one newt, snakes contained an average of 42 microg of TTX in the liver. This amount could severely incapacitate or kill avian predators, and mammalian predators may be negatively affected as well.

Animals↗
PubMedDate not supplied

The nerve-muscle synapse of the garter snake.

Snake nerve-muscle preparations are well-suited for study of both motor innervation patterns at the systems level and NMJ function at the cellular level. Their small size ( approximately 100 myofibers) and thinness (one fiber) allows access to all NMJs in one muscle. Snake NMJs are of three types, two twitch subtypes and a single tonic type. Properties of the NMJs supplied by a particular motor neuron, and of the motor unit fibers they innervate, are precisely regulated by the motor neuron in a manner consistent with the Henneman Size Principle. Unlike its amphibian or mammalian cousins, the snake NMJ comprises approximately 50 (twitch) or approximately 20 (tonic) individual one-bouton synapses, similar to synapses found in the central nervous system. Each bouton releases a few quanta per stimulus. Larger fibers, which require more synaptic current to initiate contraction, receive nerve terminals that contain more boutons and express receptor patches with higher sensitivity to transmitter. Quantal analysis suggests that transmitter release sites in one bouton do not behave independently; rather, they may cooperate to reduce fluctuations and enhance reliability. After release, two mechanisms coexist for retrieval and reprocessing of spent vesicles-one involving clathrin-mediated endocytosis, the other macropinocytosis. Unanswered questions include how each mechanism is regulated in a use-dependent manner.

Animals↗
PubMed1997

The role of nasal chemical senses in garter snake response to airborne odor cues from prey.

Garter snakes increase tongue-flick rates in the presence of airborne odorants (amyl acetate, limonene, earthworm wash vapor, fish water vapor, earthworms, goldfish) but not water vapor. Main olfactory (MO) nerve lesions result in loss of this tongue-flick rate elevation in the presence of airborne odorants. Vomeronasal (VN) nerve lesions result in a diminution of tongue-flick rate elevation. Garter snakes discriminate between the 2 arms of a maze containing airborne earthworm odor as compared with a blank control. Following MO nerve lesions, snakes fail to make this discrimination. Following VN nerve lesions or VN duct suture, snakes are initially able to make the discrimination but may eventually cease to prefer the prey-odor side of the maze and may stop eating prey rewards. These results support the idea that airborne odorants are detected by the main MO system and that such detection does not require a functional VN system.

Animals↗
PubMed1997

Sublingual plicae (anterior processes) are not necessary for garter snake vomeronasal function.

The anterior processes of snakes may transfer odorants from the tongue to the vomeronasal (VN) organ. To test whether the anterior processes are required for a vomeronasally mediated behavior, the authors tested garter snakes (Thamnophis sirtalis) preoperatively and after cauterization of the anterior processes or control cauterization with artificial earthworms covered with earthworm wash (EWW) or distilled water. Snakes in both groups attacked EWW-covered artificial worms but not controls both pre- and postoperatively. In addition, snakes with anterior processes cauterization or control cauterization tongue flicked 3H-proline. Radioautographs of the VN organs of snakes with and without anterior processes were indistinguishable: Snakes in both groups had reduced silver grains over the VN sensory epithelium as had been reported previously with intact snakes. These findings indicate that the anterior processes are unnecessary both for a behavior known to require a functional VN system and for delivery of odorants to the VN organ.

Animals↗
PubMed2006

Immobility and supination in garter snakes (Thamnophis elegans) following handling by human predators.

A common response of animals to physical restraint is tonic immobility. The authors observed the behavior of garter snakes, Thamnophis elegans, in the field to determine the frequency of immobility as a response to handling. Most snakes fled after release, but the remainder remained immobile, sometimes on their backs (supination), for up to 10 min. Immobility was seen most often in pregnant snakes, which also were more likely than other snakes not to have moved before capture. Failure to move, either before or after capture, might be a consequence of the limited locomotory ability of gravid snakes. However, the lack of observations of interactions between snakes and their natural predators impedes researchers' understanding of the antipredator value, if any, of tonic immobility.

Animals↗