Inhibition of the mammalian target of rapamycin complex 1 signaling pathway reduces itch behaviour in mice.

Activated mammalian target of rapamycin (P-mTOR) has been shown to maintain the sensitivity of subsets of small-diameter primary afferent A-nociceptors. Local or systemic inhibition of the mTOR complex 1 (mTORC1) pathway reduced punctate mechanical and cold sensitivity in neuropathic pain and therefore offered a new approach to chronic pain control. In this study, we have investigated the effects of the rapamycin analog temsirolimus (CCI-779) on itch. Bouts of scratching induced by the histamine-dependent pruritogenic compound 48/80 and histamine-independent pruritogens, chloroquine and SLIGRL-NH2, injected intradermally were significantly reduced by local (intradermal) or systemic (intraperitoneal, i.p.) pretreatment with CCI-779. We also investigated the action of metformin, a drug taken to control type 2 diabetes and recently shown to inhibit mTORC1 in vivo. Although the response to nonhistaminergic stimuli was reduced at all of the time points tested, scratching to compound 48/80 was modified by metformin only when the drug was injected 24 hours before this pruritogen. We also examined the colocalization of P-mTOR with gastrin-releasing peptide, a putative marker for some itch-sensitive primary afferents, and found that P-mTOR was coexpressed in less than 5% of gastrin-releasing peptide-positive fibers in the mouse skin. Taken together, the data highlight the role that P-mTOR-positive A-fibers play in itch signaling and underline the importance of the mTORC1 pathway in the regulation of homeostatic primary afferent functions such as pain and itch. The actions of the antidiabetic drug metformin in ameliorating nonhistamine-mediated itch also suggest a new therapeutic route for the control of this category of pruritus.

Is the red spotted green frog Hypsiboas punctatus (Anura: Hylidae) selecting its preys? The importance of prey availability.

The study of the feeding ecology of amphibians is an old issue in herpetology. Notwithstanding, the lack of food resources data in many studies of amphibians feeding has lead to partial understanding of frog feeding strategies. In this study we evaluate the trophic selectivity of a red spotted green frog (Hypsiboas punctatus) population from a Middle Paraná River floodplain pond in Argentina, and discuss the importance of prey availability data when interpreting results from diet analysis. We analyzed the gut contents of 47 H. punctatus adults and compared frog's diet with the environmental food resources. Prey availability was estimated by systematically seep-netting the microhabitat where anurans were localized foraging. We identified 33 taxonomic categories from gastrointestinal contents. Numerically, the most important prey categories were dipterans, followed by hemipterans, homopterans and coleopterans. The diet similarity between males and females was high and no statistical differences in diet composition were found. The most abundant food resources in the environment were dipterans, coleopterans, homopterans and collembolans. In order to assess whether frogs were selecting their preys, we calculated Pianka's niche overlap index and Jacobs' electivity index comparing gut contents to prey availability data. Trophic niche overlap was medium but significantly higher than expected by chance. The electivity index indicated that H. punctatus foraged dipterans slightly above their environmental abundance. Among the secondary preys, hemipterans were foraged selectively, homopterans were consumed in the same proportion to their occurrence in the environment, coleopterans were foraged quite under their availability and collembolans were practically ignored by frogs. Without food resources data, H. punctatus could be classified as a specialist feeder, but dipterans also were quite abundant in the environment. Our results show that H. punctatus fit better as a generalist feeder, foraging on their main food item and some secondary preys in similar proportion to their environmental availability; even though other secondary preys are being selectively preferred or ignored by frogs. Our data illustrate the importance of including the resource availability data on diet studies to improve the understanding of amphibian feeding ecology.

Is the red spotted green frog Hypsiboas punctatus (Anura: Hylidae) selecting its preys?: The importance of prey availability

The study of the feeding ecology of amphibians is an old issue in herpetology. Notwithstanding, the lack of food resources data in many studies of amphibians feeding has lead to partial understanding of frog feeding strategies. In this study we evaluate the trophic selectivity of a red spotted green frog (Hypsiboas punctatus) population from a Middle Paraná River floodplain pond in Argentina, and discuss the importance of prey availability data when interpreting results from diet analysis. We analyzed the gut contents of 47 H. punctatus adults and compared frog’s diet with the environmental food resources. Prey availability was estimated by systematically seep-netting the microhabitat where anurans were localized foraging. We identified 33 taxonomic categories from gastrointestinal contents. Numerically, the most important prey categories were dipterans, followed by hemipterans, homopterans and coleopterans. The diet similarity between males and females was high and no statistical differences in diet composition were found. The most abundant food resources in the environment were dipterans, coleopterans, homopterans and collembolans. In order to assess whether frogs were selecting their preys, we calculated Pianka’s niche overlap index and Jacobs’ electivity index comparing gut contents to prey availability data. Trophic niche overlap was medium but significantly higher than expected by chance. The electivity index indicated that H. punctatus foraged dipterans slightly above their environmental abundance. Among the secondary preys, hemipterans were foraged selectively, homopterans were consumed in the same proportion to their occurrence in the environment, coleopterans were foraged quite under their availability and collembolans were practically ignored by frogs. Without food resources data, H. punctatus could be classified as a specialist feeder, but dipterans also were quite abundant in the environment. Our results show that H. punctatus fit better as a generalist feeder, foraging on their main food item and some secondary preys in similar proportion to their environmental availability; even though other secondary preys are being selectively preferred or ignored by frogs. Our data illustrate the importance of including the resource availability data on diet studies to improve the understanding of amphibian feeding ecology. Rev. Biol. Trop. 57 (3): 847-857. Epub 2009 September 30.

La falta de datos sobre la disponibilidad de recursos alimenticios en muchos trabajos sobre ecología trófica de anfibios ha llevado a una comprensión parcial de las estrategias alimentarias de este grupo. Este estudio evalúa la selectividad trófica de una población de Hypsiboas punctatus en una laguna del valle aluvial del río Paraná Medio en Argentina, y discute la importancia de los datos de disponibilidad de presas para interpretar las estrategias de alimentación de las ranas. Se analizaron los contenidos gastrointestinales de 47 adultos, y se compararon con la disponibilidad ambiental de presas, estimada mediante muestreo sistemático del micro-hábitat de forrajeo de los anuros. Se identificaron 33 categorías de presas. Las más importantes fueron dípteros, hemípteros, homópteros y coleópteros. Se encontró una elevada similitud entre la dieta de machos y hembras, y no se hallaron diferencias significativas en su composición. Los recursos alimenticios más abundantes fueron los dípteros, coleópteros, homópteros y colémbolos. La superposición de nicho trófico fue media (índice de Pianka) pero significativamente más elevada que la esperada por azar. H. punctatus consumió dípteros en una proporción levemente superior a su disponibilidad ambiental (índice de selectividad de Jacobs). La estrategia de depredación de H. punctatus se ajusta mejor a una táctica generalista, ya que su principal ítem presa y algunos ítems secundarios fueron capturados en proporciones similares a su disponibilidad ambiental, y solo una porción reducida de su espectro de recursos tróficos fue consumida selectivamente. Estos resultados evidencian la importancia de incluir los datos de disponibilidad de recursos en los estudios de alimentación para lograr un mejor entendimiento de la ecología trófica de los anfibios.