Neuropharmacological effects of essential oil from the leaves of Croton conduplicatus Kunth and possible mechanisms of action involved.

ETHNOPHARMACOLOGICAL RELEVANCE: Croton conduplicatus Kunth (Euphorbiaceae) is a Brazilian aromatic medicinal plant, widely known as "quebra-faca". In folk medicine, its leaves and stem-barks are used as a natural analgesic for the treatment of headaches. AIM OF THE STUDY: In this study, we describe for the first time the neuropharmacological potential of the essential oil obtained from the leaves of Croton conduplicatus (EO) in experimental models of pain, anxiety and insomnia. The mechanisms of action involved in these activities were also investigated. MATERIAL AND METHODS: Different experimental models were used to evaluate the antinociceptive (acetic acid, formalin-induced nociception and hot plate tests), anxiolytic (elevated plus maze and hole board tests) and sedative (thiopental-induced sleeping time) effects of EO in mice. EO was evaluated in three different doses (25, 50 and 100 mg/kg, i.p.) and compared with positive and negative controls in all experimental protocols. When appropriate, animals were pretreated with pharmacological antagonists (naloxone, atropine and flumazenil) in order to evaluate the mechanisms of action involved. A docking study also was performed to identify possible targets involved. RESULTS: EO (25, 50 and 100 mg/kg, i.p.) demonstrated a significant antinociceptive activity in all experimental models. Pretreatment with naloxone or atropine reversed the antinociceptive response (p < 0.05), suggesting the involvement of opioid and muscarinic receptors, respectively. A docking study was performed with the major components identified in EO (1,8 cineole - 21.42%, spathulenol - 15.47%, p-cymene - 12.41% and caryophyllene oxide - 12.15%), demonstrating favorable interaction profile with different subtypes of muscarinic (M2, M3 and M4) and opioids (delta and mu) receptors. EO also showed anxiolytic (mainly at doses of 25 and 50 mg/kg, i.p.) and sedative (only at the dose of 100 mg/kg, i.p.) effects in mice. These pharmacological responses were reversed by flumazenil (p < 0.05), indicating possible involvement of GABAA receptors. CONCLUSION: Our findings support the traditional use of this plant as a natural analgesic and suggest that EO is a multi-target natural product, presenting not only antinociceptive effect but also anxiolytic and sedative activities depending on the dose used.

Parasitoids Turn Herbivores into Mutualists in a Nursery System Involving Active Pollination.

Nursery pollination involves pollinators that lay eggs on the flowers they pollinate and have their brood fed on flower parts or developing ovules [1-4]. Active pollination, a ritualistic behavioral sequence shown by nursery pollinators when transferring pollen from anthers to stigmas, is known in only four plant lineages [5-8], including the classical examples of fig trees-fig wasps and yuccas-yucca moths [5, 6]. We report in detail a system in which weevils actively pollinate orchids prior to having their larvae fed on the developing fruits. Sampling over five years revealed that although weevils trigger fruit set, this interaction is negative for the plant as weevil larvae often consume all contents of infested fruits. However, part of weevil-infested fruits is often "rescued" by parasitoid wasps, which kill the weevil larvae before all fruit content is consumed (Figure 1). "Rescued" fruits present high seed viability and biomass similar to that of non-infested fruits, much higher than that of fruits with weevils only. Hence, parasitoids mediate the fitness consequences of the interaction between the plant and its parasitic pollinator. Weevils constitute a megadiverse group of herbivores commonly reported as florivores [9] but are also appreciated as flower-ovipositing pollinators of cycads and palms [4, 10-13] and were previously recorded carrying orchid pollinaria [14-16]. The orchid-weevil system presented here shows that plant-floral visitor interaction outcome can be mediated by a third party (parasitoids) and illustrates a way by which the biological context may allow the emergence and persistence of active nursery pollination behavior in nature.