Acumulación y asignación de biomasa en renovales de tres especies de Nothofagus en los extremos de un gradiente de luz en claros de un bosque subantártico

Models of optimal partitioning and shade-tolerance propose that a proportional high aerial biomass contributes to plant persistence in light-limited environments. In this context, biomass accumulation and allocation in 4-year saplings of Nothofagus dombeyi, N. nervosa, and N. obliqua, growing at the edges of an irradiance gradient in canopy gaps of a Subantarctic forest, was compared. Within the gap, relative mean light transmittance for summer was 5% in the northern periphery and 36% in the centre. Total saplings biomass (B) increased with light availability. Nothofagus nervosa tend to exhibit the higher B under the reduced sunlight of the northern periphery, probably due to its less lightdemanding character. Although N. dombeyi in the adult stage is a fast-growing species, saplings accumulated less biomass than those of N. nervosa and N. obliqua, probably influenced by its comparatively lower seed nutrient content. Conversely, leaf biomass (H) was equivalent in all species. For each species, leaf mass fraction (H/B) was similar in both light conditions. This pattern is not consistent with the prediction based on optimal resource partitioning: plants invested less in the organ that would cause the strongest growth limitation at low irradiance. Nothofagus dombeyi allocated more assimilates to leaves compared to N. nervosa and N. obliqua, despite its extremely light-demanding character. Such a result does not comply with the hypothesis of a proportionally high leaf mass in species adapted to shade. This research may improve the understanding of an ecosystem encompassing trees with divergent light responses, and dependent on spatial and temporarily heterogeneous gaps for regeneration.Los modelos de optimización de la adquisición de recursos y de tolerancia a la sombra proponen que una biomasa aérea proporcionalmente alta contribuye a la persistencia de las plantas en hábitats limitados de luz. En este contexto, se comparó la acumulación y asignación de biomasa en renovales de cuatro años de Nothofagus dombeyi, N. nervosa y N. obliqua, desarrollados en los extremos de un gradiente de luz en claros de un bosque subantártico. La transmitancia lumínica media relativa de verano en el norte y el centro del claro se estimó en 5% y 36%, respectivamente. La biomasa total de los renovales (B) aumentó con la mayor disponibilidad de luz. Nothofagus nervosa tendió a exhibir la B mayor en la condición más sombría, probablemente debido a su carácter más umbrófilo. Aunque N. dombeyi es una especie de rápido crecimiento, los renovales acumularon menos biomasa que los de N. nervosa y de N. obliqua, probablemente debido a la menor cantidad de nutrientes de la semilla. En cambio, la biomasa de hojas (H) fue similar en las tres especies. Para cada especie, la fracción de biomasa foliar (H/B) fue equivalente en ambas condiciones de luz. Este patrón no se ajusta al modelo de asignación óptima: los renovales invirtieron menos en el órgano que limitaría el crecimiento a una baja intensidad de luz. Aunque N. dombeyi es considerablemente menos tolerante a la sombra que N. nervosa y N. obliqua, asignó la mayor cantidad de asimilados a las hojas. Este resultado contradice la hipótesis de la presencia de una biomasa foliar mayor en especies adaptadas a ambientes sombríos. Esta investigación puede mejorar la comprensión de un ecosistema conformado por renovales con respuestas a la luz divergentes, y dependientes de claros espacial y temporalmente heterogéneos

Subantarctic forest ecology : case study of a conifer-broadleaved stand in Patagonia, Argentina

In the temperate rainforests of southern South America, the tree genus Nothofagus (Nothofagaceae) is the dominant in extension and abundance on zonal soils at different latitudes and altitudes, as well as on intrazonal (e.g., wetlands) and azonal soils (e.g., morrenic and fluvioglacial deposits). Although concern on the global role of this biome is currently important, the existing level of ecological knowledge on its functioning is still inadequate to design a sound management to maintain or enhance forest values, services, and commodities. Vegetation misuse triggers severe biota and physical deterioration, particularly in the intrinsically fragile Andean Patagonic region characterised by seasonality of high rainfall levels, low temperature, strong intensity and frequency of winds, and extensive and deep mountain slopes. In Argentina, at low and mid elevations between 38° and 43°S and the annual isohyets of 1,500 to 2,000mm, the forest is composed of the xeric cypress Austrocedrus chilensis ("ciprés", Cupressaceae) and the mesic southern beech Nothofagus dombeyi ("coihue"). The effect of the strong east - west environmental gradient, caused by the Andes' rain shadow, on community composition and dynamics is striking. This is reflected in a clear vegetational zonation, whose edges are the sparse A.chilensis woodland surrounded by the Patagonian steppe towards the east and the Valdivian rainforest co-dominated by N.dombeyi towards the west. Both communities are separated only by tens of kilometres. The conifer-angiosperm association, characterised by two groups of plants with contrasting evolutionary histories and ecological adaptations, has received little scientific attention.At 41°11'S and 71°25'W, a mixed, virgin, post-fire stand, located on a dry north-facing slope was examined regarding regeneration, size, age, and spatial structures, and stand and tree growth. Inferences on community dynamics were made. The minimum area of the community was also estimated. Density, basal area, and volume of adult trees is calculated in 658 ind ha -1(66.6% of A.chilensis ), 72.1 m 2ha -1(65.6%), and 608.7m 3ha -1(51.2%), respectively. Total density of saplings and seedlings is 2,991 (27.1% of A.chilensis ) and 7,143 ind ha -1(34.3%), respectively. Stand growth is estimated in 7.3m 3ha -1yr -1(42.5% of A.chilensis ) and 3.7 t ha -1yr -1(32.4%). Between species, individual increments significantly differ within development stages. Adults A.chilensis and N.dombeyi grow in diameter at an individual rate of 0.36 and 0.57cm yr -1, respectively, while in height at a rate of 15.8 and 29.3cm yr -1, respectively. Saplings of A.chilensis and N.dombeyi grow in diameter at a rate of 0.11 and 0.21cm yr -1, respectively, while in height at a rate of 7.8 and 17.2cm yr -1, respectively. Within species, adults grow in diameter at rates between 2.7 (in N.dombeyi ) and 3.2 (in A.chilensis ) times significantly faster than their respective saplings, and also old trees show significantly larger diameter increments than young trees. Within species, adults grow in height at rates between 0 (in N.dombeyi ) - 2.0 (in A.chilensis ) times faster than their respective saplings. In A.chilensis , old trees grow in height at significantly higher rates than young trees, whereas this is not the case for N.dombeyi . For each A.chilensis tree, a negative relationship is found between individual diameter (range= 0.22 to 0.42cm yr -1) and height growth (12 to 21cm yr -1), and the number of neighbour trees (0 to > = 7) taller than itself within a 5m distance. Contrarily, for N.dombeyi no relationship is observed between these variables. In A.chilensis , individual growth rates do not differ significantly between sex classes: for males, mean and current diameter, and height growth rate is 0.360, 0.132, and 17.6cm yr -1, respectively, while for females is 0.348, 0.124, and 17.2cm yr -1, respectively.The inherently inferior growth capacity of A.chilensis over N.dombeyi is explained by its lower leaf photosynthetic rate. Conifers from the northern hemisphere show a primary productivity similar to their mostly associated deciduous angiosperms. However, southern hemisphere conifers show a lower productivity than broadleaved. This is probably because they cannot benefit differentially from an extended period of net photosynthesis as they co-exist mainly with broadleaved evergreen species. The greater growth disadvantage of A.chilensis in comparison to N.dombeyi during the juvenile stage is consistent with the same trend observed in gymnosperms as a group: seedling represents the ontogenetic phase of slowest growing, caused by multiple factors related to leaf productivity and carbohydrate allocation. This constraint has been used to explain the decline and retreat of gymnosperms along evolutionary scales. Within species, the dependence of growth to age and crowding is indicative of one-sided, asymmetric competition for light: trees that arrived earlier to the site have pre-empt resources, developed a larger size, and therefore at present they interfere asymmetrically with those arriving later. However, contrasting responses are found according to species and growth variables: i) In N.dombeyi , the independence of individual growth to crowding, and of height growth to age/development stage of trees suggests that this species is rather insensitive to this competition type. On the contrary, A.chilensis is highly susceptible judging from the dependence between growth to age and taller neighbours. ii) In comparison to diameter growth, height growth differs slightly between age classes/stages, which reflect the common priority that trees give to height during development. Lack of gender-related growth differences in the dioecious A.chilensis would be masked by the low reproductive development exhibited in the sampled individuals. If trees in structurally well-developed stand are unable to express the reproductive potential as observed in isolated trees, then its incidence on the individual energetic budget would be marginal and marked intersexual growth contrasts would not be expected. This hypothesis would explain the incongruence with previously results suggesting a trade-off between vegetative and reproductive investments, and needs to be tested during future studies given the ecological and silvicultural relevance of this issue.In 1860, both tree species began to colonize a heterogeneous site, following a fire that eliminated the original vegetation. This first regenerative pulse lasted 60 to 70 years after which recruitment ceased probably in response to canopy closure, resulting in the present even-aged clustered adult tree populations. Because of its lower density and higher growth rates, N.dombeyi constitutes widely spaced, big emergent trees of the stand. The build-up of the A.chilensis -dominated mixed stand probably improved autogenously local moisture conditions, encouraging establishment of N.dombeyi seedlings and defining a second continuous regenerative pulse starting ca.1930. In the understorey, the sapling population dominated by N.dombeyi represents a third regenerative pulse with ages between 1 to 10 years. The current-day stand structure is represented by a young population dominated primarily by N.dombeyi , and a mature overstorey dominated primarily by A.chilensis . In absence of large-scale impacts, changes in forest structure over time would be accounted for interspecific differences in recruitment, growth rate, and sensitivity to competition, probably resulting in a local decline of the conifer component. However, the combination of a great longevity and a light-demanding temperament of A.chilensis implies that frequent to very infrequent large-scale impacts would be sufficient to maintain its abundance in the landscape. These results, together with others described in literature, suggest that divergent development patterns occur in the A.chilensis - N.dombeyi stands, probably because these forests grow under a spatially varied environment and their responses differ consequently.Based on the concept of "quantitative minimum area", the statistically optimum plot size for the ecological study of a temperate forest was examined. Changes in the estimated tree density (N), basal area (G), stemwood volume (V), and volume growth rate (I v ) per area unit, in relation to the increase of sample plot size (X), were analysed. Means of N, G, V, and I v fluctuated considerably within a range of small plot sizes, showing stability at X >= 1,000m 2. The accuracy of the parameters estimates measured as relative error (RE) increases as long as the plot size is enlarged. For X= 1,000m 2, ER varies between ± 30% and ± 49%, and for X= 2,500m 2, RE varies between ± 20% and ± 32%. Around X= 5,000m 2should be sampled to obtain RE f (X) (P<0.05). This estimated plot size is larger than those often recommended in literature for ecological studies of temperate forests.</p

EXPOSICIÓN A PLAGUICIDAS Y CUIDADOS EN EL CINTURÓN VERDE DE LA CIUDAD DE CÓRDOBA (ARGENTINA): PRÁCTICAS Y ACTIVIDADES RELACIONALES DESPLEGADAS POR MUJERES DE FAMILIAS HORTICULTORAS

In the green belt of the city of Córdoba (Argentina), the orchard-home of horticulturalist families are configured&nbsp; as a scenario of continuous exposure to the pesticides used, which predisposes them to chronic and acute intoxications. Caring allows sustaining, recovering and reproducing people\u27s lives; it is assigned to women and,&nbsp; together withthem, it results in minoritized bodies and activities. This paper seeks to identify the relational practices and activities of care deployed by women living in these scenarios, focusing on those that contribute&nbsp; to the reduction of the previously documented exposure. A feminist qualitative approach, observational participation and ethnographic interviews with adult women and men are carried out. Several situations that constitute the life of horticultural families are described, which reaffirm the previously documented scenario of&nbsp; exposure to pesticides. In it, women deploy a variety of activities and relational practices that contribute to the health care of themselves and members of the nuclear and extended family. We argue that tracing, making&nbsp; visible, contacting and expanding the experiences of care contributes to destabilize, at least a little, the residual&nbsp; value that capitalist patriarchy imposes on feminized bodies, processes and spaces.En el cinturón verde de la ciudad de Córdoba (Argentina), los hogares quintas de las familias horticultoras se&nbsp; configuran como un escenario de exposición continua a los plaguicidas utilizados, lo que las predispone a&nbsp; intoxicaciones crónicas y agudas. El cuidado permite sostener, recuperar y reproducir la vida de las personas;&nbsp; se le asigna a las mujeres, y junto a ellas, resultan cuerpos y haceres minorizados. Este escrito busca identificar&nbsp; las prácticas y actividades relacionales de cuidado desplegadas por las mujeres que viven en estos escenarios,&nbsp; haciendo foco en aquellas que aportan a la disminución de la exposición previamente documentada. Se realiza&nbsp; un abordaje cualitativo feminista, participación observante y entrevistas etnográficas a mujeres y varones&nbsp; adultos. Se describen diversas situaciones constitutivas de la vida de las familias horticultoras que reafirman el&nbsp; escenario de exposición a plaguicidas previamente documentado. En él, las mujeres despliegan una variedad&nbsp; de actividades y prácticas relacionales que aportan al cuidado de la salud de ellas e integrantes de la familia&nbsp; nuclear y extensiva. Sostenemos que rastrear, visibilizar, contactar y expandir las experiencias de cuidado&nbsp; aporta a desestabilizar, al menos un poco, el valor residual que el patriarcado capitalista le impone a los cuerpos,&nbsp; procesos y espacios feminizados

Colonización y crecimiento de renovales de Nothofagus después de cortas selectivas de un rodal en la Patagonia, Argentina

In 1994, a group selection silvicultural system on a natural forest dominated by Nothofagus dombeyi, N. obliqua, and N. nervosa (Nothofagaceae) was implemented. Age and growth of seedlings (stem height LT &lt; 30 cm, n = 720 plants) and saplings (LT ≥ 30 cm, n = 480) randomly collected in the center and northern periphery of gaps were analysed eight years after treatment. The three species became established simultaneously within the gaps. However, the lower light demanding N. nervosa exhibited a mean age slightly larger given the presence of «advanced regeneration» established previously to cutting implementation. Although immature phases located in the centre of gaps showed an equivalent age than those in the northern periphery, they exhibited a growth rate between 7 and 29% faster probably caused by a greater amount of photosynthetically active radiation. N. dombeyi grew at rates between 13 and 30% slower than the other two species, probably due to the smaller nutrient content of its seeds which would consequently produced less competitive seedlings. Saplings belonged to the same age cohort than seedlings though they grew at rates between 2.6 and 4.8 times faster. The early development of size hierarchy within juvenile trees would be related with the particular morphology and physiology of seeds and plants, and microsite condition.En 1994 se implement&oacute; el sistema de cortas de selecci&oacute;n en bosquetes en un bosque natural compuesto por Nothofagus dombeyi, N. obliqua y N. nervosa (Nothofagaceae). Ocho a&ntilde;os despu&eacute;s se analizaron la edad y el crecimiento de los plantines (altura del tallo LT &lt; 30 cm, n = 720 plantas) y juveniles (LT &ge; 30 cm, n = 480) localizados en el centro y la periferia septentrional de los claros artificiales resultantes. Nothofagus dombeyi, N. obliqua y N. nervosa se establecieron en forma simult&aacute;nea en los claros, aunque la especie m&aacute;s tolerante a la sombra N. nervosa exhibi&oacute; una edad sensiblemente mayor debido a la presencia de &laquo;regeneraci&oacute;n avanzada&raquo; establecida antes de la realizaci&oacute;n de las cortas. Aunque los renovales localizados en el centro de los claros presentaron una edad equivalente a los de la periferia septentrional, exhibieron crecimientos entre un 7 y 29% significativamente m&aacute;s r&aacute;pidos probablemente debido a la mayor cantidad de radiaci&oacute;n fotosint&eacute;ticamente activa que recibieron. Los renovales de N. dombeyi crecieron entre un 13 y 30% significativamente menos que los de las otras dos especies, un fen&oacute;meno que se asociar&iacute;a a la menor reserva de nutrientes de la semilla lo que consecuentemente producir&iacute;a plantines menos competitivos. En las especies examinadas, los juveniles constituyeron la misma cohorte que los plantines aunque crecieron entre 2,6 y 4,8 veces m&aacute;s r&aacute;pidamente. El desarrollo temprano de la jerarqu&iacute;a de tama&ntilde;os se asociar&iacute;a con la morfolog&iacute;a y fisiolog&iacute;a particulares de la semilla y de las plantas, y la calidad del micrositio

Experiencia participativa orientada a la prevención de la exposición a plaguicidas en la producción hortícola del Cinturón Verde de la ciudad de Córdoba

O objetivo desta comunicação é refletir sobre uma experiência que visa promover ações de prevenção de riscos associados à exposição a agrotóxicos no contexto do cotidiano e do trabalho de famílias e produtores hortícolas do Cinturão Verde da Cidade de Córdoba, bem como promover diálogos e ações de promoção de hábitos saudáveis e atenção à saúde nos espaços onde implantam suas atividades produtivas e reprodutivas. Expõe o processo de troca e construção de conhecimento realizado entre horticultores e seus familiares, professores, pesquisadores e estudantes da Universidade Nacional de Córdoba, e outros atores sociais ligados ao problema, durante o período 2013-2017. Esta pesquisa participativa - experiência de ação foi realizada a partir da proposta de saúde coletiva. O processo de construção nos permitiu redimensionar a complexidade do contexto de exposição a partir das experiências compartilhadas e construir novas estratégias para evitar riscos à saúde.El objetivo de esta comunicación es reflexionar acerca de una experiencia orientada a promover acciones de prevención de riesgos asociados a exposición a plaguicidas, en el contexto de vida cotidiana y trabajo, de horticultores/as y sus familias del Cinturón Verde de la Ciudad de Córdoba, como también a favorecer diálogos y acciones de promoción de hábitos saludables y de cuidado de la salud en los espacios donde despliegan sus actividades productivas y reproductivas. Se expone el proceso de intercambio y construcción de saberes realizado entre horticultores/as y sus familias, referentes del sector, docentes, investigadores y estudiantes de la Universidad Nacional de Córdoba, y otros actores sociales vinculados a la problemática, durante 2013–2017. Esta experiencia de Investigación–Acción Participativa (IAP) se llevó a cabo desde la propuesta de la salud colectiva. El proceso de construcción permitió redimensionar la complejidad del contexto de exposición desde las experiencias compartidas y construir nuevas estrategias para prevenir riesgos a la salud.The objective of this communication is to reflect on an experience aimed at promoting risk prevention actions associated with exposure to pesticides in the context of daily life and work of horticulturists and their families in the Green Belt of the City of Córdoba, as well as also to favor dialogues and actions to promote healthy habits and health care in the spaces where they deploy their productive and reproductive activities. It exposes the process of exchange and construction of knowledge, carried out among horticulturists and their families, referring to the sector, teachers, researchers and students of the National University of Córdoba, and other social actors linked to the problem, during 2013–2017. This participatory research – action (IAP) experience was carried out from the collective health proposal. The construction process allowed to resize the complexity of the exposure context from the shared experiences and to build new strategies to prevent health risks

Colonización y crecimiento de renovales de Nothofagus después de cortas selectivas de un rodal en la Patagonia, Argentina

En 1994 se implementó el sistema de cortas de selección en bosquetes en un bosque natural compuesto por Nothofagus dombeyi, N. obliqua y N. nervosa (Nothofagaceae). Ocho años después se analizaron la edad y el crecimiento de los plantines (altura del tallo LT < 30 cm, n = 720 plantas) y juveniles (LT e 30 cm, n = 480) localizados en el centro y la periferia septentrional de los claros artificiales resultantes. Nothofagus dombeyi, N. obliqua y N. nervosa se establecieron en forma simultánea en los claros, aunque la especie más tolerante a la sombra N. nervosa exhibió una edad sensiblemente mayor debido a la presencia de "regeneración avanzada" establecida antes de la realización de las cortas. Aunque los renovales localizados en el centro de los claros presentaron una edad equivalente a los de la periferia septentrional, exhibieron crecimientos entre un 7 y 29% significativamente más rápidos probablemente debido a la mayor cantidad de radiación fotosintéticamente activa que recibieron. Los renovales de N. dombeyi crecieron entre un 13 y 30% significativamente menos que los de las otras dos especies, un fenómeno que se asociaría a la menor reserva de nutrientes de la semilla lo que consecuentemente produciría plantines menos competitivos. En las especies examinadas, los juveniles constituyeron la misma cohorte que los plantines aunque crecieron entre 2,6 y 4,8 veces más rápidamente. El desarrollo temprano de la jerarquía de tamaños se asociaría con la morfología y fisiología particulares de la semilla y de las plantas, y la calidad del micrositio

Desarrollo y costo de producción de Pinus ponderosa en etapas de vivero y secano en la Patagonia: efecto de la semilla, el sustrato y el contenedor

La producción de plantas en contenedor y con sustrato fertilizado, se lleva a cabo a mayor velocidad y calidad que a raíz desnuda, pero el costo económico y ambiental es mayor. El objetivo de este trabajo fue evaluar sustratos fertilizados, de menor valor económico, y contenedores de diferentes tamaños para la producción de plantas de pino ponderosa destinadas a la forestación en la Patagonia semiárida de la Argentina. El ensayo de desarrollo inicial se llevó a cabo en invernadero y el de establecimiento en un sitio ubicado a los 42° 21' LS y 71° 5' LO (Chubut, Argentina). Mediante un diseño factorial se evaluó durante 2 años el diámetro, la altura, el peso, la supervivencia, la calidad y el costo de producción de las plantas, teniendo en cuenta i) semillas provenientes de conos amarillo y violeta, ii) sustratos a) turba perlita + CaO (5 kg/m3 de sustrato) + fertilizante (5 kg/m3 de sustrato), b) aserrín de pino + CaO (5 kg/m3 ) + fertilizante (10 kg/m3 ) y c) suelo forestal (horizonte O de suelo de plantación) + fertilizante (10 kg/m3 ), y iii) contenedores de 120, 160 y 250 cm3 . Las semillas originadas de diferentes conos no afectaron el tamaño, el peso ni los índices de calidad de las plantas. El desempeño de las plantas exhibió una interacción significativa entre el tamaño del contenedor y el tipo de sustrato. El contenedor mediano con suelo forestal fue la opción más adecuada entre las ensayadas, para desarrollar pino ponderosa desde perspectivas productiva, ecológica y económica.The seedlings production based on the use of container and fertilized substrate is carried out at higher speed and quality compared to bare root methods, but economic and environmental costs can be higher. Substrates composed of materials discarded from the forest activity, fertilizer and different container sizes were evaluated as alternatives for the production of Pinus ponderosa (Pinaceae) seedlings for dry land afforestation of the Patagonian steppe in Argentina. The initial development and the establishment trials were carried out, respectively, in a greenhouse and in a farm located at 42° 21' SL and 71° 5' WL (Chubut, Argentina). Through an experimental factorial design, the performance and cost of production of plants were evaluated over two years, taking into account i) seeds from yellow and violet cones, ii) the substrates a) peat perlite + CaO (with 5 kg/m3 of substrate) + controlled release granular fertilizer (5 kg/m3 of substrate), b) pine sawdust + CaO (5 kg/m3 ) + fertilizer (10 kg/m3 ), and c) forest soil (O-horizon of plantation) + and fertilizer (10 kg/m3 ), and iii) containers of 120, 160 and 250 cm3 . Seeds originated from different cones did not affect the size, weight or quality indices of ponderosa pine seedlings. The plants performance exhibited a significant interaction between container size and substrate type. The medium-size container with fertilized plantation soil, represented the better tested option to grow Ponderosa Pine from the productive, ecological and economic points o view.Fil: Sbrancia, Renato Ernesto. Universidad Nacional del Comahue. Asentamiento Universidad San Martín de Los Andes; ArgentinaFil: Alejandro, Dezzotti. Universidad Nacional del Comahue. Asentamiento Universidad San Martín de Los Andes; ArgentinaFil: Mortoro, Ariel Mario. Universidad Nacional del Comahue. Asentamiento Universidad San Martín de Los Andes; ArgentinaFil: Attis Beltran, Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Universidad Nacional del Comahue. Asentamiento Universidad San Martín de Los Andes; ArgentinaFil: Velasquez, A.. Universidad Nacional del Comahue. Asentamiento Universidad San Martín de Los Andes; Argentin

The facilitatory effect of casearia sylvestris Sw. (guacatonga) fractions on the contractile activity of mammalian and avian neuromuscular apparatus

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORCNPQ – CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOMany natural products influence neurotransmission and are used clinically. In particular, facilitatory agents can enhance neurotransmission and are potentially useful for treating neuromuscular diseases in which muscular weakness is the major symptom. In this work, we investigated the facilitatory effect of apolar to polar fractions of Casearia sylvestris Sw. (guacatonga) on contractility in mouse phrenic nerve-diaphragm (PND) and chick biventer cervicis (BC) neuromuscular preparations exposed to indirect (via the nerve; 3 V stimuli) and direct (30 V stimuli) muscle stimulation in the absence and presence of pharmacological antagonists. Methanolic and ethyl acetate fractions, but not hexane or dichloromethane fractions, exerted a facilitatory effect on PND (indirect stimulation). The methanolic fraction was chosen for further assays to assess the involvement of: 1) presynaptic sites (axons or nerve terminals), 2) postsynaptic sites (cholinergic receptors, sarcolemma or T-tubules), and 3) the synaptic cleft (acetylcholinesterase enzyme). In preparations treated with d-tubocurarine, the methanolic fraction did not cause facilitation in response to direct stimuli; this fraction was also unable to reverse dantrolene-induced blockade (indirect stimulation). In curarized preparations, the methanolic fraction either restored neuromuscular transmission (mimicking the effect of neostigmine) or failed to cause any recovery of neurotransmission. In the presence of 3,4-diaminopyridine (3,4-DAP), the methanolic fraction decreased twitch amplitude, whereas at a high frequency of stimulation (40 Hz) there was an increase in tetanic tension. In BC preparations, the methanolic fraction did not affect contractures to exogenous acetylcholine or potassium chloride. Incubation with atropine showed there was certain modulation by prejunctional nicotinic receptors, whereas treatment with nifedipine showed that the neurofacilitation required the entry of extracellular calcium. Tetrodotoxin did not prevent the facilitatory effect of 3,4-DAP or neostigmine, but antagonized the response to the methanolic fraction. These findings indicate that neuronal sodium channels have an important role in the facilitatory response to the methanolic fraction, with extracellular calcium entry via calcium channels modulating this neurofacilitation. Possible modulation of prejunctional cholinoceptors was not excluded, particularly in view of certain antagonism by the methanolic fraction at muscarinic receptors. Since facilitation by the methanolic fraction involved enhanced acetylcholine release, use of this fraction could be potentially beneficial in neuromuscular diseases and in the reversal of residual paralysis in the post-operative period or after local anaesthesia.Many natural products influence neurotransmission and are used clinically. In particular, facilitatory agents can enhance neurotransmission and are potentially useful for treating neuromuscular diseases in which muscular weakness is the major symptom. In this work, we investigated the facilitatory effect of apolar to polar fractions of Casearia sylvestris Sw. (guacatonga) on contractility in mouse phrenic nerve-diaphragm (PND) and chick biventer cervicis (BC) neuromuscular preparations exposed to indirect (via the nerve; 3 V stimuli) and direct (30 V stimuli) muscle stimulation in the absence and presence of pharmacological antagonists. Methanolic and ethyl acetate fractions, but not hexane or dichloromethane fractions, exerted a facilitatory effect on PND (indirect stimulation). The methanolic fraction was chosen for further assays to assess the involvement of: 1) presynaptic sites (axons or nerve terminals), 2) postsynaptic sites (cholinergic receptors, sarcolemma or T-tubules), and 3) the synaptic cleft (acetylcholinesterase enzyme). In preparations treated with d-tubocurarine, the methanolic fraction did not cause facilitation in response to direct stimuli; this fraction was also unable to reverse dantrolene-induced blockade (indirect stimulation). In curarized preparations, the methanolic fraction either restored neuromuscular transmission (mimicking the effect of neostigmine) or failed to cause any recovery of neurotransmission. In the presence of 3,4-diaminopyridine (3,4-DAP), the methanolic fraction decreased twitch amplitude, whereas at a high frequency of stimulation (40 Hz) there was an increase in tetanic tension. In BC preparations, the methanolic fraction did not affect contractures to exogenous acetylcholine or potassium chloride. Incubation with atropine showed there was certain modulation by prejunctional nicotinic receptors, whereas treatment with nifedipine showed that the neurofacilitation required the entry of extracellular calcium. Tetrodotoxin did not prevent the facilitatory effect of 3,4-DAP or neostigmine, but antagonized the response to the methanolic fraction. These findings indicate that neuronal sodium channels have an important role in the facilitatory response to the methanolic fraction, with extracellular calcium entry via calcium channels modulating this neurofacilitation. Possible modulation of prejunctional cholinoceptors was not excluded, particularly in view of certain antagonism by the methanolic fraction at muscarinic receptors. Since facilitation by the methanolic fraction involved enhanced acetylcholine release, use of this fraction could be potentially beneficial in neuromuscular diseases and in the reversal of residual paralysis in the post-operative period or after local anaesthesia165468481FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORCNPQ – CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORCNPQ – CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP [04/09705-8, 07/53883-6, 08/50669-6, 08/52643-4, 08/11005-5, 12/08271-0, 12/20591-0]04/09705-8, 07/53883-6; 08/50669-6; 08/52643-4; 08/11005-5; 12/08271-0; 12/20591-0sem informaçãosem informaçã