I have investigated whether or not neurotrophic factors can alter the effects of an applied electric field on neurite growth. A direct current electric field (150mV/mm) applied for 5 hours affected the growth of dissociated cells from the neutral tube of stage 20 <I>Xenopus laevis. </I>Neurites turned and grew to the cathode, showed a differential rate of growth, with cathodal-facing neurites growing faster than those facing the anode, and exhibited a polarised branching pattern, with the majority of branches emanating from the cathodal-facing side of the neurite. Exposure of neurites to the neurotrophins neurotrophin 3 (NT-3; 50ng/ml and 100ng/ml), brain derived neurotrophic factor (BDNF; 50ng/ml and 100ng/ml) and neurotrophin 4 (NT-4; 100ng/ml) lowered the threshold field strength necessary to elicit a turning response to 100mV/mm. Only BDNF (100ng/ml) enhanced cathodal orientation at 150mV/mm, with neurites turning three times as far as in the field alone. Additionally, in the presence of these neurotrophins the threshold field that evoked a differential rate of growth and polarised branching was also lowered to 100mV/mm. Neurite turning did not occur in a field of 100mV/mm in the presence of 50ng/ml nerve growth factor (NGF), 100ng/ml ciliary neurotrophic factor (CNTF) or 50ng/ml glial-cell-line derived neurotrophic factor (GDNF), or when the Trk receptor tyrosine kinase inhibitors K-252a and K-252b were added concomitantly with 50ng/ml NT-3. <I>Xenopus </I>growth cones release acetylcholine (Ach) spontaneously. This is enhanced by NT-3, BDNF, NT-4. Nicotinic Ach receptor antagonists abolish field-induced cathodal turning, thus Ach release may be crucial for this response. The neurotrophins NT-3, BDNF and NT-4 may therefore modulate field-directed nerve growth because they enhance Ach release. Interactions <I>in vivo,</I> where neurotrophins and electric fields co-exist, would increase the efficacy of endogenous electric fields as modulators of nerve growth.

Made available in DSpace on 2016-12-12T20:12:28Z (GMT). No. of bitstreams: 1 PGEF14MA010.pdf: 1187055 bytes, checksum: 923d07326d5d4ff686f3c1afdb5e638e (MD5) Previous issue date: 2014-02-28 / In Brazil the damage caused by rodents in forest plantations are proven but little studied. Many forestry companies in the southern region of the country warn about the expansion and intensification of rodent attacks. The attacks occur in Pinus spp. trees from 3-4 years old in places that the weeds form a microhabitat and the native locations near areas where the intensity of the attack is bigger. The native areas of the farms studied undergo a process of environmental adaptation. These areas are characterized by the presence of regeneration in early stage, with pioneer species, such as Bracatinga (Mimosa scabrella) and several species of grasses. The low environmental quality of wild areas configures a local imbalance in the supply of resources. The presence of microhabitats in the planted forest increases the foraging areas of local fauna species offered by the shelter. The sum of the low quality of wild areas with increased foraging areas caused by the presence of microhabitat in planted forest, forced the fauna species to use alternative food sources . Pinus taeda trees have energy resource available in its sap. It consists at 8.2 ° Brix total soluble solids in solution (sugars). Much more that M. scabrella sap. The large amount of sugar in the sap, suggest the use of P. taeda as a food source for rodents.There are evidences that more than one species of rodent cause damage, because different types of lesions are found. Studies of the implications of rodents damage in growth of trees, demonstrate that in the forest plantations evaluated there are difference in growth of attacked and not attacked trees, mainly in form factor and volume. The chemical composition of wood is also affected . Indices of total extractives and ash were altered in plants attacked only in the attack area. Experimental studies that tested the reduction of attack are found in literature and apparently the results are satisfactory, but not recommended for managed areas for pulp production / No Brasil os danos causados por roedores em plantios florestais são comprovados e poucos estudados. Várias empresas florestais da região sul do país alertam sobre a ampliação e intensificação dos ataques de roedores à plantios. Os ataques ocorrem em árvores de Pinus spp., a partir do 3º-4º ano de idade do plantio, nos locais onde há formação de microhabitats por ervas daninhas e em locais próximos as áreas nativas onde a intensidade do ataque é maior. As áreas nativas das fazendas estudadas passam por um processo de adequação ambiental. Estas áreas são caracterizadas pela presença de regeneração em estágio inicial, com abundância de espécies pioneiras como a Bracatinga (Mimosa scabrella Benth.) e diversas espécies de gramíneas. A baixa qualidade ambiental das áreas de preservação permanente configura locais de desequilíbrio na oferta de recursos. A presença do microhábitat no interior da floresta plantada forma, aumenta as áreas de forrageio das espécies da fauna local pelo abrigo oferecido. A soma da baixa qualidade das áreas silvestres com o aumento de áreas de forrageio causado pela presença de microhabitat no interior da floresta plantada, faz com que as espécies da fauna local sejam forçadas a usar e recursos alimentares alternativos. As árvores de Pinus taeda possuem recurso energético disponível em sua seiva elaborada. Ela é composta por aproximadamente 8,2º Brix de sólidos solúveis totais em solução (açúcares), o dobro do encontrado para a seiva de M. scabrella. A grande quantidade de açucares na seiva, sugerem o uso de P. taeda como recurso alimentar por roedores. Existem evidências de que mais de uma espécie de roedor cause os danos, pois diferentes tipos de lesões são encontrados. Estudos referente às implicações dos danos de roedores no crescimento das árvores demonstram que nos talhões avaliados existe diferença de crescimento entre árvores atacadas e não atacadas, principalmente no fator de forma e volume. A composição química da madeira também é afetada. Índices de extrativos totais e cinzas mostraram-se alterados em plantas atacadas somente na região do ataque. Estudos experimentais que testaram a redução do ataque são encontrados na literatura e aparentemente os resultados encontrados são satisfatórios, porém não operacionalizáveis em áreas de manejo para produção de celulose