RESUMO
Following axotomy, the contact between motoneurons and muscle fibers is disrupted, triggering a retrograde reaction at the neuron cell body within the spinal cord. Together with chromatolysis, a hallmark of such response to injury is the elimination of presynaptic terminals apposing to the soma and proximal dendrites of the injured neuron. Excitatory inputs are preferentially eliminated, leaving the cells under an inhibitory influence during the repair process. This is particularly important to avoid glutamate excitotoxicity. Such shift from transmission to a regeneration state is also reflected by deep metabolic changes, seen by the regulation of several genes related to cell survival and axonal growth. It is unclear, however, how exactly synaptic stripping occurs, but there is substantial evidence that glial cells play an active role in this process. In one hand, immune molecules, such as the major histocompatibility complex (MHC) class I, members of the complement family and Toll-like receptors are actively involved in the elimination/reapposition of presynaptic boutons. On the other hand, plastic changes that involve sprouting might be negatively regulated by extracellular matrix proteins such as Nogo-A, MAG and scar-related chondroitin sulfate proteoglycans. Also, neurotrophins, stem cells, physical exercise and several drugs seem to improve synaptic stability, leading to functional recovery after lesion. This article is part of a Special Issue entitled 'Neuroimmunology and Synaptic Function'.
Assuntos
Axônios/fisiologia , Plasticidade Neuronal , Traumatismos dos Nervos Periféricos/fisiopatologia , Sinapses/fisiologia , Animais , Axônios/metabolismo , Axotomia , Encéfalo/metabolismo , Encéfalo/fisiopatologia , Humanos , Neurônios Motores/fisiologia , Neurônios Motores/ultraestrutura , Regeneração Nervosa , Neuroglia/fisiologia , Neuroglia/ultraestrutura , Traumatismos dos Nervos Periféricos/imunologia , Traumatismos dos Nervos Periféricos/metabolismo , Traumatismos da Medula Espinal/imunologia , Traumatismos da Medula Espinal/metabolismo , Traumatismos da Medula Espinal/fisiopatologia , Sinapses/metabolismo , Sinapses/ultraestruturaRESUMO
Predation is a major force shaping natural history traits of birds because of their vulnerability during nesting and higher visibility during diurnal activities. For most birds in the Neotropics, predation is the major cause of nest failure due to the region's high diversity and abundance of predators. The blue-black grassquit (Volatinia jacarina), similarly to other small passerines in the savanna region of central Brazil, suffers extremely high rates of nest predation. Additionally, males may be particularly vulnerable to predators since they are very conspicuous when executing courtship displays. We assessed some of the non-lethal costs of predation risk on this species by comparing physiological and morphological parameters of birds exposed to predator vocalizations with that of control subjects exposed to non-predator vocalizations. Birds exposed to the predator vocalizations exhibited an immune-related reaction (changes in their H/L ratio), but no changes were observed in other biological parameters measured. This article is part of a Special Issue entitled: Neotropical Behaviour.