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Effects of Optic Nerve Section in the Retina
Tipo: | Artículo |
Autores: | Germain, F.; Blanco, R.; de la Villa, Pedro. |
Títuto Revista: | Optic Nerve Disease Research Perspectives |
Referencia: | |
Centro: | 09 - UAH |
Effects of Optic Nerve Section in the Retina |
Authors: Francisco Germain, Román Blanco and Pedro de la Villa |
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Abstract: The retina is a privileged tissue to study the Central Nervous System due to the disposition in layers of different types of cells and synaptic plexus. By cutting the axon not only the nervous transmission is interrupted, but also an apoptotic death is induced in axotomized neurons. The study of morphological and functional changes of surviving retinal ganglion cells (RGCs) after axotomy is important in order to be able to predict cell survival, structure restoration and functional recovery. After axotomy there was a progressive decrease in RGCs count with a death peak in the second week. In relation with this cellular decrease in the ganglion cell layer, a significant reduction in the thickness of the inner plexiform and ganglion cell layers of retinal cross-sections was observed. Immunohistochemical studies also showed a remarkable disorganisation of the layer stratification in the inner plexiform layer. However, some RGCs survive longer and develop changes such as growth cones and abnormal processes, probably trying to adapt to a new situation. Also an increase in the diameter of the soma and dendritic field was observed. The morphometrical analysis of the surviving axotomized RGCs showed that the number of dendritic segments did not differ significantly of control animals, however, their length was longer in axotomized cells than in control cells. These few surviving cells experienced significant morphological changes that were studied by light microscopy after neurobiotin injection, transmission and scanning electron microscopy. Ultrastructural analyses showed cytoplasmic vacuolar degeneration and signs of membrane alteration suggesting that axotomy causes severe alterations in the cytoskeleton. The functionality and possible connections with other cells are unknown. To study functional changes of rabbit RGCs receptors in surviving cells two weeks after axotomy, dissociated RGCs were recorded by whole cell patch-clamp technique. The ionic currents induced by the application of excitatory (AMPA / kainate) and inhibitory (GABA) neurotransmitter agonist in injured RGCs were analyzed and compared with cells from control retinas. While excitatory neurotransmitters were unable of inducing ionic currents, the amplitudes of the GABA-induced currents were decreased to 20 % of control. After optic nerve section, large RGCs have shown greater survival than other types, possibly it might be in relation with these structural and functional adaptive changes in neurotransmitter receptor. Knowledge of the action mechanisms, as well as the determination of no return point in the evolution of the lesion are aspects that must be known before to start a therapy. |
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