Biochemical studies of the ontogenesis of the brain encounter many difficulties due to morphologic and functional heterogeneity in the central nervous system (CNS) and due to differences in the developmental timing of the various brain regions when studying the whole brain. It is also difficult to establish which is the initial response to the factor under analysis and which are the secondary responses. The retina offers a rather simple developmental system which nevertheless is applicable to the comprehension of CNS. In the retina, the number of parameters is smaller, and it is possible to investigate specific structures with relatively little interference from neighbouring structures. The retina has a relatively simple morphology consisting roughly of alternating layers of cell bodies and synaptic regions, ordered from the scleral to the vitreal side as follows: photoreceptor region (outer and inner segment of rods and cones), outer synaptic layer (outer plexiform layer), region of horizontal, bipolar and amacrine cell bodies, zone of inner synapses (inner plexiform layer), ganglion cells. Non-neuronal cells, the so-called Müller cells, span the full thickness of the retina, and constitute the chief glial component of the retina. Microdissection of fresh or frozen tissue allows one to pool enriched fractions of a given cell type. Due to the dimensions of the whole intact retina, it has been termed an “instant” tissue slice which may be immersed in an appropriate medium, and maintained in physiological state by perfusion. The versatility of this isolated system allows one to study various parameters of metabolism, to analyse the bioelectrical response (electroretinogram: ERG) to its natural physiologic stimulus: light, under various adaptation conditions, and to investigate the influence of important biochemical compounds (putative neurotransmitters, their antagonists and agonists, as well as pharmacologic drugs) on the functional behavior of the retina. Such a perfusion system of an isolated retina allows one to correlate the effects due to compounds introduced in the perfusion medium, the electroretinogram modifications, and the biochemical changes at various levels in the layers of the tissue.
KeywordsOuter Plexiform Layer Retinal Development Embryonic Life Chick Brain Chick Retina
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