EphA3 expressed in the chicken tectum stimulates nasal retinal ganglion cell axon growth and is required for retinotectal topographic map formation.

Background: Retinotopic projection onto the tectum/colliculus constitutes the most studied model of topographic mapping and Eph receptors and their ligands, the ephrins, are the best characterized molecular system involved in this process. Ephrin-As, expressed in an increasing rostro-caudal gradient in the tectum/colliculus, repel temporal retinal ganglion cell (RGC) axons from the caudal tectum and inhibit their branching posterior to their termination zones. However, there are conflicting data regarding the nature of the second force that guides nasal axons to invade and branch only in the caudal tectum/colliculus.

The chick optic tectum developmental stages. A dynamic table based on temporal- and spatial-dependent histogenetic changes: A structural, morphometric and immunocytochemical analysis.

Development is often described as temporal sequences of developmental stages (DSs). When tables of DS are defined exclusively in the time domain they cannot discriminate histogenetic differences between different positions along a spatial reference axis. We introduce a table of DSs for the developing chick optic tectum (OT) based on time- and space-dependent changes in quantitative morphometric parameters, qualitative histogenetic features and immunocytochemical pattern of several developmentally active molecules (Notch1, Hes5, NeuroD1, β-III-Tubulin, synaptotagmin-I and neurofilament-M).

Key roles of Ephs and ephrins in retinotectal topographic map formation.

Cellular and molecular mechanisms involved in the development of topographic ordered connections in the central nervous system (CNS) constitute a key issue in neurobiology because neural connectivities are the base of the CNS normal function. We discuss the roles of the Eph/ephrin system in the establishment of retinotopic projections onto the tectum/colliculus, the most detailed studied model of topographic mapping. The expression patterns of Ephs and ephrins in opposing gradients both in the retina and the tectum/colliculus, label the local addresses on the target and give specific sensitivities to growth cones according to their topographic origin in the retina.

Developmental pattern of NADPH-diaphorase positive neurons in chick optic tectum is sensitive to changes in visual stimulation.

The chick retinotectal system is a suitable model to investigate the mechanisms involved in the establishment of synaptic connections in whose refinement nitric oxide was implicated. The purpose of this work was to describe the developmental pattern of the nitric oxide synthase (NOS)-positive neurons as well as to determine if it is sensitive to changes in visual stimulation. The NADPH-diaphorase histochemical method was used to describe and quantify NOS neurons in normally stimulated and subnormally stimulated chickens.