The Experts below are selected from a list of 51 Experts worldwide ranked by ideXlab platform
Joshua R. Sanes - One of the best experts on this subject based on the ideXlab platform.
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Chemoaffinity Revisited: Dscams, Protocadherins, and Neural Circuit Assembly
Cell, 2010Co-Authors: S. Lawrence Zipursky, Joshua R. SanesAbstract:The Chemoaffinity Hypothesis for neural circuit assembly posits that axons and their targets bear matching molecular labels that endow neurons with unique identities and specify synapses between appropriate partners. Here, we focus on two intriguing candidates for fulfilling this role, Drosophila Dscams and vertebrate clustered protocadherins (Pcdhs). In each, a complex genomic locus encodes large numbers of neuronal transmembrane proteins with homophilic binding specificity, individual members of which are expressed combinatorially. Although these properties suggest that Dscams and Pcdhs could act as specificity molecules, they may do so in ways that challenge traditional views of how neural circuits assemble.
Ronald L. Meyer - One of the best experts on this subject based on the ideXlab platform.
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Roger Sperry and his Chemoaffinity Hypothesis
Neuropsychologia, 1998Co-Authors: Ronald L. MeyerAbstract:In the early 1940s, Roger Sperry performed a series of insightful experiments on the visual system of lower vertebrates that led him to draw two important conclusions: When optic fibers were severed, the regenerating fibers grew back to their original loci in the midbrain tectum to re-establish a topographical set of connections; and the re-establishment of these orderly connections underlay the orderly behavior of the animal. From these conclusions, he inferred that each optic fiber and each tectal neuron possessed cytochemical labels that uniquely denoted their neuronal type and position and that optic fibers could utilize these labels to selectively navigate to their matching target cell. This inference was subsequently formulated into a general explanation of how neurons form ordered interconnections during development and became known as the Chemoaffinity Hypothesis. The origins of this Hypothesis, the controversies that surrounded it for several decades and its eventual acceptance, are discussed in this article.
Norbert Degen - One of the best experts on this subject based on the ideXlab platform.
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Retinal specificity in eye fragments: investigations on the retinotectal projections of different quarter-eyes in Xenopus laevis
Experimental Brain Research, 1994Co-Authors: Kurt Brändle, Norbert DegenAbstract:According to Sperry's Chemoaffinity Hypothesis, the projection of a small eye fragment with a reduced amount of optic fibres should be restricted to that position in the optic tectum corresponding to its own specificity. However, previous investigations on different types of quarter-eyes in Xenopus laevis have revealed that their retinal projection was always restricted to the rostral part of the tectum, no matter what the origin of the remaining retinal quadrant. To get an indication of the state of specificity in such eye fragments, we investigated by electrophysiological and histological methods several features of the retinal projections of temporoventral (TV), naso-ventral (NV) and ventral (V) quarter-eyes which referred to their positional identity. Irrespective of their different origins, the projections were always located in the rostral part of the tectum, the size of the innervated tectal area depending for all fragment types on the size of the quarter-eyes, i.e. number of optic fibres. However, quantitative analyses revealed that with increasing eye size the various fragments expand their projections preferentially into those tectal areas that match their original specificity: TV projection is more concentrated in the rostral tectum, NV eyes expand their projections mainly to the caudal tectum, and V eyes enlarge their projections equally into the medial and caudal tectum. In addition, fibre-tracing experiments with cobaltic lysine showed that, according to the different origins of the quarter-eyes, retinal fibres follow the appropriate branch of the optic tract selectively: fibres of NV and V eyes pass mainly through the medial tract, and most fibres of TV eyes innervate the rostral tectum directly from a central position between the two side branches. All these findings suggest that the different types of quarter-eyes retain their original positional identity. Thus, their rostrally located retinotectal projections are not in register with their retinal specificity. We conclude that in X. laevis local positional markers in the tectum, if present at all, do not influence the development of the retinotectal projection. Instead we suggest a concept of self-sorting of the optic fibres, which can account for the partial innervation of the rostral tectum in different types of quarter-eyes.
Hollis T. Cline - One of the best experts on this subject based on the ideXlab platform.
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Sperry and Hebb: oil and vinegar?
Trends in neurosciences, 2003Co-Authors: Hollis T. ClineAbstract:The interface between so-called activity-dependent and activity-independent mechanisms of circuit development is discussed here in light of recent findings that question the role of activity in brain development. This debate is presented simplistically here in terms of Sperry's Chemoaffinity Hypothesis versus Hebb's rules of correlation-based synaptic change, which are often presented as being mutually exclusive - much like oil and vinegar.
S. Lawrence Zipursky - One of the best experts on this subject based on the ideXlab platform.
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Chemoaffinity Revisited: Dscams, Protocadherins, and Neural Circuit Assembly
Cell, 2010Co-Authors: S. Lawrence Zipursky, Joshua R. SanesAbstract:The Chemoaffinity Hypothesis for neural circuit assembly posits that axons and their targets bear matching molecular labels that endow neurons with unique identities and specify synapses between appropriate partners. Here, we focus on two intriguing candidates for fulfilling this role, Drosophila Dscams and vertebrate clustered protocadherins (Pcdhs). In each, a complex genomic locus encodes large numbers of neuronal transmembrane proteins with homophilic binding specificity, individual members of which are expressed combinatorially. Although these properties suggest that Dscams and Pcdhs could act as specificity molecules, they may do so in ways that challenge traditional views of how neural circuits assemble.