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Title: A search for factors controlling the formation and maintenance of connections between the thalamus and cortex in vitro
Author: Beau Lotto, R.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1994
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Although the development of the nervous system is continuous, the neurones that constitute the nervous system proceed through specific developmental stages. Such stages included: birth, differentiation, migration, the formation of efferent and afferent connections, and the organisation of these connections based on exogenous and endogenous cues. Alternatively, a neuron may undergo "natural occurring" cell death at various points during development. When considering the complexity of the nervous system, it is not surprising that our knowledge, as to the factors that control these development stages, is limited One significant obstacle for experimentally addressing these questions, for practical and/or ethical reasons, has been the animal itself. Thus, the advent of tissue culture techniques has greatly facilitated research in this area. In addition to in vivo Dil tract-tracing experiments, I have used three different in vitro techniques: (i) co-cultures of organotypic explants on a two-dimensional collagen substrate, (ii) organotypic explants co-cultured within a three-dimensional collagen gel, and (iii) co-cultures of dissociated cells. Because serum is known to contain many trophic factors, only serum-free medium was used for all of these experiments. Using the above in vitro techniques, I investigated questions concerning the development of connections between the thalamus and cortex. These experiments yielded the following results, (i) When thalamocortical and corticothalamic efferent fibres began to grow in vivo at embryonic day 15 (El5), conserved diffusible target-derived factors enhanced their neurite elongation in vitro, (ii) The survival of El 5 thalamic and cortical neurones was independent from target-derived trophic support, since both the thalamus and cortex promoted their own survival in vitro. possibly through the production of endogenous trophic factors. However (iii), between E17 and postnatal day 2, a time coincident with the arrival of their fibres to their target, the survival of thalamocortical and corticothalamic neurones was dependent on factors released from their target, (iv) The production of growth promoting factors within the cortex increased with postnatal age and was at least partially regulated by afferent activity. And finally (v), it seems that the recognition/stop-signalling molecules expressed within these targets are also highly conserved since they were recognised in inter-species co-culture experiments. Thus, in general, the development of both thalamocortical and corticothalamic efferents are highly influenced by factors produced by their target cells in vitro. In vivo, these factors may play various roles during the different developmental stages from promoting neurite outgrowth and cell survival, to regulating the reorganisation of connections.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available