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| Louis Puelles |
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Dept.Morphological Sciences, Fac.Medicine, Univ.Murcia, E-30100, Murcia, Spain
e-mail: puelles@um.es |
Presentation: |
| 2002-10-08, 09:00-09:45 |
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| Morphogenetic deformation at the thalamo-telencephalic boundary and the lamina affixa myth. |
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| One feature of forebrain morphogenesis in human embryos and other mammalian embryos that always was difficult to understand refers to the morphogenetic changes leading to the apparent inclusion of a lateral part of the dorsal thalamic surface in the floor of the mature telencephalic lateral ventricle. This phenomenon was classically explained without conclusive positive proof as an adhesion effect, by which part of the choroidal tela of the lateral ventricle would come to intimately overlap and later adhere to the adjoining thalamus, forming the so-called lamina affixa. This widespread hypothesis however implies topological conundrums, particularly when trying to understand the transitional ventral thalamus and eminentia thalami territories known to be intercalated in early embryos between the dorsal thalamus and the complex formed by the telencephalic basal ganglia, the bed nucleus of the stria terminalis and the medial amygdala. The tela choroidea of the lateral ventricle in its turn relates by neighborhood to the hem of the cortex (i.e., the hippocampal anlage). The present contribution analyses a number of published and unpublished images, as well as some graphic tridimensional representations, to postulate a model of morphogenesis at the thalamo-telencephalic transition that satisfactorily explains solely by differential growth and partial eversion of the eminentia thalami the phenomena and topographic peculiarities normally attributed to lamina affixa adhesion. I propose that the lamina affixa concept can be discounted as representing either observed data (misinterpreted) or a necessary explanation, and thus enlarges the list of forebrain developmental myths refuted in recent times (i.e., forebrain length axis entering into the telencephalon, internal capsule growing through adhesion between lateral thalamic surface and telencephalic hemisphere, or pallidal primordia originating in the hypothalamus). |
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