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F Valverde

Publications and source records attributed to F Valverde.

At least 91 records · Page 5Linked to original sources
PubMed1978

The organization of area 18 in the monkey. A Golgi study.

The organization of area 18 in monkey has been studied in Golgi preparations. In layer III large pyramidal cells with profusely ramified basal dendritic arbors are identified. They probably represent one of the major components originating association connections. Layer II and the upper part of layer III contain cells with spine-free dendrites having axons forming long bundles descending vertically to layers IV and V. Layer IV is characterized by the presence of granular cells with local axons and small pyramidal cells with ascending recurrent axons. Layer V contains various types of pyramidal cells including giant pyramidal neurons. The mean number and distribution of dendritic spines along apical shafts were computed in four varieties of pyramidal cells. Several neuronal parameters pertaining to the length of axons and dendrites were calculated. Three-dimensional aspects of cells were analyzed by means of a computer program which permits neurons to be displayed as perspective views from various positions. Attempts were made to correlate the present description with previous observations on this and other cortical visual areas.

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PubMed1976

Aspects of cortical organization related to the geometry of neurons with intra-cortical axons.

Using the Golgi method, cells with intra-cortical axons in the visual cortex of young mice were classified according to defined geometrical axonal shapes. This study principally describes a computer technique and its application to the study of neuronal morphology. Neurons were converted in a sequence of three-coordinate points which were stored in digital form on magnetic tape. From the stored data and total real length in space of dendrites and axons was obtained and the results compared in two groups of mice raised under different conditions. Preliminary observations show short axonal lengths in mice raised in darkness. Using Eulerian coordinate transformations, reconstructions of individual neurons and of groups of several neurons and fibres were obtained by generating displays of different views after rotation around the horizontal axis. Reconstructed pictures were compared with their corresponding original drawings in order to describe particular aspects of cortical organization.

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PubMedDate not supplied

Further studies on cortical tangential migration in wild type and Pax-6 mutant mice.

In this study we present new data concerning the tangential migration from the medial and lateral ganglionic eminences (MGE and LGE) to the cerebral cortex during development. We have used Calbindin as a useful marker to follow the itinerary of tangential migratory cells during early developmental stages in wild-type and Pax-6 homozygous mutant mice. In the wild-type mice, at early developmental stages, migrating cells advance through the intermediate zone (IZ) and preplate (PP). At more advanced stages, migrating cells were present in the subplate (SP) and cortical plate (CP) to reach the entire developing cerebral cortex. We found that, in the homozygous mutant mice (Pax-6(Sey-Neu)/Pax-6(Sey-Neu)), this tangential migration is severely affected at early developmental stages: migrating cells were absent in the IZ, which were only found some days later, suggesting that in the mutant mice, there is a temporal delay in tangential migration. We have also defined some possible mechanisms to explain certain migratory routes from the basal telencephalon to the cerebral cortex. We describe the existence of two factors, which we consider to be essential for the normal migration; the first one is the cell adhesion molecule PSA-NCAM, whose role in other migratory systems is well known. The second factor is Robo-2, whose expression delimits a channel for the passage of migratory cells from the basal telencephalon to the cerebral cortex.

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PubMedDate not supplied

Time of origin and early fate of preplate cells in the cerebral cortex of the rat.

The time of origin, development, and morphology of neurons originating before the establishment of the cortical plate (preplate cells) were studied in the telencephalic vesicle of the rat from the embryonic day 10 (E10) to E15. The first postmitotic neurons settle superficial to the ventricular zone in the preplate at E12. We have observed mitotic figures in the preplate at E12 and E13, and regarded them as a possible source of cortical neurons outside the ventricular zone. It is suggested that these cells may correspond to Cajal-Retzius cells. The appearance of cells before the formation of the cortical plate was studied in animals injected with tritiated thymidine at E12 and E13 and correlated with observations made using an antibody to neuron specific class III beta-tubulin that becomes detectable immediately after the last mitotic division. Immunoreactive cells detected with this antibody concentrate at E12 immediately below the pial surface constituting the preplate. Radially oriented cells, most probably subplate neurons, were also present spanning the full thickness of the neuroepithelium, suggesting that the preplate contains different cell classes. We present a working hypothesis that explains the sequence of developmental events during the early phases of cortical histogenesis.

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