Biomedical subjects
Publications and source records attributed to G Percheron.
The topographical localization of endogenous iron in rat and monkey brains coincides with the striato-pallido-nigral and the cerebellar corticonuclear pathways. EM observation reveals that iron is located in the soma and processes of glial cells and, above all, in the inner and outer loop of the myelin sheets. This raises the question of whether iron intervenes in some GABAergic systems.
We present a methodology for measuring precisely defined morphological parameters on complete dendritic arborizations. Brains are sectioned through anatomical planes which are defined with reference to ventricular landmarks. For each neuron, drawn through the camera lucida, dendritic points are defined and identified by means of a numerical topological codification. The 3-dimensional coordinates of each point are measured on a video computer microscope with reference to a cartesian system of axes which are oriented with reference to the anatomical planes of the brain. The data points from several serial sections are stored section by section and re-ordered by a computer program. Quantitative data concerning the diameters of the dendrites and the number and the dimensions of their spines are also stored. From these data, various quantitative morphological parameters may be computed. The accuracy of the video computer microscope is measured. The different existing computerized systems and the contribution of computerized techniques are discussed.
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Dendritic branching of neurons may be quantitatively studied using applications of graph theory. Dendritic ramifications may be considered as 'forests' of planted, stemmed, binary 'trees' with simple mathematical properties. Two fundamental numbers, that of dendritic tips and that of dendritic stems, usually suffice to quantify the dendritic branching of one neuron as, in most cases, they allow the computation of all other numbers of dendritic points and segments.
The fundamental dendritic numbers [14] were studied in various neuronal groups from different species. Their mean values allow group characterization on a quantitative basis. This allows group comparisons and classification. Four sets of polydendritic neuronal groups are isolated: fewly branched Golgi I groups (A), mainly stemmed Golgi I groups (B), Golgi II groups (C) and highly branched Golgi I groups (D). Numerical interspecific comparisons allow quantitative phylogenetic studies. Only groups of the D set exhibit a significant evolution. Dendritic numbers are an efficient tool for neuronal group studies.
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One may describe 4 types of individual dispositions for the postero-median choroideal and thalamic system: Type A with a single artery of anterior origin, type P with two consecutive arteries (a mesencephalothalamic artery and a posteromedian artery of posterior origin), type D with two parallel arteries and type O. One may also describe 4 types of individual dispositions for the postero-lateral choroideal and thalamic system. Type C is constituted by a single postero-lateral chorideal artery giving off thalamic branches. Type D comprises two arteries, a postero-lateral choroideal and a postero-lateral thalamic artery. According to the relative importance of the two arteries one may describe subtypes Dc, De and Dt. Type T is constituted by a single postero-lateral thalamic artery giving off choroideal branches. In type H hippocampothalamic arteries intervene. We also studied the variations of the ending point of the anterior choiroideal artery.
The anterior chor oideal artery cannot be considered as an arterial source for thalamic vascularization. Its territory is primarily pallidocapsular and reaches the thalamus only irregularly and superfically. 2. The posteromedian choroideal and thalamic system, in its infrathalamic portion, gives off lateral mesencephalosubthalamic, inferocentral (for the tips of the arcuate nucleus and the inferolateral part of the centre median nucleus), brachiopulvinarian and posterocentral arteries. In its suprathalamic portion it gives off medial pulvinarian and superomedian thalamic arteries. These arteries irriguate the major part of nucleus medialis and the nucleus anterior. 3. The posterolateral choroideal and thalamic system gives off lateral genicular arteries (for the lateral geniculate body), inferolateral pulvinarian and superolateral thalamic arteries. These arteries irriguate the dorsal part of the interal region of the thalamus.
The posterior communicating artery participates to the thalamic vascularization in 60 to 70 p. 100 of the brains. It does by one unic, well characterized artery, the polar artery. Its territory comprises the rostral pole of the lateral region up to the mamillo thalamic fasciculus.
The basilar communicating artery (or mesencephalic artery) gives off more often one than two paramedian thalamic arteries. The paramedian territory, infero-medial, has a variable extent. It can include the polar territory when the polar artery does not exist. The paramedian artery arises as often from the controlateral basilar communicating artery than from the ipsilateral one. One basilar communicating artery may so have a very extensive bilateral territory.
The most satisfactory ventricular landmarks and coordinate system for thalamic stereotaxy in the macaque are essentially the same as for man (i.e. from CA and CP). The degree of precision achieved when using this system is markedly superior to that obtained when using bony landmarks. Stereotaxy methods using ventriculographic data are described. Multivariate analyses were performed to analyse interspecific differences and more specially to determine whether a single stereotaxic atlas could be used for several species which seems to be the case for M. mulatta and M. speciosa.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
Initially, basal ganglia was a descriptive term for onto- and phylogenetic or topographic classifications. A variable list of structures were included as basal ganglia. A major step was made when the thalamus was separated from the "striated bodies" (Vic d'Azyr, 1786) which was sometimes taken into account in the French description of the noyaux gris centraux. Even if the term is not perfect, it is preferable to "the system of basal ganglia". The subdivisions of the putamen, the distinction between the striatum and the pallidum were not really made until the beginning of the twentieth century. Modern tracing methods were needed to demonstrate the main connections. It was not until the end of the 1960s that the importance of the striato-pallido-nigral network within the basal ganglia and the cortico-striatal connections, the main afferent system, were recognized. With the description of the cortico-striatal connections, the sub-cortical system with multiple complex "loops" was questioned. The term "extra-pyramidal system" had an exaggerated success. Initially, it designated descending non-pyramidal afferents (some which do not exist) and their source. In 1992, Spatz based his separation of this heterogeneous group on the iron content. The terms of extra-pyramidal "system" and "syndrome" should be abandoned by clinicians. Physiological interpretations have varied. The role of automatic "habitual" motricity, derived from a concept of hierarchic, Jacksonian cerebral organization, was questioned when the pyramidal network was described. Clinico-pathological analysis (hemiballism, Parkinson's disease ...) has placed new emphasis on the motor role, for a time the only role accepted as real. More recently, debate has centred on other roles, particularly in cognition and motivation. An illustration of functions other than purely motor functions of the basal ganglia is given by the syndromes of loss of psychic auto-activation secondary to bilateral lesions.
This paper describes a major cerebral system whose contours are only emerging: the "basal ganglia related system". This is made up of the "system of the basal ganglia" itself plus its inputs and outputs. The system of the basal ganglia may be divided into the "basal ganglia core" comprising the striatum and its pallidal and nigral targets and the "regulators of the core". Distinguishable include regulators of the striatum (the dopaminergic pars compacta and the central complex of the thalamus or centre median-parafascicularis), regulators of the pallidonigrum (the subthalamic nucleus and the pedunculopontine complex) and internal regulators (at first the lateral nucleus of the pallidum). The main input to this system comes from the cerebral cortex. The main output is the thalamus and from it to the cortex. The whole "basal ganglia related system" may thus be seen as a cortico-cortical circuit passing through the basal ganglia. Information processing in the system is very complex. New data presented here emphasize two connections: cortico-striate and striato-pallidonigral connections. It is stressed that the first uses complex combinations of confluence or difluence on small matricial islands. This step could be a selection and reorganisation of cortical information. The second process is a strong "dynamically focused convergence" combining information from different upstream sources in order to derive an adequate informational product for the production of harmonious and adapted motricity.