Biomedical subjects
Publications and source records attributed to J Szentágothai.
The outlines of an investigation into side differences between the Planum temporale (The Geschwind-Levitzky areas) of ten human brains are given. Volume of this area and cell numbers are clearly asymmetric, the left side being consequently larger by 38-34% over the same area at right. Cell density (cell No/volume) is virtually the same on both sides. Some comments upon the data are being made.
Recent neurophysiological observations are giving rise to the expectation that in the near future genuine biological experiments may contribute more than will premature speculations to the understanding of global and cognitive functions. The classical reflex principle--as the basis of neural functions--has to yield to new ideas, like autopoiesis and/or self-organization, as the basic paradigm in the framework of which the essence of the neural can be better understood. Neural activity starts in the very earliest stages of development well before receptors and afferent input become functional. Under suitable conditions, both in nervous tissue cultures and in embryonic tissue recombination experiments, the conditions of such initial autopoietic activity can be studied. This paper tries to generalize this elementary concept for various neural centers, notably for the spinal segmental apparatus and the cerebral cortex.
Speculation on neuron connectivity in the cerebral cortex, made some ten years ago, were re-evaluated in the light of modern cross identification methods. The identification of individual neurons and their synapses, including physiological characterization, detailed light microscope analysis of the same neurons, and immunocytochemical analysis of these neurones on the light microscope level and of their synapses on the level of the electron microscope, indicate that the specificity of local neuronal connections was underestimated in the earlier studies. Although the new methods revealed a higher degree of specificity in the choice of their connections, there seems to remain ample room for epigenetic (or functionally induced) plasticity of re-arrangement in neuronal circuits during later - even in postnatal - stages of development.
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Several lines of evidence suggest that gamma-aminobutyric acid is an inhibitory neurotransmitter in the cerebral cortex. To study the intracortical projection of neurons that selectively accumulate this amino acid, we injected radioactive gamma-aminobutyric acid into the upper layers of the striate cortex of monkeys along tracks at an oblique angle to the pia. Sections from the injected area were then processed by a combination of autoradiography and Golgi impregnation to reveal the distribution of labeled neurons and their morphological characteristics. Labeled neurons always occurred around the injection site in each layer. In addition, a consistent radial pattern of perikaryal labeling was observed in layers IVc-VI below the injection track in layers I-IVa. The closer the injection track was to the pia the deeper the peak density of labeled cells appeared. After injection in layers IVa and the lower part of III, the highest number of labeled neurons was in layer IVc; after injection in the upper part of layer III, most labeled neurons were in layer V; and, after injection in layers I and II, the proportion of labeled neurons increased in the lower part of layer V and in layer VI. All these neurons in the infragranular layers are presumably labeled by retrograde axonal transport via the labeled fiber bundles that extended from upper to lower layers. Thirty-four Golgi-stained neurons of various types were also examined for retrograde labeling. Two were labeled, and both were aspiny stellate cells in layer V. The arrangement of these putative GABAergic neurones, with axons that ascend from lower to upper layers in a regular pattern and arborize locally, would enable them to mediate inhibition within cortical columns and between neighboring columns.
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Intact mossy terminals observed in the granular layer of rat cerebella, two weeks after complete transection of all cerebellar peduncles, were identified as the endings of the intracerebellar nucleo-cortical afferents. A quantitative study of synaptic vesicle size spectra revealed clear differences between nucleo-cortical and true extracerebellar mossy afferents. These differences suggest that the nucleo-cortical afferents are recurrent collaterals of the projective nucleofugal fibers.
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The vascular supply of the rat hypothalamo-hypophyseal complex was studied by aid of a double injection technique (two dyes different in colour injected successively). The vascular bed of the median eminence, the arcuate nucleus, and the retrochiasmatic area are intimately interconnected among themselves, but isolated from the vascular system of all other parts of the hypothalamus. The arterial supply of this ensemble of the medial basal hypothalamus is common from the hypophyseal arteries, via the primary plexus and the specific vascular loops of the median eminence. From here a separation of the vascular bed leads the blood flow towards the pituitary portal vessels on the one hand, and over a subependymal vascular network towards the arcuate nuclei on the other. The venous drainage of the arcuate nuclei and the retrochiasmatic area is secured by a special set of tuberal and retrochiasmatic veins. --The unity of the vascular bed of the median eminence, arcuate nucleus, retrochiasmatic area complex, with a blood flow largely in the direction indicated by this sequence, is of considerable importance for the interpretation of the results of experimental interference with this region.
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An attempt is made to bring earlier circuit models of primary sensory cortical areas into better line with recent observations on (1) the distribution of excitatory feedback connexions in cortical tissue volume, (2) putative inhibitory interneurons and the distribution of inhibition in well defined space modules, and (3) the direct (monosynaptic) cortical target cells of the specific sensory afferents, and the modes of relay to secondary neurons. Even though the concept of cortical circuitry on larger 'integrative units' containing smaller modules (or fields) of specific (excitatory and inhibitory) neuronal actions, proposed in 1967 (ref. 34) and 1969 (ref. 35), had gross deficiencies in the light of newly emerging data, the basic idea of how to look at the functional organization of the cortical neuron network may still be useful as a conceptual framework for the functional interpretation of structural data.
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