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The molecular economics of the long neuron

Die molekulare Ökonomie der langen Neuronen

Kurzfassung

Im Gegensatz zu anderen Zellen ist ein Neuron in der Lage, durch Veränderung der Kern-Plasma-Relation progressiv zu wachsen. Dieses Phänomen wurde untersucht, wobei der Eiweißstoffwechsel einer Zelle als limitierender Faktor für die Erhaltung der normalen Kern-Plasma-Relation angesehen wurde. Es wurde ein Modell eines Systems konstruiert, mit voneinander abhängigen Molekülen verschiedener Halblebenszeiten, welche unter den Bedingungen molekularen Austausches operieren, die den Proteinstoffwechsel zu beherrschen und einzuschränken scheinen. Dann wurde geprüft, auf welche Weise dieses System sich durch Anstieg der Molekülzahlen auszudehnen vermag. In einer weitgehend dem Muster des unbeschränkten Wachstums der langen Neuronen ähnelnden Situation wurde dem Mangel an Molekülen mit kurzer Halblebenszeit (diese wurden in sich ausdehnenden Systemen gefunden) durch Überführung ähnlicher Moleküle aus benachbarten, nicht ausgedehnten Systemen begegnet. Das ausgedehnte System neigte aber dazu, „Molekülschulden“ auf sich zu laden, deren Höhe abhing von dem Ausmaß der Systemausdehnung. Diese Sachverhalte stimmten überein mit vielen beobachteten histologischen, biochemischen und physiologischen Charakteristika der Nervengewebe. Es wurde daher gefolgert, daß Modelle dieser Art nützlich sein können hinsichtlich einer Korrelation morphologischer und biochemischer Befunde und der Planung geeigneter Experimente.

Summary

1. Nerve cells grow by progressively changing their nucleo-cytoplasmic ratio, whereas growth in other cell types is associated with an increase in number of nuclei or degree of ploidy of a single nucleus in such a way that the nucleo-cytoplasmic ratio is maintained within its original order of magnitude.

2. Reasons are given for supposing that the primary factor in maintaining the nucleo-cytoplasmic ratio within its usual order of magnitude lies in the peculiar nature of protein metabolism which is keyed to a fixed number of DNA molecules.

3. An input-output model was constructed of a molecular system operating under similar limitations and its properties examined.

4. By altering the values under which the system operated it was possible to examine the ways in which the system could grow. Patterns emerged for both limited and indefinite growth, both ultimately depending on the supply of molecules with a short half-life.

5. The pattern of indefinite growth which most nearly resembled that of the long neuron was one in which the deficiencies in labile molecules encountered by an extending system were met by transfer of similar molecules from adjacent unextended systems. The extended system, however, became liable to contract molecular debts whose magnitude was related to the degree of extension of the system.

6. A series of comparisons were drawn between the properties of the model and the observed morphological, biochemical and physiological characteristics of neural tissue. The coincidences were found to be sufficiently numerous to suggest that models of this type may be useful in correlating morphological and biochemical findings in the nervous system and in the design of experiments.

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Smart, I.H.M. The molecular economics of the long neuron. Helgolander Wiss. Meeresunters 9, 344–355 (1964). https://doi.org/10.1007/BF01610048

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  • DOI: https://doi.org/10.1007/BF01610048

Keywords

  • Molecular System
  • Neural Tissue
  • Protein Metabolism
  • Extended System
  • Similar Limitation