Summary
The motor cortex of white mice has been studied from the first postnatal day up to an age of three weeks electronmicroscopically and with the Golgi method. Special attention has been paid to the dendritic organization in the molecular and outer granular layers. The following observations were made:
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1.
Branching of the apical dendrites of neurons of the second layer occur already from the third day, whereas the basal dendrites start branching only at the end of the first week.
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2.
The deeper laying cells of the second layer mature at an earlier stage than the more superficial cells.
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3.
Immediately after birth, the first axodendritic synapses are found on the large stem dendrites. Their spines develop by the end of the first postnatal week. The spines of the apical dendrites develop before those of the basal ones.
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4.
Axosomatic synapses are found on the cell bodies of the external granular layer in the second postnatal week.
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5.
The development of the apical dendrites from the deeper layers (III–V) is an important factor in the maturation of the external layers. These dendrites have acquired their final number of spines by the end of the second week.
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6.
During their development the dendrites of the third to fifth layer show intimate contact by mutual indentation. The cells of the second layer complete their maturation by the end of the third week.
Zusammenfassung
Der motorische Cortex von weißen Mäusen wurde vom ersten Tag nach der Geburt bis zum Alter von 3 Wochen mit Hilfe der Golgi-Methode und elektronen-mikroskopisch untersucht. Besonderes Interesse galt seiner dendritischen Organisation in Molekularis und äußerer Körnerschicht.
Die apikalen Dendriten der Nervenzellen der II. Schicht verzweigen sich nach dem 3. Tag, die basalen Dendriten am Ende der 1. Woche.
Die tiefgelegenen Zellen der zweiten Schicht reifen früher als die mehr oberflächlich liegenden Zellen. Die ersten axodendritischen Synapsen findet man unmittelbar nach der Geburt an den großen Stammdendriten. Ihre Dornen entwickeln sich am Ende der ersten postnatalen Woche. Die synaptischen Dornen der apikalen Dendriten entwickeln sich früher als jene der basalen.
Die axosomatischen Synapsen finden sich an den Zellen der äußeren Körnerschicht im Laufe der 2. Woche. Einen wichtigen Faktor in der Ausreifung der beiden oberen Schichten stellt die Entwicklung der apikalen Dendriten der unteren Schichten (III–V) dar. Diese Dendriten entwickeln ihren endgültigen Dornenbesatz am Ende der 2. Woche.
Die Dendriten der Schichten III–IV verzahnen sich im Laufe der Entwicklung eng miteinander. Ihre Ausreifung entspricht am Ende der 3. Woche den Verhältnissen bei der erwachsenen Maus.
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Aided by grant (R-209-67) from the United Cerebral Palsy Research and Educational Foundation.
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Meller, K., Breipohl, W. & Glees, P. Synaptic organization of the molecular and the outer granular layer in the motor cortex in the white mouse during postnatal development. A Golgi- and electronmicroscopical study. Z. Zellforsch. 92, 217–231 (1968). https://doi.org/10.1007/BF00335649
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DOI: https://doi.org/10.1007/BF00335649