The sequential development and growth of the subcortico-cortical fibres have been studied by means of acetylcholinesterase (AChE; acetylcholine acetylhydrolase; EC 3.1.1.7) histochemistry on the serial sections obtained from brains of human fetuses ranging from 10 to 28 weeks of gestation. It was found that thalamic and basal telencephalic fibres approaching the fetal auditory cortex have very strong AChE reactivity during a prolonged period of growth. In the youngest fetuses (10.5 weeks) a prominent fibre system was seen emerging from the ventroposterior thalamic territory while the auditory neopallium was free of AChE staining. In older fetuses (16–18 weeks) AChE-positive fibres originating in the ventroposterior thalamus and basal telencephalon penetrate the ‘subplate layer’ of the auditory cortex. On the basis of AChE reactivity of the ‘subplate layer’ the auditory cortex can be delineated from the surrounding neocortical areas. In the oldest fetuses (22–28 weeks) AChE-positive fibres of thalamic origin penetrate the developing cortical plate of the auditory cortex.
The aim of this study was to analyse cytoarchitectonic development of radial cell columns in the human auditory cortex and to correlate these 'ontogenetic' cell columns with the 'adult' pattern of radial cell arrangement. For this cytoarchitectonic analysis, brains were obtained from human fetuses and infants ranging between 9 weeks of gestation and third postnatal month. Plastic and celloidin sections containing prospective auditory areas TC, TB and TA of Economo & Koskinas were stained by Nissl method. In youngest fetuses (8-13 weeks) radially oriented cell columns (1-3 cell wide 'ontogenetic' columns) were found in the whole thickness of the developing cortical plate. During the next developmental stage (13-26 weeks of gestation), radial cell columns were present in the superficial part of the cortical plate, while the deep part of the cortical plate showed a variable cell arrangement due to the formation of the subplate layer (13-15 weeks). The appearance of the pale bands, and development of the prospective granular layer (18-26 weeks). After 28 weeks, parallel to the intensive areal cytoarchitectonic differentiation and ingrowth of callosal afferents, there was a gradual regional rearrangement in the ontogenetic pattern of vertical cell columnation. In the area supratemporalis granulosa (TC), radial columnation was observed as increased granularity and the appearance of short cords composed of drop-like cells. In the area supratemporalis simplex (TB) there was a progressive differentiation of elongated cell columns, intervening fibrillar stripes with appearance of pyramidal cell cords in layers III ('organ pipe' formations).(ABSTRACT TRUNCATED AT 250 WORDS)
In the present study cholinesterase histochemical (ChE) techniques have been used to demonstrate differentiation and maturation of the medial geniculate body (MGB) in the human fetuses (ranging between 10.5 to 28 weeks) and infants (premature and three postnatal months). In the youngest specimens examined (10.5 to 15 weeks) moderate ChE activity was found in the neuropil of MGB. In the next developmental stage ChE activity is significantly increased with stronger reactivity in the peripheral part of MGB. In the fetuses between 22 to 26 weeks of gestation peak ChE reactivity was observed in MGB. Reactivity is strong and homogeneous. In the premature infant (28 weeks and older) ChE reactivity becomes inhomogeneous and irregular with appearance of ChE positive bands in the moderately stained MGB matrix. In addition, strongly ChE reactive cell bodies can be discerned. In 3-month-old infant brain we have found significant decrease of ChE reactivity in the neuropil of the MGB. In conclusion we can say that MGB shows very strong, transient ChE reactivity during second half of gestation. Since a great majority of ChE reactivity disappears during later postnatal development, it is very likely that strong fetal activity is related to the histogenetic events and maturation of MGB.
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