Neural histology and neurogenesis of the human fetal and infant brain

The human brain develops slowly and over a long period of time which lasts for almost three decades. This enables good spatio-temporal resolution of histogenetic and neurogenetic events as well as an appropriate and clinically relevant timing of these events. In order to successfully apply in vivo neuroimaging data, in analyzing both the normal brain development and the neurodevelopmental origin of major neurological and mental disorders, it is important to correlate these neuroimaging data with the existing data on morphogenetic, histogenetic and neurogenetic events. Furthermore, when performing such correlation, the genetic, genomic, and molecular biology data on phenotypic specification of developing brain regions, areas and neurons should also be included. In this review, we focus on early developmental periods (form 8 postconceptional weeks to the second postnatal year) and describe the microstructural organization and neural circuitry elements of the fetal and early postnatal human cerebrum.

Suppression of Smad-1 mRNA expression level by Smad-2 likely control dichotomy of NF-κB and Smads mediated activation

The aim of this study was to find out how NF-κB and Smad-mediated signaling influenced the expression of astrogliogenic versus neurogenic markers of brain development in U4C cells which were either enriched (Tg Jak-1) or deprived in Jak-1 molecule (Jak-1 KO). Genetically modified U4C cells were transfected with NF-kB reporter plasmid in order to follow its activation when cells were cotransfected with different combinations of Smads constructs. In wild type cells no significant activation of NF-κB was observed while genetically modified cells exhibited somewhat different pattern of NF-κB activation depending on the Smad constructs combination used. The absence of NF-κB activation in Jak-1 transgenic cells transfected with Smad-1 plus Smad-3 was accompanied by the appearance of apoptotic cells as revealed by DAPI staining. Smad-1 expression was undetectable in Jak-1 transgenic cells and was downregulated in wild type cells upon transfection with Smad-2. The absence of p65 nuclear translocation in Smad-2 transfected cells and the presence of Smad-4 in nucleus of the same cells indicates dichotomy in NF-κB and Smads mediated signaling pathways. The significance of this study is that helps to elucidate the point of collaboration among three different signaling pathways - Jak-1 mediated cytokine signaling, NF-κB and Smads mediated pathways.

Nitrinergic neurons in the developing and adult human telencephalon: transient and permanent patterns of expression in comparison to other mammals

A subpopulation of cerebral cortical neurons constitutively express nitric oxide synthase (NOS) and, upon demand, produce a novel messenger molecule nitric oxide (NO) with a variety of proposed roles in the developing, adult, and diseased brain. With respect to the intensity of their histochemical (NADPH-diaphorase histochemistry) and immunocytochemical (nNOS and eNOS immunocytochemistry) staining, these nitrinergic neurons are generally divided in type I and type II cells. Type I cells are usually large, intensely stained interneurons, scattered throughout all cortical layers; they frequently co-express GABA, neuropeptide Y, and somatostatin, but rarely contain calcium-binding proteins. Type II cells are small and lightly to moderately stained, about 20-fold more numerous than type I cells, located exclusively in supragranular layers, and found almost exclusively in the primate and human brain. In the developing cerebral cortex, nitrinergic neurons are among the earliest differentiating neurons, mostly because the dominant population of prenatal nitrinergic neurons are specific fetal subplate and Cajal-Retzius cells, which are the earliest generated neurons of the cortical anlage. However, at least in the human brain, a subpopulation of principal (pyramidal) cortical neurons transiently express NOS proteins in a regionally specific manner. In fact, transient overexpression of NOS-activity is a well-documented phenomenon in the developing mammalian cerebral cortex, suggesting that nitric oxide plays a significant role in the establishment and refinement of the cortical synaptic circuitry. Nitrinergic neurons are also present in human fetal basal forebrain and basal ganglia from 15 weeks of gestation onwards, thus being among the first chemically differentiated neurons within these brain regions. Finally, a subpopulation of human dorsal pallidal neurons transiently express NADPH-diaphorase activity during midgestation.

Nucleus subputaminalis (Ayala): the still disregarded magnocellular component of the basal forebrain may be human specific and connected with the cortical speech area

The small magnocellular group located within the rostrolateral extension of the basal forebrain was named and described as the nucleus subputaminalis in the human and chimpanzee brain by Ayala. Analysis of cytoarchitectonic and cytochemical characteristics of this cell group has been largely disregarded in both classical and more current studies. We examined the nucleus subputaminalis in 33 neurologically normal subjects (ranging from 15 weeks of gestation to 71 years-of-age) by using Nissl staining, choline acetyltransferase immunohistochemistry, acetyl cholinesterase histochemistry and nerve growth factor receptor immunocytochemistry. In addition, we applied reduced nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry and calbindin-D28k immunocytochemistry in three neurologically normal subjects. At the most rostrolateral levels we describe the previously poorly characterized component of the lateral (periputaminal) subdivision of the subputaminal nucleus, which may be human specific since it is not described in non-human primates. Moreover, we find the human subputaminal nucleus best developed at the anterointermediate level, which is the part of the basal nucleus that is usually much smaller or missing in monkeys. The location of subputaminal cholinergic neurons within the frontal lobe, the ascension of their fibers through the external capsule towards the inferior frontal gyrus, the larger size of the subputaminal nucleus on the left side at the most rostral and anterointermediate levels and the most protracted development among all magnocellular aggregations within the basal forebrain strongly suggest that they may be connected with the cortical speech area. These findings give rise to many hypotheses about the possible role of the subputaminal nucleus in various neurodegenerative, neurological and psychiatric disorders, particularly Alzheimer's disease and primary progressive aphasia. Therefore, future studies on the basal forebrain should more carefully investigate this part of the basal nucleus.

C-pathway polysialogangliosides are transiently expressed in the human cerebrum during fetal development

Gangliosides are assumed to play a crucial role in processes of cellular recognition and interaction important for neural development. They are designated as cytochemical markers of neuronal maturation, as striking changes in the ganglioside pattern parallel the nervous system development. Of particular interest to us are numerous studies that reported during migration of postmitotic neurons and axon formation in developing avian and mammalian brains a transient accumulation of highly sialylated c-pathway gangliosides. However, it has thus far been thought that c-pathway gangliosides do not appear in the human cerebrum; their absence could be somehow interpreted in the light of an evolutionary trend in the pattern of brain gangliosides: by increasing the phylogenetic scale this pattern changes by an accretion of less sialylated gangliosides and switches from c- via b- to a-series, respectively. The present study presents both biochemical and immunocytochemical evidence for the existence of c-pathway gangliosides in the human cerebrum during prenatal life, and their localization in discrete neuronal populations and growing axonal pathways.

Transient fetal structure, the gangliothalamic body, connects telencephalic germinal zone with all thalamic regions in the developing human brain

Previous studies reported that telencephalic proliferative zones contribute to the development of the pulvinar thalamic nucleus in the human brain (Rakic and Sidman [1969] Z. Anat. Entwicklungsgesch. 129:53-82). The present study examined their possible contribution to the development of other thalamic nuclei. Postmortem brain tissue from human fetuses ranging between 10.5 and 40 weeks of gestation (wg) was processed by Nissl staining, Golgi impregnation, and MAP2 (microtubule-associated protein 2) immunocytochemistry. The gangliothalamic body, suggested to serve as a conduit for cells migrating from the ganglionic eminence to the thalamus, was found in the period from 15 to 34 wg in all rostrocaudal thalamic regions, particularly at the level of the anterior nuclear complex, mediodorsal and pulvinar nucleus, and in addition, the lateral geniculate nucleus. In Nissl-stained sections, the gangliothalamic body is a thin cellular layer situated beneath the thalamic surface, near the telencephalo-diencephalic junction. In Golgi- and MAP2-stained sections, it is a stream of mostly bipolar cells extending from the ganglionic eminence to the medial thalamus. In addition, MAP2-immunoreactivity confirms the neuronal nature of its cells. The present study further supports the hypothesis that certain neurons migrate from the ganglionic eminence to the thalamus through the transient gangliothalamic body during fetal development. Moreover, our data indicate that both the association (mediodorsal and pulvinar), as well as the anterior (limbic) and specific relay nuclei are potential recipients of the telencephalic neurons.

Volume and number of neurons of the human hippocampal formation in normal aging and Alzheimer's disease

In order to observe changes owing to aging and Alzheimer's disease (AD) in the volumes of subdivisions of the hippocampus and the number of neurons of the hippocampal formation, 18 normal brains from subjects who died of nonneurological causes and had no history of long-term illness or dementia (ten of these brains comprised the aged control group) and 13 AD brains were analyzed. An optimized design for sampling, measuring volume by using the Cavalieri principle, and counting the number of neurons by using the optical disector was implemented on 50 microns-thick cresyl-violet sections. The mean total volume of the principal subdivisions of the hippocampal formation (fascia dentata, hilus, CA3-2, CA1, and subiculum) showed a negative correlation with age in normal subjects (r = -0.56, 2P < 0.05), and a 32% mean reduction in the AD group compared with controls (P < 0.001). This finding supports the measurement of the coronal cross-sectional area and the volume of the hippocampal formation in the clinical diagnosis of AD. There was an inverse relationship between the age of normal subjects and the number of neurons in CA1 (r = -0.84, 2P < 0.0001) and subiculum (r = -0.49, 2P < 0.05) but not in other subdivisions. Pronounced AD-related reductions in neuron number were found only in the subiculum and the fascia dentata. Compared with controls, both losses represented 23% of neurons (P < 0.05). These results 1) confirm that AD is a qualitatively different process from normal aging and 2) reveal the regional selectivity of neuron loss within the hippocampal formation in aging and AD, which may be relevant to understanding the mechanisms involved in the neuron loss associated with the two processes.

Laminar distribution of neuropeptide Y-immunoreactive neurons in human prefrontal cortex during development

Neuropeptide Y (NPY) is present in neurons of the adult human cerebral cortex. In view of the reported roles of NPY in the central nervous system in health and during certain disease conditions, we have studied normal development of NPY immunoreactivity (-ir) in the human prefrontal cortex (PFC), Brodmann areas 9 and 46. Twenty-six specimens ranging from the ages of 14 postovulatory weeks to 34 years exhibited patterns that revealed six periods in the development of the laminar distribution and density of NPY-ir neurons. Changes during prenatal and perinatal periods reflect the onset, development, and resolution of the transient fetal telencephalic compartments, including the subplate zone, in which NPY-ir neurons are especially abundant. Before the age of 1 year, the majority of NPY-ir neurons were found in the subplate zone, whereas, after 1 year, the majority were seen in the cortical layers. This is in contrast with the human visual cortex, where the majority of NPY-ir neurons were still located in the white matter. The density of cortical NPY-ir neurons increased in the fifth developmental period (ages 4-7 years), coinciding with the increase of cortical volume and marked progression of cognitive functions. The adult pattern of a relatively low density of cortical NPY-ir neurons was reached in period 6 (from about 8 years), when individual variation also became apparent. Our data point to a protracted maturation of NPY-ir in the human PFC and to different distribution patterns of NPY-ir neurons in different cortical areas.

Transient patterns of calbindin-D28k expression in the developing striatum of man

In fetal and adult human brains, calbindin immunoreactivity (CB-ir) of neostriatal neuropil showed inhomogeneous pattern. A mosaic of CB-ir neuropil patches matching the acetylcholinesterase (AChE)-reactive patches and most of the encapsulated cell-dense islands was distributed in a lighter stained background matrix. During infancy, the pattern of CB expression changed from one of CB-rich patches to one of CB-poor striosomes and rich matrix. Furthermore, we observed a steady development of population of medium-sized neurons in the striatal matrix; in addition, a transient CB-expression was found in cells of the ganglionic eminence and presumably in a subset of striatal interneurons.

Transient neuronal population of the internal capsule in the developing human cerebrum

The present study reveals the presence of a distinct group of cells, resembling reticular thalamic neurones, in the internal capsule during fetal development. This cell population rapidly decreases in size during early infancy and few cells are apparent in the 1-year-old infant. Internal capsule cells are well differentiated, multipolar or polymorphous, AChE (acetylcholinesterase)-reactive neurones. The following specific molecular markers were demonstrated in the neurones of the internal capsule: MAP2 (microtubule-associated protein 2), somatostatin, calbindin-D28K and p75 low-affinity NGF (nerve growth factor) receptor. A group of neurones described here corresponds to the perireticular thalamic nucleus found in certain mammalian species, hitherto unidentified in the primate brain, which may play an important role during development.

Ontogenesis of goal-directed behavior: anatomo-functional considerations

Recent neuroanatomical and neurophysiological studies in man have revealed ontogenetic events which coincide with broadly defined phases of behavioral and cognitive development. During the early fetal period, early produced neurons make initial synapses which form the basis for the earliest electrical activity of the human brain. The overall immaturity of neuronal connections, in particularly in cortical areas, correlates with the absence of any behavioral pattern or goal-directed movements. In the late fetus and preterm infant, transient accumulation of major afferent pathways, the presence of transient layers (subplate zone) and transient pattern of transmitter-related organization form the neurological basis of cortical electric responses as well as transient behavioral states and sleep patterns. Parallel to the profound structural and chemical reorganization of the human cerebrum during the first 6 postnatal months there is a disappearance of transient behavioral and motor patterns. The previously close spatio-temporal correlation between these events becomes progressively looser. The overproduction of circuitry elements during the subsequent period peaks in associative cortex between 1 and 2 years of age, corresponding to the emergence of skilled actions and cognitive functions. After the elimination of some circuitry elements after the second year of life, the prolonged maturation of goal-directed behavior and the protracted emergence of different cognitive functions correlates with the development plateau of synapse production which can be seen up to 16 years of age. Parallel to the prolonged maturation of postsynaptic elements, there are well defined maturational changes in the chemical properties of associative pyramidal neurons of cortical layer III. These findings correspond to the prolonged maturation of movement-related brain macropotentials as well as other cognition-related potentials, where the last prominent changes were seen after 10 years of age. Although the coincidence of the developmental events does not necessarily mean a causal relationship, the combination of structural and physiological data opens new vistas for the further investigation of the neurobiological basis of goal-directed movement and cognitive behavior.

Early areal differentiation of the human cerebral cortex: entorhinal area

The early cytoarchitectonic specialization and area-specific differentiation of the prospective entorhinal cortex were studied in the postmortem human fetal brains (9.5-13.5 postovulatory weeks). At 10 weeks, using the Golgi method, we saw the appearance of area-specific large neurons (promoter neurons) with widely bifurcating apical dendrites situated at the outer margin of the cortical plate of the prospective entorhinal cortex. The analysis of the serial Nissl-stained sections revealed the concomitant appearance of a one-cell-thick layer (monolayer) at the interface between the cortical plate and the marginal zone and multilaminated spread of the deep part of the cortical plate. This is the earliest sign of area-specific cytoarchitectonic differentiation of all pallial regions characterized by the presence of the typical cortical plate. The first subareal differentiation within the entorhinal cortex begins at 13 postovulatory weeks with uneven development of fiber-rich lamina dissecans, which separates two cellular laminae principals (externa and interna), and with the appearance of characteristic cell islands of the prospective layer II. At rostral levels, cell islands begin to develop in the rostromedial entorhinal area at the subpial depths where large promoter neurons reside. At intermediate levels, both lamina dissecans and lamina principalis interna are well delineated. At caudal levels, lamina principalis interna is continuous with the upper subplate zone of the adjacent neocortex. Both area-specific neurons (promoters) and fiber-rich (afferent) strata develop synchronously during the earliest areal differentiation of the cerebral cortex. The precocious lamination of the cortical plate is the crucial event in the histogenesis of the entorhinal cortex.

[The present status and perspectives of the University of Zagreb Medical School]

Ranked as the leading school of medicine in Croatia, University of Zagreb School of Medicine has succeeded to maintain the continuity of the high quality teaching process despite of the heritage of the socialist educational system and the harsh times of war. With the introduction of the six-year curriculum, where the "problem-solving" method is given prominence to, the school has fulfilled its requirements to meet the European standards of medical education. Teaching of the basic medical sciences is faced predominantly with the problems of obsolete equipment, whereas the quality of the education of the clinical subjects has not yet reached the desirable standards in all segments. Scientists from the University of School Zagreb of Medicine contribute to the overall scientific output of the Republic of Croatia with 10 to 20%, in addition to appearance of significant number of papers published in the international periodicals. According to the latest faculty roster, the number of full professors with teaching appointments is much too excessive. The University of Zagreb School of Medicine sees its main goal in the improvement of the quality of the teaching process. This goal is to be accomplished through introduction of the new courses (molecular biology, neuroscience, emergency medicine, ecology, medical economy etc.), improvement of the teaching methods, as well as through high standards of teaching the elective courses. Overall number of exams is also to be reduced in due time, whereas the future curriculum should provide a comprehensive medical teaching, with students actively participating in the teaching process through the first-hand experience with patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuroscience in Yugoslavia

This survey is a personal account of the present status of neuroscience in Yugoslavia within the context of recent upheavals in Eastern Europe. The current situation in Yugoslavia, characterized by the absence of a Federal Ministry of Science and a poor scientific communication between federal states (republics), does not allow a comprehensive overview of neuroscience at the federal level. Even more difficult is to envisage the prospects of Yugoslav neuroscience in the light of European integration. Several problems serve to illustrate the present situation concerning Yugoslav neuroscience. First, the weakness of the self-organization of science in Yugoslavia during the past 20 years is still the most important denominator in the current trend of neuroscience. Second, different Yugoslav republics have significantly different systems of science funding and evaluation, which reflect very plainly different levels of democratic (and socioeconomic) changes that were attained during 1990. Third, due to the different numbers of trained scientists, facilities and equipment, funds and levels of international scientific cooperation there are major differences between republics in the tempo of progress towards real achievements in science. Finally, the present explosive development of neuroscience and the proclamation of the 'Decade of the Brain' will hopefully stimulate Yugoslav neuroscientists to seek better programmes of neuroscience research and to improve the extent and quality of international cooperation.

Prenatal and perinatal development of the somatostatin-immunoreactive neurons in the human prefrontal cortex

The earliest somatostatin-immunoreactive (SS-Ir) perikarya of the human fetal frontal cortex appear in the transient subplate zone at 22 weeks of gestation. Around 32 weeks of gestation there is an increase in the number of SS-Ir neurons at the interface between the subplate zone and the cortical plate. The newborn-cortex shows decline in the overall number of SS-Ir neurons parallel to the appearance of SS-Ir neurons in the superficial layers. In conclusion, the subplate neurons are the source of the earliest peptidergic activity in the cortex. Furthermore, the distribution and density of peptidergic neurons undergo significant reorganization during the perinatal development.

Structural basis of the developmental plasticity in the human cerebral cortex: the role of the transient subplate zone

We correlated neuroanatomical developmental parameters with sequential ultrasonography scans to reveal the structural basis of functional recovery after early focal hypoxic lesions of the human frontal lobe in premature infants. We studied the transient fetal subplate zone in the premotor and prefrontal cortex in premature, newborn, infant, and young adult brains by acetylcholinesterase (AChE) histochemical, Golgi, and immunocytochemical methods. The structural in vivo rearrangements of the cerebral wall after perinatal lesions were studied on serial real-time sector scans (5-MHz transducer). The subplate zone contains "waiting" axons and randomly oriented fetal neurons, its developmental peak is between 22 and 34 weeks of gestation, and it is present in the frontal cortex of newborns and disappears after the sixth postnatal month, but individual subplate-like neurons remain until adulthood. Ultrasonography revealed remarkable structural rearrangements of the cerebral wall when the hypoxic lesion occurred during the developmental peak of the subplate zone: anechoic cavities ("cysts") develop rapidly (within 3 weeks) in premature brains, the rebuilding of these lesions continues after birth, and cavities disappear around the 11th month. We propose that the transient population of "waiting" axons and cells of the subplate zone participate in the structural and functional plasticity of the human cerebral cortex after perinatal brain damage.

Early onset of synapse formation in the human hippocampus: a correlation with Nissl-Golgi architectonics in 15- and 16.5-week-old fetuses

The developmental status of some potential components of hippocampal circuitry was studied at the time of the emergence of the hippocampal cytoarchitectonic subfields. The laminar distribution of synapses as seen with electron microscopy was correlated with Golgi architectonics in 15- and 16.5-week-old human fetuses. A systematic electron microscopic analysis of the distribution of synapses demonstrated that they were restricted to the two zones bordering the cortical plate, viz. the marginal and subplate zones, which contain dendritic branches of pyramidal and large polymorphous non-pyramidal neurons. The density of synapses (number per unit area) was higher in the marginal zone than in the subplate zone. Most synapses were of the asymmetric axodendritic type, although some were symmetric axodendritic synapses. The possible origins of the axons forming these synapses are discussed. This study demonstrates that the human hippocampus shows an early onset of synapse formation, with a characteristic distribution of synapses in restricted laminae. The finding of early synapse formation is consistent with observations made in other cortical areas during development. The prevalence of synaptogenesis at a superficial level of the cortex seems, however, to be specific to the "archicortex".

Acetylcholinesterase in the human frontal associative cortex during the period of cognitive development: early laminar shifts and late innervation of pyramidal neurons

Laminar preferences in fibrillar acetylcholinesterase (AChE) staining change dramatically in the human frontal cortex during the first postnatal year and perikaryal reactivity is found only in non-pyramidal neurons. The AChE reactivity of layer III pyramidal cell bodies and surrounding fibrillar network begins to develop after the first postnatal year, increases gradually and reaches its peak intensity in young adults, displaying a cluster-like arrangement. These data suggest that AChE-rich elements participate in the innervation of cortical associative neurons and layers during the cognitive development in man.

Cytoarchitectonic parameters of developmental capacity of the human associative auditory cortex during postnatal life

In order to determine the developmental capacity of the human auditory cortex we studied the 'regressive' cytoarchitectonic events during perinatal and postnatal development: disappearance of fetal elements and cytoarchitectonic reorganization. Studies were done on Nissl-stained serial sections of human temporal cortex in the specimens ranging from 24 weeks of gestation to the 3rd postnatal year. The fetal layers were regularly found in the newborn in the posterior associative auditory cortex. The fetal subplate zone disappeared gradually over the first 3 postnatal months, indicating decline in the growth of the major cortical fibre systems. The fetal types of neurons have been found however also in older specimens in the associative auditory cortex. The auditory cortex also contains in the postnatal period some fetal elements which indicate the presence of prolonged anatomical developmental plasticity.

Serotonin and norepinephrine in the spinal cord of man

The content of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) and norepinephrine (NE) was analysed in 71 human spinal cords obtained post-mortem. The highest content of 5-HT, 5-HIAA and NE was found in the lumbar enlargement of the spinal cord. 5-HT and 5-HIAA content increased from fetal to adult spinal cord whereas the content of NE decreased. Characteristic segmental distribution of measured monoamines was present in adult spinal cord only. In two patients spinal cord lesion led to the reduction in spinal cord content of 5-HT, 5-HIAA and NE and loss of characteristic segmental distribution of these substances. These results are in general agreement with observations on spinal cord of different animal species.

Development of Cajal-Retzius cells in the human auditory cortex

We analysed the differentiation and areal distribution of Cajal-Retzius (C-R) cells in the human auditory cortex using acetylcholinesterase (AChE) technique on specimens ranging between 10 weeks of gestation (w.) and the 3rd postnatal month. AChE-reactive cells appear in the marginal zone of the prospective auditory cortex as early as 10 1/2 weeks of gestation. Analysis of primary and associative auditory cortex in subsequent stages of gestation and during early postnatal life reveals an age-dependent decrease in cell-packing density of C-R cells and an increase in thickness of the marginal zone. Large AChE-reactive cells were readily found in the early postnatal cortex. These and our previous data on the human frontal associative cortex demonstrate the presence of AChE-reactive C-R cells in both primary and associative cortical areas during late fetal and early postnatal life. The postnatal changes in the morphology and distribution of AChE-reactive C-R cells may serve as cellular parameters of the postnatal cortical maturation in man.

Prenatal development of nucleus basalis complex and related fiber systems in man: a histochemical study

To provide parameters for study of the "cholinergic" innervation of a human fetal cerebrum, we have analyzed the prenatal development of histochemical reactivity in the nucleus basalis complex (a magnocellular complex known to contain a high concentration of cholinergic perikarya). Brains from fetuses and premature infants ranging between 8 and 35 weeks of gestation were frozen cut and processed by the thiocholine method for the demonstration of acetylcholinesterase activity. Since no consistent results were obtained with inhibitors on the material younger than 15 weeks, the histochemical reactivity for early stages was expressed as the total cholinesterase reactivity. The first sign of histochemical differentiation of the basal telencephalon is the appearance of a dark cholinesterase reactive "spot" situated between the developing lenticular nucleus and basal telencephalon surface as early as 9 weeks of gestation. The first cholinesterase reactive bundle connects this reactive area (nucleus basalis complex anlage) with the strongly reactive fiber system situated along the dorsal side of the optic tract. During the next "stage" (10.5 weeks), there is a significant increase in the size of the nucleus basalis complex and strongly cholinesterase reactive neuropil occupies the sublenticular, diagonal and septal areas. At this stage we have seen two new cholinesterase-reactive bundles: one well developed cholinesterase reactive fiber stratum approaching (but not penetrating) the neocortical anlage through the external capsule and another minute bundle running towards the medial limbic cortex through the precommissural septum. The supraoptic fiber system can be traced now to the pregeniculate area and the tegmentum. At 15 weeks, the first acetylcholinesterase reactive perikarya appear and the nucleus basalis complex anlage becomes segregated into several strongly reactive territories, corresponding in position to the medial septal, diagonal and basal nuclei as defined on adjacent Nissl stained sections. At this stage, fibers from the nucleus basalis complex enter the "white" matter of frontal, temporal, parietal and occipital parts of the cerebral hemisphere via the external capsule. Between 15 and 18 weeks, acetylcholinesterase fibers spread throughout the "white" matter of the cerebral hemisphere. In the next "stage" (18-22 weeks), strongly reactive fibers can be followed from the nucleus basalis below the putamen and through the external capsule to the transient, synapse-rich subplate zone of frontal, temporal, parietal and occipital cortices.(ABSTRACT TRUNCATED AT 400 WORDS)

Development of the lateral amygdaloid nucleus in the human fetus: transient presence of discrete cytoarchitectonic units

The cytoarchitectonic development of the lateral amygdaloid nucleus has been studied on Nissl-stained sections through brains of human fetuses ranging between 11 to 24 weeks of gestation. The first sign of cytoarchitectonic inhomogeneity of the lateral amygdaloid nucleus is the appearance of 2-3 ovoid cell clusters around 12 weeks of gestation. Between 12.5-16 weeks of gestation, the ventral part of the lateral amygdaloid nucleus contains 7-11 columnar cell clusters separated by "septa" of lower cell-packing density. These columnar clusters, stretching in the rostrocaudal direction, appear on cross-section as ovoid structures elongated in the ventrodorsal direction. In subsequent development (16-24 weeks of gestation) this distinct columnar appearance becomes less obvious, owing to the disappearance of "septa" along the dorsal edges of cellular clusters. This process begins first in the medial part of the columnar field. As a result, the cytoarchitectonic units gradually fuse into a homogeneous grey mass. However, the ventral part of the columnar field retains an undulated appearance throughout late gestation, showing multiple indentations as a sign of former cytoarchitectonic inhomogeneities. In conclusion, the fetal lateral amygdaloid nucleus contains a number of cytoarchitectonic "moduli" which could serve as a new parameter for an estimation of histogenetic maturity of the human amygdala. This transient cytoarchitectonic inhomogeneity could be a sign of the temporary predominance of one characteristic afferent-efferent system during a given developmental stage. Alternatively, it could reflect a clustered type of neurogenesis.

Prenatal and perinatal development of radial cell columns in the human 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)

The development of medial geniculate body in man: changes in the cholinesterase (CHE) activity during fetal and perinatal life

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.

Development of acetylcholinesterase (AChE) staining in human fetal auditory cortex

In this study acetylcholinesterase (AChE) staining methods have been used to demonstrate the development of the prospective afferent fibres of auditory cortex in human fetuses ranging between 8 and 28 weeks of gestation. Earliest AChE positive staining was found in fetuses at 20--24 weeks in the neuropil of the marginal zone and throughout subplate layer of the auditory cortex. On the basis of this characteristic AChE staining pattern, the auditory cortex may be delineated from surrounding cortical areas. At 24--26 weeks, during intensive lamination of the cortical plate, AchE-positive reaction appears in the deep part of the cortical plate. In the oldest fetuses (28 weeks) a columnar pattern of vertical, darkly stained zones was seen in the middle third of the cortical plate. We conclude that AChE staining is characteristically distributed within cytoarchitectonic compartments and 'synaptic' layers of the developing auditory cortex. The AChE-positive layers coincide with the laminar pattern of synpatogeneis. Thus, AChE-positive reaction during development may serve as a parameter of cortical afferent (thalamic?) innervation of the auditory cortex. In addition, AChE reactivity may indicate the specific transmitter nature of the afferent fibres in the auditory cortex.

The laminar organization of the prospective auditory cortex in the human fetus (11--13.5 weeks of gestation)

The prospective auditory cortex was analysed in human fetuses at 11--13,5 post-ovulatory weeks with Nissl, Golgi and E.M. techniques. At 11--12 weeks, marginal, cortical plate, intermediate, subventricular and ventricular layers were recognized. Post-migratory neurons with developing dendrites were seen in marginal layer, cortical plate and superficial part of the intermediate zone only. At 12--13,5 weeks the superficial part of the intermediate zone is transformed into the true cortical layer--"subplate layer"--characterized by maturing neurons with growing dendrites, fine axonal arborization and low cell density. The neuronal circuitry elements are thus present very early in the prospective auditory cortex and distributed throughout the deep cortical plate of the "subplate layer" corresponding to the synaptic territory of other areas of the human fetal cortex.