Veena Bijlani

Cytodifferentiation and developing neuronal circuitry in the human lateral geniculate nucleus

The developing neural substrate in dorsal lateral geniculate nucleus of human fetuses and premature, full‐term and postnatal infants, has been analysed using rapid Golgi impregnation, computerized image analysis, electronmicroscopy, and immunocytochemical method for localization of γ‐aminobutyric acid. Nuclear and cytoplasmic neuronal maturation is observed to extend over the entire period studied. Axodendritic synapses, presumably of retinal origin, are occasionally seen at 13–14 fetal weeks. They become increasingly apparent at 18–19 weeks. Dendrodendritic contacts are visualized at 15 weeks. Cortical terminals and occasional triadic contacts are evident around 21 weeks. The inhibitory interneurons containing γ‐aminobutyric acid are present in small numbers at 15–16 weeks; their numerical density increases considerably at 17 weeks but decreases thereafter. The presence of γ‐aminobutyric acid containing nerve cells and synaptic triads is indicative of the formation of inhibitory circuitry. At 15–16 weeks neurons are mostly bipolar although different forms of multipolar cells may be seen. By 24 weeks the radiated and bitufted multipolar neurons, neurons with beaded dendrites and neurons with axon‐like dendritic processes are identifiable. There are no apparent differences in differentiation of neurons between the cranial and caudal parts of dorsal lateral geniculate nucleus. At 15–16 weeks, however, the cells of prospective magnocellular zone appear to be more mature than do the cells in the parvocellular zone. The neuronal soma increases continuously in size. Dendrite development starts at 15–16 weeks of gestation, thereafter the increase in number of their branches and their length is observed. Between 15–16 and 24 weeks, spines and filiform processes appear first on the proximal shafts of the dendrites and subsequently on their distal portion. There is increase in the number of filiform processes and hair‐like appendages on geniculate neurons of premature infants born at 32 and 37 weeks of gestation and of a 4‐day postnatal infant. Computerized quantitative data substantiate the progressive increase in growth parameters. The significance of comparative and functional aspect of the data is discussed.

Development of human lateral geniculate nucleus: An electron microscopic study

A qualitative and quantitative ultrastructural study has been carried out on lateral geniculate nuclei (LGN) of 21 human fetuses ranging in gestational age from 13–14 to 34–35 weeks. At the early age period of 13–15 weeks, LGN is characterized by immature cells with indented nuclei possessing multiple nucleoli and by a sparse neuropil. During the subsequent age periods studied progressive maturational changes lead to neurons having round nuclei with a single nucleolus and well‐developed cytoplasmic organelles as well as to an elaborate neuropil. Synaptic contacts which are seen for the first time at the age of 13–14 weeks are of retinogeniculate type. They show features of immature synapses and are located mainly on the juxtasomatic parts of dendrites. With increasing gestational age, the synapses increase in size, maturity, types and complexity; an acquisition of complex synaptic arrangement (triad) occurs by 20–21 weeks. Excitatory synapses appear earlier than do the inhibitory ones. Formation of retinogeniculate contacts precedes that of the corticogeniculate type.

Cytoarchitectural Development of the Human Dentate Nucleus: A Golgi Study

Golgi-stained sections of the human cerebellar dentate nucleus (DN) at various gestational ages were examined to study the dendritic proliferation and maturation of the DN neurons. Bipolar cells were seen at 14-15 weeks. By 19-20 weeks, three cell types were identifiable: bipolar, hemispheric and pyriform. The cells of the dorsomedial region matured earlier than those of the ventrolateral region. In addition to the above cell types, multipolar and nuclear boundary cells were observable at 24-25 weeks. The five cell types persisted during subsequent development. At no stage of development was any neuronal organizational pattern apparent. A remarkable dendritic proliferation occurred at 27-28 weeks. Spines and filiform processes were seen at 34 weeks of intrauterine life.

Substance P-immunoreactivity in the developing human retinogeniculate pathway

Substance P has been immunohistochemically localized in the human optic nerves and lateral geniculate nuclei during the prenatal period from 13-14 to 37 weeks of gestation. Substance P-immunoreactive fibres were present in the optic nerves and lateral geniculate nuclei in all these ages thereby providing direct evidence of this undecapeptide being associated with the retinogeniculate pathway. At 16-17 weeks, greater numbers of fibres were observed than in the later ages. It is likely that the reduction in number of optic nerve fibres seen quantitatively during prenatal life may partly be due to the loss of substance P fibres.

Effects of malnutrition on cell genesis and migration in developing brain in rats.

Abstract Rats were fed a diet containing either 5% (LP) or 25% (HP) casein throughout gestation. The animals, delivered by a cesarean section on the 21st day of gestation, were given a pulse of [3H]thymidine and killed 2 h later. No differences were observed in the mitotic index, but the labeling index of the ventricular zone cells of the lateral ventricle was higher in the case of litters of the LP dams. This we atribute to a disproportionate increase of the S phase in relation to the cell cycle in malnutrition. To study the effects of malnutrition on the programming of cell genesis, the dams were given [3H]thymidine on the 20th day of gestation, and the litters were killed on the 21st postnatal day. The labeled neurons reached the second layer of the cerebral cortex in both groups, indicating that the programming was not affected by gestational malnutrition. Postnatal undernutrition was induced by doubling the litter size. The cell generation cycle was prolonged in the undernourished animals. Not all phases, however, were evenly affected: S was prolonged, G2 was not affected, but G1 was shortened. The external granular layer maintained its proliferative activity in the undernourished animals beyond the stage it had ceased in the controls. The migration of the cerebellar granule neurons was slow. It is proposed that tardiness in the migration of the neurons may interfere with synaptogenesis.

Polyacrylamide as an infiltrating and embedding medium for vibratome sectioning of human fetal cerebellum containing Dil-filled axons

Polyacrylamide is widely used for the separation of proteins by electrophoresis. Here the usage of polyacrylamide as an infiltrating and embedding medium for vibratome sectioning of human fetal cerebellum containing DiI-filled axons is reported. The procedure is simple to implement and has several advantages: it does not require prior dehydration and clearing of tissue; it can be carried out at a low temperature of 4 degrees C; and the polyacrylamide neither dissolves the DiI nor does it interfere with the visualizing of DiI-filled profiles under fluorescence microscope.

Developing dentate nucleus in man a qualitative and quantitative study

SummaryHistological and quantitative studies were carried out in dentate nucleus (DN) of 14 human fetuses of gestational ages ranging from 10 weeks to 28 weeks in Nissl stained sections. The dentate nucleus was already well delineated at 11 weeks, but the adult profile was attained only by 27–28 weeks. The magnocellular dorsomedial region and the parvocellular ventrolateral region became apparent at 17–18 weeks. The numerical density of neurons showed a steady decline with advancing gestational age. However, the absolute neuronal count until 19–20 weeks was 367.1 × 103 followed by a count of 249.5 × 103 at 22–23 weeks. The reduction in the count between the two periods was significant and coincided with cell death which was striking between 19 and 23 weeks. The glial cell population continued to increase with advancing gestational age. The occurrence of significant neuronal cell death and its probable role in the developing human DN is reported for the first time.

Development of substance P, Leu-enkephalin and serotonin profiles in the lateral geniculate nuclear complex of albino rat.

Immunohistochemical studies for analysing the development of the profile of two peptides--substance P (SP) and Leu-enkephalin (Leu-ENK), and serotonin (SER)--have been conducted on the lateral geniculate nuclear (LGN) complex of albino rats at gestation day 18 and various postnatal age periods. SP immunoreactivity is found to increase from 1 day postnatal (DPN) up to 20 DPN and decrease thereafter, whereas the SER and Leu-ENK-immunoreactive fibres and terminals seen as occasional fibres at 1, 5, and 10 DPN are better visualized from 20 DPN and gradually increase up to 40 DPN. The possible role and significance of the changes seen in these putative neurotransmitters/neuromodulators with development are discussed.

Prenatal human lateral geniculate nucleus: a quantitative light microscopic study

Using morphometric methods, a quantitative study has been carried out on the lateral geniculate nucleus (LGN) of human fetuses ranging in gestational age from 13 to 38 weeks. The volume of the nucleus as well as the neuronal, glial and dead cell populations have been studied in Nissl preparations. While the volume of the LGN shows a progressive increase throughout the period of study, the age period of 15-20 weeks is identified as a period of spurt in volumetric growth. Neuronal density and total neuronal number fall continuously while glial density and total glial population show a steady increase with advancing gestational age. Pyknotic dead cells are seen throughout the period of study with a peak die off between 14 and 18 weeks. The study, for the first time, outlines the critical period for volumetric spurt and neuronal death in the developing human LGN.

Ultrastructure of marginal zone during prenatal development of human spinal cord

SummaryElectron microscopic studies were conducted in the marginal zone (lamina I) in human fetuses ranging from 8–25 weeks of gestational age. At 8 weeks the neurons have indented nuclei and sparse organelles in the cytoplasm. The neuropil shows contacts between the axons and dendritic profiles. Some of them are well defined synapses with post synaptic thickening and agranular spherical vesicles in the presynaptic terminal. At 18 weeks compactly packed organelles with long cisternae of rough endoplasmic reticulum could be visualized in the neuronal cytoplasm. At 25 weeks the neurons have heterochromatin patches in the nuclei. Axosomatic, dendrodendritic, axoaxonic, symmetrical, asymmetrical and multisynaptic contacts with agranular and dense core vesicles are seen at different sequential age periods.