Gliogenesis during embryonic development in the rat

Alpha-linolenic acid and its conversion to longer chain n-3 fatty acids: benefits for human health and a role in maintaining tissue n-3 fatty acid levels

There is little doubt regarding the essential nature of alpha-linolenic acid (ALA), yet the capacity of dietary ALA to maintain adequate tissue levels of long chain n-3 fatty acids remains quite controversial. This simple point remains highly debated despite evidence that removal of dietary ALA promotes n-3 fatty acid inadequacy, including that of docosahexaenoic acid (DHA), and that many experiments demonstrate that dietary inclusion of ALA raises n-3 tissue fatty acid content, including DHA. Herein we propose, based upon our previous work and that of others, that ALA is elongated and desaturated in a tissue-dependent manner. One important concept is to recognize that ALA, like many other fatty acids, rapidly undergoes beta-oxidation and that the carbons are conserved and reused for synthesis of other products including cholesterol and fatty acids. This process and the differences between utilization of dietary DHA or liver-derived DHA as compared to ALA have led to the dogma that ALA is not a useful fatty acid for maintaining tissue long chain n-3 fatty acids, including DHA. Herein, we propose that indeed dietary ALA is a crucial dietary source of n-3 fatty acids and its dietary inclusion is critical for maintaining tissue long chain n-3 levels.

Targetedin uterodelivery of a retroviral vector for gene transfer in the rodent brain

In vivo application of viral vectors for gene transfer is a commonly used tool in anatomical and functional studies, as well as in development of neuroprotective and restorative strategies for therapy. Although the most common route of administration is via direct injection into the brain parenchyma in adult animals, a number of short-term studies have been performed in the developing central nervous system. Here we investigated the long-term transgene expression following in utero delivery of a retroviral vector encoding for the green fluorescent protein (GFP) marker gene at embryonic days 14.5-17.5 using an ultrasound-guided injection system. Intraparenchymal injections of the ganglionic eminence were compared with vector delivery to the intracerebroventricular space. Injections into the ganglionic eminences resulted in a predominantly unilateral transduction localized to the forebrain, giving rise to GFP-positive (GFP+) neurons and astrocytes in the striatum, olfactory bulb, cortex and hippocampus. When the vector was injected into the lateral ventricle, on the other hand, widespread expression of GFP was seen throughout the brain. The total number of GFP+ cells in the striatum was estimated to be between 20,000 and 50,000 cells using a computerized stereological quantification tool. Phenotypic characterization of these transduced cells using confocal microscopical analysis showed that 64% were NeuN+ neurons, 14% APC+ oligodendrocytes and 15% glial cells labelled with GFAP, S100beta and Iba1, when the vector injection was performed at E14.5. Delivery into later embryos resulted in a reduction in neuronal profiles with a reciprocal increase in glial cells.

Brain development and assessing the supply of polyunsaturated fatty acid

Membrane lipids are necessary for structure and function of the developing nervous system. Rapid synthesis of brain tissue occurs during the last trimester of development of the human brain and the early postnatal weeks. This synthesis of brain structure involves the formation of complex lipids, many of which contain significant quantities of chain-elongated desaturated homologs of essential fatty acids. The present report discusses the implications of change in nutritional status on processes of brain development and metabolic events that involve lipids.

Small changes of dietary (n-6) and (n-3)/fatty acid content ration alter phosphatidylethanolamine and phosphatidylcholine fatty acid composition during development of neuronal and glial cells in rats

It has been suggested that the fat composition of infant formula should provide arachidonic acid [20:4(n-6)] and docosahexaenoic acid [22:6(n-3)] or increased alpha-linolenic acid [18:3(n-3)] to optimize the (n-3) and (n-6) fatty acid content of brain during infant development. This experiment examined the effects of feeding increased levels of 18:3(n-3), 20:4(n-6) and 22:6(n-3) on brain development in neonatal rats. Diets varying in (n-6) and (n-3) fatty acid content with or without 20:4(n-6) or 22:6(n-3), at levels proposed for infant formula, were fed to nursing dams from parturition and subsequently to weaned pups until 6 wk of age. Neuronal and glial cells were isolated from the frontal region, cerebellum and hippocampus of the brain. Fatty acid analyses of ethanolamine- and choline-phosphoglycerides indicated that small changes in the dietary (n-6)/(n-3) ratio significantly altered neuronal and glial membrane fatty acid composition. Brain regions and cell types varied in amount and rate of 20:4(n-6) and 22:6(n-3) accretion. Fatty acid composition of individual phosphoglycerides was distinct and exhibited changes with age. Inclusion of both 20:4(n-6) and 22:6(n-3) in the diet resulted in alteration of brain fatty acid composition reflecting the fatty acid composition of the diet. If analogous developmental changes occur in human brain, then these results imply that addition of 20:4(n-6) and 22:6(n-3) or a reduced 18:2(n-6):18:3(n-3) ratio in infant formula may result in fatty acid profiles of neuronal and glial cells in formula-fed infants similar to those observed in breast-fed infants.

Developmental fates and migratory pathways of dividing progenitors in the postnatal rat cerebellum

To investigate the developmental fates and the migratory pathways of dividing progenitors in both the white matter (WM) and the external granule layer (EGL) in the early postnatal rat cerebellum, a replication-deficient retrovirus carrying the beta-galactosidase gene (BAG) was injected into the deep cerebellar tissue or the EGL of postnatal rats to label dividing progenitors. After 1-3 days post-injection (1-3 dpi) of BAG into the deep cerebellar tissue of postnatal day 4/5 (P4/5) rats, labeled immature, unipolar cells were found mainly in the WM. From 4 to 6 dpi, similar cells appeared in the internal granule (IGL), Purkinje cell, and molecular layers, although about half of the labeled cells still resided in the WM and appeared immature. The first morphologically definable Bergmann glia, astrocytes, and oligodendrocytes were also observed. From 14 to 20 dpi, most labeled cells had developed into Bergmann glia, astrocytes, oligodendrocytes, and interneurons in their appropriate layers. When BAG injections were performed at P14, unipolar cells were initially observed, but the majority of these differentiated into myelinating oligodendrocytes in the WM and IGL by 17 dpi. Few immature cells were labeled by injections administered at P20, and these did not develop into mature glia, but into cells with lacy, fine processes, possible representing immature oligodendrocytes. In contrast, BAG-labeled progenitors of EGL produced only granule neurons. Thus, within the first 2 postnatal weeks, dividing progenitors in the WM migrate as immature cells into the cortex before differentiating into a variety of glia and interneurons. The genesis of oligodendrocytes continues through the 2nd postnatal week and largely ceases by P20. EGL cells do not produce glia, but only granule cells.

A neurochemical study of developmental impairment of the brain caused by the administration of cytosine arabinoside during the fetal or neonatal period of rats

Injection of pregnant rats with cytosine arabinoside (ara-C) (280 mg/kg) on day 15 of gestation caused a significant rise (about two times the control value) in monoamine concentrations (norepinephrine, dopamine, and serotonin) accompanied by a decrease (about 60% of the control) in the brain weight and DNA content in the cerebrum of the offspring at 60 days of age. When neonatal rats were injected with ara-C (30 mg/kg/day) for four consecutive days from the fourth to seventh days after birth, a decrease of DNA content per cerebellum and an elevation of monoamine concentrations in the cerebellum were found. However, the total content of each monoamine per cerebrum or cerebellum showed no difference from the control. These results suggest that monoaminergic neurons may remain intact, with normal monoaminergic synapses compressed into a small brain volume. The neonatal administration of ara-C caused an elevation of 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) (EC 3.1.4.37) activity and myelin protein content in the cerebellum, suggesting a relative increase in myelin concentration as a result of hypoplasia of granule cells.

In vitro transformation of rat brain cells by human adenovirus type 12

In vitro transformation of brain cells cultured from various age rats by human adenovirus type 12 (Ad-12) was studied. In cultured brain cells, five cell types could be identified light microscopically. In astrocytes, Ac-2 and Ac-1, astroprotein was demonstrated by immunofluorescence technique. In the former, intracytoplasmic microfilaments were recognized by electron microscopy. Undifferentiated cells (Ud), ependymoglioblasts (EGb) and Ac-1, grew prominently in cultures from young animals or of early passage levels. Ac-2 and fibroblasts were prominent in cultures from aged animals or of late passage levels. Transformed foci appeared within about 20 days after inoculation of Ad-12 and often located in close association with the sheets of Ac-1. Transformed cells morphologically resembled EGb or transitional cells from EGb to Ac-1. Transformation rate was high in cultures from young animals or of early passage levels. Subcutaneous transplantation of these cells into newborn rats procued tumors whose histology was similar to Ad-12-induced rat brain tumor. T-Ag were detected both in transformed and transplanted tumor cells. It was concluded, that the target cells of Ad-12 in vitro correspond with immature brain cells (EGb and/or transitional cells from EGb to Ac-1 cells.

Chronology of neuron development: animal studies and their clinical implications

Because different parts of the central nervous system form at different stages of development, there is not one critical period but many critical periods. Some neurons are formed around the time of closure of the neural tube: these include the motor horn cells of the spinal cord and some motor nuclei of the brain stem. Other neurons, most notably the granule cells of the cerebellum, olfactory bulb and hippocampus, are produced in great numbers after birth. This review focuses on the mouse, the species for which the most data on neurogenesis are available, and draws parallels with other species. The clinical significance of the chronology of neuron formation is discussed in the context of recent studies of experimentally-induced congenital brain damage.

Gliogenesis and ependymogenesis during embryonic development of the rat. An autoradiographic study

With the aid of [3H]thymidine autoradiography gliogenesis and ependymogenesis were studied in the brain of the rat during embryonic development. Gliogenesis was found to begin on day 17 of gestation in the caudal regions of the brain stem, and to spread rostrally. On days 20 and 21 of gestation gliogenesis reached a peak, and then declined. Ependymogenesis began earlier and showed the following pattern: day 14 of gestation in the 4th ventricle and cerebral aqueduct, day 15 in the 3rd ventricle, and day 17 in the lateral ventricles reaching a peak on different days in different sites. Both gliogenesis and ependymogensis continued up to the last day of gestation, day 22. Issues pertaining to gliogenesis and the formation of glioblasts, and the relationship between gliogenesis and ependymogenesis are discussed.

Light and electron microscopical investigations on the tanycyte differentiation during the perinatal period in the rat

The differentiation of tanycytes was studied light and electron microscopically during the perinatal period in rats, the time when functional connections between hypothalamus and hypophysis are established. The 3rd ventricle is slit-like between 16 and 18 days of the prenatal period. Its wall is formed by intensively proliferating matrix cells with apical processes, ovoid perikarya and a basal process. The ventral region of the 3rd ventricle becomes funnel-shaped on the 20th day of the prenatal period. As the cells differentiate, the apical process becomes shorter and broader. Moreover, on day 20 of prenatal life cells without apical processes appear. Their number increases during the postnatal period. The concentration of endoplasmic reticulum, mitochondria, polysomes, lipid droplets, dense bodies (lysosomes), lamellated and multivesicular bodies increases. Initially the cells are similar but from the 3rd day of postnatal life differentiation occurs in different regions of the infundibular recess. After the 5th day, there are no marked changes in the structure and distribution of these cells.

A light microscopic study of the developing human neural retina

Human embryonic and fetal eyes from 4 mm to 200 mm crown-rump length (26 days to 21 weeks of gestation) were studied in 0.75-micron sections impregnated with silver and toned with gold. The layer of Chievitz was formed by an inward migration of ganglion-cell and Müller-cell nuclei from the outer neuroepithelium and then, after further changes in nuclear location, the layer of Chievitz was cleared of ganglion-cell nuclei to become the definitive inner plexiform layer. Müller-cell nuclei later populated all retinal layers in the fetus. The argyrophilic Müller-cell cytoplasm associated with neuronal development is discussed in relation to glia-neuron interactions, with emphasis on the particular needs of retinal tissue.