Greater Cell Density Research Articles

The brain in iodine deficiency.

Global descriptive, epidemiological studies have established the relation of iodine deficiency to endemic cretinism which, in its fully developed form, is characterized by mental deficiency, deaf mutism and spastic diplegia. However, a second less common variant--myxedematous or hypothyroid cretinism--is characterized by severe hypothyroidism with dwarfism. Mixed forms occur. It has been shown that both conditions can be prevented by correction of the iodine deficiency before pregnancy. Cretinism and development--now termed iodine deficiency disorders (IDD). A number of recently developed animal models establish the effect of severe iodine deficiency on brain development. These include the rat, the marmoset monkey and the sheep. These models are all characterized by the production of severe maternal and fetal hypothyroidism which is associated with effects on the maturation of the cerebral cortex and cerebellum. There was a reduced brain weight with a reduced number of cells as indicated by reduced DNA, a greater density of cells in the cerebral cortex and reduced cell acquisition in the cerebellum. Studies of the mechanisms involved have been carried out in the sheep. The findings reveal significant, though less severe, effects of fetal thyroidectomy (late gestation) and a significant effect of maternal thyroidectomy on brain development in mid-gestation. A combination of maternal and fetal thyroidectomy has similar but more severe effects than iodine deficiency. In the light of current knowledge of the embryology of the brain it is suggested that the critical time for the effect of iodine deficiency is the mid-trimester (14-18 weeks) when the neurons of the cerebral cortex and basal ganglia are formed and could be damaged by the effect of iodine deficiency on maternal thyroid function. There is now recent evidence indicating transfer of maternal thyroxine across the placental barrier early in pregnancy. In this way, neurological cretinism might be produced. Impaired fetal thyroid function would follow in the third trimester and augment the effect of reduced maternal thyroid function. Impaired fetal thyroid function alone could produce the hypothyroid form of cretinism. Further experimental studies, particularly into the postnatal period, are required to substantiate these suggestions. Apart from this, further study of the effects of iodine deficiency on brain development at the subcellular and cellular levels are likely to be most productive.

Heterologous expression of a bacterial haemoglobin improves the growth properties of recombinant Escherichia coli.

Rational design of novel as well as improved cellular biocatalysts by genetic manipulation of cellular metabolism has recently attracted considerable interest. A wide range of bacteria have been genetically modified by integrating new enzymatic functions into their metabolic network. A central problem in the aerobic growth of any cell culture is the maintenance of dissolved oxygen (DO) concentrations above growth-limiting levels especially in high cell-density fermentations which are usually of a fed-batch type. The optimal rate of nutrient addition (and consequently the productivity) is ultimately limited by the rate at which cells can aerobically catabolize the carbon source without generating growth-inhibitory metabolites such as lactate and acetate. All approaches thus far have concentrated on improving the oxygen mass transfer rates by manipulating various environmental parameters. We have isolated the gene for a haemoglobin-like molecule, expressed by the aerobic bacterium Vitreoscilla in poorly-oxygenated environments, and expressed it in Escherichia coli. The recombinant cells contain enhanced haem as well as active haemoglobin, and they grow faster and to considerably greater cell densities than comparable plasmid-containing cells which do not express haemoglobin. This haemoglobin increases the rate of oxygen use, especially when dissolved oxygen is less than 5% of air saturation.

Distribution and ultrastructure of mast cells in the equine respiratory tract.

Mast cells in the equine respiratory mucosa were studied at both light--and transmission electron--microscope levels. Mast cells were identified at all levels of the tract, with the greatest cell density in the nasopharynx. The majority (57 to 94 per cent) of this cell population were located within the connective tissue of the lamina propria. Up to 20 per cent of these cells were associated with the mucosal glandular tissue, whilst small numbers were present within the surface epithelium and in association with nodular lymphoid tissue. In the peripheral lung tissue 20 per cent of the mast cell population was associated with the small airways, 25 per cent with the pleura, and 32 per cent with blood vessels. The fine and ultrastructural features of these mast cells resemble those described in other species, and their granules consist of two types which resemble human mast cells.

Immunogold localization of the site of replication of tobacco mosaic virus RNA

Previous observations have shown that the striatum contains a population of neurones that display immunoreactivity for calretinin. In order to morphologically characterize these neurones, sections of the rat striatum were immunostained to reveal calretinin and examined at both light and electron microscopic levels. The striatum contained a small population of calretinin-immunoreactive neurones, which were of medium-size (9–17 μm) and possessed few aspiny, infrequently branching dendrites which tapered to become very thin processes in their most distal portions. Although the calretinin-immunoreactive neurones were homogeneously distributed in the frontal plane, there was a marked rostrocaudal gradient with a much greater density of cells in the rostral than in the caudal parts of the striatum. At the ultrastructural level, calretinin-immunoreactive neurones were seen to possess an indented nucleus and to receive synaptic input from at least three types of boutons. In addition to the calretinin-immunoreactive neurones, the striatum also contained axons and terminal boutons that displayed immunoreactivity for calretinin. At least two types of immunoreactive terminals were identified, those forming symmetrical synaptic specialisations and those forming asymmetrical synaptic specialisations. Approximately 50% formed asymmetrical contacts with spines and 30% formed symmetrical synaptic contact with dendritic shafts. In an attempt to further chemically characterize the calretinin-containing neurones, double pre-embedding immunocytochemistry for calretinin and parvalbumin or choline acetyltransferase was carried out and calretinin immunocytochemistry was combined with histochemistry for NADPH-diaphorase. Analysis of these double-stained sections revealed that the population of calretinin-immunoreactive neurones was distinct from the populations of neurones containing parvalbumin, choline acetyltransferase or NADPH-diaphorase. It is concluded that: (1) on the basis of distribution, morphology, chemistry, ultrastructure and afferent synaptic input, the calretinin-immunoreactive neurones are distinct from the major classes of neurones that have been previously recognised in the striatum; (2) calretinin-immunoreactive terminals are heterogeneous and are probably derived from local calretinin-containing neurones and possibly other sources.

Evidence for the existence of a sexually dimorphic nucleus in the preoptic area of the rat.

The volume of an intensely staining component of the preoptic area of the male rat is markedly larger than that of the female. Moreover, its volume in both sexes is altered by perinatal hormone exposure consistent with the view that this brain region undergoes hormone dependent sexual differentiation. The present study was carried out to determine if this sexually dimorphic area of the brain has a greater cell density than that of the surround, and if a unique population or distribution of cells, either within one sex or between males and females, characterized this region. A single coronal paraffin section (10 micrometer) through the approximate center of this sexually dimorphic area in four adult gonadectomized rats of each sex was evaluated systematically. Each cell was labelled as being inside or outside of the sexually dimorphic area. In addition to cell density per unit area the following parameters were evaluated through a closed-circuit video system: cell size, staining intensity, shape, and the presence of processes and of a nucleolus. The presence of a nucleolus was further used to identify neurons within the total population of almost 5000 cells that was evaluated. In both sexes, the sexually dimorphic area was characterized by a significantly increased cell density per unit area compared to that of the surround. On this basis, the term, the Sexually Dimorphic Nucleus of the Preoptic Area (SDN-POA) is proposed, for this region. Moreover, the SDN-POA of the male was characterized by increased neuronal density per unit area. The SDN-POA in the male was also found to contain larger cells and neurons, as determined by direct measurement of their greatest diameter, as well as a greater percentage of cells and neurons rated large on a three-point scale (small, medium, and large). No consistent differences in frequency distribution by stain intensity, shape, or the presence of cell processes were found to characterize the SDN-POA or contribute to the sexual dimorphism. It is concluded that the marked sex difference in the volume of the SDN-POA is due principally to an increase in the male of the total area of higher cell and neuronal density. However, the present results do not eliminate the possibility that more subtle differences in neuronal characteristics may exist in the SDN-POA.