Concentration of free amino acids in primary cultures of neurones and astrocytes

The cellular distribution of free amino acids was estimated in primary cultures (14 days in vitro) composed principally of cerebellar interneurones or cerebellar and forebrain astrocytes. In cultured neural cells, the overall concentration of amino acids resembled that found in brain at the corresponding age in vivo. In the two neural cell types, there were marked differences in the distribution of amino acids, in particular, those associated with the metabolic compartmentation of glutamate. In neuronal cell cultures, the concentrations of glutamate, aspartate, and gamma-aminobutyric acid were, respectively, about three, four, and seven times greater than in astrocytes. By contrast, the amount of glutamine was approximately 65% greater in astroglial cell cultures than in interneurone cultures. An unexpected finding was a very high concentration of glycine in astrocytes derived from 8-day-old cerebellum, but the concentrations of both serine and glycine were greater in nerve cell cultures than in forebrain astrocytes. The essential amino acids threonine, valine, isoleucine, leucine, tyrosine, phenylalanine, histidine, lysine, and arginine were all present in the growth medium, and small cellular changes in the contents of some of these amino acids may relate to differences in their influx and efflux during culturing and washing procedures. The present results, together with our previous findings, provide further support for the model assigning the "small" compartment of glutamate to glial cells and the "large" compartment to neurones, and also underline the metabolic interaction between these two cell types in the brain.

Effects of undernutrition and thyroid state on the ontogenetic changes of D1, D2, and D3 brain-specific proteins in rat cerebellum

Disturbances in metabolic balance brought about by alterations in thyroid state and undernutrition during early life had a marked effect on the concentrations of the brain-specific proteins, D1, D2, and D3 in the developing rat cerebellum. In normal rats, the concentrations of D1 and D3 increased and that of D2 decreased during the first 3 weeks after birth. In the hyperthyroid state a small but consistent advancement was observed in the developmental curves of these proteins. The hypothyroid state caused a marked retardation in the maturational pattern of D1 and D2 but not of D3. In undernutrition, at 6 days the concentrations of D1 and D3 proteins were higher than in controls, but thereafter the developmental increase was markedly delayed for D1 only. The concentration of D2 was normal at 6 days, but after the first week a marked retardation was observed in the maturational pattern of this protein in undernourished rats. In addition, the "anodic-immature" form of D2 predominated in 6-day-old controls, but this was gradually replaced by a "cathodic-mature" form which progressively became the dominant form of D2 in 35-day-old rat cerebellum. The developmental switch in terms of the two forms was also advanced in hyperthyroidism and retarded in thyroid deficiency and undernutrition. Furthermore, daily treatment of hypothyroid rats with physiological doses of thyroxine from birth restored the concentrations of D1 and D2 to normal, but that of D3 was increased above control levels, indicating differences between the proteins in their sensitivity to mechanisms of control by thyroid hormone. Also, the overall effects of undernutrition were markedly different from those of hypothyroidism.

Distribution of glutamine synthetase and glial fibrillary acidic protein and correlation of glutamine synthetase with glutamate decarboxylase in different regions of the rat central nervous system

The concentration of soluble glial fibrillary acidic (GFA) protein and the specific activity of glutamine synthetase (GS) were estimated in 11 central nervous system (CNS) regions of the 90-day-old rat. Marked differences were observed in the regional distribution of these astrocyte marker proteins. The striatum and spinal cord contained the lowest concentration (per g wet weight) of GFA protein and GS activity, respectively, while the olfactory bulbs had the highest level of both astrocytic proteins. Differences between the lowest and the highest values were 3-fold for GS and 4-fold for GFA protein. More significant was the marked variation in the ratio of GS to GFA protein in different CNS regions; the highest and lowest values were in the striatum and the spinal cord respectively, and the difference between the highest and the lowest value was about 5-fold. The spinal cord contained low GS and high GFA protein; on the other hand, the colliculi had high GS and relatively low GFA protein. Immunochemical detection of GS and GFA proteins in whole homogenates of different regions showed that the variation of the specific activities of GS and the concentration of soluble GFA protein were due to the differences in their absolute protein concentrations. In different regions of the brain the activity of GS was significantly correlated with that of glutamate decarboxylase, but not with that of choline acetyltransferase. These observations provide further evidence for differing biochemical properties of astrocytes from various CNS regions and for the involvement of GS in processes associated with amino acid neurotransmission.

Observations on cell growth and regulation of glutamine synthetase by dexamethasone in primary cultures of forebrain and cerebellar astrocytes

Cell growth, development of glutamine synthetase and its regulation by glucocorticoids, were studied in primary cultures of two types of astrocytes derived from rat brain, one from newborn forebrain and another from either newborn or 8-day-old cerebellum. Cell number per dish increased linearly following an initial decrease due to removal of non-astrocytic cells, and after the second week reached a stationary phase in both types of cultures at more or less the same time, although the cell number in cerebellar cultures was about 35% lower than in forebrain cultures of the same age. At all ages, irrespective of cell density, the cerebellar astrocytes were larger in size than the forebrain astroglial cells. The developmental curves for glutamine synthetase activity were similar in vitro and in vivo; however, the increase in enzyme activity in vitro was significantly greater than in vivo and this difference was more marked in forebrain than in cerebellar cultures. Throughout the period studied the specific activity of glutamine synthetase was significantly higher in forebrain astrocytes than in cerebellar astroglial cells. Treatment with dexamethasone caused a marked increase in the specific activity of glutamine synthetase. However, in agreement with our previous in vivo findings, the steroid induction in forebrain astrocytes was significantly less than that in cerebellar astrocytes. In culture, both types of astrocytes remain responsive to the hormone for longer than in vivo. The differences in the biochemical properties of the forebrain and cerebellar astrocytes seem to be intrinsic, and not related to the cell density or to the purity of the cultures.

Developmental changes in the amount of glial fibrillary acidic protein in three regions of the rat brain

Glial fibrillary acidic (GFA) protein, extractable in 50 mM phosphate buffer, pH 8, was measured in the olfactory bulbs, forebrain and cerebellum of the rat during development using a double antibody radioimmunoassay. Each brain region showed a different pattern of development for GFA protein. At birth GFA protein per mg protein was highest in olfactory bulbs followed by forebrain and cerebellum, and these amounted to 15, 10 and 8% of the adult values, respectively. The relative increase in GFA protein was more marked during the first 2 postnatal weeks than in the following 7 weeks after birth. When values were expressed per brain region, the developmental increase in the amount of GFA protein from birth to adulthood was about 100-fold in olfactory bulbs, 85-fold in forebrain and 485-fold in cerebellum. The patterns of developmental increases in GFA protein and in glutamine synthetase activity, another protein enriched in astrocytes, were similar in the forebrain and olfactory bulbs, but differed markedly in the cerebellum. The major increase in content of the GFA protein during development was found to correspond with the maturation of astrocytes rather than with their proliferation; however, a small but significant amount of GFA protein acquired at an early age may be related to increase in astroglial cell numbers in the cerebellum.

Mitochondria in the postnatally developing rat cerebellar cortex: a morphological and biochemical study

Ultrastructural changes during development in the proliferating cells of the external granular layer and the granule cells of the internal granular layer of the rat cerebellar cortex were examined. Changes in the number of free ribosomes, development of membrane systems, nuclear appearance and the number of cristae and matrix density of mitochondria suggested that both the round and elongated cells of the external granular layer and the granule cells of the internal granular layer were at same stage of maturation at any given age. Quantitatively, the relative volumes of cytoplasm and of mitochondria in the granule cells of internal granular layer were significantly higher than in the proliferating external granular layer cells; however, mitochondrial density and its increase during development were not significantly different in the two cell populations. The activity of the mitochondrial enzyme, succinate dehydrogenase, was also similar in ultrastructurally preserved and metabolically competent perikaryal fractions enriched in replicating external granular layer cells, granule cells and Purkinje cells. These findings emphasize the similarities between proliferating external granular layer cells and granule cells of internal granular layer. They lend support to the view that these cell types at the ages examined, represent a continuum of maturation towards full neuronal differentiation.

Regulation of in vivo glutamine synthetase activity by glucocorticoids in the developing rat brain

Induction of glutamine synthetase in vivo by glucocorticoids was studied in different brain regions of the rat during development. Corticosterone treatment resulted in an age-dependent increase in glutamine synthetase activity. In 11-day-old rats, in comparison with controls, the increase was about 80% in the cerebellum, 50% in the olfactory bulbs and 20% in the forebrain. During development the effect diminished markedly and at day 20 a marked increase was detectable only in the cerebellum, suggesting that the elevation of glutamine synthetase was dependent on the maturational state of the region at the time of hormone treatment. The increase in enzyme activity was dose-dependent, and was also observed after treatment with dexamethasone but not with testosterone, estradiol or progesterone. Pre-treatment with the protein synthesis inhibitor anisomycin blocked the hormonal response. Also, immunochemical detection of glutamine synthetase in brain homogenates fractionated by SDS-polyacrylamide gel electrophoresis and transferred to diazobenzyloxymethyl paper showed that the increase in enzyme activity was due to induction of protein synthesis. This may be the first report showing a regulation by glucocorticoids of mammalian brain glutamine synthetase in vivo, and it is in good agreement with previous findings with chick retina in vivo and various avian and mammalian cells in vitro.

The past, present, and future of clinical specular microscopy

Since the introduction of specular microscopy into the field of clinical ophthalmology in 1975, many technological and methodological advances have been made. These have for the most part eliminated the previously discussed objections to the use of specular microscopy as a clinical tool. With the advent of new instrumentation, a number of specular microscopes are not available. The advantages and disadvantages of these clinical specular microscopes, current clinical practice with small-field and wide-field specular microscopy, and description of problems and possible future developments of specular microscopy are discussed.

Cell death in the external granular layer of normal and undernourished rats: further observations, including estimates of rate of cell loss

Pyknotic nuclei in the external granular layer (EGL) of the rat cerebellum accounted for 0.6-0.8% of the total cell population in the first and third post-natal weeks and 1.4% at day 12. A wave of cell death induced by hydroxyurea showed an exponential decrease after 12 hr, from which a mean duration for pyknoses of about 6.5 hr was calculated. Undernutrition delayed the clearance of pyknotic nuclei following hydroxyurea, the mean duration being 24.5 hr. It is concluded that cell death does not significantly influence cell acquisition in the developing cerebellar EGL, and that the increased pyknotic index seen in the EGL of undernourished rats is a consequence of delayed clearance rather than an increase in the number of cell deaths.

Effect of central nervous system acting drugs on brain cell replication in vitro

The role in the regulation of cell replication of the neurotransmitter compounds and the drugs which affect their balance was studied in vitro, using morphologically preserved brain slices. Compounds affecting noradrenergic, dopaminergic and serotoninergic neurotransmitter systems reduced the brain cell replication, measured in terms of the rate of [3H]thymidine incorporation into DNA. The reduction was dose dependent and half-maximal effects were obtained at about 1-5 x 10(-4) M concentrations. Although agonists and antagonists both showed similar inhibitory effect, the action of agonists was reversed by the appropriate antagonists. Also, the pharmacologically active isomers were several-fold more effective than the inactive isomers in forebrain slices, although with cerebellar slices the selectivity was less marked. Cyclic nucleotides and drugs affecting cholinergic neurotransmitter systems were apparently ineffective. These results indicate that monoamines may be involved in the regulation of cell replication in the developing brain. Furthermore, as some of the CNS acting drugs tested are suspected behavioural teratogens the present results suggest that the reported behavioural abnormalities in the offspring may be related, in part, to a chronologically determined interference with the formation of certain cell types.

The activities in different neural cell types of certain enzymes associated with the metabolic compartmentation glutamate

The cellular distribution of certain enzymes associated with the metabolic compartmentation of glutamate was estimated in ultrastructurally preserved and metabolically competent perikarya fractions that were enriched in astrocytes, granule cells and Purkinje cells and derived from 8-day-old rat cerebellum, and in monolayer cultures (14 days in vitro) composed principally of interneurones or astrocytes. The neuronal activities of glutamine synthetase and glutamate dehydrogenase were respectively about 4- to 8-fold and 2- to 5-fold lower than in astrocytes, depending upon the class of neurone and the type of preparation used for comparison. By contrast glutaminase activity was about 3- to 12-fold higher in neuronal than in astroglial preparations. Estimations of the specific activity of succinate dehydrogenase differed less between cell types, indicating that the differences in glutamate dehydrogenase and glutaminase were not simply related to variations in the concentration of mitochondria relative to the other cellular constituents. The findings presented provide direct evidence in support of our model assigning the 'small' glutamate compartment, where most of the labelled glutamine is synthesized, to glial cells, and the 'large' compartment to neurones, and also underline the metabolic interaction between these two cell types in the brain.

Effects of haloperidol on cell proliferation in the early postnatal rat brain

Haloperidol, a widely used neuroleptic, produced a significant depression of the rate of [3H]thymidine incorporation into the DNA of 11-day-old rat brain. The reduction of in-vivo DNA synthesis rate was detectable by 4 h after subcutaneous injection of a single dose of haloperidol (20 mg/kg) and through the period 10-24 h after drug treatment the rate was less than 50% of that of controls in the forebrain. [3H]Thymidine incorporation returned to control values by 32 h. The effect on the cerebellum was similar but less pronounced. The depression was dose-dependent and a half-maximal effect was produced with haloperidol doses of 5-10 mg/kg. Parallel histological studies on treated rats suggested prolongation of the DNA synthesis phase of the cell cycle in the forebrain subependymal layer, associated with an increase in turnover time of about 15%.

Indolic substances in plasma, cerebrospinal fluid, and frontal cortex of human subjects infused with saline or tryptophan

Psychiatric patients undergoing the psychosurgical operation of stereotactic subcaudate tractotomy were infused intravenously with either saline or L-tryptophan (15 mg/kg/h). Plasma, lumbar cerebrospinal fluid (CSF), ventricular CSF and a specimen of frontal cortex were collected. The relationships of plasma concentrations of substances claimed to influence brain tryptophan concentration (total tryptophan, free tryptophan, large neutral amino acids) with the concentration of tryptophan in the cortex and CSF were investigated. Tryptophan infusion resulted in plasma tryptophan values comparable to those found after oral doses used in treating depression or insomnia, and about sixfold increases of tryptophan in the cerebral cortex. Increased brain 5-hydroxytryptamine synthesis was indicated by significant rises of CSF 5-hydroxyindoleacetic acid. The concentration of plasma free tryptophan was a better predictor than plasma total tryptophan of cortex tryptophan concentration. As all correlation coefficients of plasma versus brain or plasma versus ventricular CSF tryptophan concentrations were decreased when allowance was made for differences of concentration of large neutral amino acids, the results suggest that the role of these substances within their physiological range as inhibitors of tryptophan transport to the brain may previously have been overemphasised.

Effect of chlorpromazine on cell proliferation in the developing rat brain. A combined biochemical and morphological study

Chlorpromazine, a widely used drug in current clinical practice, produced a severe reduction of the rate of [3H]thymidine incorporation into brain DNA of 11-day-old rats. The depression of in vivo synthesis rate was detectable by 6 h after chlorpromazine administration (50 mg/kg, s.c.) and the rate was less than 40% and 60% of controls during period 14-30 h in forebrain and 6-30 h in cerebellum respectively. The depression was dose-dependent and half maximal effect was produced with about 10 mg/kg chlorpromazine. The drug caused some retardation in the rate of conversion of [3H]thymidine to [3H]thymine nucleotides in the brain, but the severe depression in DNA labelling was also evident after correcting the values on the basis of [3H]thymine nucleotides concentration. Mitotic activity was significantly reduced in the cerebellar external granular layer. Increased numbers of cell degenerations, shown by Feulgen cytophotometry to be postmitotic, were seen in both layers 12 and 32 h after chlorpromazine. Analysis of cell cycle parameters showed no significant changes. However, the labelling index in subependymal cells was reduced, indicating an increase in turnover time of about 40%. The results are consistent with an action of chlorpromazine on cell proliferation, either by direct effects on the generation and survival of cells, or via its major pharmacological actions on neurotransmitter balance. These effects are potentially of functional and clinical significance.

Effects of undernutrition on gliogenesis and glial maturation in rat corpus callosum

Rats were undernourished by halving the mother's food intake from the sixth day of pregnancy onwards and through lactation. At weaning, the young rats were restricted to half the normal weight of food. A combination of light and electron microscopic techniques was used to study the effects of this regime on gliogenesis and glial maturation in the corpus callosum of animals aged between 15 and 48 days. A disturbance of neuroglial proliferation was suggested by the finding of an increased proportion of astroglia relative to oligodendroglia in the 15-day-old undernourished rats, indicating a delay in the acquisition of cells produced relatively late in development. Impaired differentiation of oligodendroglia was suggested by the finding in treated animals of increased light oligodendrocytes at 15 days and a deficit of dark oligodendrocytes at 48 days, relative to controls. The previously observed retardation in myelin acquisition seems thus to be related to a delay in the differentiation of oligodendroglia, although it seems likely that the proliferation of these cells is also disturbed in undernutrition.

Effects of thyroid state on brain development: beta-adrenergic receptors and 5'-nucleotidase activity

The effect of thyroid status on beta-adrenergic receptor binding and 5'-nucleotidase activity was studied in the forebrain and the cerebellum of the rat during the first 5 postnatal weeks. The developmental increase in beta-adrenergic receptor binding was significantly depressed in thyroid deficiency in both the forebrain and the cerebellum. The effect was more pronounced in the cerebellum, where at day 35 the concentration and the total number of beta-adrenergic receptor sites were reduced by 35% and 50% respectively. In contrast, hyperthyroidism had no significant effect on the development of beta-adrenergic receptors in the brain. On the other hand, hyperthyroidism led to a sustained increase in the forebrain in the activity of 5'-nucleotidase, an enzyme which is also associated with plasma membranes and has been proposed to play some role in neurotransmission. In thyroid deficiency the enzyme activity was markedly depressed. The effect was significant from day 12 in the cerebellum and from day 21 in the forebrain, the maximal depression, at day 21, being 55% and 45% respectively. In comparison with these plasma membrane markers, the accretion of membranous proteins was less affected: although this was retarded in hypothyroidism and advanced in hyperthyroidism there was no residual effect at 35 days except those attributable to changes in organ size. The results indicated, therefore, that the biochemical specialization of cells, as reflected in certain plasma membrane constituents, are chatacteristically influenced in the developing brain by thyroid disorders.

Effects of thyroid state on brain development: muscarinic acetylcholine and GABA receptors

A study was made of the effects of age, neonatal hypothyroidism and hyperthyroidism on the development in rat brain of muscarinic cholinergic and GABA receptors. The former receptors were estimated by the binding of [3H]quinuclidinylbenzilate and the latter by binding of [3H]muscimol to crude membrane preparations from the forebrain and the cerebellum. In the normal forebrain, the density of muscarinic cholinergic receptors (in terms of unit membrane proteins) doubled during the period 6-35 days after birth. Thyroid state had relatively little effect on this development. In contrast, in the normal cerebellum the peak of the density of the receptors was attained in the early neonatal period followed by a progressive decline reaching about half of the maximum at day 35. Furthermore, in the cerebellum this development was significantly influenced by thyroid disorders: the rate of decrease in receptor density was accelerated by hyperthyroidism and retarded in thyroid deficiency. In comparison with euthyroid rats, the density of muscarinic receptors in the cerebellum was 30% lower in the hyperthyroidism (at day 21) and 40% higher in thyroid deficiency (at day 35). The increase in the density of GABA receptors with age was very small in the normal forebrain relative to the marked rise in the cerebellum. In the forebrain, thyroid state had no significant effect on this development. In contrast, in the cerebellum the ontogenesis of GABA receptors was advanced by thyroid hormone treatment and retarded in thyroid deficiency. However, by day 35 receptor density was normal in both conditions. Thyroid state had no significant influence on the affinity of either [3H]muscimol or the [3H]quinuclidinylbenzilate binding. The results suggest that thyroid hormone disorders during early life may lead to distortions rather than synchronized shifts in the relative development of several central transmitter systems.

Distribution of GABA receptors in the rat cerebellum

The distribution of GABA receptors in the cerebellum is not homogeneous. In comparison with detergent-treated membranes from the whole tissue the number of [3H]muscimol binding sites per mg protein (Bmax) is about doubled in preparations enriched in large fragments of the cerebellar glomeruli, and it is about one-third in the dissected deep nuclei. On the other hand, the apparent affinity (Kd) is similar in the different preparations. Comparison of the results with earlier studies suggests a heterogeneity in cerebellar GABA receptors and/or their control.