Properties of cell nuclei isolated from various regions of rat brain: divergent characteristics of cerebellar cell nuclei

Neuronal differentiation of dental pulp stem cells from human permanent and deciduous teeth following coculture with rat auditory brainstem slices

Sensorineural hearing loss is a common disability found worldwide which is associated with a degeneration of spiral ganglion neurons (SGN). It is a challenge to restore SGN due to the permanent degeneration and viability of SGN is requisite for patients to receive an advantage from hearing aid devices. Human dental pulp stem cells (DPSC) and stem cells from human exfoliated deciduous teeth (SHED) are self-renewing stem cells that originate from the neural crest during development. These stem cells have a high potential for neuronal differentiation. This is primarily due to their multilineage differentiation potential and their relative ease of access. Previously, we have shown the ability of these stem cell types to differentiate into spiral ganglion neuron-like cells. In this study, we induced the cells into neural precursor cells (NPC) and cocultured with auditory brainstem slice (ABS) encompassing cochlear nucleus by the Stoppini method. We also investigated their ability to differentiate after 2 weeks and 4 weeks in coculture. Neuronal differentiation of DPSC-NPC and SHED-NPC was higher expression of specific markers to SGN, TrkB, and Gata3, compared to monoculture. The cells also highly expressed synaptic vesicle protein (SV2A) and exhibited intracellular calcium oscillations. Our findings demonstrated the possibility of using DPSCs and SHEDs as an autologous stem cell-based therapy for sensorineural hearing loss patients.

DNA repair in neural cells: basic science and clinical implications

As one part of a distinguished scientific career, Dr. Bryn Bridges focused his attention on the issue of DNA damage and repair in stationary phase bacteria. His work in this area led to his interest in DNA repair and mutagenesis in another non-dividing cell population, the neurons in the mammalian nervous system. He has specifically taken an interest in the magnocellular neurons of the central nervous system, and the possibility that somatic mutations may be occurring in these neurons. As part of this special issue dedicated to Bryn Bridges upon his retirement, I will discuss the various DNA repair pathways known to be active in the nervous system. The importance of DNA repair to the nervous system is most graphically illustrated by the neurological abnormalities observed in patients with hereditary diseases associated with defects in DNA repair. I will consider the mechanisms underlying the neurological abnormalities observed in patients with four of these diseases: xeroderma pigmentosum (XP), Cockayne's syndrome (CS), ataxia telangectasia (AT) and AT-like disorder (ATLD). I will also propose a mechanism for one of the observations indicating that somatic mutation can occur in the magnocellular neurons of the aging rat brain. Finally, as a parallel to Bridges inquiry into how much DNA synthesis is going on in stationary phase bacteria, I will address the question of how much DNA synthesis in going on in neurons, and the implications of the answer to this question for recent studies of neurogenesis in adult mammals.

Detection of excision nuclease in cell-free extracts from the adult mammalian brain

The autosomal recessive disorder xeroderma pigmentosum (XP) results from defects in the nucleotide excision repair (NER) pathway for DNA repair. NER normally repairs bulky DNA lesions, such as pyrimidine dimers resulting from UV radiation. XP patients have high rates of skin cancer, and some also develop progressive neurological degeneration. To better understand the mechanism of this neurodegeneration, I used a specific assay for the multicomponent excision nuclease of the NER pathway in cell-free extracts from the adult rat brain. Excision nuclease activity was detectable in whole-cell extracts prepared from the cerebellum, whereas extracts prepared from the forebrain, which has a lower density of cell nuclei, had much less activity. Nuclear extracts from both areas were equally capable of restoring activity to extracts from two different NER-deficient cell lines, despite large differences in the ratio of neurons to nonneuronal cells in the cerebellum and forebrain. These results indicate that the NER pathway is functional in neuronal cells in the adult brain. The implications of this finding for XP and other neurodegenerative diseases is discussed.

Expression of long-patch and short-patch DNA mismatch repair proteins in the embryonic and adult mammalian brain

Expression of the DNA mismatch repair (MMR) pathway was examined in the adult and developing rat brain. Rat homologues of human GTBP and MSH2, which are essential components of the post-replicative DNA MMR system, were identified in nuclear extracts from the adult and developing rat brain. Developmental studies showed that both GTBP and MSH2 levels were higher in nuclei isolated from the embryonic brain (day 16) than adult brain. However, this difference was not as dramatic as the difference in the number of proliferating cells. Levels of thymine DNA glycosylase (TDG), the enzyme which catalyzes the first step in short patch G:T mismatch repair, were also decreased in adult compared to embryonic brain. In the adult brain, MMR proteins were elevated in nuclear extracts enriched for neuronal nuclei. These results suggest that adult brain cells have the capacity to carry out DNA mismatch repair, in spite of a lack of ongoing DNA replication.

Fos-like expression and nuclear size in osmotically stimulated supraoptic nucleus neurons

This study has analysed by immunocytochemistry the pattern of expression of Fos-related proteins, as well as variations in nuclear size, after the osmotically induced activation of supraoptic nucleus neurons of the rat. In control rats most supraoptic nucleus neurons were Fos-like negative. After acute and chronic dehydration by salt-loading, the number of Fos-like positive neurons increased dramatically. The level of Fos-like immunoreactivity was higher in chronically stimulated rats, and also the neurons of the ventral region of the supraoptic nucleus were more intensely stained than those of the dorsal region. The karyometric analysis was made on electron micrographs. The mean nuclear profile area showed a significant increase in dehydrated rats with respect to the controls (73 +/- 16 microns 2 in those dehydrated for six days vs 54 +/- 13 in controls, mean +/- S.D.). However, no significant differences in this parameter were found when one-day and six-day dehydrated groups were compared. The invagination factor of the nuclear membrane, a nuclear shape indicator, decreased significantly in dehydrated rats, indicating a tendency towards spherical nuclei. It is noteworthy that the nuclear profile perimeter was constant, about 32 microns, in control and osmotically simulated rats. The higher nuclear accumulation of Fos-related antigens after six days of dehydration suggests that in chronically stimulated supraoptic nucleus neurons there is a sustained induction of cell-specific genes. Moreover, the transcription rate of the target genes containing the consensus DNA sequence TGAC/GTCA or c-AMP responsive elements recognition sites may depend upon the nuclear concentration of Fos-related antigens in supraoptic nucleus neurons. Our results also suggest that the initial Fos-related antigen expression and nuclear size increase are triggered concomitantly in supraoptic nucleus neurons after a short period of osmotic stimulation. On the other hand, we propose that nuclear envelope invaginations represent a reservoir of nuclear membrane which allows dynamic changes in nuclear size and shape depending on the metabolic status of the supraoptic nucleus neurons.

Freeze-fracture organization of chromatin and cytoplasm in neurons and astroglia of rat cerebellar cortex

The cytology of the cell nucleus and cytoplasm of neurons and astroglia of the rat cerebellar cortex has been investigated by freeze-fracture electron microscopy. The main differential characteristics in the cytoplasm of the several cell types of the cerebellar cortex were: (1) the organization of endoplasmic reticulum elements, including special configurations of lamellar bodies and hypolemmal complexes, (2) the polarity, extension and arrangement of Golgi cisterns and associated tubulovesicular elements; (3) the connection pattern among different membrane-bounded cellular compartments; and (4) the architecture of endomembranes (i.e. presence of pits and fenestrations). In the nucleus, the main differential features were the the three-dimensional view of the nuclear envelope, the distribution of nuclear pores and the aggregation pattern of chromatin, visualized as clusters of nuclear particles in cross-fractures. The quantitative analysis of chromatin revealed four peaks of nuclear particle sizes (8, 12, 17 and 21 nm) that may correspond to variable degrees of coiling of the polynucleosomal chain in the chromatin fibre. Significant differences were observed in the proportion, numerical density and size distribution of aggregated nuclear particles in heterochromatin domains among the different cell types of the cerebellar cortex. The percentage of nuclear particles in aggregates varied from 10% in Purkinje cells to 64% in granule cells. Astrocytes and Bergmann glia showed intermediate values (about 40%). The percentage of nuclear particles in aggregates showed a significant (P less than 0.05) negative linear correlation with the nuclear volume, the number of pores per unit nuclear volume and the total number of pores per nucleus. In granule cells and astroglia, heterochromatin domains had a greater percentage of large nuclear particles (greater than 10 nm) than did euchromatin domains, whereas in interneurons, Purkinje and Golgi cells heterochromatin and euchromatin showed a similar proportion of large particles. Nuclear particles in euchromatin exhibited a similar pattern of distribution in all cerebellar cells.

Organization of nucleoli and nuclear bodies in osmotically stimulated supraoptic neurons of the rat

This study has analyzed variations in the number of nucleoli and nuclear bodies, as well as in their ultrastructural and cytochemical organization, after the osmotically induced activation of supraoptic nucleus (SON) neurons of the rat. The number of nucleoli and nuclear bodies and also the nucleolar size were determined on smear preparations of previously block-impregnated SON. The mean number of nucleoli per cell was 1.35 +/- 0.6 (mean +/- SDM) in control rats. No significant variations in this value were registered either in dehydrated or rehydrated rats. The mean nucleolar volume and the total nucleolar volume per cell showed a significant increase in dehydrated rats with respect to the controls, whereas these two parameters tended to return to control values in rats rehydrated after dehydration. The mean number of nuclear bodies per cell increased significantly from 0.56 +/- 0.50 (mean +/- SDM) in control rats to 1.54 +/- 1.1 after 6 days of dehydration. By electron microscopy, SON neurons displayed a reticulated nucleolar configuration. After the osmotically induced neuronal activation, there was an increase in the proportion of the total nucleolar area occupied by the granular component, and also a reduction in the mean fibrillar-center area. The most characteristic nucleolar features in rehydrated rats were the tendency for the granular component to be segregated and the occurrence of intranucleolar vacuoles. Ultrastructural cytochemistry with a specific silver method revealed a selective silver reaction on the coiled threads of the nuclear bodies--identified as "coiled bodies"--and on the nucleolar fibrillar components in all animal groups studied. Since nucleoli play a major role in ribosome biogenesis, a relationship between these nucleolar changes and the level of cellular activity of SON neurons is proposed. Furthermore, the response of nuclear "coiled bodies" to neuronal activation suggests their participation in the processing and transport of rRNA precursors.

A procedure for purifying low-abundance protein components from the brain cytoskeleton-nuclear matrix fraction

We describe a preparative procedure for low-abundance proteins of the cytoskeleton-nuclear matrix fraction from frozen bovine brain. Strigent centrifugation and washing conditions in the preparation of the cytoskeleton-nuclear matrix fraction are avoided to minimize loss of nuclear material. A recently described horizontal isoelectric focusing column, which tolerates appreciable precipitation, is used. In concert with selection of urea concentration and temperature, this isoelectric focusing apparatus provides a new approach to the fractionation of this complex, relatively insoluble mixture of proteins and other components. In addition, a heated, sodium dodecyl sulfate-sizing column has been utilized in order to eliminate interactions between the desired low abundance proteins and more abundant contaminating proteins. Together these procedures purify a specific low-abundance protein sufficiently to be detected by Coomassie blue staining in two-dimensional gels. The methods are robust and can be applied to multiple, relatively large brain samples (150 g of crude grey matter per batch); thus they should facilitate partial peptide sequencing for brain proteins of this operational class.

Iron-dependent peroxidation of rat brain: a regional study

Iron has been shown to initiate a variety of free radical reactions in biological systems. The present study examined the in vitro susceptibility of homogenates prepared from different regions of rat brain to iron-induced peroxidation. Among the regions studied, basal thiobarbituric acid-reactive product (TBAR) formation is highest in the cerebellum and amygdala, intermediate in the cortex, hippocampus, and neostratium, and lowest in the hypothalamus, midbrain, and brainstem. In the presence of 200 microM FeCl3, there is a 20-25-fold increase in the net TBAR formation in all regions, with TBAR formation in the cerebellum and amygdala being significantly higher than in the midbrain and brainstem. Time-course and dose-response studies of iron-induced peroxidation showed that the cerebellum and amygdala are the most susceptible regions with respect to concentration of iron and duration of the incubation time, whereas the midbrain and brainstem are the least affected areas. Following low-speed (1,000 g) centrifugation of brain part homogenates, TBAR formation in the supernatant fractions is quite uniform across regions, while the pellet fractions give the same regional variations as the whole homogenates. TBAR formation in both fractions is increased 20-30-fold in the presence of 200 microM iron. Brain tissue TBAR formation induced by 200 microM iron is inhibited by the iron chelator desferrioxamine (IC50 = 600 microM), by Tris buffer pH = 8.0 (2.5 mM Tris gives 50% inhibition by trapping hydroxyl radicals), and by high concentrations of the cyclooxygenase inhibitor indomethacin (IC50 = 1.2 mM).

Low-abundance 32-kilodalton nuclear protein specifically enriched in the central nervous system

Recently, a low-abundance nuclear protein, p32/6.3, has been identified in brain tissue (Egle and Shelton: Journal of Biological Chemistry 261:2294-2298, 1986). Using a Western blot procedure, we describe its distribution in the nervous system, determine its relative enrichment in brain versus liver, kidney, and certain other tissues, and describe an isolation procedure from brain. Selective enrichment occurs in basal ganglia, diencephalon, hippocampus, cerebellum, brainstem, spinal cord, and cerebral cortex but not in retina, dorsal root ganglia, and sympathetic ganglia. Thus, enrichment is limited to areas of the central nervous system. p32/6.3 appears to be preferentially enriched in neurons, because in bulk-isolated fractions from rat grey matter it is more abundant in neuron-enriched fractions than in astrocyte-enriched fractions. p32/6.3 is approximately 20-fold more concentrated in an insoluble nuclear protein or matrix fraction from forebrain than from kidney, liver, adrenal gland, or retina. This degree of enrichment is an ancient trait, detectable in the chicken as well as mammals.

Cloning of a cDNA encoding the rat high molecular weight neurofilament peptide (NF-H): developmental and tissue expression in the rat, and mapping of its human homologue to chromosomes 1 and 22

Neurofilaments (NFs) are the intermediate filaments specific to nervous tissue. They are probably essential to the tensile strength of the neuron, as well as to transport of molecules and organelles within the axon. Three peptides with apparent molecular masses of approximately 68 (NF-L), 145 (NF-M), and 200 (NF-H) kDa appear to be the major components of NF. The expression of these peptides is specific to nervous tissue and is developmentally regulated. Recently, complete cDNAs encoding NF-L and NF-M, and partial cDNAs encoding NF-H, have been described. To better understand the normal and pathophysiology of NFs we chose to clone the cDNA encoding the rat NF-H peptide. Using monoclonal antibodies that recognized NF-H, we screened a rat brain lambda gt11 library and identified a clone that contained a 2100-nucleotide cDNA insert representing the carboxyl-terminal portion of the NF-H protein. Anti-fusion protein antibodies recognized the NF-H peptide on immunoblots and stained fibrillar structures only in neurons. The cDNA recognized a 4500-nucleotide polyadenylated mRNA that was present only in nervous tissue and a 3500-nucleotide mRNA in adrenal. Brain NF-H mRNA levels were tightly developmentally regulated and paralleled the levels of NF-H peptide on immunoblots. Nuclear runoff studies showed that the 20-fold developmental increase in the NF-H message was due only in part to a 4-fold increase in its transcription rate. Levels of NF-H mRNA varied 20-fold among brain regions, with highest levels in pons/medulla, spinal cord, and cerebellum, and lowest levels in olfactory bulb and hypothalamus. Transcription studies revealed only a 2-fold difference in the transcription rates among these brain regions. Based on these results, we infer that half of the developmental increase and most of the interregional variation in the levels of the NF-H mRNA are mediated through message stabilization. Sequence information revealed that the carboxyl-terminal region of the NF-H peptide contained a unique serine-, proline-, alanine-, glutamic acid-, and lysine-rich repeat. The serine residues are likely sites of phosphorylation in the mature peptide. Genomic blots revealed a single copy of the gene in the rat genome and two copies in the human genome. In situ hybridizations performed on human chromosomes mapped the NF-H gene to chromosomes 1 and 22. Whether one copy is a pseudogene remains to be determined.

Developmental expression and regional distribution of the scrapie-associated protein mRNA in the rat central nervous system

The scrapie associated protein (SAP) has been shown to be a normal brain protein of yet undefined function. This study demonstrates that rat brain SAP mRNA levels undergo a transcriptionally dependent increase during normal development. The interregional variation in the adult rat central nervous system (CNS) is roughly 10 fold, with highest levels in the basal ganglion/thalamus and lowest levels in the spinal cord.

Temporal profiles of proteins responsive to transient ischemia

The responses of long and short half-lived proteins to ischemia were measured in rat brain during 6 days of recovery from 30 min of transient forebrain ischemia produced by four-vessel occlusion. At the end of the ischemic interval, the neocortical activities of four vulnerable enzymes [ornithine (ODC) and S-adenosylmethionine (SAMDC) decarboxylases, and RNA polymerases I and II] were unchanged, but within 30 min of reperfusion, their activities dropped by 25-50%. The loss of substance P in the striatum and substantia nigra was slower, reaching about 50% by 12 h. On the other hand, the activities of 5 long half-lived enzymes did not change in the neocortex at 5 and 15 h of reperfusion and regional protein concentrations were essentially unaffected over 6 days survival. The rate and extent of normalization of the amounts or activities of the vulnerable proteins varied. RNA polymerase II and ODC activities were restored within 4 h, and ODC showed a biphasic increase in activity, with peaks at 10 h and 2-3 days. RNA polymerase I and SAMDC activities were restored by 18 h and 5 days, respectively, whereas substance P concentrations did not completely recover, even at 6-15 days. The greater the regional reduction of blood flow during ischemia, the larger the net change (gain or loss) of SAMDC or ODC activity and the longer the time required to normalize the activities of these enzymes. The average rate of proteolysis, assessed by measuring the rate of clearance of 14C from protein prelabeled with [14C]bicarbonate, was abnormal during the first 2 days of reperfusion. Postischemic changes in both protein synthesis and degradation could affect the amounts of some of the proteins responsive to transient ischemia.

Nuclear RNA metabolism in rat hippocampal slices incubated in vitro

Rat hippocampal slices were incubated with [3H]uridine in vitro to analyze the metabolism of nuclear RNA and the RNA precursor fractions. Labeling of total nuclear RNA was linear for 4 h of incubation and proportional to the concentration of labeled uridine in the incubation medium. Addition of 3.5 X 10(-8) M corticosterone to the incubation medium produced an enhancement of nuclear RNA labeling with no significant effect on the labeling of the RNA precursor fraction. Progesterone and dexamethasone, at the same concentration, had no effect on either variable. Labeling of RNA by cerebellar slices under the same conditions was approximately one-half the value obtained using hippocampal slices and the cerebellar RNA precursor fraction accumulated only 65% of the radioactivity from [3H]uridine found in the hippocampal pool. Corticosterone had no effect on the labeling of total nuclear RNA in cerebellar slices. Nuclear poly(A)-containing RNA constituted 19% of the total labeled nuclear RNA in these incubations, as estimated by oligo (dT)-cellulose chromatography. Cordycepin (3'-deoxyadenosine) at a concentration of 25 micrograms/ml inhibited to some extent the labeling of total nuclear RNA and the RNA precursor fraction, but preferentially diminished the amount of labeled RNA bound to oligo (dT)-cellulose. Corticosterone increased the amount of [3H]RNA which bound to oligo (dT)-cellulose, while progesterone had no effect. These results show that hippocampal slices maintained in vitro, can be used to analyze nuclear RNA metabolism, one positive regulator of which in the rat hippocampus is the adrenal steroid, corticosterone.

Astrocyte cell lineage. V. Similarity of astrocytes that form in the presence of dBcAMP in cultures to reactive astrocytes in vivo

The relationship between astrocytes forming in the presence of dibutyryl cyclic AMP (dBcAMP) in culture and reactive astrocytes responding to a cerebral cortex stab wound was investigated using computerized image analysis (Zeiss IBAS 1) and immunocytochemical staining. The diameters of the nuclei of astrocytes in primary cultures of newborn mouse neopallial cells were compared to those of the nuclei of normal and reactive astrocytes in histological sections of mouse cerebral cortex. We found that the nuclei of astrocytes that formed in the presence of dBcAMP in cultures are significantly larger than those of spontaneously occurring small stellate astrocytes in culture and of normal astrocytes of the cerebral cortex in vivo but corresponded more closely to the nuclei of reactive astrocytes in the area surrounding a stab wound in the cerebral cortex. Large stellate cells formed in the presence of dBcAMP had vimentin and an increase in GFP-containing intermediate filaments. Formation of reactive astrocytes in vivo is also associated with an increase in both vimentin and GFP-containing intermediate filaments. These observations indicate a closer relationship of astrocytes formed in the presence of dBcAMP in cultures to the reactive astrocytes in the cerebral cortex than to normal astrocytes. We propose, therefore, that the large stellate astrocytes that form in the presence of dBcAMP be referred to as reactive astrocytes in culture.

Different Rates of Synthesis and Turnover of Ribosomal RNA in Rat Brain and Liver

The kinetics of in vivo labeling of cellular free UMP and nucleolar, nucleoplasmic, and cytoplasmic rRNA with [14C]orotate in rat brain and liver were investigated. Evaluation of the experimental data shows: (a) The rate of nucleolar precursors of ribosomal RNA (pre-rRNA) synthesis and the deduced rate of ribosome formation in brain is about fivefold lower than in liver and corresponds to 220-260 ribosomes/min/nucleus. (b) The lower rate of in vivo pre-rRNA synthesis is correlated with a lower activity of RNA polymerase I in isolated brain nuclei. (c) The half-lives of nucleolar rRNA in brain and liver are 210 and 60 min, respectively, thus showing a slower rate of processing of pre-rRNA in brain nucleoli. (d) The nucleo-cytoplasmic transport of ribosomes in brain is also markedly slower than in liver and reflects the lower rates of synthesis and processing of pre-rRNA. (e) Cytoplasmic ribosomes in brain and liver turn over with half-lives of about 6 and 4 days, respectively. It is concluded that the markedly lower rate of ribosome biogenesis in brain is specified mainly at the level of transcription of rRNA genes.

In vitro measurement of cytosol and cell nuclear androgen receptors in male rat brain and pituitary

An in vitro assay procedure is described for measuring androgen receptor binding in cytosol and cell nuclei of brain and pituitary tissue using [3H]R1881 as ligand. The cell nuclear assay uses the exchange method, which permits assessment of endogenous occupancy of androgen receptors in brain and pituitary. Competition and saturation analysis indicated that [3H]R1881 binding has the specificity and nanomolar affinity expected of an androgen receptor. Moreover, we demonstrated that androgen receptor binding predominated in cytosol from castrated rats and in cell nuclei of male rats treated in vivo with testosterone. Furthermore, as expected, testicular feminized male rats showed low levels of putative androgen receptors in both cytosol and cell nuclei.

The nuclear localization of a putative neurotransmitter receptor

A high affinity strychnine binding site has been identified within a membrane fraction prepared from partially purified rat brain nuclei. This interaction appears similar in its characteristics to that occurring in the non-nuclear membrane fraction which is thought to occur at the synaptic glycine receptor complex. Both the nuclear and non-nuclear membrane binding of tritiated strychnine is greater within the pons-medulla region than in the cerebral cortex. Nuclear membrane binding sites for dopamine, norepinephrine (beta-adrenergic), acetylcholine (muscarinic), GABA, and diazepam were not detected.

Morphological identification and biochemical characterization of isolated brain cell nuclei from the developing rat cerebellum

Cell nuclei from developing rat cerebellum were isolated and the various types of nuclei were characterized and quantified. Nuclear pellets appeared to be both quantitatively and qualitatively representative of the entire cerebellum, and of sufficient purity to perform biochemical studies as well as morphological comparison with histological sections. Isolated nuclei were classified into 6 groups based on nuclear size and shape, heterochromatin aggregations, and nucleoplasmic density. The total population of cerebellar cells primarily consisted of two types of nuclei after day 10. One group of nuclei, resembling those of internal granule neurons or external germinal cells, contributed at least 70% of the total isolated cell nuclei from day 1 to day 90, whereas another nuclear group that was identified as dark oligodendrocytes constituted 8-9% of the total population on days 45 and 90. Nuclear DNA, RNA, and protein content of the cerebellum also were determined throughout postnatal development. DNA concentration markedly declined after day 15, while the RNA/DNA ratio increased until day 3 and remained constant to day 90. The nuclear protein/DNA ratio increased from birth to day 3, decreased to its lowest value on day 10, and increased to day 90. Utilizing DNA values, the total cell population as well as contributions of different cell types were calculated. At birth the cerebellum was estimated to contain 5.9 million cells, increasing to 94 million by day 21. By day 90, 107 million cells were present, of which 8.6 million oligodendrocytes and 93.6 million internal granule cells were estimated.

Effects of early visual and complex stimulation on learning, brain biochemistry, and electrophysiology

A complex stimulation regimen (visual, auditory, and somesthetic-kinesthetic with forced movements, 30 times for 30 min each within 14 days) increased significantly the amplitudes of visual cortical evoked potentials (EPs) in adult rats if applied during the second postnatal fortnight. The EP increase after stimulation during the first 14 days after birth was not significant. Visual stimulation alone was compared with complex stimulation (visual plus forced movements) during the 2nd postnatal fortnight. More specific local changes in the visual cortex were revealed in brain biochemistry (lower DNA concentration, more RNA and protein per cell) and cortical electrogenesis (enhanced visual EPs) after visual stimulation alone, whereas complex stimulation induced more diffuse changes and rather profoundly influenced higher nervous functions (viz., memory retrieval - improved 24-h). Involvement of both specific and nonspecific mechanisms in the aftereffects of early stimulation is indicated.

Changes of CTP synthetase activity during postnatal rat brain development

The activity of CTP synthetase (UTP: ammonia ligase (ADP, EC. 6.3.4.2.) was determined in rat cerebral hemispheres and cerebellum during postnatal development. It was found that enzyme activity, when expressed per unit of protein or wet tissue weight, in both parts of the brain decreased with age, the diminution proceeding more rapidly in the cerebellum than in the hemispheres. When CTP synthetase was expressed on the basis of DNA an activity peak in the hemispheres with a maximum on the 5th day after birth was observed. The enzyme content per cell was several times lower in the cerebellum than in the hemispheres at each age studied, with the exception of 1-day-old animals, in which both tissues displayed similar activity. The results obtained were compared with literature data for the intensity of RNA synthesis in the developing brain. The conclusion was reached that the changes of CTP synthetase activity were closely related to the RNA metabolism. Therefore the enzyme under study may be one of the factors involved in cell control of RNA synthesis.

Uptake of GABA by neuronal and nonneuronal cells in dispersed cell cultures of postnatal rat cerebellum

A study was made of the time course and kinetics of [3H]GABA uptake by dispersed cell cultures of postnatal rat cerebellum with and without neuronal cells. The properties of GABA neurons were calculated from the biochemical difference between the two types of cultures. It was found that for any given concentration of [3H]GABA, or any time up to 20 min, GABA neurons in cultures 21 days in vitro had an average velocity of uptake several orders of magnitude greater than that of nonneuronal cells. In addition, the apparent Kmvalues for GABA neurons for high and low affinity uptake were 0.33 X 10(-6) M and 41.8 X 10(-4) M, respectively. For nonneuronal cells, the apparent Km for high affinity uptake was 0.29 X 10(-6) M. The apparent Vmax values for GABA neurons for high and low affinity uptake were 28.7 X 10(-6) mol/g DNA/min and 151.5 mmol/g DNA/min, respectively. For nonneuronal cells, the apparent Vmax for high affinity uptake was 0.06 X 10(-6) mol/g DNA/min. No low affinity uptake system for nonneuronal cells could be detected after correcting the data for binding and diffusion. By substituting the apparent kinetic constants in the Michaelis-Menten equation, it was determined that for GABA concentrations of 5 X 10(-9) M to 1 mM or higher over 99% of the GABA should be accumulated by GABA neurons, given equal access of all cells to the label. In addition, high affinity uptake of [3H]GABA by GABA neurons was completely blocked by treatment with 0.2 mM ouabain, whereas that by noneuronal cells was only slightly decreased. Most (75-85%) of the [3H]GABA (4.4 X 10(-6) M) uptake by both GABA neurons and nonneuronal cells was sodium and temperature dependent.