Structural maturation, cell proliferation and bioelectric activity in long-term slice-cultures of immature rat hippocampus

Explants of transverse slices of the 6-day-old rat hippocampus were grown in a serum-free medium for 2-14 days. Histology performed after various culturing periods demonstrated that these slices maintain a high degree of 3-dimensional organotypy, while undergoing growth and differentiation of the main cellular elements similar to that seen in vivo. Histological indications of continuing cell proliferation were verified by autoradiography showing a labelling of neuroblasts in the dentate gyrus and of glioblasts at the sites of gliogenesis observed in vivo. Spontaneous bioelectric activity and evoked potentials were recorded, both indicating the development of impulse generation and neuronal connectivity within the explant. Silver impregnation and electron microscopic studies lent further support for the presence of neuronal networks intrinsic to the hippocampus. These findings suggest that within the period studied the hippocampal slice cultures mature in a fashion similar to that seen in situ.

Mutational analysis of the Saccharomyces cerevisiae general regulatory factor CP1

The Saccharomyces cerevisiae general regulatory factor CP1, a helix-loop-helix protein that binds the centromere DNA element I (CDEI) of yeast centromeres, is required in yeast for optimal centromere function and for methionine prototrophy. Mutant alleles of CEP1, the gene encoding CP1, were generated by linker insertion, 5'- and 3'-deletion, and random mutagenesis and assayed for DNA binding activity and their ability to confer CP1 function when expressed in yeast. A heterologous CDEI-binding protein, TFEB, was also tested for CP1 function. The results suggested that DNA binding is required for both biological functions of CP1 but is not sufficient. A direct and quantitative correlation was observed between the chromosome loss and nutritional (i.e., Met) phenotypes of strains carrying loss of function alleles, but qualitatively the chromosome loss phenotype was more sensitive to decreased CP1 expression. The data are consistent with a model in which CP1 performs the same general chromatin-related function at centromeres and MET gene promoters and is normally present in functional excess.

NMDA receptor levels in chronically depolarized long-term neonatal rat neocortical explants

The levels of the N-methyl-D-aspartate subclass of glutamate receptor were determined in organotypic neocortical explants chronically exposed to a growth medium containing 25 mM potassium (K25). Explants exposed to 25 mM potassium for 2-3 weeks evinced significantly less binding of the non-competitive N-methyl-D-aspartate receptor-associated channel antagonist 125I-MK801 than did age-matched controls. Surprisingly, cultures that were returned to control growth medium for a further 2 or 7 days showed even less binding of the ligand. The Kd values of binding were not affected and were similar to those of fresh postnatal cortex. The maximum number of binding sites did not vary between postnatal day 6 and 14 days in vitro control cultures, but were significantly less than those measured at postnatal day 20 (comparable age: 14 days in vitro). Several conclusions can be drawn from these findings: (i) the density of the N-methyl-D-aspartate subclass glutamate receptor does not attain in vivo levels under the present culturing conditions, but remains at those levels associated with the stage of development at which the tissue was brought into culture, (ii) chronic depolarization results in a drastic reduction in N-methyl-D-aspartate receptor density, which is not compensated for after the return to normal growth conditions, (iii) depolarization selectively inhibits cellular maturation of the neocortex (but not survival, as shown previously), including neurotransmitter receptor production and/or insertion into membranes or assembly.

Possible cross-regulation of phosphate and sulfate metabolism in Saccharomyces cerevisiae

CP1 (encoded by the gene CEP1) is a sequence-specific DNA binding protein of Saccharomyces cerevisiae that recognizes a sequence element (CDEI) found in both yeast centromeres and gene promoters. Strains lacking CP1 exhibit defects in growth, chromosome segregation and methionine biosynthesis. A YEp24-based yeast genomic library was screened for plasmids which suppressed the methionine auxotrophy of a cep1 null mutant. The suppressing plasmids contained either CEP1 or DNA derived from the PHO4 locus. Subcloning experiments confirmed that suppression correlated with increased dosage of PHO4. PHO4c, pho80 and pho84 mutations, all of which lead to constitutive activation of the PHO4 transcription factor, also suppressed cep1 methionine auxotrophy. The suppression appeared to be a direct effect of PHO4, not a secondary effect of PHO regulon derepression, and was PHO2-dependent. Spontaneously arising extragenic suppressors of cep1 methionine auxotrophy were also isolated; approximately one-third of them were alleles of pho80. While PHO4 overexpression suppressed the methionine auxotrophy of a cep1 mutant, CEP1 overexpression failed to suppress the phenotype of a pho4 mutant; however, a cep1 null mutation suppressed the low inorganic phosphate growth deficiency of a pho84 mutant. The results may suggest that phosphate and sulfate metabolism are cross-regulated.

Effects of spontaneous bioelectric activity and gangliosides on cell survival in vitro

Chronic suppression of spontaneous bioelectric activity in spinal cord explants in the presence of tetrodotoxin (TTX) during network formation caused a large reduction in cell number (lowered DNA levels). The addition of gangliosides failed to protect against this cell loss. Conversely, the omission of galactose from the growth medium had no effect on DNA levels. It was concluded that the presence or absence of afferent selectivity is unlikely to require the survival of a regionally specific subpopulation of preferred dorsal root ganglion target cells. Neocortical explants also showed a large reduction in DNA levels following chronic TTX treatment, and morphometric analysis confirmed that neuronal survival was affected to the same degree. Chronic ganglioside supplementation failed to influence DNA and cell counts in either control or TTX-treated explants, but one of the added gangliosides (GD1a) stimulated extensive neuritic outgrowth in electrically silenced cultures. Particular ganglioside species, therefore, may exert a growth stimulating influence that can partially compensate for the absence of bioelectric self-stimulation during early development.

Meiosis in Saccharomyces cerevisiae mutants lacking the centromere-binding protein CP1

CP1 (encoded by the CEP1 gene) is a centromere binding protein of Saccharomyces cerevisiae that binds to the conserved DNA element I (CDEI) of yeast centromeres. To investigate the function of CP1 in yeast meiosis, we analyzed the meiotic segregation of CEN plasmids, nonessential chromosome fragments (CFs) and chromosomes in cep1 null mutants. Plasmids and CFs missegregated in 10-20% of meioses with the most frequent type of aberrant event being precocious sister segregation at the first meiotic division; paired and unpaired CFs behaved similarly. An unpaired chromosome I homolog (2N + 1) also missegregated at high frequency in the cep1 mutant (7.6%); however, missegregation of other chromosomes was not detected by tetrad analysis. Spore viability of cep1 tetrads was significantly reduced, and the pattern of spore death was nonrandom. The inviability could not be explained solely by chromosome missegregation and is probably a pleiotropic effect of cep1. Mitotic chromosome loss in cep1 strains was also analyzed. Both simple loss (1:0 segregation) and nondisjunction (2:0 segregation) were increased, but the majority of loss events resulted from nondisjunction. We interpret the results to suggest that CP1 generally promotes chromatid-kinetochore adhesion.

Rhythm generation in brainstem cultures grown in a serum-free medium

Electrophysiological studies were carried out on long term cultured brainstem tissue taken from neonatal rats with the object of investigating mechanisms underlying respiratory rhythm generation. The preparations were derived from 360 microns thick horizontal medullary slices which were explanted into a chemically defined nutrient medium and which remained organotypically intact for ca. 1 month. In 44 of the 50 explants examined both periodic and aperiodic bioelectric activity was detected, the cycle length of the former ranging from 0.5 to 10 s (mean, 2.7 s) at a pH of 7.4 and bath temperature of 32 degrees C. Periodic activity could take several forms, but commonly consisted of regularly repeated, 100-300 ms long, depolarizing (D-) waves or sequences of inhibitory and/or excitatory postsynaptic potentials. Lowering the pH of the superfusate by lowering the bicarbonate concentration, increasing the pCO2 or adding H+ shortened the interval between periodic events, and increased both the amplitude and duration of the D-waves. The interval was also shortened when the bath temperature was increased (Q10: ca.2.5). The mean resting membrane potential of neurons exhibiting periodic activity was -49 mV (n = 62) and not significantly different from that of aperiodically discharging neurons either in the same preparations or in cultured explants from the neocortex. These observations suggest that brainstem cultures constitute a useful 'model' system for studying pH-dependent rhythm generation in small neuronal networks of the medulla.

Reduction in bioelectric GABA and NMDA responses in organotypic neocortical explants by chronic elevation of potassium

Long-term cultures of organotypic neonatal rat neocortex slices were maintained in a serum-free medium supplemented with 25 mM potassium. Such cultures continue to be bioelectrically silent upon return to a 5 mM potassium medium. The absence of responses to pressure ejected gamma-aminobutyric acid (GABA) and N-methyl-D-aspartate (NMDA) from neurons in treated explants suggests that one consequence of chronic depolarization is a reduction in the density of postsynaptic transmitter receptors. [3H]Muscimol binding to neocortical membrane preparations shows a large reduction in the binding of this agonist to GABAA receptors. These data show that the quantitative expression of at least one neurotransmitter receptor, the GABAA receptor, relies on voltage-dependent activity in developing neocortical neurons in vitro.

Chronic blockade of bioelectric activity in neonatal rat neocortex in vitro: physiological effects

We have examined what effect the loss of spontaneous bioelectric activity has on neural network formation in organotypic rat neocortical explants grown under serum-free culture conditions. Explants were taken from dorsal midline (presumptive visual) and lateral (presumptive auditory) occipital cortex and chronically exposed to tetrodotoxin which blocked all measurable bioelectric activity between change of medium. Extracellular recordings revealed complex, rhythmic spontaneous and evoked multiunit discharges in all explants examined (following tetrodotoxin washout in the experimental group). Control auditory explants had significantly more sites from which electric activity could be recorded compared with control visual explants. Auditory cultures showed no effect of the tetrodotoxin treatment, whereas visual explants showed significant increases over control values, equalling the auditory values. This increased level of spontaneous bioelectric activity was maintained for at least 10 days following transfer of the cultures to control growth medium. There was no significant difference between control visual and auditory explants regarding the number of sites from which evoked activity was seen. Nor did either cortex group show an effect of tetrodotoxin on the number of sites from which evoked activity was seen. The frequency with which spontaneous bioelectric discharges occurred per site increased with age in auditory vs visual cortex. These differences, however, were abolished in the tetrodotoxin-treated groups. It was concluded that neocortical explants which have experienced chronic suppression of spontaneous electric activity did not suffer deficits in neural network formation, though there is an effect on the incidence and frequency with which such activity is given.

Electrocution injuries. A case report

A case study of a high-voltage injury was presented. The short period that the patient was in contact with the electrical source prevented further systemic injury and may have saved her life. The patient's present neuritis is indicative of long-term sequelae of electrocution injury, in which ischemic necrosis of the surrounding nerves can occur near or at the site of the exit wound.

Effect of chronic exposure to high magnesium on neuron survival in long-term neocortical explants of neonatal rats in vitro

In order to assess the effect of elevated magnesium, neuronal morphology and physiology was studied in chronically cultured organotypic neonatal rat occipital neocortex. Explants grown in 10 mM magnesium were found to experience an approximate 30% cell loss (as shown by cell count and DNA-protein analysis), while 12.5 and 15 mM magnesium showed ca. 47 and 60% cell losses, respectively. Intracellular recording from 10 mM magnesium explants revealed that measurable postsynaptic potentials and action potentials could occur, apparently depending on the type of cell examined. All post-synaptic activities ceased in 12.5 mM magnesium cultures, though action potentials could be elicited by current stimulation. The effects of known depolarizing agents, viz. potassium and N-methyl-D-aspartate, on 12.5 mM magnesium-grown explants were also examined. Explants grown in the presence of 12.5 mM magnesium plus 10 mM potassium showed a dramatic increase in the loss of neurons. The simultaneous addition of 6,7-dinitro-quinoxaline-2,3-dione showed this to be due to an increase in non-N-methyl-D-aspartate mediated cell death in response to glutamate release brought about by the depolarizing effects of the potassium. The addition of 10 microM N-methyl-D-aspartate to 12.5 mM magnesium-grown cultures, on the other hand, improved cell survival to control levels. The mechanism of this reciprocal neuroprotective effect of N-methyl-D-aspartate against magnesium has yet to be elucidated. We conclude that these findings are consistent with regard to the opposing actions of N-methyl-D-aspartate and magnesium on calcium influx and various metabolic processes within the explants.

Chronic blockade of bioelectric activity in neonatal rat cortex grown in vitro: morphological effects

Culture thickness, numerical density of neurons and neuronal survival were studied in timed series of control and tetrodotoxin-silenced neocortical cultures to provide information on the role of bioelectric activity on neuronal development. In control cultures, culture thickness and number of surviving neurons decrease during the first weeks in vitro, but remain constant between 2 and 3 weeks indicating that the cultures are essentially mature. In the 4th week in vitro a further decrease in surviving neurons was observed. In tetrodotoxin-treated cultures the number of surviving neurons decreased significantly between 1 and 2 weeks in vitro, to remain constant thereafter. However, culture thickness significantly increased at 3 and 4 weeks in vitro after an initial drop between 1 and 2 weeks. Compared to age-matched controls at 2 and 3 weeks in vitro, only ca 50% of the neurons survived the loss of bioelectric activity. Similar differences were present between 1 and 2 weeks. Thus, the loss of all measurable bioelectric activity induces neuronal death in neocortical explants, but promotes neuropil formation by the surviving cells.

Elevated potassium prevents neuronal death but inhibits network formation in neocortical cultures

Chronic depolarization is inimical to neuronal growth and synaptogenesis so that spontaneous action potential generation appears to be required for the normal cytomorphological maturation of neocortical networks. The efficacy of 25 mM K in suppressing spontaneous bioelectric activity was monitored by extra- and intracellular recording from the explants. Intracellular recording from individual neurons showed that membrane potentials were reduced to ca -30 mV in potassium cultures but rapidly repolarized to ca -50 mV when returned to normal growth medium. Though action potentials could be readily evoked from these explants, spontaneous discharges and postsynaptic potentials were absent from potassium-treated cultures. Both spontaneous bioelectric activity and postsynaptic potentials returned to the cultures by 5 days after returning the explants to normal growth medium. Extracellular recordings also showed that the explants were bioelectrically silent in the presence of 25 mM K or 25 mM K plus tetrodotoxin. In contrast to tetrodotoxin alone, bioelectric activity was absent when the cultures (with or without tetrodotoxin) were returned to normal growth medium. The explants gradually began to evince spontaneous bioelectric activity between 3 and 5 days after being returned to normal growth medium. Massive cell death induced by chronic exposure to tetrodotoxin was totally prevented by concomitant addition of 25 mM potassium, though these explants were significantly thinner than controls due to a large decrease in neuropil. We conclude that chronic depolarization of neonatal cortical explants by potassium results in a delayed return of spontaneous bioelectric discharges. Chronic depolarization results in a retardation of network formation in these explants apparently due to a lack of neurite and/or synapse formation.(ABSTRACT TRUNCATED AT 250 WORDS)

On the flexible interaction of yeast factor tau with the bipartite promoter of tRNA genes

Yeast transcription factor tau (analogous to vertebrate TFIIIC) interacts specifically with the internal split promoter of tRNA genes. Binding to the two promoter elements (A block and B block) occurs within 30 seconds even when they are separated by a long intervening sequence. Dimethylsulfate protection analysis of contact points between tau and the noncoding strand of a series of internally deleted tRNA3(Leu) genes shows that the specificity of the interaction is not affected by changes in the distance or in the relative helical orientation of the promoter elements. This result is consistent with the results of previous footprinting experiments (Baker, R.E., Camier, S., Sentenac, A. and Hall, B.D., 1987, Proc. Natl. Acad. Sci. USA, 84, 8768-8772). To test if any physical constraint is imposed on the DNA molecule upon tau binding, we analyzed the effect of introducing random single-strand breaks in the noncoding strand of the tRNA gene. Whereas some nicks located in the A block were found to prevent tau binding, no single-strand break in the B block region or in the DNA between the A and B blocks were observed to inhibit or facilitate the binding of tau. We therefore propose that the great flexibility of the tau-tDNA interaction is mostly due to the tau protein itself.

Isolation of the gene encoding the Saccharomyces cerevisiae centromere-binding protein CP1

CP1 is a sequence-specific DNA-binding protein of the yeast Saccharomyces cerevisiae which recognizes the highly conserved DNA element I (CDEI) of yeast centromeres. We cloned and sequenced the gene encoding CP1. The gene codes for a protein of molecular weight 39,400. When expressed in Escherichia coli, the CP1 gene directed the synthesis of a CDEI-binding protein having the same gel mobility as purified yeast CP1. We have given the CP1 gene the genetic designation CEP1 (centromere protein 1). CEP1 was mapped and found to reside on chromosome X, 2.0 centimorgans from SUP4. Strains were constructed in which most of CEP1 was deleted. Such strains lacked detectable CP1 activity and were viable; however, CEP1 gene disruption resulted in a 35% increase in cell doubling time and a ninefold increase in the rate of mitotic chromosome loss. An unexpected consequence of CP1 gene disruption was methionine auxotrophy genetically linked to cep1. This result and the recent finding that CDEI sites in the MET25 promoter are required to activate transcription (D. Thomas, H. Cherest, and Y. Surdin-Kerjan, J. Mol. Biol. 9:3292-3298, 1989) suggest that CP1 is both a kinetochore protein and a transcription factor.

Preoperative and perioperative anesthesia considerations for the diabetic patient

Surgery involving diabetic patients requires special consideration of the possible effects of anesthesia. The authors discuss factors that affect the choice of anesthetic agent and recommendations for preparing the diabetic patient for surgery, along with potential complications.

The effects of potassium-induced depolarization, glutamate receptor antagonists and N-methyl-D-aspartate on neuronal survival in cultured neocortex explants

The effects of elevating the potassium concentration of the growth medium of neocortical explants was studied. Under control conditions, 10 mM potassium resulted in ca 20% decrease in the number of surviving neurons. The same potassium concentration, however, was clearly neurotrophic in tetrodotoxin-grown cultures: tetrodotoxin-induced neuronal death was significantly reduced. Both effects could be mimicked by the addition of 10 microM N-methyl-D-aspartate (NMDA); lower concentrations were without effect; higher concentrations were neurotoxic under both control and tetrodotoxin conditions. The neurotoxic, as well as the neurotrophic effects of 10 mM potassium appear to be mediated through depolarization-induced glutamate release since they could be influenced by the application of glutamate receptor antagonists. The addition of the NMDA receptor antagonist D-2-amino-7-phosphonoheptanoate (APH) blocked the trophic effect of 10 mM potassium in tetrodotoxin-grown cultures, resulting in low survival. On the other hand, the addition of the non-NMDA antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) resulted in neuronal survival similar to control cultures, indicating that it blocked the toxic effects of glutamate, leaving the trophic effects on the NMDA receptor untouched. Under control (non-TTX) conditions, neither DNQX nor APH showed significant effects on 10 mM potassium-induced cell death, indicating that stimulation of the non-NMDA, as well as the NMDA receptors is neurotoxic. This differential effect of NMDA receptor stimulation on neuronal survival is discussed with respect to the maturational and/or functional state of the neurons in the culture.

Purification of the yeast centromere binding protein CP1 and a mutational analysis of its binding site

CP1 is a yeast protein which binds to the highly conserved DNA element I (CDEI) of yeast centromeres. We have purified CP1 to near homogeneity; it is comprised of a single polypeptide of molecular weight 58,400. When bound to yeast CEN3 DNA, CP1 protects a 12-15-base pair region centered over CDEI. Methylation interference experiments show that methylations of residues located outside of the 8-base pair CDEI sequence have no detectable effect on CP1 binding, suggesting that the DNA sequences important for CP1 recognition are confined to the CDEI octanucleotide. The equilibrium constant for CP1 binding to CEN3 DNA is relatively low, 3 x 10(8) M-1. Using a novel method to determine relative DNA binding constants, we analyzed the effect of CDEI mutations on CP1 binding. A C to T point mutation at position 5 (CO1) reduces the equilibrium constant about 35-fold, while the insertion of an additional T at this position (CAT) reduces the equilibrium constant 1,400-fold. The effect of these mutations on mitotic centromere function in vivo was assessed using a plasmid stability assay. While the CO1 mutation had a slight effect, the CAT mutation significantly impaired function, implying that CP1 binding is required for the optimal mitotic function of yeast centromeres.

Electrophysiological properties of neurons in neonatal rat occipital cortex slices grown in a serum-free medium

The electrophysiological properties of individual neurons within organotypic explants of neonatal rat cortex were examined via intracellular recordings. The explants were grown for two weeks in a serum-free medium. The electrophysiological properties of the neurons within these explants were similar to those reported for both adult cortex in vivo and short-term in vitro slice preparations. The results of the present study show that cortical explants grown under serum-free conditions can serve as a useful model for long-term developmental studies associated with the physiological basis of neural network formation.

Gangliosides of the mouse spinal cord: a comparison in in vivo and in vitro tissues

Ganglioside profiles in spinal cord from 13-day mouse fetuses, 21-day postnatal and adult mice were compared with those harvested from organotypic cross-sections of fetal mouse spinal cord grown for 28 days in vitro in a serum-free medium. All the major species of gangliosides reported for brain were present both in the in vivo tissue and cultured spinal cord, though not necessarily at each developmental stage examined. Fresh tissues showed increases and decreases in various gangliosides as have been reported for higher brain centers at similar stages of development in mammals and birds. However, qualitative and quantitative differences exist between fresh spinal cord and cultured cord explants as well as between galactose-grown and galactose-free cultures. Spinal cord explants grown in the presence of galactose showed measurable amounts of GM2 and GM3 which were not detected in the control-defined medium-grown cultures. The differences between the two culture groups may be related to interneuronal connectivity patterns.

Non-selective afferent innervation develops in embryonic mouse spinal cord-dorsal root ganglia explants chronically exposed to GM1 ganglioside

Projection patterns of dorsal root ganglion afferents within organotypic explants of fetal mouse spinal cord were examined histologically using a horseradish peroxidase staining method. All explants were also examined electrophysiologically and showed spontaneous and evoked bioelectric discharges, which were evenly distributed across the cord explants. Explants chronically grown in a serum-free medium containing the monosialoganglioside GM1 failed to develop dorsal cord selectivity as was previously observed when a mixture of gangliosides was used. It therefore appears that not all gangliosides can induce selectivity in this model.

Differential antiepileptic effects of the organic calcium antagonists verapamil and flunarizine in neurons of organotypic neocortical explants from newborn rats

Effects of the organic calcium antagonists verapamil and flunarizine on pentylenetetrazol induced paroxysmal depolarizations were tested in organotypic neocortical explants taken from neonatal rats. In these in vitro experiments the papaverin derivative verapamil depressed, and finally abolished, epileptic discharges in all cases. The piperazine derivative flunarizine, however, which is known to suppress epileptic discharges in hippocampal CA3 neurons (Bingmann and Speckmann 1986), showed no significant antiepileptic effects in the explanted neocortical neurons. Thus, the present findings may indicate that the suppressive action of flunarizine on the generation of paroxysmal depolarizations is restricted to distinct populations of neurons.

Gene size differentially affects the binding of yeast transcription factor tau to two intragenic regions

Yeast transcription factor tau (transcription factor IIIC) specifically interacts with tRNA genes, binding to both the A block and the B block elements of the internal promoter. To study the influence of A block-B block spacing, we analyzed the binding of purified tau protein to a series of internally deleted yeast tRNA(3Leu) genes with A and B blocks separated by 0 to 74 base pairs. Optimal binding occurred with genes having A block-B block distances of 30-60 base pairs; the relative helical orientation of the A and B blocks was unimportant. Results from DNase I "footprinting" and lambda exonuclease protection experiments were consistent with these findings and further revealed that changes in A block-B block distance primarily affect the ability of tau to interact with A block sequences; B block interactions are unaltered. When the A block-B block distance is 17 base pairs or less, tau interacts with a sequence located 15 base pairs upstream of the normal A block, and a new RNA initiation site is observed by in vitro transcription. We propose that the initial binding of tau to the B block activates transcription by enhancing its ability to bind at the A block, and that the A block interaction ultimately directs initiation by RNA polymerase III.

Central neuronal responsiveness to sensory ganglion stimulation is correlated with the incidence of spontaneous bioelectric activity in developing spinal cord cultures

In spinal cord explants co-cultured with dorsal root ganglion cells for 3-4 weeks in a (horse)serum-containing medium, the spread of ganglion-evoked action potentials from monosynaptic innervation sites ("polysynaptic excitability index") was not correlated with the incidence of neuronal "background" discharges. Moreover, chronic exposure of serum-grown cultures to tetrodotoxin (TTX) in a dose sufficient to reversibly block bioelectric activity, failed to significantly affect this index. For explants grown in a chemically defined medium (CDM) similar excitability scores were obtained only if a low level of spontaneous activity was measured. The most active preparations scored considerably higher, with intermediate values being found in the moderately active cultures. Chronic TTX-exposure in developing CDM-grown cultures reduced their excitability scores to the level found in weakly active, untreated, explants despite a normal incidence of spontaneous activity. The present study indicates that low levels of spontaneous activity in untreated explants were associated with a similar sluggishness of DRG-evoked responses as previously observed after chronic treatment with TTX. These results give additional grounds for confidence that this reduced responsiveness of spinal cord neurons to sensory input is indeed attributable to prolonged reduction of centrally generated excitation during development in vitro.

Some functional effects of suppressing bioelectric activity in fetal mouse spinal cord-dorsal root ganglion explants

Organotypic explants of fetal mouse spinal cord-dorsal root ganglia were grown for 3 weeks in the presence of 10 mM magnesium ion, which effectively eliminated all recordable bioelectric activity throughout the culturing period. When tested in minimal essential medium, the chronically silenced explants had significantly fewer points from which spontaneous neuronal activity could be recorded. In addition, fewer points could be found that showed dorsal root ganglion-evoked responses, resulting from a greater tendency for the spinal cord activity to be restricted to the vicinity of the dorsally entering DRG fibers. These findings, therefore, support the hypothesis that spontaneous bioelectric activity is required for functional as well as structural maturation of neural networks.

Gangliosides restore the specificity of afferent projection patterns in spinal cord explants chronically exposed to tetrodotoxin

Sensory afferent projection patterns within organotypic explants of fetal mouse spinal cord-dorsal root ganglia (SC-DRG) were mapped out histologically using an HRP-staining method. Cultures grown in tetrodotoxin-containing medium with added gangliosides, in contrast to those grown without the addition of these compounds, showed preferential DRG innervation of the dorsal half of the cord. It therefore appears that gangliosides can compensate for the absence of functional activity during the development of selective innervation patterns.

Effects of tRNATyr point mutations on the binding of yeast RNA polymerase III transcription factor C

A physical DNA binding assay was employed to analyze the binding of yeast RNA polymerase III transcription factor C (TFIIIC) to tRNA genes. The assay allowed us to measure the equilibrium constants for specific and nonspecific TFIIIC-DNA binding and to assess the effects of tRNATyr-DNA gene promoter mutations on binding. Sequence alterations in the B block element of the promoter greatly affect the equilibrium constant for specific TFIIIC binding (K8). Mutations which decrease tRNATyr homology to the recognized B block consensus sequence drastically reduce K8 (43- to 370-fold), while mutations which increase homology increase K8 (4- to 5-fold). By contrast, point mutations in the A block element of the tRNATyr promoter have less than 2-fold effects on K8; however, total deletion of A block sequences reduces K8 2- to 5-fold. These results indicate that TFIIIC-rTNA gene binding involves interactions with both A block and B block sequences, but B block interactions dominate, and the relative contribution of A block interactions is small. Since A block sequences are absolutely required for active tRNA gene transcription, the binding results suggest that the role of A block sequences in transcription is not confined solely to TFIIIC binding.

Horseradish peroxidase tracing of dorsal root ganglion afferents within fetal mouse spinal cord explants chronically exposed to tetrodotoxin

Afferent projection patterns within organotypic explants of fetal mouse spinal cord-dorsal root ganglia (DRG) were mapped out histologically using an HRP-staining method. The role of spontaneous bioelectric activity in the development of cord-DRG connections was studied using tetrodotoxin (TTX) to eliminate action potential discharges in the experimental cultures. Cultures grown in TTX-supplemented medium had a significantly lower proportion of DRG afferents within the dorsal half of the cord explant than did untreated cultures. In addition, afferent fiber entrances were made predominantly on the dorsolateral aspect in control cord explants, in contrast with the more diffuse entrance pattern displayed by the experimental group. Comparison of those cultures in both groups where the fiber entrances were chiefly dorsal revealed a greater tendency in the TTX group for DRG afferents to grow ventrally after penetrating the cord. Thus, it appears that bioelectric activity of the target neurons may be required by DRG afferents for the development of selective innervation patterns.

Structural features of yeast tRNA genes which affect transcription factor binding

Transcription of yeast tRNA genes in vitro requires, in addition to RNA polymerase III, two accessory factors which are resolved by ion-exchange chromatography. One of these transcription factors (factor C) binds to tRNA genes. The stability of factor C-tRNA gene complexes is gene-dependent: the tRNAAGGArg gene forms a highly stable complex while tRNA3Leu and tRNATyr gene complexes are unstable under our standard assay conditions. To determine how differences in tRNA gene structure affect factor C binding, mutant tRNATyr genes, internally deleted tRNA3Leu genes and hybrid transcription units containing both tRNATyr and tRNA3Leu segments were compared in their abilities to stably bind factor C. Sequence changes in either of the two highly conserved promoter elements (A block and B block) affect factor C complex stability. Changes towards the consensus sequence increase complex stability while changes away from the consensus sequence drastically reduce stability. Also, the distance separating the A and B blocks affects complex stability; 34-53 bp gives highest stability. These results indicate that the stable binding of transcription factor C to tRNA genes involves interactions with both A block and B block sequences.

Effects of chronic suppression of bioelectric activity on the development of sensory ganglion evoked responses in spinal cord explants

Dorsal root ganglion (DRG) afferent terminals were identified, using electrophysiological techniques, within fetal mouse spinal cord cross-sections cultured in vitro. Afferent distribution patterns were monitored in explants grown for 3 to 6 weeks either in a serum-supplemented or in a serum-free, chemically defined medium (CDM). Bioelectrically active control explants from both series were compared with explants which had been reversibly silenced by chronic exposure to tetrodotoxin (TTX). The control (serum-grown) cultures showed a significant dorsal cord innervation preference, whereas in the corresponding TTX series there was an equal dorsoventral distribution. In the CDM series the mean number of DRG evoked responses was lower at first in TTX-grown than in control cultures, but with age in vitro there was a rise in excitability to normal levels. Spontaneous neuronal activity was abnormally low in cultures (serum as well as CDM-grown) which had been exposed to TTX. It is concluded that bioelectric activity may be an important factor in the proper regulation of synaptic connectivity and functional responsiveness in the developing spinal cord.

Effects of chemical additives on functional innervation patterns in mouse spinal cord-ganglion explants in serum-free medium

The distribution of sensory evoked bioelectric activity was examined in spinal cord-dorsal root ganglion (SC-DRG) preparations cultured in a chemically defined, serum-free medium (CDM). DRG afferents showed no preferential innervation of dorsal cord regions in this CDM, on the basis of electrophysiological mapping of the distribution of evoked responses at 4 weeks in vitro. Addition of chondroitin sulfate, galactose-1-phosphate or D(+)-galactose (but not glucose-1-phosphate) to the CDM resulted in a significant increase in presumed monosynaptic connections within the dorsal cord, thus mimicking the results observed in serum-supplemented medium [1,6]. Inasmuch as D(+)-galactose bears no negative charges yet restores the selective functional innervation, whereas glucose-1-phosphate (a highly charged molecule) fails to do so, it is concluded that it is galactose utilization, rather than the charged nature of the chondroitin sulfate and galactose-1-phosphate molecules, which is responsible for the effect.

Effects of gangliosides on the development of selective afferent connections within fetal mouse spinal cord explants

Monosynaptic evoked responses were used to localize dorsal root ganglion (DRG) afferent terminals within organotypic fetal mouse spinal cord explants which had been chronically exposed to purified bovine gangliosides during early development. Ganglioside grown cultures showed a highly significant increase in dorsal cord innervation preferences in comparison with control cultures. The amount of evoked activity was significantly lower than was observed in controls, suggesting that the formation of 'incorrect' functional connections was blocked by specific chemical factors. Exposure to N-acetylgalactosamine, a major ganglioside amino sugar, also resulted in an increased dorsal cord innervation preference by the DRG afferents.

A cross-national study of differences in length of stay of patients with cardiac diagnoses

To determine the reason for large regional differences in average hospital length of stay shown in federal discharge abstract data, the medical records of 482 cardiac patients from hospitals belonging to two metropolitan area PSROs of Baltimore, Maryland, and 438 cardiac patients from hospitals in the Metropolitan area PSRO from Portland, Oregon, were reviewed, stratified by diagnosis and complications, and compared for length of stay. Cardiac patients were hospitalized between 2.5 and 7 days longer in Baltimore than in Portland. Federal data on length of hospital stay were basically correct for the diagnostic categories studied. Length-of-stay differences could not be explained by patient differences and appeared to be due to differences in physician practice patterns.

Influence of growth medium, age in vitro and spontaneous bioelectric activity on the distribution of sensory ganglion-evoked activity in spinal cord explants

The role of serum added to the culture medium and of spontaneous bioelectric activity in the development of sensory afferent connections was studied, employing fetal mouse spinal cord explants with attached dorsal root ganglia (DRG) as an in vitro model system. Afferent DRG terminals in the cord explants were localized on the basis of 'fixed-latency' DRG-evoked action potentials, which were anatomically verified in several experiments using horseradish peroxidase histology. In serum-supplemented medium (HSSM), but not in chemically defined medium (CDM), those DRG fibers which grew into the dorsal side of the cord terminated predominantly within the dorsal cord region, and remained there throughout the experimental period (18-33 days in vitro). In contrast, ventrally entering fibers terminated equally in both the dorsal and the ventral cord regions in young cultures (18-24 days in vitro) but were no longer observed after 27 days in vitro. Cultures grown in HSSM with the addition of xylocaine, in order to chronically suppress spontaneous bioelectric activity, essentially corresponded (at 25-32 days in vitro) to the picture seen in the control series at the same age. On the basis of polysynaptic DRG-evoked responses in the cord, developmental changes in local neuronal networks were inferred which resulted in less spread of DRG-evoked activity with age in HSSM, and more spread with age in CDM-grown cultures. It is concluded that for the formation of selective DRG connections in the spinal cord: (i) a serum-borne factor plays a role: and (ii) functional activity is not required.

Learning disabled programs in California community colleges

In a survey of the 106 California Community Colleges, it was found that over 75% operated formal programs for the learning disabled, while an additional 12% provided informal services for their LD student population. Though diversity existed among the college LD programs surveyed, a consistency of process and practice was evident. Most colleges provided similar means for the identification and diagnosis of potential LD students and in the support services delivered. More specifically, LD programming similarities were demonstrated in intake interviewing, referral procedure and agencies, assessment tools, personnel, counseling and availability of a learning center.

Based on the model provided by the California Community Colleges, these recommendations are made for adoption by others who wish to implement LD programming at the post-secondary level: (a) a defined identification and assessment approach, IEP development, and delivery system; (b) collection of assessment data on all students that measures discrepancy; (c) appropriate, valid, and reliable assessment instruments; (d) IEPs that indicate assessment data, discrepancy, needs, goals, and programming methodology; (e) a multidisciplinary team approach to assessment, IEP development, and delivery systems; (f) consistent data reporting methods securely maintained; (g) confidentiality of material; and (h) in-service programming.

Nucleotide sequences of yeast genes for tRNASer 2 , tRNAArg 2 and tRNAVal 1 : homology blocks occur in the vicinity of different tRNA genes

Three members of a collection of pBR322-yeast DNA recombinant plasmids containing yeast tRNA genes have been analyzed and sequenced. Each plasmid carries a single tRNA gene: pY44, tRNA(2); pY41, tRNA(2); pY7, tRNA(1). All three genes are intronless and terminate in a cluster of Ts in the non-coding strand. The sequence information here and previously determined sequences allow an extensive comparison of the regions flanking several yeast tRNA genes. This analysis has revealed novel features in tRNA gene arrangement. Blocks of homology in the flanking regions were found between the tRNA genes of an isoacceptor family but, more interestingly, also between genes coding for tRNAs of different amino-acid specificities. Particularly, three examples are discussed in which sequence elements in the neighborhood of different tRNA genes have been conserved to a high degree and over long distances.

The termination of cutaneous nerves in the dorsal horn of the spinal cord in normal and in skin-rotated frogs

Following transganglionic transport of cobaltic lysine applied to the cut end of cutaneous nerves, the central terminal arbours were filled to such an extent that it was possible to visualize the dermatomal projection upon the dorsal horn in unoperated and in skin-rotated frogs. Sensory nerves of the trunk skin terminate in an oval-shaped area which probably corresponds to laminae 1-3 (or 1-4) in the mammalian spinal cord. One type of terminating collateral had a restricted terminal field either in the medial, or in the lateral, part of the oval-shaped area. Another type ended with a large terminal arbour covering almost the total extent of the oval shaped area. These terminal arbours were found for both the dorsal and the ventral cutaneous nerves. Dorsal cutaneous nerves projected preferentially to the lateral part, while ventral cutaneous nerves projected to the medial part, but both nerves sent a significant contingent of collaterals to the whole extent of the oval-shaped area. A rearrangement of the central projection patterns of the dorsal cutaneous nerves, consistently mediating misdirected responses, was not observed in skin-rotated frogs. Collaterals of trunk skin nerves terminated exclusively in the thoracic segments; they did not enter the limb-innervating (brachial and lumbosacral) segments of the spinal cord. The results corroborate the crossed pattern of sensory input in the dermatomal projection. The large, extensively overlapping, areas of termination of individual skin nerves suggest that wiping responses mediated by these nerves should be regarded as complex behaviour released from a preprogrammed centre rather than a reflex arc in which the presence specificity would be determined by wiring specificity.

Peripheral reinnervation patterns and dorsal root ganglion cell topography in skin-grafted Rana pipiens frogs

Behavioral responses to mechanical stimulation of the skin were observed in unoperated, 180 degrees skin-rotated and sham-grafted Rana pipiens frogs before and after crushing various cutaneous nerve bundles. In the two control groups, wiping responses directed towards the animal's dorsum were mediated solely via dorsomedial (DM) and dorsolateral (DL) nerve trunks. In skin-rotated frogs, DM and DL nerve trunks were responsible for almost all of the misdirected responses elicited from dorsal cutaneous areas. Six frogs (2 sham- and 4 skin-rotated) possessed some areas of plical skin from which responses could only have been mediated via more ventrally located nerve trunks. However, such dorsal expansions of ventral receptive fields never included the midline skin areas from which misdirected responses had been elicited in the intact animal. The topographic arrangement of cells within the DRG appears to be weakly polarized in cobalt-stained sections, but with large individual variations in size and observed number of neuronal profiles. For the skin-rotated group the ratio of cobalt-filled profiles in the dorsal as compared with the ventral half of the ganglion was 1.6, which did not differ significantly from the control value of 1.9. Taken as a whole, the results of the present study indicate that selective (re)innervation of displaced skin by the original nerve fibers cannot explain the origin of misdirected responses in Rana pipiens.

Immunocytochemical identification of phenylalanine hydroxylase and albumin in cultured hepatoma cells and isolated rat hepatocytes

Rhodamine-conjugated antibodies specific for phenylalanine hydroxylase and serum albumin were employed as cytochemical probes to identify these two proteins in H4 hepatoma cells and in isolated rat hepatocytes. Each fluorescent antibody stained the cells specifically and in a distinctive manner. In both cell types, albumin staining was discretely localized in cytoplasmic and in H4 cultures varied somewhat from cell to cell. Evidence from cultures of REB15 cells, a strain derived by cloning H4 cells in tyrosine-free medium, suggested that the staining variability of H4 cells could reflect a variability in phenylalanine hydroxylase content. Hydrocortisone-treated H4 cells and REB15 cultures contain increased amounts of phenylalanine hydroxylase; and all cells in the culture appear to be induced by the hormone. Evidence was presented to show that the albumin visualized within the isolated hepatocytes had been synthesized by these cells, and, furthermore, that quantitatively nearly all intracellular albumin in the isolated rat hepatocytes appeared to be entrained in the secretion pathway (analogous data already exist for H4 cells [Baker, R.E., and R. Shiman. 1979. J. Biol. Chem. 254:9633-9639]). By scoring specific fluorescence, 86 and 98% of the H4 cells and 89 and 98% of the isolated hepatocytes were found to contain phenylalanine hydroxylase and albumin, respectively. Therefore, almost all cells in each population appeared to synthesize both proteins. An implication of these findings is that in rat virtually all liver parenchymal cells must synthesize both phenylalanine hydroxylase and albumin.

Chemically defined medium enhances bioelectric activity in mouse spinal cord-dorsal root ganglion cultures

Co-cultures of mouse spinal cord with dorsal root ganglion (DRG) cultures were grown either in horse serum (HS)-supplemented medium or in a serum-free, chemically defined medium (CDM). The cytoarchitecture of cord--DRG explants was fully retained in CDM, with little or no distortion due to flattening of the explant, as is invariably observed in HS-supplemented cultures. Functional properties such as bioelectric activity and DRG--spinal cord interconnectivity were well sustained in CDM.

Peripheral reinnervation patterns and dorsal root ganglion topography in skin-grafted frogs: a behavioral and histological examination

Cutaneous respective fields for the first ventrolateral (VL1) and dorsomedial nerve trunks were mapped out behaviourally in normal and in skin-grafted Discoglossus pictus frogs. Ventrally directed wiping responses were obtained from stimulation of dorsally located belly skin grafts in all experimental animals. These misdirected responses were abolished completely by cutting either the dorsomedial nerve trunk or both the dorsomedial and the VL1 nerve trunks. The topography of cutaneous neurons of the dorsal root ganglion innervating dorsal skin areas was demonstrated by back-filling the dorsomedial nerve trunk with cobalt. In both normal and skin-grafted frogs, twice as many cobalt-filled neurons were observed in the dorsal half of the ganglion as in the ventral half although the absolute number of filled cells in different regions was the same in both groups. It was concluded that misdirected responses following skin rotation cannot be explained on the basis of a re-establishment of the original peripheral nerve connections.

Measurement of phenylalanine hydroxylase turnover in cultured hepatoma cells

A substantially new method has been developed to measure protein turnover. Its basis is the notion that in labeling experiments a secreted protein can be used to determine the specific radioactivity of the intracellular amino acid precursor pool. To measure protein turnover in the Reuber hepatoma H4 cell line, cultures were labeled with [3H]leucine for specified periods after which phenylalanine hydroxylase was isolated and its leucine specific radioactivity determined. Serum albumin secreted by the cultures was also isolated and used to estimate the leucine precursor pool specific radioactivity. The protein half-life of phenylalanine hydroxylase could them be calculated. Experiments performed at long and short labeling times and with high and low concentrations of leucine in the medium yielded equivalent results. Phenylalanine hydroxylase half-life in the H4 cells was investigated under both normal and hydrocortisone-induced growth conditions. Average half-lives of 7.4 and 8.2 h were found for induced and uninduced cultures, respectively. Although these measured enzyme half-lives were not essentially different, the steady state level of phenylalanine hydroxylase was increased 6.2-fold upon hydrocortisone induction, from 0.076 to 0.47 microgram/10(6) cells. The results demonstrated that hydrocortisone induces phenylalanine hydroxylase in the H4 cells by causing an increase in the rate of enzyme synthesis.

Topography of cutaneous mechanoreceptive neurones in dorsal root ganglia of skin-grafted frogs

1. Topographical distribution patterns of dorsal root ganglion (d.r.g.) cutaneous neurones providing innervation to various body surfaces were examined in doublypithed Discoglossus pictus frogs.2. Using electrophysiological methods, sensory neurones innervating back skin were observed to predominate on the dorsal ganglionic surfaces, while belly skin neurones were most prevalent in the caudal half of the d.r.g. ventral surfaces. Flank neurones clustered in the medial half of d.r.g. ventral surfaces.3. Cutaneous neuronal distribution patterns within the d.r.g. of 180 degrees skin grafted animals were indistinguishable from those observed in control frogs.4. Sensory neurone distribution patterns were found to be altered in all animals with single skin type grafts. Projection patterns were always heaviest towards the autograft, which was on the opposite body surface (i.e. dorsally located d.r.g. sensory neurones projected to back skin on the frog's ventrum, while ventrally located neurones projected to belly skin on the frog's dorsum).5. The results are discussed in the light of several selective outgrowth mechanisms which have been proposed as a possible underlying basis for the development of misdirected wiping reflex behaviour in skin grafted anurans. The findings indicate that none of the proposed selective growth mechanisms can account adequately for the development of misdirected wiping reflexes, at least in the species studied.6. It is suggested that selective cell replacement, based upon competition among prespecified cutaneous neurones, might best account for the development of normal and misdirected wiping reflexes in frogs.