Effects of bifemelane hydrochloride on cortical neuronal activity in cats

The effects of bifemelane hydrochloride on neuronal activity in the visual cortex of the cat were studied by microiontophoretic application under methoxyflurane anesthesia. Of 195 neurons examined with both acetylcholine (ACh) and bifemelane, 67 cells (34%) were excited and 7 cells (4%) were inhibited by ACh. The effect of bifemelane was excitatory on 122 neurons (63%), inhibitory on 20 (10%) and unchanged on the rest. In 60 cells out of the above 122 neurons, bifemelane showed a similar discharge pattern to ACh with a slow onset and delayed termination. The bifemelane-induced excitation was, in 18 out of 22 cells, antagonized by atropine (30-40 nA). Also, a potentiation in bifemelane-induced discharges by physostigmine (30-50 nA) was observed in 14 of the 32 cells tested. The firing evoked by ACh (80-100 nA) was potentiated during of after the application of bifemelane (30-40 nA) in 9 out of 29 neurons, which were not excited by bifemelane alone. These results suggest that neuronal discharges produced by bifemelane are induced at least in part, through a muscarinic ACh receptor, although other mechanisms may possibly be involved.

DNA replication of single-stranded DNA of phage fd microinjected into Xenopus laevis eggs

Single-stranded circular DNA of phage fd was microinjected into Xenopus laevis eggs and DNA synthesis was analyzed after incubation. An efficient DNA synthesis occurred in the eggs: 2.7 ng of DNA was newly formed in an egg whose volume is approximately 900 nl during a 5-h incubation at 20 degrees C. The DNA synthesis was sensitive to aphidicolin, suggesting that DNA polymerase alpha participates in the synthesis. Agarose gel electrophoresis showed that full size of fd DNA is synthesized and that replicative form I of fd DNA is the major form of the newly produced DNAs. These results suggest that priming of DNA synthesis, elongation of DNA chain and ligation of DNA strands take place co-operatively in the egg with single-stranded DNA as a template.

The fate of DNA originally existing in the zygote nucleus during achromosomal cleavage of fertilized echinoderm eggs in the presence of aphidicolin: microscopic studies with anti-DNA antibody

In fertilized echinoderm eggs, the male and female pronuclei fuse to form the diploid nucleus even in the presence of aphidicolin, a specific inhibitor of eukaryotic DNA polymerase-alpha. The subsequent first cleavage is independent of chromosomes but dependent on spindle and amphiaster. The fate of DNA originally existing in the fused nucleus during achromosomal cleavage of fertilized sea urchin and starfish eggs induced by aphidicolin was determined using antidenatured DNA antibody. The nucleus is not formed in the divided daughter cells at the two-cell stage but the nuclear-envelope-free chromatin mass which is unassociated with mitotic apparatus remains in the center region of embryos, especially near the first cleavage furrow. These results indicate that the condensed and nonreplicated chromatin can not be associated with spindle and asters in the presence of aphidicolin.

Histospecific acetylcholinesterase development in the presumptive muscle cells isolated from 16-cell-stage ascidian embryos with respect to the number of DNA replications

The presumptive muscle cells (B5.1 blastomeres) were isolated from 16-cell-stage embryos of the ascidian, Ciona intestinalis. The isolated cells were allowed to divide either twice or three times thereafter. Then further divisions of the cells were continuously inhibited by a simultaneous treatment with aphidicolin (a specific inhibitor of DNA synthesis) and cytochalasin B (an inhibitor of cytokinesis). When development of muscle-specific acetylcholinesterase in these division-arrested progeny cells of B5.1 blastomeres was examined histochemically, the B5.1 blastomeres which had been allowed two further divisions did not produce any detectable acetylcholinesterase activity. Whereas those which had been allowed three further divisions showed the tissue-specific enzyme activity. These results provide further evidence for the presence of a quantal DNA replication cycle for the tissue-specific enzyme development, which is qualitatively different from the other DNA replication cycles.

Inhibition of macrophage DNA synthesis by immunomodulators. II. Characterization of the suppression by muramyl dipeptide or lipopolysaccharide [3H]thymidine incorporation into macrophages

Guinea pig peritoneal exudate macrophages actively incorporated [3H]thymidine into trichloroacetic acid-insoluble fraction in vitro. The incorporation of [3H]thymidine was almost completely inhibited by aphidicolin, an inhibitor of DNA polymerase alpha and an autoradiograph showed heavy labeling in nuclei of 15% of macrophage populations. These results indicate that the observed thymidine incorporation was due to a nuclear DNA synthesis. The [3H]thymidine incorporation was markedly suppressed when macrophages were activated by immunoadjuvants such as muramyl dipeptide (MDP) or bacterial lipopolysaccharide (LPS). The suppression of [3H]thymidine incorporation by MDP was neither due to the decrease in thymidine transport through the cell membrane, nor due to dilution by newly synthesized "cold" thymidine. An autoradiograph revealed that MDP markedly decreased the number of macrophages the nuclei of which were labeled by [3H]thymidine. These results suggest that the suppression of [3H]thymidine incorporation by the immunoadjuvants reflects a true inhibition of DNA synthesis. The inhibition of DNA synthesis by MDP was also observed in vivo. Further, it was strongly suggested that the inhibition was not caused by some mediators, such as prostaglandin E2, released from macrophages stimulated by the immunoadjuvants but caused by a direct triggering of the adjuvants at least at the early stage of activation. Cyclic AMP appears to be involved in the inhibitory reaction.

Effect of indigestible polysaccharides on pancreatic exocrine secretion and biliary output

The present study was designed to determine the effect of purified viscous polysaccharides on pancreatic exocrine secretion and biliary output. Male Sprague-Dawley rats aged 5 weeks were fed either on the control diet which contained no fiber or on the experimental diets that contained 5% indigestible polysaccharides (agar, kappa-carrageenan, Na-alginate and konjac mannan). After pretreatment with each diet for 2 weeks, the diet was discontinued overnight, and the animals were then allowed to eat 4 g of the test diet in 1 h. Immediately after this, a polyethylene tube was placed in the common bile duct, under anesthesia. Combined, free drained pancreatic-bile juice was collected for the following 1 h. Long-term (2 weeks) administration of Na-alginate and konjac mannan gave rise to increases in the volume of secreted juice and in the output of total bile acids, amylase and protease, whereas that of agar and kappa-carrageenan had no affect. Since a single dose of Na-alginate and konjac mannan was ineffective as regards pancreatic-bile secretion, the elevated secretion observed over prolonged periods may result from processes of adaptation against highly viscous polysaccharides.

Effect of the degradation of cytochrome P-450 heme by secobarbital on polychlorinated biphenyls (PCB)-induced hepatic vitamin A reduction and lipid peroxide formation in rats

The present studies were conducted to characterize the relevance of a microsomal mixed function oxidase system to the polychlorinated biphenyls (PCB)-induced vitamin A reduction and endogenous lipid peroxide formation in the liver of rats. And also, this study dealt with an influence of scavengers on the hepatic lipid peroxide formation stimulated by PCB. Rats were given a 0.01% PCB diet supplemented with adequate nutrients, for 14 days. In an experiment, secobarbital was injected subcutaneously for the degradation of hepatic microsomal cytochrome P-450 heme. A marked liver enlargement and a significant increase of total liver lipid content were observed in the PCB group. The secobarbital enhanced the PCB-induced liver enlargement but no effect of secobarbital on the lipid content was recognized. PCB significantly induced hepatic microsomal cytochrome P-450, but not both cytochrome b5 and NADPH-cytochrome c reductase. The secobarbital suppressed the induction of cytochrome P-450 caused by PCB to approximately one-half. The hepatic vitamin A content significantly decreased on PCB administration and the secobarbital slightly enhanced the PCB-induced vitamin A reduction. However, the vitamin A content in the secobarbital-injected control group decreased to nearly the same levels as in the PCB groups. Therefore, it was presumed that the hepatic microsomal mixed function oxidase system, especially the cytochrome P-450, was possibly not directly involved in the PCB-induced hepatic vitamin A reduction or that a metabolic system related to mixed function oxidase system was involved in the reduction. On the other hand, the hepatic lipid peroxide content tended to increase on PCB administration though no significant difference was recognized. In contrast, the hepatic lipid peroxide content significantly increased in the secobarbital-injected PCB group as compared with the secobarbital-injected control group. However, there was no difference in the lipid peroxide contents between the control groups with and without the injection of secobarbital, and also between the PCB groups. The hepatic vitamin E contents lowered in the secobarbital-injected groups but no effect was observed on PCB administration. The glutathione peroxidase activity decreased significantly on PCB administration and the secobarbital further decreased the activity. Therefore, it was suggested that the significant increase and tendency of increase in hepatic lipid peroxide contents in the PCB groups with and without injection of secobarbital were ascribed to an insufficiency of lipid peroxide scavengers in the liver.(ABSTRACT TRUNCATED AT 400 WORDS)

Mitochondrial DNA synthesis in overmatured eggs of the starfish

DNA synthesis was studied during the overmaturational stage of starfish eggs. Some DNA synthesis took place in the overmature eggs of the starfish. The DNA synthesis was resistant to aphidicolin. Judging from its circularity and small molecular size, the DNA synthesized is of mitochondrial origin.

Changes in deoxyribonucleoside triphosphate pools in the starfish oocyte during maturation and early embryogenesis

dNTP pools are quite low in immature oocytes of the starfish, expand during the 1-methyladenine-induced maturational process and thereafter reach a maximal level (approx. 35, 20, 15 and 5 fmoles/egg for dTTP, dCTP, dATP and dGTP, respectively) which is maintained in overmatured eggs. Maturing oocytes were inseminated at the stage just before extrusion of the first polar body and determination of dNTP pools during early embryogenesis showed the same expansion pattern as that of the 1-methyladenine-treated oocytes. Therefore, the increase in dNTP pools during early embryogenesis is dependent on 1-methyladenine (1-MA) but independent of fertilization. Aphidicolin, a specific inhibitor of eukaryotic DNA polymerase alpha, has no effect on dNTP pool size in 1-methyladenine-treated oocytes, but causes considerable expansion of dNTP pools in fertilized eggs which cleave achromosomally in the presence of the drug.

Inhibition of intracranial self-stimulation in brain stem-transected cats--a proposed mechanism of aversive effects produced by brain stimulation

Effects of intracranial self-stimulation of central 'punishment areas' were studied on an operant conditioning of vertical eye movements in the midpontine pretrigeminal cats as well as in the encéphale isolé cats. In 36 pretrigeminal cats, the ventromedial hypothalamus (VMH), basal amygdaloid nuclei (AMY), dorsal central gray (CG) of the midbrain and the thalamic nuclei such as the ventralis posteromedialis (VPM) and ventralis posterolateralis (VPL) were tested. No suppression of eye movements indicating a passive avoidance conditioning from stimulation of these 'punishment areas' was obtained in 92 electrode tip sites. In 49 encéphale isolé cats, stimulation of the VPM associated with contraction of the facial muscles, demonstrated a marked passive avoidance effect on the eye movements. After blocking both the trigeminal (5N) and facial nerves (7N), VPM stimulation no longer produced an increase of facial EMG activity and the suppressive effect on eye movements was abolished. Extracranial blockade of 7N alone, which induced facial muscle paralysis also showed similar effects. Bilateral blockade of cranial nerves from acoustic (8N) to hypoglossal (12N) nerves had no significant effect on the avoidance conditioning. The mass neural activity recorded from the 5N showed a marked increase of discharge by VPM stimulation which was reduced significantly after 7N blockade. These results may suggest a possibility that punishing effects of brain stimulation depend on feedback from the periphery (muscles, blood vessels and visceral organs), whereas reward effects essentially depend on neural circuitry confined within the forebrain above the rostral pons.

On the 'clock' mechanism determining the time of tissue-specific enzyme development during ascidian embryogenesis. II. Evidence for association of the clock with the cycle of DNA replication

Acetylcholinesterase (AChE) is a tissue-specific enzyme of the muscle cells of ascidian embryos and its synthesis begins at the neurula stage. Embryos which had been permanently cleavage-arrested with cytochalasin B could develop AChE activity. The time of first AChE occurrence in embryos which had been arrested in the 32-cell stage with cytochalasin was about the same as in normal embryos. The nucleus in the cell of cytochalasin-arrested embryos divided in good synchrony with that of normal embryos. Embryos which had been continuously arrested with colchicine could also produce AChE activity at nearly the same time as did normal embryos. In the cell of colchicine-arrested embryos normal nuclear divisions did not occur, but the cell showed repeated cycles of nuclear envelope breakdown and nuclear envelope reformation in almost parallel with cell cycles of normal embryos. The cell of colchicine-arrested embryos incorporated [3H]thymidine. Aphidicolin, a specific inhibitor of DNA synthesis, prevented cleavages of ascidian eggs. Embryos which had been permanently arrested with aphidicolin in the cleavage stages up to the 64-cell stage did not develop AChE activity, while embryos which had been treated with it from the 76-cell stage onwards were found to be able to differentiate AChE activity. Based on these findings it was proposed that DNA replication is prerequisite for development of the histospecific protein and that the cycle of DNA replication is closely associated with the clock mechanism which is determining the time of initiation of the enzyme development.

A definite number of aphidicolin-sensitive cell-cyclic events are required for acetylcholinesterase development in the presumptive muscle cells of the ascidian embryos

In order to determine whether or not a crucial number of DNA replications are prerequisite for cellular differentiation, we have studied development of a tissue-specific enzyme, muscle acetylcholinesterase (AChE) in the presumptive muscle cells of cleavage-arrested ascidian embryos. Embryos were cleavage-arrested with cytochalasin B (an inhibitor of cytokinesis) and aphidicolin (an inhibitor of DNA synthesis). The 64-cell-stage embryos which had been permanently cleavage-arrested with cytochalasin B developed AChE in all the eight presumptive muscle cells, but the same stage embryos which had been prevented from undergoing further divisions by simultaneous treatment with aphidicolin and cytochalasin did not produce AChE at all. Cytochalasin-arrested 76-cell-stage embryos were able to differentiate AChE in the ten presumptive muscle cells, while aphidicolin-cytochalasin-arrested 76-cell stages in as many as four cells. The early gastrulae which had been arrested with cytochalasin B produced AChE in all the sixteen presumptive muscle cells, while the same stage embryos arrested with aphidicolin and cytochalasin in as many as twelve cells. Cytochalasin-arrested late gastrulae developed AChE in twenty blastomeres, while aphidicolin-cytochalasin-arrested late gastrulae in eighteen cells. The presumptive muscle cells at these four stages consist of three different (seventh, eighth, and ninth) generations, and the relative positions of the blastomeres in the cleavage-arrested embryos remained fixed. Judging from the relative positions of the blastomeres, the AChE-producing cells in aphidicolin-cytochalasin-arrested embryos were always at eighth or ninth generation, while those with no AChE activity were certainly at seventh generation. Based on these findings it was supposed that aphidicolin-sensitive cell-cycle events, presumably DNA replication, are closely associated with AChE development and that the eighth cleavage cycle may be 'quantal' for the histospecific enzyme development.

Aphidicolin: a specific inhibitor of DNA synthesis in synchronous mastocytoma P-815 cells

The influence of aphidicolin on cell multiplication and DNA synthesis was examined using synchronous mouse mastocytoma P-815 cells. Aphidicolin was cytotoxic specifically to the cells of the S phase of the cell cycle. This cytotoxicity was reversed by appropriately washing the drug-treated cells, but not by the addition of deoxyribonucleosides. Aphidicolin, a potent inhibitor of DNA synthesis, selectively inhibited the activity of partially purified DNA polymerase alpha from the nucleus and the cytosol of mastocytoma cells, but did not affect the activity of DNA polymerase beta. Furthermore, aphidicolin had no effect on the synthesis of RNA and protein, and produced no changes in cell size at least for one generation.

Inhibition by aphidicolin of cell cycle progression and DNA replication in sea urchin embryos

We have recently found that aphidicolin, a tetracyclic diterpene-tetraol produced by several fungi, blocks DNA synthesis of sea urchin embryos by interfering with the activity of DNA polyermase alpha. These cells fail to proliferate in the presence of aphidicolin. In continuation of these studies, we determined the drug-sensitive stage in the first cell cycle of the sea urchin Clypeaster japonicus embryo. In continuous exposure to aphidicolin (2 micrograms/ml) from five minutes after fertilization, mitotic division of the embryo was completely suppressed. Embryos were exposed to the drug at progressively later intervals and their capability for cytokinesis was examined. Evidence was thereby obtained that aphidicolin acts at the S-period to inhibit DNA synthesis resulting in developmental arrest of the embryo.

The mode of inhibitory action by aphidicolin on eukaryotic DNA polymerase alpha

The mode of action by aphidicolin on DNA polymerase alpha from the nuclear fraction of sea-urchin blastulae was studied. The inhibition of DNA polymerase alpha by aphidicolin was uncompetive with activated DNA and competitive with the four deoxynucleoside triphosphates using activated DNA as a template-primer. For truncated (residual or limited) DNA synthesis with only three deoxynucleoside triphosphates, aphidicolin inhibited the residual synthesis more strongly in the absence of dCTP than in the absence of each of the other three deoxynucleoside triphosphates. The inhibition was reversed with excess dCTP but not with the other three deoxynucleoside triphosphates. That is, aphidicolin inhibited DNA polymerase alpha by competing with dCTP with a Ki value of 0.5 microgram/ml and by not competing with the other three deoxynucleoside triphosphates. dTMP incorporation with the activated DNA was more sensitive to aphidicolin than dGMP or dTMP incorporation with poly(dC). (dG)12-18 or poly(dA) . (dT)12-18. Similar results were obtained for DNA polymerase alpha (B form) from mouse myeloma MOPC 104E.

Operant conditioning of vertical eye movements without visual feedback in the midpontine pretrigeminal cat

An operant conditioning of vertical eye movements was achieved in the midpontine pretrigeminal cat in total darkness by contingent reinforcement of spontaneous eye movements with lateral hypothalamic (LHT) reward stimulation, when each movement (upward direction was chosen in this experiment) exceeded a preset amplitude. However, the response rates in the dark were lower than those in the light and the time to reach the peak response rate was much longer. Recording of evoked potentials to optic chiasma (OC) stimulation revealed enhancement of late components of the visual cortex (VC) and superior colliculus (SC) responses in relation to eye movements. Sequential records of the averaged evoked responses associated with eye movements indicated that the amplitudes of the late components of the VC and SC waves gradually increased in the course of establishment of the operant conditioning, and decreased gradually during extinction. In a yoked control test, increase in amplitudes of the late components was much less significant during non-contingent reinforcement given independently of the eye movements. These results suggest that 'corollary discharge' may play a critical role as a cue in acquisition of the operant conditioning of vertical eye movements when visual feedback is absent in total darkness.

Novel epimerization of steroidal allylic alcohols

Epimerization of 4-pregnene-3 beta,20 alpha-diol into 4-pregnene-3 alpha,20 alpha-diol was achieved under the mild condition of an acidic medium at room temperature. This reaction was favorable for synthesis of 4-pregnene-3 alpha,20 alpha-diol in better yield, after chemical reduction of 20 alpha-hydroxy-4-pregnen-3-one with metal hydrides, which resulted in predominant production of 4-pregnene-3 beta,20 alpha-diol. The by-product which was formed more by raising the temperature was identified as 3,5-pregnadien-20 alpha-ol. This method was also applicable for epimerization of other delta 4-3 beta-hydroxysteroids.

Vasodilation produced by prostacyclin (PGI2) and 9(O)-thiaprostacyclin (PGI2-S) in the canine femoral circulation

The action of 9(0)-thiaprostacyclin (PGI2-S) was compared with that of prostacyclin (PGI2) and papaverine in the femoral circulation of dogs. PGI2-S, injected into the dog femoral artery in a dose of 0.1 microgram or higher, produced marked vasodilation in the femoral artery without any change in blood pressure. The potentcy of PGI2-S was one tenth that of PGI2, and was a hundred times that of papaverine. The stability of PGI2-S in neutral solution was forty times that of PGI2.

Operant discriminative conditioning of vertical eye movements in the midpontine pretrigeminal cat

In the acute midpontine pretrigeminal cat, either upward or downward eye movements above a certain preset amplitude were reinforced by electrical stimulation of the lateral hypothalamic (LHT) reward area, which did not induce a significant eye movement by itself. During the course of the reinforcement procedure, eye movements greatly increased. In a yoked control test where LHT stimulation was delivered to a cat, independently of its own eye movements, no significant enhancement of the eye movements was observed. However, when reinforcement was given contingently on each large eye movement, eye movement rate became much higher. When cats were trained for an operant discrimination between an S+ (light-off or light-on) and an S- (light-on or light-off), 5 cats acquired clearly differential responses to the S + and S-. They also learned a discrimination reversal. Furthermore, removal of the visual cue eliminated differential responses during the reinforcement and nonreinforcement periods. These data strongly suggest that, in its preparation, a real learning process in the form of a visual discrimination is maintained and an operant conditioning of eye movements with hypothalamic stimulation was achieved without feedback from the peripheral nerve or caudal central nervous system.