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1.
The repair of the mouse seminiferous epithelium after cell loss has been studied in seminiferous tubules mounted in toto . Cell loss was inflicted by injection of Myleran in a dose of 10 mg/kg body weight. In stages 7–8, in which we mainly counted, the numbers of A isolated (A is), A paired (A pr), A aligned (A al) and A 1 spermatogonia and resting primary spermatocytes decreased after injection. After about 24 days normal numbers of A 1 spermatogonia were found again. Thereafter a substantial overshoot in the number of A 1 spermatogonia was found. While normally most of the A pr and A al cells differentiate into A 1 spermatogonia in stages 3 and 4 and do not divide until stage 9, during repair they pass through one more division during stages 6 and 7. Normally, during these stages divisions of these spermatogonia are rare. Owing to this extra division the transformation of A pr and A al into A 1 spermatogonia is delayed from stage 3 or 4 to stage 8, i.e. still before stage 9, in which A 1 spermatogonia divide. From 16 days after the injection onwards the extra division takes place less generally and more and more cells transform into A 1 spermatogonia at the normal time. 相似文献
2.
The duration of the mitotic cycle and of its components was analysed for each of the six successive generations of differentiating spermatogonia (A 1, A 2, A 3, A4, intermediate and B), using radioautographed whole mounts of seminiferous tubules from testes of adult Sprague-Dawley rats. Cell cycles were determined from two successive waves of per cent labeled metaphases obtained during the period of 81 hr after a single dose of 3H-thymidine. Except for the A 1 spermatogonia, all spermatogonial types (A 2 to B) had similar cell cycle durations of 41-42.5 hr and comparable pre-DNA synthesis phases (G 1) of 11-13 hr. Although the combined duration of DNA synthesis (S) and the post-synthesis phase (G 2) remained identical for all the cell types including A 1, there was a progressive lengthening of the S period at the expense of G 2 during the process of spermatogonial maturation. This change was most marked during the transition from A 1 to A 3 spermatogonia when the S period increased from 14 hr to 21 hr, and the G 2 phase shortened from 13 hr to 7.5 hr. This feature seems to be unique to germ cells and may be associated with an increasing amount of heterochromatin in the nucleus. Excluding the development of type A 1 cells, the entire process of spermatogonial maturation lasted for 208 hr. Combined data on cell cycle times indicated that every 313 hr or 13 days, a new sequence of spermatogonial differentiation was initiated by the A 1 cells. This was equivalent to the duration of one 'cycle' of the seminiferous epithelium as measured by other techniques. 相似文献
4.
Pregnant Wistar rats were orally treated with 1 g/L l -glutamate during the entire gestational period and the status of adenosine A 1 receptor (A 1R)/adenylyl cyclase transduction pathway from maternal and fetal brain was analyzed. Glutamate consumption, estimated from the loss of water from the drinking bottles, was 110 ± 4.6 mg/kg/day. In mother brains glutamate intake did not significantly alter the B max value, although the K d value was significantly decreased. However in fetus brain, a significant decrease in B max was observed, without an alteration of K d value. Similar results were observed by western blot assays using specific A 1R antibody, suggesting a down-regulation of A 1R in fetal brain. Concerning α subunits of inhibitory G proteins (Gi), αGi 3 protein was slightly but significantly decreased in maternal brain without alterations of either Gi 1 or Gi 2. In contrast, αGi 1 and αGi 2 isoforms were increased in fetal brain. On the other hand, basal, forskolin, and forskolin plus GTPγS-stimulated adenylyl cyclase activity was significantly decreased in both maternal and fetal brain, and this was more prominent in fetal than in maternal brain. Finally, A 1R functionality was significantly decreased in mother brain whereas no significant differences were detected in fetus brain. These results suggest that glutamate administered to pregnant rats modulates A 1R signaling pathways in both tissues, showing an A 1R down-regulation in fetal brain, and desensitization in maternal brain. 相似文献
5.
During hypoxia, extracellular adenosine levels are increased to prevent cell damage, playing a neuroprotective role mainly through adenosine A 1 receptors. The aim of the present study was to analyze the effect of hypoxia in both adenosine A 1 and A 2A receptors endogenously expressed in C6 glioma cells. Two hours of hypoxia (5% O 2) caused a significant decrease in adenosine A 1 receptors. The same effect was observed at 6 h and 24 h of hypoxia. However, adenosine A 2A receptors were significantly increased at the same times. These effects were not due to hypoxia-induced alterations in cells number or viability. Changes in receptor density were not associated with variations in the rate of gene expression. Furthermore, hypoxia did not alter HIF-1α expression in C6 cells. However, HIF-3α, CREB and CREM were decreased. Adenosine A 1 and A 2A receptor density in normoxic C6 cells treated with adenosine for 2, 6 and 24 h was similar to that observed in cells after oxygen deprivation. When C6 cells were subjected to hypoxia in the presence of adenosine deaminase, the density of receptors was not significantly modulated. Moreover, DPCPX, an A 1 receptor antagonist, blocked the effects of hypoxia on these receptors, while ZM241385, an A 2A receptor antagonist, was unable to prevent these changes. These results suggest that moderate hypoxia modulates adenosine receptors and cAMP response elements in glial cells, through a mechanism in which endogenous adenosine and tonic A 1 receptor activation is involved. 相似文献
6.
In whole mounts of seminiferous tubules of C3H/101 F 1 hybrid mice, spermatogonia were counted in various stages of the epithelial cycle. Furthermore, the total number of Sertoli cells per testis was estimated using the disector method. Subsequently, estimates were made of the total numbers of the different spermatogonial cell populations per testis. The results of the cell counts indicate that the undifferentiated spermatogonia are actively proliferating from stage XI until stage IV. Three divisions of the undifferentiated spermatogonia are needed to obtain the number of A1 plus undifferentiated spermatogonia produced each epithelial cycle. Around stage VIII almost two-thirds of the Apr and all of the Aal spermatogonia differentiate into A1 spermatogonia. It was estimated that there are 2.5 × 106 differentiating spermatogonia and 3.3 × 105 undifferentiated spermatogonia per testis. There are about 35,000 stem cells per testis, constituting about 0.03% of all germ cells in the testis. It is concluded that the undifferentiated spermatogonia, including the stem cells, actively proliferate during about 50% of the epithelial cycle. 相似文献
7.
Abstract: Chronic treatment with the adenosine receptor antagonist caffeine evokes an up-regulation of A 1 adenosine receptors and increased coupling of the receptor to G proteins in rat brain membranes. However, chronic agonist exposure has not been explored. Primary cultures of cerebellar granule cells were exposed chronically to A 1 adenosine receptor agonists and antagonists. Exposure to the A 1 adenosine receptor agonist N 6-cyclopentyladenosine resulted in (1) a time- and concentration-dependent reduction in the density of receptors labeled by 1,3-[ 3H]dipropyl-8-cyclopentylxanthine, (2) an enhanced ability of guanyl nucleotides to decrease the fraction of A 1 adenosine receptor sites displaying high affinity for 2-chloroadenosine, and (3) a functional uncoupling of receptors from adenylyl cyclase (EC 4.6.1.1). The adenosine antagonists caffeine and 8- p -sulfophenyltheophylline produced alterations in A 1 adenosine receptor homeostasis that were antipodal to those associated with agonist treatment. Antagonist exposure (1) increased the density of A 1 adenosine receptors in cerebellar granule cell membranes, (2) blunted the effect of guanyl nucleotides on receptor coupling to G proteins, and (3) increased the functional coupling of receptors to adenylyl cyclase inhibition. Forskolin treatment of cerebellar granule cells did not affect receptor density, suggesting that cyclic AMP is not involved in the regulation of A 1 adenosine receptor expression. 相似文献
8.
Halińska, A. and Lewak, St. 1987. Free and conjugated gibberellins in dormancy and germination of apple seeds. The presence of gibberellin A 4 (GA 4) was confirmed in partly stratified seeds of apple ( Malus domestica Borb., cv. Antonówka) by mass spectrometry of the methyl ester. Levels of free and conjugated gibberellins A 4+7 and A 9 changed during drying of mature seeds, during cold and warm stratification, as well as during germination of dormant and non-dormant embryos. The temporary rise in GA 4+7 during cold stratification and during the culture of dormant embryos as well as the lack of it under conditions of warm stratification, allowed us to postulate a role for GA 4+7 in the removal of dormancy. In addition, GA 9 was absent in dormant embryos and increased during cold stratification and during the culture of non-dormant embryos. This suggests the involvement of GA 9, in induction of normal development of the seedling. The equivalence between changes in free and conjugated GAs suggests that formation and hydrolysis of conjugates are involved in the control of the physiologically active levels of free GA 4+7 and GA 9. 相似文献
9.
Abstract— Preparations of phospholipase Az have been obtained from human cerebral cortex. The enzyme was extracted from acetone-dried tissue and purified by heat-treatment and gel filtration on Sephadex. Although heating at 65°C or 70°C destroys most of the phospholipase A 1 activity that is present in crude extracts, a small proportion remains associated with the A 2 activity during these procedures. The heat-treated extracts hydrolyse lecithin in preference to phosphatidyl-ethanolamine but have no action on lysolecithin or neutral lipids. The results suggest that A 2 activity and the heat-stable component of A 1 may both be due to a single phospholipase A that can hydrolyse diacylglycerophosphatides at either the 2-or the 1-position, to form a mixture of isomeric lysoderivatives. A molecular weight of 55,000 was calculated for the enzyme. 相似文献
10.
Effects of gibberellins A 1, A 4/7, A 9, A 19 and A 20 and growth retardants were studied on shoot elongation in seedlings of Salix pentandra L. The growth-retarding effects of CCC and ancymidol were antagonized by all the gibberellins tested. The novel plant growth regulator prohexadione (free acid of BX-112), which is suggested to block 3β-hydroxylation of gibberellins, effectively prevented shoot elongation in seedlings grown under long photoperiod. Initiation of new leaves was only slightly reduced. GA 1, but not GA 19 and GA 20, was active in overcoming the inhibition of stem elongation of seedlings, treated with prohexadione, GA 19, GA 20 and GA 1 are native in S. pentandra , and the results are compatible with the hypothesis that GA 1 is active per se in shoot elongation, and that the effect of GA 19 and GA 20 is dependent on their conversion to GA 1. A mixture of GA 4 and GA 7 was as active as GA 1 in promoting shoot elongation in seedlings treated with prohexadione, while GA 9 showed slight activity only when applied at high doses. 相似文献
11.
Abstract. Multivariate analysis of the expression of cyclin proteins and DNA content has opened new possibilities for the study of the cell cycle. By virtue of their cell cycle phase specificity, the expression of cyclins may serve, in addition to DNA content, as another marker of a cell's position in the cycle, and provide information about the proliferative potential of cell populations. Several applications of the methodology based on bivariate analysis of DNA content v . expression of B, E and D type cyclins are reviewed: 1 expression of cyclins by individual cells during their progression through the cycle can be studied, using exponentially growing cells without the necessity of cell synchronization or other perturbations of the cycle; 2 cells having the same DNA content but residing in different phases of the cycle (e.g. G 2 diploid v. G 1 tetraploid) can be distinguished; 3 cell transition from G 0 to G 1 and progression through G 1 (e.g. mitogen stimulated lymphocytes) can be assayed; 4 the population of proliferating cells can be distinguished from noncycling cells based on dual cell labelling with a G 1 and G 2 cyclin antibody; 5 cyclin restriction points can serve as additional cell cycle landmarks to map the point of action of antitumour drugs; 6 unscheduled expression of cyclins (e.g. the presence of cyclin B1 during G 1 and S) can be detected in several tumour transformed cell lines, possibly indicating disregulation of the machmery of cell cycle progression. The last finding 6 is of special importance, because such disregulation may be of prognostic consequence in human tumours. 相似文献
12.
Abstract: The amyloid protein (βA 4) is found in the CNS of patients with Alzheimer's disease; however, the pathogenic role of this protein is not known. In the present study, a peptide fragment of βA 4βA 4 25–35; Gly-Ser-Asn-Lys-Gly-Ala-Ile-Ile-Gly-Leu-Met-NH 2), which contains the conserved C-terminal sequence of substance P (X-Gly-Leu-Met-NH 2), and the neuropeptide substance P (SP) were examined for their ability to modulate nicotine-evoked secretion from cultured bovine adrenal chromaffin cells. Secretion of the released endogenous catecholamines was monitored by electrochemical detection after separation by HPLC. Secretion induced by 10 −5 M nicotine was inhibited by SP and βA 4 25–35. The IC 50 of SP and βA 4 25–35 was 3 × 10 −6 and 3 × 10 −5 M , respectively. SP and βA 4 25–35 both protected against nicotinic receptor desensitization. However, βA 4 25–35 was ∼ 10-fold less effective than SP in its protective effect. The present work shows that βA 4 25–35 can mimic the modulatory actions of SP on the nicotinic response of cultured bovine chromaffin cells, i.e., inhibition of the nicotinic response and protection against nicotinic desensitization. These modulatory actions may be associated with changes in nicotinic receptor levels reported to occur in Alzheimer's disease. 相似文献
13.
Gibberellins A 1, A 3, A 4 and A 7 were identified by combined gas chromatography mass spectrometry (GC-MS) in leaf and stem tissues of 17-day-old seedlings of wheat ( Triticum aestivum L. ), cvs Siete Cerros (semi-dwarf, Rht1) and Møystad (tall), of F 1, hybrids from the cross Møystad × Siete Cerros and of 2 selected lines from the cross Møystad x Sonora 64 (Rht1 and Rht2). GA, and GA, were identified by full scan mass spectra separately in all 5 extracts, GA 4 and GA 7, were identified by selected ion monitoring in a bulked fraction. About 90% of the biological activity (Tan-ginbozu dwarf rice bioassay) in all 5 extracts was due to the GA 1/GA 3-fraction. 相似文献
14.
The chromatographic behaviour of abscisic acid (ABA), indole-3-acetic acid (IAA), phenylacetic acid (PAA), and gibberellins A 1, A 4, A 8, A 9, A 13 and A 20 on columns of Sephadex LH-20 and insoluble poly- N -vinylpyrrolidone (PVP) eluted with buffers of different pH values is described. PVP shows considerable batch differences that must be carefully checked. Chromatography of acidic ethyl acetate-soluble fractions of Scots pine ( Pinus sylvestris L.) extracts at pH 4.5 resulted in great losses of phytohormones, due to poor solubility of the extracts. If the extracts were applied to the column dissolved in buffer of pH 7.5, subsequent elution at pH 4.5 was possible with only small losses. The performance of the chromatographic column was strongly affected by the application volume. A combined PVP/Sephadex LH-20 column eluted at pH 4.5 allows remarkable purification of pine and spruce ( Picea abies (L.) Karst.) extracts, collection of IAA in a fraction that can be directly analyzed by e.g. the indolo-α-pyrone method, and collection of another fraction containing ABA, PAA and probably most of the known C 19-gibberellins; whereas the C 20-gibberellin A 13 is eluted later (with IAA). 相似文献
15.
In the cultivated male Japanese eel, spermatogonia are the only germ cells present in the testis. Weekly injections of human chorionic gonadotropin (HCG) can induce complete spermatogenesis from proliferation of spermatogonia to spermiogenesis. In some cases, however, HCG injection fails to induce complete spermatogenesis. Testicular morphological observations revealed that HCG-injected eels could be classified into three types based on their testicular conditions. Type 1 eels had a well-developed testis and the milt could be acquired by hand-stripping. In type 2 eels, spermatogenesis was also induced by HCG injection, but testicular size was remarkably smaller than that of type 1 eels, and the milt could not be hand-stripped. At the end of the experiment, type 2 fish had only spermatogonia and a small amount of spermatozoa, but no spermatocytes or spermatids, in their testis. Type 3 eels had thready testis, which did not develop any germ cells during the experimental period. These results suggest that, despite elevations of plasma 11–ketotestosterone levels, HCG injections were not successful in inducing the completion of spermatogenesis in type 2 and type 3 eels. In most spermatogonia of type 2 eels, meiosis was not induced by HCG injections. Furthermore, only few mitotic divisions had occurred as evidenced by the presence of 2 3 to 2 6 late type B spermatogonia in most cysts. This suggests that spermatogonial stem cells undergo four or five, and occasionally six, mitotic divisions before the interruption of spermatogenesis in type 2 eels. It is proposed that those numbers of mitotic divisions are related to a mediator that regulates entry of spermatogonia of the Japanese eel into meiosis. 相似文献
16.
Abstract: The cytokine interleukin (IL)-6 has recently been demonstrated to play a role in the pathology of Alzheimer's disease (AD). The mechanisms leading to increased IL-6 levels in brains of AD patients are still unknown. Because in experimental animals ischemia increases both the level of cytokines and the extracellular concentrations of adenosine in the brain, we hypothesized that these two phenomena may be functionally connected and that adenosine might increase IL-6 gene expression in the brain. Here we show that the mixed A 1 and A 2 agonist 5'-( N -ethylcarboxamido)adenosine (NECA) induces an increase in IL-6 mRNA levels and protein synthesis in the human astrocytoma cell line U373 MG. The A 1-specific agonists R -phenylisopropyladenosine and cyclopentyladenosine are much less potent, and the A 2a-specific agonist CGS-21680 shows only marginal effects. Increased levels of mRNA are already found within 30 min after NECA treatment. The A 2a-selective antagonists 8-(3-chlorostyryl)caffeine and KF17837 [( E )-8-(3,4-dimethoxystyryl)-1,3-dipropyl-7-methylxanthine], which have also some antagonistic properties at A 2b receptors, and the nonspecific adenosine antagonist 8-phenyltheophylline were equipotent at inhibiting the NECA-induced increase in IL-6 protein synthesis, whereas the specific A 1 antagonist 8-cyclopentyl-1,3-dipropylxanthine is much less potent. The results indicate that adenosine A 2b receptors participate in the regulation of the IL-6 gene in astrocytoma cells. 相似文献
17.
Fifteen male mosquito fish ( Gambusia affinis holbrooki ) were collected in 1989 on the 15th of each month to perform a quantitative histologic study of the annual testicular cycle including a calculation of the gonadosomatic index, testicular volume, and the total volume per testis occupied by each germ cell type. The cycle comprises two periods: spermatogenesis and quiescence. The spermatogenic period begins in April with the development of primary spermatogonia into secondary spermatogonia, spermatocytes and round spermatids. In May, the first spermatogenic wave is completed and the testicular volume begins to increase up to June when the maximum testicular volume and gonadosomatic index are reached. Germ cell proliferation with successive spermatogenetic waves continues until August. In September germ cell proliferation ceases and neither secondary spermatogonia nor spermatocytes are observed. However, spermiogenesis continues until October. In November, spermiogenesis has stopped and the testis enters the quiescent period up to April. During this period only primary spermatogonia and spermatozoa are present in the testis. In addition, a few spermatids whose spermiogenesis was arrested in November are observed. Testicular release of spermatozoa is continuous during the entire spermatogenesis period. The spermatozoa formed at the end of this period (September-October) remain in the testis during the quiescent period and are released at the beginning of the next spermatogenesis period in April. Developed Leydig cells appear all year long in the testicular interstitium, mainly around both efferent ducts and the testicular tubule sections showing S 4 spermatids. 相似文献
18.
Abstract: The ability of adenosine agonists to modulate K +-evoked 4D†-[ 3H]aminobutyric acid ([ 3H]GABA) and acetylcholine (ACh) release from rat striatal synaptosomes was investigated. The A 2a receptor-selective agonist CGS 21680 inhibited Ca 2+-dependent [ 3H]GABA release evoked by 15 m M KCI with a maximal inhibition of 29 ± 4% (IC 50 of ∼4 ± 10 −12 M ). The relative order of potency of three agonists was CGS 21680 ± 5'- N -ethylcarboxamidoadenosine > R-phenylisopropyladenosine (R-PIA), with the inhibition being blocked by A 2a receptor-selective antagonists (CP 66,713 and CGS 15943A) but not by the A 1-selective antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). When release of [ 3H]GABA was evoked by 30 mM KCI, no significant inhibition was observed. In contrast, CGS 21680 stimulated the release of [ 3H]ACh evoked by 30 m M KCI, with a maximal stimulation of 26 ± 5% (IC 50 of ∼10 −11 M ). This effect was blocked by CP 66,713 but not by DPCPX. The A 1 agonist R -PIA inhibited [ 3H]ACh release, an effect blocked by DPCPX. It is concluded that adenosine A 2a receptors are present on both GABAergic and cholinergic striatal nerve terminals where they inhibit and stimulate transmitter release, respectively. Key Words : GABA—Acetylcholine—Adenosine receptors—Striatum. 相似文献
20.
Abstract: Extracts of acetone-dried powders from ischemic gerbil brain were examined for phospholipase A 1 and A 2 activities with phosphatidylethanolamine at pH 7.2. Ischemia was induced by bilateral ligation, and the animals were killed by immersion into liquid nitrogen. Bilateral ligation with ketamine as general anesthetic resulted in a rapid, transient increase in phospholipase A 2 activity. The activity increased from 0.46 nmolihimg protein at 0 time to 0.82 nmol/h/mg protein at 1 min of ligation. Phospholipase A 1 activity also increased from 0.7 to 1.3 nmol/h/mg protein within the 1st min. When Nembutal was used as anesthetic, the phospholipase activation was earlier, within the first 30 s. Similar results were found for ischemia induced by decapitation of Wistar rats without anesthesia. Bilateral ligation of the carotid arteries of the gerbil is known to increase the concentration of free fatty acids, particularly arachidonate. This increase is, at least in part, due to phospholipase A activation. As ethanolamine phospholipase A 2 in brain does not require Ca 2+ for activity, these results suggest that phospholipase A 2 activation in ischemic brain results from a covalent modification of the enzyme. 相似文献
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