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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 Aisolated (Ais), Apaired (Apr), Aaligned (Aal) and A1 spermatogonia and resting primary spermatocytes decreased after injection. After about 24 days normal numbers of A1 spermatogonia were found again. Thereafter a substantial overshoot in the number of A1 spermatogonia was found.
While normally most of the Apr and Aal cells differentiate into A1 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 Apr and Aal into A1 spermatogonia is delayed from stage 3 or 4 to stage 8, i.e. still before stage 9, in which A1 spermatogonia divide. From 16 days after the injection onwards the extra division takes place less generally and more and more cells transform into A1 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 (A1, A2, A3, 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 A1 spermatogonia, all spermatogonial types (A2 to B) had similar cell cycle durations of 41-42.5 hr and comparable pre-DNA synthesis phases (G1) of 11-13 hr. Although the combined duration of DNA synthesis (S) and the post-synthesis phase (G2) remained identical for all the cell types including A1, there was a progressive lengthening of the S period at the expense of G2 during the process of spermatogonial maturation. This change was most marked during the transition from A1 to A3 spermatogonia when the S period increased from 14 hr to 21 hr, and the G2 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 A1 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 A1 cells. This was equivalent to the duration of one 'cycle' of the seminiferous epithelium as measured by other techniques.  相似文献   

3.
4.
Pregnant Wistar rats were orally treated with 1 g/L l -glutamate during the entire gestational period and the status of adenosine A1 receptor (A1R)/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 A1R antibody, suggesting a down-regulation of A1R in fetal brain. Concerning α subunits of inhibitory G proteins (Gi), αGi3 protein was slightly but significantly decreased in maternal brain without alterations of either Gi1 or Gi2. In contrast, αGi1 and αGi2 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, A1R 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 A1R signaling pathways in both tissues, showing an A1R 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 A1 receptors. The aim of the present study was to analyze the effect of hypoxia in both adenosine A1 and A2A receptors endogenously expressed in C6 glioma cells. Two hours of hypoxia (5% O2) caused a significant decrease in adenosine A1 receptors. The same effect was observed at 6 h and 24 h of hypoxia. However, adenosine A2A 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 A1 and A2A 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 A1 receptor antagonist, blocked the effects of hypoxia on these receptors, while ZM241385, an A2A 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 A1 receptor activation is involved.  相似文献   

6.
In whole mounts of seminiferous tubules of C3H/101 F1 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 A1 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 A1 adenosine receptor agonists and antagonists. Exposure to the A1 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 A1 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 A1 adenosine receptor homeostasis that were antipodal to those associated with agonist treatment. Antagonist exposure (1) increased the density of A1 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 A1 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 A4 (GA4) 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 A4+7 and A9 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 GA4+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 GA4+7 in the removal of dormancy. In addition, GA9 was absent in dormant embryos and increased during cold stratification and during the culture of non-dormant embryos. This suggests the involvement of GA9, 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 GA4+7 and GA9.  相似文献   

9.
ON THE PHOSPHOLIPASE A2 ACTIVITY OF HUMAN CEREBRAL CORTEX   总被引:1,自引:1,他引:0  
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 A1 activity that is present in crude extracts, a small proportion remains associated with the A2 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 A2 activity and the heat-stable component of A1 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 A1, A4/7, A9, A19 and A20 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. GA1, but not GA19 and GA20, was active in overcoming the inhibition of stem elongation of seedlings, treated with prohexadione, GA19, GA20 and GA1 are native in S. pentandra , and the results are compatible with the hypothesis that GA1 is active per se in shoot elongation, and that the effect of GA19 and GA20 is dependent on their conversion to GA1.
A mixture of GA4 and GA7 was as active as GA1 in promoting shoot elongation in seedlings treated with prohexadione, while GA9 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. G2 diploid v. G1 tetraploid) can be distinguished; 3 cell transition from G0 to G1 and progression through G1 (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 G1 and G2 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 G1 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 (βA4) 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 βA4βA4 25–35; Gly-Ser-Asn-Lys-Gly-Ala-Ile-Ile-Gly-Leu-Met-NH2), which contains the conserved C-terminal sequence of substance P (X-Gly-Leu-Met-NH2), 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 βA4 25–35. The IC50 of SP and βA4 25–35 was 3 × 10−6 and 3 × 10−5 M , respectively. SP and βA4 25–35 both protected against nicotinic receptor desensitization. However, βA4 25–35 was ∼ 10-fold less effective than SP in its protective effect. The present work shows that βA4 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 A1, A3, A4 and A7 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 F1, 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, GA4 and GA7, 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 GA1/GA3-fraction.  相似文献   

14.
The chromatographic behaviour of abscisic acid (ABA), indole-3-acetic acid (IAA), phenylacetic acid (PAA), and gibberellins A1, A4, A8, A9, A13 and A20 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 C19-gibberellins; whereas the C20-gibberellin A13 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 23 to 26 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 A1 and A2 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 A1-specific agonists R -phenylisopropyladenosine and cyclopentyladenosine are much less potent, and the A2a-specific agonist CGS-21680 shows only marginal effects. Increased levels of mRNA are already found within 30 min after NECA treatment. The A2a-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 A2b receptors, and the nonspecific adenosine antagonist 8-phenyltheophylline were equipotent at inhibiting the NECA-induced increase in IL-6 protein synthesis, whereas the specific A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine is much less potent. The results indicate that adenosine A2b 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 S4 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 A2a receptor-selective agonist CGS 21680 inhibited Ca2+-dependent [3H]GABA release evoked by 15 m M KCI with a maximal inhibition of 29 ± 4% (IC50 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 A2a receptor-selective antagonists (CP 66,713 and CGS 15943A) but not by the A1-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% (IC50 of ∼10−11 M ). This effect was blocked by CP 66,713 but not by DPCPX. The A1 agonist R -PIA inhibited [3H]ACh release, an effect blocked by DPCPX. It is concluded that adenosine A2a 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   

19.
20.
Activation of Ethanolamine Phospholipase A2 in Brain During Ischemia   总被引:20,自引:20,他引:0  
Abstract: Extracts of acetone-dried powders from ischemic gerbil brain were examined for phospholipase A1 and A2 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 A2 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 A1 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 A2 in brain does not require Ca2+ for activity, these results suggest that phospholipase A2 activation in ischemic brain results from a covalent modification of the enzyme.  相似文献   

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