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21.
Neuron-specific and state-specific differences in calcium homeostasis regulate the generation and degeneration of neuronal architecture 总被引:2,自引:0,他引:2
Many stimuli (e.g., neurotransmitters and electrical activity) regulate neuromorphogenesis by changing intracellular calcium. The ionophore A23187 was employed as a receptor-independent method to investigate neuronal calcium homeostasis. Distinctive neuron-specific (B5 versus B19) and state-specific (growing versus non-growing) differences in calcium homeostasis were observed in cultured identified Helisoma neurons. Fura-2 studies revealed that A23187 induced a transient rise in intracellular calcium in growing neurons B5 but a sustained rise in growing neurons B19. In stable-state (non-growing) cells A23187 evoked only a transient calcium rise. Both neuron-specific and state-specific differences in calcium homeostasis were dependent on extracellular sodium. Morphological studies also indicated that such differences in calcium-regulatory capacity can have profound consequences on the generation and degeneration of neuronal architecture. 相似文献
22.
Haemogregarina georgianae n. sp. occurs frequently in the bathydraconid teleost Parachaenichthys georgianus from the western Antarctic portion of the Southern Ocean. The haemogregarine and its developmental stages in the vertebrate have been found in erythrocytes of the fish: both microschizogony and macroschizogony have been seen in fish caught during the austral summer. Morphological evidence suggests the merozoites from macroschizogony give rise to the microschizont, and that the microschizont merozoites give rise to gametocytes. Comparison of H. georgianae with other haemogregarines known from teleosts shows that it has a previously undescribed morphology. 相似文献
23.
Characterization of Neurotensin Binding Sites in Intact and Solubilized Bovine Brain Membranes 总被引:1,自引:0,他引:1
Analysis of the equilibrium binding of [3H]-neurotensin(1-13) at 25 degrees C to its receptor sites in bovine cortex membranes indicated a single population of sites with an apparent equilibrium dissociation constant (KD) of 3.3 nM and a density (Bmax) of 350 fmol/mg protein (Hill coefficient nH = 0.97). Kinetic dissociation studies revealed the presence of a second class of sites comprising less than 10% of the total. KD values of 0.3 and 2.0 nM were obtained for the higher and lower affinity classes of sites, respectively, from association-dissociation kinetic studies. The binding of [3H]neurotensin was decreased by cations (monovalent and divalent) and by a nonhydrolysable guanine nucleotide analogue. Competition studies gave a potency ranking of [Gln4]neurotensin greater than neurotensin(8-13) greater than neurotensin(1-13). Smaller neurotensin analogues and neurotensin-like peptides were unable to compete with [3H]neurotensin. Stable binding activity for [3H]neurotensin in detergent solution (Kd = 5.5 nM, Bmax = 250 fmol/mg protein, nH = 1.0) was obtained in 2% digitonin/1 mM Mg2+ extracts of membranes which had been preincubated (25 degrees C, 1 h) with 1 mM Mg2+ prior to solubilization. Association-dissociation kinetic studies then revealed the presence of two classes of sites (KD1 = 0.5 nM, KD2 = 3.6 nM) in a similar proportion to that found in the membranes. The solubilized [3H]-neurotensin activity retained its sensitivity to cations and guanine nucleotide. 相似文献
24.
Samples of Arctic charr, Salvelinus alpinus (L.), were collected from the eight Cumbrian lakes containing all the known English populations. Comparative material was obtained from North Wales and southern Scotland. Comparisons were performed using otolith ages, meristic and morphological characters and by assessing allele frequencies for serum esterase and for skeletal muscle malate dehydrogenase. The results confirm that both basins of Windermere contain spring and autumn spawning races of charr. As well as differing genetically and exhibiting differing growth rates, the two races have different mean gill raker numbers and mean gill raker lengths. The latter two variables were used to derive a discriminant function which enables individual charr to be ascribed to the correct race with 94-96% accuracy. Within both principal races there were further significant differences between charr from the north and south basins of the lake and possibly also between different spawning grounds within each basin. Variation between six of the remaining seven Cumbrian populations is significant but generally no greater than that between the Windermere spring and autumn spawners. The exception is the Ennerdale charr which stands out on morphological, meristic and genetic characters, has a rapid growth rate despite its oligotrophic environment, and is a river rather than a lake spawner. The charr from North Wales and southern Scotland were clearly distinct, both from each other and from the English populations. 相似文献
25.
26.
Nattie E. E.; Mills J. W.; Ou L. C.; St John W. M. 《Journal of applied physiology》1988,65(4):1525-1534
We used the neurotoxin, kainic acid, which is known to stimulate neuronal cell bodies as opposed to axons of passage by binding to specific amino acid receptors to determine whether cells with such receptors have access to the ventrolateral medullary surface and are involved in central ventilatory chemosensitivity. Pledgets with 4.7 mM kainic acid were placed bilaterally on the rostral, intermediate, or caudal ventilatory chemosensitive areas for 1-2 min in chloralose-urethan-anesthetized, paralyzed, vagotomized, glomectomized, and servo-ventilated cats. Application of kainic acid on the caudal or intermediate areas produced no consistent significant effects on eucapnic phrenic output or on the slope or maximum value of the phrenic nerve response to increased end-tidal PCO2. Rostral area kainic acid produced immediate augmentation and then diminution of blood pressure and phrenic output. Apnea developed in six of nine cats by 40 min. In all five cats in which it could be tested, the slope of the CO2 response was clearly decreased. Of [3H]kainic acid applied to the rostral area, 88.4% was shown to be within 2 mm of the ventral surface. Comparison of surface application sites of this and other studies suggests that an area overlapping the border of the original rostral and intermediate areas allows access to neurons involved in the chemoreception process, which may also provide tonic facilitatory input to cardiorespiratory systems. 相似文献
27.
28.
Regulation of follicular development by diethylstilboestrol in ovaries of immature rats 总被引:1,自引:0,他引:1
Immature female rats received either one injection of 2 mg diethylstilboestrol (DES)/rat subcutaneously and were killed 12 h later or received two injections of DES at 0 and 24 h and were killed at 24, 36 and 48 h after the initial injection. The ovarian follicles were released by enzymic digestion with collagenase and separated into those of small, medium and large diameter (less than 200 microns, 200-400 microns and greater than 400 microns) by filtration through graded Teflon sieves and granulosa cells were extracted from these follicles. The ovaries of immature rats treated with pregnant mares' serum gonadotrophin (PMSG) were used for comparative purposes. Incorporation of [3H]thymidine into granulosa cell DNA was augmented by DES and by PMSG. Small follicles were more strongly stimulated by DES at 12 h than those of other sizes, but rates increased significantly in medium and large follicles at 48 h. Aromatase activity in the DES-treated group was low at all times and in all follicles. Rates of oestrogen and progesterone production in response to 36 h of exposure to follicle-stimulating hormone (FSH) in vitro were significantly lower than in the PMSG-treated group. FSH-stimulated steroid production in the DES group at 36-48 h was lower, particularly in the medium follicles. A significant rise in serum FSH, luteinizing hormone (LH) and progesterone concentrations was noted only at 36 h after DES treatment, while serum and follicular fluid oestrogen values remained unchanged. When these changes were compared with those in PMSG-treated rats, there were obvious differences. The pattern of thymidine incorporation and aromatase activity differed with time and follicle size. Serum FSH and LH values were not affected by PMSG treatment, but serum and follicular fluid oestradiol values increased with time. The PMSG-treated animals ovulated in response to human chorionic gonadotrophin, but the DES-treated rats did not ovulate in spite of the presence of some large antral follicles in the ovaries. These findings show that initial exposure of follicles to high concentrations of oestrogen results in follicles which fail to respond to subsequent gonadotrophin surges and are thereby restricted in their ability to differentiate fully. 相似文献
29.
Intact immature female rats were treated with 1, 2, 3 or 4 subcutaneous injections of 2 mg diethylstilboestrol (DES)/rat at intervals of 24 h and then killed. Ovaries were collected, cleaned, enzymically digested and serially filtered through Teflon sieves to yield follicles of diameter less than 200 microns (small), 200-400 microns (medium) and greater than 400 microns (large). Follicular supernatant was collected and granulosa cells were extracted from these isolated follicles. There was a general increase in [3H]thymidine incorporation in all sizes of follicles after 1 or 2 DES injections, the increase in the medium and large follicles being significant after 2 doses. With 3 and 4 injections of DES, there was a sudden decrease in the rates of [3H]thymidine incorporation, particularly in the medium-sized follicles, which also had higher concentrations of follicular supernatant protein. Protein contents in small and large follicles did not change significantly. The follicular supernatant protein had a specific and dose-dependent inhibitory effect on [3H]thymidine incorporation when added to cultures of rapidly dividing granulosa cells. Addition of the same amounts of bovine serum albumin (BSA) to the cultures had no effect. Heat-denaturing did not abolish the inhibition by the protein. Removal of the protein from the cultures after the first 48 h resulted in a rebound increase in [3H]thymidine incorporation during the following 48 h, showing that the inhibitory effects were reversible. Though aromatase activity after 1 or 2 DES injections abruptly decreased after 3 and 4 injections, follicular supernatant protein had no effect on steroidogenesis in cultured granulosa cells. Taken together, these findings suggest that oestrogen can inhibit follicular development, depending on the duration of exposure. We propose that the inhibitory effects of DES on cell proliferation are mediated via the synthesis of a specific peptide factor which is produced in high amounts in the medium-sized follicles only, on prolonged exposure to the oestrogen. This factor may be autocrine or paracrine, serving as an in-built autoregulatory control mechanism for follicle development, particularly at pro-oestrus, when oestrogen concentrations are highest. 相似文献
30.
Thirty years ago it was suggested that comets impacting on the primitive Earth may have represented a significant source of terrestrial volatiles, including some important precursors for prebiotic synthesis (Oró, 1961,Nature
190: 389). This possibility is strongly supported not only by models of the collisional history of the early Earth, but also by astronomical evidence that suggests that frequent collisions of comet-like bodies from the circumstellar disk around the star Pictoris are taking place. Although a significant fraction of the complex organic compounds that appear to be present in cometary nuclei were probably destroyed during impact, it is argued that cometary collisions with the primitive Earth represented an important source of both free-energy and volatiles, and may have created transient, gaseous environments in which prebiotic synthesis may have taken place. 相似文献