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1.
A sensitive radioimmunoassay for β-endorphin (β-EP) has been developed with an antiserum obtained from a guinea pig immunized with β-EP which was contained in crude porcine ACTH preparations (Organon). The minimal detectable quantity of β-EP was 1 pg. This antibody has the same affinity for β-EP and β-LPH on a molar basis, but human ACTH, α-MSH, β-MSH, α-EP, γ-EP, Met 5-Enkephalin and Leu 5-Enkephalin failed to displace 125I-β-EP from its antibody. Utilizing this radioimmunoassay we have demonstrated the existence of β-EP in plasma from patients with Nelson's syndrome and Addison's disease. 相似文献
2.
A quantitative study of the operation of Muller's Ratchet for the accumulation of deleterious genes in an asexually reproducing population is made. For a population of size N, in which deleterious mutations occur at rate λ/genome/ generation, and the relative fitness of an individual with k mutants is (1 ? s) k, the most important parameter is . If n0 is large (?25), deleterious mutations will accumulate very slowly, and independently of each other; if n0 is small (<1), the rate of accumulation of deleterious mutations will be greater than a natural population could plausibly bear; an estimate of the speed of the Ratchet for intermediate values of n0 is made. It is pointed out that the frequency distribution for the numbers of individuals carrying k mutants will retain its shape, but will move bodily to the right at the same average speed as the Ratchet. When favourable mutations also occur, the frequency distributions can move right of left; an estimate of the probability that any particular step is right or left is made, and it is shown that, for a given net rate of arrisal of deleterious mutations, the greater the rate of beneficial mutation, the greater the chance that beneficial mutations will accumulate. 相似文献
3.
Ecdysterone acts differently according to the period of the moulting cycle when it is applied. In period C it induces apolysis, while at the beginning of apolysis it delays ecdysis. Experiments show that the exoskeleton cannot be rejected in the presence of ecdysterone. The possibility of stopping exuviation or ecdysis with ecdysterone seems to prove that this phenomenon is controlled by a particular factor called the factor of exuviation or the ecdysis factor. Ecdysterone would control only the release of this specific factor but would not prevent its action. 相似文献
4.
Of 38 western grebe ( Aechmophorus occidentalis) colonies initiated on the Delta Marsh, Lake Manitoba, in 1973 through 1979, over half (53%) included breeding Forster's terns ( Sterna forsteri). Tern-associated colonies included 12 of the 13 largest colonies, incorporating 83% of the total nesting effort ( N=2821 nests). Such colonies were impossible to approach undetected, because grebes used the tern's aerial alarm system to warn of danger. Playbacks showed that grebes recognized the tern's alarm call, and responded by immediately leaving their nests. This essentially constitutes a form of ‘information parasitism,’ which probably is widespread in many nesting associations. This work suggests a broadening of the ‘information centre’ hypothesis to include transfer of information about any reproductive requisite, not just food. 相似文献
5.
Adler's contact pressure model for Fibonacci phyllotaxis is examined theoretically. It is shown that the model, as it stands, does not account for Fibonacci phyllotaxis, since it requires, but does not provide, a mechanism for initiating new primordia with increasingly greater precision as phyllotaxis rises. Modifications are suggested which remedy this deficiency in the model; one of these modifications involves a combination of Adler's model with Mitchison's model.From a comparison of the ranges of divergence angles permitted by Adler's model against Fujita's measurements of divergence angles in plants with low phyllotaxis, it is shown that the modified contact pressure model, if based on the concept of mechanical pressures between primordia in contact, cannot account for the divergence angles found in low phyllotaxis systems. However it is shown that this deficiency can be overcome if the contact pressure effect is regarded as a chemical phenomenon, mediated by a growth inhibitor produced by the prirnordia and moving more readily in vertical directions than in other directions.Mitchison's model, which is based on the concepts of an expanding apex and primordium initiation by existing primordia, is shown to account for Fibonacci phyllotaxis only if phyllotaxis rises sufficiently slowly; to guarantee that an Fn + Fn+1 system can develop there must already be at least Fn+1 primordia present in an Fn?1 + Fn system, at least Fn primordia in an Fn?2 + Fn?1 system, and so on down to at least three primordia in a 1 + 2 system, making a total of at least Fn+3?5 primordia (where Fn = nth term of the Fibonacci series with F1 = F2 = 1). Adler's model, modified, requires only that Fn + 1 primordia be present with divergence angles in the range 120–180° to guarantee that an Fn + Fn + 1 system can develop. 相似文献
6.
We have previously shown that phospholipase D (PLD) pathways have a role in neuronal degeneration; in particular, we found that PLD activation is associated with synaptic injury induced by oxidative stress. In the present study, we investigated the effect of α-synuclein (α-syn) overexpression on PLD signaling. Wild Type (WT) α-syn was found to trigger the inhibition of PLD1 expression as well as a decrease in ERK1/2 phosphorylation and expression levels. Moreover, ERK1/2 subcellular localization was shown to be modulated by WT α-syn in a PLD1-dependent manner. Indeed, PLD1 inhibition was found to alter the neurofilament network and F-actin distribution regardless of the presence of WT α-syn. In line with this, neuroblastoma cells expressing WT α-syn exhibited a degenerative-like phenotype characterized by a marked reduction in neurofilament light subunit (NFL) expression and the rearrangement of the F-actin organization, compared with either the untransfected or the empty vector-transfected cells. The gain of function of PLD1 through the overexpression of its active form had the effect of restoring NFL expression in WT α-syn neurons. Taken together, our findings reveal an unforeseen role for α-syn in PLD regulation: PLD1 downregulation may constitute an early mechanism in the initial stages of WT α- syn-triggered neurodegeneration. 相似文献
7.
The temperature course in the lateral semicircular canal and in the facial canal was studied in experiments during freezing of the semicircular canal. The course of the temperature was measured with thermocouples. Concurrently, the heat flow was measured, and also the total heat exchange was measured throughout the freezing period by a thermoelectric heat flowmeter incorporated in the cryotip. The measurements showed correlation between the total amount of heat exchanged, the freezing time, and the temperature in the semicircular canal. This correlation was utilized to assess and calculate (the temperature of the lateral semicircular canal) the course of the cryoprocess in vivo, where it is possible to measure the heat flow and the total heat exchange during the freezing period only. 2. Results upon Vertigo | No Vertigo | Improved | Unchanged | Number of patients | 7 | 5 | 3 | 相似文献
8.
In 1952 Turing published a paper which showed how under restricted conditions a class of chemical reactions could give biological patterns in diffusion-coupled cells. Although this theory has been much discussed, little has been learnt about the range and type of pattern it can generate. In order to do this and to see how stable the patterns are, we have examined the system in detail and written a computer program to simulate Turing's kinetics for two morphogens over various assemblies of cells. We find that on one-dimensional lines of cells, patterns can indeed be produced and that the chemical wavelengths follow all of Turing's predictions. The results show that stable repeating peaks of chemical concentration of periodicity 2–20 cells can be obtained in embryos in periods of time of less than an hour. We do find however that these patterns are not reliable: small variations in initial conditions give small but significant changes in the number and positions of observed peaks. Similar results are observed in two-dimensional assemblies of cells. On rectangles, random blotches are observed whose position cannot be reliably predicted. On cylinders whose circumference is less than the chemical wavelength, annular stripes are produced. For larger cylinders, blotches that lie very approximately on helices are generated; again sharp prediction of the detailed pattern is impossible.The significance of these results for the developing embryo is discussed. We conclude that Turing kinetics, at least in the simple cases that we have studied, are too unreliable to serve as the generating mechanism for features such as digits which are characterized by a consistent number of units. The theory is however more than adequate by these criteria to specify less well-defined developing patterns such as those of hair follicles or leaf organization. It is emphasized however that the Turing theory is quite unable to generate regulative systems, only mosaicpatterns can be produced. 相似文献
9.
China′s rich floral diversity includes more than 33000 vascular plant species, representing approximately 10 percent of all known plant species. Over half of these species are endemic to China. However, China′s rapid economic development in the last 30 years and continuous population growth have seriously damaged plant resources in the wild and the ecological environment, resulting in a dramatic increase in the number of endangered species. There are nearly 4000 to 5000 higher plants that are now threatened or on the verge of extinction. To help halt the loss of Chinese plant diversity, Botanic Gardens Conservation International (BGCI) has developed a China programme and opened its first office based in Guangzhou in 2008. This office works along with Chinese partners aiming to secure Chinese plant diversity through integrated conservation approaches with reintroduction/population reinforcement, engagement of local communities in conservation activities, capacity building in horticulture and environmental education and public outreach. 相似文献
11.
Parkinson's disease (PD) is a common neurodegenerative disease which usually associates with neuroinflammation. The main pathological characteristics of PD are dopaminergic neurons death and the presence of Lewy bodies which are composed of aggregated α-synuclein (α-Syn). Truncated forms of α-Syn are found in the brain of PD patients, and account for 10–30% of total synuclein in Lewy bodies. Caspase-1, which plays an important role in neuroinflammation, cleaves full-length α-Syn (α-Syn FL) to generate a C-terminus 19-residues truncated α-Syn (α-Syn121). However, the role of truncated α-Syn in the onset and/or pathogenesis of PD is unclear. Here, we used α-Syn121 as a model to explore its aggregation, membrane disruption and cytotoxicity properties. Compared with α-Syn FL, α-Syn121 aggregated at an accelerated rate, and formed amorphous aggregates rich in random coil structures rather than β-sheet-rich linear fibrils formed by α-Syn FL. Importantly, higher cytotoxicity with lower membrane disruption capacity was found for α-Syn121 aggregates. Furthermore, α-Syn121 aggregates could activate the apoptosis signaling pathway and stimulate the caspase-1-mediated cleavage of α-Syn FL to generate α-Syn121, which as a result leading to increased levels of endogenous α-Syn121 and intracellular S129 phosphorylated α-Syn inclusions. Together, our data suggests a hidden vicious cycle in PD that α-Syn121 rapidly forms amorphous aggregates, which activate caspase-1 to cleave α-Syn FL and generate more α-Syn121, and this cycle may contribute to the onset and/or pathogenesis of PD. 相似文献
13.
1. 1.|In 15 conscious Pekin ducks, 40 “warm sensitive” hypothalamic neurons were identified according to their discharge rates at 40°C Thy (F40), local temperature coefficients (Δ/ΔT) and Q10. 2. 2.|Q10 and either F40 or ΔF/ΔT were little or not related. 3. 3.|A positive correlation between F40 and ΔF/ΔT was observed which was particularly close (r = 0.94 and 0.96) when the neurons were classified according to their Q10 of <2 and >2. 4. 4.|The results suggest that neurons with positive temperature coefficients in the duck's hypothalamus mostly exhibit linear to exponential temperature-discharge relationships. 5. 5.|This is an contrast to observations on mammalian hypothalamic thermosensitive neurons and may relate to the absence of the thermosensory function in the duck's rostral brainstem.
Author Keywords: Neuronal thermosensitivity; hypothalamic thermosensory function; Temperature and synaptic transmission; avian thermoregulation; mammalian thermoregulation 相似文献
14.
Morphological investigations on the fungiform papilla of the frog (Rana pipiens) have shown that this taste organ contains two distinct populations of cells: associate and sensory. Messages received by the sensory cells are believed to be transmitted through the mediation of an adrenergic transmitter. This chemical was shown by fluorescence microscopy and electron histochemistry to be stored in synaptic granular vesicles which accumulate at the membrane of the cytoplasmic processes of the sensory cells in typical chemical synaptic complexes. The sensory cell cytoplasmic processes form the presynaptic component of these complexes whose post synaptic components are the nerve fibres supplying the taste buds. These sensory nerve fibres contain agranular vesticles and are probably cholinergic, since they show positive cholinesterase activity at the light and electron microscopical levels. 相似文献
15.
The cytokinin activities of various 6-acylaminopurines, 6-alkylaminopurines, 6-acylamino-9-benzyl-purines as well as a series of isosteric-nitrogen derivatives of N 6-(γ, γ-dimethylallyl)adenine (I 6Ade) have been tested using the tobacco pith and the pea bud bioassays. The interactions between active, slightly active and inactive compounds have been studied with the last assay. Acylation decreases the biological activity; e.g., N 6-benzoyl and N 6-furoyladenines are less active than Na 6-benzyladenine and kinetin. Substitution at the 9-position reduces (tobacco-pith assay) or suppresses (pea-bud assay) the phytohormonal activity of otherwise active 6-acylaminopurines. In isosteric derivatives, maximum activity occurs when the side chain has the same length as in 1 6Ade. After the analysis of interactions between more or less active compounds, it is suggested that the differences in cytokinin activity could be related to unequal affinities for a hypothetical receptor site. 相似文献
18.
Latest results on the action of adenosine A 2A receptor antagonists indicate their potential therapeutic usefulness in the treatment of Parkinson’s disease. Basal ganglia
possess high levels of adenosine A 2A receptors, mainly on the external surfaces of neurons located at the indirect tracts between the striatum, globus pallidus,
and substantia nigra. Experiments with animal models of Parkinson’s disease indicate that adenosine A 2A receptors are strongly involved in the regulation of the central nervous system. Co-localization of adenosine A 2A and dopaminergic D2 receptors in striatum creates a milieu for antagonistic interaction between adenosine and dopamine. The
experimental data prove that the best improvement of mobility in patients with Parkinson’s disease could be achieved with
simultaneous activation of dopaminergic D2 receptors and inhibition of adenosine A 2A receptors. In animal models of Parkinson’s disease, the use of selective antagonists of adenosine A 2A receptors, such as istradefylline, led to the reversibility of movement dysfunction. These compounds might improve mobility
during both monotherapy and co-administration with L-DOPA and dopamine receptor agonists. The use of adenosine A 2A receptor antagonists in combination therapy enables the reduction of the L-DOPA doses, as well as a reduction of side effects.
In combination therapy, the adenosine A 2A receptor antagonists might be used in both moderate and advanced stages of Parkinson’s disease. The long-lasting administration
of adenosine A 2A receptor antagonists does not decrease the patient response and does not cause side effects typical of L-DOPA therapy. It
was demonstrated in various animal models that inhibition of adenosine A 2A receptors not only decreases the movement disturbance, but also reveals a neuroprotective activity, which might impede or
stop the progression of the disease. Recently, clinical trials were completed on the use of istradefylline (KW-6002), an inhibitor
of adenosine A 2A receptors, as an anti-Parkinson drug. 相似文献
19.
Within the central nervous system, tetrahydrobiopterin (BH4) is an essential cofactor for dopamine and serotonin synthesis.
In addition, BH4 is now established to be an essential cofactor for all isoforms of nitric oxide synthase (NOS). Inborn errors
of metabolism affecting BH4 availability are well documented and the clinical presentation can be attributed to a paucity
of dopamine, serotonin, and nitric oxide (NO) generation. In this article, we have focussed upon the sensitivity of BH4 to
oxidative catabolism and the observation that when BH4 is limiting some cellular sources of NOS may generate superoxide whilst
other BH4 saturated NOS enzymes may be generating NO. Such a scenario could favor peroxynitrite generation. If peroxynitrite
is not scavenged, e.g., by antioxidants such as reduced glutathione, irreversible damage to critical cellular enzymes could
ensue. Such targets include components of the mitochondrial electron transport chain, alpha ketoglutarate dehydrogenase and
possibly pyruvate dehydrogenase. Such a cascade of events is hypothesized, in this article, to occur in neurodegerative conditions
such as Parkinson’s and Alzheimer’s disease. 相似文献
20.
Phylogeographic and evolutionary research programmes have successfully elucidated compelling genetic signatures of earth history. Particularly influential achievements include the demonstration of postglacial recolonization patterns for high-latitude taxa and phylogenetic demonstration of the 'progression rule' along oceanic island chains such as Hawaii. While both of these major biogeographic patterns clearly rely on rapid dispersal over long distances, their phylogeographic detection also apparently relies on the competitive exclusion of secondary dispersers. Such exclusion could occur either between or within species and might reflect fitness differences between lineages or, alternatively, neutral demographic processes (e.g. 'high-density blocking'). Regardless, such spatial genetic patterns would be rapidly eroded were it not for the failure of subsequent dispersers to contribute genetically to newly colonized populations. In addition to its role in revealing colonization patterns, competitive exclusion may also explain the maintenance of historic phylogeographic disjunctions long after the original physical barriers to dispersal have ceased to exist. Additionally, some of the most persuasive evidence of competitive exclusion comes from studies of anthropogenic extinction, where surviving lineages have subsequently expanded their ranges, apparently benefitting from the demise of their prehistoric sisters. Broadly, these biogeographic paradigms are united by the 'disconnect' between dispersal and colonization success, the latter being heavily influenced by inter- and intraspecific competition. Despite its apparent importance, such exclusion (especially within species) has received virtually no attention in the phylogeographic literature. Future studies should aim to test directly for the role of competitive exclusion in constraining the biogeography of highly dispersive taxa. 相似文献
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