Thermal Limits in Relation to Acclimation in the Neotropical Millipede Gymnostreptus olivaceus (Diplopoda,Spirostreptidae)

The neotropical millipede, Gymnostreptus olivaceus, lives at ambient temperatures of about 20ºC. Its thermal tolerance was tested after acclimation to lower and higher temperatures as occurs under winter and summer conditions in the south and southeast regions of Brazil. An increase in tolerance to low temperatures was found in adapted specimens. The ecological aspects of this capability are discussed.     

Pelagic rotifers of Lake Glubokoe from 1897 to 1984

After alteration in the pattern of drainage of run-off from the surrounding swamps and changes in the colour and transparency of the Lake Glubokoe water, the previously epilimnial Trichocerca similis, Conochilus unicornis and Keratella cochlearis showed a shift of their maximum numbers to deeper layers. Pompholyx sp. and Trichocerca capucina, which are regarded as indicators of eutrophic waters, have disappeared from the pelagic zone of the lake and Conochilus hippocrepis, Synchaeta pectinata, Gastropus stylifer, Asplanchna herricki, Ascomorpha ecaudis, Ascomorpha saltans, Euchlanis dilatata and Trichocerca porcellus have made their appearance. Most of the new species are considered to be indicators of oligotrophic conditions. However the total density of pelagic rotifers remained at the same level. Apparently the establishment of the new species of rotifers was possible due to some ‘rarefaction’ of the epilimnion, the disappearance of predaceous Mesocyclops leuckarti and the invasion of the pelagic zone by Peridinium cinctum.     

Insulin and glucagon release from the ventral and dorsal parts of the perfused pancreas of the rat. Effects of glucose, arginine, glucagon and carbamylcholine

The ventral and the dorsal parts of the rat pancreas were perfused separately via either the superior mesenteric artery (0.6 ml/min) or the coeliac artery (1.4 ml/min). Control perfusions were performed via both arteries (2 ml/min). Expressed relative to the weight of tissue, the insulin content was comparable in the ventral and dorsal parts whereas the glucagon content was 2.5 times lower in the ventral than dorsal part. In comparison to the dorsal or total pancreas, the insulin secretory activity of the ventral pancreas was markedly decreased in response to either an elevation of the glucose concentration or the administration of carbamylcholine or arginine. The difference between the ventral and dorsal response was less marked at low glucose concentrations (3.3 or 7.0 mmol/l) and, possibly, in response to glucagon. In the case of glucagon release, a decreased response of the ventral pancreas was only observed when glucagon output was fully stimulated by the administration of arginine at a low glucose concentration. These results indicate that the B cell in the ventral pancreas responds poorly to several stimuli. There was little evidence to support the involvement of endogenous glucagon in the diminished sensitivity of the ventral B cells.     

The MgATP-binding site on chicken gizzard myosin light chain kinase remains open and functionally competent during the calmodulin-dependent activation-inactivation cycle of the enzyme.

An ATP-like affinity labeling reagent, 5'-[p-(fluorosulfonyl)benzoyl]adenosine (FSBA), was used to probe the MgATP-binding site of smooth muscle myosin light chain kinase from chicken gizzard (smMLCK) and its calmodulin (CaM) complex. Native smMLCK has an absolute requirement for the binding of the calcium complex of CaM for expression of its catalytic activity. FSBA reacted with smMLCK-CaM and with the CaM-free, inactive enzyme as well. Both reactions were dependent on time and FSBA concentration. Reaction was accompanied by the incorporation of covalently bound [14C]FSBA into smMLCK protein at a molar ratio of approximately 1:1 in each case. p-(Fluorosulfonyl)benzoic acid, an analogue of FSBA lacking the adenosine targeting group, did not react at a significant rate with either form of smMLCK. Reaction of CaM-free and CaM-bound smMLCK with FSBA displayed saturation kinetics. The first-order rate constants for the conversion of the reversible, noncovalent enzyme-FSBA complex to form the irreversibly inhibited, covalently modified enzyme were similar for both smMLCK and smMLCK-CaM, 0.15 and 0.07 min-1, respectively. The concentrations of FSBA yielding the half-maximal rate of inactivation, KI, were essentially identical--0.65 and 0.64 mM, respectively--for smMLCK and smMLCK-CaM. MgATP, but not MgGTP or a substrate peptide, potently inhibited reaction with FSBA. Inhibition by MgATP was competitive. The measured inhibitory constant for MgATP was essentially the same--33 versus 34 microM--for both smMLCK and smMLCK-CaM. It therefore is concluded that the MgATP-binding site on smMLCK remains accessible and recognizable as such when the enzyme becomes inactivated upon dissociation of CaM.     

Involvement of Presynaptic Histamine H3 Receptors in the Modulation of Somatostatin Binding and Its Effects on Adenylyl Cyclase Activity in the Rat Frontoparietal Cortex

Abstract: Thioperamide (2 mg/kg, i.p.), a histamine H₃-receptor antagonist, increased the number of somatostatin (SS) receptors, with no change in the affinity constant, in the rat frontoparietal cortex. This effect was prevented by treatment with ( R )-α-methylhistamine (3.2 mg/kg, i.p.), a histamine H₃-receptor agonist. Thioperamide also induced an increase in SS binding in rats pretreated with mepyramine, a histamine H₁-receptor antagonist, or cimetidine, a histamine H₂-receptor antagonist. Pretreatment with mepyramine plus cimetidine administered simultaneously antagonized the thioperamide effect on SS binding. The increase in the number of SS receptors was accompanied by a greater SS-mediated inhibition of basal and forskolin-stimulated adenylyl cyclase (AC) activity in frontoparietal cortical membranes in the thioperamide group. Furthermore, the functional activity of the guanine nucleotide-binding inhibitory protein (G_i protein) was not altered by thioperamide or ( R )-α-methylhistamine administration in frontoparietal cortical membranes. In rats treated with mepyramine plus thioperamide or cimetidine plus thioperamide, the increase in the number of SS receptors was also accompanied by an increased SS inhibition of AC activity. Thioperamide induced a significant increase in SS-like immunoreactivity content in the frontoparietal cortex. Altogether, these results suggest that frontoparietal cortical histamine may play, at least in part, a role in the regulation of the somatostatinergic system.     

Ultrastructure of Spermiogenesis and the Spermatozoon of Mathevotaenia herpestis(Cestoda), Intestinal Parasite of Atelerix albiventrisin Senegal

Spermiogenesis in M. herpestisbegins with the formation of a differentiation zone which contains two centrioles associated with an electron–dense, finely granular material. This granular material very quickly becomes striated, a median cytoplasmic extension forms, one of the centrioles becomes laterally oriented in a cytoplasmic bud and the other gives rise to a flagellum. After the migration of the nucleus, a helicoidal crested–like body forms, then the old spermatid separates from the residual cytoplasm. The mature M. herpestisspermatozoon exhibits an apical cone of electron–dense material, a crested–like body and cortical microtubules which are electron–dense centred and spiralized except at their posterior extremity where they are parallel to the spermatozoon axis. The axoneme is of the 9 + ‘1’ pattern. It reaches the posterior extremity of the gamete where the cytoplasm is very electron–dense. The presence of centrioles flanked by ‘striated roots’ has never, to our knowledge, been reported in a platyhelminth. Likewise, a nucleus with an annular cross–section and unevenly distributed electron–dense peri–axonemal material has never been described in a cestod.     

Relaxation of reproductive suppression in non-breeding female naked mole-rats, Heterocephalus glaber

Ninety-four non-reproductive female naked mole-rats, from seven colonies, were studied in terms of vaginal perforation, vaginal smears and urinary concentrations of oestradiol-17β and progesterone in relation to the time of parturition of the breeding female, the queen. The study concentrated mainly on the period from nine days prepartum to 13 days postpartum of 12 births. Sixty-eight percent ( n = 253) of the non-reproductive females had detectable urinary concentrations of oestradiol-17β and many of these had perforated vaginas throughout the study period. These females showed a significantly increased urinary concentration of oestradiol six days prior to parturition of the queen. In females with undetectable concentrations of oestradiol-17β, the proportion with perforated vaginas increased from six days prepartum (54%) to reach a peak on the day of parturition (92%) of the queen. Urinary progesterone-concentrations were 0.7nmol/mmol creatinine at some stage in the study period in 90% of the females and scattered short peaks or spikes were experienced by all these females, but without synchronization between the females in a colony and without any detectable correlation with the time of parturition of the queen. Maximal concentrations in some females were comparable to the values in cycling breeding females during the luteal phase, but were of a much shorter duration than in breeding females. Vaginal smears did not show clear cyclic patterns.     

Large old trees increase growth under shifting climatic constraints: Aligning tree longevity and individual growth dynamics in primary mountain spruce forests

In a world of accelerating changes in environmental conditions driving tree growth, tradeoffs between tree growth rate and longevity could curtail the abundance of large old trees (LOTs), with potentially dire consequences for biodiversity and carbon storage. However, the influence of tree-level tradeoffs on forest structure at landscape scales will also depend on disturbances, which shape tree size and age distribution, and on whether LOTs can benefit from improved growing conditions due to climate warming. We analyzed temporal and spatial variation in radial growth patterns from ~5000 Norway spruce (Picea abies [L.] H. Karst) live and dead trees from the Western Carpathian primary spruce forest stands. We applied mixed-linear modeling to quantify the importance of LOT growth histories and stand dynamics (i.e., competition and disturbance factors) on lifespan. Finally, we assessed regional synchronization in radial growth variability over the 20th century, and modeled the effects of stand dynamics and climate on LOTs recent growth trends. Tree age varied considerably among forest stands, implying an important role of disturbance as an age constraint. Slow juvenile growth and longer period of suppressed growth prolonged tree lifespan, while increasing disturbance severity and shorter time since last disturbance decreased it. The highest age was not achieved only by trees with continuous slow growth, but those with slow juvenile growth followed by subsequent growth releases. Growth trend analysis demonstrated an increase in absolute growth rates in response to climate warming, with late summer temperatures driving the recent growth trend. Contrary to our expectation that LOTs would eventually exhibit declining growth rates, the oldest LOTs (>400 years) continuously increase growth throughout their lives, indicating a high phenotypic plasticity of LOTs for increasing biomass, and a strong carbon sink role of primary spruce forests under rising temperatures, intensifying droughts, and increasing bark beetle outbreaks.     

ε-聚赖氨酸抑菌性能的研究进展

ε-聚赖氨酸(ε-poly-L-lysine,ε-PL)是抑菌谱广泛的天然抑菌剂,由通过α-羧基与ε-氨基连接的25–35个赖氨酸聚合而成。ε-PL主要由白色链霉菌发酵生产所得,比化学生产更加高效和环保。ε-PL具有水溶性好、耐热和对环境无污染等特点,具有良好的应用前景。本文从发酵生产入手,着重综述了ε-PL对各种微生物抑菌性能、抑菌机制及抑菌机制模型的研究进展。推测ε-PL是通过对细胞膜的破坏而改变细胞的通透性,或者作用到细胞内引起活性氧(reactive oxygen species, ROS)胁迫而影响调节基因的表达,从而起到抑菌作用。根据这2种抑菌方式分别建立了相应的抑菌模型,即毡毯模型和ROS诱导细胞凋亡模型。本文可为ε-PL对微生物抑制性能的深入研究提供依据,同时也提出了ε-PL抑菌机制的新模型,为扩展ε-PL应用领域提供了一定的参考。