bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE MECHANISM OF LYMPHOCYTE‐MEDIATED CYTOTOXICITY
Authors: SANDERSON COLIN J. 
Published: January 2008

Summary1. Three classes of cytotoxic lymphocyte are discussed: thymus‐derived T cells, antibody‐dependent K cells and NK (natural killer) cells. Each of these cytotoxic lymphocytes has receptors allowing the formation of adhesions (contact) with a target cell (the cell to be killed). The type of receptor and the corresponding ligand on the target cell is different in each class. Cytotoxic T cells (and probably NK cells) react with a target cell antigen, in a manner rather like antibody‐antigen reactions (although not involving classical serum antibody). K cells have a receptor for the Fc part of immunoglobulin (IgG) and hence can make contact with antibody‐coated target cells.2. It seems likely that all three classes of cytotoxic lymphocyte have a similar basic mechanism of killing, which is different from the membrane leakage occurring in complement‐mediated lysis. Much more information is available on cytotoxic T cells than on the other types of cell.3. Cytotoxic T cell killing can be divided into two phases. A reversible phase in which the T cell is in contact with the target cell, but causes no apparent damage. This phase can vary from a few minutes up to several hours, when a single T cell interacts with a single target cell. If the T cell detaches or is inactivated the target cell survives. The second phase is irreversible, once the lethal event has occurred, and the target cell will progress to eventual lysis in the absence of the Tc cells.4. The lethal event initiates a period of zeiosis (membrane blebbing) in the target cell, which is accompanied by increased effiux of 86rubidium. Cell lysis occurs at a variable time after the initiation of zeiosis, when the soluble contents of the cytoplasm burst out of the target cell. The fact that both these phases are of variable length leads to the accumulation of cytoplasmic markers (such as 51chromium) in the medium in an approximately linear fashion.5. The nature of the lethal event is unknown, but it is suggested that it involves changes inside the target cell rather than at the target cell membrane. Remarkable long projections from the T cell (and also seen from K cells and NK cells), apparently arising as a result of the receptor‐ligand interaction, may be involved in the delivery of the lethal event.
EGG ACTIVATION AND PARTHENOGENETIC REPRODUCTION IN INSECTS
Authors: Went Dirk F. 
Published: January 2008

Summary1. Many insects reproduce by parthenogenesis. In one of the largest orders of the animal kingdom, the Hymenoptera, most of its members reproduce by arrhenotokous parthenogenesis. Egg activation in parthenogenetic animals obviously cannot be caused by fertilization of the egg. The question of what initiates egg development in parthenogenetically reproducing animals has been studied for a few insect species and is discussed in this article.2. The grasshopper Melanoplus differentialis is one of several Orthoptera displaying accidental parthenogenesis. In this species, egg laying provides the stimulus to the completion of meiosis and start of embryonic development in unfertilized and probably also in fertilized eggs. The same holds true for the dipteran insect Drosophila melanogaster which exhibits rudimentary parthenogenesis, and for D. mercatorum showing accidental parthenogenesis. The precise way in which oviposition affects the egg is unknown.3. The stick insect Carausius morosus reproduces by obligatory thelytoky. The triggering factor for removal of the meiotic block and initiation of embryonic development is oxygen from the air which penetrates to the egg through the micropyle immediately after oviposition. The oviposition act itself is not necessary for activation of the egg.4. Comparative studies of the different types of oogenesis in the dipteran insect Heteropeza pygmaea show that in paedogenetically developing follicles meiotic arrest in prophase is of very short duration and a meiotic block at the end of oogenesis is absent. It is suggested that in this case triggering events for egg development are dispensable. On the other hand, under certain experimental conditions a meiotic block can be established in some of these follicles.5. Investigations on the Ichneumonid wasp Pimpla turionellae have shown that unfertilized, male‐determined eggs ‐ and most likely also fertilized, femaledetermined eggs ‐ are activated by mechanical stress exerted on the eggs during natural or imitated oviposition. This mechanical stress, in addition, activates a streaming system which is independent of meiotic completion and nuclear multiplication. Egg activation by egg distortion is also found in the Pteromalid species Nasonia vitripennis and occurs presumably in many other Hymenoptera.6. Carausius morosus, Pimpla turionellae and Nasonia vitripennis are species with parthenogenetic reproduction for which the natural factors responsible for the initiation of egg development have been identified. The cases of Pimpla turionellae and Nasonia vitripennis are of particular interest because of the feasibility of artificially imitating the natural activating mechanism.7. It is concluded that apart from fertilization various events at oviposition may trigger egg development. In addition, the occurrence of rudimentary parthenogenesis in many sexually reproducing animal species suggests that sperm entry and fertilization may frequently be necessary for the continuation of egg development rather than for its initiation.
SOUND AND ITS SIGNIFICANCE FOR LABORATORY ANIMALS
Authors: GAMBLE MALCOLM R. 
Published: January 2008

Summary1. Several methods of varying accuracy have been used to assess what sounds small laboratory animals such as rodents are capable of hearing. Most rodents can detect sounds from 1000 Hz (the frequency of the Greenwich Time Signal) up to 100000 Hz, depending on the strain, with usually one or more commonly two peaks of sensitivity within this range. Dogs can detect sound most easily from 500 Hz to 55000 Hz, depending on the breed.2. Rodents also produce sound signals as a behavioural response and for communication in a variety of situations. Ultrasonic calls in the range 22000–70000 Hz are the main communicating pathway during aggressive encounters, mating, and mothering. Similar calls have also been recorded from isolated animals associated with inactivity, rest and possibly even sleep.3. Very loud sounds cause seizures in rats and mice, or can make them more susceptible to other sounds later in life. This effect is possible even when animals are fully anaesthetized. Sound tends to startle and reduce activity in several species of animal. Even offspring of mice that have been sound‐stressed exhibit abnormal behaviour patterns. Sounds also elicit various responses in rats from increasing aggression to making them more tolerant to electric shocks.4. Levels of sound above 100 dB are teratogenic in several species of animals and several hormonal, haematological and reproductive parameters are disturbed by sounds above 80 dB. When rats are chemically deafened the disturbance to their fertility disappears. Lipid metabolism is disrupted in rats when exposed to over 95 dB of sounds, leading to increases in plasma triglycerides. Atherosclerosis can be produced in rabbits by similar levels of sound.5. It has also been shown in guinea pigs and cats that hearing damage is governed by the duration as well as the intensity of the sound and is irreversible. Work on chinchillas hs demonstrated that sounds above 95 dB lead to this injury, but that sounds of 80 dB have no permanent effect on hearing sensitivity.
GASTROPOD CHEMORECEPTION
Authors: CROLL ROGER P. 
Published: January 2008

Summary(I). Gastropods use chemoreception for a wide variety of behaviours including feeding, homing, escape from predators and a variety of social and reproductive behaviours. Chemoreception is used to locate distant food sources, and to discriminate between potential foods. Responses to chemical food stimuli result from a combination of innate and experiential factors. Gastropods use chemical cues in mucus trails to home. They also home by direct olfactory orientation. Reproductive behaviour in a variety of gastropods appears to involve chemical cues. Evidence exists for pheromones controlling aggregation and mating. Numerous gastropods use chemical cues to avoid or escape from predators.(2). Amino acids appear as likely candidates for attractants and phagostimulants for gastropod feeding. Macromolecules are probably also involved. Amino acids have also been shown to stimulate reproductive behaviours in certain gastropods, thus suggesting a pheromonal function. However, the significance of this finding to the behaviour of the organisms in the field has yet to be evaluated. Saponins have been implicated as the active substances found in sea stars that elicit escape responses of marine gastropods. Choline esters may play a homologous role in gastropod—prey and gastropod‐predator interactions.(3). Gastropods can apparently use a number of different methods to orient to olfactory cues. These include anemotaxis or rheotaxis, klinotaxis and tropotaxis.(4). The major chemosensory organs of gastropods have been identified. They include the anterior and posterior tentacles and lips of terrestrial pulmonates; the cephalic tentacles, the lips and buccal cavity lining, and possibly the osphradium of aquatic pulmonates; the cephalic and mantle tentacles, the anterior margin of the foot, the siphon tip, and the osphradium of prosobranchs; and the rhinophores, tentacles, oral veil and osphradium of opisthobranchs.(5). Many of the organs named above have been examined by both light and electron microscopy. The most common anatomical organization includes bipolar primary sensory cells with cell bodies located subepithelially, and a distal dendrite extending to the free surface. Often a peripheral ganglion is located deep to the sensory epithelium. It is unclear whether axons of the sensory cells project directly to the central ganglion or by way of interneurones located in the peripheral ganglia.(6). The dendritic specializations of the sensory cells vary considerably. Most bear cilia or a combination of cilia and microvilli. The functional significance of the variation in the types of sensory endings is unknown, although the chemosensory epithelia also respond to other sensory modalities, and it is often difficult to ascribe any one cell type to any one modality. Species‐specific variations may also complicate the picture.(7). Prospects for and importance of future studies on gastropod chemoreception are discussed.
CONNECTIVE TISSUE CATCH IN ECHINODERMS
Authors: MOTOKAWA TATSUO 
Published: January 2008

Summary(1) Catch connective tissue is defined as the collagenous connective tissue whose mechanical properties can be changed rapidly (in seconds or minutes) under nervous control.(2) Catch connective tissues are found in all five classes of Echinodermata. They function in tone control of the tissues and in autotomy.(3) The change in mechanical properties occurs in viscosity.(4) Muscle cells are not responsible for the viscosity change.(5) The viscosity change is controlled by nervous activities. Neurosecretory‐like cells with large electron‐dense granules are found in all the catch connective tissues so far studied.(6) The viscosity change is quite likely caused by the change in the ionic environment in the connective tissues, which alters the weak (non‐covalent) interactions between extracellular macromolecules in the tissue.
NON‐HORMONAL STIMULATORS AND INHIBITORS OF PLANT GROWTH AND DEVELOPMENT
Authors: KEFELI V. I. , DASHEK W. V. 
Published: January 2008

Summary1. Plants contain growth regulators that are non‐hormonal in nature. These regulators change in concentration during ontogeny and when applied exogenously, can either stimulate or depress growth. While the bulk of either the phenolic or terpenoid regulators are localized within the vacuole, they can also be found within other cellular compartments where they may act upon metabolic pathways, modifying either cell multiplication or elongation.2. Non‐hormonal growth regulators may affect the synthesis and/or destruction of phytohormones, mainly indole‐3‐acetic acid (IAA). These regulators behave non‐specifically, modifying the actions of auxins, gibberellins and cytokinins upon growth.3. A variety of both uncertainties and unresolved contradictions exist that have prevented a thorough elucidation of the mechanisms of actions of both phenolic and terpenoid regulators. These uncertainties and unresolved contradictions include lack of data regarding compartmentalization of many of the inhibitors. This raises the question of whether their intracellular concentrations become elevated sufficiently to affect metabolic pathways in vivo. Exogenously applied regulators of non‐hormonal nature usually interfere with growth only at high concentrations. Therefore, the possibility cannot be excluded that under these conditions, reactions occur within the cell that are absent in vivo.4. The specific properties of natural non‐hormonal regulators are similar in certain respects to phytohormones. For example, both of them may be biogenetically bound within metabolic centres: shikimate (phenolics, indoles, alkaloids), bi‐benzi (coumarins) or acetate‐mevalonate (terpenoids, fluorens, sesquiterpenes, cytokinins). In addition, both non‐hormonal regulators and phytohormones exhibit biological activity in growth bioassays.5. Non‐hormonal regulators may possess a number of useful purposes, e.g. test substances such as fusicoccin permit the investigation of the mode of action of phytohormones, specific inhibitors blocking special forms of growth and protectors of phytohormone activity in culture.
HOMING AND OLFACTION IN SALMONIDS: A CRITICAL REVIEW WITH SPECIAL REFERENCE TO THE ATLANTIC SALMON
Authors: STABELL OLE B. 
Published: January 2008

Summary(1) Based on data from the literature, the phenomenon of homing in salmonids is examined with special reference to the Atlantic salmon. Wild, native fish demonstrate an excellent homing ability, judged from percent return to the home river (1–3 %) and straying to non‐native watersheds (less than 3 % of returning fish).(2) The homing ability in wild fish is shown to be closely related to the existence of reproductively isolated populations between and within watersheds, as demonstrated by data from salmonid ecology and biochemical genetics.(3) Two main hypotheses have dominated the literature on salmonid homing during recent years: (a) An ‘imprinting’ hypothesis based on a process of learning of stream odours during seaward migration, coupled with sun‐orientation for open sea navigation, (b) A ‘pheromone’ hypothesis related to odours from fish and based on inheritance and the seasonal migrating schedules of discrete populations.(4) The olfactory sense has been demonstrated as mandatory for salmonids, both in near range and open sea navigation. According to genetic, sensory and ecological aspects of homing, the pheromone hypothesis is therefore concluded to be the most appropriate.(5) Fish produced from artificially fertilized eggs, released within native systems or transplanted, demonstrate a reduced homing ability. Since hatchery‐raised fish demonstrate a survival in sea equivalent to that of wild fish, a genetic disturbance of navigational ability has been suggested, resulting from the production of population hybrids by man.(6) Studies made in the fields of behaviour, electrophysiology and chemistry strongly suggest that population‐specific fish odours are involved in home‐stream recognition by salmonids.(7) An evaluation of ‘imprinting’ experiments related to artificial organic compounds reveals that: (a) the odorant properties of the applied chemicals must be questioned, (b) imprinting related to olfaction may be based on a weak theoretical foundation, (c) returns obtained in census experiments may be adequately explained through ecological interpretations, and (d) behavioural preferences obtained from exposure to non‐natural compounds may be founded on mechanisms not associated with homing.(8) A logical link between the use of olfaction and the role of genetics in salmonid homing is emphasized, together with its practical implications for salmonid management.
Species–area curves
Authors: McGuinness K. A. 
Published: January 2008

Summary1. The species‐area curve has been studied now for more than one hundred years. In this time four hypotheses have been proposed to account for this pattern ‐ the Random Placement (or Passive Sampling) Hypothesis, the Habitat Diversity Hypothesis, the Equilibrium Theory (or Area Per Se Hypothesis), and the Disturbance Hypothesis. The Random Placement Hypothesis was the first of these and is the simplest, proposing that nothing other than a random placement of species and individuals over area is occurring. This should be considered the Null Hypothesis for species‐area studies and must be tested and rejected before any other hypothesis can be considered viable.2. The Habitat Diversity Hypothesis explains the species‐area curve via the addition of new habitats with increasing area. It is supposed to result in a Power Function curve. It has been invoked a number of times but has not yet been shown experimentally to give rise to a species‐area curve.3. The Equilibrium Theory proposes that species become extinct faster on small islands as a result of the lower population sizes on such islands. This is probably the hypothesis most frequently invoked to account for the species–area curve. It is also said to result in a species‐area curve of the Power Function form. Many of the tests of this hypothesis have, however, been inadequate and on only two occasions has the null hypothesis been tested.4. The Disturbance Hypothesis also proposes that species become extinct faster on small islands, but in this case it is supposed to occur because disturbances are more frequent and more intense on these islands. This hypothesis has only rarely been considered yet it is consistent with many of the observations used to support the Equilibrium Theory. Furthermore, it has been shown experimentally, in one situation at least, to give rise to a species‐area curve.5. Two methods exist by which the null hypothesis of Random Placement can be tested. One is based on probability calculations; the other on sampling in the field. Both methods have been successfully used to test the null hypothesis, and to demonstrate biologically interesting and meaningful patterns.6. The existence of a Power Function curve has been taken to indicate that the Equilibrium Theory is correct. Likewise, an Exponential curve has been taken by some as indicating that Random Placement is occurring. These views can be shown, theoretically and empirically, to be invalid. The fitting of a particular type of curve does not test any of the hypotheses described.7. Species‐area curves can be meaningfully used to measure the relative species diversity of a community, and biologically interesting patterns can be found by comparing communities in this way.8. More intensive studies, testing the null hypothesis and performing manipulative experiments, are necessary if the processes underlying the species–area curve are to be understood.
NON‐PHOTOSYNTHETIC FIXATION OF CARBON DIOXIDE AND POSSIBLE BIOLOGICAL ROLES IN HIGHER PLANTS
Authors: BASRA AMARJIT S. , MALIK C. P. 
Published: January 2008

Summary1. Non‐photosynthetic fixation of CO2/HCO3‐ occurs both under light and dark conditions and involve the addition of carbon to substrates which in higher plants are derived originally from carbon reduced to carbohydrates during photosynthesis. Despite the endergonic nature of these carboxylations, the advantages offered seem to be sufficient to outweigh the disadvantages of energy loss.2. Non‐photosynthetic carbon incorporation into metabolism is dealt mainly in relation to PEP carboxylase, acetyl‐CoA carboxylase, carbamoyl phosphate synthetase and phosphoribosylaminoimidazole carboxylase while other carboxylases await further characterization or discovery. The extent to which a carboxylase participates depends upon the need for products of its activity in metabolism.3. Non‐photosynthetic carbon fixation is intricately involved in several pathways of metabolism throughout the ontogeny of plants. The roles in relation to leaf carbon metabolism, respiratory metabolism, nitrogen metabolism, lipid and isoprenoid biosynthesis, purine and pyrimidine metabolism and metabolism associated with the action of growth regulators have been described. The fixation reactions appear to be largely concerned with the production of intermediary metabolites, circumvention of energy barriers in metabolism and regulation of plant metabolism. In addition, the activity of PEP carboxylase is involved in ionic balance and pH‐stat.4. Malate derived by way of PEP carboxylase and NAD‐malate dehydrogenase acts as an effective osmoticum and a counter‐ion for K+ accumulation in actively growing plant cells. In addition, malate may enter the TCA cycle or can be decarboxylated by cytoplasmic NADP‐malic enzyme converting NADH to NADPH. Wherever it has been sought in different plant tissues, some evidence for PEP carboxylase and metabolism of malate has always been found.5. Almost every plant process spanning from seed development and germination to flowering and fruit‐set requires the essential participation of non‐photosynthetic carbon fixation in regulating certain metabolic and cellular functions but it does not contribute in a major way to the carbon nutrition of plants. It is largely the tissue type that appears to determine which of the roles is predominant at any one time.