The anatomy, physiology, functional significance and evolution of specialized hearing organs of gerbilline rodents

Middle and inner ear anatomy correlates with neurophysiological responses to a wide range of sound frequencies for species of the Gerbillinae representing generalized, intermediate, and specialized anatomical conditions. Neurophysiological data were recorded from 81 specimens of 13 species representing six genera. Anatomical parameters involved in the process of hearing were correlated with the neurophysiological data to assess the effects of different degrees of anatomical specialization on hearing. The 13 species tested in this manner have graphic curves of auditory sensitivity of remarkably similar disposition over the frequencies tested and to those published for Kangaroo Rats. Ears with anatomical specializations show greater auditory sensitivity. The natural history of the Gerbillinae, particularly the kinds of predators, degree of predation, and habitat is reviewed and utilized to interpret the significance of the degree of auditory specialization in the forms studied and to evaluate the prevailing hypothesis that these specializations enhance the ability of these rodents to survive in open desert situations by detecting and evading predators. The middle ear anatomy of five additional genera and species was also studied. Thus, data on the entire spectrum of gerbilline middle ear morphology provide an evolutionary sequence. Certain anatomical parameters of the organ of Corti show a degree of specialization parallel to that of features of the middle ear. The morphological changes and possible functional roles of these features are considered. A very high correlation exists for degree of specialization and aridity of habitat, thus specialization increases with increasing aridity. This increased specialization may result from more effective predation in open xeric environments. Auditory acuity for a wide range of low frequency sounds augmented by auditory specialization is hence more advantageous here. There does not appear to be selection for hearing at particular frequencies in this range. The peaks of greatest auditory sensitivity appear to correspond to the resonant frequencies of the different components of the middle ear transformer and cavity.     

The cerebrospinal venous system: anatomy, physiology, and clinical implications

There is substantial anatomical and functional continuity between the veins, venous sinuses, and venous plexuses of the brain and the spine. The term "cerebrospinal venous system" (CSVS) is proposed to emphasize this continuity, which is further enhanced by the general lack of venous valves in this network. The first of the two main divisions of this system, the intracranial veins, includes the cortical veins, the dural sinuses, the cavernous sinuses, and the ophthalmic veins. The second main division, the vertebral venous system (VVS), includes the vertebral venous plexuses which course along the entire length of the spine. The intracranial veins richly anastomose with the VVS in the suboccipital region. Caudally, the CSVS freely communicates with the sacral and pelvic veins and the prostatic venous plexus. The CSVS constitutes a unique, large-capacity, valveless venous network in which flow is bidirectional. The CSVS plays important roles in the regulation of intracranial pressure with changes in posture, and in venous outflow from the brain. In addition, the CSVS provides a direct vascular route for the spread of tumor, infection, or emboli among its different components in either direction.     

The mammalian centrosome and its functional significance

Primarily known for its role as major microtubule organizing center, the centrosome is increasingly being recognized for its functional significance in key cell cycle regulating events. We are now at the beginning of understanding the centrosome's functional complexities and its major impact on directing complex interactions and signal transduction cascades important for cell cycle regulation. The centrosome orchestrates entry into mitosis, anaphase onset, cytokinesis, G1/S transition, and monitors DNA damage. Recently, the centrosome has also been recognized as major docking station where regulatory complexes accumulate including kinases and phosphatases as well as numerous other cell cycle regulators that utilize the centrosome as platform to coordinate multiple cell cycle-specific functions. Vesicles that are translocated along microtubules to and away from centrosomes may also carry enzymes or substrates that use centrosomes as main docking station. The centrosome's role in various diseases has been recognized and a wealth of data has been accumulated linking dysfunctional centrosomes to cancer, Alstrom syndrome, various neurological disorders, and others. Centrosome abnormalities and dysfunctions have been associated with several types of infertility. The present review highlights the centrosome's significant roles in cell cycle events in somatic and reproductive cells and discusses centrosome abnormalities and implications in disease.     

Idiopathic pulmonary fibrosis: a historical review.

Hamman and Rich are generally considered to have been the first to describe idiopathic pulmonary fibrosis (IPF) as a new clinical and pathological entity. However, several earlier reports in the German-language literature described autopsy findings consistent with IPF from a contemporary point of view. The author discusses these and later reports in a review of the history, diagnosis and treatment of the disease.     

The volar skin of primates: its frictional characteristics and their functional significance.

Friction of volar skin on wood is not proportional to load in human beings and prosimians, but to load raised to a fractional power. This meets theoretical expectations for the frictional characteristics of convex elastic surfaces. Although this enables small clawless primates to cling to steeper slopes and larger vertical supports than would otherwise be possible, the magnitude of the effect is not great enough to overcome the disadvantages of clawlessness in climbing vertical or steeply-sloping tree trunks and branches. In human subjects, friction appears to be more nearly proportional to load than in small prosimians used as experimental subjects. It is suggested that this is due to the fact that the small animals have discrete, elevated volar pads. Pad coalescence in large primates may be an adaptation for increasing the power to which load must be raised to become proportional to friction; increasing this exponent yields more friction per unit of adduction force on supports that are small relative to the animals' dimensions and weights.     

Histochemistry and functional significance of putative neocortical transmitter substances: a review

1. Intrinsic neuronal chains of the neocortex communicate most probably with amino acid transmitters. These involve both excitatory (glutamate, aspartate--Nadler et al. 1976) both inhibitory (GABA--Ribak 1978) amino acids, and ensure fast, ionotropic postsynaptic actions (Eccles, McGeer 1979). 2. Some interneurons of the neocortex seemingly operate with the peptide transmitter VIP (Lorén et al. 1979). Presumably, this is a metabotropic, slowly acting substance (Dodd, Kelly and Said 1979). 3. The existence of intrinsic cholinergic neurons in the neocortex is a matter of question (Krnjevic and Silver 1965). It is worth to mention that in the periphery, cholinergic terminals also contain and release VIP (H?kfelt et al. 1980). It is not known, whether this transmitter dualism can be found in neocortex, too. An ascending cholinergic system projecting from the basal forebrain to the neocortex exists and exerts profound influence on cortical function (Shute and Lewis 1967). 4. Diffusely terminating, ascending monoamine axons innervate the neocortex and modulate interneuronal transmission (Thiery et al. 1977; Morrison et al. 1981, Lidov et al. 1981). 5. The neuropeptide SP excites cortical neurons (Phillis and Limacher 1974), and its presence in thin axons can be demonstrated immunohistochemically (H?kfelt et al. 1976). 6. Neocortical efferents to the thalamus and striatum seemingly use glutamate or aspartate (Fonnum et al. 1981). The transmitters of other corticofugal projections are not known. 7. The transmitters of specific thalamic afferents and those of callosal and association projections are unknown, too. 8. The main task of future histochemistry is to explore the synaptology of neocortical neurons and afferent systems with identified or evidenced transmitters, viz. to explore the neurochemical subsystems of cortical organization. The tool for it could be the immunohistochemistry, and future development depends mainly on the synthesis and purification of suitable antigens. The knowledge on the synaptology of identified neurochemical units of the cortex would be the basis of the understanding at least partly of the pharmacological effects exerted by the putative neocortical transmitters.     

The evolution of scanning microphotometry: a historical review

This article traces the evolution of scanning microphotometry from its beginning, with an emphasis on the developing technologies that have made feasible the rapid and detailed capture of high-resolution image information. Consideration is given to future directions that may prove fruitful to clinical practice.     

Central nervous system physiology of electroreception, a review.

There are several reasons why one can expect that the study of electric fish may prove instructive about general mechanisms of sensory processing and neuronal integration. These reasons include the following: the simplicity of the electrical signals which are the normal input and output; the availability of a variety of stereotyped behaviors to characterize the system as a whole; the case with which individual receptors or primary afferents can be activated; the demonstrated presence of corollary discharge and reafference mechanisms for motor control over sensory input; the presence of highly specialized CNS structures which have evolved to meet the unusual demands of the electrosensory system. Work relating to these and other aspects of the electrosensory systems is discussed with an emphasis on the potential which these systems offer.     

Dyes,trypanosomiasis and DNA: a historical and critical review

Abstract

Trypanosomiasis, a group of diseases including sleeping sickness in humans and Nagana in cattle in Africa, and Chagas’ disease in South America, remains a considerable problem in the 21^st century. The therapies that are available, however, usually have their roots in the “dye therapy” of a century ago, knowledge gained at the microscope from parasite staining procedures and converted to chemotherapy based on compounds closely related to the laboratory reagents. Dyes such as trypan red and trypan blue led to the development of suramin, while cationic nitrogen heterocyclic dyes furnished examples of the phenanthridinium class, such as ethidium (homidium) and isometamidium. Both suramin and isometamidium remain in use. Owing to mutagenicity issues, the presence of ethidium among the phenanthridinium dyes has led to concerns over the clinical use of related derivatives. There are several mechanisms for dye-DNA interaction, however, including possible hydrogen bonding of dye to the polymer, and these are discussed together with structure-activity relations and cellular localization of the phenanthridine and isomeric acridines involved. Better understanding of nucleic acid binding properties has allowed the preparation of more effective phenanthridinium analogues intended for use as anticancer/antiviral therapy.     

Primate digestion: Interactions among anatomy,physiology, and feeding ecology

Food is vital for life. It provides nutrients for growth, maintenance, and reproduction, and is the source of energy that drives the chemical reactions occurring in every cell.^1,2 However, most food, as it is initially procured, is not in a form suitable for use; it must first be broken down so that it can be transported through cell membranes.¹ The breaking down of food molecules via a system of both mechanical and chemical processes so that they are of use to the body is called digestion.^2,3 © 1998 Wiley-Liss, Inc.     

The functional, comparative and evolutionary anatomy of myosins

Actins and myosins are generally present in all animal, plant and fungal cells, and in some, if not all, prokaryotes as well. It is proposed that, in general, myosins can carry specific loads as they move along actin filaments, thus mediating a form of active transport. Myosins exert their mechanical forces by a lever action (moklokinesis) of a part of the molecule: the S-1 "head" in the case of muscle myosins. Various portions of myosin molecules can be assigned specialized functions. Each such part can be designated by an appropriate functional name. Examples are: the enzyme portion (zymomere), the motor portion (dynamere), the lever portion (moklomere), a connecting portion (desmomere), a coupling or binding portion (haptomere), and one or more flexible portions (kamptomeres). These parts can be recognized in highly evolved and specialized muscle myosins and can be postulated in simpler, single headed myosins. A primitive myosin, represented principally by a moklomere equipped with a zymomere and a dynamere, is envisioned as an evolutionary ancestor of all myosins. This primitive myosin resembles the S-1 head of muscle myosin. I suggest that from such a primitive myosin, more elaborate single-headed myosins have evolved, equipped with specific haptomeres coupled to the moklomere by desmomeres and kamptomeres. From such general single-headed myosins have arisen the highly specialized two-headed myosins represented in muscle. It is suggested that the two-headed feature is favored in myosins capable of forming bipolar filaments.     

Peripheral electrosense physiology: a review of recent findings.

Advances, since 1974, in understanding the physiology of electroreceptors are reviewed. In brief: 1. In fish that produce a weak electric discharge with electric organs, the tuberous electroreceptors are generally most sensitive to stimulus frequencies near the species', individual's, and even local, waveform of the electric organ discharge; there is a good match between receptor sensitivity and the normal stimulus. 2. The ability of tuberous electroreceptors to detect field distortions produced by reasonably sized objects is limited; an object must be closer than a body-length to be detected, and the afferent response is a negative power function of object distance. 3. The second major electroreceptor class, the ampullary electroreceptors, is sensitive to low frequency, low intensity electric fields, and this acute sensitivity results in the ability of the receptors in marine species to detect magnetic fields on the order of the Earth's. 4. The calcium ion is essential for normal functioning of ampullary electroreceptors.     

Harvest index: a review of its use in plant breeding and crop physiology

This review charts the use of the concept of harvest index in crop improvement and physiology, concentrating on the literature from the last 20 years. Evidence from abstract journals indicates that the term has been applied most to small grain cereal crops and pulses, in India, Western Europe and the USA, and that it has been less useful for maize and tuber crops. Standard methods of measuring harvest index, the associated problems of measurement and interpretation, and representative values for a range of world species are reviewed. The values for modern varieties of most intensively-cultivated grain crops fall within the range 0.4 to 0.6. Variation between varieties of the same species is illustrated by trends in the harvest indices of old, outclassed and recent varieties of temperate and mediterranean wheat and barley (compared under uniform conditions); this shows a progressive increase throughout the present century, although improvement has been much slower in Australia and Canada than in the UK. In most cases, the improvement in harvest index has been a consequence of increased grain population density coupled with stable individual grain weight. The high heritability of harvest index is explored by examining its (rather weak) response to variation in environmental factors (fertilisation, population density, application of growth regulators) in the absence of severe stress. A fuller perspective is gained by reviewing aspects of the harvest index of rice, maize and tropical pulses. With rice, attention must be paid to the fact that the adhering lemma and palea (not primarily part of economic yield) can make up 20% of grain weight; and there are important interactions among biomass, grain yield and season length. Maize differs from most small grain crops in that harvest index (in N. American varieties) was already high at the start of this century, and increases in yield potential have been largely the consequence of increased biomass production. The harvest index of many pulse species and varieties tends to be low because selection has been for some yield in all seasons. Extension of the harvest index concept to express the partitioning of mineral nutrients as well as dry matter (e.g. the nitrogen harvest index) has provided a range of responses whose implications for production and breeding remain to be explored. It is concluded that even though the principal cereal crops appear to be approaching the upper limit of harvest index, and future yield gains will have to be sought by increased biomass production, there will still be a need for the concept of harvest index as a tool in interpreting crop response to different environments and climatic change.     

The environmental physiology of Antarctic terrestrial nematodes: a review

The environmental physiology of terrestrial Antarctic nematodes is reviewed with an emphasis on their cold-tolerance strategies. These nematodes are living in one of the most extreme environments on Earth and face a variety of stresses, including low temperatures and desiccation. Their diversity is low and declines with latitude. They show resistance adaptation, surviving freezing and desiccation in a dormant state but reproducing when conditions are favourable. At high freezing rates in the surrounding medium the Antarctic nematode Panagrolaimus davidi freezes by inoculative freezing but can survive intracellular freezing. At slow freezing rates this nematode does not freeze but undergoes cryoprotective dehydration. Cold tolerance may be aided by rapid freezing, the production of trehalose and by an ice-active protein that inhibits recrystallisation. P. davidi relies on slow rates of water loss from its habitat, and can survive in a state of anhydrobiosis, perhaps aided by the ability to synthesise trehalose. Teratocephalus tilbrooki and Ditylenchus parcevivens are fast-dehydration strategists. Little is known of the osmoregulatory mechanisms of Antarctic nematodes. Freezing rates are likely to vary with water content in Antarctic soils. Saturated soils may produce slow freezing rates and favour cryoprotective dehydration. As the soil dries freezing rates may become faster, favouring freezing tolerance. When the soil dries completely the nematodes survive anhydrobiotically. Terrestrial Antarctic nematodes thus have a variety of strategies that ensure their survival in a harsh and variable environment. We need to more fully understand the conditions to which they are exposed in Antarctic soils and to apply more natural rates of freezing and desiccation to our studies.Communicated by: I.D. Hume