On the diversity of the Cladocera in the tropics

The mythical concept of an impoverished tropical cladoceran fauna is refuted. On a planetary scale, around half of the cladoceran species presently known occur exclusively in the tropics-subtropics, often with considerable restriction to particular geographical subzones. On a regional (political) scale, the situation is often unclear because of the continued fragmentary nature of studies, and because political units are not a good basis for biogeographical comparisons. At the finest level of resolution (lake-perlake comparisons), there appears to be an upper limit of c. 50 cladoceran species per individual lake. No significant difference between lakes in the temperate zone and in the tropics could be established here. Daphnia is largely absent from the tropics, but is replaced by more Sidids, Moinids, and Bosminids, such that the average cladoceran community in the limnetic zone of a tropical lake is not characterized by less species but rather by lower population densities. This, in turn, is considered a consequence of higher prevalent predation levels in the tropics.     

On the nature of the horny scales of the pangolin

The pangolin scale is a horny derivative of the epidermis. It is complex in structure and is divisible into three distinct regions. The dorsal plate forms approximately one-sixth of the scale thickness. It is composed of flattened solid keratinized cells without basophilic nuclear remnants. This region tends to fray easily. The dorsal plate contains bound phospholipids and sulphydryl groups but is weak in disulphide bonds.
The bulk of the scale is made up of the intermediate plate formed of less flattened cells without basophilic nuclei. This region is rich in disulphide bonds but contains no appreciable bound phospholipids or sulphydryl groups.
The ventral plate is only a few cells thick and is rich in bound phospholipids, which also occur in the underlying scale bed epidermis.
These three regions of the scale are formed from separate epidermal germinal areas which do not develop a granular layer. Keratohyalin granules are, however, formed in the epidermis between the scales.
It is suggested on the basis of histological structure and dishribution of chemical constituents that pangolin scales are probably homologous with primate nails.
Evidence against the views that they are homologous with reptilian scales or are derived from compressed hairs is presented.     

Dissymmetry of the origins of the roots of the spinal cord in the dog

The spinal cord in 25 non-inbred dogs has been studied macro-microscopically. The dissymmetry in the arrangement level in the right and left root bases on the dorsal surface of the spinal cord is much greater than on the ventral surface. The same as in the human being, the dissymmetry is the greatest in the thoracic part (as compared to other spinal parts). On the ventral surface of the spinal cord both along the anterior and posterior margin of the root bases, there is a right-sided dissymmetry (with cranial shift); on the dorsal surface it is present only at the roots along the posterior margin. The dissymmetry of the dog spinal cord is quantitatively estimated along its whole extension.     

On the origin of the genetic code and the stability of the translation apparatus

An “error theory” is developed which can be applied to determine the stability of a macromolecular translation machinery which reproduces itself. It is shown that the overall effects of a multitude of possible error versions of macromolecules can be treated statistically, and that such a statistical approach is of considerable usefulness in the theoretical treatment of complex macromolecular systems. The theory is developed within the context of a detailed treatment of the “frozen accident” hypothesis for the origin of the genetic code. A model is described which permits some thermodynamic characterization of the components involved in the code nucleation. The model also proves useful in resolving a stability “paradox” described by Orgel, which relates to the translation stability in present-day organisms and mechanisms of ageing. It indicates that any experimentally found decrease in translation accuracy with age is probably not due to an inherent instability in the translation apparatus. Relevant experiments are suggested.     

Tracking in the Wlds--the hunting of the SIRT and the luring of the Draper

Wallerian degeneration of distal axons after nerve injury is significantly delayed in the Wlds mutant mouse. The Wlds protein is a fusion of nicotinamide mononucleotide adenyltransferase-1 (Nmnat1), an essential enzyme in the biosynthesis pathway of nicotinamide adenine dinucleotide (NAD), with the N-terminal 70 amino acids of the Ube4b ubiquitination assembly factor. The mechanism of Wlds action is still enigmatic, although recent efforts suggest that it is indirect and requires sequences flanking or linking the two fused open reading frames. Three papers in this issue of Neuron now show that Wlds action is conserved in Drosophila and that a critical role of Wlds may be the suppression of axonal self-destruct signals that induce Draper-mediated clearance of damaged axons by glial cells.     

Characteristics of the membranes of the pellicle of the ciliatePseudomicrothorax dubius

Summary The membranes of the pellicle of the ciliatePseudomicrothorax dubius are investigated using thin section electron microscopy and freeze-fracture replicas. The plasma membrane is covered by a surface coat and is connected to the outer alveolar membrane by short, sometimes branched, bridges. The inner alveolar membrane is coated on both sides. The epiplasm lies in intimate contact with the cytoplasmic surface of this membrane, and there is a corresponding deposit on the other surface. This deposit is regularly striated.The epiplasmic layer and the alveoli are interrupted at sites of cytotic activity,e.g., the attachment sites of trichocysts, the cytoproct, and the parasomal sacs. The striated deposit ends where the epiplasm ends, indicating a direct relationship between these two epimembranous layers.There is a deposit along the sides of the first part of the tip of the trichocysts, and in this region the trichocyst membrane is free of intramembranous particles.The membrane of the parasomal sacs has a coat on both surfaces. That on the extraplasmic surface is similar to the surface coat of the plasma membrane. The origin of the cytoplasmic coat is unknown. The cytotic activity of these sacs is indicated by their highly irregular profiles.     

Individual variability in the structure of the walls of the principal trunks of the subcutaneous veins of the lower extremities of the human fetus

Certain regional peculiarities are noted in the development process of the human principle trunks of the subcutaneous veins during antenatal period. In the fetuses of all ages the wall thickness of the subcutaneous veins is the greatest in the femur, and the middle tunic is better developed in the shin. The vein structure depends on the type of architectonics: at the magistral type (86%) the walls in the large and minor subcutaneous veins are thick with well developed smooth myocytes and connective tissue fibers; at the reticulate type (14%) the walls are thin, their elements are poorly developed. When there is mentioned varicosity of the lower extremity veins in the parents' anamnesis, in fetuses (57%) all the tunics in the venous wall develop more poorly, there is retardation in formation of smooth myocytes and in maturation of collagen fibers. This results in less amount of contractile structures in the middle tunic and optic density of collagen is less manifected.     

Ectogenesis and the case against the right to the death of the foetus

Ectogenesis, or the use of an artificial womb to allow a foetus to develop, will likely become a reality within a few decades, and could significantly affect the abortion debate. We first examine the implications for Judith Jarvis Thomson’s violinist analogy, which argues for a woman’s right to withdraw life support from the foetus and so terminate her pregnancy, even if the foetus is granted full moral status. We show that on Thomson’s reasoning, there is no right to the death of the foetus, and abortion is not permissible if ectogenesis is available, provided it is safe and inexpensive. This raises the question of whether there are persuasive reasons for the right to the death of the foetus that could be exercised in the context of ectogenesis. Eric Mathison and Jeremy Davis have examined several arguments for this right, doubting that it exists, while Joona Räsänen has recently criticized their reasoning. We respond to Räsänen’s analysis, concluding that his arguments are unsuccessful, and that there is no right to the death of the foetus in these circumstances.     

Exploring the origin of the ion selectivity of the KcsA potassium channel

The availability of structural information about biological ion channels provides an opportunity to gain a detailed understanding of the control of ion selectivity by biological systems. However, accomplishing this task by computer simulation approaches is very challenging. First, although the activation barriers for ion transport can be evaluated by microscopic simulations, it is hard to obtain accurate results by such approaches. Second, the selectivity is related to the actual ion current and not directly to the individual activation barriers. Thus, it is essential to simulate the ion currents and this cannot be accomplished at present by microscopic MD approaches. In order to address this challenge, we developed and refined an approach capable of evaluating ion current while still reflecting the realistic features of the given channel. Our method involves generation of semimacroscopic free energy surfaces for the channel/ions system and Brownian dynamics (BD) simulations of the corresponding ion current. In contrast to most alternative macroscopic models, our approach is able to reproduce the difference between the free energy surfaces of different ions and thus to address the selectivity problem. Our method is used in a study of the selectivity of the KcsA channel toward the K+ and Na+ ions. The BD simulations with the calculated free energy profiles produce an appreciable selectivity. To the best of our knowledge, this is the first time that the trend in the selectivity in the ion current is produced by a computer simulation approach. Nevertheless, the calculated selectivity is still smaller than its experimental estimate. Recognizing that the calculated profiles are not perfect, we examine how changes in these profiles can account for the observed selectivity. It is found that the origin of the selectivity is more complex than generally assumed. The observed selectivity can be reproduced by increasing the barrier at the exit and the entrance of the selectivity filter, but the necessary changes in the barrier approach the limit of the error in the PDLD/S-LRA calculations. Other options that can increase the selectivity are also considered, including the difference between the Na+...Na+ and K+...K+ interaction. However, this interesting effect does not appear to lead to a major difference in selectivity since the Na+ ions at the limit of strong interaction tend to move in a less concerted way than the K+ ions. Changes in the relative binding energies at the different binding sites are also not so effective in changing the selectivity. Finally, it is pointed out that using the calculated profiles as a starting point and forcing the model to satisfy different experimentally based constraints, should eventually provide more detailed understanding of the different complex factors involved in ion selectivity of biological channels.     

Occurrence of the neurosecretory substance during the embryonic development of the guinea pig

Summary The time and place of occurrence of the neurosecretory substance in the hypothalamo-neurohypophysial system of the guinea pig during embryogenesis have been investigated. Use is made of the luminiscence of neurosecretion stained with paraldehydefuchsin when observed in a dark field. It is established that the neurosecretory material occurs first in some cells of the supraoptic nucleus about the 39th–40th day of intrauterine development. In the paraventricular nucleus it is observed about the 44th–45th day. At that time it is seen also in Eminentia mediana and in the neurohypophysis. In the latter, however, it is in a smaller amount than in the areas situated above it. These results are discussed in connection with the transport theory of Bargmann and Scharrer.     

A Note on the Evolution of the Stamens in the Laurales,with Emphasis on the Lauraceae

The number of pollen sacs per anther and their position have traditionally been among the most important systematic characters in the Lauraceae. Opinions differ, however, about the evolutionary direction in these characters. This paper is intended to draw attention to little known morphological features of the stamens, in particular to transitions between disporangiate and tetrasporangiate anthers. In addition, the phylogenetic derivation of the stamen appendages is discussed. It is hypothesized that branched androecial structures may be primitive within the Laurales, if not in the angiosperms as a whole.     

Visualizing the microtubule-associated protein tau in the nucleus

Although tau is mainly known as an axonal microtubule-associated protein,many studies indicate that it is not restricted to this subcellular compartment.Assessing tau’s subcellular distribution,however,is not trivial as is evident from transgenic mouse studies.When human tau is over-expressed,it can be immunohistochemically localized to axons and the somatodendritic domain,modeling what is found in neurodegenerative diseases such as Alzheimer’s disease.Yet,in wild-type mice,despite its abundance,tau is difficult to visualize even in the axon.It is even more challenging to detect this protein in the nucleus,where tau has been proposed to protect DNA from damage.To establish a framework for future studies into tau’s nuclear functions,we compared several methods to visualize endogenous nuclear tau in cell lines and mouse brain.While depending on the fixation and permeabilization protocol,we were able to detect nuclear tau in SH-SY5Y human neuroblastoma cells,we failed to do so in N2a murine neuroblastoma cells.As a second method we used subcellular fractionation of mouse tissue and found that in the nucleus tau is mainly present in a hypophosphorylated form.When either full-length or truncated human tau was expressed,both accumulated in the cytoplasm,but were also found in the nuclear fraction.Because subcellular fractionation methods have their limitations,we finally isolated nuclei to probe for nuclear tau and found that the nuclei were free of cytoplasmic contamination.Together our analysis identifies several protocols for detecting tau in the nucleus where it is found in a less phosphorylated form.     

On the structure of the pulmonate osphradium

Summary The cellular organisation of the osphradium of Planorbarius as revealed by the previously described light microscope studies is confirmed in the present study. A third epithelial cell type, the basal cell, is described. Perception is carried out by dendritic processes from osphradial sensory neurones, forming free nerve-endings in the sensory region of the osphradial epithelium. Ciliated cells and secretory cells of the osphradial epithelium are concerned with the transport of material in the osphradial canal. Many of the ultrastructural features of molluscan central ganglia are present in the osphradial ganglion, including inter-axonal chemical synapses. Neuromuscular junctions are present in the sheath surrounding the organ and these may be involved in a behavioural response of the organ. The need for further electrophysiological studies is emphasised.     

Reflection in the electrical activity of the brain of the activities of the mechanisms regulating the functional state

On the basis of analysis of the results of author's studies and literature data, theoretical notions are developed, according to which spatial-temporal organization of cortical biopotentials is a result of activity of nonspecific different level systems subtly regulating current alertness in conformity with needs of the actual and forthcoming activities. In the hierarchy of regulating systems, in conditions of alertness, nonspecific thalamic and midbrain system is leading. Activity of these regulation levels provides in alertness for formation and destruction of functional neuronal ensembles which realize elementary informational transformations. The role is emphasized of asynchronous processes in the central nervous system activity.     

Purinergic signalling in the subretinal space: a role in the communication between the retina and the RPE

The retinal pigment epithelium (RPE) is separated from the photoreceptor outer segments by the subretinal space. While the actual volume of this space is minimal, the communication that occurs across this microenvironment is important to the visual process, and accumulating evidence suggests the purines ATP and adenosine contribute to this communication. P1 and P2 receptors are localized to membranes on both the photoreceptor outer segments and on the apical membrane of the RPE which border subretinal space. ATP is released across the apical membrane of the RPE into this space in response to various triggers including glutamate and chemical ischemia. This ATP is dephosphorylated into adenosine by a series of ectoenzymes on the RPE apical membrane. Regulation of release and ectoenzyme activity in response to light-sensitive signals can alter the balance of purines in subretinal space, and thus coordinate communication across subretinal space with the visual process.     

Cytological Identification of the Chromosomes Involved in Searle''s Translocation and the Location of the Centromere in the X Chromosome of the Mouse

The autosome in Searle's X-autosome translocation has been shown to be chromosome 16. The breakpoint in chromosome 16 is slightly proximal to the middle and in the X is slightly distal to the middle.-Available evidence indicates that either Linkage Group XV or Linkage Group XIX is carried on chromosome 16.-The centromere of the X chromosome is at the spf end of the linkage group.     

Contribution of internal layers of the retina to the genesis of the light peak in the electrooculogram in the chicken

We report that in the Chicken retina, Na aspartate which selectively blocks signal transmission between the photoreceptors and second order neurons also largely modifies the EOG. In treated eyes, the standing potential is reduced and the LP which is very transient in the Chicken eye is substituted for by a reactivity to light with much slower rise and delayed culmination time. The data are discussed in terms of interaction between pigment epithelium and neuroretina in the pharmacological determinism of the LP.     

On the neurodynamics of the creation of consciousness

Consciousness is expected to have a specific temporal dynamics. The COrollary Discharge of Attention Movement (CODAM) model of consciousness is deduced from an engineering approach to attention and motor attention. This model is briefly described, as is support arising from brain dynamics, especially that for the attentional blink. The understanding of known temporal dynamics in the brain associated with the emergence of consciousness is then developed from CODAM, and specifically related to the N2 ERP brain signal. How the pre-reflective self, as content-free, interacts with the content of experience is discussed in terms of the possibility that such experience arises from some proto-self generated by body signals; experiments are described which indicate that no pre-reflective self based on body signals is observable. Only a content-free pre-reflective self is consistent with this data, as CODAM suggests. How such a pre-reflective self can be further fused to give temporal continuity of a sense of self is considered in terms of various mechanisms which could be present for preserving the sense of self. The observation of the N2 signal in hippocampal encoding is proposed as providing a justification for the encoding of the N2–P3 sequence of brain signals. This would correspond to episodic encoding of the sequence of experiences of the pre-reflective self; this will thereby provide the necessary control signals in time so that ‘I’ is experienced as part of the retrieval of such memories.     

Observations on the permeability of the choriocapillaris of the eye

Summary The choriocapillaris is a fenestrated capillary bed located posterior to the retinal pigment epithelium. It serves as the main source of supply to the photoreceptors, retinal pigment epithelium, and other cells of the outer retina. The permeability of these capillaries to intravenously injected ferritin (MW — approx. 480,000; mol. diam. 11 nm) was examined in the mouse, rabbit, and guinea pig, each of which is characterized by a different type of retinal vascularization. In all three species, the bulk of the ferritin remained in the capillary lumina, where it appeared to be blocked at the level of the diaphragmed fenestrae. Some ferritin was present in endothelial cell vacuoles. The results confirm previous work on the rat choriocapillaris and indicate that the barrier function of the choriocapillary endothelium is present even among species in which the retinal circulation differs significantly.Supported by NIH grant EY03418     

Evolutionary and morphological significance of the deflecting wrinkle in the lower molars of the Hominoidea

The deflecting wrinkle is a well-known character state of the lower m2 and M1 of the human dentition, but there is little information regarding its presence in great apes. The deflecting wrinkle is more frequent on M2-3 in all extant pongid genera studied in this paper except Pan paniscus, in which M1 has the highest frequency (16.0%) and in which this wrinkle is absent on M3. In Gorilla, it is absent on M1, with only a low incidence on M2-3. Its greatest frequency in Pongo is always on M2 (20.2%), which is the greatest expression of the trait in the great apes. We interpret the presence of the deflecting wrinkle as an incidental effect and suggest that it represents a plesiomorphic character state in the Hominoidea.