γ-Aminobutyric acid system in isolated dorsal and ventral horn neurons from bovine spinal cord

In order to search for the relationship between the structure and the function of the nervous system, the spinal cord provides suitable material. We devised a procedure for isolation of large ventral and small dorsal horn neurons. Then we examined the -aminobutyric acid (GABA) system in both neurons isolated using our procedure. Glutamic decarboxylase (GAD) activity in dorsal horn neurons was much higher than that in ventral horn neurons. Further, GABA uptake activity by the dorsal horn neurons was also somewhat higher than that by the ventral horn neurons, although some properties of GABA uptake were found to be almost the same in both neuronal fractions. However, we could not find any difference of GABA--ketoglutarate transaminase (GABA-T) activity between the dorsal and ventral horn neurons. These results suggest that GAD and GABA uptake may be indicators for cell specificity to some extent.     

The formation of the mesoderm in urodelean amphibians

Summary Dorsal (D), lateral (L and R), and ventral (V) portions of the endoderm of blastulae ofAmbystoma mexicanum of different age (stages 8⁺ to 10^–) were combined with ectodermal caps of stage 8⁺ blastulae. All V and most L and R portions induced only ventrocaudal mesodermal structures — ventral type of mesoderm induction. Almost all D portions induced much more voluminous structures of predominantly axial character — dorsal type of mesoderm induction. The difference in mesoderm-inducing capacity of the dorsal as against the lateral and ventral endoderm is probably purely quantitative in character. The dorsal endoderm exhibits a pronounced dominance in mesoderm-inducing capacity. During the early symmetrization of the amphibian egg it is apparently especially the presumptive dorsal endoderm that becomes endowed with strong mesoderm-inducing properties.A comparison of the results obtained with endodermal portions of blastulae of different age showed that the mesoderm-inducing capacity first begins to decline in the dorsal endoderm (around stage 9), subsequently in the lateral, and finally in the ventral endoderm (at stage 10^–). At stage 10^– the dorsal endoderm no longer has mesoderm-inducing capacities.In the recombinates there is a striking correspondence between the regional differentiation of the mesoderm and that of the endoderm. The latter differs markedly from the presumptive significance of the various endodermal regions in the normal embryo.Primordial germ cells, which constitute a characteristic component of the ventral type of mesoderm induction, can be induced not only by ventral, but also by lateral and to some extent even by dorsal endoderm. The development of primordial germ cells from the ectodermal component of the various recombinates indicates that in the urodeles the origin of the primordial germ cells differs markedly from that in the anurans.The authors want to thank Miss A. de wit for expert technical assistance, Miss E. Bartová for making the drawings, and Dr. J. Faber for editorial help.     

Immunocytochemical study of the hypothalamo-neurohypophysial system

Summary An antiserum cross-reactive against ovine neurophysins-I-II and -III has been used in conjunction with the immunoperoxidase histochemical procedure to localize the cells of the sheep paraventricular (PVN) and supraoptic nuclei (SON). In order to describe the topographical distribution of the SON and PVN a study was made on the serial sections cut (a) transversely from rostral to caudal positions and (b) sagittally from lateral to medial positions of the hypothalamus.The cells of the SON, when examined in the transverse aspect, extended approximately 1900 caudally and when examined in the sagittal plane were contained within a lateral-medial distance of 4830 . In each case the SON cells lay adjacent to the optic chiasm.As sections were cut transversely, the cells of the PVN first appeared in a rostral position defined as 0 and close to the ventral lining of the third ventricle. This general ventral and ventro-lateral distribution of cells maintained up to a caudal distance of approximately 840 . From positions 1260–2310 there was a dramatic dorsal shift of the PVN cells which by this time had also extended laterally. The total rostral-caudal distance occupied by the PVN cells was 3150 . That the lateral-medial distance occupied by the PVN was small (1050 ) was determined on examining the magnocellular nuclei in sagittal section.This work was financed by a grant awarded by the Medical Research Council of New Zealand     

Morphogenetic processes inAttheya decora (Bacillariophyceae,Biddulphiineae)

The valva of the diatomAttheya decora is formed within a silica deposition vesicle which enlarges centrifugally by the fusion of small vesicles. The silica deposition vesicle can already be seen when the spindle has not yet disappeared completely. Valva formation seems to begin with the shaping of an organic matrix within a silica deposition vesicle. Later, this material silicifies. The complicated shape of the labiate process is preformed by the silica deposition vesicle, the inner membrane of which is associated with electron dense material on both faces. The horns are formed when the expanding silica deposition vesicle has reached the cell corners. They are elaborated without participation of microtubules. Swelling of local depositions of polysaccharides seems to provide the forces that spread the silicified horns during daughter cell separation and to cause the local spontaneous plasmolyses under the valva and along the cell flanks in the region of the intercalary bands. The inner organic wall layers and the organic continuations of the intercalary bands are formed on the surface of the plasmalemma; each of the continuations is produced simultaneously with the intercalary band belonging to it and becomes attached to the latter when the silica deposition vesicle opens.     

Enzyme formation,cellular breakdown and the distribution of gibberellins in the endosperm of barley

Summary The -amylase contents of the dorsal and ventral sides of the endosperm of barley grains increase approximately equally during germination. Aleurone tissue from all locations in the grain is equally able to make -amylase in response to gibberellic acid, so the distribution of this enzyme reflects the distribution of endogenous gibberellins.Variations occurred in both the rate and pattern of cellular breakdown of the starchy endosperm. Generally breakdown progressed away from, and parallel to the scutellum, ultimately advancing faster adjacent to the aleurone layer. The sheaf cells, above the furrow, were relatively resistant to enzymic breakdown. The results indicate that gibberellins are released generally from the scutellum and induce hydrolytic enzymes equally on the dorsal and ventral sides of the grain.     

Molecular signatures that correlate with induction of lens regeneration in newts: lessons from proteomic analysis

Background

Amphibians have the remarkable ability to regenerate missing body parts. After complete removal of the eye lens, the dorsal but not the ventral iris will transdifferentiate to regenerate an exact replica of the lost lens. We used reverse-phase nano-liquid chromatography followed by mass spectrometry to detect protein concentrations in dorsal and ventral iris 0, 4, and 8 days post-lentectomy. We performed gene expression comparisons between regeneration and intact timepoints as well as between dorsal and ventral iris.

Results

Our analysis revealed gene expression patterns associated with the ability of the dorsal iris for transdifferentiation and lens regeneration. Proteins regulating gene expression and various metabolic processes were enriched in regeneration timepoints. Proteins involved in extracellular matrix, gene expression, and DNA-associated functions like DNA repair formed a regeneration-related protein network and were all up-regulated in the dorsal iris. In addition, we investigated protein concentrations in cultured dorsal (transdifferentiation-competent) and ventral (transdifferentiation-incompetent) iris pigmented epithelial (IPE) cells. Our comparative analysis revealed that the ability of dorsal IPE cells to keep memory of their tissue of origin and transdifferentiation is associated with the expression of proteins that specify the dorso-ventral axis of the eye as well as with proteins found highly expressed in regeneration timepoints, especially 8 days post-lentectomy.

Conclusions

The study deepens our understanding in the mechanism of regeneration by providing protein networks and pathways that participate in the process.

     

THE DYNAMICS OF WOUND CLOSURE AND ITS ROLE IN THE PROGRAMMING OF PLANARIAN REGENERATION I—BLASTEMA EMERGENCE

Observations in vivo show that the edges of the wound are brought into close contact by muscle contraction and fuse by first intention immediately after transaction. The wound epithelium forms later by the stretching of the epidermal cells when the muscles relax.
Dorsal and ventral half-thickness fragments were associated in vitro by their anterior or posterior edges. The epidermis only fuses by first intention when the free borders are pressed into close contact. Blastemas of various localizations and sizes are formed from the suture between dorsal and ventral epidermis, in those places where it has been stretched. The opposing forces which cause the stretching are particularly due to the rolling-up of the fragments or to their relaxation after they have been forced to fuse.
Contrary to what was previously assumed, the simple fusion of dorsal and ventral epidermis is not sufficient to initiate blastema emergence. The need for stretching may be explained by the fact that certain epidermal cells are brought close to tissues of the opposite side, forming a transitional epidermis analogous to one edge. As a result of the formation of this distal level close to transection, intercalary regeneration would ensue, whose first step would be blastema emergence.     

Synchondroseal growth in the first cervical vertebra of the rat

Growth and remodelling of the first cervical vertebra were studied in the rat by means of biometry, vital staining (alizarin red S and oxytetracycline), and histology. The measurements showed a change in the ratio of the dorso-ventral to the transversal diameter in the lumen after obliteration of the dorsal synchondrosis. The pattern of labelling between the three segments of the vertebrae joined by synchondroses in the young animals indicated that expansion of the vertebral lumen took the form of a displacement of all three parts making up the bony ring. After closure of the dorsal synchondrosis the two ventral ones were still active and the lumen size increased more in the dorso-ventral direction than transversally. Alizarin red S and oxytetracycline tended to persist in the ventral part of the vertebra, while the staining almost disappeared from the dorso-lateral segment. Resting lines were found laterally to the ventral synchondroses in haematoxylin and eosin stained sections, but not in the ventral segment between the cartilages. The growth of the rat atlas is the result of an early rapid cartilage-mediated expansion of the vertebral lumen in conjunction with the growth of the spinal cord and, at a later age, mainly of a displacement of the ventral vertebral segment, leading to the final form of the vertebra and its lumen.     

Absence of sensory input does not affect persistent neurons in Tenebrio molitor metamorphosis (Insecta: Coleoptera)

Summary The ventral nerve cord of holometabolous insects is reorganized during metamorphosis. Certain elements, however, persist from the larval to the adult stage. A group of dorsal unpaired median neurons and a set of thoracic serotonin-immunoreactive interneurons are shown to be persistent elements in the ventral nerve cord of Tenebrio molitor. These persistent neurons retain their bauplan even after deprivation of the sensory neurons projecting onto them. These persistent neurons might provide a network into which newly developing sensory neurons fit during reorganization of the nervous tissue.     

Organization of the cell membrane inEuglena

Summary The cell membrane ofEuglena gracilis has been investigated with the freeze-fracture technique. When split, this membrane produces two fracture faces which are striking in their non-complementarity. The P fracture face is covered with a high density of 110 Å (average diameter) particles, while the E face is made up of a complex series of striations occurring at regular angles to the pellicle ridges which encircle the organism. Under certain conditions, however, the structure of the P fracture face assumes a more ordered configuration, and striations are visible on this fracture face which are precisely complementary to those observed on the E face. These observations suggest that the cortical cell membrane ofEuglena may be organized along the lines of a two dimensional crystal. However, this pattern of organization is restricted to the cortical region of the cell membrane; as the membrane invaginates near the anterior end of the cell the fracture faces change abruptly, and organization more typical of other cell membranes is observed. This invagination forms an extensive reservoir in the anterior of the cell, and the membrane bounding it is distinctly fluid in structure, with clear examples of endo- and exocytosis observable. These differences suggest that the cell membrane inEuglena is divided into two distinct but contiguous regions, each specialized with regard to structure and function.     

The eyes of hyperiid amphipods: relations of optical structure to depth

Summary In many oceanic hyperiid amphipods the eyes are double structures, with a specialized upward-pointing region covering a narrow field of view. Inter-ommatidial angles were measured across the eyes of 10 species from different depth ranges. With increasing depth (decreasing light) there is a trend towards greater dorso-ventral asymmetry resulting in the separation of the two retinae and an increase in the size of the upper eye. The diameters (D) of the dorsal ommatidia increase with depth, and the inter-ommatidial angles () decrease. There are no corresponding changes in the lower eyes. These features can be explained on the assumption that the upper eyes are used to detect small opaque targets against the downwelling light from the surface. In contrast to the resolution of grating-like targets, where the productD should increase as light intensity decreases (the eye-parameter; Snyder 1979), the detection of single targets requires that the ratioD/ should increase in dim light. Amongst hyperiids this ratio does indeed show a 50-fold increase from surface-to deep-living species, whereas the eye-parameter hardly changes.     

Positional information,compartments, and the cercal sensory system of crickets

Sensory neurons on the cricket cercus preserve the spatial order of the receptor array by forming an orderly afferent projection to the CNS. To examine the mechanisms underlying the production of the receptor array and the corresponding afferent projection, we transplanted epidermis to ectopic sites. The grafted tissue was identified by transplanting epidermis from a black cricket, Gryllus, to a tan cricket, Acheta. The results revealed that apposition of normally nonadjacent tissue usually produced intercalary growth from either donor or host, but not both. The experiments showed that tissue of more lateral origin always produced the intercalary growth. Since the cercus is circular in cross section, two separate hierarchies must exist, dividing the cercus into dorsal and ventral compartments. The border between the dorsal and ventral compartments appears to represent a line of lineage restriction. Transplants from one compartment to another caused more complex responses where both donor and host contributed to the intercalary tissue. Within the dorsal or ventral compartment, positional information guides the intercalary growth. Intercalated receptors always have the phenotype of receptors normally found between the positions represented by donor and host at the graft boundary. This result provides strong support for the idea that orderly synaptic connections between afferents and interneurons are controlled by the position of the receptor at the time of its differentiation.     

Origin of the pituitary innervation in the goldfish

Despite the large number of studies devoted to the pituitary of teleosts, the origin of the direct pituitary innervation is still largely unknown. Although such a model is ideal for applying retrograde transport techniques, these methods involve the difficult in vivo injection of tracers into the pituitary and have never been applied. Recently, a lipophilic fluorescent dye (1-1-dioctadecyl-3,3,3,3-tetramethylindocarbocyanin; DiI) has been introduced and shown to have the capacity of being transported by the membranes of paraformaldehydefixed tissues. Microcrystals of DiI were implanted via a ventral approach into the pituitary of goldfish previously fixed by intracardiac perfusion of paraformaldehyde. The goldfish heads were kept immersed in paraformaldehyde for various periods of time (2–6 weeks). The brains were then dissected and cut transversally using a Vibratome. The results demonstrate that hypophysiotrophic areas are essentially restricted to the preoptic region, the mediobasal hypothalamus and the nucleus dorsolateralis thalami. In addition, cell bodies probably containing gonadotrophin releasing-hormone were also retrogradely stained along a pathway that can be traced up to the olfactory bulbs. The results also confirm that cell bodies, located around the ventral aspect of the preoptic recess and probably corresponding to dopaminergic neurons, project to the pituitary. Large neurons have also been observed in the rostral dorsal midbrain tegmentum just caudal to the posterior commissure. Most neurons of the so-called paraventricular organ remain unstained. Finally, a fiber tract originating from an undetermined territory of the posterior brain has been observed. The results are discussed in relation to the possible chemical nature of the hypophysiotropic neurons.     

Swimming in a sub-adult monogenean of the genus Entobdella.

Swimming in a sub-adult monogenean parasite is reported for the first time. When detached from the substrate, a specimen of an undescribed species of Entobdella from the ventral skin surface of the cow-tailed ray, Dasyatis sephen, was found to propel itself vigorously through the water, head-first, by rapid dorso-ventral body undulations travelling in an antero-posterior direction. These waves pass in the opposite direction to the slower breathing (?) undulations exhibited by the attached parasite. Benedeniella macrocolpa from another elasmobranch host and benedeniines from teleost fishes merely made uncoordinated wriggling movements when detached from the substrate. The possible function of swimming in monogeneans is discussed.     

Measuring the Arousal Space of a Sit-and-Wait Predator: A Comparison of Predictive Models

The present study set out to compare two predictive models, Holling (1966) and Hardman and Turnbull (1980), to describe the arousal space for the aquatic sit-and-wait predator, Ranatra dispar. When tested in the horizontal plane the fit of Holling's model was good, although a better fit was achieved by using the untransformed angle of prey to body axis term . The second, multiple regression model, gave smaller residuals for low food deprivation periods but larger for longer periods. In the vertical plane the Holling model was unsatisfactory. It is suggested that the changes in number and size of ommatidia from dorsal to ventral region of the eye is largely responsible. A multiple regression model is described that predicts the arousal field of R. dispar in the vertical plane. It is suggested that the general applicability of such models to other visual predators is restricted if apparent hunger effects are not included in their development.     

Ultrastructural heterogeneity of the mesocoxal muscles of Periplaneta americana

Summary Ultrastructural studies have been performed upon the posterior coxal depressor muscle (136) and a coxal branch of the main depressor group (135d) from the mesocoxa of the cockroach, Periplaneta americana. The quantitative stereometric analyses performed have shown the latter muscle to consist of a dorsal band of fibers having 25.5% mitochondria and 13.6% sarcoplasmic reticulum (SR) and T-tubules (TTS), and a ventral group of fibers with only 4.4% mitochondria and 26.6% SR/TTS. The volume fractions characteristic of the ventral fibers of muscle 135 d are also typical of muscle 136.This work was supported by a grant from the McCandless Foundation, Atlanta, Georgia, to D.R. Stokes     

The cell biology of Drosophila wing metamorphosis in vitro

Summary We have examined the metamorphosis of the wing imaginal disc of Drosophila during culture in vitro in the continuous presence of 20-hydroxy ecdysone (0.1 g/ ml). We find that the sequence of cellular changes in the wing blade during culture closely match those occurring in situ, involving two periods at which the dorsal and ventral surfaces are joined only by cell processes containing trans-alar microtubule arrays. Good pupal and imaginal cuticle secretion is found in this system.     

Relocations of cell convergence sites and formation of pharyngula-like shapes in mechanically relaxed <Emphasis Type="Italic">Xenopus</Emphasis> embryos

Influence of the relaxation of mechanical tensions upon collective cell movements, shape formation, and expression patterns of tissue-specific genes has been studied in Xenopus laevis embryos. We show that the local relaxation of tensile stresses within the suprablastoporal area (SBA) performed at the early-midgastrula stage leads to a complete arrest of normal convergent cell intercalation towards the dorsal midline. As a result, SBA either remains nondeformed or protrudes a strip of cells migrating ventralwards along one of the lateral lips of the opened blastopore. Already, few minutes later, the tissues in the ventral lip vicinity undergo abnormal transversal contraction/longitudinal extension resulting in the abnormal cell convergence toward ventral (rather than dorsal) embryo midline. Within a day, the dorsally relaxed embryos acquire pharyngula-like shapes and often possess tail-like protrusions. Their antero-posterior and dorso-ventral polarity, as well as expression patterns of pan-neural (Sox3), muscular cardiac actin, and forebrain (Otx2) genes substantially deviate from the normal ones. We suggest that normal gastrulation is permanently controlled by mechanical stresses within the blastopore circumference. The role of tissue tensions in regulating collective cell movements and creating pharyngula-like shapes are discussed.     

The filter apparatus of Rana temporaria and Bufo bufo larvae (Amphibia,Anura)

Summary In larvae of Rana temporaria and Bufo bufo the location of filter apparatus within the larval organization, the arrangement of the morphological parts as branchial food trap, ventral velum, and filter rows, as well as their surface anatomy, are similar to that of other species of Orton's larval type IV. The means by which mucous with its entrapped food particles is transported from the filter rows to the esophagus is finally resolved. The dorsally positioned ciliary cushion extends far ventrally between the filter plates. From their contact with the filter rows, the cilia transport the mucous to Kratochwill's caudally positioned Flimmerrinne and from there to the esophagus. The original chordate principle of mucous entrapment and ciliary transport is thus retained by these anuran larvae. The only modification specific to the latter is the division into a ventral filter apparatus, whose epithelia serve for mucus entrapment, and a dorsal ciliary area.Six different types of cell may be distinguished ultrastructurally: (1) The ubiquitous squamous epithelium with merocrine extrusions; (2) the large supporting cells of the filter rows and of the ventral velum; (3) the ciliary cells of the ciliary cushion; (4) three different types of mucous producing secretory cells: (a) A type of cell similar to the goblet cell is found in the ciliary cushion (merocrine extrusion); (b) The secretory pits of the ventral velum and the secretory ridges have similar bottle-shaped merocrine secretory cells; (c) The merocrine apical cells of the filter rows are the final kind. It is evident that the ciliary cushion epithelium resembles that of both the manicotto glandulare of anuran larvae and the trachea and bronchus of Mammalia.Supported by the Deutsche Forschungsgemeinschaft-DFG     

De Novo Formation of Left–Right Asymmetry by Posterior Tilt of Nodal Cilia

In the developing mouse embryo, leftward fluid flow on the ventral side of the node determines left–right (L-R) asymmetry. However, the mechanism by which the rotational movement of node cilia can generate a unidirectional flow remains hypothetical. Here we have addressed this question by motion and morphological analyses of the node cilia and by fluid dynamic model experiments. We found that the cilia stand, not perpendicular to the node surface, but tilted posteriorly. We further confirmed that such posterior tilt can produce leftward flow in model experiments. These results strongly suggest that L-R asymmetry is not the descendant of pre-existing L-R asymmetry within each cell but is generated de novo by combining three sources of spatial information: antero-posterior and dorso-ventral axes, and the chirality of ciliary movement.