Ragnar Olsson

The skin of Amphioxus

SummaryThe skin of the lancelet, Amphioxus lanceolatus, was investigated with the aid of the electron microscope and some histochemical techniques. It was shown that the single type of epidermal cells is capable of performing several activities. These cells produce and attach a thin mucous surface layer and it is also suggested that a primitive form of keratinization occurs in them. Furthermore they may produce pigment granules and serve as glycogen stores. A thin lamina below the epidermal cells cements their basal surfaces and is itself basally anchored in the underlying corium with the aid of an elaborate system of processes. The corium fibre layer in most cases rests upon a single fibrocyte layer. It is at irregular intervals penetrated by bundles of fibres which originate as branches of the corium collagen fibres.

The praeoptico-hypophysial system, Nucleus tuberis lateralis and the subcommissural organ of Gasterosteus aculeatus after changes in osmotic stimuli

SummaryThe histology and cytology of the praeoptico-hypophysial system, nucleus tuberis lateralis and subcommissural organ in Gasterosteus aculeatus were analyzed after the fishes had been put in waters of different salinity (see Tables 1–4).These three structures are all identical in fishes which are accustomed to fresh water and to 32‰ salt-water. A transference to hypertonic water causes changes in the neurosecretory system which suggest the existence of an antidiuretic principle in the neurosecretory substance. No such relationship is found when the fishes are put into hypotonic water. Further, no connection is found between either the secretion production in nucleus tuberis lateralis or in the subcommissural organ and variations in osmotic value.

The infundibular organ of the lancelet (Branchiostoma lanceolatum, acrania) : an immunocytochemical study

Reissners fibers are secretions produced by different ependymal areas of the chordate brain, viz., in adult vertebrates, by the dorsal subcommissural organ, and in all stages of cephalochordates (Branchiostoma lancelets), by the ventral infundibular organ. Fibers produced by these different organs are seemingly identical and the two fiber sources also share some immunocytochemical and lectin-binding properties. The secretions in these two glands are, however, not identical; the infundibular organ cells are strongly reactive with antibodies against vertebrate Reissners fibers, but they do not react with antibodies raised against the source of the vertebrate fibers, viz., the subcommissural organ. The results support the possibility that, in adult vertebrates, the Reissners fibers are composed of material not only from the subcommissural organ, but also from another, not yet identified, source that is identical or equivalent to the infundibular organ of the lancelet. There are indications that the infundibular organ is immunocytochemically closely akin to some secretory cells in the vertebrate embryonic brain and also to those that produce the juvenile vertebrate Reissners fibers, viz., secretory cells in the flexural organ.

Subcommissural ependyma and pineal organ development in human fetuses

Abstract The pineal regions of five human fetuses of 180–230 mm crown-heel lengths have been investigated in serial sections. Man possesses a subcommissural organ at these ages which has glandular properties and closely resembles that of most subhuman animals. The subcommissural secretion, which is discharged into the cerebrospinal fluid, does not, however, form a Reissners fiber. The subcommissural epithelium is extensively distributed in the epithalamus, and it is found in the pineal diverticulum as well, where the cells have the same glandular properties. The posterior lobe of the pineal organ is apparently built up from this specialized ependyma, and there are signs that the ependymal cells may retain their secretory properties for some time in the developing pineal organ.

Iodine binding in the endostyle of larval Branchiostoma lanceolatum (Cephalochordata)

The asymmetrical endostyle of Branchiostoma larvae contains two different zones of mucus-producing cells which metamorphose to the paired zones 2 and 4 respectively in the endostyle of the adult. In both the larva and the adult these zones are parts of the food-trapping mechanism. An endostyle zone, which has a position corresponding to that of the paired iodinating zones in the endostyle of the adult, binds iodine selectively. The ultrastructure and labeling pattern indicate that the labeled cells in the larval endostyle belong to functionally different types. In one region of the iodinating zone iodine is mainly bound extracellularly at the apical cell surface. Also in the second region grains are located at the apical cell surface as well as over the cytoplasm and extracellularly at the basal plasma membrane. It is possible that iodination takes place in the lumen close to cells in the first region and that the labeled product is taken up and eventually released by cells of the second region. Our observations show that this primitive endostyle already has iodinating capacity and may synthesize and release thyroid hormones.

A cytopharmacological study of the myxine adenohypophysis.

Abstract The pituitary adeno components of juvenile and adult Atlantic hagfish, Myxine glutinosa , were investigated with regard to cellular appearances which could repeatedly be seen in the glands. The cells were also studied after administration of various drugs (hormones, goitrogens, corticosteroid blocking agents, and reserpine), that could be expected to interfere with possible feed-back mechanisms, and in gonadectomized female animals. A pronounced individual variation in appearance of the pituitary is characteristic for the normal animals and for the groups of treated animals as well. This is true for both the general morphology and for the cytology of the gland and it makes the interpretation of the results difficult. It is concluded that the observed structural variations reflect different functional stages of several cell types, some of which seem to synthesize simple proteins, others glycoproteins. It has not been possible to correlate morphological features with the functional stage of the gonads. Thus, the pituitary control of the gonads, if any, is not established by these observations. One “acidophil” cell type (A3) is suggested to be the equivalent of the ACTH-cells of other craniates, because of its morphology and response to corticosteroid blocking agents. Another acidophil (A2) that is occasionally seen in normal pituitaries contains coarse erythrosinophil inclusions. A special cell type (C1) is characteristically oriented with the perikaryon in the center of the cell nests and a process reaching the connective tissue that surrounds the nest. It is frequently seen in large nests and it is suggested to be involved in the nourishment of the cell nests and the transportation of hormones. The nests are devoid of blood vessels.

An experimental breakage ofReissner's fibre in the central canal of the pike (Esox lucius)

SummaryThe spinal cords of newly hatched pike (Esox lucius) fry were divided into two pieces by transverse cuts. After periods of different lengths, the appearances of the brokenReissners fibres were investigated anatomically. The fibre normally terminates in the caudal end as a secretory accumulation, a caudal mass. After the operation this mass gradually disappears, apparently through the spinal cord wall cells. The new termination of the broken fibre, in front of the scar, forms a new caudal mass. This fact indicates thatReissners fibre is a secretory transport mechanism.

General review of the endocrinology of the protochordata and myxinoidea

Since E. J. W. Barrington presented his review on protochordate endocrinology in 1959 [in “Comparative Endocrinology” (A. Gorbman, ed.), Wiley, New York], considerable interest has been aroused in this field. Nevertheless, our knowledge of the evolution of different chordate endocrines is still very fragmentary. For several reasons it is difficult to obtain a clear picture of the lower chordate endocrines: 1. 1. Taxonomic diversity. Tunicates, acranians and the two cyclostome groups are taxonomically widely separated. Their recent survivors are structurally and functionally adapted to special living conditions. Consequently it is hard to determine which features really reflect the conditions of a more generalized ancestor and which are lately acquired specializations. 2. 2. Functional adaptability. Function is a very labile manifest of a morphologic pattern (“Bauplan”) which, during evolution, easily changes according to the needs of the organism. Functional equivalence between such remote groups can be expected only in very conservative patterns. 3. 3. Limits of form. Analytical approaches to establish homologies are difficult because of incomplete knowledge of the ontogeny of relevant structures and because palaeontology so far is unable to help us to bridge taxonomic gaps. Available evidence suggests that craniate endocrines have evolved in at least two ways, viz. by transformation of exocrine glands into endocrine glands and by concentration of scattered gland cells to form organs. The endostyle-thyroid transformation is the best-known example of how part of a complex exocrine gland has developed into an endocrine gland. Although this drastic transformation is demonstrated to us during the life cycle of some recent forms, we still have to find out when the active principle becomes a hormone and also which are the original target cells. The pancreatic β-cells and the hypothalamic neurosecretory cells were probably scattered elements in the alimentary and nervous tissues of the chordate progenitor. The condition in myxinoids seems to indicate that the pituitary-adeno component originally had neither topological nor functional relationship to an endocrine neural component. It is also possible that those craniates with the rostral pars distalis opening into the buccal cavity (polypterids, some primitive teleosts) reflect a very primitive condition. In Elops and Clupea, cells have been seen that are released through this duct, an observation that recalls the phagocytic process in ascidian neural glands. Although most recent authors seem to agree that the tunicate neural complex is no counterpart of the vertebrate pituitary (or part of it), this cellular release, the existence of the asymmetrical gland in some ascidians together with some possible secretory phenomena at the tip of the ciliary duct in appendicularians, call for further analysis.

Club-shaped gland and endostyle in larval Branchiostoma lanceolatum (Cephalochordata)

SummaryThe larval endostyle consists of two ridges of secretory cells, which correspond to the two paired muciparous bands in the endostyles of the adult Branchiostoma, most tunicates, and the lamprey ammocoete. The peculiar shape of the larval endostyle is an effective adaption for food-trapping in the asymmetrical body of the larva. Contrary to general belief, the internal opening of the club-shaped gland is the site of the secretory release, while the exernal opening is an inlet for sea water. The water is mixed with the mucous substance, probably containing neutral glycoproteins, which is produced in the gland tube. This material is released through the internal pore dorsally in the buccal cavity at a position where it is carried with the endostylar secretion towards the intestine. The club-shaped gland is not part of the food-trapping mechanism, but it is apparently an important larval gland which produces substances which may act in the processing of the food or in some other way may direct larval life.

Fine structure of the brain and brain nerves ofOikopleura dioica (Urochordata, Appendicularia)

SummaryEach second brain nerve consists of only one single fibre terminating at two different types of touch receptors in the oral region. The two nerves are the dendrites of two perikarya in the forebrain and are the master neurons for ciliary reversal in the stigmata, which is a two-neuron reflex. By axoaxonal synapses they control one motor neuron in the midbrain, i.e. the command neuron for ciliary reversal in both rings. This cell sends one axon branch in each third nerve to the cilia cells. In the left nerve this fibre is closely associated with a coarsely granulated accessory fibre, which apparently regulates the ciliary beat. The third nerves also contain one fibre each from another motor neuron in the hindbrain. These fibres make synaptic contacts at some specialized epidermal cells in the lateral trunk behind the ciliary rings. A few previously unknown nerves in the dorsal forebrain innervate epidermal cells. It is likely that the complicated epidermal motor innervation regulates the secretory activity of the oikoplasts or of the epidermal cells in constructing a new house, including the necessary complicated filters and food trapping mechanisms.