The pineal complex of the three-spined stickleback,Gasterosteus aculeatus L.

Summary The pineal complex of the three-spined stickleback (Gasterosteus aculeatus L.) was investigated by light and electron microscopy, as well as fluorescence histochemistry for demonstration of catecholamines and indolamines. The pineal complex of the stickleback consists of a pineal organ and a small parapineal organ situated on the left side of the pineal stalk. The pineal organ, including the entire stalk, is comprised mainly of ependymal-type interstitial cells and photoreceptor cells with well-developed outer segments. Both unmyelinated and myelinated nerve fibres are present in the pineal organ. Nerve tracts from the stalk enter the habenular and posterior commissures. A small bundle of nerve fibres connects the parapineal organ and the left habenular body. The presence of indolamines (5-HTP, 5-HT) was demonstrated in cell bodies of both the pineal body and the pineal stalk, and catecholaminergic nerve fibres surround the pineal complex.     

Peroxisomes in intestinal and gallbladder epithelial cells of the stickleback,Gasterosteus aculeatus L. (Teleostei)

Summary The occurrence of microbodies in the epithelial cells of the intestine and gallbladder of the stickleback, Gasterosteus aculeatus L., is described. In the intestine the organelles are predominantly located in the apical and perinuclear zone of the cells and may contain small crystalline cores. In gallbladder epithelial cells the microbodies are distributed randomly. The latter organelles are characterized by the presence of large crystalloids. Cytochemical and biochemical experiments show that catalase and D-amino acid oxidase are main matrix components of the microbodies in both the intestinal and gallbladder epithelia. These organelles therefore are considered peroxisomes. In addition, in intestinal mucosa but not in gallbladder epithelium a low activity of palmitoyl CoA oxidase was detected biochemically. Urate oxidase and L- hydroxy acid oxidase activities could not be demonstrated.     

Characterization and localization of gonadotropin-releasing hormone in the brain and pituitary of the three-spined stickleback,Gasterosteus aculeatus

Radioimmunoassay (RIA) studies on highperformance liquid chromatography (HPLC) fractions of brain extracts of the three-spined stickleback, Gasterosteus aculeatus, provided evidence for at least two forms of gonadotropin-releasing hormone (GnRH). One form showed chromatographic and immunological properties similar to that of synthetic salmon GnRH (sGnRH). A second, unidentified form of GnRH eluted in the same position as chicken GnRH I (cGnRH-I); however, it did not cross-react in a cGnRH-I RIA. Furthermore, it cannot be excluded that chicken GnRH II (cGnRH-II) and maybe one other unidentified form are present in the stickleback. The distribution of GnRH in the brain of breeding adult male sticklebacks was studied by use of immunohistochemistry. Two antisera against sGnRH and antisera against mGnRH and cGnRH-II were applied on cryosections and visualized using the peroxidase-antiperoxidase method. Staining patterns were similar after incubations with all four antisera. Immunoreactive fibers were found in most parts of the brain. Three distinct groups of GnRH-immunoreactive perikarya were found in the nucleus olfactoretinalis, in the nucleus anterior periventricularis, and in the nucleus lateralis tuberis. Moreover, weakly stained cells occurred in a periventricular position in the midbrain. The proximal pars distalis of the pituitary, housing the gonadotropic cells, was richly innervated by GnRH-positive fibers. In the pars intermedia and in the rostral pars distalis, immunoreactive fibers were absent.     

Habitat-dependent and -independent plastic responses to social environment in the nine-spined stickleback (Pungitius pungitius) brain

The influence of environmental complexity on brain development has been demonstrated in a number of taxa, but the potential influence of social environment on neural architecture remains largely unexplored. We investigated experimentally the influence of social environment on the development of different brain parts in geographically and genetically isolated and ecologically divergent populations of nine-spined sticklebacks (Pungitius pungitius). Fish from two marine and two pond populations were reared in the laboratory from eggs to adulthood either individually or in groups. Group-reared pond fish developed relatively smaller brains than those reared individually, but no such difference was found in marine fish. Group-reared fish from both pond and marine populations developed larger tecta optica and smaller bulbi olfactorii than individually reared fish. The fact that the social environment effect on brain size differed between marine and pond origin fish is in agreement with the previous research, showing that pond fish pay a high developmental cost from grouping while marine fish do not. Our results demonstrate that social environment has strong effects on the development of the stickleback brain, and on the brain''s sensory neural centres in particular. The potential adaptive significance of the observed brain-size plasticity is discussed.     

Genetics of osteal plate polymorphism and microevolution of threespine stickleback (Gasterosteus aculeatus L.)

Summary The results of genetical studies of osteal plate polymorphism of threespine stickleback Gasterosteus aculeatus reported to date (Munzing 1959; Hagen and Gilbertson 1973; Avise 1976) are discussed and proposed inheritance models are considered. Results of crosses between the morphs of G. aculeatus from the White Sea are presented. An attempt has been made by the author to devise a unifying model for the inheritance of plate morphs within the whole range of G. aculeatus. The role of polymorphism in the microevolutionary processes taking place within this complex species is discussed.     

Some effects of low oxygen tensions on the distribution of the three-spined stickleback Gasterosteus aculeatus L. and the nine-spined stickleback Pungitius pungitius (L.)

During extensive sampling of populations of sticklebacks for parasites, it became apparent that marked differences existed in the distribution of the 2 British freshwater species. Observation of the survival, respiratory rates and distribution of three- and nine-spined sticklebacks from a variety of habitats supports the suggestion that physiologically, the nine-spined stickleback is much better adapted to life in closed, shallow, weedy, eutrophic waters, depleted in oxygen. By comparison, Gasterosteus aculeatus favours more open well oxygenated water.     

Habitat-specific adaptation of immune responses of stickleback (Gasterosteus aculeatus) lake and river ecotypes

Freshwater populations of three-spined sticklebacks (Gasterosteus aculeatus) in northern Germany are found as distinct lake and river ecotypes. Adaptation to habitat-specific parasites might influence immune capabilities of stickleback ecotypes. Here, naive laboratory-bred sticklebacks from lake and river populations were exposed reciprocally to parasite environments in a lake and a river habitat. Sticklebacks exposed to lake conditions were infected with higher numbers of parasite species when compared with the river. River sticklebacks in the lake had higher parasite loads than lake sticklebacks in the same habitat. Respiratory burst, granulocyte counts and lymphocyte proliferation of head kidney leucocytes were increased in river sticklebacks exposed to lake when compared with river conditions. Although river sticklebacks exposed to lake conditions showed elevated activation of their immune system, parasites could not be diminished as effectively as by lake sticklebacks in their native habitat. River sticklebacks seem to have reduced their immune-competence potential due to lower parasite diversity in rivers.     

Genetic relationships among marine and freshwater populations of the European three-spined stickleback (Gasterosteus aculeatus) revealed by microsatellites

To assess the population genetic structure of the three-spined stickleback, Gasterosteus aculeatus, variability at 18 microsatellite loci was examined in 1724 individuals from 74 locations covering most of the species distribution range in Europe. The results revealed high overall degree of differentiation (F(ST) = 0.21) but contrasting level of divergence and genetic variability between habitat types. Marine populations were genetically relatively uniform even across great geographical distances as compared to substantial differentiation among freshwater populations. Analysis of molecular variance indicated low but significant (2.7%) variation in allele frequencies between geographical regions, but a negligible effect of habitat type (0.2%). The phylogenetic pattern was not explained by habitat type, but a weak signal of populations clustering according to geographical or water system origin was found. The results support the view that three-spined stickleback marine ancestors colonized northern European fresh waters during the postglacial marine submergence c. 10,000 years ago, whereas in the Mediterranean region colonization probably dates back to the Pleistocene. The independent origins of river and lake populations indicate that they originate from multiple colonizations rather than sharing common ancestry. In the continuous marine environment, the low degree of differentiation among populations can be explained by gene flow among subpopulations and large effective population size buffering divergence in neutral markers. In contrast, among postglacially established freshwater populations differentiation appears to be driven by genetic drift and isolation. The stepwise mutations appear to have contributed to the population differentiation in the southern part of the three-spined stickleback distribution range.     

Effects of Schistocephalus solidus (Cestoda) on the food intake and diet of the three-spined stickleback, Gasterosteus aculeatus

Seasonal differences were detected between uninfected sticklebacks and those infected with Schistocephalus solidus in their stomach fullness and diet composition.     

Synaptonemal Complex Analysis in Oocytes and Spermatocytes of Threespine Stickleback Gasterosteus Aculeatus (Teleostei, Gasterosteidae)

A surface-spreading synaptonemal complex (SC) technique was employed to analyze spermatocytes and oocytes of stickleback, Gasterosteus aculeatus, in order to visualize the process of chromosome synapsis. The mean SC length was 150±18m in three males and 143±12m in one female analyzed. A representative SC karyotype with 21bivalents was also presented. Each SC had lateral elements of equal length. No bivalent displaying the atypical synaptic behaviour which is often associated with heteromorphic sex chromosomes was observed neither in males nor in the female analyzed.     

The breeding colouration of male three-spined sticklebacks (Gasterosteus aculeatus) as an indicator of energy investment in vigour

Summary A necessary condition of most models of intersexual selection requires that secondary sexual traits are costly so that cheating is prevented. If the conspicuous breeding colouration of male three-spined sticklebacks (Gasterosteus aculeatus L.) is such a handicap, it must involve costs. I examined the energetic costs of the breeding colouration by varying the energy contents of the daily food supply among five groups of sticklebacks over a 10 week period. The nutritional carotenoid level, i.e. the colour pigment used in the breeding colouration, was constant for all fish. Both the increase of their condition factor and the condition level they finally achieved correlated positively with the food ration of the groups. Individuals whose condition increased during the experiment developed a more intensive red colouration. However, a direct correlation between food quantity and the red breeding colouration reached at the end of the experiment did not exist. Nevertheless, given the limitation of pigment availability, there was still variation in the breeding colouration and the costs for the metabolism of the colouration were sufficient to render it an honest signal: a female stickleback can assess a male's condition and condition change over the past few weeks by the intensity of the colour of his blue eyes (which is not based on carotenoids and whose pigments were therefore not controlled in the food) and his red jaw, respectively. How much an individual male fish invests in increase of length and increase of condition (which correlate negatively with each other) seems to be, at least partly, his own strategic decision, which could have important consequences in the competition for female mates. It is eventually this decision that a male stickleback seems to signal with his red jaw.     

A cobalt-lysine study of primary olfactory projections in king salmon fry (Oncorhynchus tshawytscha Walbaum)

Summary Primary olfactory projections in king salmon fry, Oncorhynchus tshawytscha, were studied with the cobaltlysine technique and after sectioning the entire head in a frozen state. The labeled axons can be traced from the olfactory epithelium, where cobalt was applied, into the olfactory bulb and to the ventral and lateral regions of the ventral telencephalon. The latter projection has not previously been reported, and may in actuality represent a transneuronal transport of cobalt. The terminations in the glomerular layer and in the external cellular layer of the bulb appear to be distributed differently in different parts of the bulb, suggesting regional specializations. A few neurons in the bulb were also always labeled suggesting that they may project to the olfactory epithelium.     

Central connections of the olfactory bulb in the weakly electric fish,Gnathonemus petersii

Summary We have investigated the central connections of the classical olfactory system in the weakly electric fish Gnathonemus petersii using HRP and cobalt labelling techniques. The olfactory bulb projects bilaterally via the medial and lateral olfactory tracts to restricted areas of the telencephalon, namely to its rostromedial, lateral and posterior medial parts. The most extensive telencephalic target is the posterior terminal field, which arcs around the lateral forebrain bundle at levels posterior to the anterior commissure. Projections to the contralateral hemisphere cross in the ventral telencephalon rostral to the anterior commissure and via the posterior dorsal part of the anterior commissure; endings are also present within the anterior commissure. Bilateral projections to the preoptic area, to the nucleus posterior tuberis and to an area in the thalamus are apparent. In all cases, contralateral projections are less extensive than those on the side ipsilateral to the injected bulb. A projection via the medial olfactory tract can be followed to the contralateral bulb. Following injections into the olfactory bulb, retrogradely labelled neurons are found in the contralateral bulb and in six telencephalic areas; they are also present in the periventricular diencephalon and in an area lateral to the nucleus posterior tuberis. The present results support the suggestion that a reduction in olfactory input to the telencephalon occurs together with increased telencephalic differentiation in actinopterygian fishes.     

Amphibian larvae and zinc sulphate: a suitable model to study the role of brain-derived neurotrophic factor (BDNF) in the neuronal turnover of the olfactory epithelium

The vertebrate olfactory system has fascinated neurobiologists over the last six decades because of its ability to replace its neurons and synaptic connections continuously throughout adult life, under both physiological and pathological conditions. Among the factors that are proposed to be involved in this regenerative potential, brain-derived neurotrophic factor (BDNF) is a candidate for having an important role in the neuronal turnover in the olfactory epithelium (OE) because of its well-documented neurogenic and trophic effects throughout the nervous system. The aim of the present study was to generate a suitable model to study the participation of BDNF in the recovery of the OE after injury in vivo. We developed an experimental design in which the OE of Rhinella arenarum tadpoles could be easily and selectively damaged by immersing the animals in ZnSO₄ solutions of various concentrations for differing time periods. Image analysis of histological sections showed that different combinations of each of these conditions produced statistically different degrees of injury to the olfactory tissue. We also observed that the morphology of the OE was restored within a few days of recovery after ZnSO₄ treatment. Immunohistochemical analysis of BDNF was performed with an antiserum whose specificity was confirmed by Western blotting, and which showed drastic changes in the abundance and distribution pattern of this neurotrophin in the damaged olfactory system. Our results thus suggest that BDNF is involved in the regeneration of the OE of amphibian larvae, and that our approach is suitable for further investigations of this topic. This work was supported by grants from CONICET (PIP 5842), Universidad de Buenos Aires (UBACYT X131) and ANPCYT (PICT 32219).     

Morphometrical analysis with the light and electron microscope of the kidney of the anadromous three-spined stickleback Gasterosteus aculeatus,form trachurus,from fresh water and from sea water

Summary The renal corpuscles, juxtaglomerular cells, nephronic tubules, and ureters of female sticklebacks were studied.In fresh water fishes, the diameter of the renal corpuscles is similar to that found in fishes obtained from the sea, whereas the diameter of the glomeruli and the nuclei of the podocytes are slightly larger. Furthermore, in fresh water the podocytes produce secretory globules, which show some of the histochemical characteristics of the substance constituting the glomerular basement membrane. In sea water animals, secretory phenomena are absent. Mesangial cells, which are scarce in fresh water fishes, are numerous in marine animals. Similarly, juxtaglomerular cells, hard to find in fresh water fishes, are prominent in specimens from the sea.The development of the epithelia of the nephronic tubules and of the ureters is better in fresh water. The cells and the nuclei are larger. In the first proximal tubule, which is involved in the reabsorption and the digestion—by lysosomes—of macromolecules, micropinocytosis vermiformis occurs.The results of stereological analysis of the fractional volume of the mitochondria and of the relative extent of the infoldings of the basal cell membranes—the location of the ion transport mechanisms—in the three different segments of the nephronic tubule and in the ureter, point to the existence of a structural gradient along the kidney tubules. In fresh water fishes the mitochondrial volume, per surface unit of basal cell membrane, is low in the first proximal segment and is increasingly higher in the other segments, while the highest value is found in the ureter. This structural gradient may be functionally linked with osmotic and ionic gradients, which exist in the renal tubules in fresh water. In the kidney tubules of marine sticklebacks, which do not show a major osmotic gradient, the structural gradient is small.The results are discussed on the basis of the known physiological differences in the function of the kidney of euryhaline teleosts in fresh water and in the sea.The author is indebted to Mr. J. Cappon and Mr. M. Veenhuis (Laboratory for Ultrastructural Biology, University of Groningen) for technical assistance.     

Vergleichende histophysiologische Tracer-Untersuchungen an verschiedenen Organsystemen von Branchiostoma lanceolatum (Cephalochordata) und Brachydanio rerio (Teleostei)

Zusammenfassung In vergleichend autoradiographischen Untersuchungen wurde der Einbau von percutan applizierten 3H-Uridin, 3H-Histidin und 3H-Glucose in die wichtigsten Organsysteme (Epidermis, ZNS, Muskeln, Chorda, Leber, Kiemendarm, Darm) von Branchiostoma lanceolatum (Acranier) und Brachydanio rerio (Teleosteer) nach Inkorporationszeiten von 11 min bis zu 7 Tagen verfolgt. Der Stoffwechsel der markierten Substanzen in den einzelnen morphologisch miteinander zu homologisierenden Organen war bei den beiden Spezies sehr ähnlich, bei Branchiostoma allerdings (mit Ausnahme des ZNS) 4–5mal stärker als bei Brachydanio. Bei dem letzteren wurde außerdem eine zeitliche Verzögerung in der Tracer-Aufnahme (lag-Phase) beobachtet. Insbesondere der ZNS-Stoffwechsel von Acraniern zeigte ähnliche Charakteristika wie der von Vertebraten: Verbleib des Hauptanteils der neusynthetisierten RNS im Perikaryon, axonalen Protein-Transport, Vorwiegen der Glykogensynthese in den Nervenfaserendformationen. Allerdings fanden sich im ZNS von Branchiostoma niedrigere Stoffwechselraten als im ZNS von Brachydanio.

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Comparative histophysiological investigations of different organs in Branchiostoma lanceolatum (Cephalochordata) and Brachydanio rerio (Teleostei)

Summary Incorporation of 3H-uridine, 3H-histidine and 3H-glucose into some organs (epidermis, CNS, muscles, spinal cord, notochord, liver, gills, intestine) of Branchiostoma lanceolatum (Acrania) and Brachydanio rerio (Teleostei) was investigated by means of comparative autoradiograms following incorporation periods of 11 min to 7 days. The metabolism of the labeled substances in the various homologous organs examined was quite similar, although it was 4 to 5 times higher in Branchiostoma than in Brachydanio; in the latter there was also a delay of tracer incorporation of about 3 hrs, a so-called lag-phase. In particular the metabolism of the CNS of Branchiostoma showed the same characteristics as the CNS of vertebrates, e. g. storage of neuronally synthesized RNA in the neuronal perikarya, axonal flow of proteins, glycogen synthesis in nerve endings. However, metabolic activity of the CNS was lower in Branchiostoma.

Mit dankenswerter Unterstützung durch die Deutsche Forschungsgemeinschaft.