Cellular basis of an avian countercurrent multiplier system

A kidney from the budgerigar (budgie, parakeet; Melopsittacus undulatus) is composed of cortical reptilian-type nephrons (without loops of Henle) and mammalian-type nephrons (with loops) grouped together in medullary cones. The loop of the mammalian-type nephrons has a descending segment composed of thin and highly interdigitated cells. These thin limb cells have few mitochondria (15% of cell volume), undetectable Na+,K(+)-ATPase activity, and virtually no basolateral surface amplification. Prior to the hairpin turn, the descending limb thickens, but the cells continue to lack basolateral amplification. Cells just prior to and within the hairpin turn resemble cells of the entire ascending limb. These cells are thick (there is no thin ascending segment in the avian loop), with extensive infoldings of the basolateral membrane surrounding numerous mitochondria (45% of cell volume). The area of basolateral membrane is 25 times that of the apical membrane. The basolateral membrane (but not the apical membrane) is enriched in Na+,K(+)-ATPase activity. The structure of the avian mammalian-type nephron (as epitomized by the budgie nephron) and the fact that NaCl accounts for over 90% of the osmotic activity of avian urine leads to the conclusion that the countercurrent multiplier of the avian kidney functions by active NaCl transport from the entire ascending limb. No explanation is offered for the transport specializations found in the thick descending segment of the loop, just prior to the hairpin turn.     

Termination of gonadal refractoriness in Turkish hamsters, Mesocricetus brandti

The Turkish hamster (Mesocricetus brandti) is a photoperiodic species. In this investigation, we characterized the photoperiodic requirements for termination of gonadal refractoriness, defined as the inability of the animal to respond to short-day treatment with gonadal regression. Paired testes weights were reduced to less than 20% of their original weight by 10 wk of 12L:12D treatment. This was followed by spontaneous testicular recrudescence (completed by Week 25 of 12L:12D treatment), the overt indication of refractoriness to short photoperiods. Next, the period of long-day exposure sufficient for termination of refractoriness was determined. Refractory males were exposed to 16L:8D for 5 to 20 wk. Ten weeks of 16L:8D treatment was enough for the animals to regain the sensitivity to a second challenge of 12L:12D treatment. Fifteen weeks of 20L:4D or 16L:8D terminated refractoriness in female Turkish hamsters; 20L:4D therefore was not interpreted as a short day by refractory hamsters. This was unexpected because in photosensitive animals this photoperiod acts like a short day, causing gonadal regression. These results suggest that Turkish hamsters are similar to Syrian hamsters in that both species require two or more months of long days in summer to recover sensitivity to the short days of the following fall.     

A major difference between the divergence patterns within the lines-1 families in mice and voles

L1 retroposons are represented in mice by subfamilies of interspersed sequences of varied abundance. Previous analyses have indicated that subfamilies are generated by duplicative transposition of a small number of members of the L1 family, the progeny of which then become a major component of the murine L1 population, and are not due to any active processes generating homology within preexisting groups of elements in a particular species. In mice, more than a third of the L1 elements belong to a clade that became active approximately 5 Mya and whose elements are > or = 95% identical. We have collected sequence information from 13 L1 elements isolated from two species of voles (Rodentia: Microtinae: Microtus and Arvicola) and have found that divergence within the vole L1 population is quite different from that in mice, in that there is no abundant subfamily of homologous elements. Individual L1 elements from voles are very divergent from one another and belong to a clade that began a period of elevated duplicative transposition approximately 13 Mya. Sequence analyses of portions of these divergent L1 elements (approximately 250 bp each) gave no evidence for concerted evolution having acted on the vole L1 elements since the split of the two vole lineages approximately 3.5 Mya; that is, the observed interspecific divergence (6.7%-24.7%) is not larger than the intraspecific divergence (7.9%-27.2%), and phylogenetic analyses showed no clustering into Arvicola and Microtus clades.      

Maternal transfer of photoperiodic information in Siberian hamsters. V. Effects of melatonin implants are dependent on photoperiod.

Photoperiodic information is transferred from female Siberian hamsters to their fetuses during gestation. Although maternal melatonin is known to be essential for the transfer of prenatal photoperiodic information, its specific role is not well defined. The duration of the daily melatonin signal, expressed as an elevation of serum melatonin levels in the maternal circulation, has been hypothesized to convey day length information to the fetus. If this hypothesis is valid, it predicts that identical maternal melatonin signals should affect the fetuses identically, regardless of the prenatal photoperiod. To test this hypothesis, adult females received melatonin in beeswax or beeswax alone. They were paired with males and housed in photoperiods of 12L:12D or 16L:8D. On the day of parturition, mother and young were transferred to constant light (LL). Young males were killed on Day 28 of life, and weights of testes were determined. Prenatal treatment with beeswax alone did not affect the nature of the signal transferred from mother to fetus; young gestated in 12L:12D and reared in LL developed small testes, while those gestated in 16L:8D had large testes. On the other hand, the effect of the prenatal melatonin treatment on postnatal testicular development in LL was inversely dependent on the prenatal photoperiod: testicular growth was stimulated in young gestated in 12L:12D, but inhibited in young gestated in 16L:8D. To verify that the melatonin pellets produced equivalent serum melatonin levels in adult females in 12L:12D and 16L:8D, unmated adult females were killed 6-10 wk after receiving melatonin pellets. Serum levels were elevated in both groups throughout the day and night.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sensitive gas chromatographic assay for the quantitation of bretylium in plasma,urine and myocardial tissue

A sensitive analytical method has been developed for the quantitation of bretylium in plasma, urine and myocardial tissue. Bretylium and the internal standard, UM-360 (o-iodobenzyltrimethylammonium), are extracted and isolated as the iodide salts. Sodium benzenethiolate is added and the mixture heated to 100° for one hour. This results in the formation of 2-bromobenzyl phenyl thioether and 2-iodobenzyl phenyl thioether, which can be separated and quantitated by gas chromatography. Good reliability and reproducibility can be obtained using electron-capture detection with quantities of bretylium as small as 1 ng.     

Einige endokrinologische Besonderheiten der V?gel

Zusammenfassung Anhand neuer embryologischer, morphologischer, physiologischer und biochemischer Befunde werden die vogelspezifischen Eigentümlichkeiten von drei endokrinen Systemen diskutiert: Pinealkomplex, hypothalamo-hypophysäres System und gastrointestinales Endokrinium.Trotz der allgemein besonders starken Beeinflußbarkeit der Vögel durch photoperiodische Veränderungen ist bei ihnen der Pinealkomplex zu einer intracranialen endokrinen Drüse reduziert. Diese Epiphyse (Pinealorgan) zeigt unter experimentellen Bedingungen eine außerordentliche Unabhängigkeit von photoperiodischer Steuerung. Das völlige Fehlen des Pinealkomplexes bei den relativ nahe verwandten Krokodilen deutet auf die Möglichkeit hin, daß dies wohl eher phylogenetisch als funktionell zu erklären ist.Das hypothalamo-hypophysäre System ist im wesentlichen reptilienartig, zeigt aber drei auffallende Spezialisierungen: 1. Eine hochentwickelte Eminentia mediana, welche aus zwei getrennten Regionen besteht. 2. Die Pars distalis ist mit der Eminentia so verbunden, daß ihre beiden Unterabteilungen (cephaler und caudaler Lappen) von beiden Regionen der Eminentia über getrennte Portalgefäße versorgt werden. 3. Den Vögeln als Gruppe fehlt die Pars intermedia.Die auffallendsten Besonderheiten des gastrointestinalen Endokriniums stehen mit dem Inselorgan in Verbindung: insulinproduzierende B-Zellen und glukagonbildende A-Zellen sind weitgehend in besondere Inseln getrennt. Im Gegensatz zu dem der anderen Tetrapoden ist das Fettgewebe der Vögel insulin-unempfindlich. Die endokrine Kontrolle des Fettgewebes erfolgt über eine indirekte anabole Route (durch prolaktinstimulierte Lipogenese in der Leber) sowie eine direkte katabole Route durch Pankreasglukagon.Bei einem Vergleich mit anderen Gnathostomengruppen zeigen Epiphyse, Adenohypophyse und Inselorgan einen besonders starken Trend zur Unabhängigkeit von direkter Innervation. In bezug auf Adenohypophyse und Inselorgan repräsentieren dabei die Vögel das entgegengesetzte Extrem zu den Knochenfischen (Teleostier), bei denen diese Drüsen besonders stark innerviert sind.Die Vögel und Teleostier werden kurz mit den Myxiniden verglichen, deren endokrines System besonders schwach entwickelt ist. Die Unterschiede zwischen den drei Gruppen werden durch drei verschiedene Wege der Anpassung an Umweltbedingungen gedeutet: 1. Aktive Anpassung durch ein hochentwickeltes neuro-endokrines Kontrollsystem (Teleostier). 2. Passive, osmokonforme Anpassung, welche ein stark entwickeltes Endokrinium überflüssig macht (Myxiniden). 3. Vermeidung ungünstiger Umweltbedingungen durch Flugvermögen; eine verfeinerte, sekretomotorische Kontrolle der endokrinen Drüsen des normalen Stoffwechsels ist unnötig (Vögel).

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Some endocrine specializations of the birds

Summary Against the background of recent embryological, morphological, physiological and biochemical studies, peculiarities of three different avian endocrine systems are discussed: pineal complex, hypothalamo-hypophysial system, and gastrointestinal endocrine system.Despite the marked photosensitivity of the birds in general, their pineal complex is reduced to an intracranial pineal gland, which shows a very high degree of functional autonomy when released from photoperiodic control. The complete absence of the pineal complex in the alligators suggests that this may be due to phylogenetic rather than adaptive reasons.The hypothalamo-hypophysial system is basically of reptilian type, but shows three marked specializations: (1) the highly developed median eminence consists of two distinct regions; (2) the Pars distalis is located so, that both of its subdivisions (cephalic and caudal lobe) appear to receive distinctly separate vascularisation from the median eminence; (3) the birds as a group lack a Pars intermedia.Within the gastrointestinal endocrine system of birds, the most obvious peculiarities identified so far are connected with the islet organ: insulin-producing B-cells and glucagonproducing A-cells are largely separated in different islets, and contrary to the situation in other tetrapodes, the avian adipose tissue is insulin-insensitive. The endocrine control of the adipose tissue involves an indirect anabolic route via prolactin-induced hepatic lipogenesis, and a direct catabolic route, via pancreatic glucagon.When compared with other groups of gnathostomes, the pineal gland, adenohypophysis and islet organ of the birds show a particularly strong trend towards independence from secretomotor innervation. With respect to the adenohypophysial and islet innervation, the birds represent the opposite extreme to the teleosts, whose adenohypophysis and islet organ are particularly well innervated.Birds and teleosts are compared with the Myxinidae, whose endocrine system is particularly poorly developed. It is hypothesized that the differences between the endocrine systems of these three groups reflect three different ways of adjustment to environmental conditions: (1) teleosts actively adjust to a continuous challenge from external osmolarity, whose control has to be integrated with the milieu interne and nutritional factors. They developed a highly sophisticated control system of their endocrines, which is capable of overriding humoral stimuli by nervous interference. (2) The Myxinidae passively conform with the osmotic environment, which makes a highly developed endocrine control system unnecessary. (3) The birds are shielded from environmental factors by a specialized body surface, and they can easily avoid unfavorable conditions by flight. This makes a sophisticated and fast acting (i.e. nervous) control of such endocrines unnecessary, which are involved in the maintenance of the normal milieu interne.Wir danken MissKathleen Matt für die Hilfe bei der Anfertigung der Zeichnungen.

     

Multifactorial diversity sustains microbial community stability

Maintenance of a high degree of biodiversity in homogeneous environments is poorly understood. A complex cheese starter culture with a long history of use was characterized as a model system to study simple microbial communities. Eight distinct genetic lineages were identified, encompassing two species: Lactococcus lactis and Leuconostoc mesenteroides. The genetic lineages were found to be collections of strains with variable plasmid content and phage sensitivities. Kill-the-winner hypothesis explaining the suppression of the fittest strains by density-dependent phage predation was operational at the strain level. This prevents the eradication of entire genetic lineages from the community during propagation regimes (back-slopping), stabilizing the genetic heterogeneity in the starter culture against environmental uncertainty.