Healthily Nourished but Depleted? Is It Possible to Improve the Health of Shift Workers through Lifestyle Interventions?

The relationship between diet and health is well-researched, and there is also information regarding the effects of diet on mental health. This study aimed to investigate whether motivation to optimize lifestyles without regulations or restrictions could improve the health of rotating shift workers. In this pilot study, 18 male shift workers were randomly divided into two groups. All participants completed the Short Form Health Survey-36 questionnaire (SF-36) before the start and at the end of the study. Group I (n = 9, mean age 42 ± 6.6 y) received dietary and lifestyle information every other month for one year, and the other, Group II (n = 9 mean age 36 ± 7.3 y), one year later. All participants were motivated to follow the trained dietary recommendations and to engage in physical activity. Almost all scores had improved. Surprisingly, physical performance scores worsened, which was not expected. The impairment in mental health due to the change in ownership of the company could have been better explained. Nutritional advice over a longer period and the motivation to integrate more exercise into everyday life can potentially improve the health of rotating shift workers.

The Popeye domain containing 2 (popdc2) gene in zebrafish is required for heart and skeletal muscle development.

The Popeye domain containing (Popdc) genes encode a family of transmembrane proteins with an evolutionary conserved Popeye domain. These genes are abundantly expressed in striated muscle tissue, however their function is not well understood. In this study we have investigated the role of the popdc2 gene in zebrafish. Popdc2 transcripts were detected in the embryonic myocardium and transiently in the craniofacial and tail musculature. Morpholino oligonucleotide-mediated knockdown of popdc2 resulted in aberrant development of skeletal muscle and heart. Muscle segments in the trunk were irregularly shaped and craniofacial muscles were severely reduced or even missing. In the heart, pericardial edema was prevalent in the morphants and heart chambers were elongated and looping was abnormal. These pathologies in muscle and heart were alleviated after reducing the morpholino concentration. However the heart still was abnormal displaying cardiac arrhythmia at later stages of development. Optical recordings of cardiac contractility revealed irregular ventricular contractions with a 2:1, or 3:1 atrial/ventricular conduction ratio, which caused a significant reduction in heart frequency. Recordings of calcium transients with high spatiotemporal resolution using a transgenic calcium indicator line (Tg(cmlc2:gCaMP)(s878)) and SPIM microscopy confirmed the presence of a severe arrhythmia phenotype. Our results identify popdc2 as a gene important for striated muscle differentiation and cardiac morphogenesis. In addition it is required for the development of the cardiac conduction system.

Slim larks and overweight owls? A two years dietary intervention in shift workers.

Previous studies have shown that shift workers are more prone to non-communicable diseases. The aim of the present crossover study is to investigate whether it is possible to improve the health status of shift workers. Nineteen male shift workers (38.5 years ± 7.4) received every other month a dietary counseling for one year. All subjects kept a seven-day diet diary during a night shift, received bioelectrical impedance analysis, and a laboratory examination was performed at the beginning of the study, after one year and at the end of the study. The laboratory blood test included the main metabolic parameters, melatonin and serotonin. Beside subjects were also motivated to incorporate more physical training into their daily routine. After the intervention period, participants reduced energy intake, mean portion size, table salt, consumption of sugar and saturated fat. C-reactive protein (CRP), mean corpuscular volume (MCV), liver enzymes, triglycerides, and uric acid decreased, while melatonin level increased. Participants lost body weight and reduced waist circumference after the intervention. Lifestyle modification and dietary information could contribute to the health of shift workers. However, further studies are needed to investigate whether this can prevent disease and whether melatonin production can be influenced by diet.

First Nationwide Monitoring Program for the Detection of Potentially Invasive Mosquito Species in Austria.

In Austria, only fragmented information on the occurrence of alien and potentially invasive mosquito species exists. The aim of this study is a nationwide overview on the situation of those mosquitoes in Austria. Using a nationwide uniform protocol for the first time, mosquito eggs were sampled with ovitraps at 45 locations in Austria at weekly intervals from May to October 2020. The sampled eggs were counted and the species were identified by genetic analysis. The Asian tiger mosquito Aedes albopictus was found at two sites, once in Tyrol, where this species has been reported before, and for the first time in the province of Lower Austria, at a motorway rest stop. The Asian bush mosquito Aedes japonicus was widespread in Austria. It was found in all provinces and was the most abundant species in the ovitraps by far. Aedes japonicus was more abundant in the South than in the North and more eggs were found in habitats with artificial surfaces than in (semi-) natural areas. Further, the number of Ae. japonicus eggs increased with higher ambient temperature and decreased with higher wind speed. The results of this study will contribute to a better estimation of the risk of mosquito-borne disease in Austria and will be a useful baseline for a future documentation of changes in the distribution of those species.

Zebrafish mutants in the von Hippel-Lindau tumor suppressor display a hypoxic response and recapitulate key aspects of Chuvash polycythemia.

We have generated 2 zebrafish lines carrying inactivating germline mutations in the von Hippel-Lindau (VHL) tumor suppressor gene ortholog vhl. Mutant embryos display a general systemic hypoxic response, including the up-regulation of hypoxia-induced genes by 1 day after fertilization and a severe hyperventilation and cardiophysiologic response. The vhl mutants develop polycythemia with concomitantly increased epo/epor mRNA levels and erythropoietin signaling. In situ hybridizations reveal global up-regulation of both red and white hematopoietic lineages. Hematopoietic tissues are highly proliferative, with enlarged populations of c-myb(+) hematopoietic stem cells and circulating erythroid precursors. Chemical activation of hypoxia-inducible factor signaling recapitulated aspects of the vhl(-/-) phenotype. Furthermore, microarray expression analysis confirms the hypoxic response and hematopoietic phenotype observed in vhl(-/-) embryos. We conclude that VHL participates in regulating hematopoiesis and erythroid differentiation. Injections with human VHLp30 and R200W mutant mRNA demonstrate functional conservation of VHL between mammals and zebrafish at the amino acid level, indicating that vhl mutants are a powerful new tool to study genotype-phenotype correlations in human disease. Zebrafish vhl mutants are the first congenital embryonic viable systemic vertebrate animal model for VHL, representing the most accurate model for VHL-associated polycythemia to date. They will contribute to our understanding of hypoxic signaling, hematopoiesis, and VHL-associated disease progression.

Claudin 28b and F-actin are involved in rainbow trout gill pavement cell tight junction remodeling under osmotic stress.

Permeability of rainbow trout gill pavement cells cultured on permeable supports (single seeded inserts) changes upon exposure to freshwater or treatment with cortisol. The molecular components of this change are largely unknown, but tight junctions that regulate the paracellular pathway are prime candidates in this adaptational process. Using differential display polymerase chain reaction we found a set of 17 differentially regulated genes in trout pavement cells that had been exposed to freshwater apically for 24 h. Five genes were related to the cell-cell contact. One of these genes was isolated and identified as encoding claudin 28b, an integral component of the tight junction. Immunohistochemical reactivity to claudin 28b protein was concentrated in a circumferential ring colocalized to the cortical F-actin ring. To study the contribution of this isoform to changes in transepithelial resistance and Phenol Red diffusion under apical hypo-or hyperosmotic exposure we quantified the fluorescence signal of this claudin isoform in immunohistochemical stainings together with the fluorescence of phalloidin-probed F-actin. Upon hypo-osmotic stress claudin 28b fluorescence and epithelial tightness remained stable. Under hyperosmotic stress, the presence of claudin 28b at the junction significantly decreased, and epithelial tightness was severely reduced. Cortical F-actin fluorescence increased upon hypo-osmotic stress, whereas hyperosmotic stress led to a separation of cortical F-actin rings and the number of apical crypt-like pores increased. Addition of cortisol to the basolateral medium attenuated cortical F-actin separation and pore formation during hyperosmotic stress and reduced claudin 28b in junctions except after recovery of cells from exposure to freshwater. Our results showed that short-term salinity stress response in cultured trout gill cells was dependent on a dynamic remodeling of tight junctions, which involves claudin 28b and the supporting F-actin ring.

In vivo and in vitro assessment of cardiac beta-adrenergic receptors in larval zebrafish (Danio rerio).

ß-Adrenergic receptors (ßARs) are crucial for maintaining the rate and force of cardiac muscle contraction in vertebrates. Zebrafish (Danio rerio) have one ß1AR gene and two ß2AR genes (ß2aAR and ß2bAR). We examined the roles of these receptors in larval zebrafish in vivo by assessing the impact of translational gene knockdown on cardiac function. Zebrafish larvae lacking ß1AR expression by morpholino knockdown displayed lower heart rates than control fish, whereas larvae deficient in both ß2aAR and ß2bAR expression exhibited significantly higher heart rates than controls. These results suggested a potential inhibitory role for one or both ß2AR genes. By using cultured HEK293 cells transfected with zebrafish ßARs, we demonstrated that stimulation with adrenaline or procaterol (a ß2AR agonist) resulted in an increase in intracellular cAMP levels in cells expressing any of the three zebrafish ßARs. In comparison with its human ßAR counterpart, zebrafish ß2aAR expressed in HEK293 cells appeared to exhibit a unique binding affinity profile for adrenergic ligands. Specifically, zebrafish ß2aAR had a high binding affinity for phenylephrine, a classical α-adrenergic receptor agonist. The zebrafish receptors also had distinct ligand binding affinities for adrenergic agonists when compared with human ßARs in culture, with zebrafish ß2aAR being distinct from human ß2AR and zebrafish ß2bAR. Overall, this study provides insight into the function and evolution of both fish and mammalian ß-adrenergic receptors.

Chronic reduction in cardiac output induces hypoxic signaling in larval zebrafish even at a time when convective oxygen transport is not required.

In the present study, the zebrafish breakdance mutant (bre) was used to assess the role of blood flow in development because it has been previously shown that bre larvae have a chronically reduced cardiac output as a result of ventricular contraction following only every second atrial contraction in addition to an atrial bradycardia. We confirmed a 50% reduction compared with control fish and further showed that blood flow in the caudal part of the dorsal aorta decreased by 80%. Associated with these reductions in blood flow were indications of developmental retardation in bre mutants, specifically delayed hatching, reduced cell proliferation, and a transiently decreased growth rate. Surprisingly, an increased red blood cell concentration and an earlier appearance of trunk vessels in bre larvae indicated some compensation to convective oxygen transport, although in previous studies it has been shown that zebrafish larvae at this stage obtain oxygen by bulk diffusion. In bre animals immunohistochemical analyses showed a significant increase in hypoxia inducible factor 1 (HIF)-α protein expression, comparable with wild-type larvae that were raised under hypoxic conditions. Accordingly, the expression of some hif downstream genes was affected. Furthermore, Affymetrix microarray analyses revealed a large number of genes that were differently expressed comparing control and bre larvae, and the number even increased with proceeding development. The results showed that a chronic reduction in blood flow generated hypoxic molecular signals despite partial compensation by increased oxygen carrying capacity and transiently slowed the overall development of zebrafish bre larvae.

Cardiovascular and respiratory developmental plasticity under oxygen depleted environment and in genetically hypoxic zebrafish (Danio rerio).

Known vertebrate response to low oxygen concentration include change in carbohydrate metabolism, increase in nitric oxide, stimulation of red blood cell and hemoglobin production and induction of gene expression for glycolytic enzymes and hormones. Also, extreme hypoxia plays main role in pathological studies of cardiac dysfunction. The morphological and physiological developmental studies of the cardiovascular system under low oxygen are important as it is directly related to oxygen supply and consumption. Furthermore, cardiac function demands high energy during system development and thus it is most likely to be affected by hypoxia. Zebrafish (Danio rerio) can act as a model organism for oxygen demand management study as in natural environment, due to ecological disturbances, it is exposed to changes in oxygen concentrations routinely and thus would have natural ability to cope with it for survival. We have studied, in zebrafish, i) cardiovascular flexibility under extreme hypoxia (PO(2)=20 Torr, 3 kPa) at 3-10 dpf (days post-fertilization), ii) cardiac re-animation in normoxia (PO(2)=152 Torr, 20 kPa) after 90 min of anoxia (PO(2)=0 Torr, 0 kPa)-induced suspended animation at 4 dpf and iii) oxygen consumption in 8 dpf von Hippel-Lindau (vhl(-)(/)(-)) mutant that exhibits an artificial hypoxic response under normoxic conditions. In hypoxic fish, cardiac output, stroke volume and end-diastolic volume were elevated while intersegmental blood vessels vascularization index at 6 dpf and at 10 dpf was 22% and 11% higher respectively as compared to the normoxic fish. The heart rate in hypoxic fish was lower until 6 dpf and then showed an elevated trend. There was no significant difference in body length between the hypoxic and normoxic individuals. The observed changes may have enhanced the performance of the cardiovascular system for oxygen uptake. We also report for the first time that the post-anoxia re-animated heart rate returns to normal after 48h. Measurement of oxygen consumption in 8 dpf hyperventilating vhl(-)(/)(-) mutant was, unexpectedly, significantly lower than the non-mutant fish of the same age which point towards artificial hypoxic signal from brain in these mutants.

Orientation-Dependent Reflection of Structurally Coloured Butterflies.

Keywords: orientation-dependent reflection; structural color; butterflies; imprinting technique; instrument adaptation.

Functional optical coherence tomography and photoacoustic microscopy imaging for zebrafish larvae.

We present a dual modality functional optical coherence tomography and photoacoustic microscopy (OCT-PAM) system. The photoacoustic modality employs an akinetic optical sensor with a large imaging window. This imaging window enables direct reflection mode operation, and a seamless integration of optical coherence tomography (OCT) as a second imaging modality. Functional extensions to the OCT-PAM system include Doppler OCT (DOCT) and spectroscopic PAM (sPAM). This functional and non-invasive imaging system is applied to image zebrafish larvae, demonstrating its capability to extract both morphological and hemodynamic parameters in vivo in small animals, which are essential and critical in preclinical imaging for physiological, pathophysiological and drug response studies.

Ontogenetic development of erythropoiesis can be studied non-invasively in GATA-1:DsRed transgenic zebrafish.

For the erythroid cell lineage development in vertebrates, GATA-1 transcription factor is essential. In our report, we have demonstrated that the approximate developmental status of erythrocytes and the progression of blood formation can be studied non-invasively in GATA-1:DsRed transgenic zebrafish (Danio rerio) embryo and larva by characterization of fluorescence luminance spectra. The study was carried out for animals maintained under normoxic and hypoxic (152 and 20 torr PO(2) respectively) conditions up to 10 days post-fertilization (dpf) and total blood cell concentrations and fluorescent cells' percentage were determined for this purpose. The erythroids were classified into five intensity stages (IS) on the basis of their fluorescence intensity. The luminescent cells with medium intensities (IS3) in normoxic animals were found throughout 2 to 10 dpf although in lower quantity while in hypoxic group they appeared from 5 dpf to 10 dpf showing a maximum of 15% of the total luminescent cells at 8 dpf. The total blood cell concentration dropped after 8 dpf in contrast to hypoxic group which showed further increasing trend. The fluorescent cells' percentage in normoxic group was generally higher as compared to the hypoxic ones. Our method successfully defined various stages of erythroid development. An effort was also made to correlate our luminance data (GATA-1 expression) and total blood cell concentrations with Epo mRNA production. Quantitative RT-PCR of 2-15 dpf old zebrafish was carried out for this purpose. Normoxic animals showed 1-3 Epo mRNA copies per ng RNA in contrast to the hypoxic larvae that showed remarkable fluctuation of 1 to 12 Epo mRNA copies per ng RNA during development. The blood volume (aortic diameter) and production time scale proved to be important factors to define the relationship of Epo mRNA with total blood cell concentration and GATA-1 protein expression respectively.

Morpho peleides butterfly wing imprints as structural colour stamp.

This study presents the replication of a color-causing nanostructure based on the upper laminae of numerous cover scales of Morpho peleides butterfly wings and obtained solely by imprinting their upper-wing surfaces. Our results indicate that a simple casting technique using a novel integrated release agent can obtain a large positive replica using negative imprints via Polyvinylsiloxane. The developed method is low-tech and high-yield and is thus substantially easier and less expensive than previous methods. The microstructures were investigated with light microscopy, the nanostructures with both scanning and transmission electron microscopy, and the reflections with UV visible spectrometry. The influence of the release agent and the quality of the master stamp were determined by comparing measurements of the cover-scale sizes and their chromaticity values obtained by their images and with their positive imprints. The master stamp provided multiple positive replicas up to 3 cm(2) in just 1 h with structural coloration effects visible to the naked eye. Thus, the developed method proves the accuracy of the replicated nanostructure and its potential industrial application as a color-producing nanostamp.

Sensing and surviving hypoxia in vertebrates.

Surviving hypoxia is one of the most critical challenges faced by vertebrates. Most species have adapted to changing levels of oxygen in their environment with specialized organs that sense hypoxia, while only few have been uniquely adapted to survive prolonged periods of anoxia. The goal of this review is to present the most recent research on oxygen sensing, adaptation to hypoxia, and mechanisms of anoxia tolerance in nonmammalian vertebrates. We discuss the respiratory structures in fish, including the skin, gills, and air-breathing organs, and recent evidence for chemosensory neuroepithelial cells (NECs) in these tissues that initiate reflex responses to hypoxia. The use of the zebrafish as a genetic and developmental model has allowed observation of the ontogenesis of respiratory and chemosensory systems, demonstration of a putative intracellular O2 sensor in chemoreceptors that may initiate transduction of the hypoxia signal, and investigation into the effects of extreme hypoxia on cardiorespiratory development. Other organisms, such as goldfish and freshwater turtles, display a high degree of anoxia tolerance, and these models are revealing important adaptations at the cellular level, such as the regulation of glutamatergic and GABAergic neurotransmission in defense of homeostasis in central neurons.

POPDC1(S201F) causes muscular dystrophy and arrhythmia by affecting protein trafficking.

The Popeye domain-containing 1 (POPDC1) gene encodes a plasma membrane-localized cAMP-binding protein that is abundantly expressed in striated muscle. In animal models, POPDC1 is an essential regulator of structure and function of cardiac and skeletal muscle; however, POPDC1 mutations have not been associated with human cardiac and muscular diseases. Here, we have described a homozygous missense variant (c.602C>T, p.S201F) in POPDC1, identified by whole-exome sequencing, in a family of 4 with cardiac arrhythmia and limb-girdle muscular dystrophy (LGMD). This allele was absent in known databases and segregated with the pathological phenotype in this family. We did not find the allele in a further screen of 104 patients with a similar phenotype, suggesting this mutation to be family specific. Compared with WT protein, POPDC1(S201F) displayed a 50% reduction in cAMP affinity, and in skeletal muscle from patients, both POPDC1(S201F) and WT POPDC2 displayed impaired membrane trafficking. Forced expression of POPDC1(S201F) in a murine cardiac muscle cell line (HL-1) increased hyperpolarization and upstroke velocity of the action potential. In zebrafish, expression of the homologous mutation (popdc1(S191F)) caused heart and skeletal muscle phenotypes that resembled those observed in patients. Our study therefore identifies POPDC1 as a disease gene causing a very rare autosomal recessive cardiac arrhythmia and LGMD, expanding the genetic causes of this heterogeneous group of inherited rare diseases.

Prolonged hypoxia increases survival even in Zebrafish (Danio rerio) showing cardiac arrhythmia.

Tolerance towards hypoxia is highly pronounced in zebrafish. In this study even beneficial effects of hypoxia, specifically enhanced survival of zebrafish larvae, could be demonstrated. This effect was actually more pronounced in breakdance mutants, which phenotypically show cardiac arrhythmia. Breakdance mutants (bre) are characterized by chronically reduced cardiac output. Despite an about 50% heart rate reduction, they become adults, but survival rate significantly drops to 40%. Normoxic bre animals demonstrate increased hypoxia inducible factor 1 a (Hif-1α) expression, which indicates an activated hypoxic signaling pathway. Consequently, cardiovascular acclimation, like cardiac hypertrophy and increased erythrocyte concentration, occurs. Thus, it was hypothesized, that under hypoxic conditions survival might be even more reduced. When bre mutants were exposed to hypoxic conditions, they surprisingly showed higher survival rates than under normoxic conditions and even reached wildtype values. In hypoxic wildtype zebrafish, survival yet exceeded normoxic control values. To specify physiological acclimation, cardiovascular and metabolic parameters were measured before hypoxia started (3 dpf), when the first differences in survival rate occurred (7 dpf) and when survival rate plateaued (15 dpf). Hypoxic animals expectedly demonstrated Hif-1α accumulation and consequently enhanced convective oxygen carrying capacity. Moreover, bre animals showed a significantly enhanced heart rate under hypoxic conditions, which reached normoxic wildtype values. This improvement in convective oxygen transport ensured a sufficient oxygen and nutrient supply and was also reflected in the significantly higher mitochondrial activity. The highly optimized energy metabolism observed in hypoxic zebrafish larvae might be decisive for periods of higher energy demand due to organ development, growth and increased activity. However, hypoxia increased survival only during a short period of development and starting hypoxia before or after this phase reduced survival, particularly in bre animals. Thus, the physiological plasticity, which enables zebrafish larvae to benefit from a hypoxia, occurs only within a narrow developmental window.

Chronodisruption increases cardiovascular risk in zebrafish via reduced clearance of senescent erythrocytes.

The circadian clock and the hypoxic signaling pathway play critical roles in physiological homeostasis as well as in pathogenesis. The bi-directionality of the interaction between both pathways has been shown on physiological and only recently also on molecular level. But the consequences of a disturbed circadian rhythm for the hypoxic response and the cardiovascular system have never been addressed in any organism. Here we show that the hypoxic response of animals subjected to chronodisruption is reduced by approximately 30%, as reflected by decreased expression levels of hypoxia inducible factor 1 and its down-stream target genes erythropoietin, responsible for the generation of red blood cells (RBC) and vascular endothelial growth factor, which is essential for proper vascularization. Beside malformations of their vascular beds, chronodisrupted animals surprisingly revealed elevated numbers of senescent erythrocytes under normoxic conditions, due to a reduced clearance rate via apoptosis. Over-aged erythrocytes in turn are characterized by decreased oxygen transport capacities and an increased tendency for aggregation, explaining the higher mortality of chronodisrupted animals observed in our study. The present study shows for the first time that chronodisruption strongly interferes with the hypoxic signalling cascade, increasing the cardiovascular risk in zebrafish due to elevated proportions of senescent erythrocytes. The results might shed new light on the etiology of the increased cardiovascular risk observed among shiftworkers.

Linking oxygen to time: the bidirectional interaction between the hypoxic signaling pathway and the circadian clock.

The circadian clock and the hypoxic signaling pathway play critical roles in physiological homeostasis as well as in tumorgenesis. Interactions between both pathways have repeatedly been reported for mammals during the last decade, the molecular basis, though, has not been identified so far. Expression levels of oxygen-regulated and circadian clock genes in zebrafish larvae (Danio rerio) and zebrafish cell lines were significantly altered under hypoxic conditions. Thus, long-term hypoxic incubation of larvae resulted in a dampening of the diurnal oscillation amplitude of the period1 gene expression starting only several hours after start of the hypoxic incubation. A significant decrease in the amplitude of the period1 circadian oscillation in response to hypoxia and in response to the hypoxic mimic CoCl2 was also observed using a zebrafish luciferase reporter cell line in constant darkness. In addition, activity measurements of zebrafish larvae using an infrared-sensitive camera demonstrated the loss of their usual circadian activity pattern under hypoxic conditions. To explore the functional basis of the observed cross-talk between both signaling pathways ChIP assays were performed. Increasing with the duration of hypoxia, a nearly 4-fold occupancy of hypoxia-inducible factor 1 (Hif-1α) at two specific E-box binding sites located in the period1 gene control region was shown, demonstrating therewith the transcriptional co-regulation of the core clock gene by the major transcription factor of the hypoxic pathway. On the other hand, circadian transgenic zebrafish cells, simulating a repressed or an overstimulated circadian clock, modified gene transcription levels of oxygen-regulated genes such as erythropoietin and vascular endothelial growth factor 165 and altered the hypoxia-induced increase in Hif-1α protein concentration. In addition, the amount of Hif-1α protein accumulated during the hypoxic response was shown to depend on the time of the day, with one maximum during the light phase and a second one during the dark phase. The direct binding of Hif-1α to the period1 gene control region provides a mechanistic explanation for the repeatedly observed interaction between hypoxia and the circadian clock. The cross-talk between both major signaling pathways was shown for the first time to be bidirectional and may provide the advantage of orchestrating a broad range of genes and metabolic pathways to cope with altered oxygen availabilities.

The paracrine role of 5-HT in the control of gill blood flow.

Storage of serotonin in teleost gill cells has been detected in neurons, polymorphous granular cells and in neuroepithelial cells. Innervation from the glossopharyngeal nerve (first gill arch) and the vagus nerve (all gill arches) carries afferent as well as efferent fibers. This innervation extends to the efferent filament artery, including the sphincter muscle associated with the efferent filament artery, but except for the Antarctic fish does not reach the afferent filament artery. Serotonergic nerves as well as neuroepithelial cells have been shown to release serotonin, while very little is known about the polymorphous granular cells. The paracrine action of the released serotonin may affect vascular smooth muscle cells and pillar cells, which also contain contractile filaments. Already the earliest functional studies revealed a severe increase in branchial resistance as a result of serotonin application, combined with an increase in the perfusion of the arterio-venous path and the central sinus spaces of the gills. Pharmacological analysis demonstrated that this is a serotonin specific effect, which in Antarctic fish is due to activation of the 5-HT(2) receptor, while inhibition of the 5-HT(1) receptor does not reduce the serotonin induced vasoconstriction of gill blood vessels. Hypoxic degranulation of serotonergic cells evoked the hypothesis that serotonergic vasoconstriction might result in more even and overall better perfusion of gill lamellae. Microscopic analysis indicated, however, that perfusion of distal lamellae was reduced after serotonin application. Furthermore, a serotonergic increase in branchial resistance caused a decrease in dorsal arterial oxygen saturation, not an increase as would be expected as a result of a better perfusion of gill lamellae. A detailed analysis of hypoxic effects on gill perfusion revealed that hypoxia induced changes in gill blood flow are due to cholinergic effects, but serotonergic influences could not be detected. These observations contradict the hypothesis that serotonergic vasoconstriction might support hypoxic gas exchange. The functional significance of the serotonergic control of gill blood flow therefore is not yet totally clear. Recent observations indicate that specific inhibitors of serotonin re-uptake accumulate in freshwater and in estuaries. Considering the negative effect of serotonin on arterial blood oxygenation this may become a threat to teleost species.

Functional plasticity of the developing cardiovascular system: examples from different vertebrates.

Technical advances that have made it possible to perform physiological measurements on very small organisms, including those in embryonic and larval stages, have resulted in the formation of the discipline of developmental physiology. The transparency and size of developing organisms in some areas permit insights into physiological processes that cannot be obtained with opaque, adult organisms. On the other hand, it is widely accepted that without eggs, there are no chickens, so physiological adaptations during early life are just as important to species survival as those manifested by adults. Physiological adaptations of early developmental stages, however, are not always the same as patterns known in adults; they often follow their own rules. The adaptability of early developmental stages demonstrates that development is not stereotyped and a phenotype is not just the result of genetic information and the expression of a certain series of genes. Environmental factors influence phenotype production, and this in turn results in flexibility and plasticity in physiological processes. This article comprises exemplary studies presented at the Fourth International Conference in Africa for Comparative Physiology and Biochemistry (Maasai Mara, Kenya, 2008). It includes a brief introduction into technical advances, discusses the developing cardiovascular system of various vertebrates, and demonstrates the flexibility and plasticity of early developmental stages. Fluid forces, oxygen availability, ionic homeostasis, and the chemical environment (including, e.g., hormone concentrations or cholesterol levels) all contribute to the shaping and performance of the cardiovascular system.