Metabolic reorganization and signal transduction during estivation in the spadefoot toad

The maximal activities of 28 enzymes, representing multiple pathways of intermediary metabolism, were quantified in the brain, liver and skeletal muscle of spadefoot toads Scaphiopus couchii, comparing control toads with animals that had estivated for 2 months. Estivation-induced changes in brain enzyme activities were consistent with suppressed glycolysis and increased ketone body and amino acid catabolism. In liver, estivation resulted in reduced activities of eight enzymes representing carbohydrate, amino acid, ketone body and phosphagen metabolism, but the maximal activity of malic enzyme increased by 2.4-fold. Estivation led to a large-scale reorganization of skeletal muscle affecting most of the enzymes analyzed. Activities of enzymes of carbohydrate catabolism were generally elevated except for glycogen phosphorylase and hexokinase, whereas those of enzymes of fatty acid synthesis and ketone body metabolism were reduced. Increased glutamate dehydrogenase activities in both brain and muscle, as well as activities of other amino-acid-catabolizing enzymes in muscle, correlated with specific changes in the free amino acids pools in those tissues (reduced glutamine activity, increased glutamate, alanine and valine activities) that appear to be related to protein catabolism, for the purposes of elevating urea levels. The effects of estivation on signal transduction systems were also assessed. Total activities of protein kinases A and C (PKA and PKC) were largely unaltered in toad tissues during estivation (except for a 57% reduction in liver total PKC), but in seven organs there were strong reductions in the percentage of PKA present as the active catalytic subunit in estivating animals, and three contained a much lower percentage of membrane-bound active PKC during estivation. Activities of protein phosphatase types 1, 2A, 2B, and 2C were also frequently reduced during estivation. Overall, these results suggest that anuran estivation involves metabolic reorganization, including changing the maximal activities of key enzymes of intermediary metabolism as well as depressing the metabolic rate by suppressing signal transducing enzymes.     

Metabolic tolerance of the cold-water coral Lophelia pertusa (Scleractinia) to temperature and dissolved oxygen change

Lophelia pertusa is the world's most common and widespread framework-forming cold-water coral. It forms deep-water coral reefs and carbonate mounds supporting diverse animal communities on the continental shelf and on seamounts. These recently discovered ecosystems have been damaged by deep-sea fishing and are threatened by predicted shallowing of the aragonite saturation horizon. Despite this, very little is known about the ecophysiology of L. pertusa and its likely response to environmental changes. Here we describe the first study of the respiratory physiology of L. pertusa and the effects of altered temperature and oxygen level. This study shows that L. pertusa can maintain respiratory independence over a range of PO₂ illustrated by a high regulation value (R = 78%). The critical PO₂ value of 9-10 kPa is very similar to the lower values of oxygen concentration recorded in the field. This suggests that oxygen level may be a limiting factor in the distribution of this cold-water coral. L. pertusa survived periods of anoxia (1 h), hypoxia (up to 96 h), but high Q₁₀ values revealed sensitivity to short-term temperature changes (6.5-11 °C). For the first time vital data have been gathered on the physiology of this species that is essential to understand distribution and underpin future climate change studies.     

Iron nutrition and physiological responses to iron stress in Nitrosomonas europaea

Nitrosomonas europaea, as an ammonia-oxidizing bacterium, has a high Fe requirement and has 90 genes dedicated to Fe acquisition. Under Fe-limiting conditions (0.2 μM Fe), N. europaea was able to assimilate up to 70% of the available Fe in the medium even though it is unable to produce siderophores. Addition of exogenous siderophores to Fe-limited medium increased growth (final cell mass). Fe-limited cells had lower heme and cellular Fe contents, reduced membrane layers, and lower NH₃- and NH₂OH-dependent O₂ consumption activities than Fe-replete cells. Fe acquisition-related proteins, such as a number of TonB-dependent Fe-siderophore receptors for ferrichrome and enterobactin and diffusion protein OmpC, were expressed to higher levels under Fe limitation, providing biochemical evidence for adaptation of N. europaea to Fe-limited conditions.     

Growth-rate adaptation of Phycomyces sporangiophores to partial depletion of oxygen

The growth rate of Phycomyces blakesleeanus sporangiophores was found to be very sensitive to sudden changes in the oxygen concentration. A change from 20% to 15% oxygen elicits a transient decrease in the growth rate which returns to normal 10 min after altering the concentration. After a step change to 10% oxygen, the growth rate shows two minima at 6–8 and 30–35 min and it reaches about 80% of its original value 50 min after this change. A threshold curve for this negative growth response shows that sporangiophores begin to sense a decrease in the oxygen concentration from 20% to 17%. Seven phototropically abnormal mutants with defects in the genes madA to madG were tested for the oxygen response. Two strains, C149madD120 and C316madF48, were found to have recoveries different from those of the wild type after step changes from 20% to 10% oxygen.     

Behavioural and physiological responses of infective juveniles of the entomopathogenic nematode Heterorhabditis to desiccation

Infective juveniles (IJs) of entomopathogenic nematodes (EPNs) are susceptible to a wide variety of environmental factors, including desiccation, which limit their usefulness as biocontrol agents. Although EPNs can be subjected to a gradual loss of water in their natural environment they are not full anhydrobiotes, being able to survive only moderate levels of desiccation at high relative humidities (rh). We investigated the desiccation tolerance of IJs of several Heterorhabditisspecies and strains when exposed to fast and slow desiccation regimes. We also investigated the behavioural and biochemical responses of Heterorhabditis IJs when exposed to 98% rh for 4 days. IJs of H. megidis UK211 (but not IJs of H. indica) aggregate into large clumps when desiccated at high rh, but unlike Steinernema spp., neither H. megidis nor H. indica IJs showed any tendency to coil. Preincubation of H. megidis UK211 IJs at high (98%) rh enhances their ability to survive for 150 min at 57% rh. We show that preincubation of H. megidis and H. indica at 98% rh induces the synthesis of glycerol but not of trehalose, whereas identical preincubation conditions do induce trehalose synthesis in Steinernema carpocapsae and Aphelenchus avenae. The biosynthesis of glycerol rather than trehalose by IJs of two species of Heterorhabditis in response to moderate levels of desiccation indicates that Heterorhabditis is unlikely to have the necessary metabolic responses to desiccation required to enable it to enter into a fully anhydrobiotic state.     

Validation of manometric microrespirometers for measuring oxygen consumption in small arthropods

Scientists have used numerous techniques to measure organismal metabolic rate, including assays of oxygen (O(2)) consumption and carbon dioxide (CO(2)) production. Relatively few studies have directly compared estimates of metabolic rate on the same groups of animals as determined by different assay methods. This study directly compared measures of the metabolic rate of three lines of Drosophila simulans as determined either from direct measures of CO(2) production using infrared gas analysis (IRGA), or from estimates of O(2) consumption based on manometeric techniques. Determinations of metabolic rate of the same cohorts of flies using these two methods produced results that often differed widely. Typically metabolic rate as determined by the manometric method was significantly greater than that determined by CO(2) output. These differences are difficult to explain by simple biotic or abiotic factor(s). Because of the idiosyncratic nature of these differences it is not possible to use a simple factor to convert from metabolic rate measurements done using manometric techniques to those expected from direct measures of CO(2) output or O(2) consumption. Although manometric devices are simple to construct and use, measurements of metabolic rate made with this method can vary significantly from measurements made by directly assaying CO(2) production or O(2) consumption.     

Flooding tolerance of Tabebuia cassinoides: Metabolic, morphological and growth responses

Tabebuia cassinoides (Lam.) DC (Bignoniaceae) is a tree species that occurs in swampy areas of the coastal “restinga” in SE Brazil (a coastal sandy plains scrub and forest formation). To elucidate possible adaptive strategies that enable this species to occupy areas subjected to seasonal or perennial waterlogging, metabolic, morphological and growth responses of plants under flooding conditions were studied. The root system of T. cassinoides plants presented elevated amounts of ethanol (10.6 μmol g⁻¹ fresh wt) only in the first 5 d of soil water saturation. The two-fold increase in ethanol production under flooding was corroborated by an increase in ADH activity in the same period. Lactic acid concentrations did not change significantly during four months of flooding treatment. The decrease of alcoholic fermentation under hypoxia was associated with the appearing of new roots. The induction of aerenchyma formation in roots developed under flooding conditions, allowed oxygen transport from the shoot to these organs, thus maintaining an aerobic respiration. We conclude that this characteristic and the capacity to oxidize the rhizosphere are probably responsible for the survival and growth of plants while flooded and for their success in an environment, which restricts the presence of the majority of competing tree species.     

Effects of food concentration on clearance rate and energy budget of the Arctic bivalve Hiatella arctica (L) at subzero temperature

The influence of food concentration on clearance rate, respiration, assimilation, and excretion at −1.3 °C was studied on individuals of the bivalve Hiatella arctica (L.) from Young Sound, NE Greenland. Clearance rate, assimilation efficiency, respiration, and excretion rates were determined over a range of food concentrations using the microalga Rhodomonas baltica as food source. Physiological rates were generally low but responded significantly to increased food levels. Clearance rates and assimilation efficiency were reduced at increased food levels, whereas respiration and excretion increased. Assimilation efficiency was generally high, which may be an adaptation to the low food concentration during most of the year in NE Greenland. Low filtration rates limited ingestion rates and resulted in a low maximum assimilation of 3 J h⁻¹. Despite the low food intake, very low food concentrations were required for individual specimens to obtain a positive energy budget. Predicted growth based on rates of assimilation and respiration were compared to published estimates of annual growth in Young Sound. We estimate that 3 weeks of growth in the laboratory under optimal food conditions could match annual growth in situ. We interpret this as evidence that food limitation is the primary impediment to growth in this Arctic population.     

Effects of dehydration rate on physiological responses and survival after rehydration in larvae of the anhydrobiotic chironomid

Strategies to combat desiccation are critical for organisms living in arid and semi-arid areas. Larvae of the Australian chironomid Paraborniella tonnoiri resist desiccation by reducing water loss. In contrast, larvae of the African species Polypedilum vanderplanki can withstand almost complete dehydration, referred to as anhydrobiosis. For successful anhydrobiosis, the dehydration rate of P. vanderplanki larvae has to be controlled. Here, we desiccated larvae by exposing them to different drying regimes, each progressing from high to low relative humidity, and examined survival after rehydration. In larvae of P. vanderplanki, reactions following desiccation can be categorized as follows: (I) no recovery at all (direct death), (II) dying by unrepairable damages after rehydration (delayed death), and (III) full recovery (successful anhydrobiosis). Initial conditions of desiccation severely affected survival following rehydration, i.e. P. vanderplanki preferred 100% relative humidity where body water content decreased slightly. In subsequent conditions, unfavorable dehydration rate, such as more than 0.7 mg water lost per day, resulted in markedly decreased survival rate of rehydrated larvae. Slow dehydration may be required for the synthesis and distribution of essential molecules for anhydrobiosis. Larvae desiccated at or above maximum tolerable rates sometimes showed temporary recovery but died soon after.     

Behavioural and physiological stress responses to handling in wild guanacos

Both ethology and physiology can provide insights about stress conditions in wild animals during handling. Lama guanicoe (guanaco) is the major large herbivore inhabiting arid zones in Argentina. Since 2005, the Payún Matrú Cooperative, a business established and run by native people, has captured and handled guanacos for shearing at Payunia Reserve, Mendoza Province, Argentina, to market the species’ fibre for clothing and other products. The aim of our study was to evaluate the behavioural and physiological stress responses to handling of wild guanacos during these shearing activities. We evaluated stress conditions in guanacos by monitoring the frequency of agonistic behaviour in the holding corrals, following capture, the rate of vocalisation and agonistic behaviour during handling, and by estimating cortisol levels in handled animals. Crowding increased agonistic behaviour; this appeared to be related to dominance conflicts between males in the corrals. Time of corralling increased rate of agonistic behaviour and vocalisations during handling. The rate of behavioural stress responses was negatively related to cortisol levels in males; which may be due to animal fatigue or because behavioural stress responses may help mitigate physiological stress responses. Incorporating our results into animal welfare practices could help reduce stress conditions in wild guanacos. Our results suggest that both behavioural and physiological responses are important measures of stress in handled animals, and that behavioural stress responses cannot be used as a simple surrogate for glucocorticoid levels.     

温度对鳊鱼静止代谢和耐低氧能力的影响

以鳊鱼(Parabramis pekinensis)幼鱼[体重(8.13±0.15)g,n=31]为研究对象,以密闭式代谢测定法分别在15、20、25、30℃条件下测定其静止代谢率(Rest Metabolic Rate,RMR),并以双线法推算临界氧浓度Pcrit等相关参数。结果显示,鳊鱼幼鱼的静止代谢水平呈随温度上升而升高的变化趋势[(132.22±4.97)mg O2/(h.kg)(15℃),(182.67±12.49)mg O2/(h.kg)(20℃),(218.44±9.20)mgO2/(h.kg)(25℃),(298.32±9.96)mg O2/(h.kg)(30℃)],除20～25℃间,其他各温度组差异显著(P0.05);Q10值均低于2(15～20℃1.91,20～25℃1.43,25～30℃1.87);本研究还发现,随着温度的升高,鳊鱼幼鱼的Pcrit逐渐下降,而临界氧饱和度Scrit则相对保守[15、20、25、30℃的Pcrit分别为(1.35±0.09)、(1.16±0.19)、(0.97±0.12)和(0.86±0.09)mg O2/L,Scrit分别为13.87%±0.74%、13.32%±1.72%、12.15%±1.35%和11.34%±0.65%。这表明,采用不同指标考察鱼类耐低氧能力可能会得到相异的结论。这种结论的不一致提示,在鱼类应对环境溶氧降低的适应中,相对溶氧水平而不是绝对溶氧水平影响并决定着鱼类的适应性进化,因此采用相对饱和度作为指标研究鱼类耐低氧能力可能更具理论价值。     

Respiration of Artemia franciscana embryos after continuous anoxia over 1-year period

Encysted embryos of the brine shrimp, Artemia franciscana, exhibit extraordinary longevity when exposed to continuous anoxia. To explore the metabolic basis of this ability, the post-anoxic respiration of embryos exposed to anoxia for periods exceeding 1 year was measured. Since anoxic metabolism might result in the accumulation of metabolic end products, an O₂ debt would be expected. Contrary to that expectation, post-anoxic embryos exhibited a marked depression in respiration rate whether embryos were hydrated under anoxic conditions or were exposed to a previous aerobic incubation and then placed under anoxia. These results, and those of previous studies, suggest that extended anoxia may bring the metabolism of these embryos to a reversible standstill.     

Metabolic responses of homing pigeons to flight and subsequent recovery

This study examines metabolic changes occurring during short to endurance flights and during subsequent recovery in free-flying pigeons, in particular the change towards lipid utilization with increasing flight duration, lipid supply to the flight muscles, protein utilization and the time needed to metabolically recover. Eight plasma metabolite concentrations were measured in homing pigeons released from sites 20–200 km from the loft (0.3–4.8 h flight duration) just after landing and after keeping birds fasting at rest for 30 and 60 min, respectively, after their return. Birds kept in the loft fasting at rest were used as controls. Plasma free fatty acid and glycerol concentrations increased rapidly with flight duration and leveled off after about 1.5 h. This indicates a marked change towards a high and stable lipid utilization from adipose tissues within 1–2 h of flight. Plasma triglyceride levels and very-low-density lipoproteins were decreased after short flights, but subsequently regained or surpassed fasting levels at rest. This indicates that re-esterification of free fatty acids and delivery as very-low-density lipoproteins to the flight muscles to circumvent constraints of fatty acid supply, as described previously for small passerines, is not as significant in the pigeon which has a much lower mass-specific energy rate. An initial increase in plasma glucose levels and a transient decrease to fasting levels at rest was observed and may reflect the initial use and subsequent exhaustion of glycogen stores. Contrary to other birds and mammals, -hydroxy-butyrate levels increased markedly with flight duration. This may suggest a more important sparing of carbohydrates and protein as gluconeogenic precursors in the pigeon than in other species. Plasma uric acid levels increased linearly up to about 4 h flight duration. This indicates an accelerated protein breakdown during flight which may primarily serve to deliver amino acids as glucogenic precursors and citrate cycle intermediates. With increasing flight duration, the energy sources change from an initial phase based primarily on carbohydrates to a lipid-based endurance phase. It is discussed whether this metabolic change depends on the level of power output or the performed work (energy spent) since the start of flight. During the first hour of recovery, most metabolites reached or approached fasting levels at rest, indicating a marked reduction in lipolysis and protein breakdown. -hydroxy-butyrate levels remained at flight levels and glucose levels increased slightly, indicating a restoration of glycogen stores.Abbreviations VLDL very-low-density lipoproteins - FFA free fatty acids     

Effects of experimental anemia on blood ion and acid-base status of turtles during submergence in aerated water at 3 degrees C

The importance of blood hemoglobin to aquatic oxygen uptake by turtles (Chrysemys picta bellii) submerged in aerated water at 3 degrees C was tested by comparing the responses of anemic turtles (hematocrit approximately 6%) to turtles with normal hematocrits (hematocrit approximately 33%). All turtles were submerged for 42 days and blood samples were collected at 0, 7, 21, 32 and 42 days. Blood was analyzed for pH, PCO(2), PO(2), hematocrit, hemoglobin concentration ([Hb]) and plasma was analyzed for concentrations of lactate, glucose, Na(+), K(+), Ca(2+) and Mg(2+). Plasma [HCO(3)(-)] was calculated. [Hb] correlated closely with hematocrit levels. [Lactate] reached higher final values in anemic turtles (34.5+/-5.3 mmol l(-1)) than in normal turtles (14.5+/-4.6 mmol l(-1)) indicating a greater reliance of the anemic animals on anaerobic metabolism. Both groups compensated for acidosis by reduced PCO(2) and anemic turtles also had increased [Ca(2+)] and [Mg(2+)]. Blood pH fell significantly in the anemic turtles but not in the controls. Although the data indicate that the anemic turtles relied more on anaerobic metabolism than the controls, the effect was much less than expected on the basis of the reduced blood O(2) carrying capacity. Possible compensatory mechanisms utilized by the anemic turtles to minimize anaerobic metabolism are discussed.     

Metabolic impact of redox cofactor perturbations in Saccharomyces cerevisiae

Redox cofactors play a pivotal role in coupling catabolism with anabolism and energy generation during metabolism. There exists a delicate balance in the intracellular level of these cofactors to ascertain an optimal metabolic output. Therefore, cofactors are emerging to be attractive targets to induce widespread changes in metabolism. We present a detailed analysis of the impact of perturbations in redox cofactors in the cytosol or mitochondria on glucose and energy metabolism in Saccharomyces cerevisiae to aid metabolic engineering decisions that involve cofactor engineering. We enhanced NADH oxidation by introducing NADH oxidase or alternative oxidase, its ATP-mediated conversion to NADPH using NADH kinase as well as the interconversion of NADH and NADPH independent of ATP by the soluble, non-proton-translocating bacterial transhydrogenase. Decreasing cytosolic NADH level lowered glycerol production, while decreasing mitochondrial NADH lowered ethanol production. However, when these reactions were coupled with NADPH production, the metabolic changes were more moderated. The direct consequence of these perturbations could be seen in the shift of the intracellular concentrations of the cofactors. The changes in product profile and intracellular metabolite levels were closely linked to the ATP requirement for biomass synthesis and the efficiency of oxidative phosphorylation, as estimated from a simple stoichiometric model. The results presented here will provide valuable insights for a quantitative understanding and prediction of cellular response to redox-based perturbations for metabolic engineering applications.     

Influence of long-term hypoxia on the energy metabolism of the haemoglobin-containing bivalve Scapharca inaequivalvis: critical O2 levels for metabolic depression

Summary The oxygen consumption rate of Scapharca inaequivalvis measured under normoxic conditions over 48 h showed a significant daily cycle with lowest values occurring shortly after the dark period; all hypoxia exposure experiments were carried out during the declining part of the cycle. Animals were exposed to a constant level of hypoxia for a 12-h period in a series of 14 experiments, each at a different oxygen tension. The oxygen consumption was measured continuously, and the extent of accumulation of end-products (succinate and propionate), and the inhibitory effect of adenosine triphosphate on phosphofructokinase were determined at the end of exposures. All three parameters (oxygen consumption, end-product accumulation, phosphofructokinase inhibition) showed a remarkable correlation with major changes occurring between 2.5 and 1.5 ppm (7 and 4 kPa) O₂. The oxygen consumption rates showed a drop to 6% of the normoxic rate, but a consistent low consumption remained below 2 ppm (5.5 kPa) which partly recovered over the 12-h exposure period by about three-fold. Succinate and propionate accumulated progressively between 2.5 and 1.5 ppm (7 and 4 kPa); at [O₂]<1.5 ppm (4kPa) the concentration did not increase further, indicating that anaerobic metabolism had reached a maximum. Over the same range, phosphofructokinase showed an increased sensitivity for adenosine triphosphate, the lower inhibitor concentration at 50% V _max value pointing to depression of glycolytic rate. Despite the activation of anaerobic metabolism and the evident depression of aerobic metabolism, simple calculation demonstrates that Scapharca inaequivalvis relies mainly on aerobic metabolism even during severe hypoxia. It is assumed that the occurrence of haemoglobin in this species is essential for its capacity to survive long periods of hypoxia.Abbreviations ATP adenosine triphosphate - I₅₀ inhibitor concentration at 50% V _max - PFK phosphofructokinase - P _c critical PO₂ - SEM standard error of mean - VO₂ oxygen consumption rate - ww wet weight     

Reactive oxygen and ethylene are involved in the regulation of regurgitant-induced responses in bean plants

Application of regurgitant from Leptinotarsa decemlineata Say on wound surfaces of one wounded leaf of intact bean (Phaseolus vulgaris L.) plants resulted in activation of ethylene biosynthesis followed by an increase of both peroxidase and polyphenol oxidase activity. The aim of the present investigation was to study the source of increased oxidative enzyme activities in regurgitant-treated bean leaves and to determine if hydrogen peroxide and ethylene biosynthesis is responsible for regurgitant-induced amplification of wound responses in bean plants. As the regurgitant contained relative high activities of both peroxidase and polyphenol oxidase, there is a possibility that increased enzyme activities in bean leaves following regurgitant treatment is an artifact of insect-derived enzymes. Localisation experiments and electrophoretic analysis revealed that only part of the increased enzyme activities could be attributed to regurgitant-derived enzymes. Both increase of ethylene production and oxidative enzyme activities depended on protein synthesis. To demonstrate if the increase of oxidative metabolism was ethylene-dependent, seedlings were pretreated with aminooxyacetic acid, an inhibitor of ethylene biosynthesis, and 1-methylcyclopropene (1-MCP), a competitive inhibitor of ethylene action. Increase of both peroxidase and polyphenol oxidase activity in wounded and subsequently regurgitant-treated leaf was abolished by both aminooxyacetic acid and 1-MCP. Inhibitor studies indicated that H2O2 generated through NADPH oxidase and superoxide dismutase is necessary for regurgitant-induced increase of ethylene production and oxidative enzyme activities.     

Functional differential immune responses of Mytilus galloprovincialis to bacterial challenge

Bivalves are filter-feeders that can accumulate large numbers of bacteria, in particular Vibrio species; these can persist within bivalve tissues largely depending on their sensitivity to the hemolymph bactericidal activity. In this work, functional parameters of the hemolymph of Mytilus galloprovincialis were evaluated in response to in vivo challenge with different bacteria (Gram(−) Vibrio anguillarum and V. splendidus, Gram(+) Micrococcus lysodeikticus). Mussels were injected with heat-killed bacteria or PBS-NaCl (controls) and hemolymph sampled from 3 to 48 h post-injection (p.i.). In hemocytes, all bacteria induced significant lysosomal membrane destabilisation (LMS) from 3 h p.i. with V. splendidus > V. anguillarum > M. lysodeikticus. LMS showed recovery for both M. lysodeikticus and V. anguillarum, whereas a further time-dependent decrease was observed for V. splendidus. Bacterial challenge also induced a rapid (from 3 h p.i.) and significant increase in serum lysozyme activity; the effect was persistent with M. lysodeikticus and transient for the two Vibrio species. In order to evaluate whether in vivo challenge may affect the subsequent capacity of hemolymph to kill bacteria, the bactericidal activity was tested in an in vitro assay towards E. coli. At 48 h. p.i. hemolymph samples from V. anguillarum-injected mussels showed a significant increase in E. coli killing (+ 35% with respect to controls); a smaller effect was observed with V. splendidus-injected mussels (+ 16%), whereas M. lysodeikticus was ineffective. Moreover, hemolymph from V. anguillarum-injected mussels showed an in vitro bactericidal activity towards V. anguillarum 2-folds higher than that of controls. Changes in total hemocyte counts (THC) and in hemocyte populations were evaluated by Flow cytometry at 6 and 48 h p.i., indicating a decrease in THC followed by recovery with all bacteria. Moreover, at 6 h p.i. a general decrease in the percentage of granulocytes was observed (V. splendidus > V. anguillarum > M. lysodeikticus), followed by complete and partial recovery with M. lysodeikticus and V. anguillarum, respectively, but not with V. splendidus. The results demonstrate the existence of differential functional immune responses in M. galloprovincialis to different bacteria.     

Immunohistochemical localization and radioenzymatic measurements of serotonin (5-hydroxytryptamine) in hearts of Aplysia and several bivalve mollusks

Summary Serotonin immunoreactivity was localized in hearts of the opisthobranch gastropod, Aplysia californica (sca hare) and several species of bivalve mollusks, the heterodonts, Mercenaria mercenaria (quahog or cherry stone clam), Protothaca staminea (little neck clam), and the pteriomorphs, Hinnites multirugosus (rock scallop), Crassostrea virginica (eastern oyster), Mytilus edulis (eastern mussel), and Geukensia demissa (ribbed mussel). In addition, serotonin was assayed in the ventricles, auricles and heart-associated tissues in A. californica, M. mercenaria, H. multirugosus, and G. demissa with a sensitive radioenzymatic assay. Serotonin concentrations and the density of innervation were significantly higher in members of the subclass Heterodonta compared to the subclass Pteriomorpha. Serotonin immunoreactivity was observed in all species surveyed except G. demissa, which also contained relatively low concentrations of serotonin. Varicose fibers presumably corresponding to release sites were localized in the ventricles, auricles, and the auricular-ventricular valves. We hypothesize that in the species where serotonin-immunoreactive fibers are present, serotonin serves to modulate cardiac myogenic activity. The significance of the observed distribution and concentration of serotonin to the physiological effects of serotonin on cardiac function in these species is discussed.