摘要:

AbstractIt is known that leg positioning is important for reducing drag during escape mediated by the medial giant (MG) axon of the crayfish (Cooke and Macmillian, '85). This report examines the question of whether the legs also have a role in escape mediated by the lateral giant (LG) neuron. The trajectory and the dynamics of the lateral giant (LG) escape behaviour of the crayfishCherax destructorwere analyzed using high speed cinematographic techniques. The LG escape flip was found to be stereotyped for each particular animal but rested animals produce their own characteristic trajectories. We tested to see if denervation of the legs would alter the escape trajectory. Interference with the articulating membrane at the base of the legs alters escape performance and a new set of displacement curves characteristic of each animal is produced. This is the outcome whether or not the nerves are severed. Electrophysiological recordings confirmed earlier latency measurements (Cooke, '85) and indicate that the efferent signals to the legs evoked by LG activation arrive too late to position them to influence the escape trajectory. We suggest that operations on the articulating membrane produce their effects by altering the starting position of the legs. We provide some preliminary evidence that supports this hypothesis.

ISSN:0022-104X    

DOI:10.1002/jez.1402590302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe effect of inorganic slow channel blockers on the calcium paradox in the frog heart was examined. Addition of the divalent cations of manganese, cobalt, nickel, or barium during calicium depletion protected the frog heart against a calcium paradox. This protective effect was indicated by reduced protein release, maintenance of electrical activity, and recovery of mechanical activity during reperfusion.Tissue calcium determination results showed that in the control paradox in the absence of divalent cations, there is an efflux of calcium from myocardial cells during calcium depletion and a massive influx of calcium during the following reperfusion, leading to a calcium overload. Divalent cations protected frog myocardial cells, when present in the calcium‐free perfusion medium, by reducing both calcium efflux during calcium depletion and the massive calcium influx during reperfusion.The effectiveness of the added divalent cations showed a strong dependence upon their ionic radius. The most potent inhibitors of the calcium paradox in the frog heart were the divalent cations having an ionic radius closer to the ionic radius of calcium.These results are discussed in terms of the possible mechanism involved in the protective effect of manganese, cobalt, nickel, and bariu

ISSN:0022-104X    

DOI:10.1002/jez.1402590303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractCarbonic anhydrase (CA) activity was measured in the gills, branchiostegite, and cuticle of 5 species of decapod crustaceans displaying fully aquatic, semi‐terrestrial, and fully terrestrial lifestyles. Density‐gradient and differential ultracentrifugation were used to separate 2 subcellular fractions from these tissues, basal‐lateral membranes, and cytoplasm, in which CA activity was determined.Callinectes sapidus, a euryhaline aquatic species, had high levels of CA activity in both the cytoplasmic and membrane fractions of the gills. These pools of CA are believed to function in ion transport and CO2excretion, respectively. The branchiostegite and cuticle, which do not play an apparent role in either process in the blue crab, possess much lower levels of CA activity in both fractions. In contrast, a stenohaline, stenothermal species,Chaceon fenneri, which has a low metabolic rate, has low levels of CA activity in the cytoplasm and membrane fractions of the gills. As decapod crustaceans invade the terrestrial habitat and make the transition to breathing air, gill surface area is reduced and the branchiostegite develops into a primitive lung. InCardisoma guanhumi, a semi‐terrestrial crab, branchiostegal tissue has very little CA activity in either fraction, and enzyme activity is not different from that in the general cuticle; the gills still possess the bulk of CA activity in the animal. In fully terrestrial species (Gecarcinus lateralis and Birgus latro), however, the membrane fraction of the branchiostegite has the same level of CA activity as that of the gills, regardless of species, while CA in the cuticle remains low. It appears, according to the distribution of membrane‐associated CA, that while the gills of aquatic crustaceans are the primary route of CO2excretion, the branchiostegite can supplement branchial CO2elimination in terrestria

ISSN:0022-104X    

DOI:10.1002/jez.1402590304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe urinary bladder of euryhaline teleosts is an important osmoregulatory organ which absorbs Na+, Cl−, and water from urine. Using patch clamp technique, single stretch‐activated channels, which were permeable to K+and Na+(PNa/PK≈︁ 0.75) and had conductances of 55 and 116 pS, were studied. In excised, inside‐out patches which were voltage‐clamped in the physiological range of membrane potential, the single‐channel open probability (P0) was low (≈︁0.02), and increased to a maximum of 0.9 with applied pipette suction. Single‐channel conductance also increased with suction. The channels showed adaptation to applied suction and relaxed to a steady‐state activity about 20 seconds after application of suction. The P0increased up to 0.9 with strong membrane depolarization (Vm= 0 to + 80 mV); however, there was little dependence of P0on membrane potential in the physiological range. The kinetic data suggest that there is one conducting state and at least two non‐conducting states of the channel. The open‐time constant increased with suction but remained unchanged with membrane potential (Vm= −70 to + 60 mV). The mean closed‐time of the channel decreased with suction and membrane depolarization. These results demonstrate the presence of a non‐selective monovalent cation channel which may be involved in cell volume regulation in the goby urinary bladder. Additionally, this channel may function as an enhancer of Na+influx and K+efflux across the bladder cell as part of transepithelial ion transport if i

ISSN:0022-104X    

DOI:10.1002/jez.1402590305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe spleen of the newtTriturus cristatus carnifex(Laurenti), an urodele amphibian, hoards erythrocytes when the animal is well‐oxygenated and releases them into the bloodstream when the animal is in a hypoxic condition. Between the extremes of congestion and decongestion the weight of the spleen varies up to a ratio of 6:1. However, the degree of the phenomenon depends on the temperature, which, in ectotherms, regulates metabolic rate and thus oxygen demand. In order to assay the degree of hypertrophy reached by congested spleens in standard respiratory conditions, groups of eight animals—previously anesthetized by immersion for 20 minutes in a 0.2% solution of chlorbutol in tap water at 18°C—were exposed to 100% humid air in a thermostatic chamber set at a temperature of 6, 12, 18, 24, 27, 30, or 33°C. Each animal remained at the set temperature until surpassing the minimum time necessary for maximum hypertrophy to be reached, equal to the time necessary for 4,000 heartbeats. At 33°C the spleens are almost completely bloodless, while at the other temperatures their hypertrophy from congestion increases linearly as the temperature diminishes, reaching maximum values at 6°C. Though the progressive congestion of the spleen as the temperature descends is due mainly to blood cells and only very slightly to plasma, erythrocyte concentration in the blood remains constant at all the lower temperatures up to that of anesthesia (18°C); this phenomenon implies variability of blood volume in the newt. Instead, above 18°C, the values of the hematic parameters increase as the temperature rises, reaching a maximum increment of about

ISSN:0022-104X    

DOI:10.1002/jez.1402590306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe majority of recent studies on the terminal nerve (nt) in various vertebrates either involved tracer injections into the nasal cavity or made use of the LHRH‐/FMRFamide‐like immunoreactivity (ir) of a portion of its fibers. The present investigation was designed to determine the extent of overlap between data rendered by the two methods inXenopus. The findings reveal no overlap of nt projections visualized by the two experimental techniques. This result sheds doubt on the validity of current definitions of the nt sys

ISSN:0022-104X    

DOI:10.1002/jez.1402590307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractDetails concerning the endogenous regulation of hepatic cytochrome P450 mono‐oxygenases in teleosts, and the features of this regulation common among fish species, are poorly known. Gonadally mature female winter flounder (Pseudopleuronectes americanus) have been reported to have severalfold lower levels of microsomal cytochromes P450 and b5and NADPH cytochrome c reductase than do males (Stegeman and Woodin ('84) Mar. Environ. Res., 14:422–425). These strong sex differences prompted more detailed study of P450 regulation in winter flounder liver, and a comparison with sex differences in another marine teleost, scup (Stenotomus chrysops). Ethoxyresorufin O‐deethylase (EROD) activity/nmol P450 was less in gonadally mature females than in males of both species. Immunoblot analysis with MAb 1‐12‐3 to P450E (the EROD catalyst) showed that the content of P450E counterpart was also much less in females of both species. Aminopyrine N‐demethylase (APND) and testosterone 6β‐hydroxylase (6β‐OHase) activities per nmol P450 were higher in gonadally mature female than in mature male flounder, differences not seen in scup. Polyclonal antibodies to scup P450A were shown to detect proteins in a number of teleosts. The levels of anti‐P450A cross‐reacting protein were greater in mature female than in male flounder, but as with 6β‐OHase activity, the content of this protein was not sexually differentiated in scup. Estradiol treatment of winter flounder depressed the rates of EROD, APND, 6β‐OHase, and estradiol 2‐OHase activities per mg protein, but APND and 6β‐OHase activities per nmol P450 were unchanged. Thus, E2promotes general decreases in some hepatic P450‐catalyzed activities, but in achieving sex differences there is also specific regulation of the P450E counterpart, and possibly of the 6β‐OHase (P450A?). Other factors, temporal or hormonal, can modify the effect of E2treatment, and may contribute to the specific regulation of P450 forms in naturally maturing fish, and to s

ISSN:0022-104X    

DOI:10.1002/jez.1402590308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractMale and female gulf killifish,Fundulus grandis, were kept in large cages submerged in their natural habitat in the Gulf of Mexico. Gonadosomatic indices (GSI: 100 × gonad weight/body weight) and blood samples were obtained from male and female fish every 4 hours (beginning at 1600) throughout a day on 3 separate days of the semilunar cycle: at the GSI and spawning peak (July 27–28), at midcycle (August 2–3), and on a day prior to the probable spawning peak (August 9–10). Blood samples of females were assayed for cortisol, estradiol‐17β (E2), progesterone, testosterone, thyroxine (T4), and triiodothyronine (T3). The daily rhythms of hormones at each of the three days during the cycle differed markedly from one another. At the spawning peak, E2and T3peaks occurred at 1200, testosterone and progesterone peaks were found at 2400 and the GSI and cortisol peaks were at 0400. The GSI decreased sharply at 0800 indicating a period of probable spawning. At midcycle, most hormone levels were low throughout the day and the amplitudes of the hormone rhythms were suppressed. One day prior to the spawning peak, testosterone and progesterone variations (peaks at 2400) were similiar to those found on the day of the first semilunar GSI and spawning peaks. Daily variations of other hormones, especially E2, were prominent on the day prior to peak spawning but different from those found on the day of peak GSI/spawning. In males, plasma concentrations of cortisol, testosterone, T3and T4also underwent daily variations that differed from one another on the 3 days of the cycle. The results clearly demonstrate that there are dramatic changes in the daily variations of plasma hormone concentrations during the semilunar spwn

ISSN:0022-104X    

DOI:10.1002/jez.1402590309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe effects of the phorbol ester, phorbol 12‐myristate‐13‐acetate (PMA), and the calcium ionophore, A23187, on prostaglandin E (PGE) and F (PGF) levels were investigated using incubates of brook trout (Salvelinus fontinalis) and yellow perch (Perca flavescens) ovarian tissue. The combination of PMA (0.1 μg/ml) and A23187 (0.1 μg/ml) synergistically stimulated an increase in PGE and PGF levels in incubates of brook trout follicles obtained from females prior to germinal vesicle breakdown, prior to ovulation and postovulation. The highest levels were observed in incubates of follicles taken just prior to ovulation. By itself, PMA also stimulated PGE and PGF accumulation while A23187 was much less effective. A23187, but not PMA, stimulated in vitro ovulation of brook trout follicles. Both cycloheximide and actinomycin inhibited PGE and PGF accumulation in incubates of preovulatory brook trout follicles stimulated with PMA but these inhibitors did not block ovulation induced by A23187 or PMA/A23187.The effect of PMA and A23187 were tested on the following 3 yellow perch tissue preparations: 1) isolated follicles [free of extrafollicular tissue (EF)], 2) EF tissue, and 3) intact tissue (containing undissected follicles attached to EF tissue). Incubates with all tissue types were performed in the presence or absence of 17α,20β‐dihydroxy‐4‐pregnen‐3‐one (17,20β‐PG, 0.1 μg/ml). PMA (0.1 μg/ml) in combination with A23187 (0.01 μg/ml) stimulated PGE and PGF accumulation in all tissue types though the greatest increase was generally observed in intact preparations. There was a lower accumulation of PGE in intact and EF tissue incubates stimulated with 17,20β‐PG and PMA. In addition, in incubates of ovarian tissue from several perch there was a higher accumulation of PGF in intact preparations stimulated by PMA or PMA/A23187 in the presence of 17,20β‐PG.The results for both species indicate that phorbol esters (PEs) can stimulate prostaglandin synthesis in follicles and, given that PEs have been shown to stimulate protein kinase C, it is possible that this enzyme is naturally involved in the control of ovarian PG synthesis in fish. It also appears that the stimulation is related to maturational stage in brook trout and ster

ISSN:0022-104X    

DOI:10.1002/jez.1402590310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractProliferative activities of gonadal somatic cells were examined autoradiographically during gonadal development inRana nigromaculata. Both the germinal epithelium and the sexual cord appeared to be of coelomic epithelial origin, as indicated ultrastructurally by the observation that the 2 regions were covered with a common basal lamina. Cell‐proliferative activity was higher in the sexual cord than in the germinal epithelium at stage 29, suggesting that topographically specific active proliferation of coelomic epithelial cells contributed to the formation of the sexual cord. In the course of testicular development, high proliferative activity of the sexual cord was recognized until stage 32 (just after gonadal sex differentiation). At stage 43 (during metamorphosis), higher proliferative activity was noted in the germinal epithelium than in the sexual cord, and the germinal epithelium differentiated into seminiferous cords. There were no differences in proliferative activity between the germinal epithelium and sexual cord at stages 32 and 34 in the ovaries. At stage 43, there was higher proliferative activity in the germinal epithelium than in the sexual cord, and the germinal epithelium differentiated into follicular cells. These results suggest that both seminiferous cords and follicular cells are derived from germinal epithelium and that both pass through similar processes of developmen

ISSN:0022-104X    

DOI:10.1002/jez.1402590311

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY