Hormone-induced and maturational changes in electric organ discharges and electroreceptor tuning in the weakly electric fishApteronotus

Summary Plasticity in the frequency of the electric organ discharge (EOD) and electroreceptor tuning of weakly electric fish was studied in the genusApteronotus. Both hormone-induced and maturational changes in EOD frequency and electroreceptor tuning were examined.Apteronotus is different from all other steroid-responsive weakly electric fish in that estradiol-17, rather than androgens, induces discharge frequency decreases. This result can account for the reversed discharge frequency dimorphism found inApteronotus in which, counter to all other known sexually dimorphic electric fish, females have lower discharge frequencies than males. Studies of electroreceptor tuning inApteronotus indicate that electroreceptors are closely tuned to the frequency of the EOD. This finding was noted not only in adult animals, but also in juvenile animals shortly after the onset of their EODs. Tuning plasticity inApteronotus, as in other species studied, is associated with altered EOD frequencies and was noted in both maturational EOD changes and in estrogen-induced changes. Thus, tuning plasticity appears to be a general phenomenon which occurs concurrent with a variety of EOD changes.     

Single electrocytes produce a sexually dimorphic signal in South American electric fish,Hypopomus occidentalis (Gymnotiformes,Hypopomidae)

Summary Hypopomus occidentalis is a weakly electric Gymnotiform fish with a pulse-type electric organ discharge (EOD).Hypopomus used in this study were taken from one of the northernmost boundaries of this species, the Atlantic drainage of Panama where the animals breed at the beginning of the dry season (December). In normal breeding populations,Hypopomus occidentalis exhibit a sexual dimorphism in EOD and morphology. Mature males are large with a broad tail and have an EOD characterized by a low peak power frequency. Females and immature males are smaller, having a slender tail and EODs with higher peak power frequencies (Fig. 1). This study describes differences in the EOD and electric organ morphology between breeding field populations of male and femaleHypopomus. Changes in physiology, morphology and EOD shape which may accompany this seasonal change were examined in steroid injected fish, using standard histological and physiological techniques.A group of females were injected with hormones (5-dihydrotestosterone (DHT), estrogen or saline) to assess changes in their morphology and EOD. Animals treated with DHT developed characteristics which mimicked the sexually dimorphic characteristics of a male, while the other groups did not (see Fig. 5). Tissue from the tails of breeding males and females, and females treated with DHT, were sampled to measure the size of the electrocytes in the tail. The broader tail of males and DHT-females is composed of large electrocytes, whereas the slender tail of normal females is composed of smaller electrocytes. Therefore, the increase in the tail width in the female DHT group is caused by an enlargement of the electrocytes in this area.Intracellular recordings from the electrocytes of saline and DHT injected females show a difference in the responses of the rostral faces of the electrocytes from the two groups, which reflect the differences in their EODs. Saline-treated animals had symmetrical EODs (the first and second phase of the EOD were equal in duration and amplitude), while the physiological responses from each face of the electrocytes yielded responses that were similarly equal in duration and amplitude. DHT-treated animals had asymmetrical EODs (the first phase of the EOD was similar to that of saline treated fish and larger in amplitude and shorter in duration than the second phase) and the physiological responses of the electrocytes reflected this asymmetry. The differential recordings across the caudal face were similar to those from saline treated fish, while the responses from the rostral face were longer in duration and smaller in amplitude.These data suggest that the effects of androgens underlie the changes in single electrocytes which produce the sexually dimorphic signals and morphology present in natural breeding populations ofHypopomus occidentalis.     

Hormonal control of sex differences in the electric organ discharge (EOD) of mormyrid fishes

Summary Field studies have demonstrated that several species of mormyrid fish from Gabon, West Africa have a sex difference in the pulse-like waveform of their Electric Organ Discharge (EOD). Administration of androgen hormones (testosterone or dihydrotestosterone) to a female or juvenile can induce the EOD typical of a sexually mature male. Data for two such species —Brienomyrus brachyistius (triphasic) andStomatorhinus corneti — are presented, showing that transformation of a female's or juvenile's EOD to a male-like EOD involves a 2–3 fold increase in EOD duration and a downward shift in the peak frequency of the EOD's power spectrum (as determined by Fourier analysis). ForBrienomyrus brachyistius (triphasic), estradiol can also induce changes in the EOD waveform, although not as dramatic as that for androgens. Changes in EOD duration and power spectra are often accompanied by an alteration of the wave-shape or morphology of the EOD pulse, i.e., the relative amplitude of its peaks and the presence of inflection points in its negative and positive phases.A third species,Hippopotamyrus batesii (triphasic), not previously known to have an EOD sex difference, also responds to testosterone treatment with an increase in EOD duration. Preliminary field data indicate this species may have a sexual dimorphism in its EOD, suggesting that the response to a steroid hormone may be an indicator of a sex difference in a species' EOD waveform. Such findings are discussed in relation to the affects of steroids on vertebrate neurons and muscle, and the evolution of electric communication systems.Abbreviations DHT 5-dihydrotestosterone - EOD electric organ discharge - F mature female - HTI interval between peaks (H and T) in EOD's first derivative - IF juvenile female - IM juvenile male - M mature male - PPW peak frequency of power spectrum     

A hormone-sensitive communication system in an electric fish

The electric communication system includes both special muscle-derived cells or electrocytes that produce species-typical electric signals, or electric organ discharges (EODs), and specialized sensory receptors, or electroreceptors, that encode the electric fields set up by EODs. Steroid hormones can influence the characteristic properties of both EODs and electroreceptors. Steroids appear to directly effect the anatomy and physiology of the electrocytes that generate an EOD. In contrast, the steroid effect on electroreceptors may be predominantly via an indirect mechanism whereby changes in the spectral characteristics of the EOD appear to induce changes in the spectral sensitivity of electroreceptors. Continued studies of electrosensory and electromotor systems will offer insights into the cellular bases for the development and evolution of steroid-sensitive pathways in the vertebrate nervous system.     

Life cycle of Calanus chilensis Brodsky in Bay of San Jorge,Antofagasta, Chile

The copepod Calanus chilensis is an endemic component of the zooplankton community in northern Chile. Size distributions of adult females, relative frequency of copepodid stages and relative numbers of adult males and nauplii, suggest the presence of at least 6 generations during the year, although the species seems to continuously reproduce through all seasons. Temperature profiles from 0 to 175 m indicated the presence of the El Niño current during March and April. Surface temperature ranged between 21.1 and 13.1 °C. Warm waters during the El Niño event seemed to affect the body size of adult females and the normal course of cohort development, although the population tended to recover rapidly through the subsequent months. We discuss the role of oceanographic conditions in controlling the life cycle of this species, as well as its continuous growth through the year compared to other Calanus species.     

Stimulus discrimination in the diencephalon ofEigenmannia: the emergence and sharpening of a sensory filter

Summary Neuronal reliability and sensitivity to behaviorally relevant stimulus patterns were investigated in a higher-order nucleus of the diencephalon believed to participate in the jamming avoidance response (JAR) of the weakly electric fish,Eigenmannia. The fish raises or lowers its frequency of electric organ discharge (EOD) to minimize interference from a neighboring fish's EOD. Proper JARs require determination of the sign of the difference frequency (Df) between the neighboring fish's EOD and the fish's own EOD. Bastian and Yuthas (1984) recently described diencephalic neurons within the nucleus electrosensorius that are able to make this determination. In the present study, response properties of such neurons were compared with those of lower-level sign-selective cells found in the torus semicircularis and the optic tectum (Heiligenberg and Rose 1985) as well as with properties of the intact behavior.Most sign-selective cells within the nucleus electrosensorius show a high degree of selectivity for one sign of the difference frequency; cells with either sign preference were found in approximately equal numbers. The sign preference and the degree of sign selectivity is most often independent of the spatial orientation of the jamming stimulus. In contrast, the responses of toral and tectal cells are less robust and consistent and are often highly dependent on the geometry of the jamming stimulus.Determination of the sign of the difference frequency requires the analysis of amplitude modulations coupled with modulations in phase (timing) differences between pairs of areas of the body surface. The most sensitive cells recorded in the nucleus electrosensorius can determine the sign of the difference frequency with timing differences of 1 s or less, roughly comparable to the behavioral threshold of 400 ns (Carr et al. 1986). The best toral/tectal response required at least a 16 s modulation.Cells within the nucleus electrosensorius thus code the sign of Df with a high degree of reliability and sensitivity. Ambiguities persist, however, which suggest that single cells at this level cannot completely account for the behavioral discrimination. Additional processing may be necessary to transform a still primarily sensory code into a motor program for control of the JAR (Rose et al. 1988).Abbreviations EOD electric organ discharge - JAR jammning avoidance response - Df difference frequency between jamming signal and fish's own EOD - S ₁ sinusoidal EOD mimic of subject fish - S ₂ sinusoidal EOD mimic of neighbor     

Responses of cells in the mormyrid electrosensory lobe to EODs with distorted waveforms: implications for capacitance detection

Mormyrid fish (Gnathonemus petersii) can discriminate between ohmic and capacitive electrical objects during active electrolocation. The neural basis of this ability was investigated by recording cells in the dorsolateraland medial zones of the electrosensory lobe. Natural electric organ discharges (EODs) distorted by capacitive objects and EODs with computer generated phase shifts were used as stimuli.Cells in the dorsolateral zone were very sensitive to phase shifted EODs with constant amplitude spectra. Phase shifts as small as 1 were effective. Cells in this zone also responded more to EODs with capacitance induced distortions than to non-distorted EODs. These effects were very similar to the effects on B-type primary afferents from mormyromast electroreceptors which project to this zone.Cells in the medial zone were not sensitive to phase shifted EODs. Capacitance induced waveform distortions were effective, but the effect of such distortions was opposite to the effect on dorsolateral zone cells. These effects were very similar to the effects on A-type primary afferents from mormyromast electroreceptors which project to this zone.The results show that peripheral information about capacitive objects is preserved in the electrosensory lobe, but do not indicate any further processing of capacitive information in the lobe.     

The effects of androgens and estrogen on the external morphology and electric organ discharge waveform of Gnathonemus petersii (Mormyridae, Teleostei)

The effects of androgens and estrogen on the external morphology and electric organ discharge (EOD) waveform in Gnathonemus petersii, a weakly discharging electric fish, were investigated. Following preimplant data collection, juvenile and adult fish were gonadectomized and implanted with silastic capsules containing either high or low doses of testosterone (T), dihydrotestosterone (DHT), estradiol-17 beta (E2), or cholesterol. One group of fish was treated with high doses of DHT + E2. Radioimmunoassays revealed that low-dose implants resulted in plasma T levels comparable to and high-dose implants about sixfold greater than those found in adult males imported during breeding season. High-dose E2 implants resulted in higher plasma E2 levels in adults than those in juveniles. At either dose, both androgens induced male-like indentations in the dorsal margin of the anal fin of juveniles and adult females by 4 weeks postimplant. Both low and high doses of T decreased the peak power spectrum frequency (PPSF) of Fourier transformations of EODs and increased the durations of phases 2 and 3 of the EOD in juveniles and adults, but the high doses caused more rapid and profound effects. The two doses of T caused opposite effects on the durations of phases 1 and 4 juveniles. The low dose of T decreased the durations of phases 1 and 4, while the high dose increased them. In adults, the high dose of T increased the duration of phase 1, but had inconsistent effects on the duration of phase 4. Total EOD durations were increased by both doses of T in juveniles, while adults showed inconsistent effects possibly due to individual variability in hormone sensitivity. Compared to T, DHT exerted similar, but less dramatic effects on all measures, but only at high doses. E2 significantly increased adult PPSFs, the first such finding in a mormyrid species. E2 had no effects on juvenile PPSFs, or on adult or juvenile EOD phase durations. The effects of DHT + E2 on PPSF and phases 2 and 3 were similar to those of DHT alone. These findings demonstrate quantifiable steroid-dependent plasticity in the durations of individual phases of EODs in an electric fish and are the first to show that the external morphology in Gnathonemus petersii is androgen-dependent. The results are discussed with regard to methodological considerations and hormone studies involving sex differences in EODs reported for this and other species.     

RFLP markers to identify the alleles on the Mla locus conferring powdery mildew resistance in barley

Summary To identify the mildew resistance locus Mla in barley with molecular markers, closely linked genomic RFLP clones were selected with the help of near-isogenic lines having the Pallas and Siri background. Out of 22 polymorphic clones 3 were located around the Mla locus on chromosome 5 with a distance of 5.1 + 2.9 cM (MWG 1H068), 4.2±1.7 cM (MWG 1H060) and 0.7 ± 0.7 cM (MWG 1H036), respectively. The polymorphic clone MWG 1H036 displayed the same RFLP pattern in both Pallas and Siri near-isogenic lines and in different varieties digested with six restriction enzymes possessing the same mildew resistance gene. The alleles of the Mla locus were grouped in 11 classes according to their specific RFLP patterns; 3 of these groups contain the majority of Mla alleles already used in barley breeding programs in Europe.     

Microhabitat location and niche segregation in two sibling species of Drosophilid parasitoids: Asobara tabida (Nees) and A. rufescens (Foerster) (Braconidae: Alysiinae)

Summary Olfactometer tests with Asobara tabida (Nees 1834), a larval endo-parasitoid of frugivorous Drosophilidae showed that females are attracted to the odour of host food: a suspension of living yeast. This attraction decreased as the fermenting medium grew older and became less likely to contain suitable host stages. Olfactometer tests with — what was considered to be — A. tabida from two different microhabitats (fermenting fruits and decaying plants) showed a genetically determined difference in microhabitat odour preference between the two microhabitat strains. Each strain preferred the odour of its own microhabitat. This odour preference was not modified by larval conditioning. Hybridization tests indicated that we were dealing with two sibling species: A. tabida and A. rufescens (Foerster 1862), reproductively isolated by a pre-mating isolation mechanism only. Enforced matings resulted in fertile female offspring. Some small morphological differences were detected. The two species live sympatrically, although each inhabits and is most attracted to its own microhabitat.     

Mutants in position 69 of the Trp repressor ofEscherichia coli K12 with altered DNA-binding specificity

Structural analysis by X-ray crystallography has indicated that direct contact occurs between Arg69, the second residue of the first helix of the helix-turn-helix (HTH) motif of the Trp repressor, and guanine in position 9 of the -centred consensustrp operator. We therefore replaced residue 69 of the Trp repressor with Gly, Ile, Leu or Gln and tested the resultant repressor mutants for their binding to synthetic symmetrical -or -centredtrp operator variants, in vivo and in vitro. We present genetic and biochemical evidence that Ile in position 69 of the Trp repressor interacts specifically with thymine in position 9 of the -centredtrp operator. There are also interactions with other bases in positions 8 and 9 of the -centredtrp operator. In vitro, the Trp repressor of mutant RI69 binds to the consensus -centredtrp operator and a similartrp operator variant that carries a T in position 9. In vivo analysis of the interactions of Trp repressor mutant RI69 with symmetrical variants of the -centredtrp operator shows a change in the specificity of binding to a -centred symmetricaltrp operator variant with a gua-nine to thymine substitution in position 5, which corresponds to position 9 of the -centredtrp operator.     

Intracellular sites of the synthesis of sweet potato mitochondrial F1ATPase subunits

Summary Five subunits (-, -, -, - and -subunits) of the six -and -subunits) in the F₁ portion (F₁ATPase) of sweet potato (Ipomoea batatas) mitochondrial adenosine triphosphatase were isolated by an electrophoretic method. The - and -subunits were not distinguishable immunologically but showed completely different tryptic peptide maps, indicating that they were different molecular species. In vitro protein synthesis with isolated sweet potato root mitochondria produced only the -subunit when analyzed with anti-sweet potato F₁ATPase antibody reacting with all the subunits except the -subunit. Sweet potato root poly(A)⁺RNA directed the synthesis of six polypeptides which were immunoprecipitated by the antibody: two of them immunologically related to the -subunit and the others to the - and -subunits. We conclude that the -subunit of the F₁ATPase is synthesized only in the mitochondria and the -, - and -subunits are in the cytoplasm.     

The effects of bromocriptine and prolactin on porphyrin biosynthesis and morphology in the female hamster Harderian gland

Porphyrin biosynthesis was examined in the Harderian gland of the female golden hamster by fluorometric assays of gland porphyrin content and by measuring the activity of a rate-limiting enzyme for haem biosynthesis, -aminolaevulinic acid synthase. Both porphyrin content and enzyme activity are high in normal female glands. Enzyme activity was lowered in females ovariectomised for 6 weeks, and both enzyme activity and porphyrin content were greatly lowered in ovariectomised females given the dopamine agonist bromocriptine; this suppression could be prevented by simultaneous prolactin administration. Bromocriptine (but not ovariectomy alone) also masculinised the morphology of the Harderian gland, resulting in the appearance of type II cells and polytubular complexes; again, the simultaneous administration of prolactin prevented masculinisation. The results support the hypothesis that while androgens have an inhibitory effect on porphyrin synthesis within this model, prolactin may have a major facilitatory role.Abbreviations ALA -aminolaevulinic acid - ALA-s -aminolaevulinate synthase     

Structure of the yolksac epithelium and gills in the early developmental stages of rainbow trout (Salmo gairdneri) maintained in different ambient salinities

Synopsis Small numbers of mitochondria-rich (chloride) cells were found in the yolksac epithelium of rainbow trout (Salmo gairdneri) embryos just before hatching and in eleuthero-embryos up to 14 days after hatching. This suggests that the yolksac epithelium may play a limited ionoregulatory role in this species.Mitochondria-rich cells were also present in small numbers in the branchial epithelium of embryos just before hatching and in increasing numbers in eleutheroembryos during the first two weeks after hatching. The cells in the branchial epithelium showed marked variations in appearance, particularly in the fine structure of the tubular (smooth) endoplasmic reticulum. Few of the mitochondria-rich cells examined here had the pitted apex which is characteristic of homologous cells in other species.There appeared to be no differences in the numbers or appearance of mitochondria-rich cells in embryos and eleutheroembryos reared in different ambient salinities (distilled water, 110/00 and 130/00 sea water), possibly indicating that the genesis of the ionoregulatory function of the gills has not occurred at that interval of development.     

TROSY experiment for refinement of backbone psi and phi by simultaneous measurements of cross-correlated relaxation rates and 3,4J(H alpha HN) coupling constants

The TROSY principle has been introduced into a HNCA experiment, which is designed for measurements of the intraresidual and sequential H-C/H^N-N dipole/dipole and H-C/N dipole/CSA cross-correlated relaxation rates. In addition, the new experiment provides values of the ^3,4 J _{H HN} coupling constants measured in an E.COSY manner. The conformational restraints for the and angles are obtained through the use of the cross-correlated relaxation rates together with the Karplus-type dependencies of the coupling constants. Improved signal-to-noise is achieved through preservation of all coherence transfer pathways and application of the TROSY principle. The application of the [¹⁵N,¹³C]-DQ/ZQ-[¹⁵N,¹H]-TROSY-E.COSY experiment to the 16 kDa apo-form of the E. coli Heme Chaperon protein CcmE is described. Overall good agreement is achieved between and angles measured with the new experiment and the average values determined from an ensemble of 20 NMR conformers.     

Effect of cell-surface binding on development of Ascidian egg

Summary The early development ofPhallusia mammillata eggs, dechorionated with trypsin and treated with Concanavalin A, was studied. Vital staining with a very dilute solution of acridine orange (0.01 g/ml) helped to visualize the mitochondrial crescent by fluorescence. At high concentrations of Concanavalin A (20–200 g/ml) fertilized eggs did not cleave, but went through early ooplasmic segregation movements (formation of the crescent) and multinuclear syncytia were formed. At lower concentrations of Concanavalin A (less than 10 g/ml), cleavage occurred, but the blastomeres remained rounded, leading to a grapelike embryo. Eggs attached to Concanavalin A treated nylon surfaces either did not cleave or produced grapelike embryos. Attachment of the eggs did not affect ooplasmic segregation. Considering modern theories of membrane structure it was concluded that Concanavalin A prevented cleavage either by immobilizing surface structures connected with microfilaments or by indirectly modifying other membrane structures. These structures could not have been involved in ooplasmic segregation, but their mobility was necessary for further morphogenesis.This work was performed at the Station Zoologique, Villefranche-sur-Mer and at the Station de Biologie Marine et Lagunaire. Sète     

An internal current source yields immunity of electrosensory information processing to unusually strong jamming in electric fish

Summary The electric organ of a fish represents an internal current source, and the largely isopotential nature of the body interior warrants that the current associated with the fish's electric organ discharges (EODs) recruits all electroreceptors on the fish's body surface evenly. Currents associated with the EODs of a neighbor, however, will not penetrate all portions of the fish's body surface equally and will barely affect regions where the neighbor's current flows tangentially to the skin surface. The computational mechanisms of the jamming avoidance response (JAR) in Eigenmannia exploit the uneven effects of a neighbor's EOD current to calculate the correct frequency difference between the two interfering EOD signals even if the amplitude of a neighbor's signal surpasses that of the fish's own signal by orders of magnitude. The particular geometry of the fish's own EOD current thus yields some immunity against the potentially confusing effects of unusually strong interfering EOD currents of neighbors.Abbreviations DF frequency difference - ELL electrosensory lateral line lobe - EOD electric organ discharge - JAR jamming avoidance response     

Effect of liquid culture on the growth and development of miniature rose (Rosa chinensis Jacq. ‘Minima’)

The growth of miniature rose (Rosa chinensis Jacq. Minima) shoots cultured on liquid medium was greater relative to those cultured on two-phase (solid + liquid) medium or solid medium alone. Shoot multiplication ratio (number of multiple shoots per explant per subculture) on liquid medium was higher with 17.8–26.6 M 6-benzyladenine at compared to that at 0–8.9 M. Shoots grown on 30 ml or more of liquid medium had a higher multiplication ratio than those grown on 10 or 20 ml. The growth and multiplication ratio increased when the culture period was extended from 3 to 6 weeks, although plantlets began to exhibit some chlorosis by the 6^th week. These conditions were maintained over four subcultures for cultivars Baby Katie, Lavender Jewel, Red Sunblaze and Royal Sunblaze, with no significant change in multiplication ratio over time.Abbreviations BA 6-benzyladenine - NAA 1-naphthaleneacetic acid