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At least 19 recordsLinked to original sources
PubMed1989

A temporal analysis of testosterone-induced changes in electric organs and electric organ discharges of mormyrid fishes.

The electric organ discharge (EOD) of several species of mormyrid fishes within the genus Brienomyrus is sexually dimorphic during the breeding season: the duration of the male's EOD is much longer than the duration of the female's (for a review see Hopkins, 1986). The mormyrid used here, Brienomyrus sp., exhibits similar alterations in the duration of the triphasic EOD after treatment with testosterone, as do other members of this genus (for reviews see Bass, 1986a,b). In this experiment, animals were intraperitoneally implanted with pellets of either 11-ketotestosterone or 17 a-methyltestosterone, and the time course of the changes in the duration of each of the three phases of the EOD were quantified. Additionally, the time course of changes in the morphology of the electric organ, after testosterone treatment, was also quantified using electron microscopic techniques. The results suggest that the change in the duration of the first phase of the EOD is due exclusively to the change in the thickness of the electrocyte body: this is consistent with a model proposed by Bennett and Grundfest (1961) for the electrogenesis of a triphasic EOD. Changes in the duration of the second and third phases of the EOD are highly correlated with the changes in the surface area of the posterior and anterior faces of the electrocyte, respectively. The results support the hypothesis that gonadal steroid hormone-induced changes in the EOD are due to structural changes in the electrocyte's membranes, and that all of the observed changes in the discharge of this system can be explained by the action of steroid hormones on the peripheral target cells (electrocytes).

Action Potentials↗
PubMed1995

Individual variation in and androgen-modulation of the sodium current in electric organ.

Electric fish of the genus Sternopygus produce a sinusoidal electric organ discharge (EOD) of low frequencies in males, high frequencies in females, and overlapping and intermediate frequencies in juveniles. Correspondingly, the cells of the electric organ, the electrocytes, generate action potentials which are of long duration in mature males, short duration in females, and intermediate duration in immatures. The androgen dihydrotestosterone (DHT) lowers EOD frequency and increases electrocyte action potential duration. We examined the electrocytes under voltage clamp to determine whether variations in the kinetic properties of the Na+ current might underlie these phenomena. We found that the fast inactivation time constants of the peak Na+ current (0 mV) ranged from 0.5 to 4.7 msec and varied systematically with EOD frequency and action potential duration. Voltage dependence of steady-state inactivation also varied with EOD frequency with the midpoint of inactivation being more positive in fish with low EOD frequencies. There was no correlation between the voltage at which the Na+ current activates, voltage at peak current, reversal potential, rate of recovery from inactivation, or TTX sensitivity and EOD frequency. We tested whether DHT influenced Na+ current inactivation by recording from electrocytes before and after juvenile fish of both sexes were implanted with a DHT-containing or empty capsule. We found that inactivation time constants were significantly slower in DHT implanted, but not control, fish. This is the first observation of functionally relevant individual variation in the kinetics of a Na+ current and the first demonstration that the kinetics of a Na+ current may be modulated by an androgen.

Animals↗
PubMed1985

Detergent-soluble form of acetylcholinesterase in the electric organ of electric rays. Its isolation, characterization and monoclonal antibodies.

The detergent-soluble form of acetylcholinesterase was purified from the electric organ of the electric rays Narke japonica and Torpedo californica, and its properties were examined. The electric organ of N. japonica and T. californica contains three types of acetylcholinesterase: low-salt-soluble, asymmetric or tailed, and detergent-soluble forms. Results showed that in N. japonica, asymmetric forms were predominant, whereas in T. californica the detergent-soluble form was predominant. Low-salt-soluble acetylcholinesterase constituted 10% of the total acetylcholinesterase in both species. Detergent-soluble acetylcholinesterase was purified by immunoaffinity chromatography with a monoclonal antibody (Nj-601) to acetylcholinesterase. Triton X-100 extracts of these electric organs were applied to a column of Nj-601-Sepharose, and the bound acetylcholinesterase was eluted quantitatively by lowering the pH to 2.8. This simple procedure gave good yields. The purified enzymes gave single peaks at 6 S on sucrose gradients in the presence of detergent and polydisperse aggregates in the absence of detergent. Reduction of disulfide bonds gave peaks at 4.4 S. On polyacrylamide gel electrophoresis in sodium dodecyl sulfate, the purified acetylcholinesterases gave bands with Mr of about 130 000 in the unreduced state and with Mr of 66 000 in addition to a very faint band of Mr 130 000 in the reduced state. The Mr-66 000 polypeptides were labeled with diisopropylfluorophosphate. Thus, the detergent-soluble acetylcholinesterases exist as dimers of the Mr-66 000 components. Two-dimensional electrophoresis of the purified enzymes indicated their homogeneity. The isoelectric points of both enzymes were 5.1 under the conditions employed. The two enzymes had very similar amino acid compositions, and contained more than 14% of neutral sugars and glucosamine. Monoclonal antibodies were raised to detergent-soluble acetylcholinesterase by the hybridoma technique; eight were obtained. All of them recognized the catalytic subunits of detergent-soluble and asymmetric acetylcholinesterase, and reacted only with detergent-soluble acetylcholinesterase in immunoblots. Four of the monoclonal antibodies inhibited the activities of both the detergent-soluble and asymmetric forms of acetylcholinesterase.

Acetylcholinesterase↗
PubMed1997

Ontogeny of the electric organ discharge and the electric organ in the weakly electric pulse fish Brachyhypopomus pinnicaudatus (Hypopomidae, Gymnotiformes).

I recorded the electric organ discharges (EODs) of 331 immature Brachyhypopomus pinnicaudatus 6-88 mm long. Larvae produced head-positive pulses 1.3 ms long at 7 mm (6 days) and added a second, small head-negative phase at 12 mm. Both phases shortened duration and increased amplitude during growth. Relative to the whole EOD, the negative phase increased duration until 22 mm and amplitude until 37 mm. Fish above 37 mm produced a "symmetric" EOD like that of adult females. I stained cleared fish with Sudan black, or fluorescently labeled serial sections with anti-desmin (electric organ) or anti-myosin (muscle). From day 6 onward, a single electric organ was found at the ventral margin of the hypaxial muscle. Electrocytes were initially cylindrical, overlapping, and stalk-less, but later shortened along the rostrocaudal axis, separated into rows, and formed caudal stalks. This differentiation started in the posterior electric organ in 12-mm fish and was complete in the anterior region of fish with "symmetric" EODs. The lack of a distinct "larval" electric organ in this pulse-type species weakens the hypothesis that all gymnotiforms develop both a temporary (larval) and a permanent (adult) electric organ.

Animals↗
PubMed1986

Acetylcholine, ATP, and proteoglycan are common to synaptic vesicles isolated from the electric organs of electric eel and electric catfish as well as from rat diaphragm.

Cholinergic synaptic vesicles were isolated from the electric organs of the electric eel (Electrophorus electricus) and the electric catfish (Malapterurus electricus) as well as from the diaphragm of the rat by density gradient centrifugation followed by column chromatography on Sephacryl-1000. This was verified by both biochemical and electron microscopic criteria. Differences in size between synaptic vesicles from the various tissue sources were reflected by their elution pattern from the Sephacryl column. Specific activities of acetylcholine (ACh; in nmol/mg of protein) of chromatography-purified vesicle fractions were 36 (electric eel), 2 (electric catfish), and 1 (rat diaphragm). Synaptic vesicles from all three sources contained ATP in addition to ACh (molar ratios of ACh/ATP, 9-12) as well as binding activity for an antibody raised against Torpedo cholinergic synaptic vesicle proteoglycan. Synaptic vesicles from rat diaphragm contained binding activity for the monoclonal antibody asv 48 raised against a rat brain 65-kilodalton synaptic vesicle protein. Antibody asv 48 binding was absent from electric eel and electric catfish synaptic vesicles. These antibody binding results, which were obtained by a dot blot assay on isolated vesicles, directly correspond to the immunocytochemical results demonstrating fluorescein isothiocyanate staining in the respective nerve terminals. Our results imply that ACh, ATP, and proteoglycan are common molecular constituents of motor nerve terminal-derived synaptic vesicles from Torpedo to rat. In addition to ACh, both ATP and proteoglycan may play a specific role in the process of cholinergic signal transmission.

Acetylcholine↗
PubMed2006

Identification and distribution of chondroitin sulfate in the three electric organs of the electric eel, Electrophorus electricus (L.).

The electrogenic tissue of the electric eel Electrophorus electricus (L.) is distributed in three well-defined electric organs, the Main electric organ, Sach's organ and Hunter's organ. Sulfated glycosaminoglycan (GAG) composition was characterized in the three electric organs of the electric eel. Sulfated GAGs were analyzed in the electric organs using metachromatic staining, biochemical analysis including electrophoresis before and after specific enzymatic or chemical degradations, and immunostaining with an antibody against chondroitin sulfate (CS). Our results showed in the three electric organs that CS was the main sulfated GAG species detected, accompanied by small and diminutive amounts of CS/dermatan sulfate hybrid chains and heparan sulfate (HS), respectively. However, HS was not detected in the Sach's organ. CS was predominantly detected in the innervated membrane face of the electroplaques in the three electric organs. Our findings extend previous observations on the GAG composition in the electric organs of E. electricus and provide new information regarding the tissue distribution and location of CS.

Animals↗
PubMed1991

Coupled in vivo activity of creatine phosphokinase and the membrane-bound (Na+,K+)-ATPase in the resting and stimulated electric organ of the electric fish Narcine brasiliensis.

Physiological control of the plasma membrane sodium pump, (Na+,K+)-ATPase, is essential for proper function of eukaryotic cells. In the electric organ of the elasmobranch Narcine brasiliensis, the normal demands placed upon the pump during the process of generation of electrical currents call for large and rapid changes in activity of this enzyme, making this a good model for the study of its cellular regulation. 31P NMR spectroscopic techniques were used to study metabolic regulation of membrane pump function in resting and stimulated electric organ and in skeletal muscle of the live, intact N. brasiliensis. Because the ATP synthetic abilities of the electric organ by glycolysis or oxidative phosphorylation are extremely limited, depletion of phosphocreatinine (PCr) could be used to determine the activity of the (Na+,K+)-ATPase after the electric organ was stimulated to discharge, and to measure the net flux from PCr to ATP through the creatine phosphokinase (CPK) reaction in the electric organ. Saturation transfer, an NMR technique which measures exchange rates, was applied to determine the unidirectional flux in the forward direction through the same reaction in the electric organ and in skeletal muscle as a control. The pseudo first-order rate constant kf for the CPK reaction at 24 degrees C in resting electric organ was 0.000 +/- 0.002 s-1 (n = 10) and in skeletal muscle was 0.08 +/- 0.03 s-1 (n = 3). The results demonstrate that in resting electric organ, which is well supplied with CPK, there was no measurable flux through this reaction, although CPK when extracted is highly active. Measured and calculated levels of all substrates for the creatine kinase reaction in the electric organ are similar to those in unstimulated skeletal muscle, where the creatine phosphokinase reaction rates are high in vivo. In contrast to the resting electric organ, during stimulation of the electric organ the measured net rate constant was greater than 0.08 s-1. In addition, as shown by lack of PCr depletion, there was virtually no net turnover of ATP in the resting organ compared to the stimulated organ. The marked difference in the (Na+,K+)-ATPase activity in the resting and activated electric organ confirmed earlier results (Blum, H., Nioka, S., and Johnson, R. G., Jr. (1990) Proc. Natl. Acad. Sci. U. S. A. 87, 1247-1251). Together, these results suggest that there is a novel method of coordinate regulation of cellular enzymes of great sensitivity and rapidity.

Adenosine Triphosphate↗
PubMed1996

Desmin filaments in the electrocytes of the electric organ of the electric eel Electrophorus electricus.

Desmin protein is an abundant constituent of the intermediate filaments in the electrocytes of the electric organ of the electric eel Electrophorus electricus. Polyclonal antibodies were raised against purified desmin from the electric organ and used for immunolabeling of the protein in reconstituted filaments. In thick sections of the main electric organ that has been stained with fluorescein-labeled desmin-specific antibodies, light microscope revealed a diffuse meshwork of desmin filaments dispersed in the cytoplasm of electrocytes. In the region under the membrane, the immunostaining was slightly more intense than elsewhere. The meshwork of intermediate filaments composed of desmin was examined by electron microscopy of the main electric organ. Immuno-gold labeling demonstrated a widespread meshwork of desmin filaments in the cytoplasm and in close association with the plasma membrane. These observations suggest that intermediate filaments play a role in the maintenance of the morphology of electrocytes and, as an intracellular meshwork spanning the width of the cell, they may contribute to the organization of the intracellular compartments.

Actin Cytoskeleton↗
PubMed1997

Molecular cloning of synaphins/complexins, cytosolic proteins involved in transmitter release, in the electric organ of an electric ray (Narke japonica).

Synaphins/complexins are cytosolic proteins associated with the docking/fusion complex crucial to transmitter release. The electric organ of the electric ray Narke japonica contained at least two kinds of synaphins as revealed by immunoblotting. cDNAs for three synaphins were cloned from a cDNA library prepared from the electric lobe where cell bodies of electromotor nerves innervating the electric organ exist. The proteins encoded by these cDNAs were named Nj-synaphins 1a, 1b and 2 on the basis of their high homologies (83-93%) to mammalian synaphins 1 and 2. Nj-Synaphins were immunoprecipitated by an anti-syntaxin monoclonal antibody, together with syntaxin, SNAP-25 and VAMP (synaptobrevin), suggesting the presence of a docking/fusion complex similar to that in the mammalian brain.

Adaptor Proteins, Vesicular Transport↗
PubMed1986

Species differences in electric organs of mormyrids: substrates for species-typical electric organ discharge waveforms.

The organization of electric organs is described for the mormyrid fishes from Africa. The electric organ's spike-generating cells or electrocytes are wafer-shaped cells with a special geometry that relates to the number of phases and polarity of their pulsatile electric organ discharge (EOD) waveform. Six "families" of electrocytes are recognized on the basis of cell geometry. Each family includes species with EODs of similar polarity and phase number. Despite such similarities, there are still dramatic species differences in EOD waveforms for a given family that may further depend on specialized features of the electrocyte's excitable membranes. It is each species' particular electrocyte "profile" that must underlie the development of species-specific and hormone-dependent sex differences in the EOD waveforms.

Animals↗
PubMed2001

Androgens alter electric organ discharge pulse duration despite stability in electric organ discharge frequency.

Weakly electric fish in the genus Sternopygus emit a sinusoidal, individually distinct, and sexually dimorphic electric organ discharge (EOD) that is used in electrolocation and communication. Systemically applied androgens decrease EOD frequency, which is set by a medullary pacemaker nucleus, and increase pulse duration, which is determined by the cells of the electric organ (the electrocytes), in a coordinated fashion. One possibility is that androgens broaden the EOD pulse duration by acting on the pacemaker neurons, thereby effecting a change in pacemaker firing frequency, and that the change in EOD pulse duration is due to an activity-dependent process. To determine whether androgens can alter pulse duration despite a stable pacemaker nucleus firing frequency, we implanted small doses of dihydrotestosterone in the electric organ. We found that androgen implants increased EOD pulse duration, but did not influence EOD frequency. In addition, using immunocytochemistry, we found that electrocytes label positively with an androgen receptor antibody. While it is not known on which cells androgens act directly, together these experiments suggest that they likely act on the electrocytes to increase EOD pulse duration. Since pulse duration is determined by electrocyte action potential duration and ionic current kinetics, androgens may therefore play a causative role in influencing individual variation and sexual dimorphism in electrocyte electrical excitability, an important component of electrocommunicatory behavior.

Androgens↗
PubMed1983

A monoclonal antibody against catalytic subunits of acetylcholinesterase in the electric organ of an electric ray, Narke japonica.

A hybridoma cell line secreting a monoclonal antibody against catalytic subunits of acetylcholinesterase in the electric organ of Narke japonica has been obtained by using a mouse immunized with the nerve terminal membranes prepared from the electric organ of Narke japonica. This monoclonal antibody (Nj-501) reacted with asymmetric, low salt-soluble and detergent-soluble forms of acetylcholinesterase of the electric organ of Narke japonica. Immunoblot analysis showed that the catalytic subunits of the asymmetric, low salt-soluble and detergent-soluble forms of acetylcholinesterase were polypeptides of molecular weight (Mr) 70K, 70K / 66K and 66K, respectively. Nj-501 markedly inhibited the activity of all these forms of acetylcholinesterase.

Acetylcholinesterase↗
PubMed1972

Purification by affinity chromatography of the molecular forms of acetylcholinesterase present in fresh electric-organ tissue of electric eel.

An acetylcholinesterase inhibitor-Sepharose conjugate was prepared by coupling a derivative of the powerful acetylcholinesterase inhibitor, N-methylacridinium, to CNBr-activated Sepharose. Use of this conjugate permitted direct purification, by affinity chromatography, of the two molecular forms of acetylcholinesterase, 14 and 18 S, present in fresh electric organ tissue. The purified 14S and 18S acetylcholinesterases retained the capacity to aggregate at low ionic strength displayed by crude extracts of the enzyme. The major polypeptide components of the 14S and 18S enzymes, as revealed by acrylamide gel electrophoresis, closely resemble those observed in the 11S form of acetylcholinesterase, previously purified after tryptic digestion of electric-organ tissue.

Acetylcholinesterase↗
PubMed1993

Rapid heat production associated with excitation of electric organs of the electric eel.

By constructing a new type of thermal detector, rapid production of heat was demonstrated during the rising phase of the action potential of the eel electric organs evoked by direct electric stimulation. Following the indirect (synapse-mediated) action potential of the organs, the existence of very large and variable production of heat of unknown origin was revealed.

Action Potentials↗
PubMed1998

Phospholipid translocation from the outer to the inner leaflet of synaptic vesicle membranes isolated from the electric organ of Japanese electric ray Narke japonica.

The phospholipid translocation from the outer to the inner leaflet of synaptic vesicles isolated from the electric organ of the Japanese electric ray, Narke japonica, was measured using fluorescent phospholipid probes. Phosphatidylcholine (PC), phosphatidylethanolamine (PE), or phosphatidylserine (PS) with a fluorescent NBD-labeled short acyl chain at the sn-2 position was mixed with purified synaptic vesicles and the probe in the outer leaflet of the membranes was reduced with dithionite to quench the fluorescence from time to time. The percentage of fluorescence remaining after the dithionite treatment served as an index for the phospholipid translocation. The results obtained indicated that about 30, 13, and 9% of NBD-PE, NBD-PS, and NBD-PC, respectively, were translocated from the outer to the inner leaflet in 3 h. Thus, the translocation activity in synaptic vesicle membranes was much higher for PE than for PS, in contrast to the previous results obtained with plasma membranes, including synaptosomal membranes. The percentages of the phospholipid in the inner leaflet at equilibrium were estimated to be 41, 31, and 14% for PE, PS, and PC, respectively. The translocation was inhibited by pretreatment with an SH reagent, iodoacetamide, indicating the involvement of a proteinaceous translocator. These data may provide a biochemical basis for elucidating the mechanisms of membrane fusion and exocytosis at nerve endings.

4-Chloro-7-nitrobenzofurazan↗
PubMed1999

Electric organ discharges and electric images during electrolocation.

Weakly electric fish use active electrolocation - the generation and detection of electric currents - to explore their surroundings. Although electrosensory systems include some of the most extensively understood circuits in the vertebrate central nervous system, relatively little is known quantitatively about how fish electrolocate objects. We believe a prerequisite to understanding electrolocation and its underlying neural substrates is to quantify and visualize the peripheral electrosensory information measured by the electroreceptors. We have therefore focused on reconstructing both the electric organ discharges (EODs) and the electric images resulting from nearby objects and the fish's exploratory behaviors. Here, we review results from a combination of techniques, including field measurements, numerical and semi-analytical simulations, and video imaging of behaviors. EOD maps are presented and interpreted for six gymnotiform species. They reveal diverse electric field patterns that have significant implications for both the electrosensory and electromotor systems. Our simulations generated predictions of the electric images from nearby objects as well as sequences of electric images during exploratory behaviors. These methods are leading to the identification of image features and computational algorithms that could reliably encode electrosensory information and may help guide electrophysiological experiments exploring the neural basis of electrolocation.

Animals↗