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PubMed1990

Buccalin is present in the cholinergic motor neuron B16 of Aplysia and it depresses accessory radula closer muscle contractions evoked by stimulation of B16.

The accessory radula closer (ARC) buccal muscle motor neuron B16 is buccalin-immunoreactive and it synthesizes a peptide with chromatographic properties identical to those of buccalin. Terminal varicosities in the ARC muscle are buccalin-immunoreactive, and buccalin reduces muscle contractions evoked by stimulation of neuron B16, probably by a presynaptic action.

Animals↗
PubMed1994

Myomodulin application increases cAMP and activates cAMP-dependent protein kinase in the accessory radula closer muscle of Aplysia.

Myomodulin A (MMA) application or stimulation of neuron B16, which releases MMA, increases cAMP levels in the accessory radula closer (ARC) muscle of Aplysia. MMA application also increases cAMP-dependent protein kinase (cAPK) activity in one subcellular compartment of the muscle. These results suggest that at least part of MMA's effects in this system are mediated via the cAPK signal transduction pathway. Since the effects of the small cardioactive peptides (SCPs) on ARC muscle contraction are similar to those of MMA, our results suggest that the convergent physiological effects of MMA and SCPB in this system may be due, in part, to the two peptide neuromodulators utilizing the same signal transduction pathway.

Animals↗
PubMed2005

Composition of the essential oil of the liverwort Radula perrottetii of Japanese origin.

Analysis of the essential oil of the liverwort Radula perrottetii afforded two novel viscidane diterpenes, viscida-3,9,14-triene (1), viscida-3,11(18),14-triene (2), four bisabolane sesquiterpenes, bisabola-2,6,11-triene (3), bisabola-1,3,5,7(14),11-pentaene (4), bisabola-1,3,5,7,11-pentaene (5), 6,7-epoxybisabola-2,11-diene (6), and 1-methoxy-4-(2-methylpropenyl)benzene (7) as new natural products. In addition, the known compounds bisabola-1,3,5,7(14),10-pentaene (8), ar-tenuifolene (9), alpha-helmiscapene (10), and beta-helmiscapene (11) were also isolated. Isolation was carried out by preparative gas chromatography, and the structures were established by extensive NMR analysis. This is the first finding of viscidane diterpenes in liverworts. Compounds 8, 9 and the rarely encountered eudesmane sesquiterpene hydrocarbons 10 and 11 are reported for the first time from R. perrottetii.

Hepatophyta↗
PubMed2000

Glutamate is the fast excitatory neurotransmitter of small cardioactive peptide-containing Aplysia radula mechanoafferent neuron B21.

B21 is a radula mechanoafferent neuron in the mollusc Aplysia which likely plays a crucial role in integrating environmental cues into the feeding motor program. To facilitate understanding B21's interactions with its postsynaptic followers, we sought to identify its neurotransmitter. We find that B21 makes a chemical synapse onto the follower neuron B8. Although B21-induced excitatory postsynaptic potentials (EPSPs) in B8 paradoxically diminish in amplitude with B8 hyperpolarization, we show that an inwardly rectifying current is responsible. We conclude that these B21-induced EPSPs are likely glutamatergic as they are blocked by the glutamate antagonist DNQX. Furthermore, B8 exhibits a depolarizing response to exogenous glutamate, which is antagonized by DNQX. Finally, exogenous glutamate occludes B21-evoked EPSPs in B8.

Animals↗
PubMed2006

Experimental habitat fragmentation increases linkage disequilibrium but does not affect genetic diversity or population structure in the Amazonian liverwort Radula flaccida.

Habitat fragmentation increases the migration distances among remnant populations, and is predicted to play a significant role in altering both demographic and genetic processes. Nevertheless, few studies have evaluated the genetic consequences of habitat fragmentation in light of information about population dynamics in the same set of organisms. In a 10,000-km(2) experimentally fragmented landscape of rainforest reserves in central Amazonia, we examine patterns of genetic variation (amplified fragment length polymorphisms, AFLPs) in the epiphyllous (e.g. leaf-inhabiting) liverwort Radula flaccida Gott. Previous demographic work indicates that colonization rates in this species are significantly reduced in small forest reserves. We scored 113 polymorphic loci in 86 individuals representing five fragmented and five experimentally unmanipulated populations. Most of the variation (82%) in all populations was harboured at the smallest (400 m(2)) sampling unit. The mean ((+/-) SD) within-population genetic diversity (Nei's), of forest remnants (0.412 +/- 0.2) was indistinguishable from continuous (0.413 +/- 0.2) forests. Similarly, F(ST) was identical among small (1- and 10-ha) and large (> or = 100-ha) reserves (0.19 and 0.18, respectively), but linkage disequilibrium between pairs of loci was significantly elevated in fragmented populations relative to those in continuous forests. These results illustrate that inferences regarding the long-term viability of fragmented populations based on neutral marker data alone must be viewed with caution, and underscore the importance of jointly evaluating information on both genetic structure and demography. Second, multilocus analyses may be more sensitive to the effects of fragmentation in the short term, although the effects of increasing linkage disequilibrium on population viability remain uncertain.

Environment↗
PubMed1994

Characterization of the membrane ion currents of a model molluscan muscle, the accessory radula closer muscle of Aplysia california. I. Hyperpolarization-activated currents.

1. The simple neuromuscular circuit consisting of the accessory radula closer (ARC) muscle of the mollus Aplysia californica together with its innervating motor and modulatory neurons has been extensively studied as a model preparation in which it might be possible to reach an integrated understanding of the neural and cellular mechanisms of behavioral plasticity, in this case of a component of Aplysia feeding behavior. Previous work has suggested that much of the plasticity of this behavior is implemented by appropriate release of modulatory neurotransmitters and peptide cotransmitters that modulate several parameters of the contractions of the ARC muscle. However, little is as yet known about the underlying cellular mechanisms. 2. We have begun to study single, functionally intact fibers dissociated from the ARC muscle to assess to what extent the modulation of its contraction might be mediated by one candidate mechanism, modulation of its membrane ion currents. First, however, it was necessary to gain a thorough understanding of the unmodulated currents and their likely roles in normal contraction. Using voltage-clamp techniques, we have therefore identified and characterized the major currents present in the ARC muscle fibers. We describe these currents in this and the following two papers. These results constitute the first detailed description of ion currents in a molluscan muscle and lay the foundation for further study, to be presented in subsequent papers, of the roles of two currents that we have indeed found to be modulated in ways likely to contribute to the modulation of contraction. 3. In this paper we first describe the general electrophysiological characteristics of the dissociated fibers and present evidence that the fibers can be adequately space clamped. 4. The physiological operating voltage range of the nonspiking ARC muscle most likely extends from about -80 to about -25 mV. The steady-state current-voltage (I-V) relation of total membrane current rectifies inwardly in the negative and outwardly in the positive portion of this voltage range, with a plateau region of high or even negative slope resistance separating the two regions of rectification. 5. The current responsible for the inward rectification at negative voltages is a classical inwardly rectifying K current. It is activated by hyperpolarization with quasi-instantaneous kinetics; its whole I-V relation shifts along the voltage axis in a Nernstian manner with altered extracellular K+ concentration; it is blocked by low extracellular Ba2+ and Cs+, and the block is promoted by hyperpolarization.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Characterization of the membrane ion currents of a model molluscan muscle, the accessory radula closer muscle of Aplysia californica. II. Depolarization-activated K currents.

1. The accessory radula closer (ARC) muscle of Aplysia californica and its innervation is a model preparation for the study of the neural and cellular mechanisms of behavioral plasticity. Much of the plasticity is mediated by release of neurotransmitters and peptide cotransmitters that modulate contractions of the muscle. Preliminary to investigating the cellular mechanisms of action of these modulators, we have characterized the major membrane ion currents present in the unmodulated ARC muscle and their likely roles in normal contraction. We have studied single dissociated but functionally intact ARC muscle fibers under voltage clamp. This is the second of three papers describing this work. In the preceding paper we described the electrophysiological properties of the fibers at hyperpolarized voltages, and characterized the two major hyperpolarized-activated currents present, a classical inwardly rectifying K current and a Cl current induced by elevated intracellular Cl-. 2. In this paper we dissect the large outward current that becomes activated when the fibers are depolarized above -50 or -40 mV. We find that this current consists of two major depolarization-activated K currents, a fast transient "A"-type current and a slower maintained delayed rectifier, with perhaps a small component of Ca(2+)-activated K current. 3. The A current begins to activate with voltage steps above -50 or -40 mV. It activates in milliseconds, then inactivates virtually completely within 100-200 ms. It is fully available for activation below -80 mV, and almost completely inactivated above -40 mV. It is Ca2+ independent, half-maximally blocked by approximately 3 mM 4-aminopyridine (4-AP) but only 460 mM tetraethylammonium (TEA). 4. The delayed rectifier both activates and inactivates more slowly and more positive than the A current. Thus it begins to activate only above -30 or -20 mV; it activates in tens of milliseconds, then inactivates incompletely over several seconds; it is fully available below -70 mV and inactivated above 0 mV. It is Ca2+ independent, half-maximally blocked by 10 mM TEA and 3-10 mM 4-AP. 5. In the following paper we describe a depolarization-activated Ca current that underlies the K currents and most likely provides Ca2+ necessary for contraction of the muscle. By activating simultaneously with the Ca current, the K currents serve to prevent spikes, so that the depolarization is confined to a range where small voltage changes provide fine control over a wide range of contraction strengths.

Animals↗
PubMed1994

Characterization of the membrane ion currents of a model molluscan muscle, the accessory radula closer muscle of Aplysia californica. III. Depolarization-activated Ca current.

1. The accessory radula closer (ARC) muscle of Aplysia californica and its innervation is a model preparation for the study of the neural and cellular mechanisms of behavioral plasticity. Much of the plasticity is due to modulation of contractions of the muscle by a variety of neurotransmitters and peptide cotransmitters. Preliminary to investigating the cellular mechanisms of this modulation, we have characterized the major membrane ion currents present in the unmodulated ARC muscle and their likely roles in normal contraction. We have studied single dissociated but functionally intact ARC muscle fibers under voltage clamp. This is the last of three papers describing this work. In the first paper we characterized two currents prominent at hyperpolarized voltages, a classical inwardly rectifying K current and a Cl current induced by elevated intracellular Cl-. In the second paper we examined two large outward K currents activated at more depolarized voltages, an "A" current and a delayed rectifier. 2. In this paper, we describe an inward depolarization-activated Ca current that underlies and is normally completely masked by the K currents and is revealed when they are blocked. 3. The Ca current begins to activate above -40 or -30 mV. It is fully available for activation at voltages more negative than -60 mV. It activates in milliseconds, then inactivates relatively slowly with maintained depolarization. The current is larger and inactivates slower when it is carried by Ba2+ rather than Ca2+. The inactivation is current rather than voltage dependent. The current is blocked by Co2+, Cd2+, and with a characteristic time dependence, by the dihydropyridine Ca-channel antagonist nifedipine. 4. These properties of the current characterize it as a high-threshold, L-type Ca current. 5. This current most likely provides Ca2+ necessary for contraction of the ARC muscle.

Animals↗
PubMed1999

Modulation of radula opener muscles in Aplysia.

We observed fibers immunoreactive (IR) to serotonin (5-HT), the myomodulins (MMs), and FMRFamide on the I7-I10 complex in the marine mollusk Aplysia californica. The I7-I10 muscle complex, which produces radula opening, is innervated primarily by one motor neuron, B48. B48 is MM-IR and synthesizes authentic MM(A). When B48 is stimulated in a physiological manner, cAMP levels are increased in opener muscles. cAMP increases also are seen when the MMs are applied to opener muscles but are not seen with application of the B48 primary neurotransmitter acetylcholine (ACh). Possible physiological sources of 5-HT and FMRFamide are discussed. When modulators are applied to resting opener muscles, changes in membrane potential are observed. Specifically, 5-HT, MM(B), and low concentrations of MM(A) all depolarize muscle fibers. This depolarization is generally not sufficient to elicit myogenic activity in the absence of neural activity under "rest" conditions. However, if opener muscles are stretched beyond rest length, stretch- and modulator-induced depolarizations can summate and elicit contractions. This only occurs, however, if "depolarizing" modulators are applied alone. Thus other modulators (i.e., FMRFamide and high concentrations of MM(A)) hyperpolarize opener muscle fibers and can prevent depolarizing modulators from eliciting myogenic activity. All modulators tested affected parameters of motor neuron-elicited contractions of opener muscles. MM(B) and 5-HT increased contraction size over the range of concentrations tested, whereas MM(A) potentiated contractions when it was applied at lower concentrations but decreased contraction size at higher concentrations. FMRFamide decreased contraction size at all concentrations and did not affect relaxation rate. Additionally, the MMs and 5-HT increased muscle relaxation rate, decreased contraction latency, and decreased the rate at which tension was developed during motor neuron-elicited muscle contractions. Thus these modulators dramatically affect the ability of opener muscles to follow activity in the opener motor neuron B48. The possible physiological significance of these findings is discussed.

Animals↗
PubMed2006

Chemical constituents of malagasy liverworts, part V: prenyl bibenzyls and clerodane diterpenoids with nitric oxide inhibitory activity from Radula appressa and Thysananthus spathulistipus.

3Beta,4beta:15,16-diepoxy-13(16),14-clerodadiene (1) and a new clerodane diterpenoid designated thysaspathone (2) were isolated from the liverwort Thysananthus spathulistipus, while Radula appressa produced radulannin A (3), radulannin L (4), 2-geranyl-3,5-dihydroxybibenzyl (5), 2(S)-2-methyl-2-(4-methyl-3-pentenyl)-7-hydroxy-5-(2-phenylethyl) chromene (o-cannabichromene) (6), 6-hydroxy-4-(2-phenylethyl) benzofuran (7), and o-cannabicyclol (8). All of the isolated compounds inhibited nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells and the greatest inhibition was attributed to compound 5, with an IC50 value of 4.5 microM.

Animals↗
PubMed2006

Diterpenoids and aromatic compounds from the three New Zealand liverworts Jamesoniella kirkii, Balantiopsis rosea, and Radula species.

Three new aromatics were isolated from the New Zealand liverwort Balantiopsis rosea. A new bibenzyl was isolated from an unidentified Radula species, together with known bibenzyls. Jamesoniella kirkii yielded three known ent-isopimarane and two ent-kaurane diterpenoids. Their structures were confirmed by NMR techniques, chemical reaction, and X-ray crystallographic analysis.

Abietanes↗
PubMed2006

Variability of motor neuron spike timing maintains and shapes contractions of the accessory radula closer muscle of Aplysia.

The accessory radula closer (ARC) muscle of Aplysia has long been studied as a typical "slow" muscle, one that would be assumed to respond only to the overall, integrated spike rate of its motor neurons, B15 and B16. The precise timing of the individual spikes should not much matter. However, but real B15 and B16 spike patterns recorded in vivo show great variability that extends down to the timing of individual spikes. By replaying these real as well as artificially constructed spike patterns into ARC muscles in vitro, we examined the consequences of this spike-level variability for contraction. Replaying the same pattern several times reproduces precisely the same contraction shape: the B15/B16-ARC neuromuscular transform is deterministic. However, varying the timing of the spikes produces very different contraction shapes and amplitudes. The transform in fact operates at an interface between "fast" and "slow" regimens. It is fast enough that the timing of individual spikes greatly influences the detailed contraction shape. At the same time, slow integration of the spike pattern through the nonlinear transform allows the variable spike timing to determine also the overall contraction amplitude. Indeed, the variability appears to be necessary to maintain the contraction amplitude at a robust level. This phenomenon is tuned by neuromodulators that tune the speed and nonlinearity of the transform. Thus, the variable timing of individual spikes does matter, in at least two, functionally significant ways, in this "slow" neuromuscular system.

Action Potentials↗
PubMed2005

Investigation of antimicrobial activity of Pelargonium radula (Cav.) L'Hérit.

Antimicrobial activities of two ethanolic extracts, made from fresh and dried leaves of Pelargonium radula (Cav.) L'Hérit, were tested against fourteen species of bacteria and fifteen species of fungi. The well-diffusion method indicated the strongest activity against Pseudomonas aeruginosa. The broth dilution method revealed that the most sensitive microorganisms were Bacillus pumilus, Bacillus subtilis, Escherichia coli and Serratia marcescens. Extract prepared from fresh leaves showed significantly higher antimicrobial activity than the extract prepared from dried leaves.

Anti-Infective Agents↗
PubMed2005

Antimicrobial activity of flavonoids from Pelargonium radula (Cav.) L'Hérit.

Flavonoids from Pelargonium radula (Cav.) L'Hérit were purified by column chromatography. Two fractions were obtained: F1 (main flavonoid isoquercitrin) and F2 (main flavonoid rutin). In vitro antimicrobial activity of F1 and F2 were tested against eleven species of bacteria and eleven species of fungi. Both fractions demonstrated strong inhibitory activity against Staphylococcus aureus, Proteus rettgeri, Candida tropicalis and Microsporum gypseum. Staphylococcus sp. (coagulase-negative) and Candida lusitaniae were strongly inhibited only by fraction F1 and Fusarium graminearum only by fraction F2.

Anti-Infective Agents↗
PubMed1994

Enhancement of Ca current in the accessory radula closer muscle of Aplysia californica by neuromodulators that potentiate its contractions.

A major goal of neuroscience is to identify the neural and cellular mechanisms of behavior and its plasticity. Progress toward this goal has come particularly from work with a small number of tractable model preparations. One of these is the simple neuromuscular circuit consisting of the accessory radula closer (ARC) muscle of the mollusk Aplysia californica and its innervating motor and modulatory neurons. Contraction of the ARC muscle underlies a component of Aplysia feeding behavior, and plasticity of the behavior is in large part due to modulation of the amplitude and duration of the contractions of the muscle by a variety of modulatory neurotransmitters and peptide cotransmitters, among them the small cardioactive peptides (SCPs), myomodulins (MMs), and serotonin (5-HT). We have studied single dissociated ARC muscle fibers in order to determine whether modulation of membrane ion currents in the muscle might underlie these effects. First, we confirmed that the dissociated fibers were functionally intact: just as with the whole ARC muscle, their contractions were potentiated by 5-HT and SCPB and potentiated as well as depressed by MMA, and their cAMP content was greatly elevated by 5-HT, SCPA and SCPB, and to a lesser extent by MMA and MMB. Next, using voltage-clamp techniques, we found that two ion currents present in the fibers were indeed modulated. The fibers possess a dihydropyridine-sensitive, high-threshold "L"-type Ca current. This current was enhanced by the modulators that potentiate ARC-muscle contractions--5-HT, SCPA and SCPB, and MMA and MMB--but not by buccalinA, a modulator that does not act directly on the ARC muscle. All of the potentiating modulators, as well as elevation of cAMP in the fibers by forskolin or a cAMP analog, maximally enhanced the current about twofold and mutually occluded each other's effects. Since the Ca current supplies Ca2+ necessary for contraction of the muscle, the enhancement of the current is a good candidate to be a major mechanism of the potentiation of the contractions. In the following article we report that the modulators also, to different degrees, activate a distinctive K current and thereby depress the contractions. Net potentiation or depression then depends on the balance between the relative strengths of the modulation of the two ion currents.

Animals↗
PubMed1994

Activation of K current in the accessory radula closer muscle of Aplysia californica by neuromodulators that depress its contractions.

The neural and cellular mechanisms of plasticity apparent in the feeding behavior of the mollusk Aplysia californica have been extensively studied in a simple neuromuscular circuit consisting of the accessory radula closer (ARC) muscle and its innervating motor and modulatory neurons. In this circuit, the plasticity is largely due to modulation of the amplitude and duration of the contractions of the muscle by a variety of modulatory neurotransmitters and peptide cotransmitters, among them the small cardioactive peptides (SCPs), myomodulins (MMs), and serotonin (5-HT). We have studied dissociated but functionally intact ARC muscle fibers to determine whether modulation of membrane ion currents in the muscle might underlie these effects. Using voltage-clamp techniques, we found that two currents were indeed modulated. In the preceding article, we proposed that enhancement of "L"-type Ca current is the mechanism by which the modulators potentiate the amplitude of ARC-muscle contractions. Here, we report that the modulators also activate a distinctive K current. Large K currents were activated, in particular, by MMA, while MMB, the SCPs, and 5-HT activated much smaller currents most likely of the same kind. Buccalins, modulators that do not act directly on the ARC muscle, were ineffective. The modulator-induced K current was strongly enhanced by depolarization, but relatively slowly so that its amplitude continued to increase for several hundred milliseconds following a depolarizing voltage step. The current was Ca2+ independent, not readily blocked by extracellular Cs+ or Ba2+ and only by high concentrations of tetraethylammonium. However, it was almost completely blocked by as little as 10 microM 4-aminopyridine. In contrast to the modulator-induced enhancement of Ca current, activation of the K current was not significantly mimicked by elevation of cAMP. In the intact as well as the dissociated ARC muscle, although low levels of all of the modulators potentiate contractions, even moderate levels of MMA strongly depress them, whereas the other modulators depress them weakly only at high concentrations. The modulator-induced K current appears well suited to counteract depolarization of the muscle and thus limit activation of the "L"-type Ca current that provides Ca2+ essential for contraction. We therefore propose that the modulators depress ARC-muscle contractions in large part by activating the K current. This occurs simultaneously with the enhancement of the Ca current; net potentiation or depression then depends on the balance between the relative strengths of the modulation of the two ion currents.

Animals↗