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R M Harris-Warrick

Publications and source records attributed to R M Harris-Warrick.

At least 73 records · Page 4Linked to original sources
PubMed1987

cAMP elevation modulates physiological activity of pyloric neurons in the lobster stomatogastric ganglion.

1. We analyzed the physiological effects of the adenylate cyclase activator forskolin, and other adenosine 3',5'-cyclic monophosphate (cAMP)-elevating agents, on neurons of the pyloric circuit from the stomatogastric ganglion of the lobster Panulirus interruptus. Agents were bath applied to pyloric neurons either in the synaptically intact pyloric circuit or following isolation from all known synaptic input. 2. Several cAMP-elevating agents, including forskolin, 3-isobutyl-1-methylxanthine, Ro20-1724, and 8-bromo-cAMP, generated similar motor patterns from the pyloric circuit. The motor patterns exhibited an increased cycle frequency and enhanced spike activity from all classes of pyloric neurons. Since these agents differ both in structure and site of action in the cAMP pathway, their physiological effects on the motor pattern probably result from increased cAMP levels in pyloric neurons. 3. When forskolin was applied to synaptically isolated neurons, it caused a strong activation or enhancement of activity of all pyloric cells. However, it induced different types of activity in different cells, including the induction of bursting pacemaker potentials in one cell type, activation of plateau potentials in another, and depolarization with activation or enhancement of tonic spike activity in the remaining cells. Thus there is no single physiological response to cAMP elevation in the pyloric circuit; its effects can be quite diverse, mediating several activity states, in different cells. 4. Radioimmunoassays were performed on whole stomatogastric ganglia to determine whether known neuromodulators can affect cAMP concentrations. Both forskolin and octopamine increased cAMP levels, whereas dopamine, serotonin, proctolin, and FMRFamide did not appreciably affect cAMP levels. The physiological effects of octopamine and forskolin are similar in most, but not all, pyloric cells. Octopamine is thus a candidate neuromodulator whose actions may be mediated, at least in part, by increased cAMP in some pyloric cells; however, forskolin does not completely mimic the physiological effects of octopamine on all pyloric neurons, suggesting that octopamine can also act by other biochemical mechanisms.

1-Methyl-3-isobutylxanthine↗
PubMed1987

Multiple mechanisms of bursting in a conditional bursting neuron.

The anterior burster (AB) neuron in the stomatogastric ganglion of the spiny lobster, Panulirus interruptus, is a conditional burster in the pyloric motor circuit. Bath application of the monoamines dopamine, serotonin, and octopamine induces rhythmic bursting pacemaker potentials in a silent, synaptically isolated AB cell. However, each amine produces a unique and characteristic burst shape, resulting from different ionic dependences of the burst mechanisms. Bursting induced by serotonin or octopamine is critically dependent upon sodium entry through tetrodotoxin-sensitive channels; dopamine-induced bursting is not TTX-sensitive. Dopamine-induced bursting is abolished when extracellular calcium is reduced to 25% of normal; serotonin- and octopamine-induced bursts continue in this saline, although they are abolished in salines with calcium reduced to 10% or less of normal. Quantitative differences between the amines are also seen in the tetraethylammonium (TEA) sensitivity of the burst amplitude and in the dependence of the interburst hyperpolarization on extracellular potassium. These experiments demonstrate that there are both quantitative and qualitative differences in the ionic currents underlying every phase of the bursts induced by the 3 amines. Thus, a single neuron can burst via more than one ionic mechanism.

Animals↗
PubMed1986

Aminergic modulation in lobster stomatogastric ganglion. I. Effects on motor pattern and activity of neurons within the pyloric circuit.

We investigated the effects of dopamine, octopamine, and serotonin on the motor output of the pyloric circuit in the stomatogastric ganglion of the lobster, Panulirus interruptus. Amines were bath applied at concentrations from 10(-8) to 10(-4) M, and the responses of the six classes of pyloric neurons were monitored both intracellularly and extracellularly. Each amine modified the pyloric motor pattern in a specific way. In addition, dopamine and octopamine were each able to produce different motor patterns at different concentrations. Amine effects on pyloric neurons included initiation and enhancement or inhibition of spike activity, changes in the phase relationships of neurons, and changes in the cycle frequency of the pyloric rhythm. These results show that the motor pattern produced by this well-studied central pattern generator circuit is highly plastic and can be modulated by endogenous biogenic amines.

Action Potentials↗
PubMed1986

Aminergic modulation in lobster stomatogastric ganglion. II. Target neurons of dopamine, octopamine, and serotonin within the pyloric circuit.

In the preceding paper, we describe how dopamine, octopamine, and serotonin modulate the neural circuit generating a well-described motor pattern, the pyloric rhythm of the stomatogastric ganglion in the spiny lobster, Panulirus interruptus. In this paper, we identify the neurons within the pyloric circuit that are directly affected by each amine. We accomplished this by isolating each pyloric neuron from all known synaptic input, using a combination of Lucifer yellow photoinactivation of presynaptic neurons and pharmacological blockade by pyloric neurotransmitters. Dopamine, octopamine, and serotonin were bath applied to the preparation, and the responses of synaptically isolated neurons were recorded. Each amine had a unique constellation of effects on the neurons of the pyloric circuit. Almost every neuron in the circuit was directly affected by each amine. Dopamine and octopamine modulated every neuron, whereas serotonin affected four of the six cell types. Each amine had multiple effects among pyloric neurons including the induction of endogenous rhythmic bursting activity, initiation or enhancement of tonic firing activity, and inhibition accompanied by hyperpolarization. All three amines induced rhythmic bursting in one neuron (the AB neuron), but the form of the underlying slow-wave membrane-potential oscillations was different with octopamine than with dopamine and serotonin. Our knowledge of the effects of each amine on each pyloric neuron, combined with the extensive knowledge of the synaptic organization of the pyloric circuit, has allowed us to explain qualitatively the major aspects of the unique variants of the pyloric motor rhythm that each amine produces in the synaptically intact circuit.

Afferent Pathways↗
PubMed1985

Distribution of serotonergic neurons and processes in the lamprey spinal cord.

The distribution of serotonin in the spinal cord in two species of lamprey, Ichthyomyzon unicuspis and Petromyzon marinus, was studied by indirect immunofluorescence techniques. Multipolar cell bodies containing serotonin-like immunoreactivity were found along the length of the spinal cord, along the midline and slightly ventral to the central canal. These cell bodies send a diffuse projection of processes throughout the spinal cord, including: (1) a dense projection to the ventral surface; (2) a strong projection to the ventromedial longitudinal fiber tracts; (3) a less intense projection to the dorsal longitudinal fiber tracts; and (4) a weak projection to the lateral fiber tracts. Lesion experiments showed that processes descending from the brain or rostral spinal cord provide a major projection to the lateral fiber tracts and smaller contributions to the dorsal and ventromedial fiber tracts. Fluorescent processes were also observed in the dorsal roots and serotonergic peripheral cell bodies were seen adjacent to the dorsal roots. Our results suggest that the serotonergic innervation of the lamprey spinal cord arises from three sources: spinal interneurons, descending tracts and peripheral (possibly sensory) input. This provides an anatomical substrate for our recent finding that serotonin modulates the central pattern generator for locomotion in the lamprey spinal cord.

Animals↗
PubMed1985

Serotonin modulates the central pattern generator for locomotion in the isolated lamprey spinal cord.

The central pattern generator for locomotion in the spinal cord of the lamprey can be activated in vitro by the addition of D-glutamate to the bathing saline. Serotonin has no effects when bath-applied alone, but it modulates the D-glutamate-activated swimming pattern. Three major effects are observed: a dose-dependent reduction in the frequency of rhythmic ventral root burst discharge; enhancement of the intensity of burst discharge, due in part to the recruitment of previously inactive motoneurones; prolongation of the intersegmental phase lag. Motoneurone activation appears to result from enhanced synaptic drive from the central pattern generator; no direct effects of serotonin on the motoneurones themselves (resting potential, input resistance or threshold for action potential generation) were observed. Theoretical and experimental studies suggest that the prolongation of the intersegmental phase lag results at least in part from differential effects of serotonin on segmental oscillators in different parts of the spinal cord. Isolated caudal pieces of the cord were more strongly affected by serotonin than isolated rostral pieces. We propose that serotonin may be an endogenous modulator of the central pattern generator for locomotion in the lamprey. It may have a role in the generation of a family of related undulatory movements (swimming, crawling, burrowing) by a single central pattern generator.

Animals↗
PubMed1984

Strychnine eliminates alternating motor output during fictive locomotion in the lamprey.

The motor program for swimming in the lamprey includes rhythmic bursting of motoneurons with output from the two sides of a spinal segment alternating strictly out of phase. This motor program can be observed in vitro in the isolated spinal cord. Addition of strychnine (5-10 microM) can selectively eliminate the alternation between sides without blocking the temporal pattern of bursting on each side. This result suggests that temporal bursting on the right and left sides of the spinal cord is generated by independent neuronal oscillators, while the alternation between the two sides results from crossed inhibitory coupling between these oscillators.

Animals↗
PubMed1984

Serotonergic innervation and modulation of the stomatogastric ganglion of three decapod crustaceans (Panulirus interruptus, Homarus americanus and Cancer irroratus).

The serotonergic innervation of the stomatogastric ganglion (STG) of three decapod crustacean species, Panulirus interruptus, Homarus americanus and Cancer irroratus, was studied. Immunohistochemical techniques were used to study the distribution of serotonin-like staining in regions of the stomatogastric system in the three species. In C. irroratus and H. americanus, but not in P. interruptus, serotonin-like staining was found in fibres in the stomatogastric nerve and in neuropil regions of the STG. High performance liquid chromatography confirmed the presence of serotonin in STG of C. irroratus and H. americanus, but serotonin was not found in STG of P. interruptus. Electrophysiological experiments showed that the pyloric motor output of the STG of all three species was influenced by bath applications of serotonin. The STG of P. interruptus responded to serotonin concentrations as low as 10-9M; however the STG of the other two species did not respond until serotonin concentrations in excess of 10-6M were applied. We conclude that serotonin may play a hormonal role in the control of the STG of P. interruptus, but is likely to be a neurotransmitter released by inputs to the STG of H. americanus and C. irroratus.

Animals↗
PubMed1984

Cellular mechanisms for modulation of posture by octopamine and serotonin in the lobster.

Injection of the monoamines octopamine and serotonin into the hemolymph of lobsters causes them to assume opposing static postures: octopamine causes a tonic extension of all extremities, while serotonin induces a tonic flexion. These amines have been shown previously to act as circulating neurohormones and to cause contraction of isolated exoskeletal muscles. The opposing postures elicited by amine injection do not appear to arise from peripheral actions, however, since serotonin and octopamine have similar effects on both flexor and extensor muscles. Instead, the amines are present within the central nervous system where they are probably released synaptically to activate coordinated patterns of tonic motor activity generating the observed postures. These motor patterns have been recorded from abdominal ganglia and involve the synchronized activation and inhibition of multiple excitatory and inhibitory motoneurons innervating the postural flexor and extensor muscles. These effects can be observed in an isolated abdominal ganglion. To begin a search for the cellular targets of amine action within the central nervous system, we recorded from identified postural motoneurons in abdominal ganglia. In two motoneurons that act to produce postural extension, octopamine reduced and serotonin raised the apparent threshold for action potential generation recorded in the somata. The amines do not significantly affect the resting potential or input resistance of the motoneurons measured in the cell bodies. Although the amine effect on motoneuron excitability could be due to actions directly on the motoneurons, our evidence suggests that at least part of the effect results from activation or inhibition of premotor interneurons: (1) an increase in EPSP frequency is observed in the motoneurons during octopamine superfusion, while a small decrease is observed during serotonin superfusion; (2) the amine effects on action potential threshold are abolished by cobalt ion. These results suggest that octopamine and serotonin have dual effects on posture: within the central nervous system, they act specifically to generate coordinated motor patterns for flexion or extension; as circulating neurohormones, they act nonspecifically to enhance the responses of exoskeletal muscles to motoneuronal activation.

Animals↗
PubMed1981

Noradrenaline augments tetanic potentiation of transmitter release by a calcium dependent process.

Noradrenaline (25 microM-50 microM) causes an increase in tetanic potentiation and in the augmentation phase of posttetanic potentiation of miniature and plate potential frequency. These effects were observed at both the frog and the rat neuromuscular junctions. The action of noradrenaline on quantal transmitter release depends on the presence of calcium ions in the extracellular medium.

Animals↗
PubMed1980

Subunit interactions inhibit the binding of beta nerve growth factor to receptors on embryonic chick sensory neurons.

The binding of the beta nerve growth factor subunit in the 7 S nerve growth factor complex to the two nerve growth factor receptors on chick embryo dorsal root ganglion cells was investigated. Under conditions where the 7 S nerve growth factor complex is maximally stable (in the presence of excess alpha and gamma subunits and of 20 to 30 microM zinc ion), no binding to either receptor was detectable. The time course of the decrease in the binding of beta nerve growth factor to the receptors upon addition of alpha and gamma subunits and zinc ion paralleled the formation of the 7 S complex. Addition of alpha and gamma subunits and zinc ion to the bisdes-arginine118-nerve growth factor, which does not re-form the 7 S complex, failed to inhibit the binding of the derivative to either receptor. While the alpha subunit alone had no effect on beta nerve growth factor binding, the gamma subunit decreased its binding in proportion to the amount of complex formed between these two subunits, suggesting that the beta . gamma complex, like the 7 S complex, does not bind to nerve growth factor receptors.

Animals↗
PubMed1980

A peptide action in a lobster neuromuscular preparation.

The neuropeptide proctolin causes a sustained contraction of the opener muscle of the dactyl of the lobster walking leg. This substance acts directly on the muscle at concentrations as low as 10(-10)M. The contraction is dependent on extracellular calcium. Neither a significant depolarization nor a detectable change in the input resistance accompanies the response. No presynaptic action of proctolin is indicated; excitatory and inhibitory junctional potential sizes and the frequency of spontaneous miniature excitatory junctional potentials are unaffected.

Animals↗
PubMed1980

Amines and a peptide as neurohormones in lobsters: actions on neuromuscular preparations and preliminary behavioural studies.

In this communication we report that four substances, thought to function as neurohormones in Crustacea, all produce long-term changes in the physiological properties of lobster opener muscle preparations. The substances are the amines, octopamine, serotonin and dopamine, and the peptide, proctolin. The actions of these substances are superimposed on the normal synaptic apparatus that utilizes the amino acids GABA and glutamate (probably) as the inhibitory and excitatory neurotransmitter compounds. Serotonin acts on excitatory and inhibitory nerve endings to facilitate transmitter release and directly on muscle fibres to produce a contracture and to induce the appearance of Ca2+ action potentials. The latter two actions of serotonin are shared by proctolin and octopamine as well. Dopamine, on the other hand, relaxes muscle baseline tension. The mechanism of action of these substances at their target site (or sites) has been explored with electrophysiological and biochemical techniques and the results will be presented. In addition preliminary behavioural experiments have been carried out with serotonin and octopamine. These substances produce opposite postures when injected into lobsters. The amines act on central ganglia to produce these effects where they cause a programmed readout of firing of neurones that will produce either a flexed posture (serotonin) or an extended posture (octopamine).

Action Potentials↗
PubMed1979

Nerve growth factor receptors. Characterization of two distinct classes of binding sites on chick embryo sensory ganglia cells.

Steady state and kinetic studies on the binding of 125I-beta nerve growth factor (NGF) to single cells from sensory ganglia of 8-day-old chick embryos show two distinct, saturable binding sites with dissociation constants of Kd(I) = 2.3 X 10(-11) M and Kd(II) = 1.7 X 10(-9) M. The difference in the affinities is due to different rate constants of dissociation (k-1(I) = 10(-3) s-1, k-1(II) = 2 X 10(-1 s-1). The association to both sites is apparently diffusion controlled (k+1(I) = 4.8 X 10(7) M-1s-1, k+2(II) = 10(7) to 10(8) M-1s-1). The binding of betaNGF to both sites is specific, since none of a number of hormones or proteins tested compete for the binding of 125I-betaNGF to either of those two sites. The heterogeneity of the binding of 125I-betaNGF is not due to heterogeneity of the 125I-betaNGF preparation nor to a negatively cooperative binding. In experiments where the dissociation of 125I-betaNGF is induced by the addition of saturating amounts of unlabeled betaNGF, the ratio of the 125I-betaNGF released with either of the two dissociation rate constants is solely dependent on the occupancy of the two sites before dissociation is started and is independent of the total occupancy of the sites during dissociation. The rate of dissociation of 125I-betaNGF from the higher affinity binding site I is accelerated by unlabeled betaNGF under conditions where the occupancy is both increased and decreased. Although the dissociation characteristics of 125I-beta NGF change with increasing times of exposure of the cells to the ligand, and 125I-beta NGF is degraded after it binds to the cells, these secondary processes do not interfere with the analysis of the binding data. At the lowest concentration of 125I-beta NGF used for the analysis less than 10% of the 125I-beta NGF is degraded. Both kinetic and steady state binding data reveal the two NGF binding sites at 2 degrees C as well as at 37 degrees C.

Animals↗
PubMed1979

The heterogeneity of nerve growth factor receptors.

Chick embryonic sensory ganglia cells have two specific nerve growth factor receptors, site I and site II receptors, whose binding affinities differ by two orders of magnitude. As judged by both steady state binding and kinetic data, the two receptors behave independently. The rate of dissociation of the labeled nerve growth factor from site I receptors is increased in the presence of unlabeled nerve growth factor even when its concentration is below that of the labeled growth factor used to equilibrate the cells, a phenomenon which cannot be explained by negative cooperativity. Site I receptors are present only on neurons while site II receptors are present on both neurons and nonneuronal cells. At the concentration of nerve growth factor which produces half maximal stimulation of neurite outgrowth 8% of site I and 0.1% of site II receptors are occupied. This occupancy of site II receptors falls to about 0.01% with bisdesarginine beta nerve growth factor, a derivative which is as biologically active as the unmodified factor but which binds with lower affinity to site II receptors. These data support the idea that interaction of nerve growth factor with site I receptors is responsible for the initiation of neurite outgrowth.

Animals↗
PubMed1978

Interspecies transformation in Bacillus: sequence heterology as the major barrier.

The relative contribution of DNA restriction and of sequence heterology as barriers to interspecies transfer of DNA was studied in the heterologous transformation of Bacillus subtilis recipients by DNA was studied in the heterologous transformation of Bacillus subtilis recipients by DNA isolated from B. globigii. Transformants were obtained at very low frequencies in the evolutionarily nonconserved aromatic region; high cotransfer of linked markers was observed. New mutations were introduced into the B. globigii intergenote sequence in the resulting hybrids; these markers could be transformed with high efficiency by both B. globigii and B. subtilis DNA, representing a 10(5)-fold increase in heterologous transforming efficiency. A restriction activity in B. globigii crude extracts inactivated the biological activity of B. subtilis and hybrid DNA but not B. globigii DNA in vitro, demonstrating different sites for restriction and modification between these species. In vivo, however, B. globigii and hybrid DNA transformed the B. globigii sequence in a hybrid recipient with the same efficiency. These results show that sequence heterology is the major barrier to interspecies transformation and that, in this system, enzymatic restriction does not prevent interspecies transformation.

Bacillus↗
PubMed1978

Interspecies transformation in Bacillus: mechanism of heterologous intergenote transformation.

Bacillus subtilis-Bacillus globigii hybrids were made by integration of the B. globigii aromatic region (aroB to aroE) as an intergenote in the B. subtillis chromosome. Transformation of the heterologous intergenote by B. subtillis DNA (or vice versa) occurred at about 10% of the frequency of homologous transformation by hybrid donors into the same region. Heterologous intergenote crosses were unusually sensitive to shear fragmentations of donor DNA to sizes less than 30 X 10(6) to 40 X 10(6) daltons. In all cases, the entire intergenote was transferred en bloc. Homologous transformation of intergenote markers by B. globigii DNA was not unusually shear sensitive, and linkage was normal for markers in the intergenote. A model is proposed in which efficient heterologous intergenote transformation occurs by recognition and base pairing of homologous DNA sequences of both flanks of the intergenote.

Bacillus↗