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R Gillette

Publications and source records attributed to R Gillette.

At least 37 records · Page 2Linked to original sources
PubMed1990

pH-sensitive, Ca2+/calmodulin-dependent phosphorylation of unique protein in molluscan nervous system.

Intracellular pH and Ca2+ are prominent co-regulators of neuron excitability that act on ion channels. In looking for a possible mechanism of their action, we tested their combinatorial effect on the phosphorylation state of nervous system proteins. 32PO4 labelling in endogenous phosphorylation reactions of homogenates of nervous tissue of the sea-slug Pleurobranchaea showed steep pH sensitivity in protein migrating at a molecular mass of 108 kDa with pI 6.9-7.0 (pp108). Phosphorylation of pp108 was highest below reaction pH 7.0 and declined steeply as pH rose to 7.4 pp108 phosphorylation was Ca2+/calmodulin-dependent. pp108 constituted a significant part of the total protein (0.15%) and phosphoprotein (8.9%) of the nervous system. The specifically and uniquely combinatorial pH and Ca2+ sensitivity of the phosphorylation of pp108, and its relative abundance, suggest that it could mediate integrated actions of H+ and Ca2+ in the molluscan neuron.

Animals↗
PubMed1988

Enhancement of cyclic AMP-dependent sodium current by the convulsant drug pentylenetetrazol.

The convulsant drug pentylenetetrazol (PTZ) causes paroxysmal depolarizing shifts (PDS) and bursting in molluscan neurons. PDS has been found to be accompanied by increased levels of cyclic AMP (cAMP) and supported by persistent Na+ current. In neurons of the snail Lymnaea stagnalis the blocker of cAMP degradation isobutylmethylxanthine (IBMX) mimicks PTZ action. Na+ dependence of PTZ-induced inward shift in holding current in voltage-clamped cells supports the potential Na+ current origin of PDS. Intracellular cAMP injection elicits a transient Na+ current whose amplitude and duration are enhanced by both PTZ and IBMX. PTZ may cause PDS partly through slowing cAMP degradation, thus enhancing the cAMP-dependent Na+ current. PDS-generated bursts cause partial inactivation of the Na+ current, which may contribute towards burst termination.

1-Methyl-3-isobutylxanthine↗
PubMed1988

Cyclic AMP-stimulated sodium current in identified feeding neurons of Lymnaea stagnalis.

Iontophoretic injection of cAMP elicits a slow, transient inward current in identified buccal feeding motoneurons and in the giant cerebral interneuron of the snail, Lymnaea stagnalis. The current is voltage independent, and is abolished in the absence of extracellular Na+. Application of the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX) causes a marked increase in both amplitude and duration of cAMP-stimulated inward current. The amplitude of the current is reduced following prolonged application of depolarizing pulses to the cell. However, generation of high-frequency bursts of action potentials lasting up to 20 s has no significant effect on the amplitude of the cAMP-induced current measured subsequently. Bath application of the cAMP analogue 8-chlorophenylthio-cAMP or of IBMX leads to enhanced bursting activity in buccal motoneurons. It is suggested that cAMP sensitivity in feeding motoneurons provides a mechanism for adjusting the cells' responsiveness to rhythmic synaptic inputs during the generation of feeding motor output.

1-Methyl-3-isobutylxanthine↗
PubMed1988

Regulation of cAMP-stimulated ion current by intracellular pH, Ca2+, and calmodulin blockers.

1. Iontophoretic injection of adenosine 3',5'-cyclic monophosphate (cAMP) into identified neurons elicited a slow transient Na+ current whose amplitude and duration were sensitive to altered intracellular pH (pHi), calmodulin blocking drugs, depolarization, and manipulations of internal and external Ca2+. 2. Intracellular acidification between resting pHi to several tenths of a pH unit increased the amplitude of the cAMP-stimulated current and prolonged its duration. 3. Intracellular alkalinization of similar magnitude also increased the amplitude and duration of the current response. The effects of alkalinization were somewhat labile. In cells alkalinized by NH4+-containing salines, washout of NH4+ with normal saline caused acidification and further enhanced the cAMP current response. The immediacy of the increase and the dual acid/basic sensitivity of the response suggest an accommodative process whereby the responsiveness of the cell to cAMP adapts to a maintained pHi. 4. The calmodulin blockers trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide increased the amplitude and duration of the current response. Phorbol ester activators of Ca2+/phospholipid-dependent kinase had no effect on the current. 5. Periods of depolarization preceding tests significantly reduced current response amplitude. This effect was dependent on saline Ca2+ and was blocked by Co2+. 6. Intracellular injection of the Ca2+ chelator ethylene glycol-bis(beta-aminoethyl ether)N,N,N',N',-tetraacetic acid also augmented the amplitude and duration of the current response. 7. The above effects are consistent with a possible common site of action on cAMP degradation. This interpretation is consistent with previous evidence for pH-sensitive and Ca2+/calmodulin-dependent cAMP phosphodiesterase activity in Pleurobranchaea nervous tissue.

Animals↗
PubMed1987

Calcium dependence of voltage sensitivity in adenosine 3',5'-cyclic phosphate-stimulated sodium current in Pleurobranchaea.

1. Ionophoretic injection of cyclic AMP into a voltage-clamped molluscan neurone caused a transient slow inward current (Isi) whose amplitude was enhanced by depolarization. Na+-replaced salines abolished the current, placing it with cyclic AMP-stimulated Na+ currents of other gastropod species. 2. Isi amplitude was suppressed by extracellular Ca2+. The amplitude increased up to 4-fold at holding potentials of -50 mV in nominally Ca2+-free saline. Ion substitutions showed that Ca2+ suppressed Isi more effectively than Mg2+, Co2+, Cd2+, Mn2+, Ba2+ or Sr2+. 3. Voltage sensitivity of Isi was abolished by low-Ca2+ salines, by the Ca2+ current blocker Co2+ and by substitution of Ba2+ or Sr2+ as Ca2+ channel current carriers. In such salines Isi showed no appreciable change in amplitude at holding potentials between -70 and -25 mV. 4. Intracellular injection of the Ca2+ chelator EGTA both augmented the amplitude of the current and its duration. EGTA injection failed to suppress the Ca2+-dependent voltage sensitivity of Isi. Intracellular injection of concentrated 3-N-(morpholino) propanesulphonic acid (MOPS) pH buffer to inhibit secondary, Ca2+-dependent intracellular acidification also failed to suppress the voltage sensitivity, as did injections of a mixed EGTA and MOPS solution. 5. While the data indicate a requirement for extracellular Ca2+ in conferring voltage sensitivity, they do not support a role for an intracellular action. An extracellular binding site for Ca2+ could mediate the voltage sensitivity, either by local depolarization-dependent changes in extracellular Ca2+ concentration or through direct voltage-sensitive block of the Isi channel.

Action Potentials↗
PubMed1985

pH sensitivity of calmodulin distribution in nervous tissue fractions.

Alkalinization of nervous system extracts of the mollusk, Pleurobranchaea, from pH 7.0 to 8.0 markedly increases the ratio of soluble to total calmodulin. This effect is independent of pH effects on free Ca2+ concentration and is pronounced at micromolar (near intracellular) levels of Ca2+. These data may relate to recent evidence that Ca2+/calmodulin-activated cyclic nucleotide phosphodiesterase mediates the effects of small changes in intracellular pH (0.1-0.2 units) on the electrical activity of neurons. Calmodulin redistribution could reflect altered availability to stimulate phosphodiesterase activity and supports a role for calmodulin in mediating effects of intracellular pH fluxes on cellular activity.

Animals↗
PubMed1984

Functional roles and circuitry in an inhibitory pathway to feeding command neurones in Pleurobranchaea.

The paracerebral neurones (PCNs) of the brain of Pleurobranchaea californica serve a command role in the initiation of feeding behaviour (Gillette, Kovac & Davis, 1978). The PCNs are synaptically excited by food stimuli applied to the oral veil of hungry, naive animals. In food avoidance-conditioned animals, the PCNs are inhibited by a barrage of inhibitory postsynaptic potentials concomitant with the suppression of feeding (Davis & Gillette, 1978). In this paper, an interneuronal pathway is described which causes inhibition of the PCNs and potentially mediates the effects of learning. The inhibitory pathway consists of three serially connected interneurones. One population, designated the Interneurone 1s (Int-1s), monosynaptically inhibits the PCNs. A second population, the Interneurone 2s (Int-2s), excites the Int-1 population. They also excite other neurones of the brain including the metacerebral giant neurones. A third population, the Interneurone 3s (Int-3s), monosynaptically excites the Interneurone 2 population. Dual intracellular recordings and current injection show that ipsilateral members of the Int-2 population are electrically coupled via a nonrectifying connection. Contralateral members of the Int-2 population are excitatorily coupled via a polysynaptic pathway. The Int-1 population is phasically active during the rhythmic motor activity that underlies feeding. In the isolated nervous system Int-1 activity is phase-locked with rhythmic PCN activity; Int-1 activity occurs maximally at the end of a PCN burst, during the retraction phase of the cycle. Int-2 activity also occurs during the retraction phase. During actual feeding in the whole animal preparation, the Int-2s are also phasically active; maximal excitation occurs during buccal mass retraction and maximal inhibition during protraction and the bite. Stimulated activity in a single Int-2 can entirely suppress the rhythmic motor activity of the feeding network evoked by electrical stimulation of the stomatogastric nerve. The suppressant effects of Int-2 activity must be mediated widely within the feeding network because the rhythmic motor output so driven is not dependent on PCN spiking. Application of an appetitive chemosensory stimulus to whole and semi-intact animal preparations initiated feeding and elicited excitation of the Int-1 and Int-2 populations. Noxious chemosensory stimuli, such as a dilute soap solution or ethanol, elicited oral veil withdrawal and inhibition of the Int-2s by multiple inhibitory postsynaptic potentials.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1983

Phenothiazines mimic the action of cAMP in potentiating slow inward current in a bursting molluscan neuron.

Trifluoperazine and chlorpromazine, blockers of calmodulin action, potentiate slow inward current in molluscan neurons identically to the action of cAMP. The sulfoxide derivative of chloropromazine does not appreciably bind to calmodulin and also fails to enhance the inward current. The likelihood that these effects are mediated by cAMP via inhibition of a Ca2+-calmodulin-activated phosphodiesterase is discussed and related to other data.

Animals↗
PubMed1983

Ca2+ activated and pH sensitive cyclic AMP phosphodiesterase in the nervous system of the mollusc Pleurobranchaea.

Regulation of cyclic AMP through its synthesis is known to be important in modulating the activity of molluscan neurons; however, no data exists regarding the regulation of cyclic AMP degradation. We find that cyclic AMP phosphodiesterase (PDE) activity in homogenates of the nervous system of the mollusc Pleurobranchaea is significantly stimulated by calcium ion. Ca2+ stimulation is suppressed by the calmodulin antagonist trifluoperazine (TFP), indicating resemblance to the Ca2+-calmodulin PDEs of mammalian neurons. Ca2+ also accentuates the pH sensitivity of PDE. The qualities of Ca2+ and pH sensitivity of PDE are fitted into a model for cAMP regulation of neuronal activity in an identified feeding command neuron; the postulated role of PDE is consistent with effects of cAMP, TFP, and pH on the neuron's activity.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1983

Intracellular alkalinization potentiates slow inward current and prolonged bursting in a molluscan neuron.

1. The bilaterally paired ventral white cells (VWCs) of the buccal ganglion of Pleurobranchaea drive the cyclic motor output of ingestive feeding behavior during prolonged and endogenously sustained burst episodes (7). The capacity to support burst episodes is specifically induced by appetitive (food) stimulation of chemosensory pathways (5). Cyclic 3',5'-adenosine monophosphate (cAMP) and its agonists also induce prolonged burst episodes (8) through potentiation of a slow inward current (6). 2. Intracellular alkalinization of the VWC by externally applied ammonium ion and methylamine (5-20 mM) induces bursting and enhances slow inward current measured under voltage-clamp conditions. The enhancement of slow inward current is seen in the induction or augmentation of a negative slope resistance region in the current-voltage relation and in the enhancement of slowly decaying inward current tails recorded near the K+ equilibrium potential following depolarizing voltage commands. 3. Intracellular injection of alkalinizing agents, bicarbonate ion and a strong buffer solution at pH 8.1, also enhance the inward current. In ammonium saline, enhancement of inward current is dependent on NH3 content, not NH4+; NH3 is the intracellular alkalinizing agent of ammonium saline. Therefore, the change in slow inward current is an effect specific to intracellular pH. 4. The time courses of inward current enhancement and intracellular pH change in NH4+ saline are similar. The results of this study suggest that normal fluctuations in intracellular pH may be significant determinants of the excitability and consequent activity of these and perhaps other neurons. The potential interaction of intracellular pH and cyclic AMP metabolism is discussed.

Acid-Base Equilibrium↗
PubMed1983

Organization of synaptic inputs to paracerebral feeding command interneurons of Pleurobranchaea californica. III. Modifications induced by experience.

Phasic paracerebral feeding command interneurons (PCP's) were studied in whole-animal preparations of Pleurobranchaea drawn from four populations with different behavioral histories: food avoidance conditioned, yoked controls, food satiated, and naive. PCP responses to chemosensory food stimuli (liquefied squid) and mechanosensory touch stimuli (tactile stimulation of anterior and posterior structures) were recorded intracellularly, scored blind, and compared quantitatively across the four populations. PCP's from avoidance-conditioned specimens (10, 18, 19) showed decreased excitatory and increased inhibitory responses to food and touch in comparison with naive (untrained) specimens. Control animals did not show these effects. PCP's from satiated specimens showed decreased excitatory and increased inhibitory responses to food and touch in comparison with PCP's from control, naive, and conditioned specimens. Inhibitory postsynaptic potentials (IPSPs) induced in PCP's of conditioned and satiated specimens by food and touch are indistinguishable in amplitude and waveform from IPSPs produced in the same PCP's by the previously described cyclic inhibitory network (CIN; Ref. 13). In addition, tonic paracerebral neurons (PCT's) that lack input from the CIN, are not inhibited but rather are excited in trained and satiated animals. Therefore the inhibitory responses to food and touch by PCP's of conditioned and satiated specimens appear to be mediated by the CIN. This study demonstrates that associative and nonassociative processes (learning and food satiation, respectively) manifest similarly at the level of command interneurons. The findings furnish a neurophysiological explanation for behavioral motivation in Pleurobranchaea, namely, modulation of the balance of excitation/inhibition in command neurons controlling the corresponding behavior. A cellular model of food avoidance learning and food satiation is formulated to account for these data, based on the identified neural circuitry of the paracerebral command system (15, 17).

Animals↗
PubMed1982

Antigenic determinants of high mobility group chromosomal proteins 1 and 2.

The antigenic determinants of nonhistone high mobility group chromosomal proteins 1 (HMG-1) and 2 (HMG-2) were studied with rabbit antisera elicited against HMG-1 and against HMG-2 and monoclonal antibodies elicited by HMG-1. The monoclonal antibodies did not distinguish between the two proteins, suggesting that they have specificity toward a shared determinant. Whereas anti-HMG-1 did not, anti-HMG-2 did distinguish between the proteins, suggesting that the anti-HMG-2 serum contains antibodies against peptides which differ between the proteins. Peptides were generated from HMG-1 and HMG-2 by controlled digestion with trypsin and pepsin. Analysis of the digests by ELISA and by sodium dodecyl sulfate electrophoresis followed by diazobenzyloxymethyl transfer, antibody binding and autoradiography revealed that most of the antibodies are against sequential determinants some of which are smaller than 3000 in molecular weight.

Animals↗
PubMed1982

Control of feeding motor output by paracerebral neurons in brain of Pleurobranchaea californica.

1. A population of interneurons that control feeding behavior in the mollusk Pleurobranchaea has been analyzed by dye injection and intracellular stimulation/recording in whole animals and reduced preparations. The population consists of 12-16 somata distributed in two bilaterally symmetrical groups on the anterior edge of the cerebropleural ganglion (brain). On the basis of their position adjacent to the cerebral lobes, these cells have been named paracerebral neurons (PCNs). This study concerns pme subset pf [MCs. the large, phasic ones, which have the strongest effect on the feeding rhythm (21). 2. Each PCN sends a descending axon via the ipsilateral cerebrobuccal connective to the buccal ganglion. Axon branches have not been detected in other brain or buccal nerves and hence the PCNs appear to be interneurons. 3. In whole-animal preparations, tonic intracellular depolarization of the PNCs causes them to discharge cyclic bursts of action potentials interrupted by a characteristic hyperpolarization. In all specimens that exhibit feeding behavior, the interburst hyperpolarization is invariably accompanied by radula closure and the beginning of proboscis retraction (the "bite"). No other behavorial effect of PCN stimulation has been observed. 4. In whole-animal preparations, the PCNs are excited by food and tactile stimulation of the oral veil, rhinophores, and tentacles. When such stimuli induce feeding the PCNs discharge in the same bursting pattern seen during tonic PCN depolarization, with the cyclic interburst hyperpolarization phase locked to the bit. When specimens egest an unpalatable object by cyclic buccal movements, however, the PCNs are silent. The PCNs therefore exhibit properties expected of behaviorally specific "command" neurons for feeding. 5. Silencing one or two PCNs by hyperpolarization may weaken but does not prevent feeding induced by natural food stimuli. Single PCNs therefore can be sufficient but are not necessary to induction of feeding behavior. Instead the PCNs presumably operate as a population to control feeding. 6. In isolated nervous system preparations tonic extracellular stimulation of the stomatogastric nerve of the buccal ganglion elicits a cyclic motor rhythm that is similar in general features to the PNC-induced motor rhythm. Bursts of PCN action potentials intercalated at the normal phase position in this cycle intensify the buccal rhythm. Bursts of PCN impulses intercalated at abnormal phase positions reset the buccal rhythm. The PCNs, therefore, also exhibit properties expected of pattern-generator elements and/or coordinating neurons for the buccal rhythm. 7. The PCNs are recruited into activity when the buccal motor rhythm is elicited by stomatogastric nerve stimulation or stimulation of the reidentifiable ventral white cell. The functional synergy between the PCNs and the buccal rhythm is therefore reciprocal. 8...

Animals↗
PubMed1982

Functional and structural correlates of cell size in paracerebral neurons of Pleurobranchaea californica.

1. The paracerebral neurons (PCNs) in the brain of the mollusk Pleurobranchaea are a population of 12-16 interneurons that send axons to the buccal ganglion and control cyclic feeding behavior (9). In the present study we show that the PCNs differ in size and that a number of functional and structural properties of the PCNs are closely correlated with cell size. 2. PCN soma diameter varies from about 30 to 120 micrometers. The diameters segregate into two distinct but overlapping populations, which correspond to independently assigned functional classifications of "tonic" and "phasic" PCNs. The mean soma diameters of two populations were 63 and 84 micrometers, respectively. 3. Two morphological features vary systematically with PCN soma size. First, soma diameter, axonal conduction velocity, and extracellular spike amplitude were positively correlated; therefore, PCN axon diameter presumably increases with soma diameter. Second, intrasomatic injection of lucifer yellow revealed that the small, tonic PCNs are multipolar, while the large, phasic PCNs are generally monopolar neurons. 4. Small PCNs discharge tonically in response to sustained current injection and have a weak effect on cyclic motor output recorded from nerves that innervate feeding muscles. In contrast, the large PCNs discharge phasically in bursts of action potentials that are coordinated with the cyclic motor output and have a comparatively strong effect on the rhythm. The motor effects of simultaneous tonic and phasic PCN stimulation are additive. 5. Tonic and phasic PCNs innervate different but partially overlapping populations of feeding motor neurons. Phasic PCNs typically inhibit motor neurons exiting buccal root 3, while tonic PCNs either have no effect or are weakly excitatory. 6. Tonic and phasic PCNs exhibit different intrinsic properties. In comparison with phasic PCNs, tonic PCNs have higher input resistances, higher spontaneous discharge rates at rest potential, lower firing thresholds to intrasomatically injected current, lower absolute voltage thresholds, greater pacemaker sensitivity, and greater total capacitance. 7. Tonic and phasic PCNs exhibit different input properties. Tonic PCNs are recruited before phasic ones during cycylic buccal motor output induced by stomatogastric nerve stimulation. Phasic PCNs receive powerful, cycylic inhibition that is not shared by tonic PCNs. In addition, extracellular stimulation of the large oral veil nerve of the brain excites tonic PCNs but causes a biphasic postsynaptic potential (PSP) in phasic PCNs that has a net inhibitory effect. Some excitatory synaptic input to phasic and tonic PCNs is unshared, while some is shared. 8. It is concluded that these command interneurons obey the size principle discovered earlier in motor neurons (4, 13-16). Cell size per se is not the causal variable, however; instead the underlying causes of the differences between small and large PCNs include different input and output organizations as well as different intrinsic functional and morphological properties.

Animals↗
PubMed1980

Action-potential broadening and endogenously sustained bursting are substrates of command ability in a feeding neuron of Pleurobranchaea.

1. The ventral white cells (VWC's) of the buccal ganglion of Pleurobranchaea, so named for their position and color, are a bilateral pair of neuron somata. Each sends a single axon out its contralateral stomatogastric nerve and has a dendritic field originating close to the soma. 2. The vwcs exhibit spontaneous episodes of prolonged depolarization (duration 1--4 min) accompanied by repetitive action-potential activity and separated by regular intervals of 3--30 min. Such prolonged burst episodes can be triggered by short pulses of depolarizing current. During the repetitive activity of the spontaneous bursts or that driven by imposed depolarization, the action potentials progressively broaden to 5--16 times their initial duration. 3. During spontaneous bursting or activity driven by imposed depolarization, the cyclic motor output of the feeding network is initiated or accelerated with a latency corresponding with the development of appreciable VWC spike broadening. When broadening of antidromic VWC spikes is suppressed by imposed hyperpolarization of the soma, the frequency of feeding cycles is significantly lower than when broadened spikes are allowed to develop. When trains of spikes are driven by depolarizing current, the motor output of the feeding network is not initiated until the VWC spikes have broadened to a repeatable "threshold" duration, regardless of the intensity of the depolarizing current. 4. The endogenous production of prolonged burst episodes, triggered by depolarizing current pulses, and progressive spike broadening can be demonstrated in the surgically isolated VWC soma. 5. The paired VWCs are strongly electrically coupled and display highly synchronous activity. They receive synaptic inputs from many previously identified interneurons of the feeding network and are thus reciprocally coupled within the network. 6. These results demonstrate that the capacity of this neuron to generate broadened action potentials during repetitive activity confers the ability to command coordinated motor-network output. The appropriate repetitive activity can be produced endogenously in the form of prolonged bursts of spikes.

Action Potentials↗
PubMed1978

Command neurons in Pleurobranchaea receive synaptic feedback from the motor network they excite.

Command neurons that cause rhythmic feeding behavior in the marine mollusc Pleurobranchaea californica have been identified in the cerebropleural ganglion (brain). Intracellular stimulation of single command neurons in isolated nervous systems, semi-intact prepartions, and restrained whole animals causes the same rhythmic motor output pattern as occurs during feeding. During this motor output pattern, action potentials recorded intracellularly from the command neurons occur in cyclic bursts that are phase-locked with the feeding rhythm. This modulation results from repetitive, alternating bursts of excitatory and inhibitory postsynaptic potentials, which are caused at least in part by synaptic feedback to the command neurons from identified classes of neurons in the feeding network. Central feedback to command neurons from the motor network they excite provides a possible general physiological mechanism for the sustained oscillation of neural networks controlling cyclic behavior.

Action Potentials↗