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H M Gerschenfeld

Publications and source records attributed to H M Gerschenfeld.

At least 19 recordsLinked to original sources
PubMed1995

Enhancement by muscarinic agonists of a high voltage-activated Ca2+ current via phosphorylation in a snail neuron.

1. In previous work we have shown that in the snail Helix aspersa neuron F1 carbamylcholine (CCh) and other muscarinic agonists enhance the inward current carried through high voltage-activated Ca2+ channels by Ba2+ (HVA-ICa). It was also found that cyclic nucleotides, inositol trisphosphate or arachidonic acid are not involved in this modulation. Moreover, despite the effect of CCh being blocked by intracellular injection of EGTA, neither protein kinase C nor Ca(2+)-calmodulin-dependent protein kinase II appeared to play a role. 2. In the present paper, the intracellular mechanism of this muscarinic modulation was investigated further by studying the effects of inhibitors of Ser-Thr protein phosphatases (PP) on both the HVA-ICa of neuron F1 and its enhancement by CCh. 3. Intracellular injections in the F1 neuron of either microcystin LR or okadaic acid, both inhibitors of PP1 and PP2A, mimic the action of CCh on the HVA-ICa and occlude the effects of CCh on this current. In contrast, cyclosporin A, an inhibitor of PP2B (calcineurin), affects neither the HVA Ca2+ current itself nor its modulation by CCh. 4. The efficacy of PP inhibitors was tested in F1 neurons in which serotonin (5-HT) induces an inward current involving intracellular increases in cAMP and a protein kinase A-dependent closing of K+ channels. We found that intracellular injection of either microcystin LR or okadaic acid mimicked the 5-HT-induced inward current and occluded the effect of further application of 5-HT.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Inhibitory synaptic currents in stellate cells of rat cerebellar slices.

1. In thin cerebellar slices of rats aged 14-21 days, voltage-gated currents, synaptic currents and GABA responses were studied with the tight-seal whole-cell recording technique from stellate cells (8-9 micrograms soma diameter) located in the outer two-thirds of the molecular layer. 2. In symmetrical Cl- conditions, stellate cells voltage-clamped at -60 mV showed spontaneous inhibitory postsynaptic currents (IPSCs). As were the GABAA responses of the same cells, the IPSCs were blocked by bicuculline. The frequency of occurrence of IPSCs ranged from 0.2 to 1.9 events per second (21 cells). The mean amplitude of the events ranged from 61 to 226 pA (mean +/- S.E.M.: 132 +/- 11; n = 21). 3. The temporal course of IPSCs was characterized by a rapid rise (mean +/- S.E.M. of the time to peak: 1.1 +/- 0.1 ms, n = 7) and a slow decay. The decay phase was described by a double exponential function with time constants of 8.7 +/- 0.6 ms, and 40.9 +/- 3.7 ms respectively (means +/- S.E.M.; n = 7). 4. A minor fraction (15 to 20%) of the spontaneous synaptic events recorded in control saline had a faster onset than that of the IPSCs and decayed with a rapid mono-exponential decay (time constant of 1.0-1.3 ms). These were excitatory postsynaptic currents (EPSCs) unaffected by bicuculline and blocked by the glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). 5. Bath application of TTX (0.5-1 microM), which blocked voltage-gated Na+ currents in stellate cells, induced a variable decrease in the frequency of IPSCs (mean +/- S.E.M. of the frequency ratio in TTX over control: 0.47 +/- 0.09; n = 12). However, the toxin had no significant effect either on the mean amplitude or on the kinetics of the IPSCs. The mean amplitude of the miniature IPSCs was 141 +/- 13 pA (mean +/- S.E.M.; n = 22). 6. In TTX-containing solutions, the frequency of the IPSCs was unaffected when Ca2+ currents were eliminated either by removal of extracellular Ca2+ and addition of EGTA, or by addition of Cd2+. Miniature IPSCs of 200-300 pA were still observed. 7. In symmetrical Cl- conditions, local application of GABA to stellate cells induced an inward current and an increase in membrane noise. Responses to prolonged applications of GABA showed desensitization in both whole-cell mode and somatic outside-out patches. The chord conductance estimated from recording single GABA channel events in somatic outside-out patches was 28 pS.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1991

Muscarinic enhancement of the voltage-dependent calcium current in an identified snail neuron.

1. In the F1 neuron of the snail Helix aspersa bathed in a Ba2+ and 4-aminopyridine-containing saline, carbamylcholine (CCh) enhanced the inward current carried by Ba2+ through the voltage-dependent Ca2+ channels. 2. This effect of CCh on the F1 neuron was not affected by the nicotinic antagonists (+)-tubocurarine and hexamethonium, but it was mimicked by oxotremorine and blocked by both atropine and pirenzepine. 3. The intracellular injection of GTP gamma S (guanosine 5'-O-(3- thiotriphosphate] into the F1 neuron caused both a decrease in Ca2+ current and a blockade of the CCh-induced enhancement of the Ca2+ current. 4. Neither cyclic AMP, cyclic GMP nor arachidonic acid mimicked the effect of CCh on the Ca2+ current in the F1 neuron. In contrast, the intracellular injection of EGTA blocked the CCh-induced enhancement of the Ca2+ current thus suggesting that cytosolic Ca2+ is involved in the CCh-induced response. 5. We then investigated the possible role of inositol 1,4,5-trisphosphate (InsP3) and Ca(2+)-dependent protein kinases in the CCh-induced enhancement of the Ca2+ current. The intracellular injection of InsP3 in the F1 neuron elicited no consistent change in the Ca2+ current. Diacylglycerol analogues (OAG and DOG) decreased the Ca2+ current amplitude, i.e. an effect opposite to that produced by CCh. This effect of the diacylglycerol analogues resulted from the activation of protein kinase C (PKC) since it was blocked by staurosporine. In addition, staurosporine did not affect the CCh-induced increase in Ca2+ current. 6. The intracellular injection of either Ca(2+)-calmodulin-dependent protein kinase II (Ca(2+)-CaM-PK) or a peptide inhibitor of this enzyme into the F1 neuron affected neither the Ca2+ current nor its enhancement by CCh. 7. We conclude that the CCh-induced enhancement of the Ca2+ current in the snail F1 neuron involves the activation via muscarinic receptors of an intracellular transduction mechanism in which cytosolic Ca2+ plays a key role. However, InsP3, protein kinase C and Ca(2+)-CaM-PK do not appear to be directly involved in this CCh-induced response.

Action Potentials↗
PubMed1989

Intracellular mechanism of neurotransmitter-induced modulations of voltage-dependent Ca current in snail neurons.

This paper reviews our work on the modulation of voltage-dependent Ca currents in identified snail neurons. Ca currents of snail neurones are enhanced or decreased by neurotransmitters. Serotonin and acetylcholine enhance the Ca current of identified neurons, the effect of serotonin being mediated by cGMP and cGMP-dependent protein kinase. Cholecystokinin (CCK8) and dopamine both decrease the Ca current of identified neurons. The effect of CCK8 is irreversible and involves the activation of protein kinase C. The dopamine-induced decrease in Ca current is reversible and involves an alpha 40 subunit of a snail G protein immunologically and functionally related to alpha o of mammalian brain.

Animals↗
PubMed1988

An alpha 40 subunit of a GTP-binding protein immunologically related to Go mediates a dopamine-induced decrease of Ca2+ current in snail neurons.

Dopamine induces a decrease in voltage-dependent Ca2+ current in identified neurons of the snail H. aspersa. This effect is blocked by intracellular injection of activated B. pertussis toxin and of an affinity-purified antibody against the alpha subunit of bovine Go protein. The dopamine effect is mimicked by intracellular injection of mammalian alpha o. In snail nervous tissue, pertussis toxin ADP-ribosylates a single protein band on SDS gels, and this band is recognized in immunoblots by the anti-alpha o antibody. We propose that this is a 40 kd alpha subunit of a molluscan G protein immunologically related to alpha o and that it mediates the effect of dopamine on Ca2+ currents in identified snail neurons.

Animals↗
PubMed1986

Serotonin and cyclic GMP both induce an increase of the calcium current in the same identified molluscan neurons.

Serotonin (5-HT) has previously been shown to evoke an increase in the duration of the Ca2+-dependent spike of molluscan neurons by decreasing the S current (Klein et al., 1982), a K+ current controlled by cAMP. However, in a group of identified ventral neurons of the snail Helix aspersa in which 5-HT (1-10 microM) also prolonged the duration of the Ca2+-dependent action potential, no 5-HT-induced depression of S current or of any other outward current was observed. Instead, 5-HT was found to evoke the prolongation of the somatic spike by inducing an increase in Ca2+ membrane conductance. This 5-HT-induced increase of Ca2+-current was mimicked neither by the intracellular injection of cAMP nor by the extracellular application of forskolin (20 microM). In contrast, it was mimicked by the intracellular injection of cGMP and by the extracellular application of 100 nM zaprinast, a cGMP-phosphodiesterase inhibitor. The extracellular application of phorbol ester TPA (100 nM), an activator of protein kinase C, was also found to increase the Ca2+ current in the identified snail ventral neurons, but this enhancing effect had a different time course from that induced by 5-HT. These results indicate that there is a second mechanism for prolonging the Ca2+ spike of molluscan neurons, consisting of an increase in Ca2+ current, in which cGMP may play a role as second messenger.

Action Potentials↗
PubMed1985

The neuropeptide FMRF-amide decreases both the Ca2+ conductance and a cyclic 3',5'-adenosine monophosphate-dependent K+ conductance in identified molluscan neurons.

The molluscan neuropeptide FMRF-amide (10 to 50 microM) decreases the duration of the Ca2+-dependent action potential recorded in the cell body of identified neurons of the snail Helix aspersa (cells D3 and E2). In these neurons, FMRF-amide evokes a decrease of the Ca2+ current resulting from a decrease in Ca2+ conductance. In another single neuron, cell E11, FMRF-amide, besides evoking a decrease of the Ca2+ conductance, induces a decrease of the S-current (Klein, M., J. S. Camardo, and E. R. Kandel (1982) Proc. Natl. Acad Sci. U. S. A. 79: 5713-5717), a K+ current controlled by cyclic AMP. However, in this E11 cell, FMRF-amide also evokes a decrease of the amplitude of the Ca2+ spike plateau. As discussed in the preceding paper (Paupardin-Tritsch, D., L. Colombaioni, P. Deterre, and H. M. Gerschenfeld (1985) J. Neurosci. 5: 2522-2532), it is suggested that these FRMF-amide-induced modulations of ionic conductances involved in the Ca2+-dependent spike recorded in these neuronal somata may intervene in processes of presynaptic inhibition and facilitation.

Action Potentials↗
PubMed1985

Two different mechanisms of calcium spike modulation by dopamine.

Dopamine (10 to 50 microM) modulates in two different ways the duration of the Ca2+-dependent action potential recorded in the cell body of identified neurons of the snail Helix aspersa. In some neurons (cells E13 and F1) dopamine increases the amplitude of their Ca2+-dependent spike plateau by decreasing the S-current (Klein, M., J.S. Camardo, and E. R. Kandel (1982) Proc. Natl. Acad. Sci. U.S.A. 79: 5713-5717), a K+ current controlled by cyclic AMP. In another neuron (cell D2), dopamine decreases the Ca2+-dependent plateau of the somatic action potential by evoking a decrease in Ca2+-current resulting from a decrease in Ca2+ conductance. Both modulatory effects could be observed in the same single neuron in which dopamine induces decreases of both the Ca2+ conductance and cyclic AMP-dependent K+ conductance. Nevertheless, in these cells (such as cell F5) dopamine only evokes a decrease of the amplitude of the Ca2+ spike plateau. Since the modulation of the duration of the Ca2+ action potential recorded in the neuronal soma has been shown to constitute a good model of events taking place at synaptic endings, it is suggested that these modulatory mechanisms evoked by dopamine may be involved in processes of presynaptic facilitation and inhibition.

Action Potentials↗
PubMed1984

Decrease of gap junction permeability induced by dopamine and cyclic adenosine 3':5'-monophosphate in horizontal cells of turtle retina.

The axon terminals of the H1 horizontal cells of the turtle retina are electrically coupled by extensive gap junctions. Dopamine (10 nM to 10 microM) induces a narrowing of the receptive field profile of the H1 horizontal cell axon terminals, increases the coupling resistance between them, and decreases the diffusion of the dye Lucifer Yellow in the network formed by the coupled axon terminals. These actions of dopamine involve the activation of D1 receptors located on the membrane of the H1 horizontal cell axon terminals proper. Increases of the intracellular cyclic AMP concentration induced by either stimulating the adenylate cyclase activity with forskolin or inhibiting the phosphodiesterase activity with isobutylmethylxanthine, theophylline, aminophylline, or compound RO 20-1724 elicit effects similar to those of dopamine on the receptive field profile of the H1 horizontal cell axon terminals, on their coupling resistance, and on the diffusion of Lucifer Yellow in the axon terminal network. It is concluded that dopamine decreases the permeability of the gap junctions between the axon terminals of the H1 horizontal cells of the turtle retina and that this action probably involves cyclic AMP as a second messenger.

Animals↗
PubMed1982

gamma-Aminobutyric acid antagonists decrease junctional communication between L-horizontal cells of the retina.

The antagonists of gamma-aminobutyric acid, bicuculline and picrotoxin, were found to narrow the receptive field profile of the large field horizontal cell (L1HC) in the turtle retina when added to the perfusion medium in micromolar concentrations. The coupling resistance between neighboring L1HCs was increased by bicuculline or picrotoxin. Under control conditions, the dye Lucifer yellow injected into one L1HC diffused into a large number of neighboring L1HCs; bicuculline or picrotoxin greatly restricted dye passage between these same cells. We conclude that antagonists of gamma-aminobutyric acid decrease the conductance of gap junctions between L1HCs.

Animals↗
PubMed1982

cAMP-mediated decrease in K+ conductance evoked by serotonin and dopamine in the same neuron: a biochemical and physiological single-cell study.

The extracellular application of either serotonin or dopamine and the intracellular injection of cAMP all evoke in the same identified neurons of the snail Helix aspersa inward currents associated with a decrease in K+ conductance. The serotonin-, dopamine-, and cAMP-induced inward currents all show the same maximal amplitude. When the response to one transmitter is maximal, the response to the other is blocked. Using a single-cell microassay, we found that both serotonin and dopamine stimulate the adenylate cyclase [adenosine triphosphate pyrophosphate-lyase (cyclizing), EC 4.6.6.1] activity of the neurons giving the inward-current responses; on the other hand, the adenylate cyclase activity of a neuron that does not show the serotonin- and dopamine-induced currents was not stimulated by the transmitters. In contrast with the nonsummation of the maximal inward-current responses, the maximal stimulating effects of the transmitters on the enzyme activity are additive. The diterpene forskolin, which stimulates the adenylate cyclase activity of the single cells 9-fold, also evokes an inward current. We conclude that single snail neurons are endowed with independent serotonin and dopamine receptors linked to the adenylate cyclase. Activation of each of these receptors evokes a cAMP-mediated decrease in K+ conductance. The physiological interaction between the transmitters probably takes place at a late step in the chain of events leading from the increase in cAMP to the closing of the K+ channels.

Adenylyl Cyclases↗
PubMed1981

Relationship between two voltage-dependent serotonin responses of molluscan neurones.

A serotonin (5-HT)-induced slow inward current was reanalyzed in identified snail neurones and found to result from a decrease in a voltage-dependent K+-conductance, sensitive to [Ca2+]0 changes. 5-HT evoked in the same neurones an increase in the spike plateau known to be associated to a K+-conductance decrease. Both 5-HT responses appear to reflect the same decrease in K+-conductance.

Animals↗
PubMed1981

Role of cyclic AMP in a serotonin-evoked slow inward current in snail neurones.

One model of synaptic transmission suggests that transmitters modify postsynaptic permeability through the intermediary of cyclic AMP. Thus, serotonin (5-hydroxytryptamine) evokes in molluscan neurones a decrease in a voltage-dependent K+ conductance which in turn generates a slow inward current when studied in steady voltage-clamp conditions. The serotonin-induced increase of the plateau phase of the spike of an Aplysia sensory neurone can be mimicked by both intracellularly injected cyclic AMP and extracellularly applied phosphodiesterase inhibitors, suggesting that cyclic AMP mediates the effect. We have tested whether a similar mechanism could account for the serotonin slow inward current in identified snail neurones and have found that the intracellular injection of cyclic AMP, but not of cyclic GMP or 5'-AMP, evokes a slow inward current showing similar voltage dependence, inversion potential and ionic properties to the serotonin slow inward current. Phosphodiesterase inhibitors at low concentrations (1-20 microM) potentiate the serotonin slow inward current and at higher concentrations evoke by themselves an inward current, partially or totally occluding the serotonin and cyclic AMP currents. Finally, we have found that in homogenates of pooled identified snail neurones serotonin stimulates the adenylate cyclase, increasing its activity by 50-100%.

Animals↗
PubMed1981

Involvement of small-field horizontal cells in feedback effects on green cones of turtle retina.

Light stimuli depolarize green cones of turtle retina through a circuit involving a feedback connection from luminosity horizontal cells (L-HC) to green cones. In turtle retina two types of L-HC have been distinguished: large-field L-HC and small-field L-HC. The spatial properties of the feedback depolarizations of green cones were compared with those of both large- and small-field L-HC. Green cones were found to be more effectively depolarized by relatively small spots of red light than by large red annuli. Moreover, red light stimulation of the periphery of the receptive field could reduce the depolarizing influence of central red stimuli. These spatial properties greatly differ from those of the large-field L-HC, whereas they strongly resemble those of the small-field L-HC. These results suggest that the small-field L-HC mediate the feedback action on green cones.

Animals↗
PubMed1980

Characteristics and ionic processes involved in feedback spikes of turtle cones.

In about 20% of the cones of untreated retinas of turtles, bright flash illumination of the periphery of their receptive field evokes a spike through the feedback mechanism from the L-horizontal cell. Such feedback spikes, never observed with central stimulation, are labile, but after they have disappeared they can be regained by depolarizing the cone. Feedback spikes are actual regenerative responses, since they show a critical threshold potential, are facilitated by cone depolarization and are blocked by hyperpolarization. They are associated with a membrane resistance decrease; tetrodotoxin (10(-5) M) does not block them. High Ca2+ media facilitate their appearance, but their effect is transient because of the cone hyperpolarization and the light response block that Ca2+ ions induce. Sr2+ ions (4-10 mM) facilitate the discharge of feedback spikes in response to peripheral illumination in every cone, whether or not it has previously shown feedback effects. In Sr2+ media, feedback spikes are stable and can be evoked by dim lights. Ba2+ (2-6 mM) also facilitates and stabilizes the discharge of feedback spikes. Co2+ and D-600 block the feedback spikes. Pharmacological agents that depolarize the L-horizontal cells, such as GABA, glutamate or nicotine, also block the feedback spikes. Both Sr2+ and Ba2+ also induce the appearance of spontaneous and off spikes, which are also blocked by Co2+, but these are not related to the feedback mechanism. These results strongly suggest that every turtle cone receives a feedback input from the L-horizontal cells, which would be able to induce an increase of the cone Ca2+ conductance, which may become regenerative.

Action Potentials↗
PubMed1980

Sustained feedback effects of L-horizontal cells on turtle cones.

Prolonged stimulation of the periphery of their receptive field can evoke in turtle cones sustained complex depolarizations or sustained membrane oscillations. In cones in which such effects of prolonged peripheral stimulation are not apparent, the injection of short depolarizing pulses can reveal a sustained increase of electrical excitability in response to prolonged peripheral illumination. The sustained effects of prolonged peripheral illumination have characteristics similar to those of the feedback depolarizations evoked by flash peripheral stimulation: they are labile in untreated retinas, can be blocked by either hyperpolarization, Co2+ or agents that depolarize the L-horizontal cells. They are associated with a decrease in the membrane input resistance. In retinas bathed in Sr2+- or Ba2+-containing media, prolonged peripheral illumination evokes a sustained repetitive discharge of spikes. These experiments demonstrate that the feedback effects of the L-horizontal cells on the cones are not only transient but also sustained and that the sustained effects of peripheral stimulations are associated with an increase in membrane Ca2+ conductance. The possible nature of the feedback connection between L-horizontal cells and the cones is discussed.

Animals↗