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F Strumwasser

Publications and source records attributed to F Strumwasser.

At least 19 recordsLinked to original sources
PubMed1996

Antipsychotic drugs block IP3-dependent Ca(2+)-release from rat brain microsomes.

Cellular Ca(2+)-dysregulation has been proposed as an important mechanism in certain diseases such as bipolar affective disorder (BPAD) and malignant hyperthermia. Recently it has been found that in BPAD, the plasma membrane Ca(2+)-channel blockers verapamil and nimodipine are useful substitutes in Li(+)-treatable patients. We have investigated the effects of these drugs and the antipsychotic drugs (clozapine, fluspirilene, and haloperidol) on IP3-induced Ca(2+)-release from Ca(2+)-loaded rat brain microsomes. In the presence of either the Ca(2+)-channel blockers or the neuroleptic drugs, Ca(2+)-release was blocked in a dose-dependent fashion. For the neuroleptics, the EC50 ranged from 22 microM for fluspirilene to 145 microM for haloperidol. The EC50 for nimodipine was 160 microM and 450 microM for verapamil. Carbamazapine and valproic acid, anticonvulsants recently used for treating BPAD, were relatively ineffective, as were various haloperidol metabolites. The research described in this paper establishes for the first time that antipsychotic drugs, as well as certain Ca(2+)-channel blockers, directly block the IP3-induced Ca(2+)-release in a rat brain microsome assay.

Animals↗
PubMed1994

The relations between neuroscience and human behavioral science.

Neuroscience seeks to understand how the human brain, perhaps the most complex electrochemical machine in the universe, works, in terms of molecules, membranes, cells and cell assemblies, development, plasticity, learning, memory, cognition, and behavior. The human behavioral sciences, in particular psychiatry and clinical psychology, deal with disorders of human behavior and mentation. The gap between neuroscience and the human behavioral sciences is still large. However, some major advances in neuroscience over the last two decades have diminished the span. This article reviews the major advances of neuroscience in six areas with relevance to the behavioral sciences: (a) evolution of the nervous system; (b) visualizing activity in the human brain; (c) plasticity of the cerebral cortex; (d) receptors, ion channels, and second/third messengers; (e) molecular genetic approaches; and (f) understanding integrative systems with networks and circadian clocks as examples.

Animals↗
PubMed1991

Purification and characterization of a molluscan egg-specific NADase, a second-messenger enzyme.

An egg-specific NADase has been purified to homogeneity from the ovotestis of the opisthobranch mollusk Aplysia californica. Unlike other NADases, the Aplysia enzyme generates primarily cyclic-ADP-ribose (cADPR) rather than ADP-ribose from NAD. cADPR has been shown to stimulate the release of Ca2+ from microsomes prepared from sea urchin egg and, when injected into intact eggs, to activate the cortical reaction, multiple nuclear cycles, and DNA synthesis. The Aplysia enzyme was initially identified as an inhibitor of cholera and pertussis toxin-catalyzed ADP-ribosylation. By the use of an NADase assay, it was purified from the aqueous-soluble fraction of ovotestis by sequential column chromatography. The enzyme has an apparent molecular mass of 29 kDa, a Km for NAD of 0.7 mM, and a turnover rate of approximately 27,000 mol NAD.min-1.mol enzyme-1 at 30 degrees C. Monoclonal antibodies were generated to the NADase. Immunoblots of two-dimensional gels revealed multiple isoforms of the enzyme, with pls ranging from 8.1 to 9.8. The multiple isoforms were resolved with a cation exchange high-pressure liquid chromatography column and shown to generate cADPR. Immunohistochemical analysis of cryostat sections of Aplysia ovotestis shows that the enzyme is specific to the eggs and restricted to large 5- to 10-microns granules or vesicles. To date the cADPR-generating enzyme activity has been identified in various organisms, including mammals. The Aplysia enzyme is the first example in which the enzyme that generates cADPR has been purified. All of the available evidence indicates that this NADase is a second-messenger enzyme, implying that other NADases may serve a similar function.

Adenosine Diphosphate Ribose↗
PubMed1991

Primary structure of a molluscan egg-specific NADase, a second-messenger enzyme.

An egg-specific NADase has been purified from the ovotestis of the marine mollusk Aplysia californica. The enzyme converts NAD to cyclic ADP-ribose (cADPR), which is a potent mobilizer of Ca2+. It is likely that the NADase serves to raise Ca2+ levels in the ova at appropriate times. A 1.2-kb cDNA clone containing the complete coding sequence of the native NADase protein was isolated from an unamplified ovotestis cDNA library and represents the first cloning of an NADase that generates cADPR. In vitro translation studies indicate that the protein initially has a signal sequence that may help to target it to discrete vesicles of the ova in which it is found. There are 12 cysteines in the open reading frame, two of these being in the signal sequence. No part of the sequence has significant similarity to other proteins or known nucleotide binding site consensus sequences. Northern blot analysis of poly(A)+ selected ovotestis RNA has identified an NADase mRNA of 1.85 kb. In situ hybridization analysis of cryostat sections from ovotestis has shown that the NADase mRNA is restricted to the immature ova, although the NADase protein is present in both immature and mature eggs.

Amino Acid Sequence↗
PubMed1988

Calcium changes in isolated peptidergic neurons during activation by a cAMP analog.

The bag cell neurons of intact Aplysia control egg-laying by producing an approximately 30 min afterdischarge of action potentials, during which the neuropeptide egg-laying hormone is released. Previous studies have shown that cAMP, protein phosphorylation and Ca2+ are involved in the mechanisms of the afterdischarge. Spontaneous discharge and afterdischarge can be produced in dissociated bag cells by treatment with cAMP analogs. While pharmacological evidence exists for a large calcium component in the action potentials of bag cells, direct evidence by measuring (Ca2+)i has not appeared, nor has Ca-buffering during cAMP activation been examined. Our studies were directed at measuring (Ca2+)i changes in isolated bag cells in attached cell culture using the metallochromic indicator, arsenazo III, simultaneously with voltage recordings across the cell membrane. It was found that a single induced action potential causes a negligible rise in (Ca2+)i while a train of 35 spikes causes a significant rise (about 3 X 10(-4) absorbance units). Increasing external (Ca2+) enhances the action potential and Ca2+ signal while cobaltous ions block both the action potentials and the rise in (Ca2+)i. Lengthening the duration of spikes by TEA (50 mM) or 8-benzylthio cAMP (8-BTcAMP; 0.5 mM) enhances Ca2+ influx and allows the detection of Ca2+ transients due to single spikes. During spontaneous groups of action potentials in either TEA or 8-BTcAMP, (Ca2+)i increases but the bag cell's Ca-buffering systems are able to restore the Ca2+ levels with a half-time of about 20 s.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1984

Regional specializations in the eye of Aplysia, a neuronal circadian oscillator.

The eye of the opisthobranch mollusc, Aplysia californica, contains a neuronal circadian oscillator system as well as a photoreceptor system. The retina contains five classes of receptors, several of which are described for the first time in this paper, and two types of neurons. The most conspicuous photoreceptor has long microvilli and is densely packed with small vesicles. The other four receptor types bear both microvilli and cilia and lack densely packed vesicles. Because of their small size, these four receptors occupy only a small fraction of the retinal area, but numerically they account for about half of the receptors. There are marked differences between the dorsal and ventral portions of the eye of Aplysia. The optic nerve head and associated bundles of axons within the retina form a boundary between two anatomically distinct regions of the eye. The microvillous photoreceptor and one of the receptors bearing both microvilli and cilia are found throughout the eye. The other three receptor types are restricted to the region ventral to the optic nerve head. One type of neuron, which has been shown in other studies to produce compound action potentials whose frequency varies with a circadian rhythm, is also found only ventral to the optic nerve head and associated axon bundles. There are also marked regional variations in cellular dimensions. The rhabdom originating from the microvillous photoreceptors is thickest in the dorsal and central retina, and the cross-sectional areas of these photoreceptors are largest dorsally. The pigmented layer is also much thicker in the dorsal retina. No other molluscan eye has been reported to have as many receptor types as Aplysia, nor has restriction of a receptor or neuronal type to a limited area been described. Regional variations in cellular dimensions have been reported previously primarily in the advanced cephalopod eyes. The significance of these unusual features is discussed in relation to both the visual properties of the eye and the circadian oscillator it contains.

Animals↗
PubMed1984

Two neuronal populations in the head ganglia of Aplysia californica with egg-laying hormone-like immunoreactivity.

The egg-laying hormone (ELH) is a polypeptide of known structure, which is synthesized and released by the neurosecretory bag cells in the abdominal ganglion of the mollusc, Aplysia californica. We have used immunohistochemical procedures to reveal organized groups of specific cells and fiber tracts within the pleural and cerebral ganglia in adult Aplysia which are immunopositive when reacted with antibodies generated against ELH. These antibodies are highly specific in that they only stain the bag cells within the abdominal ganglion. The ELH+ systems in the head ganglia persisted in two animals 43 days and 67 days after surgical removal of their abdominal ganglia and pleurovisceral connectives. It is therefore likely that these immunoreactive neurons and their processes are independent of the bag cell system. The pleural ganglia neurons, with ELH-like immunoreactivity, bear a striking resemblance to bag cells in somal and nuclear dimensions, neuritic morphology and association with the pleurovisceral connectives. This suggests that both populations of cells may have descended from a common precursor pool during embryogenesis. In the cerebral ganglion, a pair of bilateral clusters of 6-10 small immunopositive neurons are located on the dorsal surface in the vicinity of the C clusters, and send their processes into the neuropil. Intensely stained tracts of ELH+ fibers are prominent at all levels of section in the cerebral neuropil; stained fibers can also be traced into most of the nerves emanating from the cerebral ganglion. Although the functions of these systems, as well as the specific nature of the immunoreactive molecule(s) they contain, remain unknown, 5 ELH-like genes of Aplysia have now been cloned and 3 of these have been sequenced. Our results suggest that the immunoreactive molecules in the pleural and cerebral neurons are due to peptides controlled by one or more of these genes. ELH is known to markedly change the electrical activity of neurons in the head ganglia in vitro. This demonstration of the presence and distribution of ELH-like molecules endogenous to the head ganglia raises the possibility that ELH target neurons in the head ganglia may be activated by local sources of ELH-like neuroactive peptides in vivo.

Animals↗
PubMed1984

A voltage-clamp analysis of currents underlying cyclic AMP-induced membrane modulation in isolated peptidergic neurons of Aplysia.

A variety of chemical and electrophysiological evidence indicates that the onset of afterdischarge and the subsequent profound enhancement of spike broadening that occur in the bag cell neurons of Aplysia are related to an increase in adenosine 3',5'-monophosphate-(cAMP) dependent protein phosphorylation. We have now used a two-electrode voltage clamp to study the properties of isolated bag cell neurons in cell culture and their response to 8 benzylthio-cAMP (8BTcAMP) and N6-n-butyl 8BTcAMP. These membrane-permeant and phosphodiesterase-resistant cAMP analogs induce spontaneous discharge and spike broadening in both the intact bag cell cluster and isolated bag cell neurons in cell culture. The dominant inward current in these cultured cells was found to be the calcium current, Ica, which was abolished by Co2+ (20 mM) or Ni2+ (10 mM) and could be observed in Na+-free media. In a minority of cells (2 of 12), in normal ionic media, a transient inward current was observed that was unaffected by Co2+ and Ni2+ and probably represents a sodium current. The three characterized potassium currents, the delayed rectifying current IK, the calcium-dependent current IC, and the early transient current IA, distinguished by their differing pharmacological and voltage-activation properties, were present in all healthy cells. Three effects of the cyclic AMP analogs (0.5 mM) on the electrical properties of these cells were 1) the emergence of a region of negative slope resistance in the steady-state I-V relations, 2) a depression of the net sustained outward currents due to depolarizing commands, and 3) a marked reduction in IA. When outward currents had been largely suppressed using high concentrations of tetraethylammonium (TEA) ions (100-460 mM) no effects of the cyclic AMP analogs could be observed on peak inward currents using NA+ and Ca2+ or Ba2+ as carriers of inward current. At least part of these electrical effects of the cyclic AMP analogs could be accounted for by a depression of a delayed potassium current and the A current.

Animals↗
PubMed1982

An early sodium and a late calcium phase in the afterdischarge of peptide-secreting neurons of Aplysia.

Following brief electrical stimulation of a pleuroabdominal connective nerve, the clusters of peptidergic bag cell neurons of Aplysia generate a long-lasting (or approximately 30 min) synchronous afterdischarge. In a normal seawater medium, the afterdischarge comprises an early phase of rapid firing (2-6 Hz) lasting for less than one minute, followed by a second, prolonged phase of lowering firing rate (less than 0.5 Hz). We have found that the transition from the first, rapid-firing phase to the prolonged second phase of afterdischarge is associated with an increase both in the width and height of intracellularly recorded action potentials. In addition, we find that in the presence of the potassium channel-blocker, TEA, such biphasic afterdischarges may be triggered by depolarizing current that evokes action potentials in a single bag cell neuron in a cluster. Afterdischarges resembling either the first or the second phase of a normal afterdischarge may be produced by using media deficient in calcium or sodium, respectively, in combination with potassium channel-blockers. Brief stimulation in media deficient in calcium give rise to afterdischarges of high firing frequency (2-6 Hz) lasting for less than one minute (mean duration = 41 s) while, in a sodium-free medium, longer afterdischarges (mean duration = 18 min) of lower firing rate (less than 0.3 Hz) were generated. At the end of afterdischarge in a normal seawater medium, containing both sodium and calcium ions, the bag cell neurons become refractory to stimulation. Thus, further stimulation either fails to induce afterdischarge or results in afterdischarges that are attenuated both in frequency of firing and in duration compared with the first afterdischarge. In these experiments we found that the brief afterdischarges, observed in low-calcium media, which resemble the first phase of a normal afterdischarge, did not induce subsequent refractoriness while afterdischarges evoked in the normal calcium, sodium-free medium did result in refractoriness to further afterdischarge. Our data indicate that both phases of a bag cell afterdischarge are due to intrinsic bag cell mechanisms and suggest that the firing pattern in the first phase is largely sodium dependent and that of the second, slow phase is calcium dependent. Moreover, our data indicate that it is the second, calcium-dependent phase that induces the refractoriness that follows bag cell afterdischarge.

Animals↗
PubMed1982

Intracellular modulation of membrane channels by cyclic AMP-mediated protein phosphorylation in peptidergic neurons of Aplysia.

The peptidergic bag cell neurons of the opisthobranch mollusc Aplysia control egg laying and its correlated behavior by release of the neuroactive peptide, egg-laying hormone, during the extended electrical discharge termed afterdischarge. This paper examines the evidence for the involvement of cyclic AMP (cAMP) and protein phosphorylation in the mediation of this electrical afterdischarge. It is concluded that an important component in the mechanism of afterdischarge is the suppression of a potassium channel, mediated by cAMP-dependent protein kinase-induced protein phosphorylation. The exact identity of the potassium channel remains to be worked out.

Action Potentials↗
PubMed1981

An immunohistochemical study of the neuropeptidergic bag cells of Aplysia.

The bag cell neurosecretory system of Aplysia californica synthesizes and releases a neuropeptide, the egg-laying hormone (ELH), which can induce egg-laying behavior. While ELH acts as a neurohormone on distant neuronal and non-neuronal targets, it also can moderate the electrical activity of neurons within the abdominal ganglion. Using antibodies generated against pure ELH, our immunohistochemical study provides direct morphological support for this dual function of ELH by defining the distribution of this neuropeptide within the abdominal ganglion of A. californica. We also find ELH cross-reactivity in the bag cell systems of three other species of Aplysia. In sections of abdominal ganglia stained for ELH by the peroxidase-antiperoxidase method, bag cell clusters were found to be homogeneous populations of ELH-immunoreactive neurons, extending processes in a complex array within the connective tissue sheath overlying the ganglion and the proximal regions of neighboring nerves. This association of neurites with the sheath is the neurohemal organ which facilitates release of ELH into circulating hemolymph. Stained processes also invade the interior of the ganglion in association with septal sheets of connective tissue and as scattered fibers in the neuropil. Local modulation by ELH probably occurs through release from these intraganglionic sites. A few ELH-positive ectopic cells were seen outside of the confines of the bag cell clusters as far displaced as the base of the branchial nerve; they appear to be bag cells which have mis-migrated during development. Specificity of the antiserum was confirmed by the total lack of staining of all other neurons within the abdominal ganglion as well as the absence of staining of bag cells with pre-immune serum. Although th ELHs of Aplysia vaccaria, Aplysia braziliana, and Aplysia dactylomela have not been characterized biochemically, it is known that abdominal ganglion extracts from A. californica can induce egg laying in all three species. We find that antiserum against A. californica ELH stains the bag cell systems of A. vaccaria, A. braziliana, and A. dactylomela and not other parts of their abdominal ganglia. It is likely that this staining represents cross-immunoreactivity of the egg-laying neurohormones from these species which also share cross-bioactivity.

Animals↗
PubMed1980

Microinjection of catalytic subunit of cyclic AMP-dependent protein kinase enhances calcium action potentials of bag cell neurons in cell culture.

We have found that the calcium action potentials of bag cell neurons from the abdominal ganglion of Aplysia may be enhanced by intracellular microinjection of the catalytic subunit of cyclic AMP-dependent protein kinase (ATP:protein phosphotransferase, EC 2.7.1.37). The catalytic subunit was purified from bovine heart and shown to be effective in stimulating the phosphorylation of bag cell proteins in homogenates at concentrations of 10-50 nM. Intracellular injection into isolated bag cell neurons maintained in primary culture was through pressure applied to microelectrodes filled at the tip with catalytic subunit (5-22 muM). In 11 of 16 injected cells, both the slope of the rising phase and the height of the action potentials evoked by a constant depolarizing current were markedly enhanced relative to the pre-injection control (mean increases, 73% and 35%, respectively). This effect could occur with no change in resting potential or in the latency of the action potential from the onset of the depolarizing pulse. The effect was observed with enzyme dissolved in three different salt solutions (Na phosphate, K phosphate, or KCl). In two experiments, tetrodotoxin (50 muM) added to the extracellular medium had no effect on the enhanced action potentials. Subsequent addition of the calcium antagonist Co(2+), however, diminished or abolished the spikes. In more than half of the experiments, the injection of catalytic subunit was accompanied by an increase in the input resistance of the cells as measured by applying small hyperpolarizing current pulses. In three experiments, subthreshold oscillations in membrane potential resulted from the injections. Control injections (24 cells), carried out either with carrier medium alone or with heat-inactivated enzyme preparations, did not produce spike enhancement, increased input resistance, or oscillations. Our data suggest that the stimulation of intracellular protein phosphorylation by the catalytic subunit of cyclic AMP-dependent protein kinase enhances the excitability of bag cell neurons by modifying calcium and potassium channels or currents.

Action Potentials↗