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K Elekes

Publications and source records attributed to K Elekes.

At least 37 records · Page 2Linked to original sources
PubMed1999

Ionic mechanism mediating Mytilus inhibitory peptides elicited membrane currents in identified Helix neurons.

Effects of seven, pressure applied MIP (Mytilus inhibitory peptides) had been studied on D-neurons of the CNS of Helix pomatia in voltage-clamp experiments. In physiological saline, the peptides produced a hyperpolarization usually coupled with the cessation of any spontaneous spiking activity. Clamped at the resting potential ( approximately -60 mV), peptide applications elicited an outward current, which increased its amplitude by shifting the holding potential towards depolarisation. The response was concentration-dependent and accompanied by an increased membrane conductance. Reversal potentials obtained at different [K+]o were plotted with a slope of 52 mV per ten-fold change in [K+]o showing that the peptide-elicited current was mainly due to the increased K+-conductance(s). The peptide-induced outward current could partially be blocked by Ba2+ (5 mM), CdCl2 (1 mM), TEACl (10 mM) or apamin (2.5x10(-5) M) or furosemide (10 mg/ml) and decreased either in Na+-free or Cl--free solutions. 4-Aminopyridine at 5 mM concentration completely blocked the peptide-induced current. In the presence of high [K+]o, the peptide(s) was still found to induce an outward current at membrane potentials beyond K+-reversal potential. This component was not present in Cl--free saline, suggesting that the current was due to the inward flow of Cl- ions. Our results show that the MIPs have at least two (three) independent actions, each associated with different voltage-, concentration-dependence and ionic mechanisms. It is suggested, that the peptide-induced currents are carried by K+, and Cl- ions. According to our present finding, the observed effects are mediated by the same receptor, activating different second messenger systems, inducing multiple conductance changes in the membrane of neurons of the snail ganglia.

Animals↗
PubMed1999

Development of catecholaminergic neurons in the pond snail, Lymnaea stagnalis: I. Embryonic development of dopamine-containing neurons and dopamine-dependent behaviors.

The embryonic development of the catecholaminergic system of the pond snail, Lymnaea stagnalis, was investigated by using chromatographic and histochemical methods. High performance liquid chromatography suggested that dopamine was the only catecholamine present in significant concentrations throughout the embryonic development of Lymnaea. Dopamine first became detectable at about embryonic stage (E) 15 (15% of embryonic development) and then increased in amount during early development to reach about 120-140 fmol per animal by around E40. Dopamine content remained stable during mid-embryogenesis (E40-65), increased slowing for the next couple of days, and then increased rapidly to culminate at about 400 fmol per animal by hatching. The detection of aldehyde- and glyoxylate-induced fluorescence and of tyrosine hydroxylaselike immunoreactivity indicated that the first catecholaminergic cells appeared in the late trochophore or early veliger stage of embryonic development (E32-35). The paired perikarya of these transient apical catecholaminergic (TAC) neurons were located beneath the apical plate, remained outside of the central ganglia during embryogenesis, and no longer contained detectable catecholamines close to hatching. TAC neurons bore cilia on the ends of short processes that penetrated the overlying epithelium; their long processes branched repeatedly under the ciliated apical plate. Several smaller catecholaminergic cells first appeared in the anterior margin of the foot at a stage when the embryos began to metamorphose from the veliger form (E55). Similar bipolar cells later appeared in the tentacle and lips. The axons of all of these small peripheral cells projected centrally and terminated within the neuropil of different central ganglia. Central catecholaminergic neurons, including RPeD1, differentiated only after metamorphosis was complete (E75). Development of locomotor, respiratory, and feeding behaviors correlated with maturation of catecholaminergic neurons, as indicated by histology and chromatography.

Animals↗
PubMed1999

Development of catecholaminergic neurons in the pond snail, Lymnaea stagnalis: II. Postembryonic development of central and peripheral cells.

Catecholamines have long been thought to play important roles in different mollusc neural functions. The present study used glyoxylate- and aldehyde-induced histofluorescence to identify central and peripheral catecholaminergic neurons in the snail Lymnaea stagnalis. The majority of these cells were also found to react to antibodies raised against tyrosine hydroxylase. A minority of the catecholaminergic neurons, however, exhibited no such immunoreactivity. The number of central catecholaminergic neurons nearly doubled (from about 45 to about 80 cells) during the first 2-3 days of postembryonic development. Thereafter, catecholaminergic neurons again doubled in number and generally grew by about 100-200% in soma diameter as the snails grew by 1,000% in overall linear measurements. In contrast to the relatively meager addition of central catecholaminergic neurons, several thousand catecholaminergic somata were added to different peripheral tissues during postembryonic development. These small, centrally projecting neurons were particularly concentrated in the lips, esophagus, anterior margin of the foot, and different regions of the male and female reproductive tracts. Chromatographic analyses indicated that dopamine was the major catecholamine present in the central ganglia, foot, and esophagus, although detectable levels of norepinephrine (approximately 20% of dopamine levels) were also found in the ganglia. The total content but not the concentration of dopamine increased within the tissue samples during postembryonic development. The companion study (Voronezhskaya et al. [1999] J. Comp. Neurol. 404:285-296) and the present study furnish a complete description of central and peripheral catecholaminergic neurons from their first appearance in early embryonic development to adulthood.

Animals↗
PubMed1999

Pigment-dispersing hormone-like immunoreactive neurons in the central nervous system of the gastropods, Helix pomatia and Lymnaea stagnalis.

By using an antiserum raised against a crustacean beta-pigment-dispersing hormone (PDH), the distribution and chemical neuroanatomy of PDH-like immunoreactive neurons was investigated in the central nervous system of the gastropod snails, Helix pomatia and Lymnaea stagnalis. The number of immunoreactive cells in the Helix central nervous system was found to be large (700-900), whereas in Lymnaea, only a limited number (50-60) of neurons showed immunoreactivity. The immunostained neurons in Helix were characterized by rich arborizations in all central ganglia and revealed massive innervation of all peripheral nerves and the neural (connective tissue) sheath around the ganglia and peripheral nerve trunks. A small number of Helix nerve cell bodies in the viscero-parietal ganglion complex were also found to be innervated by PDH-like immunoreactive processes. Hence, a complex central and peripheral regulatory role, including neurohormonal actions, is suggested for a PDH-like substance in Helix, whereas the sites of action may be more limited in Lymnaea.

Animals↗
PubMed1999

MIP-immunoreactive innervation of the snail, Helix pomatia, heart. An ultrastructural study.

The ultrastructural characteristics of the innervation established by MIP-(Mytilus inhibitory peptide) immunoreactive neurons was investigated in the heart of the snail, Helix pomatia, applying correlative light- and electron microscopic pre-embedding immunocytochemistry on Vibratome-slices. In both the auricle and ventricle, the muscle fibers receive a rich innervation by MIP-immunoreactive (IR) varicose fibers. However, the innervation is seasonally changing in the two parts of the heart. The varicosities, containing a morphologically uniform population of large (120-150 nm) electron-dense granules, can be found in three different positions in relation to the muscle fibers: (i) close (15-20 nm) but unspecialized membrane connections between MIP-(IR) varicosities and muscle fibers; (ii) MIP-IR varicosities located relatively far (0.5-several microm) from the muscles fibers; (iii) MIP-IR profiles localized freely in the extracellular space among the loosely arranged muscle fibers. A general modulatory role of MIP in regulating the heart activity of Helix is suggested.

Animals↗
PubMed1998

NADPH-diaphorase activity in the nervous system of the embryonic and juvenile pond snail, Lymnaea stagnalis.

Nicotinamide-adenine-dinucleotide-phosphate-diaphorase (NADPH-d) histochemistry has been applied in the present study to determine the distribution of putative nitric oxide (nitric oxide synthase)-producing cells during embryonic and early postembryonic development in the pond snail, Lymnaea stagnalis L., with special reference to the nervous system. The first NADPH-d-positive structures appear as early as 18% of development (E18, trochophore stage) and correspond to the pair of protonephridia. These structures later show disintegration, although after metamorphosis (E26=75%) staining of their individually spreading cells can be observed until hatching. Peripheral sensory neurons in the foot, mantle edge and lips, and their afferents projecting to the central nervous system reveal NADPH-d activity in the postmetamorphosis period (E25-E27=E60%-E80%) of embryogenesis. After hatching (P1-P3), a number of stained sensory cells appear in the pharynx and esophagus. Some NADPH-d positive neuronal perikarya occur in the pedal and pleural ganglia, and a few weakly stained cells in the cerebral and buccal ganglia of juvenile snails. At the same time, a continuous bundle of reactive fibers is formed in the neuropil both through and through around the circumesophageal ganglion ring. The localization of NADPH-d activity in the developing nervous system of Lymnaea suggests that nitric oxide participates mainly in sensory processes. However, its role in specific intraganglionic integrative events cannot be excluded following embryonic metamorphosis.

Animals↗
PubMed1998

The organization of serotonin-, dopamine-, and FMRFamide-containing neuronal elements and their possible role in the regulation of spontaneous contraction of the gastrointestinal tract in the snail Helix pomatia.

The distribution of serotonin-, tyrosine hydroxylase-, and FMRFamide-immunoreactive neuronal elements, as well as the concentrations of serotonin and dopamine in the different parts of the gastrointestinal tract, were studied in the snail Helix pomatia. The sensitivity of the spontaneous contractions of the alimentary tract to serotonin, dopamine, and FMRFamide was also tested. Serotonin-, tyrosine hydroxylase-, and FMRFamide-immunoreactive elements could be demonstrated in each part of the gastrointestinal tract, but they showed different innervation patterns. Serotonin- and tyrosine hydroxylase-immunoreactive elements were dominant in the submucosal layer, whereas FMRFamide-immunoreactive elements were dominant in both the mucosal and submucosal layers. Tyrosine hydroxylase-immunoreactive elements were confined to the longitudinal muscle trabeculae of submucosa, whereas serotonin-immunoreactive elements were distributed throughout the submucosal layer. No serotonin-immunoreactive cell bodies, but only fibers, could be detected in the gastrointestinal tract, and therefore they represent extrinsic elements. Tyrosine hydroxylase- and FMRFamide-immunoreactive cell bodies represent intrinsic elements of the tract. The occurrence and density of the serotonin- and tyrosine hydroxylase-immunoreactive elements showed significant differences in the different parts of the alimentary tract, in accordance with HPLC assays, which revealed a significant frontocaudal decrease in both the serotonin (from 2.11 to 1.21 pM/mg) and dopamine (from 3.28 to 0.52 pM/mg) contents of the different parts of the alimentary tract. Dopamine at 10(-5) M concentration proved to be effective only on the longitudinal muscles by increasing the tone and frequency of contractions, but was ineffective on the circular muscles. Serotonin affected both the longitudinal and circular muscles. Serotonin at 10(-5) M concentration decreased the tone and increased the frequency of low-amplitude contractions of the longitudinal muscles of the esophagus and the gizzard but increased both the tone and frequency of the crop. Serotonin at 10(-9) M concentration slightly decreased the tone and blocked the contractions of the circular muscles in the crop but at 10(-5) M concentration induced contractions of the circular muscles in the gizzard. FMRFamide at 10(-6) M concentration decreased the tone and was shown to block the contractions of both the longitudinal and circular muscles.

Animals↗
PubMed1997

Octopamine-containing neurons in the alimentary tract of the earthworm (Eisenia fetida).

Octopamine-containing nerve cells have been demonstrated in the enteric plexus of the earthworm (Eisenia fetida), applying immunocytochemistry and HPLC assay. A few octopamine-immunoreactive neurons occurred in the fore- and hindgut, whereas their number in the midgut was considerably greater. Octopamine levels detected by HPLC correlated with the distribution of octopamine-containing nerve cells. A regulatory role for these intrinsic octopaminergic neurons is suggested in the enteric plexus in the earthworm alimentary tract. This is the first report on the occurrence of octopamine-containing nerve cells in the peripheral nervous system of an invertebrate.

Animals↗
PubMed1997

Distribution of FMRFamide-like immunoreactivity in the nervous system of Lumbricus terrestris.

The distribution of FMRFamide-like immunoreactive cell bodies and fibers in the nervous system of the earthworm Lumbricus terrestris has been studied by means of immunocytochemistry. The cerebral ganglion contains 150-170 immunoreactive nerve cells that are organized into six major groups in the rostral and five major groups in the caudal part of the ganglion; 160-180 immunoreactive nerve cells are present in the subesophageal ganglion, and 80-90 in the ventral cord ganglia. Immunoreactive neurons of the subesophageal and the ventral cord ganglia show similar distributions, in that FMRFamide-like immunoreactive cells form a ventromedial and a lateral cell group. Neuropil in all parts of the central nervous system shows intensively stained varicose and non-varicose fibers. Each segmental nerve contains FMRFamide-like immunoreactive fibers that can partly be traced to the two muscle layers of the body wall, and a fine immunoreactive network lies among the muscle fibers. A similar network is found in the wall of the alimentary canal. Immunopositive perikarya and fibers have been detected in the prostomial nerves, in the stomatogastric system. Some epithelial cells of the body wall are also immunopositive. The morphological characteristics and localization of FMRFamide immunoreactive neurons suggest that they may be involved in: (1) central integratory processes; (2) neuromuscular regulation in both the body wall and enteric system; (3) sensory processes.

Animals↗
PubMed1996

Tyrosine hydroxylase-negative, dopaminergic neurons are targets for transmitter-depleting action of haloperidol in the snail brain.

1. The effects of long term administration of micromolar concentrations of the D2 antagonist haloperidol upon monoaminergic neurons in the snail Lymnaea stagnalis was investigated. 2. Treatment by bath application with 0.5-2.0 micromolar haloperidol, caused a significant, continuous depletion of dopamine levels in the nervous system as revealed by high performance liquid chromatography. 3. A transient depletion of serotonin was also observed, but DOPA and norepinephrine levels were unaffected. Similar depletion of dopamine was observed after the land snail, Achatina fulica, was injected with haloperidol on each of 4 consecutive days. 4. The depletion of dopamine as revealed with glyoxylate-induced fluorescence in Lymnaea appears to be restricted to a subpopulation of catecholaminergic neurons which are immuno-negative for tyrosine hydroxylase, the synthetic enzyme responsible for the conversion of tyrosine to DOPA. 5. The results thus demonstrate a depleting action of low micromolar doses of chronic haloperidol on specific subsets of dopaminergic neurons and a novel preparation for studying catecholaminergic mechanisms operating across the animal kingdom.

Animals↗
PubMed1996

Transient and sustained expression of FMRFamide-like immunoreactivity in the developing nervous system of Lymnaea stagnalis (Mollusca, Pulmonata).

1. In the present study we have investigated the ontogeny of FMRFamide expression in the snail, Lymnaea stagnalis, from its first appearance to its distribution in young adults. 2. The first FMRFamide-like immunoreactive (FaLI) cells within CNS appear by E45 embryonic stage (premetamorphic veliger). The number of FaLI neurons increases throughout both pre- and post-hatching development. 3. Both transient and sustained expression of FMRFamide-like immunoreactivity by specific sets of neurons occurs. Two cells which transiently express immunoreactivity appear outside the future CNS by the stage E45. Other population of transient FaLI neurons includes bilaterally symmetric groups of cells in the cerebral and pedal ganglia during posthatching stages P1 (hatchlings) to P5 (juveniles). All other immunostained cells which appear during development maintain their transmitter phenotype into adulthood. 4. The possible role of FMRFamide-related peptides in the processes of morpho- and neurogenesis is discussed.

Animals↗
PubMed1996

Octopamine in the developing nervous system of the pond snail, Lymnaea stagnalis L.

Development of the octopaminergic system in the pond snail, Lymnaea stagnalis, was investigated by means of immunocytochemistry and radioenzymatic assay. The earliest octopamine-immunoreactive neurons appear at a late embryonic stage (E85) of development following metamorphosis. At this moment of development, the adult-like pattern of distribution and projection (arborization) characteristics of octopamine-immunoreactive neurone can already be observed. During hatching and postembryonic (juvenile) development the number of labelled neurons increases only within the ventro-medial cell groups of the cerebral ganglia, whereas the extent of varicose axon arborization of the labelled neurons increases gradually. No peripheral projections of the embryonic and postembryonic octopamine-immunoreactive neurons were observed. The postembryonic increase in number of immunoreactive neurons and development of axonal arborization is accompanied by a rapid, exponential enhancement of octopamine content of Lymnaea CNS, as detected radioenzymatically. A possible role of the octopaminergic neurons in the regulation of certain physiological function(s), active only from a late stage of embryonic development, is suggested.

Animals↗
PubMed1995

Evidence that locustatachykinin I is involved in release of adipokinetic hormone from locust corpora cardiaca.

The glandular cells of the corpus cardiacum of the locust Locusta migratoria, known to synthesize and release adipokinetic hormones (AKH), are contacted by axons immunoreactive to an antiserum raised against the locust neuropeptide locustatachykinin I (LomTK I). Electron-microscopical immunocytochemistry reveals LomTK immunoreactive axon terminals, containing granular vesicles, in close contact with the glandular cells cells. Release of AKH I from isolated corpora cardiaca of the locust has been monitored in an in vitro system where the amount of AKH I released into the incubation saline is determined by reversed phase high performance liquid chromatography with fluorometric detection. We could show that LomTK I induces release of AKH from corpora cardiaca in a dose-dependent manner when tested in a range of 10-200 microM. This is thus the first clear demonstration of a substance inducing release of AKH, correlated with the presence of the substance in fibers innervating the AKH-synthesizing glandular cells, in the insect corpora cardiaca.

Animals↗
PubMed1995

Opioid peptides in the nervous system of Aplysia: a combined biochemical, immunocytochemical, and electrophysiological study.

1. We have used biochemical, immunocytochemical, and electrophysiological techniques to evaluate the role of opioid peptides in the central nervous system of the marine mollusc, Aplysia californica. 2. Binding studies using 3H-D-Ala2, met-enkephalinamide (3H-DAMA) showed a single class of high-affinity binding sites with a Kd of 1.3 nM and a binding density of 45 pmol/g. 3. HPLC extracts of ganglia revealed multiple peaks with immunoreactivity for either leu (LEU-IR)- or met-enkephalin (MET-IR), but the amounts were not uniformly distributed in all ganglia. 4. LEU-IR and MET-IR neurons were demonstrated immunocytochemically in all ganglia, but MET-IR neurons were more frequent and were concentrated in pedal and pleural ganglia. While absorption control studies abolished MET-IR, LEU-IR was only partially abolished in the neuropil. 5. In electrophysiological studies, both depolarizing and hyperpolarizing responses were found to D-Ala2-leu-enkephalin (DALEU) and D-Ala2-met enkephalin (DAMET) on some and different neurons. 6. HPLC fractions from regions with retention times corresponding to authentic leu- or met-enkephalin showed physiologic responses similar to those of DALEU and DAMET, respectively. 7. These studies suggest that a variety of endogeneous opioid peptides play physiologically important roles in the nervous system of Aplysia, including but not necessarily limited to leu- and met-enkephalin.

Analgesics, Opioid↗
PubMed1995

Neurons with different immunoreactivity form clusters in the CNS of Helix pomatia.

The distribution of serotonin (5HT-ir), FMRF amide (FMRF a-ir), catch-relaxing-peptide (CARP-ir), dopamine (DA-ir), gamma-amino-butyric-acid (GABA-ir), and leucokinin (LK-ir) immunoreactive neurons were compared in the ganglia of Helix CNS. These neurons are not distributed randomly, but their location outlines distinct groups in the ganglia. In a few groups only DA-ir, GABA-ir and LK-ir neurons can be seen, whereas in the majority of groups FMRFa-ir, CARP-ir and 5HT-ir neurons are localized together. In the latter groups of immunoreactive neurons either FMRFa- and CARP- or 5HT- and FMRFa-immunoreactivities coexist in numerous neurons. Immunoreactive groups composed of DA-ir, GABA-ir and LK-ir neurons are localized exclusively in the areas of the origin of skin nerves, suggesting that these neurons are related to the processing of cutaneous afferent information. Other groups constituted by 5HT-ir, FMRFa-ir and CARP-ir neurons are localized first of all in ganglia the neurons of which innervate large masses of muscle fibers. The primary role of these neurons in motor/efferent processes is assumed.

Animals↗
PubMed1995

Tachykinin- and leucokinin-related peptides in the molluscan nervous system.

Distribution of locustatachykinin-like immunoreactive (LomTKLI) and leucokinin like immunoreactive (LKLI) neurons in the central nervous system (CNS) of the pond snail, Lymnaea stagnalis was investigated and compared to that found in Helix pomatia. Occurrence of LomTKLI neurons in different ganglia of the freshwater bivalve, Anodonta cygnea, was also studied. Similar to Helix, the Lymnaea CNS contained LomTKLI and LKLI neurons mainly in the cerebral and pedal ganglia, but the number of labelled neurons was found to be significantly lower in Lymnaea (150-184 LomTKLI and 86-104 LKLI neurons). LomTKLI elements in anodonta ganglia were mainly confined to the neuropil, whereas the immunostained perikarya were only randomly distributed. LomTKLI and LKLI neurons were also demonstrated in a similar pattern of distribution in the intestine of Lymnaea and Helix. Analyzing the membrane effects of locustatachykinin-I, leucokinin-I and anodontatachykinin, Helix neurons were found to be either depolarized or hyperpolarized. Voltage-clamp experiments revealed the role of Ca- or K-currents in peptide effects. Our results indicate that the different tachykinin- and leucokinin-systems are involved in different central and peripheral regulatory processes of the molluscan nervous system.

Animals↗
PubMed1994

Tachykinin-related neuropeptides in the central nervous system of the snail Helix pomatia: an immunocytochemical study.

The distribution of neurons reacting with an antibody raised against an insect neuropeptide, locustatachykinin I, was investigated in the CNS of the snail Helix pomatia. The localization of the neurons was compared with that of the substance P-like immunoreactive (SPLI) neurons in the different ganglia. Altogether, there are approximately 800-1000 locustatachykinin-like immunoreactive (LomTKLI) neurons in the Helix CNS, occurring with an overwhelming dominancy (83.5%) in the cerebral ganglia. Within the cerebral ganglia, the majority of LomTKLI neurons were localized in the procerebrum. The number of SPLI neurons was high; approximately 2000 SPLI nerve cells were found in the Helix CNS. The majority (44.5%) of SPLI neurons was also found in the cerebral ganglia and they were also concentrated in the procerebrum. The neuropils of all ganglia were densely innervated by both LomTKLI and SPLI fibers except the medullary mass of the procerebrum where only SPLI elements form an extremely dense innervation. In addition to the neutrophil processes, LomTKLI neurons sent axon processes to the peripheral nerves. SPLI fibers also formed a dense network of varicose fibers in the connective tissue sheath around the ganglia where they innervated the blood vessel walls too. Immunolabeling on alternating cryostat sections revealed that LomTKLI and SPLI neurons are localized near each other in most cases; co-localization of the two immunoreactive materials could be seen in a very small number of neurons of the pedal and pleural ganglia. The present results show that the Helix CNS possesses distinct neuronal populations using different tachykinin-related peptides. It is suggested that the differential distribution of these neuropeptides also implies a diversity in their central and peripheral functions.

Animals↗