Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Nephropidae”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14Linked to original sources
PubMed1977

Types and arrangements of neurons in the crayfish optic lamina.

The neural arrangements in the optic lamina of the crayfish Pacifastacus leniusculus Dana have been studied by light microscopy by means of silver impregnation techniques. The lamina is composed of columnar synaptic compartments (cartridges). Each cartridge is composed of seven receptor terminals distributed in two layers and second-order monopolar neurons connecting the lamina with the second synaptic region, the medulla externa. The neurons found in the lamina consist of five classes: monopolar neurons, centrifugal small-field neurons, tangential neurons, multipolar cells (possibly of a glial nature) and photoreceptor axons (fig. 13). Among the monopolar cells, five types are classified (M1-M5) according to their lamina arborizations. Two types are stratified (M3 and M5) corresponding to the photoreceptor terminal strata. On this basis, the lamina plexiform layer is subdivided into two layers (epl1 and epl2). The remaining monopolar neurons have lateral processes in both layers, two of them within one cartridge (M1 and M2) and one over several cartridges (M5). There is one type of small-field centrifugal neuron (C1) and two types of tangential medulla to lamina neurons (Tan1 and Tan2), both having processes covering a large number of cartridges. Multipolar cells with cell bodies distal (MP1) or proximal (MP2) to the plexiform layer send processes to several cartridges. The receptor axons consit of three types. One has terminals in epl1 or epl2, the second has its terminal in epl1 and a thin process to epl2, and the third (corresponding to the 8th retinular cell) bypasses the lamina and has a terminal in the medulla externa. A brief comparison is made with the neural arrangements in the lamina of the Norway lobster Nephrops norvegicus L.

Animals↗
PubMed1990

Inhibitory innervation of a lobster muscle.

Inhibitory neuromuscular synapses formed by the common inhibitor (CI) neuron on the distal accessory flexor muscle (DAFM) in the lobster, Homarus americanus, were studied with electrophysiological and electron-microscopic (thin-section and freeze-fracture) techniques. Postsynaptic inhibition as indicated by inhibitory junctional potentials was several-fold stronger on distal compared to proximal muscle fibers. This difference correlated with the results of serial thin-section studies, which showed more inhibitory synapses on distal fibers than on their proximal counterparts. Effects of postsynaptic inhibition on excitatory junctional potentials via current shunting had a morphological correlate in the spatial relationship between inhibitory and excitatory synapses on the distal fibers. Inhibitory synapses were larger than their excitatory counterparts and had fewer glial processes. In freeze-fracture views, inhibitory synapses did not appear as raised plateaus in the P-face as do excitatory synapses, and their active zones were more widely scattered. The intramembrane particles in the inhibitory postsynaptic membrane - representing neurotransmitter receptors - are arranged in parallel rows in the sarcolemmal P-face and have complementary furrows in the sarcolemmal E-face. Altogether, our findings help to describe a population of inhibitory neuromuscular synapses formed by the CI neuron in lobster muscle.

Action Potentials↗
PubMed1992

Quaternary and subunit structure of Calliphora arylphorin as deduced from electron microscopy, electrophoresis, and sequence similarities with arthropod hemocyanin.

Arylphorin was purified from larvae of the blowfly Calliphora vicina and studied in its oligomeric form and after dissociation at pH 9.6 into native subunits. In accordance with earlier literature, it was electrophoretically shown to be a 500 kDa hexamer (1 x 6) consisting of 78 kDa polypeptides (= subunits). Electron micrographs of negatively stained hexamers show a characteristic curvilinear, equilateral triangle of 12 nm in diameter (top view) and a rectangle measuring 10 x 12 nm (side view). Alternatively, particles in the top view orientation exhibit a roughly circular shape 12 nm in diameter. Crossed immunoelectrophoresis revealed the presence of a major subunit type; the nature of a very minor and a third immunologically separated component remains unclear. A novel 2 x 6 arylphorin particle was detected and isolated. It comprises less than 10% of the total arylphorin material and shows a long, narrow interhexamer bridge in the electron microscope. An arylphorin dissociation intermediate identified as a trimer (1/2 x 6) was isolated; its possible quaternary structure is discussed on the basis of electron micrographs. The epitope of monoclonal antibody Ec-7 directed against tarantula (Eurypelma californicum) hemocyanin subunit d and also reactive to Calliphora arylphorin was traced to a highly conserved peptide of 27 amino acids localized in the center of the protein. The primary structure of Calliphora arylphorin as published in our preceding paper (Naumann and Scheller 1991) is compared in detail to the sequences of spider and spiny lobster hemocyanin. This revealed a basic framework of 103 strictly conserved amino acids. Isofunctional exchanges are proposed for another 76 positions. On the basis of these similarities, and the published three-dimensional model of spiny lobster hemocyanin, a detailed model of the quaternary structure of Calliphora arylphorin is presented. A second larval storage protein previously termed protein II was purified from Calliphora hemolymph. It was demonstrated to be a 500 kDa hexamer of 83 kDa subunits. In the electron microscope it shows a cubic view 9 nm in length with a large central hole and a rectangular view (9 x 10 nm) with a large central cavity. A morphologically very similar hemolymph protein was detected in Drosophila melanogaster larvae. From its structural appearance it is uncertain whether protein II belongs to the hemocyanin superfamily or not.

Amino Acid Sequence↗
PubMed1991

Differential distribution of beta-pigment-dispersing hormone (beta-PDH)-like immunoreactivity in the stomatogastric nervous system of five species of decapod crustaceans.

Pigment-dispersing hormone (PDH) acts to disperse pigments within the chromatophores of crustaceans. Using an antibody raised against beta-PDH from the fiddler crab Uca pugilator, we characterized the distribution of beta-PDH-like immunoreactivity in the stomatogastric nervous system of five decapod crustaceans: the crabs, Cancer borealis and Cancer antennarius, the lobsters, Panulirus interruptus and Homarus americanus, and the crayfish, Procambarus clarkii. No somata were stained in the stomatogastric ganglion (STG) or the esophageal ganglion in any of these species. Intense PDH-like staining was seen in the neuropil of the STG in P. interruptus only. In all 5 species, cell bodies, processes, and neuropil within the paired circumesophageal ganglia (CGs) showed PDH-like staining; the pattern of this staining was unique for each species. In each CG, the beta-PDH antibody stained: 1 large cell in C. borealis; 3 small to large cells in C. antennarius; 3-8 medium cells in P. clarkii; 1-4 small cells in H. americanus; and 13-17 small cells in P. interruptus. The smallest cell in each CG in C. antennarius sends its axon, via the inferior esophageal nerves, into the opposite CG; this pair of cells, not labeled in the other species studied, may act as bilateral coordinators of sensory or motor function. These diverse staining patterns imply some degree of evolutionary diversity among these crustaceans. A beta-PDH-like peptide may act as a neuromodulator of the rhythms produced by the stomatogastric nervous system of decapod crustaceans.

Animals↗
PubMed1979

Pattern generation in the lobster (Panulirus) stomatogastric ganglion. I. Pyloric neuron kinetics and synaptic interactions.

There are a number of perspectives gained from a quantitative analysis of the pyloric system which may be applicable to other simple pattern generators: 1. The system is organized around a dominant, endogenously-bursting neuron group, and its properties are tailored to that dominance. In particular, synaptic strengths and firing frequencies of that group appear just sufficient to suppress postsynaptic "follower" cells if the latter are not too highly excited. 2. Repetitive firing properties of follower neurons are such as to facilitate their switch-like mode of activity. This includes pacemaker response nonlinearities, rebound properties, and "burstiness" properties. 3. Proper sequencing of follower cells may be controlled by particular synaptic strengths and time-courses, feedback on the oscillator cells, and functional cellular properties of follower neurons (e.g., rebound; see also next paper). All such properties interact and must be tuned to each other for proper patterns to result.

Adaptation, Physiological↗
PubMed1979

Pattern generation in the lobster (Panulirus) stomatogastric ganglion. II. Pyloric network simulation.

1. Results from the companion paper were incorporated into a physiologically realistic computer model of the three principal cell types (PD/AB, LP, PY) of the pyloric network in the stomatogastric ganglion. Parameters for the model were mostly calculated (sometimes estimated) from experimental data rather than fitting the model to observed output patterns. 2. The initial run was successful in predicting several features of the pyloric pattern: the observed gap between PD and LP bursts, the appropriate sequence of the activity periods (PD, LP, PY), and a substantial PY burst not properly simulated by an earlier model. 3. The major discrepancy between model and observed patterns was the too-early occurrence of the PY burst, which resulted in a much shortened LP burst. Motivated by this discrepancy, additional investigations were made of PY properties. A hyperpolarization-enabled depolarization-activated hyperpolarizing conductance change was discovered which may make an important contribution to the late phase of PY activity in the normal burst cycle. Addition of this effect to the model brought its predictions more in line with observed patterns. 4. Other discrepancies between model and observation were instructive and are discussed. The findings force a substantial revision in previously held ideas on pattern production in the pyloric system. More weight must be given to functional properties of individual neurons and less to properties arising purely from network interactions. This shift in emphasis may be necessary in more complicated systems as well. 5. An example has been provided of the value quantitative modeling can be to network physiology. Only through rigorous quantitative testing can qualitative theories of how the nervous system operates be substantiated.

Animals↗
PubMed1992

Ecto-ATPase/phosphatase activity in the olfactory sensilla of the spiny lobster, Panulirus argus: localization and characterization.

Electrophysiological studies have shown that the olfactory organ (antennule) of the spiny lobster, Panulirus argus, has chemoreceptors that are selectively excited by adenine nucleotides in seawater. Biochemical studies have revealed that these same nucleotides can be rapidly dephosphorylated by ectoenzymes associated with the olfactory sensilla (aesthetascs). In this study the distribution of ecto-ATPase/phosphatase activity within aesthetascs was determined cytochemically and the nature of the adenine-nucleotide dephosphorylating activity was dissected biochemically. Cytochemically, the distribution of ATP-dephosphorylating activity was similar to that shown previously for AMP and beta-glycerol phosphate; i.e., cerium phosphate reaction product was specifically localized to the transitional zone where the sensory dendrites develop cilia and branch to form the outer dendritic segments. Unlike the dephosphorylation of AMP and beta-glycerol phosphate, Mg2+ or Ca2+ was required for ecto-ATPase/phosphatase activity. Biochemical measures of both AMP- and ATP-dephosphorylating activity within aesthetascs corroborated the cytochemical evidence that these activities are localized to the transitional zone. A major portion of the AMP dephosphorylation (about 67%) derives from nonspecific alkaline phosphatase activity that is insensitive to levamisole and L-bromotetramisole. In contrast, nonspecific phosphatase activity accounted for a much smaller part of the ATP dephosphorylation (about 15%). Ectoenzymatic activity in the transitional zone may be an important means of removing excitatory/inhibitory nucleotides from this region.

Adenosine Monophosphate↗
PubMed1995

Analysis of evoked and spontaneous quantal release at high pressure in crustacean excitatory synapses.

The cellular mechanisms underlying the effect of high pressure on synaptic transmission were studied in the opener muscle of the lobster walking leg. Excitatory postsynaptic currents (EPSCs) were recorded using a loose macropatch-clamp technique at normal pressure and 3.5, 6.9 MPa helium pressure. Responses of the single excitatory axon could be grouped into two types: low-yield (L) synapses exhibiting small EPSCs with a considerable number of failures, and high-yield (H) synapses having larger EPSCs with very few failures. High pressure reduced the average EPSC amplitude in all synapses and shifted their amplitude histograms to the left by decreasing the quantal content (m) without changing their quantum current (q). A binomial distribution fit of EPSC amplitudes revealed that high pressure greatly decreased n, the number of available active zones, but the effect on p, the probability of release for each zone, was not consistent. Many of the spontaneous miniature EPSCs (mEPSCs), observed only in L-type synapses, were "giant" (size = 2-5 q). High pressure increased the frequency of the giant mEPSCs but had little effect on their amplitude histogram. High pressure depressed evoked synaptic transmission by modulating the presynaptic quantal release parameters, but concomitantly enhanced spontaneous quantal release by an unknown mechanism.

Air Pressure↗
PubMed1994

Descending neurons with dopamine-like or with substance P/FMRFamide-like immunoreactivity target the somata of olfactory interneurons in the brain of the spiny lobster, Panulirus argus.

Two sets of descending neurons primarily target the somata of neurons in the olfactory deutocerebrum of the spiny lobster, Panulirus argus. Hundreds to thousands of dopamine-like immunoreactive fibers originate in the lateral protocerebrum and terminate among the clustered somata of the olfactory deutocerebrum projection neurons (lateral soma cluster) and those of the olfactory deutocerebrum local interneurons (medial soma cluster). A pair of giant neurons with substance P- and FMRFamide-like immunoreactivity from the median protocerebrum terminate primarily in the lateral soma cluster, but also branch in the core of the olfactory lobe itself. Neurons of both types terminate in numerous bouton-like swellings. The terminals in the lateral cluster at least contain numerous, large, dense-core and small, clear vesicles. The terminals contact the somata and the primary neurites through both traditional chemical synapses and large zones of direct membrane appositions. In most instances, a vesicle-containing profile forms a triadic arrangement with a neurite and a soma the latter being frequently connected via large gap-junction-like structures. Rosette-like arrangements formed by a vesicle-containing profile surrounded by up to eight neurites are also common. Dissociated lateral cluster somata support both fast inward and sustained outward voltage-activated currents. Substance P, but not dopamine or FMRFamide-related peptides, alters the fast inward current. The somata of the olfactory projection neurons, and possibly those of the olfactory local interneurons, appear to serve an integrative, and not merely a supportive role in these invertebrate central neurons.

Animals↗
PubMed1977

Aspartate and other inhibitors of excitatory synaptic transmission in crayfish muscle.

Synaptic currents were measured in voltage clamped crayfish muscle fibers which were triggered either by stimulation of the motor axon (EPSC), or by L-gutamate (gEPSC) applied by microiontophoresis or superfusion. Among a number of analogues of glutamate, L-glutamic-acid-gamma-methyl ester, L-glutamic-acid-dimethyl ester and L-aspartate, were reasonably specific antagonists at the motor synapses, although at relatively high concentrations. Aslo, 2-amino-4-phosphono-butyric acid and morphine were effective antagonists; the action of morphine, however, seemed to be unspecific. Aspartate was further shown to decrease the size of the quantum EPSC, without affecting the probability of release of transmitter or the potential change recorded from the presynaptic nerve terminal. The results also indicate that aspartate, after longer incubations, is released as a false transmitter. The dose-response curve to short glutamate pulse is shifted by aspartate to higher glutamate concentrations, without affecting the steep slope of the dose-response curve or the saturation level. This effect can be interpreted as competitive inhibition by aspartate, with an equilibrium concentration of aspartate at the receptor of 0.3--1.5 mmol/l. In longer glutamate applications the receptor desensitizes rapidly. Aspartate reduces this desensitization in addition to its competitive inhibitory effect. Suppression of desensitization can be more effective than inhibition in long glutamate applications; in this case aspartate apparently potentiates the effects of glutamate.

Aspartic Acid↗
PubMed1984

Excitability and depolarization-release characteristics of excitatory nerve terminals in a tail muscle of spiny lobster.

In the deep abdominal L1-extensor muscle of the spiny lobster (Panulirus penicillatus) quantal excitatory postsynaptic currents (EPSCs) were recorded through macro-patch-clamp electrodes. Release of transmitter quanta from terminals was also elicited by depolarizing current pulses given through the recording electrode. The majority of terminals were excitable: on increasing the depolarization pulses, release was triggered at a threshold in an all-or-nothing manner. If excitation was blocked by tetrodotoxin (TTX), release was graded with depolarization reaching the amplitude of the all-or-nothing response at pulse amplitudes several times higher than the former threshold level. Some inexcitable terminals were also found: in these, release was graded for increasing depolarization pulses, and TTX did not alter the depolarization-release relation. Among the other types of terminals studied with the same technique, the proportion of excitable terminals in this lobster tail muscle is higher than in the crayfish opener and lower than in the frog's cutaneous pectoris muscle. The contribution of the increase in intraterminal Ca concentration to the control of release was estimated using facilitation of a test EPSC as an indicator of Ca inflow during a preceding depolarization pulse. This facilitation was found to have a maximum at a certain pulse amplitude, PF, and to decline for larger depolarizations. Release, however, rose considerably for depolarizations larger than those effected at PF. It is concluded that, like in crayfish and frog motor terminals, release is controlled directly by depolarization in addition to the control by Ca-inflow.

Action Potentials↗
PubMed1989

Ion permeation through hyperpolarization-activated membrane channels (Q-channels) in the lobster stretch receptor neurone.

In the lobster stretch receptor neurone it is possible to demonstrate a hyperpolarization-activated membrane current, IQ, which appears to be carried by Na+ and K+ in combination. The ion permeability of the membrane channel conducting this current (Q-channel) was investigated using conventional electrophysiological techniques including intracellular ion concentration measurements. It was found that none of the ions choline, protonated Tris, Rb+, NH4+, Li+, and protonated hydroxylamine was able to pass through the Q-channel which, thus, appears to be permeable to Na+ and K+ only. With increasing extracellular Na+ concentrations, IQ was increased up to a saturation level. This behaviour could be described by a one-site-two-barriers version of the Eyring rate theory, assuming that the permeant ions are turned over at specific saturable channel sites which 'sense' 70% of the transmembrane potential difference. With increasing extracellular K+ concentrations, IQ was increased in accordance with a simple first-order dose-response relationship. This finding can be accounted for by assuming that K+ increases all rates of turn-over of the permeant ions at their specific sites by similar relative amounts. Changes in extracellular Na+ and K+ concentrations were found to have no effect on the gating properties of the Q-channel.

Animals↗
PubMed1987

Synaptic responses produced in lobster abdominal postural motor neurons by mechanical stimulation of the swimmeret.

1. Intracellular recordings were obtained from the somata of identified abdominal postural motor neurons in lobster to examine their subthreshold and suprathreshold responses to tactile stimulation of the swimmeret. 2. Pressure stimulation of the swimmeret surface evoked abdominal extension by producing tonic spiking in the extensor excitors and the synergistic flexor inhibitor (f5) and hyperpolarizing responses in the extensor inhibitor and antagonistic flexor excitors. These responses often continued for several seconds following the termination of the stimulus. The receptive fields of these motor responses extended over most of the swimmeret surface. 3. More localized tactile stimulation of the swimmeret surface elicited EPSPs in f5 and the extensor excitors, and IPSPs in the flexor excitors. The amplitude of these synaptic potentials decreased as the stimulus intensity was reduced. 4. Stimulation of feathered hair (both sexes) and smooth hair (female only) sensilla produced responses characteristic of extension whereas bristly spines on the male accessory lobe excited only two flexor excitors without affecting any of the other postural motor neurons. 5. Summed synaptic responses recorded from the motor neurons differed in their amplitudes and latencies according to the type of mechanoreceptor stimulated-cuticular receptors, feathered hairs or smooth hairs. Stimulation of the swimmeret cuticle produced the strongest responses (shortest latency, largest amplitude), while feathered hair stimulation initiated the weakest responses (longest latency, smallest amplitude). 6. The relatively long latencies (greater than 35 ms) and the complex form of the EPSPs and IPSPs indicate the involvement of multisynaptic interneuronal pathways in the reflex arcs.

Animals↗
PubMed1988

Adaptation in chemoreceptor cells. I. Self-adapting backgrounds determine threshold and cause parallel shift of response function.

1. The self-adapting effects of chemical backgrounds on the response of primary chemoreceptor cells to superimposed stimuli were studied using lobster (Homarus americanus) NH4 receptor cells. 2. These receptors responded for several seconds to the onset of the backgrounds, and then returned to their initial level of spontaneous activity (usually zero). The strongest response always occurred only during the steepest concentration change; the response then decayed back to zero or to the earlier spontaneous firing level, while the background concentration was still rising, and remained silent during the entire time that the background was maintained constant (20-30 min) 3. Exposure to constant self-adapting backgrounds eliminated the response of NH4 receptor cells to stimuli of concentration lower than the background, and reduced the responses to all higher stimulus concentrations tested by a nearly equal amount. This resulted in a parallel shift of the stimulus-response function to the right along the abscissa. 4. Since the response threshold was completely re-set by adaptation to backgrounds, NH4 receptors seem to function mostly as detectors of relative rather than absolute stimulus intensity across their entire dynamic range: the response to a given stimulus-to-background ratio remained the same over 3 log step increases of background concentration. 5. As in other sensory modalities, a parallel shift of response functions appears to be an important property of chemoreceptor cells, allowing for this sensory system to function over a wider stimulus intensity range than the instantaneous dynamic range of individual receptor cells.

Action Potentials↗