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K Graubard

Publications and source records attributed to K Graubard.

At least 19 recordsLinked to original sources
PubMed2001

Tiling of the body wall by multidendritic sensory neurons in Manduca sexta.

A plexus of multidendritic sensory neurons, the dendritic arborization (da) neurons, innervates the epidermis of soft-bodied insects. Previous studies have indicated that the plexus may comprise distinct subtypes of da neurons, which utilize diverse cyclic 3',5'-guanosine monophosphate signaling pathways and could serve several functions. Here, we identify three distinct classes of da neurons in Manduca, which we term the alpha, beta, and gamma classes. These three classes differ in their sensory responses, branch complexity, peripheral dendritic fields, and axonal projections. The two identified alpha neurons branch over defined regions of the body wall, which in some cases correspond to specific natural folds of the cuticle. These cells project to an intermediate region of the neuropil and appear to function as proprioceptors. Three beta neurons are characterized by long, sinuous dendritic branches and axons that terminate in the ventral neuropil. The function of this group of neurons is unknown. Four neurons belonging to the gamma class have the most complex peripheral dendrites. A representative gamma neuron responds to forceful touch of the cuticle. Although the dendrites of da neurons of different classes may overlap extensively, cells belonging to the same class show minimal dendritic overlap. As a result, the body wall is independently tiled by the beta and gamma da neurons and partially innervated by the alpha neurons. These properties of the da system likely allow insects to discriminate the quality and location of several types of stimuli acting on the cuticle.

Animals↗
PubMed2001

Neural network partitioning by NO and cGMP.

The stomatogastric ganglion (STG) of the crab Cancer productus contains approximately 30 neurons arrayed into two different networks (gastric mill and pyloric), each of which produces a distinct motor pattern in vitro. Here we show that the functional division of the STG into these two networks requires intact NO-cGMP signaling. Multiple nitric oxide synthase (NOS)-like proteins are expressed in the stomatogastric nervous system, and NO appears to be released as an orthograde transmitter from descending inputs to the STG. The receptor of NO, a soluble guanylate cyclase (sGC), is expressed in a subset of neurons in both motor networks. When NO diffusion or sGC activation are blocked within the ganglion, the two networks combine into a single conjoint circuit. The gastric mill motor rhythm breaks down, and several gastric neurons pattern switch and begin firing in pyloric time. The functional reorganization of the STG is both rapid and reversible, and the gastric mill motor rhythm is restored when the ganglion is returned to normal saline. Finally, pharmacological manipulations of the NO-cGMP pathway are ineffective when descending modulatory inputs to the STG are blocked. This suggests that the NO-cGMP pathway may interact with other biochemical cascades to partition rhythmic motor output from the ganglion.

Animals↗
PubMed2000

Molecular underpinnings of motor pattern generation: differential targeting of shal and shaker in the pyloric motor system.

The patterned activity generated by the pyloric circuit in the stomatogastric ganglion of the spiny lobster, Panulirus interruptus, results not only from the synaptic connectivity between the 14 component neurons but also from differences in the intrinsic properties of the neurons. Presumably, differences in the complement and distribution of expressed ion channels endow these neurons with many of their distinct attributes. Each pyloric cell type possesses a unique, modulatable transient potassium current, or A-current (I(A)), that is instrumental in determining the output of the network. Two genes encode A-channels in this system, shaker and shal. We examined the hypothesis that cell-specific differences in shaker and shal channel distribution contribute to diversity among pyloric neurons. We found a stereotypic distribution of channels in the cells, such that each channel type could contribute to different aspects of the firing properties of a cell. Shal is predominantly found in the somatodendritic compartment in which it influences oscillatory behavior and spike frequency. Shaker channels are exclusively localized to the membranes of the distal axonal compartments and most likely affect distal spike propagation. Neither channel is detectably inserted into the preaxonal or proximal portions of the axonal membrane. Both channel types are targeted to synaptic contacts at the neuromuscular junction. We conclude that the differential targeting of shaker and shal to different compartments is conserved among all the pyloric neurons and that the channels most likely subserve different functions in the neuron.

Amino Acid Sequence↗
PubMed1998

The NO/cGMP pathway and the development of neural networks in postembryonic lobsters.

The nitric oxide/cyclic 3',5'-guanosine monophosphate (NO/cGMP) signaling pathway has been implicated in certain forms of developmental and adult neuronal plasticity. Here we use whole-mount immunocytochemistry to identify components of this pathway in the nervous system of postembryonic lobsters as they develop through metamorphosis. We find that the synthetic enzyme for NO (nitric oxide synthase, or NOS) and the receptor for this transmitter (NO-sensitive soluble guanylate cyclase) are broadly distributed in the central nervous system (CNS) at hatching. In the brain, NOS immunoreactivity is intensified during glomerular development in the olfactory and accessory lobes. Whereas only a few neurons express NOS in the CNS, many more neurons synthesize cGMP in the presence of NO. NO-sensitive guanylate cyclase activity is a stable feature of some cells, while in others it is regulated during development. In the stomatogastric nervous system, a subset of neurons become responsive to NO at metamorphosis, a time when larval networks are reorganized into adult motor circuits. cGMP accumulation was occasionally detected in the nucleus of many cells in the CNS, which suggests that cGMP may have a role in transcription. Based on these findings, we conclude that the NO/cGMP signaling pathway may participate in the development of the lobster nervous system. Furthermore, NO may serve as a modulatory neurotransmitter for diverse neurons throughout the CNS.

1-Methyl-3-isobutylxanthine↗
PubMed1998

Pharmacologically and functionally distinct calcium currents of stomatogastric neurons.

Previous studies have suggested the presence of different types of calcium channels in different regions of stomatogastric neurons. We sought to pharmacologically separate these calcium channel types. We used two different preparations from different regions of stomatogastric neurons to screen a range of selective calcium channel blockers. The two preparations were isolated cell bodies in culture, in which calcium current was measured directly, and isolated neuromuscular junction, in which synaptic transmission was the indirect assay for presynaptic calcium influx. The selective blockers were two different dihydropyridines, omega-Agatoxin IVA, and omega-Conotoxin GVIA. Cultured cell bodies possessed both high-threshold calcium current and calcium-activated outward current, similar to intact neurons. The calcium current had transient and maintained components, but both components had the same voltage dependence of activation and inactivation. Dihydropyridines at >/=10 microM blocked both high-threshold calcium current and calcium-activated outward current. Nanomolar doses of omega-Agatoxin IVA did not block calcium current, but micromolar doses did. omega-Conotoxin GVIA did not block either current. In contrast, at the neuromuscular junction, dihydropyridines reduced the amplitude of postsynaptic potentials by only a modest amount, whereas omega-Agatoxin IVA at doses as low as 64 nM reduced the amplitude of postsynaptic potentials almost entirely. These effects were presynaptic. omega-Conotoxin GVIA did not change the amplitude of postsynaptic potentials. The different pharmacological profiles of the two isolated preparations suggest that there are at least two different types of calcium channel in stomatogastric neurons and that omega-Agatoxin IVA and dihydropridines can be used to pharmacologically distinguish them.

Animals↗
PubMed1997

Organization of the stomatogastric neuropil of the crab, Cancer borealis, as revealed by modulator immunocytochemistry.

We used antibodies to a number of neuromodulatory substances, including serotonin, FLRF amide, red pigment-concentrating hormone, substance P, proctolin and cholecystokinin, to investigate the distribution of molecules similar to these substances in the stomatogastric ganglion of the crab, Cancer borealis. No immunoreactivity was seen in the region of the cell bodies that surrounds the neuropil and little was found in the core of the neuropil (where the primary neurites of the intrinsic neurons occupy most of the space). Instead, modulator immunolabel was densely packed in the more peripheral portion of the neuropil that surrounded the core. Within this peripheral neuropil, profiles appeared quite uniformly distributed. Double-labeling showed that there were limited differences in distribution between the labels examined in our study. The only immunolabeled structures that showed a distinct differential distribution within the stomatogastric neuropil were a population of >/=10 microm varicosities that arose from a pair of input fibers that we termed the large varicosity fibers. These varicosities were immunolabelled by antisera for three different peptides. Taken collectively, these data shows that there is a stereotyped distribution of modulator immunoreactivity within the crab stomatogastric neuropil. However, this segregation is more rudimentary than that reported for the intrinsic stomatogastric neurons.

Animals↗
PubMed1996

Nitric oxide and peptide neurohormones activate cGMP synthesis in the crab stomatogastric nervous system.

In the neural circuits that comprise the crustacean stomatogastric nervous system (STNS), synaptically delivered neurotransmitters and circulating neurohormones elicit a wide range of rhythmic motor outputs. However, functional roles for second messengers in this system are poorly understood. Here we demonstrate two different signaling pathways that control the synthesis of 3',5'-cGMP in the crab STNS. One pathway is activated by nitric oxide (NO) and is mediated by a cytoplasmic guanylate cyclase. A second pathway is stimulated by peptide-containing extracts from a crab neurohemal organ that activate a membrane-associated guanylate cyclase. Using whole-mount immunocytochemistry to localize individual cGMP-containing cells, we find that NO elevates intracellular cGMP in a small subset of STNS neurons. Immunopositive cells are found predominantly in the stomatogastric ganglion, with a few additional cells located in the oesophageal and commissural ganglia. Crab tissues differ in their sensitivities to NO and to the peptide-containing extract. The NO-mediated pathway is apparently restricted to the nervous system, whereas the peptidemediated pathway is present in every tissue tested. The results of these experiments demonstrate that multiple signaling pathways involving cGMP are present in the STNS and suggest that this second messenger may help control the metabolic and physiological status of these motor circuits.

Animals↗
PubMed1995

Distribution of fine neurites of stomatogastric neurons of the crab Cancer borealis: evidence for a structured neuropil.

The neuropil of the stomatogastric ganglion of the crab Cancer borealis contains many neuronal processes that may be arranged either at random or in some form of orderly structure. In this study, we provide evidence for two types of order in the neuropil, a segregation of the processes based on their size and a cell-specific distribution to the fine neurites. Identified neurons were injected with Lucifer yellow, fixed, and imaged as whole mounts with a confocal microscope. Four cell types were analyzed using the serial images, two pyloric neurons, one mixed pyloric/gastric neuron, and one gastric neuron. All of the neurons consisted of a approximately 60-microns-diameter soma, a approximately 20-microns-diameter primary neurite projecting into the center of the neuropil, a number of < 10-microns-diameter medium-sized neurites radiating away from the center, and many < 3-microns-diameter fine neurites around the periphery of the neuropil. The neuropil can, therefore, be divided into three layers, a central core containing the largest neurites, an intermediate region containing both medium-sized and fine neurites, and a peripheral neuropil containing mostly fine neurites. The distribution of the fine neurites was mapped using a three-dimensional grid. We found that the fine neurites were distributed not at random within the neuropil but in consistent, cell-specific patterns.

Animals↗
PubMed1995

Immunocytochemical localization of multiple cholecystokinin-like peptides in the stomatogastric nervous system of the crab Cancer borealis.

Three anti-cholecystokinin antibodies were used to label the stomatogastric nervous system of the crab Cancer borealis. Labeled tissues were examined as whole mounts using laser scanning confocal microscopy. Although each of the anti-cholecystokinin antibodies labeled a variety of structures within the stomatogastric nervous system (including somata, fibers and neuropil), the pattern of labeling produced by each antibody was distinct. These results indicate that there is a family of cholecystokinin-like molecules that are differentially distributed among a subpopulation of the neurons in the stomatogastric nervous system of Cancer borealis.

Animals↗
PubMed1993

Nickel induces oscillatory behavior and enhanced synaptic and electrotonic transmission between stomatogastric neurons of Panulirus interruptus.

The pyloric pattern generator network of the stomatogastric ganglion uses a mixture of burst-inducing plateau potentials, synaptic transmission, and electrical coupling to produce its patterned output. This study examines the effects of two divalent, calcium channel blockers, nickel and cadmium, on voltage oscillations, synaptic transmission, and electrical coupling between the two pyloric dilator (PD) neurons and lateral pyloric (LP) neuron of Panulirus interruptus. The in vitro stomatogastric ganglion was bathed in saline containing tetrodotoxin (TTX) to eliminate Na-spikes and the spontaneous voltage oscillations of the pyloric rhythm, resulting in a steady resting potential. Addition of 50-100 microM Ni2+ to the TTX-saline induced voltage oscillations of similar amplitude and frequency as the endogenous rhythmic activity (before the application of TTX). 25-50 microM nickel enhanced graded synaptic transmission and electrical coupling and altered voltage waveforms, while producing little change in the input resistance measured in the soma. 10-1000 microM Cd2+ acted as a dose-dependent blocker of graded synaptic transmission, but had no other detectable effects. We propose that nickel, in contrast to cadmium, exerts a modulator-like effect deep in the pyloric neuropil.

Animals↗
PubMed1991

Voltage clamp analysis of intact stomatogastric neurons.

Two-electrode voltage clamp of intact, identified pyloric neurons of the spiny lobster stomatogastric ganglion reveals two major outward currents. A rapidly inactivating, tetraethylammonium- (TEA) insensitive, 4-aminopyridine- (4AP) sensitive, outward current resembles IA of molluscan neurons; it activates rapidly on depolarizations above rest (e.g. -45 mV), delaying both the axonal-sodium and the neuropil-calcium spikes which escape voltage-clamp control. We infer that A-current is distributed both in a space clamped region (on or near the soma) and in a non-space clamped region with access to the generators for sodium and calcium spikes. A calcium-dependent outward current, IO(Ca), activates rapidly at clamp steps above -25 mV and inactivates at depolarizing holding voltages. Increasing depolarization results in an increase in both IO(Ca) and firing rate but a reduction in the amplitude of the sodium spike current. Blockage of IO(Ca) with Cd2+ causes little change in spike firing pattern. These observations are consistent with IO(Ca) being activated primarily in the soma and nearby regions which are under good control with a soma voltage clamp (and distant from the Na(+)-spike trigger zone). While the lack of space clamp limits resolution of charging transients and tail currents, the identification of the major current subgroups can still be readily accomplished, and inferences about the location and function of currents can be made which would not be possible if the cells were space clamped or truncated.

4-Aminopyridine↗
PubMed1989

Spatially and temporally resolved calcium concentration changes in oscillating neurons of crab stomatogastric ganglion.

Calcium concentration changes during oscillations of the membrane potential of crab (Cancer irroratus or Cancer borealis) stomatogastric neurons were monitored at many positions by using the calcium indicator dye arsenazo III and a photodiode array. Data analysis algorithms using signal averaging techniques were developed to improve the time resolution of the measured calcium changes. As previously reported, calcium oscillations were detected from all regions of the neuropil but not from the soma or axon. In some cells step increases in intracellular neuropil calcium were correlated with each of the action potentials in the burst (on the peak of the voltage oscillation). In other cells we observed calcium oscillations phase-locked to the membrane potential with no spike-related component. A few cells had both spike-evoked and graded potential components to the calcium oscillations. In those cells, the spatial distribution of the spike-correlated calcium influx differed from that of the voltage-oscillation-correlated calcium influx, suggesting that different neurites might interact with their postsynaptic targets with different mixtures of graded and spike-correlated transmitter release.

Action Potentials↗
PubMed1987

Full-wave rectification from a mixed electrical-chemical synapse.

Electrical and chemical synapses usually reinforce one another, but the pyloric late-to-lateral pyloric (PL-to-LP) neuronal connections in lobster stomatogastric ganglia create an inverted U-shaped transfer function between the two neurons: regardless of whether the PL membrane voltage swings positive or negative, the postsynaptic LP voltage will go negative. When the presynaptic cell voltage goes negative, the effect on the LP voltage is due to electrical coupling. During positive presynaptic voltages, the strong contribution of graded chemical inhibition from the PL to the LP neuron overrides the positive electrical coupling to produce net negativity.

Animals↗
PubMed1987

Co-localization of SCPB-like and FMRFamide-like immunoreactivities in crustacean nervous systems.

A monoclonal antibody to the molluscan small cardioactive peptide SCPB and a polyclonal antibody to FMRFamide were used to localize antigens in the stomatogastric nervous system and brain of two species of Cancer. Both antibodies labeled cell bodies, axons, and neuropilar processes in the brain and in the stomatogastric nervous system. All of the SCPB immunoreactive neurons were co-labeled with antibody to FMRFamide. However, antibody to FMRFamide labeled additional neurons of the commissural ganglion and the brain that were not immunoreactive to the monoclonal SCPB antibody.

Antibodies, Monoclonal↗
PubMed1985

Regional distribution of calcium influx into bursting neurons detected with arsenazo III.

Absorbance changes of the metallochromic indicator arsenazo III were used in conjunction with an array of 100 photodiodes to measure changes in intracellular calcium concentration at many positions simultaneously in identified neurons of the crab stomatogastric ganglion. When stimulated with intrasomatically injected current, several of these neurons showed calcium changes all over the cell, indicating that calcium channels were distributed widely in the neuropil and on the soma. When the membrane potential was allowed to oscillate without stimulation, absorbance oscillations were detected all over the neuropil but not in the soma. A comparison between the membrane potential recorded in the soma and the calcium signal in the neuropil shows that calcium entry followed the slow voltage oscillation with the peak calcium signal detected 50-150 msec after the end of the voltage plateau.

Animals↗
PubMed1983

Graded synaptic transmission between identified spiking neurons.

Graded synaptic transmission between spiking motoneurons of the pyloric group was studied in the stomatogastric ganglion of the spiny lobster, Panulirus interruptus. Intracellular microelectrodes were placed in the cell bodies of both pre- and postsynaptic neurons. Graded synaptic transmission was found between all tested cell pairs that were known to display spike-evoked synaptic transmission, including PD to LP, PD to PE, PD to PL, PL to LP, and LP to PD. Graded synaptic transmission was effective below the threshold for spikes. Thus, it was possible to study the influence of graded synaptic transmission in normally active ganglia without blockage of spikes by tetrodotoxin. PD and LP neurons that were known to produce spike-evoked inhibitory postsynaptic potentials (IPSPs) were also capable of producing inhibitory effects on postsynaptic cells below the threshold for spikes. When tetrodotoxin (TTX) was used to eliminate both spikes and endogenous membrane oscillations, depolarization of presynaptic neurons produced hyperpolarization of postsynaptic cells. The presynaptic response to a current step usually showed a small early peak and a maintained, slightly lower plateau. The postsynaptic response had a delay, then a rise to a pronounced peak, and a roughly exponential decline to a maintained plateau. There was a presynaptic voltage threshold for any postsynaptic response; beyond the threshold, both pre- and postsynaptic peak and plateau responses increased with increasing current. PD neurons normally are depolarized beyond their release threshold in tetrodotoxin and, thus, released transmitter tonically for the many-hour duration of these experiments. Chemical, tonic synaptic transmission, here called graded synaptic transmission, was demonstrated by the presence of the following criteria: 1) reversal in sign of the postsynaptic response, 2) synaptic delay, 3) reversal potential, 4) postsynaptic conductance increase, 5) graded and reversible block by reduction of external Ca2+, and 6) specific graded block of the LP-to-PD synapse without effect on the PD-to-LP synapse by less than 10 microM picrotoxin added to the bathing medium.

Action Potentials↗
PubMed1980

Graded synaptic transmission between spiking neurons.

Graded synaptic transmission occurs between spiking neurons of the lobster stomatogastric ganglion. In addition to eliciting spike-evoked inhibitory potentials in postsynaptic cells, these neurons also release functionally significant amounts of transmitter below the threshold for action potentials. The spikeless postsynaptic potentials grade in amplitude with presynaptic voltage and can be maintained for long periods. Graded synaptic transmission can be modulated by synaptic input to the presynaptic neuron.

Action Potentials↗