bluuebunny/crossref_metadata_2025_split huggingface dataset:
Increasing external K+ blocks phase shifts in a circadian rhythm produced by serotonin or 8‐benzylthio‐cAMP
Authors: Eskin Arnold 
Published: January 2005

AbstractSerotonin (5‐HT) phase shifts the circadian rhythm from the isolated eye of Aplysia. The discovery of the mechanisms involved in phase shifting by 5‐HT may help elucidate the nature of the circadian oscillator. We have found that 5‐HT appears to phase shift by causing a change in membrane K+ conductance. Solutions containing zero K+ (O‐K+) phase shift the rhythm and the phase response curve (PRC) for O‐K+ is similar to one previously obtained for 5‐HT. The similarity in PRCs for O‐K+ and 5‐HT suggested that these treatments may be phase shifting the rhythm through a common mechanism. The nonadditivity of phase shifting by O‐K+ and 5‐HT supports this suggestion. A common mechanism of action of 5‐HT and O‐K+ might be effects on membrane potentials. The possible involvement of a membrane potential change in mediating the effect of 5‐HT and the lack of an effect of large reductions in Na+, Cl−, and Ca2+ ions on phase shifting by 5‐HT led us to examine the role of K+ ions in phase shifting by 5‐HT. A change in K+ conductance may mediate the effects of 5‐HT on the rhthym because HiK (30mM) solutions blocked the phase shift normally produced by 5‐HT. The conductance change produced by 5‐HT may be an increase in K+ conductance which would produce a hyperpolarization and not a decrease in K+ conductance which would produce a depolarization since depolarizing treatment, HiK (30–110mM), had no effect on the rhythm at the phase where 5‐HT produces its largest phase shifts. Since we previously found that the effects of 5‐HT appear to be mediated by cAMP, we examined whether HiK solutions could block the effects of 8‐benzylthio‐cAMP on the rhythm. HiK (40mM) blocked the phase shifts normally produced by 8‐benzylthio‐cAMP. Our working hypothesis for the 5‐HT phase‐shifting pathway based on these results is 5‐HT → increased cAMP → elevates K+ conductance → membrane hyperpolarization → phase shifts the rhythm.
Electrophysiological correlates of rapid escape reflexes in intact earthworms, Eisenia foetida. I. Functional development of giant nerve fibers during embryonic and postembryonic periods
Authors: O'Gara B. , Vining E. P. , Drewes C. D. 
Published: January 2005

AbstractGrids of recording electrodes etched onto printed circuit boards were used for noninvasive recording of medial (MGF) and lateral (LGF) giant nerve fiber spikes in developing earthworms, Eisenia foetida. Stereotyped patterns of throughconducted giant fiber spikes, evoked by light tactile stimulation, were first detectable in the normal crawling embryonic stage and continuned to be detectable throughout postembryonic development. Giant fiber spiking activity in normal crawling embryos was accompanied by stereotyped muscle activity and rapid escape withdrawal, suggesting that giant fiber reflex pathways are functionally intact before the worm hatches. For both the MGF and LFG, several age‐de‐pendent changes were noted, including the following: increases in spike conduction velocity, increases in giant fiber diameter, and decreases in spike duration. The MGF conduction velocity in normal crawling embryos was 1.1–1.6 m s−1 (6–7 μm diameter) and increased to 7.0–8.5 m s−1 (20–25 μm diameter) by 60 days after hatching. The LGF conduction velocity in normal crawling embryos was 0.7–1.1 m s−1 (2.5–4.0 μm diameter) and increased to 4.0–5.5 m s−1 (8–14 μm diameter) by 60 days after hatching. During postembryonic development MGF and LGF conduction velocities were linearly related to fiber diameter.
Electrophysiological correlates of rapid escape reflexes in intact earthworms, Eisenia foetida. II. Effects of food deprivation on the functional development of giant nerve fibers
Authors: Vining E. P. , O'Gara B. , Drewes C. D. 
Published: January 2005

AbstractNoninvasive electrophysiological recording methods were used to study the effects of prolonged food deprivation on the postembryonic patterns of giant fiber growth, as indicated by age‐dependent changes in giant fiber conduction velocity and diameter, in the earthworm, Eisenia foetida. In addition, giant fiber growth was compared to patterns of somatic growth, as indicated by increases in body weight. Within a wide range of food deprivation levels, normal age‐dependent increases in conduction velocity and diameter occurred in spite of marked stunting of somatic growth. Stunting of giant fiber velocity and diameter occurred only during severe food deprivation, but giant fiber spikes and associated rapid escape responses were still readily evoked. The stunting effects of prolonged and severe food deprivation upon giant fiber conduction velocity and diameter were readily reversed by replenishing food. The results demonstrate the persistence of rapid escape reflex functioning, as well as the priority of giant fiber growth relative to somatic growth, during severe and prolonged food deprivation. As a consequence of the priority of giant fiber growth during limited food availability, giant fiber conduction velocity appears to be a more reliable predictor of animal age than body size.
Structural comparison of a homologous neuron in gryllid and acridid insects
Authors: Wilson John A. , Phillips Christine E. , Adams Michael E. , Huber Franz 
Published: January 2005

AbstractThe fast extensor tibiae (FETi) motor neuron is responsible for exciting the extensor tibiae muscle to produce most of the force for jumping in acridids. Because of its relatively large size and crucial role in jumping, FETi has been studied in an ever‐increasing number of orthopteran species. Here we describe the structure of the metathoracic FETi neuron in six species of acridids and in two species of gryllids. The morphology of FETi within the respective groups is essentially equivalent, but marked differences are apparent between acridid and gryllid FETis. There are similarities in the size and location of the cell body and the course of the neurite through the ganglion. Differences are found in the number of large branches, density of branching, and the volume of neuropil receiving branches. We propose that the gryllid FETi is an intermediate form between slow extensor tibiae motor neurons involved in walking and acridid fast extensor tibiae motor neurons specialized for jumping.
Swelling of the Müller fibers in the chicken retina
Authors: Van Harreveld A. 
Published: January 2005

AbstractA high potassium concentration (33 meq) in the solution superfusing the isolated chicken retina causes an increase in the tissue transparency. An L‐glutamate (1mM) or L‐proline (10mM) solution has the same effect. Swelling of the Müller fibers, which have a radial position in the retina, could explain the transparency increase. This possibility was investigated in electron micrographs of retinas subjected to these treatments and fixed by freeze‐substitution to preserve the water distribution in the tissue. The Müller fibers in the controls had a mean diameter of 0.22 μm. The fibers in retinas bathed for 2 min in the high [K+] solution were more than three times as thick (0.74 μm); the fibers in glutamate‐treated retinas were more than twice as thick (0.49 μm). The fibers in the proline‐treated retinas had a diameter of 0.39 μm. The glutamate‐ and proline‐induced swelling may be due to a K+ release from neuronal elements, acting on the Müller fibers. The fiber swelling was postulated to be the expression of different Donnan equilibriums of fibers bathed in solutions of different K+ concentrations. The observed swelling caused by the high [K+] solution was compared with the theoretical swelling of the fiber as an ideal Donnan system, postulating permeabilities for different ions of the fiber membrane. This suggested that the high [K+] solution causes an increase in Na+ permeability in addition to the permeability of the membrane for K+, Cl−, and HCO. Chemical fixation with glutaraldehyde and formaldehyde in an Na‐phosphate buffer yielded micrographs in which the Müller fibers of retinas treated with a high [K+] or a glutamate solution had diameters similar to those of the control preparations.
Dependence of batrachotoxin block of axoplasmic transport on sodium
Authors: Worth Robert M. , Ochs Sidney 
Published: January 2005

AbstractBatrachotoxin (BTX) in the low concentration range of 19–190nM blocks axoplasmic transport in the desheathed cat peroneal nerve in vitro. When the level of Na+ in the incubation medium was reduced to 10mM, the blocking effect of BTX was much diminished, and in an Na+‐free medium BTX had no effect on transport at all. The blocking action of BTX with Na+ present was inhibited by increasing the concentration of Ca2+ in the experimental medium. Relatively small increases were effective with a maximum protection seen when the Ca2+ concentrations were 7–10mM. The results support the view that an increase in axonal Na+ is inhibitory to the transport mechanism. The results are discussed on the basis of the recently developed transport filament model of axoplasmic transport which takes into account and obligatory role for Ca2+ in transport and its axonal regulation. The possible relation of intraaxonal Na+ concentration to the Ca2+ level is also discussed.
Morphology and odor sensitivity of regenerated snail tentacles
Authors: Chase Ronald , Kamil Rifa'at 
Published: January 2005

AbstractThis study examined certain structural and functional aspects of the olfactory system in regenerated posterior tentacles of the terrestrial snail Achatina fulica. Regeneration of the epithelial sensory pad occurs with accurate size regulation. All five neuronal cell types which are normally revealed by horseradish peroxidase backfilling are also regenerated. The sensory cells attain normal numbers at about 20 weeks postlesion. The organization of neuronal elements within the tentacle is chaotic, however, at early stages of regeneration. Even later, the digitlike extensions of the ganglion, which are characteristic of intact tentacles, fail to appear. The recovery of odor sensitivity was evaluated using a tentacular olfactometer and a behavioral assay that involved locomotor orientation towards the odor stimulus. Thresholds and concentration‐dependent response rates were equivalent for regenerated and intact tentacles, tested in the same animals, at 10 weeks post‐lesion.
Axonal transport involvement in long‐lasting synaptic modifications in blatta orientalis
Authors: Fernandez Hugo L. , Alejandro Donoso J. 
Published: January 2005

AbstractTo determine whether axonal transport plays a role in the establishment of long‐lasting changes in synaptic transmission, the effects of colchicine on transport and on synaptic modifications induced by hyperactivity were studied in the nerve cord of the cockroach Blatta orientalis. Application of a lead weight on the insect′s dorsum, and the consequent exaggerated use of antigravity reflexes, facilitated synaptic transmission along a particular nervous pathway in the metathoracic ganglion. Application of colchicine in the prothoracic ganglion reversibley blocked such synaptic facilitation and temporarily interfered with the transport of proteins along the cord. Five components of axonal transport, moving at 2, 10, 25, 75, and 150 mm/day, were altered by colchicine treatment with a temporal course that coincided with the reversible inhibition of synaptic facilitation. These results were brought about by colchicine acting directly on axonal transport at the level of the prothoracic ganglion, rather than on synaptic transmission measured at the metathoracic ganglion. The temporal correlation observed between the effects of colchicine on axonal transport and on synaptic facilitation strongly suggest that the transport process is essential for long‐lasting synaptic modifications to take place.
Veratridine‐stimulated central synapses in culture: A quantitative ultrastructural analysis
Authors: Janka Z. , Da Cruz M. , Jones D. G. 
Published: January 2005

AbstractSynapses in explant cultures of fetal rat neocortex at day 18 in vitro were stimulated by veratridine (10−4M) for 20 min. The cultures were subsequently processed for electron microscopy and the synapses were analyzed by quantitative techniques, incorporating set mathematical treatment. The mean values of area, perimeter, and form factor of the presynaptic elements significantly increased following veratridine stimulation, compared to the values of control synapses. The length of the postsynaptic thickening also increased, while synaptic curvature did not change significantly in the veratridine group. A fivefold reduction was observed in the mean number of synaptic vesicles per presynaptic element and in the vesicle‐terminal area ratio, following veratridine stimulation. The cytoplasm‐terminal area ratio and the occurrence of vacuoles/cisternae significantly increased after veratridine application. Planar measurement of membranes (boundary length) of different presynaptic organelles revealed that the total membrane did not change significantly in the veratridine group. The data indicated an increase in volume and swelling of the pre‐ and postsynaptic elements, considerable depletion of synaptic vesicles, and preservation of the total presynaptic membrane following veratridine stimulation in nerve tissue culture.
Recovery of slow axonal transport after colchicine treatment in rat sciatic nerve
Authors: Komiya Yoshiaki 
Published: January 2005

AbstractColchicine (4 μg), injected into the fifth lumbar (L5) dorsal root ganglion of the rat, preferentially inhibited tubulin transport with little, if any, effect on the transport of other slowly migrating proteins. This inhibitory effect of colchicine on slow axonal transport persisted at least two days after the treatment, but no more than four days. Within these days the damaged axons were recovered to start regenerating with the rate of 4.7 ± 0.1 mm/day.
Effect of CO2 on neurons of the house cricket, acheta domestica
Authors: Clark Mary Anne , Eaton Douglas C. 
Published: January 2005

AbstractThe effect of elevated levels of CO2 on the neurons of the metathoracic ganglion of the common house cricket was examined. Elevated CO2 produced a profound depolarization of the neurons without a substantial change in conductance. The depolarization was not due to CO2 acidification of the external solution since exposure of the neurons to a solution which was nominally CO2 free, but at an acid pH, produced little effect. The effect of elevated CO2 appeared to be due to intracellular acidification, since other treatments which acidified the cell interior also produced deplorization. Agents which block intracellular pH regulation also substantially enhance the effect and prevent recovery. The mechanism producing the deplorization appears to be blockage of a metabolic component of the resting potential, since the action of metabolic blockers mimics the effect of elevated CO2.
Further evidence for an opioid receptor complex
Authors: Rothman Richard , Westfall Thomas C. 
Published: January 2005

AbstractWe recently presented evidence that distinct morphine and enkephalin receptors coexist in an opioid receptor complex. These studies used membranes prepared from whole rat brain. In this paper the receptor complex is demonstrated to occur in membranes prepared from rat striatum, cortex, and pooled nonstriatal‐noncortical regions of the brain. The observation that morphine masks enkephalin receptors is confirmed using 3H‐methionine enkephalin to label the enkephalin receptor. These data further support the hypothesis that populations of morphine and enkephalin receptors coexist in an opioid receptor complex.
Evidence for a presynaptic blockage of transmission in a temperature‐sensitive mutant of Drosophila
Authors: Koenig J. H. , Ikeda Kazuo 
Published: January 2005

AbstractIn the temperature sensitive mutant of Drosophila, shibirets1 (shi), synaptic transmission in the dorsal longitudinal flight muscles (DLM) is normal at 19°C, but is diminished progressively as the temperature is raised, and is blocked at 29°C. The purpose of this paper is to determine whether this defect is located presynaptically, postsynaptically, or both. It is demonstrated here that the postsynaptic sensitivity to L‐glutamate, the putative transmitter for this synapse, is not decreased at 29°C. Furthermore, studies conducted with genetic mosaics of this mutant show that transmission is blocked when a mutant motor neuron synapses on a wild‐type muscle fiber, but is not blocked when a wild‐type motor neuron synapses on a mutant muscle fiber. Thus, the shi phenotype (temperature dependent transmission block) correlates with a shi motor neuron, not with a shi muscle fiber. The data, therefore, suggest that the defect is not postsynaptic, but presynaptic.
Are different proteins synthesized in distinct domains in a neuron?
Authors: Tedeschi Bruce , Wilson David L. 
Published: January 2005

AbstractAre different messenger RNA species translated in distinct, limited domains within a cell? For the particular case of the giant R2 neuron from Aplysia californica an answer to this question is possible for the more abundantly synthesized proteins. After brief labeling with 35S‐methionine, the R2 neuron soma was frozen and divided into two or three parts. The newly synthesized proteins were analyzed following two‐dimensional polyacrylamide gel electrophoresis. No evidence for limited domains of synthesis for 26 abundantly synthesized polypeptides in the R2 neuron was found.
Subcellular sites of processing of precursors to neurosecretory peptides in the bag cells of Aplysia: Inferences from the effects of monensin, FCCP, and chloroquine
Authors: Yates Michael E. , Berry Robert W. 
Published: January 2005

AbstractThe effects of the sodium ionophore monensin were examined in the bag cells of Aplysia californica in order to identify the subcellular sites of processing of precursors to their neurosecretory products. Incubation of bag cells in media containing 10 μM monensin led to a marked disruption of the morphology of the Golgi apparatus without affecting that of other organelles. Exposure of bag cells to monensin led to a significant impairment of processing of the largest precursor and of an intermediate protein which gives rise to the immediate precursors to the final secreted products, the egg‐laying hormone (ELH) and the acidic peptide (AP). Furthermore, ELH and AP were never produced in the presence of monensin during the time course of these experiments. When axonal transport was allowed to proceed, the contents of bag‐cell terminals indicated that the intermediate protein is the first to be packaged in Golgi‐derived vesicles, and in monensin‐treated cells may be transported without being processed further. In contrast to these results, the protonophore FCCP‐impaired precursor and intermediate cleavage equally, indicating that monensin and FCCP have different effects on intracellular transport and precursor processing. These data are interpreted to indicate that the largest ELH‐AP precursor is normally processed within the Golgi apparatus, and that the disruption of this organelle induced by monensin produces the impairment seen in its processing. The impairment of cleavage of the intermediate species, and the blockade of production of AP and ELH, are probably the result of monensin‐induced impairment of production of proteolytically competent secretory granules by the Golgi apparatus.
β‐Bungarotoxin antagonizes the effect of α‐latrotoxin from black widow spider venom on the neuromuscular junction
Authors: Tzeng Mu‐Chin , Tian Shin Shay 
Published: January 2005

AbstractSustained contraction of the chick biventer cervicis nerve‐muscle preparations evoked by α‐latrotoxin was antagonized quickly by β‐bungarotoxin. This effect of β‐bungarotoxin was dependent on its phospholipase A2 activity. In contrast, pancreatic phospholipase A2 was ineffective even at a much higher dose. It is concluded that α‐latrotoxin needs intact presynaptic membrane to exert its effect.
Dual effects of proctolin on the rhythmic burst activity of the cardiac ganglion
Authors: Sullivan Robert E. , Miller Mark W. 
Published: January 2005

AbstractThe neuropeptide proctolin has distinguishable excitatory effects upon premotor cells and motorneurons of Homarus cardiac ganglion. Proctolin's excitation of the small, premotor, posterior cells is rapid in onset (5–10 s) and readily reversible (< 3 min). Prolonged bursts in small cells often produce a “doublet” ganglionic burst mode via interactions with large motorneuron burst‐generating driver potentials. In contrast to small cell response, proctolin's direct excitatory effects upon motorneuron are slow in onset (60–90 s to peak) and long‐lasting (10–20 min). The latter include: (a) a concentration‐dependent (10−9–10−7M) depolarization of the somatic membrane potential; (b) increases in burst frequency and (c) enhancement of the rate of depolarization of the interburst pacemaker potential. Experiments on isolated large cells indicate: (a) the slow depolarization is produced by a decrease in the resting GK and (b) proctolin can produce or enhance motorneuron autorhythmicity. A two‐tiered non‐hierarchical network model is proposed. The differential pharmacodynamics exhibited by the two cell types accounts for the sequential modes of ganglionic burst activity produced by proctolin.
Endogenous burst capability in a neuron of the gastric mill pattern generator of the spiny lobster Panulirus interruptus
Authors: Hartline Daniel K. , Russell David F. 
Published: January 2005

AbstractThe gastric system of the lobster stomatogastric ganglion has previously been thought to include no neurons capable of endogenous bursting. We describe conditions under which one of the motorneurons, the CP cell, can burst endogenously in a free‐running manner in the absence of other phasic network activity. Isolated preparations of the foregut nervous system were used, and the CP bursting was either spontaneous or was activated by continuous stimulation of an input nerve.Three criteria were applied to establish the endogenous nature of such burst generation in CP: absence of phasic input, reset of the bursting pattern by pulses of current in a characteristic phase‐dependent manner, and modulation of burst rate by sustained injected current. (1) The firing of other cells which are known to be related synaptically to CP was monitored in nerve records. These other cells were either silent or fired only tonically. Cross‐correlograms showed that CP bursting was not ascribable to phasic activity in these other network cells. (2) A depolarizing current pulse of sufficient strength injected intracellularly between bursts triggered a burst prematurely and reset the subsequent rhythm. A hyperpolarizing pulse during a burst terminated it and reset the subsequent rhythm. Reset behavior was similar to that described for other endogenous bursters. (3) Application of a positive‐going ramp current initially caused an increase in burst rate, as described for other endogenous bursters. However, further depolarization caused a slower burst rate due to lengthening of the individual bursts, although mean firing frequency continued to increase throughout the range tested.Such free‐running endogenous repetitive bursting appeared to result from the CP's ability to produce slow regenerative depolarizations (“plateau potentials”). When bursting was present, so was the plateau property, as determined by I–V analysis and by the ability of brief current pulses to trigger and terminate bursts. The previous inability to observe endogenous bursting in preparations with central input removed may be due to the usual absence of the plateau property in such preparations.