bluuebunny/crossref_metadata_2025 huggingface dataset:
Bidirectional axonal transport of 16S acetylcholinesterase in rat sciatic nerve
Authors: Fernandez Hugo L. , Duell Myron J. , Festoff Barry W.
Published: January 2005

Axonal transport of the 16S molecular form of acetylcholinesterase (16S‐AChE) in doubly ligated rat sciatic nerves was studied by means of velocity sedimentation analysis on sucrose gradients. This form of AChE was selectively confined to motor, and not to sensory, fibers in the sciatic nerve, where it represented 3–4% of total AChE. Its activity increased linearly with time (4–20 hr) in nerve segments (7 mm) proximal to the central ligature (4.5 mU/24 hr) and distal to the peripheral ligature (2.0 mU/24 hr). From the linear rates of accumulation of 16S‐AChE, we conclude that the enzyme is conveyed by anterograde and retrograde axonal transport at velocities close to those previously defined for the movement of total AChE (410 mm/day, anterograde; 220 mm/day, retrograde). The transport of AChE molecular forms, other than the 16S form, could not be resolved presumably due to their presence in blood as well as at extraaxonal sites. The present findings are consistent with the view that in rat sciatic nerve most, if not all, of the small portion of total AChE (approximately 3%) which is transported may be accounted for by 16S‐AChE.
Intensity and motion responses of giant vertical neurons of the fly eye
Authors: Soohoo Spencer L. , Bishop Lewis G.
Published: January 2005

There are nine “giant vertical” neurons in the lobula plate of the fly optic lobe. Intracellular recordings were obtained from the three most peripheral of these cells. These cells respond to a light flash with graded changes in the membrane potential. The response consists of an “on” transient, a sustained depolarization, an increase in membrane potential fluctuations, and an “off” transient. Signal averaging showed that only the “on” and “off” transients are correlated to the stimulus. A pattern of horizontally oriented stripes moving in the vertical direction evokes a response larger than the response to a stationary pattern. The response is most sensitive to vertical movement; motion in the downward direction evokes a net membrane potential depolarization, and upward motion results in a net hyperpolarization. We conclude that the giant vertical cells function primarily as vertical motion detectors and that the direction of the motion is encoded in the polarity of the shift in the membrane potential.
Cholesterol is a component of the rapid phase of axonal transport
Authors: Blaker William D. , Toews Arrel D. , Morell Pierre
Published: January 2005

Twenty‐two‐day‐old rats were injected intraocularly with [3H]acetate and killed between 1 hr and 35 days later. Cholesterol was isolated from the retinas, optic tracts, lateral geniculate bodies, and superior colliculi. Within the retina, radioactivity was rapidly incorporated into cholesterol with maximal labeling present one hour after injection. Transported labeled cholesterol (contralaterally corrected for systemic background labeling) was present in the superior colliculus by three hours. Radioactive cholesterol accumulated in all visual strctures throughout the 35‐day period, but the rate of accumulation was maximal at about the time of arrival of the initial pulse of radioactivity. Colchicine treatment of the retina blocked transport of cholesterol but not its synthesis by the retina. The results indicate that cholesterol is rapidly transported in the visual system and also released from the retina for a prolonged period after its synthesis.
Block of axoplasmic transport in vitro by vinca alkaloids
Authors: Chan S. Y. , Worth R. , Ochs S.
Published: January 2005

The three potent antimitotic vinca alkaloids: vincristine (VCR), vinblastine (VLB), and vindesine (VDS) were compared for their effect in blocking axoplasmic transport in vitro using a desheathed preparation of the peroneal branch of cat sciatic nerve. A range of vinca alkaloid concentrations from 1–100μM was examined. The relative order of potency in blocking axoplasmic transport was VCR > VLB > VDS at a concentration of 25μM. At the higher concentrations block occurred so rapidly that a statistically significant difference between these agents could not be obtained. The relation of vinca block ot the transport mechanism is discussed.
Dynamic properties of cockroach cercal “bristlelike” hair sensilla
Authors: Buño W. , Monti‐Bloch L. , Crispino L.
Published: January 2005

Responses of cercal “bristlelike” hair sensilla (BHS) on Periplaneta americana L. to movement were investigated by recording generator (GP) and spike potentials with an extracellular pipette electrode which held the bristle by its tip. BHSs had no resting discharge, were purely phasic, with sensitivity only to stimulus transitions. They were directionally sensitive. Sinusoidal analysis suggested, to a first approximation because of the important nonlinearities, the behavior of a first‐order lead system with corner frequencies distributed between 8 and 20 Hz. Responses elicited by step‐ and ramplike displacements were roughly in accord with the above behavior. Nonlinearities occurred both at GP level and at the level of spike generation. The phasic and the nonlinear behaviors at GP level may have a mechanical origin. The lack of spontaneous activity and the threshold nature of the spike generator account for other nonlinearities. The operation of BHS could be separated conceptually into a linear element followed by nonlinear elements. A computer simulation based on these concepts showed a close fit to the biological responses.
Dynamic properties of cockroach cercal “threadlike” hair sensilla
Authors: Buño W. , Monti‐Bloch L. , Mateos A. , Handler P.
Published: January 2005

Input‐output (I‐O) relationships were studied in cercal “thread‐hair” sensilla (THS) on Periplaneta americana L. by recording from individual axons of THS while displacing the corresponding hair with a galvanometric device. Sinusoidal analysis was attempted and pulse‐ and ramplike displacements were then tested. The effects of stimulus orientation were also investigated. THS were spontaneously active and purely phasic and did not respond to sustained displacements. With small sinusoidal displacements (<30°) they behaved as a linear, secondorder lead system sensitive to velocity. With larger amplitudes, however, they exhibited prominent nonlinear features with minimal consequences of displacements at the extremes. Responses to other waveforms indicated secondorder response components. THS were directionally sensitive. Phasic behavior and the nonlinearities may be due to mechanical properties at the base of the hair. The spike‐firing threshold may also contribute. Resting activity appears to be due to neuronal factors since it was not abolished by preventing hair movements. Transducer operations were simulated in a digital computer.
Pineal glands of immature rats: Rise and fall in N‐Acetyltransferase activity in vitro
Authors: Brammer Mildred , Binkley Sue
Published: January 2005

N‐acetyltransferase activity in the pineal glands of immature rats (12‐14 days old) shows a spontaneous rise and fall when the glands are placed in organ culture. The peak of the 28‐fold change occurs 5–16 hr after the cultures are initiated. This observation can be interpreted in two ways: (1) the pup pineal gland is responding to norepinephrine released when nerve endings degenerate in culture, or (2) the pup pineal gland has an innate ability which is responsible. Whatever the mechanism, the phenomenon is associated with the development of pineal gland function since pineal glands of adult rats do not show a spontaneous rise and fall in identical experiments.
Interneurons of the crayfish brain: The relationship between dendrite location and afferent input
Authors: Glantz Raymon M. , Kirk Mark , Viancour Terry
Published: January 2005

This study was undertaken to examine the relationship between the structure and function of the descending interneurons of the crayfish brain. In particular, the dendritic fields were examined to ascertain if the location of an interneuronal dendrite in any of the six cerebral hemineuromeres (which subserve specific sensory modalities) is a necessary or sufficient condition to determine the functional and/or synaptic input to the interneuron. If a neuron projects a dendrite to a hemineuromere of the deutocerebrum or tritocerebrum, the neuron derives sensory input from the corresponding afferent root in 95% of our observations. Most of these inputs (86%) contain at the least a monosynaptic component. Conversely, if a cell derives monosynaptic input from any one of three of the four deutocerebral and tritocerebral roots tested, it has a corresponding dendrite (in 98% of our observations) in the appropriate hemineuromere. Input from the contrlateral antennal nerve is an exception to this rule. The presence of a dendrite in the protocerebrum is not sufficient for predicting detectable visual input, but every instance of detectable visual input is associated with a protocerebral dendrite. Polysynaptic inputs are frequently (42%) not associated with corresponding dendrites. In neurons that were repeatedly dye filled in different animals, we observed significant variation only in the number and precise location of the smaller secondary and tertiary neurites. This variation rarely influenced the subset of sensory lobes innervated by the neuron.
In vivo electrical stimulation alters sensitivity of the brain (Na+ + K+)ATPase toward inhibition by vanadate
Authors: Křivánek Jiři
Published: January 2005

It has recently been shown that electrical stimulation of the brain cortex in vivo blocks invasion of cortical spreading depression (SD) into the stimulated area. The effect has been interpreted as a result of activating a K+ pumping mechanism that prevents the accumulation of this ion in the extracellular space to the high levels required for SD propagation. In the present experiments (Na+ + K+)ATPase activity was determined in the electrically stimulated region of the rat brain cortex. When ATP preparations containing vanadate were used as substrate, elevation of K concentration in the assay medium from 2 to 20 μM inhibited enzyme activity in homogenates from the normal cortex but not that from homogenates of the electrically stimulated cortical region. With vana‐date‐free ATP (Boehringer) as a substrate, slight stimulation by 20 μM K+ has been observed in both cases. Vanadate (0.25 μM) added to the assay medium containing Boehringer ATP and 20 μM K+ inhibited ATPase activity from the normal cortex but not that from the stimulated cortical area. Electrical stimulation may activate (Na+ + K+)ATPase at least partly by diminution of its susceptibility toward the inhibitory action of vanadate.
Axonal branching pattern and coupling mechanisms of the cerebral giant neurones in the snail, lymnaea stagnalis
Authors: Goldschmeding J. T. , van Duivenboden Yvonne A. , Lodder J. C.
Published: January 2005

The axonal branching pattern of the two cerebral giant neurones (CGCs) of Lymnaea stagnalis was studied with intrasomatically applied horseradish peroxidase. The cells are symmetrical. Each CGC projects to the ipsilateral n. labialis medius and n. arteriae labialis, the subcerebral commissure, and to all ipsi‐ and contralateral buccal nerves. The contralateral buccal nerves are reached via the ipsilateral cerebro‐buccal connective and the buccal commissure. The CGC fire action potentials 1:1 in a driver‐follower relationship. Each cell is capable of both driving and following. The relationship depends on the membrane potentials of the somata. In driving CGC spikes are initiated in a cerebral spike trigger zone located near the soma. In following cells spikes are initiated in a distal zone located in the buccal ganglia. The buccal zone is only affected by the partner CGC. CGC are synchronized by three coupling mechanisms: mutual excitatory chemical synapses, electrotonic coupling, and common input. The chemical and electrotonic connections are located in the buccal ganglia. All spikes are relayed to the partner cell via the chemical synapses. The electrotonic coupling improves the efficiency of the chemical synapses. The dual connection selectively synchronizes the CGC‐axonal spikes from each side of the buccal mass. Common excitatory input affects the cerebral spike trigger zones and can initiate simultaneous spikes in both cells. This results in bilateral synchrony of spikes in the CGC‐axons in both the buccal and the lip nerves.
Serotonergic inhibition of afterdischarge in peptidergic bag cells
Authors: Jennings K. R. , Host J. J. , Kaczmarek L. K. , Strumwasser F.
Published: January 2005

The neuroendocrine bag cells of Aplysia generate a long‐lasting afterdischarge causing the release of the peptide egg‐laying hormone (ELH) into the hemolymph (Stuart and Strumwasser, 1980). This afterdischarge activity can be elicited in vitro by electrical stimulation of a pleurovisceral connective (PVC) nerve. It has been shown previously that bag cell afterdischarge and egg‐laying behavior can also be induced by a purified neuroactive peptide isolated from the atrial gland in the reproductive tract (Heller et al., 1980). The authors find that the afterdischarge can be inhibited in a dose‐dependent manner by the extracellular application of low concentrations of serotonin (5 × 10−7 M). This inhibitory action of serotonin is blocked by the serotonin antagonist D‐butaclamol. Serotonin has been found to prevent egg laying (and associated behaviors) induced by injection of this atrial gland peptide in vivo but not that induced by injection of ELH. Afterdischarge activity in bag cells consists of a short initial phase during which the spike frequency is high and a longer, secondary phase in which the spike frequency is much lower (Kupfermann and Kandel, 1970). Intracellular recordings during serotonin inhibition of afterdischarge indicate significant decreases in spike amplitude (15%) and duration (18%) compared with controls. In addition, the latency and threshold of directly elicited spikes, in the absence of afterdischarge, were increased considerably as a result of serotonin. Arguments are presented from these data that serotonin may be preventing the conductance decrease associated with the long‐lasting second phase of afterdischarge and that this effect of serotonin can be overcome by application of the potassium channel blocker tetraethylammonium (TEA). Although a serotonergic input to the bag cell neurons has not yet been described, the pleurovisceral connective nerves, known to contain bag cell process, have the highest concentration of serotonin receptors of any nervous tissue in Aplysia (Drummond, Bucher, and Levitan, 1980). It remains to be determined whether these represent serotonergic synapses on bag cell processes. The authors speculate that serotonin, considered a transmitter mediating sensitization (arousal) in other systems in Aplysia, may act to suppress an ongoing peptide hormone release, which would have triggered a behavior program in the freely behaving animal, thus allowing some degree of behavioral plasticity as a result of changed conditions in the external environment.
Nickel chloride for intracellular staining of neurons in insects
Authors: Delcomyn Fred
Published: January 2005

The advantages of nickel chloride (NiCl2) for intracellular staining of insect neurons are described. Nickel shares with cobalt the features of rapid migration, easy precipitation, and the capability of being silver‐intensified. But, nickelfilled electrodes also have lower average resistances and pass current more readily than comparable electrodes filled with cobalt, making it the ion of choice for intracellular marking in many instances.
Neuritic growth and neuroma formation by an isolated molluscan ganglion
Authors: Stamler J. F. , Kater S. B. , Murphy A. D. , Bulloch A. G. M.
Published: January 2005

The isolated, paired buccal ganglia of the snail Helisoma trivolvis were cultured in vivo (i.e., in host snails) for periods up to 377 days. Such ganglia typically become enveloped in a white mass of fibrous tissue which reaches a maximum plateau of size within four weeks. The scanning electron microscope revealed the newly formed tissue to be composed of fine fibers which also pervaded the neuropil. Injection of individual neurons with Lucifer Yellow CH filled many new neurites within the tissue mass. It is concluded that these masses are largely of neuronal origin and they are therefore designated as neuromas. The maximum size of neuromas may be limited by intrinsic mechanisms which limit neuronal volume.
Age‐diminished motor neuronal function of central neuron L7 in Aplysia
Authors: Peretz Bertram , Ringham Gary , Wilson Randall
Published: January 2005

The efficacy of central neuron L7 to elicit gill pinnule contractions was tested in mature and old Aplysia. The difference in age between groups was no less than 70 days and as much as 150 days. Spike trains in L7 were necessary to elicit pinnule contractions in both age groups. Spike rates of 8 spikes per second and higher elicited pinnule contractions that were significantly smaller in old than in mature animals. Synaptic acitivity in the pinnule muscles innervated by L7 was recorded extracellularly during contractions, and it was significantly less facilitated by spike trains in old as compared to that in mature Aplysia. This suggests that the reduction of facilitated synaptic transmission between L7 and pinnule muscles results in diminished motor neuron function.
Testosterone increases acetylcholine receptor number in the “levator ani” muscle of the rat
Authors: Bleisch William V. , Harrelson Allan L. , Luine Victoria N.
Published: January 2005

The “levator ani” muscle of male rats provides a neuromuscular system in which both the muscle and its motoneurons have high levels of androgen receptors. Two weeks of castration caused a 48% loss of acetylcholine receptors in this muscle. One week of testosterone propionate injections initiated one week after castration increased receptor number by 27% over untreated castrate levels. These changes paralleled changes in muscle protein content. In contrast, castration and testosterone treatments of castrates had no effect on total, Triton X‐100‐extractable acetylcholinesterase activity. This system may provide a useful model of synaptic plasticity.
Increasing external K+ blocks phase shifts in a circadian rhythm produced by serotonin or 8‐benzylthio‐cAMP
Authors: Eskin Arnold
Published: January 2005

Serotonin (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

Grids 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

Noninvasive 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

The 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

A 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

Batrachotoxin (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

This 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

To 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

Synapses 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

Colchicine (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

The 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

We 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

In 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

Are 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

The 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

Sustained 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

The 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

The 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.
Transfer of habituation in Aplysia: Contribution of heterosynaptic pathways in habituation of the gill‐withdrawal reflex
Authors: Goldberg Jeff I. , Lukowiak Ken
Published: January 2005

Habituation of the Aplysia gill‐withdrawal reflex (and siphon‐withdrawal reflex) has been attributed to low‐frequency homosynaptic depression at central sensory–motor synapses. The recent demonstration that transfer of habituation between stimulation sites occurs in this model system has prompted the hypothesis that heterosynaptic inhibitory pathways also play a role in the mediation of habituation behavior. To test this hypothesis, the sites and mechanisms of neural plasticity which underlie transfer of habituation in Aplysia were examined. Transfer of habituation is a reduction in the reflex evoked at one stimulation site (siphon) due to repeated presentation of a stimulus to a second site (gill). Centrally mediated transfer of habituation, measured in a preparation lacking the siphon–gill peripheral nervous system (PNS), was associated with a reduced excitatory response in central motor neurons. Repeated tactile stimulation of the gill did not attenuate the gill response evoked by electrical stimulation of the branchial nerve nor the mechanoreceptor response recorded in LE sensory neurons. In contrast, repeated stimulation of siphon or gill at a site which was “off” the sensory field of a specific mechanoreceptor led to a diminution in synaptic transmission between that sensory neuron and its followers (motor neurons and interneurons). These data demonstrate that centrally mediated transfer of habituation results from heterosynaptic modulation of synaptic transmission at the sensory–motor (and sensory–interneuron) synapses. Therefore, habituation behavior in Aplysia is mediated through the conjoint action of homosynaptic and heterosynaptic inhibitory processes.
Photoreceptors and visual interneurons in the medicinal leech
Authors: Peterson Eric L.
Published: January 2005

The medicinal leech has five pairs of eyes, each with about 50 photoreceptors. Receptors produce propagating impulses which constitute their output to second order neurons in the CNS. Within the eye, receptors have diverse thresholds, and thus the aggregate output of the eye is graded with light intensity. By having many receptors in parallel, the eye may achieve better intensity discrimination and temporal response than would be predicted from the relatively poor characteristics of individual receptors. Receptors in eyes 3–5 on one side of the animal excite the ipsilateral LV (lateral visual) cell, an interneuron in the first segmental ganglion. By physiological tests the receptor axons are electrically coupled to the LV cell. Moreover, the LV cell is Lucifer Yellow dye‐coupled to many fine fibers that appear to be receptor axons of the ipsilateral eyes 3–5. The receptors of the contralateral eyes 3–5, and those of the photosensitive sensilla lining the body inhibit the LV cell via polysynaptic pathways. Thus, the LV cells are central elements of the neural circuit processing input from the leech's spatially distributed visual system.
Membrane mechanism of neuroendocrine caudo‐dorsal cell inhibition by the ring neuron in the pond snail Lymnaea stagnalis
Authors: Jansen R. F. , Maat A. Ter , Bos N. P. A.
Published: January 2005

Ovulation in the pond snail Lymnaea stagnalis is controlled by the neuroendocrine caudo‐dorsal cells (CDCs) in the cerebral ganglia, which release an ovulation hormone during a period of impulse activity. Firing of the single RN in the right cerebral ganglion hyperpolarizes the CDCs. This hyperpolarization is caused by the opening of potassium channels in the axons that connect both the CDC clusters. By this action, that presumably is mediated by axonal branches of the RN in the intercerebral commissure closely associated with these CDC axons, the RN decouples both the CDC clusters. Although the RN has negative feedback on the CDC, it does not control afterdischarge characteristics. The authors suggest that the RN, next to the egg‐laying behavior, is involved in another behavior, not compatible with ovulation. Male reproductive activity is presented as a possible candidate for such behavior.
Regulation of calcium influx into buccal muscles of Aplysia by acetylcholine and serotonin
Authors: Ram Jeffrey L. , Parti Rajesh
Published: January 2005

Acetylcholine (ACh) causes contraction of Aplysia buccal muscles E1 and I5, and serotonin (5‐hydroxytryptamine, 5‐HT) enhances ACh‐elicited contractions of these muscles. Possible roles of calcium influx in mediating these responses were examined by studying influx of 45Ca++. 5‐HT increased calcium influx into both I5 and E1. Maximal influx occurred at 10−6M 5‐HT and the increased influx could be sustained in the presence of 5‐HT for at least 10 min. ACh also caused calcium influx, and calcium influx increased approximately in proportion to log[ACh] from 10−5M to 10−3M ACh. 5‐HT and ACh probably bring about calcium influx by different mechanisms since the effect of ACh was additive to a maximal 5‐HT response, and 10−4M hexamethonium bromide inhibited the increased influx caused by ACh but did not affect influx caused by 5‐HT. Cyclic AMP analogues and forskolin neither caused an increase in calcium influx nor an increase in the influx caused by ACh. The data support a model in which ACh‐elicited contractions of I5 and E1 are due primarily to calcium entry across the extracellular membrane, and 5‐HT can “load” an intracellular site by a mechanism different from that activated by ACh. The data do not support a role for cyclic AMP in mediating the calcium influx response to 5‐HT.