bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fast axonal transport by neurons from the jellyfish Cyanea capillata
Authors: Anderson Peter A. V. , Schwab Walter E. , Gilbert Susan , Allen Robert D. 
Published: January 2005

AbstractNeurons of the motor nerve net of Cyanea capillata were examined using video‐enhanced DIC optics. A variety of organelles were visible within the axons and many were mobile. To quantify the movement organelles were divided into three classes (large, medium, and small) and the rates, direction, and types of movement displayed by the different particle types examined. The overall behavior and rates of movement of transported particles were camparable with those in axons from other species. The largest particles, mainly mitochondria were the slowest moving but were the only particles to reverse their direction of movement or to undergo interactions with other particles. The fastest movement was by the small particles, but both they and medium sized particles were transported continuously. In addition, the linear elements in these axons underwent considerable lateral movement.
A hormone‐sensitive communication system in an electric fish
Authors: Bass Andrew H. 
Published: January 2005

AbstractThe electric communication system includes both special muscle‐derived cells or electrocytes that produce species‐typical electric signals, or electric organ discharges (EODs), and specialized sensory receptors, or electroreceptors, that encode the electric fields set up by EODs. Steroid hormones can influence the characteristic properties of both EODs and electroreceptors. Steroids appear to directly effect the anatomy and physiology of the electrocytes that generate an EOD. In contrast, the steroid effect on electroreceptors may be predominantly via an indirect mechanism whereby changes in the spectral characteristics of the EOD appear to induce changes in the spectral sensitivity of electroreceptors. Continued studies of electrosensory and electromotor systems will offer insights into the cellular bases for the development and evolution of steroid‐sensitive pathways in the vertebrate nervous system.
Extension and retraction of axonal projections by some developing neurons in the leech depends upon the existence of neighboring homologues. I. The HA cells
Authors: Gao Wei‐Qiang , Macagno Eduardo R. 
Published: January 2005

AbstractThe role of homologues in the establishment of the pattern of axonal projections of identified segmentally homologous neurons was investigated by means of selective cell ablation and dye injection. The cells studied were the bilateral pairs of heart accessory (HA) neurons found in the fifth and sixth segmental ganglia of the leech ventral nerve cord. Homologues start their morphological differentiation with identical axonal projections, and segmental differences are manifested later, when specific branches stop growing and disappear. The deletion of single HA cells at early stages, however, permits these branches to survive in their ipsilateral homologues and to grow and take over the projections of the deleted neurons. In addition, if both HA homologues on the same side of the nerve cord, or three of the four HA cells, are deleted in an animal, the remaining HA cells often extend novel projections. These observations suggest that either competition for targets, inputs or growth factors, or direct interactions among homologous cells may play a role in the differentiation of segment specific patterns of axonal projections.
Formation, maintenance, and functional uncoupling of connections between identified Helisoma neurons in situ
Authors: Cohan C. S. , Haydon P. G. , Mercier A. J. , Kater S. B. 
Published: January 2005

AbstractPrevious work with identified Helisoma neurons has characterized an array of neuroplastic responses to axotomy that include the generation of new neuritic outgrowth, the reinnervation of target organs, and the formation of new electrical synapses. These responses are not random, but rather occur in a precise, predictable manner under a variety of culture conditions. The present investigation demonstrates that specific identified neurons display similar neuroplastic “behavior” within the living animal. In response to in situ nerve crushes, neurons B4 and B5 generate new neuritic outgrowth, neuron B4 functionally reinnervates the salivary glands, and new electrical synapses form between the left and right neurons B5.The in situ paradigm employed in the present experiments made it possible to examine responses to axotomy over longer periods than in earlier studies with organ cultures. New B5R‐B5L connections, previously found to be stable over the short term in culture, gradually decreased in strength in situ, and the cells effectively uncoupled by 8 weeks after axotomy. This uncoupling did not depend upon target reinnervation and occurred in the continued presence of neurites in the buccal commissure. It is suggested that the stability of new connections is related to whether the connection previously existed in the unperturbed nervous system. The similarities between the ability of identified neurons to grow and to form synaptic connections in situ and in culture suggests that neurons are endowed with a specific program of regenerative responses that can be expressed reliably in a wide variety of environmental conditions.
Effect of auditory deafferentation on the synaptic connectivity of a pair of identified interneurons in adult field crickets
Authors: Brodfuehrer Peter D. , Hoy Ronald R. 
Published: January 2005

AbstractIn adult crickets, Teleogryllus oceanicus, unilateral auditory deafferentation causes the medial dendrites of an afferent‐deprived, identified auditory interneuron (Int‐1) in the prothoracic ganglion to sprout and form new functional connections in the contralateral auditory neuropil. The establishment of these new functional connections by the deafferented Int‐1, however, does not appear to affect the physiological responses of Int‐1's homolog on the intact side of the prothoracic ganglion which also innervates this auditory neuropil. Thus it appears that the sprouting dendrites of the deafferented Int‐1 are not functionally competing with those of the intact Int‐1 for synaptic connections in the remaining auditory neuropil following unilateral deaferentation in adult crickets. Moreover, we demonstrate that auditory function is restored to the afferent‐deprived Int‐1 within 4–6 days following deafferentation, when few branches of Int‐1's medial dendrites can be seen to have spouted. The strength of the physiological responses and extent of dendritic sprouting in the deafferented Int‐1 progressively increase with time following deafferentation. By 28 days following deafferentation, most of the normal physiological responses of Int‐1 to auditory stimuli have been restored in the deafferented Int‐1, and the medial dendrites of the deafferented Int‐1 have clearly sprouted and grown across into the contralateral auditory afferent field. The strength of the physiological responses of the deafferented Int‐1 to auditory stimuli and extent of dendritic sprouting in the deafferented Int‐1 are greater in crickets deafferented as juveniles than as adults. Thus, neuronal plasticity persists in Int‐1 following sensory deprivation from the earliest juvenile stages through adulthood.
Generation of motor patterns for walking and flight in motoneurons supplying bifunctional muscles in the locust
Authors: Ramirez J. M. , Pearson K. G. 
Published: January 2005

AbstractIn the flight system of Locusta migratoria certain muscles move a wing and a leg (bifunctional muscles) and are active during the performance of walking and flight. A preparation that allowed intracellular recordings during these behaviors was developed to analyze the activity of motoneurons supplying these and other muscles.Motoneurons innervating bifunctional muscles were active during walking and flight, whereas motoneurons innervating unifunctional flight muscles were active only during flight.Both motor patterns, walking and flight, were sometimes generated simultaneously in our preparation. In bifunctional motoneurons the two patterns were superimposed, whereas in unifunctional motoneurons only the flight motor pattern was observed.All flight interneurons we examined were either inactive or tonically inhibited during walking. All interneurons that were strongly modulated during walking were either inactive, inhibited, or only weakly modulated during flight.Anatomical investigations showed that unifunctional flight motoneurons have their main processes in the extreme dorsal region of neuropil. With the exception of the second basalar motoneurons, all bifunctional motoneurons have their processes extending more ventrally in the neuropil. Flight interneurons have their processes restricted to the dorsal neuropil. Interneurons that were rhythmically active during walking had their processes distributed more ventrally.We conclude that motoneurons innervating bifunctional muscles are active during both motor patterns, walking and flight, and that these patterns are produced by two distinct interneuronal networks. The pattern‐generating network for flight appears to be located in the extreme dorsal regions of the thoracic ganglia, and the network for walking is located more ventrally.
Joint hormonal and sensory stimulation modulate neuronal number in adult canary brains
Authors: Bottjer Sarah W. , Dignan Timothy P. 
Published: January 2005

AbstractTreatment of adult female canaries with testosterone (T) causes them to produce male‐typical vocalizations and results in striking growth of brain nuclei that control song behavior (Nottebohm, 1980). The song‐control nucleus HVc (caudal nucleus of the ventral hyperstriatum) contains cells that concentrate testosterone or its metabolites, suggesting that steroid hormones may induce the growth of HVc directly by regulating the expression of specific genes in those HVc neurons that have steroid receptors. However, we have previously provided evidence that is inconsistent with the idea that steroids promote growth of HVc solely via a direct action on hormone receptors: testosterone treatment of deafened adult females results in very little growth of HVc, relative to T‐treated hearing birds (Bottjer et al., 1986b). Thus, birds in the former group undergo very little overall growth of HVc despite high circulating levels of hormone. We show here that the slightly increased size of HVc in T‐treated deaf birds is attributable to an increase in neuronal spacing; the greatly increased size of HVc in T‐treated hearing birds is due to an increase in neuronal number as well as spacing. There was virtually no increase in number of HVc neurons in T‐treated deafened birds relative to control groups, whereas T‐treated hearing birds showed a marked increase in neuron number. The song‐control nucleus RA (robust nucleus of the archistriatum), which receives direct afferent input from HVc, also increases in size in response to testosterone treatment. However, the volume of RA increases in both hearing and deafened birds; this increase is primarily due to an increase in neuronal spacing as well as a small increase in neuron number. These results demonstrate that the number of neurons in a specific vocal‐control nucleus (HVc) can change dramatically in adult canaries and suggest that some synergistic action of hormonal and sensory stimulation is necessary to induce such a change.
The differential regulation of formation of chemical and electrical connections in Helisoma
Authors: Haydon P. G. , Kater S. B. 
Published: January 2005

AbstractNovel chemical and electrical connections form between neurons not normally connected in the buccal ganglia of the snail Helisoma. We examined the cellular and environmental conditions required for the formation of each type of connection. Previous work in situ showed that novel electrical connections could form in response to axotomy. We have now found that axotomy can evoke the formation of novel unidirectional chemical connections between neurons B5 and B4 in addition to a novel electrical connection. The novel chemical connections display all of the normal properties of chemical synapses in Helisoma ganglia. These connections, however, are transient in nature and break 4 days following axotomy.Previous work has shown that conjoint outgrowth is required for the formation of electrical connections. In cell culture we have investigated whether conjoint outgrowth is also required for chemical synaptogenesis. Using neurons B5 and B19 we have found that when neuron pairs make contact in cell culture, under conditions of synchronous neurite extension, both electrical and chemical synapses form. However, if one neuron has ceased extension prior to contact by a growing neuron, electrical synapses never form (Hadley et al., 1983, 1985) but chemical synapses do form. Furthermore, the addition of serotonin (10−6 M) to culture medium to inhibit neurite extension of B19, but not that of B5, selectively prevents the formation of electrical connections while permitting the formation of chemical synapses. Thus, the timing of contact in relation to the state of neurite extension can specify the type of connection a given neuron can form.
Absence of competitive interactions among axon terminals of regenerating motor neurons
Authors: Denburg Jeffrey L. , Powell Susan L. , Murphy Bernard F. 
Published: January 2005

AbstractCompetition among axon terminals is usually considered to contribute to the formation of patterned synaptic connections. During axonal regeneration of motor neurons in the cockroach, leg muscles initially become innervated by appropriate and inappropriate motor neurons. All axon terminals from inappropriate neurons eventually are eliminated, resulting in the reformation of the original innervation pattern. Destruction of an identified motor neuron by the intracellular injection of pronase did not prevent the eilimenation of inappropriate axon terminals in the muscle normally innervated by that motor neuron. Therefore, competition does not play a role in the reinnervation of the leg muscles. This indicates a major role for specific cell‐cell recognition.
Involvement of the Golgi apparatus in sorting of materials to opposite ends of frog rod retinal photoreceptors
Authors: Schmied Robert , Holtzman Eric 
Published: January 2005

AbstractWe have studied the rod cells of retinas of Rana pipiens by phosphatase cytochemistry and immunocytochemistry. We find that the Golgi apparatus of these cells, although different in its intracellular distribution from that of other neurons, has a cis‐trans organizations like that of other neurons as regards morphological features and the distribution of phosphatase activities. Antibodies against opsin bind to several sacs of the rod Golgi apparatus, especially those at the trans side of the Golgi stack. This suggests that Golgi involvement in the packaging of opsin for eventual delivery to the photoreceptive outer segments of the cell involves passage through trans Golgi systems. Proteins destined for the opposite end of the cell—the presynaptic terminal—also seem to pass through trans Golgi systems, as in indicated both by immunocytochemical localization of the synaptic vesicle protein p38 (synaptophysin) and by the presence of thiamine pyrophosphatase activity in some of the synaptic vesicles. Our findings suggest that sorting of membrane proteins destined for opposite ends of the photoreceptor takes place in systems at or near the trans Golgi face.
The refinement of invertebrate synapses during development
Authors: Lnenicka G. A. , Murphey R. K. 
Published: January 2005

AbstractEvidence is provided that during invertebrate development synapses undergo a period of refinement during which there are changes in synaptic connectivity and specific synaptic properties. It appears that extrinsic cues such as competition and neural activity are involved in guiding these synaptic changes in invertebrates. Comparisons are made with findings in the vertebrate literature.
Laser microbeam axotomy and conduction block show that electrical transmission at a central synapse is distributed at multiple contacts
Authors: Gu Xiaonan , Macagno Eduardo R. , Muller Kenneth J. 
Published: January 2005

AbstractTouch (T) sensory neurons in the leech innervate defined regions of skin and synapse on other neurons, including other T cells, within the ganglionic neuropil. The cells' receptive fields in the periphery are comprised of a central region, innervated by thick axons, and adjoining regions (minor fields) innervated by thinner axons. Secondary branches, known to be sites of synapses, emerge from the thinner and thicker axons. Pairs of T cells appear to make up to 200 separate contacts distributed within the neuropil. When the T cell is hyperpolarized, as occurs during natural stimulation of the cell, action potentials generated in the minor field and travelling into the ganglion along the thin axons may fail to conduct at central branch points. Evidence is presented, using axon conduction block and laser axotomy of cells filled with 6‐carboxy‐fluorescein, that synapses between separate groups of branches can function independently. Thus, selective activation of branches of the thin anterior axon produced a synaptic potential 36 ± 6% of control amplitude, which was consistent with counts of 39 ± 6% of contacts made by these branches. Laser axotomy of postsynaptic neurons showed that the anterior contacts indeed made the principal or only contacts activated during anterior conduction block. The results show that conduction block can modulate transmission within the ganglion, and it operates by silencing particular contacts between cells.
Changes in protein phosphorylation in the eye of Aplysia associated with circadian rhythm regulation by serotonin
Authors: Zwartjes Raymond E. , Eskin Arnold 
Published: January 2005

AbstractSerotinin (5‐HT) shifts the phase of the circadian oscillator of the eye of Aplysia californica in a phase dependent manner. This indicates that 5‐HT acts, either directly or through some intermediaries, on a component of the oscillator. Since our goal is to identify the components of the oscillator, we are following the pathway through which 5‐HT has its effect on the rhythm. The effect of 5‐HT on the rhythm has been shown to be mediated by an increase in intracellular cyclic adenosine‐3′,5′‐monophosphate (cAMP). The most likely action of cAMP is to activate cAMP‐dependent protein kinase. Therefore, we used two‐dimensional polyacrylamide gel electrophoresis to investigate changes in 32P labelled phosphoproteins which occur with 5‐HT and other treatements. Fourteen proteins showed increased incorporation of 32P when eyes were exposed to treatments of 5‐HT from CT 06 to 12. Two proteins showed decreased incorporation. 8‐bt‐cAMP mimicked all but one of the increases and both decreases in incorporation produced by 5‐HT. 8‐bt‐cAMP increased incorporation into three additional proteins and decreased incorporation into three additional proteins and decreased incorporation into three other that were not affected by 5‐HT. Incorporation into one protein was increased by 5‐HT but decreased by 8‐bt‐cAMP. By comparison, light, which has little or no effect on the rhythm at this phase, only affected one protein. The protein increased by light was also increased by 5‐HT. Tetradecanoic phorbol acetate (TPA), administered during CT 06‐12, also had little effect on the rhythm at this phase. TPA increased incorporation into twenty proteins and decreased incorporatoin into three. Seven of the increased proteins were also increased by 5‐HT. Some of the phosphoproteins altered by 5‐HT and cAMP analogue may mediate the effect of 5‐HT on the circadian rhythm.
Frequency‐dependent and cell‐specific effects of electrical activity on growth cone movements of cultured Helisoma neurons
Authors: Cohan Christopher S. 
Published: January 2005

AbstractThe present experiments address the question of how stimulation parameters, which evoke action potentials in neuronal cell bodies, influence growth cone movements of different identified neurons. The motility of growth cones of Helisoma buccal neurons B19 and B4 was monitored while somata were stimulated simultaneously via an intracellular microelectrode. The findings show that the responses of growth cones of B19 and B4 contain components that are common as well as unique to each neuron. Whereas rates of growth cone advance were suppressed in a graded fashion by stimulus frequencies beyond a threshold of 2 s−1 for both neurons, B4 was more sensitive to electrical stimulation and exhibited a new response, namely, growth rates were enhanced during the poststimulation recovery period after stimulation at specific frequencies. Thus, electrical activity can result in enhancement as well as in inhibition of growth cone movement. Changes in number of filopodia on B19 and B4 were graded also, with B4 again displaying greater sensitivity. The frequency dependence of filopodia compared to growth rate changes was different and suggests a possible dissociation between filopodial activity and growth cone motility. Patterned electrical acivity produced effects similar to constant stimulation for B19 growth cones, whereas it decreased the threshold frequency and eliminated the growth enhancement effect for B4. Taken together, these data demonstrate that the quantitative features of electrical activity as well as intrinsic properties of neurons both determine the growth cone response to changes in neuronal activity.
Mapping of the presumptive brain regions in the neural plate of Xenopus laevis
Authors: Eagleson Gerald W. , Harris William A. 
Published: January 2005

AbstractTwo cell autonomous fluorescent labels (DiI and Hoechst) were used as vital markers in a fate map study of the Xenopus neural plate and ridge. Most areas of the brain derive from the neural plate in a fate map that is consistent with the topology of a sheet rolling into a tube, i.e., neighboring areas are maintained as neighbors. This has enabled us not only to plot the fates of larval brain structures, but also to suggest their primordial orientation in the neural plate. Since overlapping areas of the plate gave rise to overlapping regions of the central nervous system (CNS), we have been able to construct a space‐filling model of the neural plate, whereby the number of founder cells for each brain region fate‐mapped may be estimated roughly. Much of the telencephalon, ventral forebrain, and dorsal brain stem derives from the neural ridge and not the neural plate in the stage 15 Xenopus embryo. The strctures of the forebrain were examined in detail because there were indications of substantial cell movements in this region. The anterior pituitary arises from the mid‐anterior ridge, while hypothalamic structures arise from the midline regions of the anterior neural plate. Consistent groups of ventral hypothalamic structures were labeled when fluorescent markers were applied to these parts of the neural plate, indicating stereotyped cell movements. Detailed comparisons were made between the fate map of the Ambystoma neural plate (Jacobson, 1959) and that of Xenopus.