bluuebunny/crossref_metadata_2025_split huggingface dataset:
Leptinotarsin‐D, a neurotoxic protein, evokes neurotransmitter release from, and calcium flux into, isolated electric organ nerve terminals
Authors: Miljanich George P. , Yeager Robert E. , Hsiao Ting H. 
Published: January 2005

AbstractPrevious work has demonstrated that the neurotoxin leptinotarsin elicits release of neurotransmitter from mammalian nerve terminals, and it has been suggested that the toxin may act either as a direct agonist of voltage‐sensitive calcium channels in these terminals (Crosland et al., 1984) or as a calcium ionophore (Madeddu et al., 1985a,b). Preliminary studies (Yeager et al., 1987) demonstrated that leptinotarsin also evokes transmitter release from isolated elasmobranch electric organ nerve terminals. We now report further investigations of the effects of leptinotarsin in this system. The action of the toxin is saturable, releasing about the same small fraction of total transmitter as that released by depolarization. An upper limit for the concentration for half maximal release is estimated to be 4 nM. Leptinotarsin‐evoked transmitter release exhibits behavior very similar to depolarization‐evoked release with respect to dependence on Ca2+, Ba2+, and Sr2+ and blockade by Co2+, Cd2+, and trifluoperazine. Leptinotarsin also promotes the uptake of calcium into synaptosomes to a degree similar to that caused by depolarization by K+. The binding of leptinotarsin to nerve terminals is probably Ca2+ dependent and receptor mediated. Taken together with the behavior of leptintoarsin‐evoked release in other preparations, these results are consistent with the hypothesis that this toxin acts by opening a presynaptic calcium channel. However, the possibility that leptinotarsin is a calcium ionophore cannot be excluded.
Synaptic competition and the elimination of polyneuronal innervation follwoing reinnervation of adult frog sartorius muscles
Authors: Werle Michael J. , Herrera Albert A. 
Published: January 2005

AbstractThe elimination of polyneuronal innervation (synapse elimination) that occurs following reinnervation was studied in sartorius muscles of adult Rana pipiens. The percentage of neuromuscular junctions that were polyneuronally innervated declined from 47% at 40–80 days after nerve crush to 22% at greater than 250 days after nerve crush. We measured the size, synaptic strength, and position of competing nerve terminals at identified dually innervated neuromuscular junctions at these two different periods of synapse elimination. Our goal was to determine if any of these parameters play a role in the competition between nerve terminals that ultimately results in the elimination of polyneuronal innervation. Our data support the hypothesis that polyneuronal innervation will persist if competing nerve terminals are of similar synaptic efficacies but will be eliminated if the competing terminals are of different synaptic efficacies. We also tested, but failed to find any evidence, that the spatial proximity of competing nerve terminals at the same synaptic site influences the elimination of polyneuronal innervation.
Wind‐activated thoracic interneurons of the cockroach: II. Patterns of connection from ventral giant interneurons
Authors: Ritzmann Roy E. , Pollack Alan J. 
Published: January 2005

AbstractA number of thoracic interneurons (TIs) have been found to receive inputs from ventral giant interneurons (vGIs). Each of these cells responds to wind with short latency depolarizations. The previous paper described response properties of several TIs to wind stimuli, including those excited by vGIs. The data showed a correlation between the shape of the TI's wind fields and its morphology. The presence of ventral branches located near the midline of the ganglion predicts a strong response to wind on that side. These ventral median (VM) branches are in the proper location to permit overlap with processes from vGIs. Here we describe the patterns of connections between individual vGIs and 13 of the thoracic interneurons located in the meso‐ and metathoracic ganglia. A correlation was found between the presence of VM branches and excitation by vGIs. TIs were only excited by vGIs on the side(s) on which VM branches exist. However, presence of a VM branch does not imply that all vGIs on that side make connections with the TI.Summation was found between various vGIs that excited each individual thoracic interneuron. In unilateral thoracic interneurons, no sign of inhibition was found from vGIs on the sides opposite that which contained excitatory vGI axons. Neither was there any evidence of inhibition from dorsal giant interneurons. In addition preliminary evidence indicated that left‐right homologues do not inhibit one another. Thus, the data suggest that directional wind fields are primarily the result of selective connection from specific vGIs.
Primary afferent responses of a crustacean mechanoreceptor are modulated by proctolin, octopamine, and serotonin
Authors: Pasztor Valerie M. , Bush Brian M. H. 
Published: January 2005

AbstractModulation of sensory responses recorded intracellularly in primary sensory afferents of a crustacean proprioceptor is described. The neuropeptide proctolin enhances the sensory response, whereas the bioamines octopamine and serotonin depress it.The lobster oval organ of the second maxilla, a simple stretch receptor lacking centrifugal control, provides a useful model for studies on nonsynaptic modulation at peripheral sensory loci. Its three large afferents, X, Y, and Z, were prepared for intracellular recording and tested under five experimental conditions: (1) when fully rested, (2) when adapted to maintained stretch and firing tonically, (3) when showing reduced responses after habituation to repetitive stimulation, (4) not stretched but depolarized with current injections, (5) after TTX blockade.The results, taken together, indicate that conductances contributing to the overall amplitude of the receptor potential are major targets for modulators. Thus proctolin increased receptor potential amplitudes with consequent augmentation of spiking, whereas serotonin and octopamine depressed the receptor potentials, often to subthreshold levels with loss of spiking. Octopamine was a less potent agent than serotonin and failed to act upon fibers under TTX blockade.Fibers Y and Z consistently showed sensitivity to the modulators tested. The largest fiber, X, typically was resistant to proctolin, octopamine, and serotonin.Threshold concentrations of 10−10−10−11 M determined in vitro are well below the circulating levels for serotonin and octopamine found in vivo. Proctolin, however, is usually not detectable in the hemolymph, and it is suggested that a significant site of proctolin release may be the oval organ itself.
Parallel processing and selection of the responses to serotonin during reinnervation of an identified leech neuron
Authors: Drapeau Pierre , Sanchez‐Armass Sergio 
Published: January 2005

AbstractIn an attempt to define the mechanism of synaptic specificity, we have been studying pairs of identified leech neurons isolated in tissue culture. The cultured neurons reform specific synapses when paired with appropriate partners in the absence of other cell types. In recent studies, we have examined in detail the reformation of a serotoninergic synapse between the Retzius cell and one of its targets, the pressure sensitive (P) cell. The P cell in vivo and its soma in vitro have two types of responses to serotonin (5‐HT). From voltage clamp analysis of cultured P cells, we demonstrated the parallel activation of chloride (gCls) and monovalent cation (gCations) channels coupled to distinct receptor subtypes and gated by separate second messengers. Only gCls was activated by 5‐HT released from the presynaptic Retzius cell both in vivo and in vitro. This demonstrates the remarkable specificity of the reformation of this synapse in culture since only the correct 5‐HT receptor subtype is activated.An 80% reduction of gCations was observed in P cells that had failed to be innervated by Retzius cells in culture, suggesting that gCations may be lost prior to synapse formation. Retzius cells depleted of 5‐HT also reduced gCationss in the paired P cells and incubating single P cells in 5‐HT did not reduce gCations. In addition, aldehyde‐fixed Retzius cells were able to selectively reduce gCations when paired with P cells. We conclude that the loss of gCations was due to contact between the neurons. The early clearing of counter‐effective receptor subtypes may be a prelude to synapse formation.
Changes in contralateral protein metabolism following unilateral sciatic nerve section
Authors: Menéndez José A. , Cubas Susana C. 
Published: January 2005

AbstractChanges in nerve biochemistry, anatomy, and function following injuries to the contralateral nerve have been repeatedly reported, though their significance is unknown. The most likely mechanisms for their development are either substances carried by axoplasmic flow or electrically transmitted signals. This study analyzes which mechanism underlies the development of a contralateral change in protein metabolism. The incorporation of labelled amino acids (AA) into proteins of both sciatic nerves was assessed by liquid scintillation after an unilateral section. AA were offered locally for 30 min to the distal stump of the sectioned nerves and at homologous levels of the intact contralateral nerves. At various times, from 1 to 24 h, both sciatic nerves were removed and the proteins extracted with trichloroacetic acid (TCA). An increase in incorporation was found in both nerves 14–24 h after section. No difference existed between sectioned and intact nerves, which is consistent with the contralateral effect. Lidocaine, but not colchicine, when applied previously to the nerves midway between the sectioning site and the spinal cord, inhibited the contralateral increase in AA incorporation. It is concluded that electrical signals, crossing through the spinal cord, are responsible for the development of the contralateral effect. Both the nature of the proteins and the significance of the contralateral effect are matters for speculation.
Development and survival of thoracic motoneurons and hindlimb musculature following transplantation of the thoracic neural tube to the lumbar region in the chick embryo: Anatomical aspects
Authors: O'Brien Michael K. , Oppenheim Ronald W. 
Published: January 2005

AbstractThoracic spinal cord transplanted to the lumbar region at the time of neural tube closure in the chick embryo survives and initially differentiates normally similar to in situ thoracic cord. Normal numbers of motoneurons are produced that innervate the host hindlimb musculature. In control thoracic cord approximately 70% of the motoneurons are lost by normal cell death between embryonic day (E) 6 and E11–E12. By contrast, the transplanted thoracic cord loses only about 30% of the motoneurons during this period. Transplantation of one hindlimb to the thoracic region also reduces the normal loss of in situ thoracic motoneurons. We conclude that some factor(s) associated with the increased target size provided by the hindlimbs promotes the survival of thoracic motoneurons. In contrast, by E16–E18 motoneuron numbers in the thoracic transplants decrease to below control levels. Dorsal root ganglion cells in the transplant were also initially increased (on E8) but later decreased to below control values. Hindlimb muscles innervated by thoracic motoneurons in the transplant also differentiated normally up to E10 to E12. Myotube size and numbers, muscle size and myotube types (fast versus slow) all developed normally in several thoracically‐innervated hindlimb muscles. However, beginning on E14 myotube numbers and muscle size were markedly decreased resulting in muscle atrophy. Injections of horse‐radish peroxidase (HRP) into the thoracic transplants labelled neurons in the host spinal cord and brainstem rostral to the transplant thereby indicating an anatomical continuity between host and transplant neural tube. Injections of HRP into specific thoracically innervated hindlimb muscles on E8 labelled distinct pools of motoneurons in the transplants. The location of the labelled motor pools were similar to the location of the motor pools serving these muscles in normal lumbar cord. For example, the sartorius motor pool, which is normally restricted to the first two segments of the lumbar cord, was located in the first two segments of the thoracic transplant. We conclude that thoracic neural tube transplanted to the lumbar region initially differentiates normally, innervates hindlimb muscles and that the thoracically innervated hindlimb muscles also differentiate normally. Subsequently, however, thoracic innervation of hindlimb muscles somehow becomes incompatible with normal development and the motoneurons and muscles eventually undergo regressive changes.
Conservation of antigen 3G6: A crystalline cone constitutent in the compound eye of arthropods
Authors: Edwards John S. , Meyer Mark R. 
Published: January 2005

AbstractA monoclonal antibody (MAb), 3G6, highly selective for neuropil glia in the CNS of the house cricket Acheta domesticus, also demonstrates remarkable selectivity for the nonneuronal crystalline cone cells of the compound eye. MAb 3G6 labels cone cells in eucone eyes throughout Insecta, from ancestral forms such as the bristle tail to the more recent honeybee; eucone structures are also recognized in Crustacea. Analogous nonneural structures found in pseudocone or acone eyes also express detectable 3G6 immunoreactivity. Immunoblot analysis demonstrates that MAb 3G6 binds to similar Mr 85 kDa glycoproteins in the cricket CNS and retina, corresponding to the glial and crystalline cone forms of the antigen. Further, polypeptides of similar relative mass are also recognized in the eucone eye of the butterfly Pieris and the pseudocone eye of the fly Calliphora. The properties and function of glycoprotein 3G6 in the CNS and retina are yet to be explored. However, the finding that a unique antigen is highly conserved within the crystalline cone or analogous regions of the retina throughout the Arthropoda lends support at the molecular level to the notion that the arthropod compound eye has a monophyletic origin.
A developmental analysis of spontaneous and reflexive reversals in the nematode Caenorhabditis elegans
Authors: Chiba Catherine M. , Rankin Catharine H. 
Published: January 2005

AbstractReversals of forward locomotion in the nematode Caenorhabditis elegans are thought to be mediated by a common neural circuit, the touch withdrawal circuit. Despite substantial neuroanatomical changes over postembryonic development, one reversal behavior, the head‐touch withdrawal reflex, does not appear to change over development (Chalfie and Sulston, 1981). The experiments reported here indicate that two other reversal behaviors, spontaneous reversals and the tap reversal reflex to vibratory stimuli, show developmental changes. Young adult animals showed higher frequencies of spontaneous reversals than all other developmental stages, while larval stages differed from adults in their pattern of responses to tap. Although animals of all stages reversed in response to touch, taps elicited both reversals and accelerations of forward movement. In response to single taps, larval stages reversed on approximately half the occasions; young adult and 4‐day‐old adults almost always reversed. Increasing stimulus magnitudes increased the probability of accelerations at all developmental stages, but larval stages showed fewer reversals and more accelerations than adults. The behavioral changes observed coincide with known periods of neuroanatomical change in the touch withdrawal circuit. The addition of a late‐developing sensory neuron, AVM, is implicated in the behavioral differences between juveniles and adults.
Inhibition of protein synthesis prevents cell death in sensory and parasympathetic neurons deprived of neurotrophic factor in vitro
Authors: Scott Sheryl A. , Davies Alun M. 
Published: January 2005

AbstractShortly after neurons begin to innervate their targets in the developing vertebrate nervous system they become dependent on the supply of a neurotrophic factor, such as nerve growth factor (NGF) for survival. Recently, Martin et al. (1988) have shown that inhibiting protein synthesis prevents the death of NGF‐deprived sympathetic neurons, suggesting that NGF promotes neuronal survival by suppressing an active cell death program. To determine if other neurotrophic factors may regulate neuronal survival by a similar mechanism we examined the effects of inhibiting protein and RNA synthesis in other populations of embryonic neurons that require different neurotrophic factors, namely: (1) trigeminal mesencephalic neurons, a population of proprioceptive neurons that are supported by brain‐derived neurotrophic factor; (2) dorsomedial trigeminal ganglion neurons, a population of cutaneous sensory neurons that are supported by NGF; (3) and ciliary ganglion neurons, a population of parasympathetic neurons that are supported by ciliary neuronotrophic factor. Blocking either protein or RNA synthesis rescued all three populations of neurons from cell death induced by neurotrophic factor deprivation in vitro. Thus, at least three different neurotrophic factors appear to promote survival by a similar mechanism that may involve the suppression of an endogenous cell death program.
Cholinergic activation of the lobster cardiac ganglion
Authors: Sullivan Robert E. , Miller Mark W. 
Published: January 2005

AbstractThe frequency of rhythmic burst activity of the isolated lobster cardiac ganglion is increased by exogenously applied acetylcholine and muscarinic agonists. Responses of individual motor neurons isolated from the ganglion by transection consist of a slow depolarization and repetitive bursting. The pharmacological profile of the receptors mediating this response is similar to that of vertebrate neuronal muscarinic receptors. Isolated ganglia incubated in the presence of [3H]‐choline (18‐19 h) exhibited radiolabelled acetylcholine accumulation. It is suggested that ganglionic excitation may be accomplished by extrinsic or intrinsic activation of muscarinic receptors on the motor neurons.
Involvement of pedal peptide in locomotion in Aplysia: Modulation of foot muscle contractions
Authors: Hall Jon D. , Lloyd Philip E. 
Published: January 2005

AbstractPedal peptide (Pep) is a 15‐amino‐acid neuropeptide that is localized within the Aplysia central nervous system (CNS) predominantly to a broad band of neurons in each pedal ganglion. Pep‐neurons were identified by intracellular staining and immunocytology or by radioimmunoassay (RIA) of extracts from identified neurons. RIA reveals that 97% of all Pep‐like immunoreactivity (IR‐Pep) in pedal nerves is found in the three nerves that innervate the foot. Nearly every Pep‐neuron sends an axon out at least one of these three nerves. Application of Pep to foot muscle causes an increase in the amplitude and relaxation rate of contractions driven by nerve stimulation or intracellular stimulation of pedal motor neurons. The increase in relaxation rate was the predominant effect. Intracellular recording in “splitfoot” preparations reveals that Pep‐neurons increase their overall firing rates and fire in bursts with each step during locomotion. Recovery of IR‐Pep from foot perfusate following pedal nerve stimulation increases in a frequency‐dependent fashion. Thus it appears that one function of Pep‐neurons is to modulate foot muscle contractility during locomotion in Aplysia.
Activity‐driven sharpening of the regenerating retinotectal projection: Effects of blocking or synchronizing activity on the morphology of individual regenerating arbors
Authors: Schmidt John T. , Buzzard Marlene 
Published: January 2005

AbstractBoth blocking activity with intraocular tetrodotoxin (TTX) and synchronizing activity with a xenon strobe light (1 Hz) prevent retinotopic sharpening of regenerating optic projection in goldfish (Meyer, 1983; Schmidt, 1985; Cook and Rankin, 1986). In this study, we tested, in both normal and regenerating projections, the effects of these two treatments on individual optic arbors. Arbors were stained via anterograde transport of HRP, drawn in camera lucida from tectal whole mounts, and analyzed for spatial extent in the plane of the retinotopic map, order of branching, number of branch endings, depth of termination, and the caliber of the parent axon. In normal tectum, fine, medium, and coarse caliber axons gave rise to small, medium, and large arbors, which averaged 127 μm, 211 μm and 275 μm in horizontal extent, and terminated at characteristic depths. All three classes averaged roughly 21 branch endings. Optic arbors that regenerated with normal patterns of activity returned to a roughly normal appearance by 6–11 weeks postcrush: the same three calibers of axons gave rise to the same three sizes of arbors at the same depths, but they were much less stratified and were on average about 16% larger in horizontal extent. At this time point, arbors regenerated under TTX or strobe were on the average 71 and 119% larger, respectively, than the control‐regenerated arbors (larger in all classes), although they had approximately the same number of branch endings and were equally poorly stratified. Synapses formed under strobe were also normal in appearance. Thus the only significant effect of both strobe and TTX treatment was to enlarge the spatial extent of arbor branches. Arbors that were not regenerating were very slightly (but significantly) enlarged by TTX block of activity or strobe illumination. As previous staining showed that regenerating axons initially make widespread branches and later retract many of those branches (Schmidt, Turcotte, Buzzard, and Tieman, 1988; Stuermer, 1988), the present findings support the idea that blocking activity or synchronizing activity prevents retinotopic sharpening by interfering with the elimination of some of the errant branches.
The development of the lamprey pattern generator for locomotion
Authors: Cohen Avis H. , Dobrov Tamara A. , Li Guan , Kiemel Timothy , Baker Margaret T. 
Published: January 2005

AbstractThe life cycle of the lamprey includes a larval stage that can last for several years. The motor behavior of the larval lamprey, the ammocoete, has been only minimally studied and little is known of the neural correlates of that behavior. Comparison of known larval behavior to that of adults leaves unclear whether there are large or small changes in the spinal nervous system during transformation. The motor output of isolated larval and transforming spinal cords when stimulated to “swim” with d‐glutamate has some differences from that of comparable adult preparations, but shares many important features with adults. Primarily, the fictive swimming is less well regulated and less stable than adults of the same species. We propose that a major difference in the structure and organization of the central pattern generator for locomotion between adults and ammocoetes is a relative lack or immaturity of some cell types that participate in the coordination of the segments and the generation of the rhythm of the periodic bursting.
Constant topological organization of the coleopteran metamorphosing nervous system: Analysis of persistent elements in the nervous system of Tenebrio molitor
Authors: Breidbach Olaf 
Published: January 2005

AbstractEvidence is provided that the topological organization of the larval neuropil is preserved during metamorphosis of Tenebrio molitor. Constancies in neuronal organization were due in part to persistence of individual neurons whose morphologies were individually followed. It appears that the phenomenologically static situation of the metamorphosing neuropil is achieved by stabilization and regulation due to cellular interactions. Comparisons are made with features of hemimetabolan postembryogenesis.