bluuebunny/crossref_metadata_2025_split huggingface dataset:
Proctolin: A review with emphasis on insects
Authors: Orchard Ian , Belanger Jim H. , Lange Angela B. 
Published: January 2005

AbstractThe distribution, physiological role, mode of action, and pharmacology of the pentapeptide neuroregulator proctolin are reviewed, with special emphasis on insects. Whereas proctolin is distributed extensively throughout arthropods, its presence in molluscs, annelids, or chordates is not well established. In the arthropods, proctolin acts as a neuromodulator and possibly as a neurohormone. It does not appear to function as a conventional neurotransmitter. Two model proctolinergic systems are highlighted: motor control of the visceral muscles of the locust oviduct and of the skeletal muscles of the locust ovipositor. In these preparations proctolin is a cotransmitter acting to enhance neuromuscular transmission and muscular contraction.The mode of action of proctolin is not well understood, although the second messengers cAMP, phosphatidyl inositol, and calcium have been implicated in various systems. Pharmacologically, the proctolin receptor has been examined with structure/activity studies, and the effects of a variety of amino acid substitutions and deletions of the pentapeptide are described. It is unfortunate that no specific antagonists of the proctolin receptor appear to be available and that no receptor‐binding studies have been reported.The prospects are good for advances in our understanding of modulatory mechanisms, since proctolin appears to be emerging as the model for studies of this type.
Identification of protein‐bound oligosaccharides on the surface of growth cones that bind to muscle cells
Authors: Ambron Richard T. , Protic John , Den Halina , Gabel Christopher A. 
Published: January 2005

AbstractIn the accompanying paper (Gabel, Den, and Ambron, in press) it was shown that eight populations of glycopeptides are synthesized by single neurons of Aplysia californica. To see which glycopeptides might mediate interactions with target cells, we first identified glycopeptides that are transported selectively to synapses and growth cones. The giant neuron R2 was injected intrasomatically with 3H‐glucosamine. Twenty‐four hours later, 3H‐glycopeptides in the axon and cell body were isolated and resolved by serial lectin affinity chromatography. Of the eight populations, the biantennary‐type glycopeptides (GPbi) and those that bind to WGA (GPwga) were preferentially associated with rapidly transported glycoproteins. In contrast, the glycopeptide that consists of N‐acetylglucosamine O‐linked to ser/thr was mostly retained in the cell body. GPbi and GPwga were also preferentially transported to growth cones. Analyses of RUQ cells, exposed to 3H‐glucosamine in vitro for 36 h showed an enrichment of GPbi and GPwga at the growth cone relative to the cell body. The disposition of the various glycopeptides in growing neurons was also examined using FITC lectins. FITC‐coupled WGA, Vicia vellosa, and lentil lectin showed extensive staining of the cell body, but only WGA stained the growth cones.To investigate if GPwga interacts specifically with target cells, these glycopeptides were isolated from the neurons of 180 abdominal ganglia. GPwga, other Aplysia glycopeptides, and glycopeptides prepared from ovalbumin were coupled separately to fluorescent spheres. The spheres were then added to muscle cells isolated from the auricle of the heart, which is innervated by many neurons from the ganglion. While spheres coupled to GPwga bound to the muscle cell surface, the other glycopeptides did not. These results indicate that glycopeptide class GPwga, found among rapidly transported glycoproteins and on the growth cone surface, is able to bind to muscle cells and may therefore play some role in neuron‐target interactions.
Giant fiber activation of flight muscles in Drosophila: Asynchrony in latency of wing depressor fibers
Authors: Hummon Margaret Raper , Costello Walter J. 
Published: January 2005

AbstractIn Drosophila, brain stimulation of the giant fiber pathway brings about highly stereotyped electrical responses in target muscles involved in the escape response. Both the order of muscle response and the latency of that response are predictable in wild‐type flies. The neuronal circuit to the targets is well defined and has been used in the analysis of a number of mutant phenotypes, including induced anomalies in temperature‐sensitive (ts) mutations such as shibire (shi). It has been assumed that the stereotyped response includes simultaneous activation of all six fibers of the wing depressor muscle, DLM, resulting in equal latencies for all fibers. We report here a small, but distinct, inherent difference in latency between two sets of DLM fibers in a proportion of two wild‐type strains as well as in a strain carrying the ts mutation shi. This difference may occur on one or both sides of an individual, is stable over time, and persists when the motor axon is stimulated peripherally. These results, due to the circuit leading to the target, suggest that the difference in latency arises peripherally. In flies reared at the shi permissive temperature (22°C), the difference is more common in shi than in wild‐type flies; however, in shi flies reared at 18°C, the prevalence resembles that of wild‐type flies. This indicates a subtle expression of the shi defect even at the presumed permissive temperature of 22°C. The difference in latency is similar to that induced in shi flies whose development is affected by pupal heat pulse. Thus, correct interpretation of differences in latency, e.g., in shi/wild‐type mosaic flies or in flies with mutations affecting the GF pathway, requires recognition of the inherent asynchrony that can occur between DLM fibers.
A role for cAMP in the development of functional neuromuscular transmission
Authors: Dubinsky J. M. , Fischbach G. D. 
Published: January 2005

AbstractWe have found that the incidence of functionally connected neuron‐myotube pairs in chick ciliary‐myotube cultures increases from 58% to more than 90% when the cells are treated for several hours with 8‐bromo‐cyclic adenosine monophosphate (8‐br‐cAMP) or with agents known to increase intracellular cAMP. The increase in connectivity was not accompanied by a change in neuron survival, or in the length of neurite‐myotube contact. Moreover, there was no change in the shape of the presynaptic action potential, in mean end plate potential (epp) amplitude or in the sensitivity of postsynaptic acetylcholine receptors (AChRs). One interpretation of these results is that a cAMP‐dependent phosphorylation acts as a trigger to activate a previously “silent” synapse.
Developmental maps of acetylcholinesterase and G4‐antigen of the early chicken brain: Long‐distance tracts originate from AChE‐producing cell bodies
Authors: Weikert Thomas , Rathjen Fritz G. , Layer Paul G. 
Published: January 2005

AbstractAfter approaching the outer surface of the neuroepithelium, postmitotic cell bodies abruptly start to synthesize acetylcholinesterase (AChE). Their easy histochemical detection allows us to trace sensitively spationtemporal patterns of differentiation processes of the chicken nervous system. To investigate the relationship between postmitotic AChE production and the first formation of neurites, AChE histochemistry is combined here with immunohistochemistry using the neurite‐specific G4‐antibody. Spatial computer reconstructions from double‐stained serial sections of whole brains of H.H. stages 10–20 demonstrate that G4‐neurite expression spatiotemporally follows the expression of AChE in its complex polycentric pattern closely, the details of which have been described earlier. By comparing both differentiative steps at the single cell level reveals that a great majority (if not all) of the G4‐positive neurites originate from AChE‐positive cell bodies. Based on both the computer reconstructions as well as single cell analysis, including [3H]‐thymidine pulse‐experiments followed by autoradiography, we conclude, that AChE expression precedes formation of G4‐neurites by about 15 h. In addition, the reconstructions provide the first detailed maps of G4‐fiber tract formation and shows that G4‐neurites form fascicles, most of which travel over long distances to targets within or without the central nervous system (CNS). This is the first demonstration for the entire young chicken brain which verifies that AChE‐expressing cells, generally, are those that will establish efferents to distant targets.
Metamorphosis alters the response to spinal cord transection in Xenopus laevis frogs
Authors: Beattie Michael S. , Bresnahan Jacqueline C. , Lopate Glenn 
Published: January 2005

AbstractA series of studies has examined the response of the spinal cord to lesions made at various stages prior to and after metamorphic climax in the clawed frog Xenopus laevis. Complete transections made between Nieuwkoop and Faber (1956) stages 50 and 62 were followed by gradual recovery of righting and coordinated swimming as animals metamorphosed into juveniles (stage 66). Examination of descending axonal projections using horseradish peroxidase (HRP) showed fibers crossing the lesion site and distributing to the caudal lumbar spinal cord. These fibers could be traced from more rostral spinal segments as well as from brainstem injections of HRP. No evidence for rostrally projecting fibers crossing the lesion was obtained. Juvenile frogs of varying ages failed to demonstrate recovery of coordinated swimming or reconstitution of spinal descending pathways. In an additional series of animals, spinal transections were made within 1 or 2 days of tail resorption to assess whether regenerative capacities extended at all into post‐metamorphic stages. No evidence for regeneration was found. Studies of metamorphosing frogs after spinal transections showed that fibers crossed the lesion within 5–12 days of transection, well prior to the end of metamorphic climax; however, in some cases in which metamorphosis seemed arrested, little regeneration was observed. Immunocytochemical studies showed that fibers containing serotonin (5‐HT) were included in the population of axons that rapidly crossed the lesion after transection at metamorphic stages. These results are compared to those for lesions of the dorsal columns and other systems in developing and juvenile Xenopus. It is suggested that both metamorphosis‐related hormonal changes, and axon substrate pathways, may affect the regenerative response in the Xenopus central nervous system (CNS).
Directed early axonal outgrowth from retinal transplants into host rat brains
Authors: Hankin Mark H. , Lund Raymond D. 
Published: January 2005

AbstractAxons from retinae transplanted to the brain stem of neonatal rats exhibit two patterns of outgrowth that can be experimentally uncoupled from each other depending upon the location of the graft. Retinae placed close to the surface of the rostral brain stem (as much as 5 mm from the tectum) emit axons that project toward the superior colliculus along the subpial margin of the rostral brain stem. In contrast, axons from grafts embedded deep within the midbrain parenchyma project through the neuropil directly to the overlying superior colliculus, as long as the retina is within about 1 mm of the tectal surface. The present study shows that, as long as the retina is located outside the superior colliculus, and regardless of whether the axons derive from grafts in subpial or intraparenchymal locations, the earliest projections are oriented towards the superior colliculus. We have also found, however, that axons from retinae transplanted directly onto the superior colliculus can form projections that extend along the subpial margin away form the tectum. There are several major conclusions that may be drawn from these observations. First, the final tectopetal, transplant‐derived projection does not result from the reorganization of an initially random outgrowth but is directed from the start toward an appropriate region of termination. Second, it appears that the interaction of retinal axons with a primary target alters the ability of the growth cone to respond to directional cues along the optic tract. Thus, although adding support to the proposal that optic axons attain the superior colliculus through an interaction involving substrates distributed along the optic tract and diffusible factors originating in the target region, it is increasingly clear that such interactions are likely to be complex and hierachical.
Developmental regulation of type II calcium/calmodulin‐dependent kinase isoforms in rat cerebellum
Authors: Vallano Mary Lou 
Published: January 2005

AbstractTwo distinct isoforms of a Type II calcium/calmodulindependent protein kinase were separated from highspeed supernates (cytosol) of rat neonatal [postnatal day 10 (P10)] and adult [postnatal day 40 (P40)] cerebellum using cation‐exchange chromatography. The isoenzymes contained variable amounts of three subunits of apparent Mr's of 50 kDa (α), 58 kDa (β'), and 60 kDa (β). The specific activity of calmodulin‐dependent kinase (CaM kinase II) in crude homogenates increased sixfold between P10 and P40 using exogenous MAP 2 as substrate. Cytosol from cerebellum at P40 contained a predominant isoform (∼40% of total cytosolic activity) with a 1:5 molar ratio of α:β',β subunits that eluted with 150 mM NaCl (designated 150) and a less abundant isoform (∼20% of total cytosolic activity) containing a 1:8 molar ratio of α:β',β subunits that eluted with 350 mM NaCl (designated 350). In neonatal cerebellum at P10, the relative abundance of the two isoforms was reversed such that ∼50% of the cytosolic calmodulin‐dependent kinase activity was recovered in the 350 isoform, whereas only 20% of the total cytosolic kinase activity was recovered in the 150 isoform. Previous studies indicate that cerebellar granule cells may contain an all β',β isoform of CaM kinase II that lacks α subunit. Thus, to assess the cell‐specific localization of kinase isoforms within cerebellum, cytosol prepared from primary cultures of rat cerebellar granule cells was applied to cation‐exchange chromatography and analyzed for calmodulin‐dependent kinase activity. The cells contained both isoforms of the kinase that were present in fresh tissue suggesting that granule cell‐enriched cultures express all three kinase subunits. The data demonstrate that rat cerebellum contains unique mixtures of CaM kinase II isoenzymes and that their expression is developmentally regulated.
Odorant‐binding‐protein subfamilies associate with distinct classes of olfactory receptor neurons in insects
Authors: Vogt Richard G. , Prestwich Glenn D. , Lerner Michael R. 
Published: January 2005

AbstractThe olfactory receptors of terrestrial animals exist in an aqueous environment, yet detect odorants that are primarily hydrophobic. The aqueous solubility of hydrophobic odorants is thought to be greatly enhanced via odorant binding proteins (OBP) which exist in the extracellular fluid surrounding the odorant receptors. We have isolated and partially sequenced 14 candidate OBPs from six insect (moth) species. All 14 represent a single homologous family based on conserved sequence domains. The 14 proteins can be divided into three subfamilies based on differences in tissue specific expression and similarities in amino acid sequences. All 14 proteins are specifically expressed in antennal olfactory tissue. Subfamily I represents previously described pheromone binding proteins (PBP), which are malespecific, associate with pheromone‐sensitive neurons, and are highly variable in their sequences when compared among species. Subfamilies II and III are expressed in both male and female antennae, appear to associate with general‐odorant‐sensitive neurons, and are highly conserved when compared among species. The properties of the subfamily II and III proteins suggest these are general‐odorant binding proteins (GOBP). The properties of the respective insect OBP subfamilies suggest that they have different odorant binding specificities. The association of different insect OBP subfamilies with distinct classes of olfactory neurons having different odorant specificities suggests that OBPs can act as selective signal filters, peripheral to the actual receptor proteins.
Phosphorylation of membrane‐associated proteins by phorbol esters in isolated bag cell neurons of Aplysia
Authors: Azhderian Edward M. , Kaczmarek Leonard K. 
Published: January 2005

AbstractFollowing brief synaptic stimulation, the bag cell neurons in the abdominal ganglion of Aplysia undergo a series of changes in electrophysiological and secretory properties that triggers egg laying behavior. Activation of protein kinase C appears to play an important role in these changes and, in particular, causes the unmasking of a new species of voltage‐dependent calcium channel. We have now used isolated bag cell neurons maintained in cell culture to study changes in protein phosphorylation that are induced by exposure to an activator of protein kinase C. Primary cultures of bag cell neurons were labeled with 32P orthophosphate and then incubated with either tetradecanoyl phorbol 13‐acetate (TPA), a potent activator of protein kinase C, or with an inactive phorbol ester. When protein extracts were separated with 2D electrophoresis approximately 100 phosphoproteins could be distinguished. Only four of these proteins, with molecular weights of 20, 32, 200, and 250 kD, underwent a reproducible increase in the extent of phosphorylation of at least twofold in response to TPA. TPA‐induced changes in phosphate incorporation were blocked by pretreatment with the protein kinase C inhibitor H7. One of the TPA‐regulated phosphoproteins was localized in a plasma membrane‐containing fraction and was sensitive to trypsin treatment of intact cells, suggesting that it is a membrane protein with sites exposed to the extracellular medium. Two of the other TPA‐regulated phosphoproteins may be associated with the inner face of the plasma membrane. Our results indicate that only a small number of proteins undergo a major change in phosphorylation state following the activation of protein kinase C in isolated bag cell neurons. One or more of these proteins may contribute to the unmasking of the calcium channels.
Connectivity of identified central synapses in the cricket is normal following regeneration and blockade of presynaptic activity
Authors: Chiba Akira , Murphey R. K. 
Published: January 2005

AbstractCercal sensory neurons in the cricket innervate interneurons in the central nervous system (CNS) and provide a model system for studying the formation of central synapses. When axons of the sensory neurons were transected during larval development, the cell bodies and the soma‐bearing portion of axons, which are located within the cercus, survived but lost their excitability for 9–10 days. During this period, the sensory neurons grew new axons and reinnervated the terminal abdominal ganglion. Physiological recordings showed that sensory neurons of known identity reestablished monosynaptic contacts with their normal postsynaptic interneuron. Moreover, each synapse exhibited a characterstic strength indistinguishable from the intact synapse in an unoperated cricket. Since this selective connectivity was apparent immediately after the excitability of the axotomized sensory neurons was restored, action potentials in the sensory neurons appear to be unnecessary for normal synaptic regeneration to occur. Consistent with this, the reinnervation process was unaffected even when action potentials in the sensory neurons were blocked by tetrodotoxin (TTX) immediately following axotomy until just before testing. During the normal course of development, the characteristic strength of individual synapses changes systematically, resulting in the developmental rearrangement of these synapses (Chiba et al., 1988). This synaptic rearrangement was also unaffected when action potentials in the sensory neurons were blocked by TTX for the last 30% of larval development. Therefore, in the cricket cercal sensory system, both regeneration of the central synapses following axotomy of the presynaptic sensory neurons and the normal rearrangement of connectivity during larval development appear not to require axonal action potentials.
Regeneration of the projection and synaptic connections of tympanic receptor fibers of Locusta migratoria (orthoptera) after axotomy
Authors: Lakes Reinhard , Kalmring Klaus 
Published: January 2005

AbstractThe tergite nerve N6 of the first abdominal segment of the locust Locusta migratoria contains receptor fibers, from the tympanic organ, and hair sensilla as well as motoric axons. The nerve was axotomized in nymphal instars or adults, and the regeneration of nerve fibers was studied. The sensory fibers regrow and regenerate their projection pattern within the central nervous system. They recognize their specific neuropile areas even after entering the ganglion through different pathways. The receptor fibers of the tympanic organ reestablish synaptic connections to auditory interneurons, even though the physiological characteristics of the interneurons are not fully restored. This regenerative capability contrasts with the lack of regeneration of peripheral structures in locusts, but supports the described plasticity in the auditory system of monaural locusts (Lakes, Kalmring, and Engelhard, 1990). The motor fibers do not regenerate nerves innervating muscles of the body wall.
Down‐regulation of quantal size at frog neuromuscular junctions: Possible roles for elevated intracellular calcium and for protein kinase C
Authors: Van der Kloot William 
Published: January 2005

AbstractPrevious work showed that quantal size can be at least doubled at the frog neuromuscular junction by pretreatment with hormones or hypertonic solutions, primarily by the release of more acetylcholine (ACh) per quantum. Once increased, quantal size slowly declined over hours. Quantal size was measured from miniature endplate potentials (MEPPs) or currents (MEPCs). In the present experiments, preparations in which quantal size had been increased were exposed to 17–25 mM [K+], quantal size decreased within minutes. Release of comparable numbers of quanta by nerve stimulation did not decrease size. K+‐solutions did not decrease size if Ca2+ was omitted or replaced with Sr2+. The phosphokinase C (PKC) activators phorbol 12,13‐diacetate (PDA) and 1‐oleoyl‐2‐acetyl‐rac‐glycerol (OAG) also decreased quantal size within minutes when applied in a hypertonic solution that increased the rate of spontaneous release. Phorbol 12,13‐dideconate, which does not activate PKC, did not decrease quantal size. The size decrease triggered by K+‐solutions or PKC activators was blocked by 100 μM 1‐(5‐isoquinolinyl‐sulfonyl)‐2‐methyl‐piperazine (H7), a protein kinase inhibitor. Apparently, in creasing [K+]elevated intracellular [Ca2+], which activates PKC, and which leads to the down‐regulation of quantal size. During the period in which size is decreasing, there appears to be large and normal subpopulations of MEPP sizes, with normal gradually replacing large. This suggests that large quanta are formed by adding additional ACh to preformed quanta shortly before they are available for release.