bluuebunny/crossref_metadata_2025_split huggingface dataset:
Motor and sensory mechanisms of feeding in Pleurobranchaea
Authors: Lee Richard M. , Liegeois Richard J. 
Published: May 2005

AbstractNerves of the cerebropleural ganglion play a major role in the sensory and motor aspects of feeding in the marine mollusk, Pleurobranchaea. Investigations of these nerves were carried out using whole‐body preparations capable of essentially normal feeding behavior. Chemosensory nerves which function in food arousal are the rhinophore, tentacle (large branch) and large oral veil nerves, and a nerve of the pedal ganglion (P3). Recordings from these nerves are consistent with previous behavioral findings concerned with the location of receptor regions.The feeding cycle of proboscis extension, thrusting, and withdrawal, is controlled primarilly by cerebral nerves. The mouth nerve and small oral veil nerve supply muscles which control the oral tube. When these muscles contract, the oral tube and mouth are pulled open, and the buccal mass, which forms the core of the proboscis, advances part way. At his time, the body wall musculature, innervated by the body wall nerve and a pedal nerve (P4), contracts behind the buccal mass, forcing it out of the open mouth. Proboscis thrusting is accomplished by rhythmic bursts of the mouth and small oral veil nerves. Withdrawal of the buccal mass is accomplished essentially by the reverse process.This conception of the feeding cycle was developed by considering the muscular anatomy and by behavior simulation. It was confirmed by recording motor nerve output and muscle activity during food stimulation.
Innervation pattern and electric organ discharge waveform in Gymnotus carapo (Teleostei; Gymnotiformes)
Authors: Trujillo‐Cenóz O. , Echagüe J. A. , Macadar O. 
Published: May 2005

AbstractThe electrogenic organ (EO) of Gymnotus carapo has two main portions: a posterior region consisting of four bilaterally arranged electrocyte rows; and an anterior portion composed of only two. The lateral row (LR) of the anterior portion contains doubly innervated electrocytes with axon terminals from different nerves on their rostral and caudal faces. The LR is continuous with the most dorsal row of the caudal region. This row also contains doubly innervated electrocytes. The medial row (MR) electrocytes of the anterior region and ventral rows of the caudal region are exclusively caudally innervated. All caudal faces of the anterior or abdominal region are supplied by two nerves which originate from spinal roots VIII to XXI. Roots I to VII give origin to pure rostral nerves whose electromotor axons terminate on the rostral surfaces of the first seven LR electrocytes.A given doubly innervated electrocyte is supplied on its caudal face by a nerve originating several segments (usually seven) posterior to the spinal root supplying its rostral face.Transections of the spinal cord at the level of root VIII isolate the activity of the rostral surfaces of the first electrocytes. The EO discharge (EOD) then appears as a head negative deflection which arises from abdominally located electrocytes. Its monophasic character reveals that the activity remains restricted to the rostral electrocyte surfaces. Damage of the abdominal portion of the EO abolishes the first negative deflection of the normal pulse.Transections of the spinal cord at the level of root XXI isolate the activity of the whole abdominal portion of the EO. Since both doubly and singly innervated electrocytes remain active, the EOD appears biphasic.Comparative studies have shown that the EOD of Hypopomus sp. lacks any early negative wave and correspondingly all its electrocytes are exclusively caudally innervated.
Modified cobalt staining and silver intensification techniques for use with whole‐mount gastropod ganglion preparations
Authors: Croll Roger P. 
Published: May 2005

AbstractWhile silver intensification of cobalt‐filled cells is a common procedure for use with many arthropod preparations, it has not been routinely applied to gastropods. Several modifications in cobalt‐staining techniques currently used with gastropods along with adaptations of silver intensification techniques used in insects are described. Cobalt was introduced into cells through axonal filling of cut nerve trunks or by either pressure injection or iontophoresis from intracellular, micropipette electrodes that had previously had their tips etched in dilute hydrofluoric acid. Etching produced consistent, sharp tips with large lumina. Further procedural modifications allowed complete, even intensification of neurons in large gastropod ganglia. These techniques have proved to be reliable and apparently broadly applicable, having been successfully used on three diverse gastropod species.
Neurites show pathway specificity but lack directional specificity or predetermined lengths in Xenopus embryos
Authors: Huang Sen , Jacobson Marcus 
Published: May 2005

AbstractThe earliest outgrowth of nerve fibers from identified spinal neurons labeled with horseradish peroxidase (HRP) was traced along surgically rearranged pathways in the central nervous system (CNS) of Xenopus embryos. Parts of the CNS were misaligned or inverted rostrocaudally by grafting a segment of labeled spinal cord in place of the same or different spinal cord segment of an unlabeled embryo or by joining two rostral half embryos (head‐to‐head) or two caudal half embryos (tail‐to‐tail), one half of which was derived from a labeled embryo in each combination. Donor embryos were labeled by injection of HRP into a selected blastomere at the 16‐ or 32‐cell stage. Host embryos were unlabeled. Grafts from labeled donors to unlabeled host embryos were made at early neural tube stages before out‐growth of any nerve fibers had started (Jacobson and Huang, 1985). Routes taken by labeled nerve fibers growing into unlabeled CNS were observed at later stages, and the rates of nerve fiber elongation were calculated. Labeled nerve fibers were normal in appearance, and elongated without branching, at normal rates (22–71 μm/h). In head‐to‐head and tail‐to‐tail embryos and in embryos with inverted spinal cord grafts, nerve fibers continued elongating without branching in the direction opposite to normal in the CNS. Many fibers reached lengths that were far greater than normal. No reorientation of such maldirected nerve fibers was seen. These results indicate that nerve fiber elongation is not guided by axially polarized pathway cues or markers and that nerve fibers do not grow to predetermined lengths. However, neurites preferred to grow along streotyped nerve fiber pathways even when forced to grow in the wrong direction or when confronted with nonneural tissue.
Brain cells that command sexual behavior in the snail Helix aspersa
Authors: Chase Ronald 
Published: May 2005

AbstractEvidence is presented indicating that the mesocerebrum of the terrestrial snail, Helix aspersa, has a major role in the control of sexual behavior. Morphological and physiological results demonstrate a right‐sided bias in the mesocerebrum that is consistent with the fact that sexual behavior is executed almost entirely on the animal's right side. Thus, the right lobe has 23% more neurons than the left lobe, and they are 24% larger. Excitatory synaptic inputs derive predominately from neurons on the right side. The axons of right‐side mesocerebral neurons go to the right pedal ganglion almost without exception, and even the axons of left‐side neurons travel mostly in right‐side connective nerves. Direct evidence for a role of the mesocerebrum in commanding sexual behavior comes from experiments with electrical stimulation.Extracellular stimulation of the right mesocerebrum, but not the left mesocerebrum, resulted in movements of the “love dart” sac and the penis. Intracellular stimulation of neurons in the right mesocerebrum evoked measurable movements of either the dart sac or the penis, or both, in 17% of the cells tested. The latencies ranged between 5 and 50 s. In an intact animal, these movements would cause a release of the dart and an eversion of the penis. The motor effects were mediated through the right cerebropedal connective and the pedal nerve NCPD, with the motorneurons probably situated in the right pedal ganglion.
Control of leech swimming activity by the cephalic ganglia
Authors: Brodfuehrer Peter D. , Friesen W. Otto 
Published: May 2005

AbstractWe investigated the role played by the cephalic nervous system in the control of swimming activity in the leech, Hirudo medicinalis, by comparing swimming activity in isolated leech nerve cords that included the head ganglia (supra‐ and subesophageal ganglia) with swimming activity in nerve cords from which these ganglia were removed. We found that the presence of these cephalic ganglia had an inhibitory influence on the reliability with which stimulation of peripheral (DP) nerves and intracellular stimulation of swim‐initiating neurons initiated and maintained swimming activity. In addition, swimming activity recorded from both oscillator and motor neurons in preparations that included head ganglia frequently exhibited irregular bursting patterns consisting of missed, weak, or sustained bursts. Removal of the two head ganglia as well as the first segmental ganglion eliminated this irregular activity pattern. We also identified a pair of rhythmically active interneurons, SRN1, in the subesophageal ganglion that, when depolarized, could reset the swimming rhythm. Thus the cephalic ganglia and first segmental ganglion of the leech nerve cord are capable of exerting a tonic inhibitory influence as well as a modulatory effect on swimming activity in the segmental nerve cord.
Aminergic cellular organization in the gills of Aplysia species
Authors: Kurokawa Makoto , Kuwasawa Kiyoaki , Otokawa Minoru , Yamada Chifumi , Kobayashi Hideshi 
Published: May 2005

AbstractThe constituent elements of the gills of Aplysia kurodai and A. juliana were examined for the presence of biogenic amines using histochemical, immunocytochemical, and HPLC techniques. Aminergic elements were revealed by glyoxylic acid‐induced fluorescence in the branchial nerve, branchial ganglion, branchial vessels, and pinnules in both species. Three types of fluorescent cells were found in the neural plexus of the gill in each species. Two of them might be sensory neurons. Although HPLC analysis showed the presence of serotonin and dopamine in all gill structures including fluorescent neural elements, there were regional differences in concentrations of the monoamines. It was noted in the pinnules that there was a much higher concentration of dopamine than serotonin. Serotonin immunocytochemistry revealed neural processes which were immunoreactive to antiserotonin antibody, but serotonin immunoreactivity could not be found in a population of branchioganglionic neuron (BGN) somata. Serotonergic elements in the ganglion may be processes of the central ganglion, while dopaminergic elements may be processes of neurons in the neural plexus, located beyond the branchial ganglion. BGNs were activated by bath‐applied dopamine and serotonin. These results suggest that dopaminergic sensory inputs from the neural plexus and serotonergic descending inputs from the abdominal ganglion may be among the inputs received by BGNs.It was found that serotonin depressed excitatory junctional potentials in muscle cells of the efferent branchial vessel, which were induced by an identified neuron of the abdominal ganglion. The aminergic cellular organization of the gill may involve serotonergic presynaptic‐inhibitory fibers arising from the abdominal ganglion.
Multiple cAMP‐binding proteins in Aplysia tissues
Authors: Palazzolo Michael , Katz Flora , Kennedy Timothy E. , Schwartz James H. 
Published: May 2005

AbstractWhile it is recognized that cAMP is able to regulate distinct cellular processes differentially, the molecular basis for the diversity of its effects remains unclear. Using photoaffinity labeling with 32P‐8 azido‐cAMP and two‐dimensional gel analysis, we have identified 26 electrophoretic variants of cAMP‐binding proteins in the six different tissues of the marine mollusc Aplysia californica sampled. Some of these proteins are found in most tissues, others only in a few; still others appear to be restricted to a single tissue. All of these proteins bind cAMP specifically. The two‐dimensional polyacrylamide gel electrophoretic patterns of binding proteins seen in the different tissues fall into three classes. One pattern is shared by the nervous system and embryos. The second is found in muscular tissues (heart, buccal muscle, siphon, and gill). The third pattern is specific to sperm. The presence of distinct subsets of cAMP‐binding proteins in different tissues suggests that at least some of the diversity in cAMP's regulatory function may result from diversity in the proteins that bind it.
Activity‐dependent tuning and the NMDA receptor
Authors: Debski Elizabeth A. , Cline Hollis T. , Constantine‐Paton Martha 
Published: May 2005

AbstractThe refinement of the topographic map of visual space within the optic tectum of the frog is activity‐dependent. The use of the three‐eyed frog preparation to assay the operation of this fine‐tuning mechanism indicates that this process is mediated by the NMDA receptor: Chronic in vivo treatment with APV, an NMDA antagonist, disrupts the segregation of retinal afferents into eye‐specific zones while NMDA treatment sharpens this pattern. This latter effect is accompanied by a decreased sensitivity of the system to applied NMDA. Activation of the NMDA receptor may mediate the fine‐tuning mechanism by initiating the stabilization of appropriate synapse. The requirements for NMDA receptor activation necessitate the convergence of terminals carrying correlated activity patterns. Such patterns of activity are provided by ganglion cells whose cell bodies lie near one another in the retina, and who should therefore, in an accurate visual map, terminate near one another in the tectum. Synapses from ganglion cells who do not neighbor one another in the retina have uncorrelated firing patterns and therefore do not activate the NMDA receptor. These synapses then would not be stabilized relative to one another.In addition to organizing the retinal projection, NMDA receptor activation may also modulate retinal ganglion cell arbor morphology, since chronic in vivo APV or NMDA treatments decrease arbor density. These results are discussed in terms of the effect of NMDA receptor activation on branch initiation and the rate of branch retraction.
Specification of synaptic connections between sensory and motor neurons in the developing spinal cord
Authors: Frank Eric , Mendelson Bruce 
Published: May 2005

AbstractExperimental studies of mechanisms underlying the specification of synaptic connections in the monosynaptic stretch reflex of frogs and chicks are described. Sensory neurons innervating the triceps brachii muscles of bullfrogs are born throughout the period of sensory neurogenesis and do not appear to be related clonally. Instead, the peripheral targets of these sensory neurons play a major role in determining their central connections with motoneurons. Developing thoracic sensory neurons made to project to novel targets in the forelimb project into the brachial spinal cord, which they normally never do. Moreover, these foreign sensory neurons make monosynaptic excitatory connections with the now functionally appropriate brachial motoneurons. Normal patterns of neuronal activity are not necessary for the formation of specific central connections. Neuromuscular blockade of developing chick embroys with curare during the period of synaptogenesis still results in the formation of correct sensory‐motor connections. Competitive interactions among the afferent fibers also do not seem to be important in this process. When the number of sensory neurons projecting to the forelimb is drastically reduced during development, each afferent still makes central connections of the same strength and specificity as normal. These results are discussed with reference to the development of retinal ganglion cells and their projections to the brain. Although many aspects of the two systems are similar, patterned neural activity appears to play a much more important role in the development of the visual pathway than in the spinal reflex pathway described here.
Competitive and positional cues in the patterning of nerve connections
Authors: Fraser Scott E. , Perkel Donald H. 
Published: May 2005

AbstractThe visual system of lower vertebrates has served as an important testing ground for the mechanisms that generate topographic neuronal connections. During both the outgrowth and the regeneration of the optic nerve, a smoothly ordered map of the retina is formed on its major target, the optic tectum (the retinotectal projection). Experiments performed on this projection have offered support for a variety of mechanisms, including the matching of positional cues in the retina and tectum, the guidance of nerve fibers by interactions between fibers, competition for synaptic space, and the refinement of connections based on neuronal activity. Unfortunately, individual experiments that support any one of these mechanisms have been taken at times as evidence against the involvement of any other mechanism; for example, experiments demonstrating the importance of positional cues have been thought mistakenly to indicate that activity‐based interactions are unimportant. Computer simulations, in which multiple, somewhat opposed, mechanisms are allowed to operate in concert demonstrate that such a hybrid model is able to generate a full range of experimental results. More importantly, the elimination of any one of the mechanisms renders the model unable to fit entire classes of findings. Thus, the patterning of the retinotectal projection is best viewed as a process in which the optic nerve terminals attempt to satisfy multiple constraints in selecting their target sites.
Synaptic dynamics at the neuromuscular junction: Mechanisms and models
Authors: Van Essen David C. , Gordon H. , Soha J. M. , Fraser S. E. 
Published: May 2005

AbstractDuring development, the neuromuscular junction passes through a stage of extensive polyinnervation followed by a period of wholesale synapse elimination. In this report we discuss mechanisms and interactions that could mediate many of the key aspects of these important developmental events. Our emphasis is on (1) establishing an overall conceptual framework within which the role of many distinct cellular interactions and molecular factors can be evaluated, and (2) generating computer simulations that systematically test the adequacy of different models in accounting for a wide range of biological data. Our analysis indicates that several relatively simple mechanisms are each capable of explaining a variety of experimental observations. On the other hand, no one mechanism can account for the full spectrum of experimental results. Thus, it is important to consider models that are based on interactions among multiple mechanisms. A potentially powerful combination is one based on (1) a scaffold within the basal lamina or in the postsynaptic membrane which is induced by nerve terminals and which serves to stabilize terminals by a positive feedback mechanism; (2) a sprouting factor whose release by muscle fibers is down‐regulated by activity and perhaps other factors; and (3) an intrinsic tendency of motor neurons to withdraw some connections while allowing others to grow.
Role of postnatal androgens in sexual differentiation of the lordosis‐inhibiting effect of central injections of cholecystokinin
Authors: Ulibarri Catherine , Popper Paul , Micevych Paul E. 
Published: May 2005

AbstractThe neuropeptide cholecystokinin (CCK) inhibits lordosis behavior when infused into the ventromedial nucleus of the hypothalamus (VMN) of female rats and has no effect when infused into the VMN of male rats. To test whether this sex difference develops under the control of perinatal steroids, male rats were castrated or given sham surgeries within 3 h of birth and female rats were injected with either 0 or 100 μg testosterone propionate on postnatal day 5. As adults, these rats were castrated as necessary, implanted with unilateral cannulae directed at the VMN, and tested for their ability to display female sexual behavior and to respond to CCK. Neonatal castration of males prevented defeminization of this response. When treated with 5 μg estradiol benzoate (EB), neonatally castrated males showed both lordosis behavior and a profound inhibition of that behavior after infusions of CCK. Neonatally castrated males did not display lordosis behavior when treated with 2 μg EB. Control males showed no lordosis behavior and, therefore, no response to CCK. Both doses of EB induced lordosis behavior in neonatally androgenized females. Significantly, these neonatally androgenized females were less responsive to CCK's inhibition of lordosis and were also anovulatory. These results imply that androgens alter the development of CCK responsive circuits as well as defeminize cyclic gonadotropin release. Levels of 125I‐sCCK‐8 binding in the VMN were correlated closely with an individual's ability to respond to sCCK‐8. In summary, the inhibition of female sexual behavior caused by exogenously administered CCK in normal adult female rats appears to be controlled at least partially by levels of CCK receptors in the VMN and to differentiate under the control of perinatally present testosterone.
Cytochrome oxidase activity as a measure of synaptogenesis by mutifunctional neuron L7 of Aplysia
Authors: Ambron Richard T. , Dotty Stephen B. , Goldberg Daniel J. , Smedman Marilyn 
Published: May 2005

AbstractNeuron L7 of the marine mollusc, Aplysia californica, is unique in that it innervates five different target tissues in the animal. We show that when L7 is grown in vitro with two of these targets, that is, muscle cells isolated from the auricle or the gill vein, newly formed L7 neurites contact the muscle cells. Chemical synapses are formed since intracellular stimulation of L7 elicits contraction of individual muscle cells. Interestingly, auricle muscles are also innervated by neuron RBhe and co‐cultures of RBhe and auricle muscle cells also exhibit synapse formation. To explore the molecular basis for synaptogenesis between L7 and its targets, it would be useful to quantify the extent of synapse formation in vitro, that is, to determine how many muscle cells can be innervated by a single L7. We show that this can be attained by staining for cytochrome oxidase activity. Cultures of auricle and gill vein muscles were exposed to the appropriate neurotransmitter in order to elicit contraction. The cells were then fixed and stained. In both cases, only cells that contracted were stained and electron microscopy showed reaction product associated with the cristae of mitochondria. When this procedure was applied to cultures of L7 and muscle cells, 38 ± 2.8% (S.E.M.;n=7) of the cells on the neurites were stained and therefore responded to L7 stimulation. Thus, part of the L7‐RBhe circuit can be assembled in vitro and the extent of synaptogenesis can be accurately quantitated.