bluuebunny/crossref_metadata_2025_split huggingface dataset:
Human chorionic gonadotropin‐induced shifts in the electrosensory system of the weakly electric fish, Sternopygus
Authors: Zakon Harold H. , Yan Hong‐Young , Thomas Peter 
Published: May 2005

AbstractSternopygus macrurus of both sexes were injected with human chorionic gonadotropin (hCG) or saline. Electric organ discharge (EOD) frequency rose after hCG injections in females and gradually declined to baseline levels over the next few weeks. EOD changes in males were more complex and variable; most males showed an initial minor rise in EOD frequency followed by a larger decrease, or simply a decrease. hCG treatment also resulted in a rise in electroreceptor best frequency and shortened electric organ pulse duration in females, and had the opposite effect on these parameters in males. The saline‐injected controls showed no changes in any of these parameters. Levels of testosterone (T) and 11‐ketotestosterone, but not estrogen (E), were elevated in males preceding the fall in EOD frequency, whereas neither T nor E changed significantly in females before EOD frequency increases. Saline injections caused a drop in T in the male control group and had no effect in the female control group. We presume that the effect of hCG on the electrosensory system of males is mediated via androgens. Whether the effects of hCG on females are mediated by slight increases in circulating levels of gonadal steroids, the release of hormones other than T or E, or are due to direct effects on the nervous system is not known.
Seasonal differences in the physiology and morphology of crayfish motor terminals
Authors: Lnenicka Gregory A. , Zhao Yangu 
Published: May 2005

AbstractThe physiology and morphology of identified crayfish motor terminals were compared at different seasons. We examined initial excitatory postsynaptic potential (EPSP) amplitudes, synaptic fatigue, and the frequency of synaptic varicosities along the motor terminals of an identified phasic motoneuron in animals collected over a period of 5 years. The physiology and morphology of identified crayfish motor terminals are different for animals collected in summer and winter. In winter animals, phasic axon motor terminals in the claw closer muscle produce large EPSPs initially, but show dramatic synaptic fatigue during repetitive stimulation. In summer animals, these terminals produce smaller initial EPSPs, but are more fatigue resistant. Due to their greater fatigue resistance, synaptic terminals have a greater overall capacity for transmitter release in summer animals than do those of winter animals. Morphologically, terminals in summer animals have more synaptic varicosities, this result supports earlier studies that have shown that fatigue‐resistant motor terminals have more synaptic varicosities. Experiments in which the electrical activity of the motoneuron was experimentally altered suggest that these differences in motor terminals may be due to seasonal differences in activity.
Axotomy accelerates slow component b of axonal transport
Authors: Jacob Jane M. , McQuarrie Irvine G. 
Published: May 2005

AbstractBecause the integrity of an axon depends on the supply of proteins synthesized in the cell body, we examined the effect of axotomy on the transport of structural proteins in rat motor axons, and the effect of altered transport on the rate of outgrowth after a subsequent testing axotomy. To examine the axonal transport of structural proteins, we labeled newly synthesized proteins with 35 S‐methiomine 7 days after a “conditioning” lesion of the sciatic nerve, and removed the nerve 7–21 days later for SDS‐PAGE. Tubulin, actin, calmodulin, and the 68‐kD light neurofilament protein (NF‐L) were identified by fluorography and removed for liquid scintillation counting. The fastest moving structural proteins were carried by slow component b (SCb) of axonal transport, which advanced 20% faster in conditioned axons: 4.2 versus 3.5 mm/day (p < 0.01). NF‐L was not accelerated, indicating that the motor for subcomponent a (SCa) of slow axonal transport was unaffected by axotomy. To measure outgrowth distances, the testing lesion was made 7 days after the conditioning lesion, and growth cones were located by the fast transport method 3 or 9 days later. The regression analysis of outgrowth distance on time showed that sprouts elongated 25% faster in conditioned axons: 4.0 versus 3.2 mm/day (p < 0.001). These accelerated sprouts were formed too far from the spinal cord to contain SCb proteins that were synthesized after axotomy. Because the rate of outgrowth correlates closely with the rate of SCb in outgrowing sprouts (McQuarrie and Jacob, J. Comp. Neurol. 305:139–147, 1991), we conclude that SCb is accelerated throughout the length of the axon by 7 days after axotomy.
Release of pedal peptide from Aplysia neurons in primary culture
Authors: Hall Jon D. , Lloyd Philip E. 
Published: May 2005

AbstractPedal peptide (Pep) is a modulatory neuropeptide that is predominantly synthesized in a group of neurons on the dorsal surfaces of the pedal ganglia of Aplysia. Following the determination that Pep is the major peptide selectively present in these neurons in situ, primary cell culture of single Pep‐neurons was used to study the release of this neuropeptide. Individual Pep‐neurons were grown in culture where they extended many branched neurites with large varicosities. Immunocytology revealed that these newly grown varicosities were intensely Pep immunoreactive. Cultured Pep‐neurons, grown in a medium containing radiolabeled methionine, synthesized labeled Pep and transported it into their regenerated neurites. Finally, these neurons released radiolabeled Pep in a calcium‐ and stimulation‐dependent fashion. These results, taken together with previous findings, strongly support the proposition that Pep is a transmitter in Aplysia.
Localization of ventral giant interneuron connections to the ventral median branch of thoracic interneurons in the cockroach
Authors: Casagrand Janet L. , Ritzmann Roy E. 
Published: May 2005

AbstractA detailed morphological study was performed to localize the probable sites of connections between two identified populations of interneurons (ventral giant interneurons and type‐A thoracic interneurons) in the cockroach. Type‐A thoracic interneurons (TIAs) appear to play an important role in orienting the cockroach during windmediated escape. However, their large number, approximately 100 neurons, precludes analyzing each cell's role electrophysiologically. The TIAs are characterized by a prominent branch located on one or both sides of the ventral median (VM) region of the thoracic ganglion in which their soma resides. The presence of this ventral median branch can be used to predict connectivity with left or right ventral giant interneurons (vGIs) (Ritzmann and Pollack, 1988) and is correlated with the TIA's directional response to wind (Westin, Ritzmann, and Goddard, 1988), suggesting that this is the locus of synaptic connection. Two approaches were employed to address this hypothesis. Morphological overlap of differentially labelled cells (ethidium bromide, Lucifer Yellow) was examined at the light microscopic level to locate areas of possible synaptic contact. Experiments were also performed in which one‐half of the vGI input to the TIAs was surgically removed early in postembryonic development. Although no changes in the overall branching pattern were observed, the VM branches on the operated side were significantly shorter than were those on the unoperated side. Thoracic interneurons that do not receive inputs from vGIs were unaffected by this surgery. The data reported here thereby confirm previous observations by localizing the vGI inputs specifically to the VM branch, and provide a morphological cue for predicting connectivity and function.
Gonadal steroids affect LHRH preoptic cell number in a sex/role changing fish
Authors: Grober Matthew S. , Jackson Ivor M. D. , Bass Andrew H. 
Published: May 2005

AbstractIn diandric sex‐reversing fishes, sexually active males and females (primary phase) regularly transform into an alternative reproductive morph, terminal‐phase males, that are morphologically and behaviorally distinct. The transformation from primary to terminal phase is associated with a twofold increase in the number of luteinizing hormone‐releasing hormone (LHRH) immunopositive cells in the forebrain preoptic area, a region involved in both the initial development and daily control of reproductive physiology and behavior. We now show that implants of 11‐ketotestosterone induce increases in LHRH cell number in both primary phase sexes to the level observed in field‐collected terminal phase males. Conversely, gonadal steroids had no effect on the number of LHRH preoptic cells in terminal phase males, suggesting that this is indeed a terminal stage in the development of this species. These results demonstrate that transition to the terminal phase by both sexes involves a parallel and convergent change in LHRH cell number, which utilizes an evolutionarily conserved mechanism of sexual differentiation: the inductive effects of gonadal steroid hormones.
Early estrogen treatment alone causes female zebra finches to produce learned, male‐like vocalizations
Authors: Simpson H. Blair , Vicario David S. 
Published: May 2005

AbstractThe male zebra finch produces learned song and long calls while the female does not. This difference in behavior is believed to result from the action of sex steroids on brain areas responsible for vocal production and learning. In this study, the female zebra finch was used to explore further the specific role sex steroids play in vocal masculinization. We show that estradiol (E2) treatment at birth was sufficient to masculinize the vocal behavior of female zebra finches. Thirteen of 18 females treated with E2 as nestlings produced song‐like vocalizations. Fifteen of 18 produced long calls with male‐typical features. The degree of masculinization varied between individuals. Of the 15 early E2 females that produced at least one type of male‐like vocalization, 7 showed evidence of vocal learning from their tutors. The ability of E2 to cause masculinization of vocal behavior was age dependent: treatment from birth was most effective, treatment at 20 days of age was partially effective, and treatment in adulthood was ineffective. The effect of subsequent testosterone exposure in adulthood differed depending on the quality of the vocalization produced after E2 treatment alone. These results suggest that E2 may play a more important role than previously thought in the development of sex differences in vocal behavior. Further‐more, this study demonstrates that exogenous E2 treatment alone can induce vocal learning.
Early estrogen treatment of female zebra finches masculinizes the brain pathway for learned vocalizations
Authors: Simpson H. Blair , Vicario David S. 
Published: May 2005

AbstractTelencephalic nucleus HVC and its two efferent targets, RA and X, play essential roles in the production of complex, learned vocalizations in the male zebra finch. Normal females do not produce these learned vocalizations; HVC, RA, and X are small in volume, and HVC and RA are not synaptically connected. We have shown that estrogen treatment during development causes females to learn and produce male‐like vocalization. This article describes the neural masculinization of these E2 females, replicating and extending the work of others. Female zebra finches were treated with 17β‐estradiol (E2) at hatching, at 14–22 days of age, or as adults. In adulthood, the volumes of nucleus RA and area X were measured and the efferent projections of nucleus HVC examined using the anterograde tracer PHA‐L. Early, sustained E2 treatment caused the greatest increase in the volume of RA and X, the innervation of RA and X by HVC axons, and the masculinization of auditory responses of cells in RA. Treatments that lasted for a shorter period or started later in development resulted in different patterns of partial brain masculinization. E2 treatment in adulthood had no effect on the volume of RA or X or their innervation by HVC. Bilateral lesions of the tracheosyringeal nerves or of HVC had the same effects on the male‐typical vocalizations produced by E2 females as they do on the vocalizations produced by males. These results demonstrate that the neural masculinization of telencephalic nuclei induced by E2 treatment sets up a functional circuit in females similar to one in males that enables the learning and production of complex vocalizations.
Development and specificity of inhibitory terminal arborizations in the central nervous system
Authors: Sanes Dan H. , Siverls Veronica 
Published: May 2005

AbstractThis study examined the morphological development of single inhibitory arborizations in the gerbil central auditory brain stem. Using a brain slice preparation, neurons of the medial nucleus of the trapezoid body (MNTB) were filled with horseradish peroxidase (HRP), and their complete arborizations were analyzed along the tonotopic axis of the lateral superior olive (LSO). The projections in neonatal animals displayed well‐defined arbors that were ordered appropriately within the LSO. It was evident from the axonal pathways that the MNTB afferents could correct for projection errors after reaching the postsynaptic population. As development progressed, a number of arbors established diffuse or inappropriate projections within the LSO. These immature arborizations were no longer apparent by 18–25 days postnatal. The anatomical specificity of arbors at 12–13 and 18–25 days was quantified by measuring the distance that terminal boutons spread across the frequency axis. There was a significant reduction of this distance in older animals. In addition, there was a significant reduction in the mean number of boutons per arbor between 12–13 days and 18–25 days. The maximum nucleus cross‐sectional area continued to increase through 15–16 days, indicating that the refined arbors occupied an even smaller fraction of the postsynaptic structure. Taken together, these observations suggest that central inhibitory arbors form exuberant contacts that must be eliminated during development.
Intracellular recordings from nonspiking interneurons in a semiintact, tethered walking insect
Authors: Schmitz Josef , Büschges Ansgar , Kittmann Rolf 
Published: May 2005

AbstractNonspiking interneurons were investigated in a tethered, walking insect, Carausius morosus, that was able to freely perform walking movements. Experiments were carried out with animals walking on a lightweight, double‐wheel treadmill. Although the animal was opened dorsally, the walking system was left intact. Intracellular recordings were obtained from the dorsal posterior neuropil of the mesothoracic ganglion. Nonspiking inter‐neurons, in which modulations of the membrane potential were correlated with the walking rhythm, were described physiologically and stained with Lucifer Yellow. Interneurons are demonstrated in which membrane potential oscillations mirror the leg position or show correlation with the motoneuronal activity of the protractor and retractor coxae muscles during walking. Other interneurons showed distinct hyperpolarizations at certain important trigger points in the step cycle, for example, at the extreme posterior position. Through electrical stimulation of single, nonspiking interneurons during walking, the motoneuronal activity in two antagonistic muscles—protractor and retractor coxae—could be reversed and even the movement of the ipsilateral leg could be influenced. The nonspiking interneurons described appear to be important premotor elements involved in walking. They receive, integrate, and process information from different leg proprioceptors and drive groups of leg motoneurons during walking.
Fiber‐type proportions in mammalian soleus muscle during postnatal development
Authors: Wigston Donald J. , English Arthur Wm. 
Published: May 2005

AbstractWe analyzed the fiber‐type composition of the soleus muscle in rats and mice to determine whether the adult proportion of fiber types is fixed soon after birth or whether it changes during postnatal maturation. We examined muscles from animals varying in age from 1 week to 1 year using monoclonal antibodies that distinguish between fast and slow isoforms of myosin heavy chains. In cross sections of unfixed muscle containing profiles of all myofibers in the muscle, we counted the fibers that stained with antibodies to fast myosin, and in adjacent sections, those that stained positive with an antibody to slow myosin. We also counted the total number of fibers in each section. Rat soleus contained about 2500 myofibers, and mouse about 1000 at all ages studied, suggesting that myogenesis ceases in soleus by 1 week after birth or sooner. In mouse soleus, the relative proportions of fibers staining positive with fast and slow myosin antibodies were similar at all ages studied, about 60%–70% being fast and 30%–40% slow. In rat soleus, however, the proportions of fast antibody‐positive and slow antibody‐positive fibers changed dramatically during postnatal maturation. At 1 week after birth, about 50% of rat soleus fibers stained with fast myosin antibodies, whereas between 1 and 2 months this value fell to about 10%. In mouse, about 10% of fibers at 1 week, but none at 1 year, reacted with both fast and slow antibodies, whereas in rat, fewer than 3% bound both antibodies to a significant degree at 1 week. It is puzzling why, in rat soleus, the majority of apparently fast fibers present at 1 week is converted to a slow phenotype, whereas in mouse soleus the predominant change appears to be the suppression of fast myosin expression in a subset of fibers that expresses both myosin types at 1 week. It is possible that this may be related to differences in size and the amount of body growth between these two species.
Differential expression of neuropeptide gene mRNA within the LUQ cells of Aplysia californica
Authors: Landry Claire , Crine Philippe , Desgroseillers Luc 
Published: May 2005

AbstractTwo neuropeptide precursor cDNAs (LUQ‐1 and L5‐67) have been recently isolated from the Left Upper Quadrant (LUQ) neurons of the abdominal ganglion of Aplysia californica (Shyamala, Fisher, and Scheller, 1986; Wickham and DesGroseillers, 1991). Using in situ hybridization techniques as well as dot blot and polymerase chain reaction (PCR) assays, we have studied the expression of these genes in the central nervous system (CNS) of Aplysia californica. The LUQ‐1 gene was found to be expressed in neuron L5 in the abdominal ganglion, whereas the expression of the L5‐67 gene was observed in the other four LUQ cells (L2‐4 and L6). When in situ hybridization was performed on paraffin sections of the abdominal ganglion, clusters of smaller cells located in the left hemiganglion, were also found to express either the LUQ‐1 on the L5‐67 gene, never both. In many sections, the mRNAs coding for the two neuropeptides were found not only in cell bodies but also in the axon of individual LUQ neurons and even as far as the pericardial nerve. The presence of neuropeptide mRNA in axons, pericardial nerve, and kidney has been confirmed by polymerase chain reaction. A specific, although diffuse hybridization in the left upper quadrant also suggests that mRNA is present in the neuritic field. Taken together these results indicate that neuron L5 is the only giant neuron expressing the LUQ‐1 gene and might therefore have a physiological function different from the other four LUQ cells. Neuropeptide mRNAs were also found in the axon and/or the neuritic field of giant neurons and could play important roles related to cell signalling in axons and nerve termini.
Regulation of motoneuron death in the spinal nucleus of the bulbocavernsus
Authors: Forger Nancy G. , Hodges Lynn L. , Roberts Sarah L. , Breedlove S. Marc 
Published: May 2005

AbstractA sexual dimorphism in the number of motoneurons in the spinal nucleus of the bulbocavernosus (SNB) of rats is engendered by a sex difference in ontogenetic cell death. Testicular secretions, specifically androgenic steroids, reduce SNB motoneuron death in males. The fate of the target muscles generally mirrors that of the motoneurons, and androgens appear to exert their effects upon the target muscles, sparing the motoneurons as a secondary consequence. Treatment with ciliary neurotrophic factor can also spare SNB motoneurons in newborn females, raising the possibility that this factor normally mediates androgen's effect upon motoneuron survival. The ontogeny of calcitonin gene‐related peptide immunoreactivity is delayed in SNB cells compared with other motoneurons and is further delayed in the SNB cells of females. In both sexes, calcitonin gene‐related peptide is detected after the period of SNB motoneuron death is complete. A sex difference in motoneuron number is also seen in the human homologue of the SNB and, because ontogenetic death of motoneurons in humans overlaps the period of androgen secretion, may arise in a manner similar to that in the rat SNB. © 1992 John Wiley & Sons, Inc.
Claw asymmetry in lobsters: Case study in developmental neuroethology
Authors: Govind C. K. 
Published: May 2005

AbstractAn enduring debate in the study of development is the relative contribution of genetic and epigenetic factors in the genesis of an organism, that is, the nature vs. nurture debate. The behavior of the paired claws in the lobster offers promising material for pursuing this debate because of the way they develop. The paired claws and their closer muscles are initially symmetrical; both are slender in appearance and have a mixture of fast and slow fibers in their closer muscles. During a critical period of development, they become determined into a major (crusher) and minor (cutter) claw and during subsequent development acquire their final form and behavior: The crusher becomes a stout, molar‐toothed claw capable of closing only slowly because its closer muscle has 100% slow fibers while the cutter becomes a slender, incisor‐toothed claw capable of closing rapidly because its closer muscle has 90% fast fibers. Our initial hypothesis was that the more active claw became the crusher and its less active counterpart the cutter. Presumably, nerve activity would influence muscle transformation, which in turn would influence the exoskeleton to which they attach and hence claw morphology. Curtailing nerve activity to the claw prevented crusher development, while reflex activation of a claw promoted its development; both results support the notion that nerve activity directly regulates claw form and function. This is not, however, the case, for when both claws were reflexly exercised neither formed a crusher, signifying rather that bilateral differences in predominantly mechanoreceptive input to the paired claws somehow lateralized the claw ganglion [central nervous system (CNS)] into a crusher and cutter side. The side experiencing the greater activity becomes the crusher side while the contralateral side becomes the cutter and is also inhibited from ever becoming a crusher. This initial lateralization in the CNS is expressed, via as yet unknown pathways, at the periphery in claw morphology, muscle composition, and behavior. The critical period defines a time when the CNS is susceptible to being lateralized into a crusher and cutter side. Such lateralization is dependent upon experience of the environment in the form of mechanoreceptive input. In the absence of such experience, the CNS is not lateralized and paired cutter claws develop. Thus, while the critical period for crusher determination is genetically determined the actual trigger is influenced by experience. © 1992 John Wiley & Sons, Inc.