bluuebunny/crossref_metadata_2025_split huggingface dataset:
Neuroeffectors for vocalization in Xenopus laevis: Hormonal regulation of sexual dimorphism
Authors: Kelley Darcy B. 
Published: January 2005

AbstractSouth African clawed frogs use sex‐specific vocalizations during courtship. In the male, vocalizations are under the control of gonadal androgen. Though females have moderate levels of circulating androgen, they do not give male‐typical mate calls. Both muscles of the vocal organ and neurons of the central nervous system (CNS) vocal pathway are sexually dimorphic and androgen‐sensitive. Recent studies suggest that the failure of androgen to masculinize adult females results from a male‐specific, androgen‐regulated developmental program. At metamorphosis the larynx is sexually monomorphic and feminine in morphology, muscle fiber number and androgen receptor content. During the next six months, under the influence of increasing androgen titers and high receptor levels, myoblasts proliferate in the male and muscle fibers increase at an average rate of 100/day. Females have much lower hormone levels, receptor values decline and they display no net addition of fibers. At metamorphosis, both males and females have approximately 4000 muscle fibers. By adulthood, males have eight times the female fiber number. In the CNS, adult laryngeal motor neurons are more numerous with larger somata and dendritic trees in males than in females. Certain connections of neurons in the vocal pathway are also less robust in females. Unlike the periphery, motor neuron number does not appear to be established by androgen‐induced proliferation. Our current hypothesis is that androgen acts at the level of laryngeal muscle to produce more muscle fibers and thus provide more target for motor neurons in the male. This process could regulate cell number by ontogenetic cell death. In the CNS, androgen‐target neurons become capable of accumulating hormone shortly before metamorphosis. Androgen receptor in larygeal motor neurons may permit the dendritic growth characteristic of males by increasing sensitivity to afferent stimuli. Such a process could account for the observed differences in CNS vocal “circuitry” in X. laevis and thus behavioral differences between the sexes.
Central actions of R15, a putative peptidergic neuron in Aplysia
Authors: Brown Richard O. , Mayeri Earl 
Published: January 2005

AbstractWe report that the bursting pacemaker neuron R15 has central actions on other identified neurons in the abdominal ganglion of Aplysia californica. The follower cells are located on the dorsal surface of the left lower quadrant of the ganglion and include members of the LC cell cluster. A spontaneous burst of impulses in R15 produces a slow, graded, excitatory potential of up to 8 mV in follower cells. The response begins about 2–3 s after the first impulse in an R15 burst, and reaches its speak at about 4–6 s (corresponding approximately to the end of the R15 burst). In some preparations a biphasic response was seen composed of the early depolarization followed by a slower excitatory or inhibitory phase. All the responses were blocked when R15 was hyperpolarized to prevent spiking. The magnitude of the response was reduced in a graded fashion by prematurely terminating the R15 burst with hyperpolarizing current and was increased when depolarizing current was injected into R15 during a burst. Central actions of R15 were observed in only 28% of our preparations, and their presence may depend on unknown physiological factors. The effects are likely to be mediated by R15 neuropeptides. The accessibility of both R15 and its targets in this preparation should facilitate further analysis of this interaction.
Increased levels of testosterone have little effect on visual cortex plasticity in the kitten
Authors: Daw N. W. , Baysinger K. J. , Parkinson D. 
Published: January 2005

AbstractWe tested the hypothesis that increased levels of sex steroids preceeding puberty are an important factor in the termination of the critical period for monocular deprivation. Male kittens were injected with Depo‐testosterone in order to elevate plasma testosterone to a higher level than that in normal prepubertal male kittens. Control animals did not receive testosterone injections. All kittens were monocularly deprived for 7–18 days, then cells in the visual cortex were examined electrophysiologically, and an ocular dominance histogram was constructed.Treated animals showed an increase in plasma testosterone (1.82–15.16 ng/mL) when compared with the control animals (0.80 ± 0.25 ng/mL). The fraction of cells driven exclusively by the experienced eye was slightly lower in the treated animals, and there was a slight increase in the dominance of cells by both eyes. However, in both groups of animals, the majority of cells were dominated by the experienced eye, with no significant difference in the weighted parameter used to describe this dominance. In summary, although there is a slight difference between treated and control animals, the results do not support the hypothesis that elevated levels of sex steroids play a crucial role in the termination of the critical period.
Seasonal variation in mammalian striated muscle mass and motoneuron morphology
Authors: Forger Nancy G. , Breedlove S. Marc 
Published: January 2005

AbstractFeral white‐footed mice are seasonal breeders that undergo predictable cycles of reproductive function. Photoperiod‐induced fluctuations in gonadal function of white‐footed mice were associated with morphological changes in perineal muscles and their motoneurons. Exposure to short daylengths resulted in testicular regression, decreased perineal muscle mass, and shrinkage of somata and nuclei of motoneurons of the spinal nucleus of the bulbocavernosus (SNB). These effects were reversed by reinstatement of long daylengths. Similar reductions in muscle mass and SNB soma size were seen following gonadectomy of white‐footed mice. In addition, dendritic trees of SNB motoneurons were reduced in gonadectomized mice compared with dendritic arbors of intact mice or castrates provided with testosterone capsules. Androgen‐mediated annual changes in muscle mass and motoneuron morphology appear to be a natural part of this species' physiology.
The effect of temperature on flight initiation in the cockroach Periplaneta americana
Authors: Diekman Lynda J. , Ritzmann Roy E. 
Published: January 2005

AbstractThe effect of temperature during development of the flight system of the American cockroach was tested. Animals were raised at three different temperatures from egg cases to adulthood then various parameters of flight were tested. Animals raised at cooler temperatures were found to require significantly stronger wind puffs to initiate flight than did animals raised in warmer temperatures. Some animals were raised at one temperature during embryonic development (i.e. while the animals were still in egg cases) and then switched to a different temperature for nymphal development. In these cases only the temperature experienced during embryonic development had a significant permanent effect on flight. Parameters associated with pattern generation such as interburst interval were not affected by temperature during either developmental period.
Regenerated fibers of the lamprey spinal cord can coordinate fictive swimming in the presence of curare
Authors: Cohen Avis H. 
Published: January 2005

AbstractRecently evidence was presented that, following transection, spinal cords of larval lampreys could regenerate functional connections. The demonstration in isolated spinal cord–notochord preparations consisted of fictive swimming coordinated across the lesion site. In the study reported here curare was added to the bath to eliminate the possible contribution from reflexes mediated by contractions from any remaining muscle fibers attached to the notochord. Coordination remained in the presence of curare, adding further evidence that indeed the regenerated fibers formed functionally appropriate connections.
Small sex differences in song control dendrites are associated with minimal differences in song capacity
Authors: Devoogd T. J. , Brenowitz E. A. , Arnold A. P. 
Published: January 2005

AbstractPrevious work on canaries and zebra finches has shown that large differences between the sexes exist in the structure of dendrites in n. robustus archistriatalis (RA), one of the principal nuclei involved in the control of song. This sex difference is associated with a general or complete absence of song in females. If dendritic morphology in RA is causally related to capacity for song, large sex differences in structure should not occur in avian species in which both sexes sing. We now report this prediction confirmed for buff‐breasted wrens (Thryothorus leucotis), a species in which the members of a breeding pair sing duets with each other. Total dendritic length and number of dendritic branches in RA do not differ in this species. Dendrites from males project about 8 μm further from the cell body than dendrites from females, apparently because of longer dendritic segments near the cell body. We argue that this suggests that differential influences on the structure of RA occurred early in the lives of the wrens.
The release of axonally transported material from an in vitro amphibian sciatic nerve preparation
Authors: Snyder R. E. 
Published: January 2005

AbstractThe rapid axonal transport of a pulse of [35S]methionine‐labelled material was used to study the release of transported material from amphibian nerve maintained in vitro. Following creation of a moving pulse of activity in a dorsal root ganglion‐sciatic nerve preparation, the ganglion was removed and the nerve placed in a three‐compartment tray, the section of nerve in the middle compartment containing no truncated branches (unbranched section). All three compartments were filled with a saline solution that in some studies contained nonradioactive methionine (1.0 mmol/L). Analysis of studies in which nonradioactive methionine was absent revealed that labelled material appeared in the bathing solution of the end compartments that contained truncated branches, but not in the solution of the middle (unbranched) compartment. The quantity of label released in the branched compartments was approximately 6% of that remaining in the corresponding section of nerve following an 18–20 h incubation period. However, when nonradioactive methionine was present, all compartments showed an additional activity in the bathing solution of approximately 10% of that remaining in the nerve. In another study in which a position‐sensitive detector of ionizing radiation was used to monitor progress of the pulse, it was found that activity did not enter the bathing solution of a compartment prior to the pulse of activity. It is concluded that in the absence of methionine from the bathing solution, axonally transported material is released only from regions of nerve that contain severed axons; however, the presence of methionine allows transported material to be released from nerve containing intact axons. Ultrafiltration studies and thin‐layer chromatography revealed the majority of material released to be of low‐molecular weight (≤ 30,000 daltons) and not free [35S]methionine.
Sex differences in the motor nucleus of cranial nerve IX‐X in Xenopus laevis: A quantitative Golgi study
Authors: Kelley Darcy B. , Fenstemaker Suzanne , Hannigan Patricia , Shih Scott 
Published: January 2005

AbstractIn the clawed frog (Xenopus laevis), motor neurons in cranial nerve nucleus IX‐X control contraction of laryngeal muscles responsible for sexually dimorphic vocal behaviors. We examined sex differences in dendritic arbors of n.IX‐X cells using the Golgi–Cox method. Three morphological classes of somal types (ovoid, triangular, and elongate) are present in similar frequencies in n.IX‐X of both males and females. The male n.IX‐X neuron is a more complex and hypertrophied version of the female n.IX‐X cell. The number of primary dendrites is the same for both sexes, but males have more total dendritic segments. The overall dendritic length of male n.IX‐X neurons is two to three times that of the female. Males have longer dendritic segments between all branch points.Male and female frogs differ in levels of circulating androgens; neurons of n.IX‐X are targets for androgenic steroids. To determine if androgen can affect dendritic morphology in adult females, we examined Golgi‐impregnated cells in n.IX‐X from ovariectomized females treated with testosterone for 1 month. The total number of dendritic segments was reduced by androgen treatment due to reduction in the number of higher order dendritic segments; the number of primary dendritic segments was unchanged. Androgen treatment may induce resorption of higher order dendritic branches. The overall dendritic length of androgen‐treated female n.IX‐X neurons was unchanged, and dendritic segments were longer. Thus, although androgen can alter dendrites of n.IX‐X cells in adult females, this short‐term treatment does not produce a masculine dendritic architecture.
Neural attrition following limb loss and regeneration in juvenile lobsters
Authors: Govind C. K. , Pearce J. , Potter D. J. 
Published: January 2005

AbstractLobsters have considerable regenerative capacity, being able to regrow an entire, albeit smaller, limb in one intermolt. Whether there is a corresponding downscaling in the hemiganglion and its nerves to the regenerate side compared with its contralateral intact side was examined in juvenile lobsters which had undergone single or multiple (2, 4, and 6) cycles of limb loss and regeneration on the one side. The limbs studied were the enlarged thoracic chelipeds or claws which appeared as paired symmetrical cutter‐type claws. The size of the regenerate limb, as indicated by its propus length, was approximately 30% smaller than its intact counterpart. Correspondigly, the total number of axons in the nerves to the regenerate side was smaller than on the intact, contralateral side. Such attrition was also by about 30% in lobsters experiencing a single cycle of limb loss and regeneration, but was considerably greater with multiple cycles. Tissue degeneration was occasionally seen in the nerves to the regenerate side but not in the ganglion. The paired hemiganglia were equivalent in all respects except in the size of the neuropil, which was smaller on the regenerate side compared with the contralateral intact side. Neuropil attrition was most marked with multiple cycles of limb loss and regeneration. Such attrition in nerve and neuropil are most likely due to the reduced number of sensory elements in the newly regenerated, but smaller, limb.
Structural plasticity at crustacean neuromuscular synapses
Authors: Govind C. K. , Walrond J. P. 
Published: January 2005

AbstractCrustacean motor axons innervate muscle fibers via a multiplicity of synaptic terminals which release small but variable amounts of transmitter. Differences in release performance appear to be correlated with the size of synaptic contacts and presynaptic dense bars (active zones). These structural parameters proliferate via sprouting from existing synaptic terminals and relocate to ever more distal sites during development and growth of an identified axon. Moreover, alterations in number of synaptic contacts and active zones occur in adults following stimulation or decentralization, demonstrating structural plasticity of crustacean neuromuscular synapses.
Premotor neurons in the feeding system of Aplysia californica
Authors: Kirk Mark D. 
Published: January 2005

AbstractCentral pattern generator (CPG) circuits control cyclic motor output underlying rhythmic behaviors. Although there have been extensive behavioral and cellular studies of food‐induced feeding arousal as well as satiation in Aplysia, very little is known about the neuronal circuits controlling rhythmic consummatory feeding behavior. However, recent studies have identified premotor neurons that initiate and maintain buccal motor programs underlying ingesion and egestion in Aplysia. Other newly identified neurons receive synaptic input from feeding CPGs and in turn synapse with and control the output of buccal motor neurons. Some of these neurons and their effects within the buccal system are modulated by endogenous neuropeptides. With this information we can begin to understand how neuronal networks control buccal motor output and how their activity is modulated to produce flexibility in observed feeding behavior.
Regulation of high affinity choline uptake
Authors: Breer H. , Knipper M. 
Published: January 2005

AbstractHigh affinity uptake of choline, the rate‐limiting, regulatory step for the synthesis of acetylcholine (ACh), was found to be regulated via presynaptic auto‐ and hetero‐receptors. The transport rate was reduced by a muscarinic agonist and neuropeptides, but was significantly enhanced by octopamine. Intracellular messengers, including cyclic nucleotides, appear to modulate the transport activity, apparently by activating specific protein kinases.
Depolarization regulates expression of a synaptic vesicle protein in rat superior cervical ganglia in vitro
Authors: Linderman Karen M. , Greif Karen F. 
Published: January 2005

AbstractThe role of membrane depolarization in the regulation of expression of a neuron specific protein was evaluated by culturing superior cervical ganglia from neonatal rats in defined medium and manipulating neuronal activity by depolarizing agents. P65 is an integral membrane protein of synaptic vesicles and can be used as a marker for general neuronal maturation. P65 antigen levels were quantified by indirect radioimmunoassay, using monoclonal antibodies. The expression of p65 in ganglion explants increased by 40–100% when the cultures were treated with the depolarizing agents, veratridine or high potassium. The veratridine effect could be blocked by simultaneous treatment with the sodium channel blocker, tetrodotoxin (TTX). The rise in p65 was not evident until 36 h after depolarizing treatment had begun and reached peak levels after 48 h, with no further increases observed with sustained treatment. After removal of the depolarizing treatment, p65 levels returned to control values after 24 h. P65 joins a growing number of molecules whose expression is regulated by membrane depolarization.
Giant Drosophila neurons differentiated from cytokinesis‐arrested embryonic neuroblasts
Authors: Wu Chun‐Fang , Sakai Kuniyoshi , Saito Mitsuyoshi , Hotta Yoshiki 
Published: January 2005

AbstractThe relative contributions of the intrinsic and extrinsic factors in determining neuronal differentiation are not fully understood yet. We found that isolated neuroblasts from Drosophila gastrulae were able to differentiate neuron‐specific properties in culture even when cell divisions were inhibited. The resultant giant multinucleated neurons displayed thickened neurites with a variety of distinct branching patterns. Neuronal antigens were expressed as in normal cultured neurons, and action potentials could be evoked by current injection within two days after plating. These results indicate that the factors for initiating specific differentiation programs for basic neuronal form and function are present in a neuroblast already. The cells of increased sizes in this culture system are more accessible to physiological and cell biological analyses and could facilitate future studies of the Drosophila nervous system.
Patterns of appearance of serotonin and proctolin immunoreactivities in the developing nervous system of the American lobster
Authors: Beltz Barbara S. , Pontes Manuel , Helluy Simone M. , Kravitz Edward A. 
Published: January 2005

AbstractSerotonin (5‐HT) and proctolin, neurohormones widely distributed in the lobster nervous system, have been implicated in a variety of behaviors and also are known to coexist in large pairs of identified neurons in the fifth thoracic (T5) and first abdominal ganglia (A1) of adults (Siwicki, Beltz, and Kravitz, 1987). Earlier studies also have shown that these paired neurons already contain 5‐HT in embryos approximately halfway through development, whereas protolin immunoreactivity does not appear in these cells until near the time of hatching (Beltz and Kravitz, 1987a). In the current studies, the brain and ventral nerve cord have been screened for the appearance of serotonin and proctolin immunoreactivities using immunocytochemical and biochemical methods, in order to determine whether the late appearance of proctolin in the paired T5 and A1 cells is a general feature of development in other neurons as well. In embryos approximately halfway through development, the adult complement of 5‐HT‐staining cells is already present. In several cases, embryonic serotonin cells are proportionally very large and prominent, suggesting possible developmental roles. In contrast to serotonin, fewer than 10% of the proctolin‐staining neurons of juvenile animals are seen in embryos halfway through development. The number of immunoreactive cells gradually increases, but even by the sixth larval stage only half the number of cells that will eventually stain for proctolin are observed. Therefore, the developmental appearance of proctolin in lobster neurons, assayed using immunocytochemical methods, is relatively late and protracted compared to the appearance of serotonin. Quantitative measurements for 5‐HT in lobster larvae were performed using high pressure liquid chromatography (HPLC) with dual electrochemical detection, and for proctolin using radioimmunoassay. A gradual, probably growth‐related increase in the amounts of serotonin and proctolin were seen during larval development. The implications of the biochemical data, in light of the immunocytochemical studies, are discussed.
Coexpression of sensory and autonomic neurotransmitter traits by avian neural crest cells in vitro
Authors: Leblanc Gabrielle G. 
Published: January 2005

AbstractThis study shows that explants of quail neural crest cultured in a medium containing serum and chick embryo extract give rise to large numbers of cells expressing immunoreactivity for substance P (SP), a neuropeptide found in sensory neurons. These cells arise from cycling precursors, but do not appear to divide after expressing SP. The SP‐positive cells in cranial neural crest cultures express both neurofilament and the Q211 antigen, but those in trunk cultures express only the Q211 antigen. In both cranial and trunk cultures, large subpopulations of the SP‐positive cells express tyrosine hydroxylase and/or choline acetyltransferase, neurotransmitter markers characteristic of autonomic neurons. This finding argues against the idea that SP expression necessarily indicates commitment to the sensory neuron lineage. I further show that embryonic dorsal root ganglion (DRG) cells retain the ability to coexpress SP and tyrosine hydroxylase in vitro although to a lesser extent than do neural crest cells.