bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison of calcium homeostasis in isolated and attached growth cones of the snail Helisoma
Authors: Rehder Vincent , Jensen John R. , Dou Ping , Kater S. B.
Published: January 2005

This study examines the capability of growth cones from identified neurons of the snail Helisoma trivolvis to perform calcium homeostasis. Calcium influx into the cytoplasm was eliminated or increased experimentally to alter [Ca]i, and the compensatory response of the growth cone was measured with the fluorescent calcium indicator Fura‐2. Growth cones compensated for both increases and decreases in calcium influx by restoring [Ca]i towards basal levels under both types of challenges. The intrinsic ability of growth cones to control [Ca]i was examined in physically isolated growth cones. Isolated growth cones demonstrated essentially identical calcium homeostatic properties to their intact counterparts, indicating that mechanisms governing calcium homeostasis exist intrinsically in the growth cone. Such independence may add significantly to the growth cone's potential to locally interpret and respond to stimuli encountered en route to its appropriate target.
Evidence for homologous peptidergic neurons in the buccal ganglia of diverse nudibranch mollusks
Authors: Watson Winsor H. , Willows A. O. Dennis
Published: January 2005

The buccal ganglia of seven nudibranches (Aeolidia papillosa, Armina californica, Dirona albolineata, D. picta, Hermissenda crassicornis, Melibe leonina, and Tritonia diomedea) were examined to explore possible homologies between large cells that reacted with antibodies directed against small cardioactive peptide B (SCPB). The buccal ganglion of each species possessed a pair of large, dorsal–lateral, whitish neurons that contained an SCPB‐like peptide. We refer to these neurons as the SLB (SCPB‐immunoreactive Large Buccal) cells. In all species examined, the SLB cells project out the gastroesophageal nerves and appear to innervate the esophagus.

In each species, an apparent rhythmic feeding motor program (FMP) was observed by intracellular recording from both SLB neurons and other neurons in isolated preparations of the buccal ganglia. SLB cells often fire at a high frequency, and usually burst in a specific phase relation to the FMP activity. Stimulation of SLB cells enhances expression of the feeding motor program, either by potentiating existing activity or eliciting the FMP in quiescent preparations. Finally, perfusion of isolated buccal ganglia with SCPB excites the SLB cells and activates FMPs. Thus, both the immunohistochemical and electrophysiological data suggest that the SLB cells within three suborders of the opistobranchia (Dendronotacea, Arminacea, and Aeolidacea) are homologous. A comparison of our data with previously published studies indicates that SLB cell homologs may exist in other gastropods as well.
Structure of the caudal neural tube in an ascidian larva: Vestiges of its possible evolutionary origin from a ciliated band
Authors: Crowther Robert J. , Whittaker J. R.
Published: January 2005

Ultrastructural analysis and differential immunocytochemical staining with two antitubulin monoclonal antibodies were used to reexamine the organization and development of the neural tube in the larva of an ascidian, Ciona intestinalis, in appraisal of a theory that the dorsal tubular nervous system of the chordates evolved from two halves of a ciliated band in an auricularia‐like larva of the kind found in echinoderms and hemichordates. One of the antibodies stained cilia in the nervous system and elsewhere; the other reacted primarily with neuronal axons. The caudal neural tube consists of four rows of large ciliated ependymal‐glial cells enclosing an axial neural canal into which their single cilia extend. Two ventrolateral nerve tracts, containing axons, arise in the posterior brain region and extend along the length of the caudal tube, partially surrounded by the ependymal cells. The nonnervous, ciliated, ependymal neural tube of the ascidian larva with its two associated nerve tracts survives as a primitive early condition that could result from a ciliated band transformation. Tissues in the distal‐most part of the ascidian larval tail have cell lineage origins that indicate an evolutionary history different from those in the proximal majority of the tail. The ependymal cells in this presumed later addition to the tail are not ciliated, although all of the others in the caudal ependymal tube appear to be.
Progestin receptors in substance P‐immunoreactive neurons in the hypothalamus of male guinea pigs after behaviorally effective estradiol pulse treatment
Authors: Olster Deborah H. , Blaustein Jeffrey D.
Published: January 2005

Pulsatile administration of estradiol effectively primes orchidectomized (ORCH) male guinea pigs to display progesterone‐facilitated lordosis. In contrast, a single injection of estradiol benzoate (EB) is not behaviorally effective. In ovariectomized female guinea pigs, estradiol pulses induce progestin receptors selectively in substance P neurons in the ventrolateral hypothalamus (VLH), a site at which estradiol primes females to respond behaviorally to progesterone. To test the hypothesis that behaviorally effective estradiol pulses induce progestin receptors selectively in substance P neurons in the VLH in males, ORCH animals received a single injection of EB 40 h before, or two pulses of estradiol‐17β, 39 and 11 h before perfusion. Colchicine was administered intracerebroventricularly prior to perfusion. The only difference found between the two estradiol treatment groups was a higher number of progestin receptorimmunoreactive (PR‐IR) cells in the rostral VLH of estradiol pulse‐treated males. There were no significant differences in the number of PR‐IR cells in the mid‐ or caudal VLH, nor in the number of substance P‐immunoreactive (SP‐IR) neurons in the VLH/ventromedial hypothalamus (VMH) of animals receiving the two estradiol treatments. Furthermore, the percentage of PR‐IR cells in the VLH also immunoreactive for SP did not differ between the estradiol pulse‐ (22%–25%) and the EB‐injected animals (22%–32%). These data do not support the hypothesis that administration of behaviorally effective estradiol pulses, as compared to behaviorally ineffective EB injections, induce progestin receptors selectively in substance P neurons in the VLH of male guinea pigs.
High vocal center growth and its relation to neurogenesis, neuronal replacement and song acquisition in juvenile canaries
Authors: Alvarez‐Buylla Arturo , Ling Chang‐Ying , Nottebohm Fernando
Published: January 2005

It is generally thought that most circuits of the adult central nervous system (CNS) are sculpted, in part at least, by selective elimination of some of the neurons present in an initial overabundant set. In this scenario, the birth of neurons precedes the period when brain functions, such as learning, first occur. In contrast to this form of brainassembly, we describe here the delayed development of the high vocal center (HVC) and one of its efferent pathways in canaries. The retrograde tracer Fluoro‐Gold (FG) was injected into one of HVC's two efferent targets, the nucleus robustus archistriatalis (RA), to define the boundaries of HVC. The HVC grows markedly between 1 and 4 months, invading neighboring territories of the caudal telencephalon. During this same period, 0.43%–0.64% of the HVC neurons present at 1 year of age are labeled per day of [3H]‐thymidine injection. [3H]‐Thymidine labeling is a marker of cell birth, and during the first 4 months HVC neuron number increases, probably accounting for part of the HVC growth observed. Thereafter, the number of HVC neurons remains constant, but neuronal birth persists. We infer from this that neuronal replacement starts as early as 4 months after hatching and perhaps before then. About half of the neurons born after posthatching day 10 grow an axon to RA to form the main efferent pathway exiting from HVC. HVC growth, neurogenesis, axogenesis, and the observed replacement of neurons happen during the period of juvenile vocal learning. However, the recruitment of neurons that are still present at 1 year shows no particular inflections corresponding to the various stages in song learning, and continues at essentially the same rate after the more stereotyped adult song has been acquired. We suggest that a combination of neurogenesis and neuronal replacement provides unique advantages for learning.
Development of coordinated movement in chicks: II. Temporal analysis of hindlimb muscle synergies at embryonic day 10 in embryos with spinal gap transections
Authors: Bradley N. S. , Bekoff A.
Published: January 2005

Spinal neural circuits can recruit muscles to produce organized patterns of activity early in embryonic development. In a previous study, using multichannel electromyographic (EMG) recordings, we characterized burst parameters for these patterns in the legs of chick embryos during spontaneous motility in ovo at embryonic days (E) 9 and E10 (Bradley and Bekoff, 1990). Results of the study suggested both neural and biomechanical factors play an important role in the development of coordinated limb movements. In this study, to explore the contribution of descending neural inputs to the control of leg movements during motility, we applied similar methods to characterize motor patterns produced by the spinal cord in the absence of descending inputs. Thoracic spinal gap transections were performed at E2 and EMG patterns were recorded at E10. Several EMG features for chronic spinal embryos were similar to those for normal embryos and demonstrate that lumbar spinal circuits can be correctly assembled to control limb movements in the absence of connectivity with more rostral neural structures during early differentiation processes. However, certain aspects of the EMG patterns in chronic spinal embryos were different from patterns in normal embryos and provide support for conclusions drawn earlier by Oppenheim (1975). Specifically, our data support the view that propriospinal and/or supraspinal inputs function to regulate the timing of cyclic limb movements controlled by spinal neural circuits. Finally, we consider the possible long‐term effects of chronic spinal gap transections as compared to acute spinal transections on the development of motility. © 1992 John Wiley & Sons, Inc.
The role of matrix molecules in regeneration of leech CNS
Authors: Masuda‐Nakagawa L. M. , Wiedemann C.
Published: January 2005

Extracellular matrix (ECM) molecules extracted from the leech central nervous system (CNS) provide substrates that induce extensive growth of processes of identified leech nerve cells in culture. Two ECM molecules, laminin and tenascin, have been identified. The laminin‐like molecule has been purified and shown to be a cross‐shaped molecule similar to vertebrate laminin with subunits of 340, 220, 180, and 160 kD. Purified laminin as a substrate induces rapid outgrowth of Retzius (R) and Anterior Pagoda (AP) cells in culture. The tenascin molecule has been partially purified. In electronmicrographs, leech tenascin, like vertebrate tenascin, has six arms of equal size joined in a central globule. Highly enriched fractions of leech tenascin induce rapid and extensive outgrowth of Retzius and AP cells in culture. Substrate molecules not only induce outgrowth of processes but also affect the growth patterns of individual nerve cells. Neurites are straight with few branches in laminin, but curved with profuse branches on tenascin. During regeneration of the CNS in the animal, laminin appears at new sites associated with growth cones. The appearance of laminin correlates with the accumulation of microglial cells. Thus, ECM molecules with growth‐promoting activity for leech nerve cells in vitro appear to be involved in inducing regeneration and allowing the neurites to reconnect with former targets. © 1992 John Wiley & Sons, Inc.
Evidence that synaptic transmission between giant interneurons and identified thoracic interneurons in the cockroach is cholinergic
Authors: Casagrand Janet L. , Ritzmann Roy E.
Published: January 2005

In the cockroach, a population of thoracic interneurons (TIs) receives direct inputs from a population of ventral giant interneuons (vGIs). Synaptic potentials in type‐A TIs (TIAs) follow vGI action potentials with constant, short latencies at frequencies up to 200 Hz. These connections are important in the integration of directional wind information involved in determining an oriented escape response. The physiological and biochemical properties of these connections that underlie this decision‐making process were examined. Injection of hyperpolarizing or depolarizing current into the postsynaptic TIAs resulted in alterations in the amplitude of the postsynaptic potential (PSP) appropriate for a chemical connection. In addition, bathing cells in zero‐calcium, high magnesium saline resulted in a gradual decrement of the PSP, and ultimately blocked synaptic transmission, reversibly. Single‐cell choline acetyltransferase (ChAT) assays of vGI somata were performed. These assays indicated that the vGIs can synthesize acetylcholine. Further more, the pharmacological specificity of transmission at the vGI to TIA connections was similar to that previously reported for nicotinic, cholinergic synapses in insects, suggesting that the transmitter released by vGIs at these sypapses is acetylcholine. © 1992 John Wiley & Sons, Inc.
Ipsilateral retinal projections into the tectum during regeneration of the optic nerve in the cichlid fish Haplochromis burtoni: A dil study in fixed tissue
Authors: Wilm Claudia , Fritzsch Bernd
Published: January 2005

Retinal projections were experimentally manipulated in a bony fish to reveal conditions under which considerably enlarged ipsilateral projections developed and persisted. Three experimental groups were studied: animals after unilateral enucleation, after unilateral nerve crush, and after enucleation and crush of the remaining optic nerve. At 29 days after unilateral enucleation alone, no enhanced ipsilateral projection had developed. After nerve crush, however, large numbers of retinal fibers regenerated into the ipsilateral tectum. Retrogradely filled, ipsilaterally projecting ganglion cells were distributed throughout the entire retina. After 15 days regenerating retinal fibers covered the entire ipsilateral tectum. At later stages the ipsilateral projection showed progressive reduction in coverage of the tectum. Combining enucleation with nerve crush led to an ipsilateral projection that covered the tectum at 28 days and later. In this experimental situation the development of an ipsilateral projection appears to be a two‐step process: (1) Fibers are rerouted to the ipsilateral side at the diencephalon, and (2) ipsilateral fibers persist in the tectum only in the absence of a contralateral projection while they appear to be eliminated in the other cases. © 1992 John Wiley & Sons, Inc.
Synaptic plasticity in a regenerated crayfish phasic motoneuron
Authors: Stewart Bryan A. , Atwood Harold L.
Published: January 2005

Crustacean neuromuscular systems provide many advantages for the study of synaptic transmission and plasticity. The present study examines aspects of synaptic transmission in the phasic, fast closer excitor (FCE) motoneuron of regenerated crayfish claws. Excitatory postsynaptic potentials (EPSPs) fatigued rapidly and showed poor long‐term facilitation (LTF) in the smallest of regenerating claws. EPSPs in larger regenerating claws fatigued less and showed pronounced facilitation. These observations were not the same as those previously made during primary development of this motoneuron (Lnenicka and Atwood, 1985a, J. Neuroscience 5:459–467). Hence, regeneration is not the recapitulation of primary development. In situ stimulation of the FCE is known to lead to long‐lasting adaptation of synaptic performance. This adaptation is age dependent; it is expressed in young but not old animals. In the regenerated FCE of old animals, we observed a novel form of long‐lasting adaptation to imposed activity: EPSPs showed large initial EPSPs and did not exhibit resistance to fatigue during maintained stimulation. This indicates that aged motoneurons can express adaptive changes to increased activity following axonal regeneration, but that the adaptive changes are the opposite to what is observed in nonregenerated motoneurons. © 1992 John Wiley & Sons, Inc.
Electric organ morphology of Sternopygus macrurus, a wave‐type, weakly electric fish with a sexually dimorphic EOD
Authors: Mills Alice , Zakon Harold H. , Marchaterre Margaret A. , Bass Andrew H.
Published: January 2005

In several species of electric fish with a sex difference in their pulse‐type electric organ discharge (EOD), the action potential‐generating cells of the electric organ (electrocytes) of males are larger and more invaginated compared to females. Androgen treatment of females and juveniles produces a longer‐duration EOD pulse that mimics the mature male EOD, with a concurrent increase in electrocyte size and/or membrane infolding. In Sternopygus macrurus, which generates a wave‐type EOD, androgen also increases EOD pulse duration. To investigate possible morphological correlates of hormone‐dependent changes in EOD in Sternopygus, we examined electric organs from both fish collected in the field, and untreated and androgen‐treated specimens in the laboratory. The electrocytes are cigar shaped, with prominent papillae on the posterior, innervated end. Electrocytes of field‐caught specimens were significantly larger in all parameters than were electrocytes of specimens maintained in the laboratory. EOD pulse duration and frequency were highly correlated, and were significantly different between the sexes in sexually mature fish. Nevertheless, no sex difference in electrocyte morphology was observed, nor did any parameters of electrocyte morphology correlate with EOD pulse duration or frequency. Further, whereas androgen treatment significantly lowered EOD frequency and broadened EOD pulse duration, there was no difference in electrocyte morphology between hormone‐treated and control groups. Thus, in contrast to results from studies on both mormyrid and gymnotiform pulse fish, electrocyte morphology is not correlated with EOD waveform characteristics in the gymnotiform wave‐type fish Sternopygus. The data, therefore, suggest that sex differences in EOD are dependent on changes in active electrical properties of electrocyte membranes. © 1992 John Wiley & Sons, Inc.
Normal and abnormal pathfinding of facial nerve fibers in the chick embryo
Authors: von Bartheld Christopher S. , Yang Wenhua , Rubel Edwin W.
Published: January 2005

Development of the facial nerve was studied in normal chicken embryos and after surgical disruption of ingrowing sensory facial nerve fibers at 38–72 h of incubation. Disruption of facial nerve fibers by otocyst removal often induced a rostral deviation of the facial nerve and ganglion to the level of the trigeminal ganglion. Cell bodies of the geniculate ganglion trailed their deviating neurites and occupied an abnormal rostral position adjacent to the trigeminal ganglion. Deviating facial nerve fibers were labeled with the carbocyanine fluorescent tracer Dil in fixed tissue. Labeled fibers penetrated the cranium adjacent to the trigeminal ganglion, but they did not follow the trigeminal nerve fibers into the brain stem. Rather, after entering the cranium, they projected caudally to their usual site of entrance and proceeded towards their normal targets. This rostral deviation of the facial nerve was observed only after surgery at 48–72 h of incubation, but not in cases with early otocyst removal (38–48 h). A rostral deviation of the facial nerve was seen in cases with partial otocyst removal when the vestibular nerve was absent. The facial nerve followed its normal course when the vestibular nerve persisted. We conclude that disruption of the devloping facial pathway altered the routes of navigating axons, but did not prevent pathfinding and innervation of the normal targets. Pathfinding abilities may not be restricted to pioneering axons of the facial nerve; later‐developing facial nerve fibers also appeared to have positional information. Our findings are consistent with the hypothesis that navigating axons may respond to multiple guidance cues during development. These cues appear to differ as a function of position of the navigating axon. © 1992 John Wiley & Sons, Inc.
SSB, an antigen that selectively labels morphologically distinct synaptic boutons at the Drosophila larval neuromuscular junction
Authors: Budnik Vivian , Gorczyca Michael
Published: January 2005

In this report we describe the expression of Small Synaptic Bouton (SSB), an antigen that is selectively expressed in a specific subset of neuromuscular junction terminals in the body wall of Drosophila larva. The expression of SSB was studied with a polyclonal antibody raised against the cAMP phosphodiesterase of the Drosphila learning mutant dunce (Nighorn et al., 1991, Neuron 6:455–467); however, immunoreactivity was not abolished by the dunce (dnc) alleles dncM14 and dncM11 or deficiencies of the dnc gene, indicating that the antigen labelled could not be the dnc gene product, but another antigen that we termed SSB. Immunoreactivity was localized in the body wall muscles to a specific subset of neuromuscular junction terminals that have been implicated in activity‐dependent plasticity. This demonstrates that these morphologically distinct terminals can be immunocytochemically distinguished and that they probably represent innervation by a distinct neuronal population. Confocal and electron microscopic examination demonstrated that staining was restricted to the synaptic boutons themselves, not to neurites or motor axons. Ultrastructural analysis showed label close to synaptic vesicles in the presynaptic terminal and in the surrounding subsynaptic reticulum. Central nervous system (CNS) staining was restricted to a segmentally repeated pattern of cell bodies in the ventral ganglion and to a few small groups of cells in the brain lobes. © 1992 John Wiley & Sons, Inc.
Rapid and protracted phases of retinal ganglion cell loss follow axotomy in the optic nerve of adult rats
Authors: Villegas‐Pérez Maria‐Paz , Vidal‐Sanz Manuel , Rasminsky Michael , Bray Garth M. , Aguayo Albert J.
Published: January 2005

To investigate the short‐and long‐term effects of axotomy on the survival of central nervous system (CNS) neurons in adult rats, retinal ganglion cells (RGCs) were labelled retrogradely with the persistent market diI and their axons interrupted in the optic nerve (ON) by intracranial crush 8 or 10 mm from the eye or in intraorbital cut 0.5 or 3 mm from the eye. Labelled RGCs were counted in flat‐mounted retinas at intervals from 2 weeks to 20 months after axotomy. Two major patterns of RGC loss were observed: (1) an inital abrupt loss that was confined to the first 2 weeks after injury and was more severe when the ON was cut close to the eye; (2) a slower, persistent decline in RGC densities with one‐half survival times that ranged from approximately 1 month after intraorbital ON cut to 6 months after intracranial ON crush. A small population of RGCs (approximately 5%) survived for as long as 20 months after intraorbital axotomy. The initial loss of axotomized RGCs presumably results from time‐limited perturbations related to the position of the ON injury. A. persistent lack of terminal connectivity between RGCs and their targets in the brain may contribute to the subsequent, more protracted RGC loss, but the differences between intraorbital cut and intracranial crush suggest that additional mechanisms are involved. It is unclear whether the various injury‐related processes set in motion in both the ON and the retina exert random effects on all RGCs or act preferentially on subpopulations of these neurons. © 1993 John Wiley & Sons, Inc.
Gene elav of Drosophila melanogaster: A prototype for neuronal‐specific RNA binding protein gene family that is conserved in flies and humans
Authors: Yao Kwok‐Ming , Samson Marie‐Laure , Reeves Ronald , White Kalpana
Published: January 2005

Regulated gene activity is crucial to the formation and function of the nervous system. It is well known that gene regulation can occur at the transcriptional, post‐transcriptional, translational, and post‐translational levels. In this review our focus has been on the post‐transcriptional regulation in neurons and on neural‐specific RNA binding proteins that may be involved in post‐transcriptional modulation of gene activity. We have taken advantage of this opportunity to review our work on the elav gene of Drosophila melanogaster which encodes a neural‐specific RNA binding protein and relate it to other members of this elav‐like gene family. We report new data that suggests that elav is post‐transcriptionally regulated and we demonstrate that below‐threshold levels of ELAV protein severely affects neuronal differentiation. © 1993 John Wiley & Sons, Inc.
Neuronal specificity and its development in the Drosophila wing disc and its derivatives
Authors: Palka John
Published: January 2005

The imaginal wing disc of flies gives rise to the adult wing blade and dorsal thorax (notum). A great deal has been learned in recent years about the process of neurogenesis in this disc; a number of genes that play crucial roles in the formation of sensory mother cells and in the differentiation of the sensory organs have been identified and their roles defined. Given this extensive background of developmental genetics, it has seemed profitable to summarize what is known about the end‐products of neural development, the adult sensory organs. Discussed are their physiological function and role in behavior, the pathways followed by their axons in the CNS, and both genes and epigenetic processes that might play some role in the later stages of neural development and in adult function. The highly individual characteristics of certain of the sensory organs is emphasized, both in the context of their adult roles and as a challenge for future studies in developmental genetics. © 1993 John Wiley & Sons, Inc.
Molecules and cognition: The latterday lessons of levels, language, and iac. Evolutionary overview of brain structure and function in some vertebrates and invertebrates
Authors: Miklos George L. Gabor
Published: January 2005

The characteristics of the nervous systems of a number of organisms in different phyla are examined at the recombinant DNA, protein, neuroanatomic, neurophysiological, and cognitive levels. Among the invertebrates, special attention is paid to the advantages as well as the shortcomings of the fly Drosophila melanogaster, the worm Caenorhabditis elegans, the honey bee Apis mellifera, the sea hare Aplysia californica, the octopus Octopus vulgaris, and the squid Loligo pealei. Among vertebrates, the focus is on Homo sapiens, the mouse Mus musculus, the rat Rattus norvegicus, the cat Felis catus, the macaque monkey Macaca fascicularis, the barn owl Tyto alba, and the zebrafish Brachydanio rerio. Vertebrate nervous systems have also been compared in fossil vs. extant organism. I conclude that complex nervous systems arose in the Early Cambrian via a big bang that was underpinned by a modular method of construction involving massive pleiotropy of gene circuits. This rapidity of construction had enormous implications for the degrees of freedom that were subsequently available to evolving nervous systems. I also conclude that at the level of neuronal populations and interactions of neuropiles there is no model system between phyla except at the basic macromolecular level. Further, I argue that to achieve a significant understanding of the functions of extant nervous systems we need to concentrate on fewer organisms in greater depth and manipulate genomes via transgenic technologies to understand the behavioral outputs that are possible from an organism. Finally, I analyze the concepts of “perceptual categorization” and “information processing” and the difficulties involved in the extrapolation of computer analogies to sophisticated nervous systems. © 1993 John Wiley & Sons, Inc.
Regenerating retinal fibers display error‐free homing along undamaged normal fibers
Authors: Wilm Claudia , Fritzsch Bernd
Published: January 2005

After crushing one optic nerve in a bony fish, retinal fibers regenerate to both tecta. Anterograde labelling indicates that the ipsilaterally regenerating fibers have a rather straight growth, apparently along the undamaged fibers of the contralateral retina. In contrast, the contralaterally regenerating fibers deviate widely from a straight course. Retrograde labelling shows a mirror‐symmetric distribution of regenerated ipsilateral and resident contralateral ganglion cells in a comparable annulus. In contrast, ganglion cells in the regenerated contralateral retina show no topological order after comparable small Dil applications to the ventrolateral tectum. These data suggest that regenerating fibers can orient on the undisturbed, contralateral fibers. © 1993 John Wiley & Sons, Inc.
Intracellular partitioning of androgen receptor immunoreactivity in the brain of the male syrian hamster: Effects of castration and steroid replacement
Authors: Wood R. I. , Newman S. W.
Published: January 2005

The effect of castration and steroid replacement on the intracellular partitioning of the androgen receptor in the brain of the male Syrian hamster was determined using immunocytochemistry. Androgen receptors were visualized using the PG‐21 antibody (G. S. Prins) on 40‐μm coronal brain sections from hamsters perfused with 4% paraformaldehyde with or without 0.4% glutaraldehyde. Control studies confirmed antibody specificity in gonad‐intact and castrate males. In the normal adult male, androgen receptor immunocytochemistry reveals intense staining confined to the cell nucleus. Castration caused a gradual increase in cytoplasmic labelling within 2 weeks, accompanied by a reduction in nuclear staining intensity in androgen receptor‐containing neurons throughout the brain. Cytoplasmic androgen receptor staining was eliminated after treatment of orchidectomized males for only 8 h with exogenous testosterone. Likewise, long‐term exposure to testosterone and dihydrotestosterone, a nonaromatizable androgen, maintained nuclear androgen receptor immunoreactivity. However, exposure to low physiologic concentrations of estrogen was not effective in this regard. In addition, we determined that nuclear androgen receptor immunoreactivity decreases in response to inhibitory short‐day photoperiod, but without an increase in cytoplasmic immunostaining. This appears to be due to the decrease in androgen production by the testis, rather than a direct photoperiodic effect, because testosterone supplementation to short‐day males restored the intensity of nuclear androgen receptor immuno‐reactivity to levels comparable to those in the intact male. These findings are compatible with a new model for the intracellular localization of androgen receptors, in which a subset of unoccupied receptors is located in the cell cytoplasm in the absence of ligand. They further demonstrate the repartitioning of such cytoplasmic receptors, thereby confirming and extending previous observations using biochemical techniques on the regulation of neuronal androgen receptors. © 1993 John Wiley & Sons, Inc.
Ultrastructure of neuromuscular junctions in Drosophilal: Comparison of wild type and mutants with increased excitability
Authors: Jia Xi‐Xi , Gorczyca Michael , Budnik Vivian
Published: January 2005

The ventral longitudinal muscles of the Drosphila larval body wall are innervated by at least four types of synaptic terminals that can be distinguished on morphological grounds at the light microscopical level. The innervation of these muscles has been previously shown to be regulated by neuronal activity. In this report we investigate the ultrastructural basis for synaptic bouton differences by using serial sections, and examine the structure of synaptic terminals in mutants with increased excitability. We report that individual identifiable muscle fibers are innervated by terminals containing two to three types of synaptic boutons that can be distinguished in terms of synaptic vesicle population, presynaptic and postsynaptic specialization, and general shape. We propose a model to account for the bouton types observed at the light microscopical level. We find that in the hyperexcitable mutant eag Sh, there are dramatic ultrastructural alterations at synaptic boutons. These alterations include a partial depletion of two types of synaptic vesicles and a change in appearance of a third type, changes in number and appearance of synaptic densities, and the presence of multivesicular bodies. Our results show that an increase in neuronal excitability produces profound effects in synaptic terminal structure. © 1993 John Wiley & Sons, Inc.
The quantitative relationship between olfactory axons and mitral/tufted cells in developing Xenopus with partially deafferented olfactory bulbs
Authors: Byrd Christine A. , Burd Gail D.
Published: January 2005

Partial deafferentation of the olfactory bulb in Xenopus embryos was performed to analyze the effects of afferent innervation on the development of the central olfactory structure. In an attempt to analyze a possible early inductive role of the olfactory axons, one olfactory placode was removed before differentiation of the neural tube began (stages 26–31). A morphological and quantitative analysis was performed on larvae at the onset of metamorphic climax (stage 58). When the single olfactory nerve innervated one side of the rostral telencephalon, a single olfactory bulb developed on that side and no olfactory bulb formed on the contralateral side. When the nerve innervated the midline of the rostral telencephalon, a smaller‐than‐normal, fused olfactory bulb developed. Partial deafferentation at these early stages resulted in a significant reduction in the number of olfactory axons (to approximately one‐half of control values) and a corresponding decrease in the number of mitral/tufted cells (output neurons of the olfactory bulb). To control for possible damage to the neural tube during olfactory‐placode removal, a portion of the neural tube directly beneath one of the olfactory placodes was removed in embryos. In these animals, the neural tube regenerated within 24 h and formed a normal olfactory bulb; olfactory axon and mitral/tufted‐cell numbers were not significantly different from controls. In conclusion, olfactory‐afferent innervation was critical for differentiation of the olfactory bulb, and decreasing the number of olfactory axons resulted in a reduction in the number of output neurons of the olfactory bulb. © 1993 John Wiley & Sons, Inc.
Insulin‐like growth factors: Putative muscle‐derived trophic agents that promote motoneuron survival
Authors: Neff Nicola T. , Prevette David , Houenou Lucien J. , Lewis Michael E. , Glicksman Marcie A. , Yin Qin‐Wei , Oppenheim Ronald W.
Published: January 2005

Treatment of chick embryos in ovo with IGF‐I during the period of normal, developmentally regulated neuronal death (embryonic days 5–10) resulted in a dose‐dependent rescue of a significant number of lumbar motoneurons from degeneration and death. IGF‐II and two variants of IGF‐I with reduced affinity for IGF binding proteins, des(1‐3) IGF‐I and long R3 IGF‐I, also elicited enhanced survival of motoneurons equal to that seen in IGF‐I‐treated embryos. IGF‐I did not enhance mitogenic activity in motoneuronal populations when applied to embryos during the period of normal neuronal proliferation (E2‐5). Treatment of embryos with IGF‐I also reduced two types of injury‐induced neuronal death. Following either deafferentation or axotomy, treatment of embryos with IGF‐I rescued approximately 75% and 50%, respectively, of the motoneurons that die in control embryos as a result of these procedures. Consistent with the survival‐promoting activity on motoneurons in ovo, IGF‐I, ‐II, and des(1‐3) IGF‐I elevated choline acetyltransferase activity in embryonic rat spinal cord cultures, with des (1‐3) IGF‐I demonstrating 2.5 times greater potency than did IGF‐I. A single addition of IGF‐I at culture initiation resulted in the maintenance of 80% of the initial ChAT activity for up to 5 days, during which time ChAT activity in untreated control cultures fell to 9%. In summary, these results demonstrate clear motoneuronal trophic activity for the IGFs. These findings, together with previous reports that IGFs are synthesized in muscle and may participate in motoneuron axonal regeneration and sprouting, indicate that these growth factors may have an important role in motoneuron development, maintenance, and recovery from injury. © 1993 John Wiley & Sons, Inc.
Calcium channels and GABA receptors in the early embryonic chick retina
Authors: Yamashita Masayuki , Fukuda Yutaka
Published: January 2005

The properties of calcium channels were studied at the period of neurogenesis in the early embryonic chick retina. The whole neural retina was isolated from embryonic day 3 (E3) chick and loaded with a Ca2+‐sensitive fluorescent dye (Fura‐2). The retinal cells were depolarized by puff application of high‐K+ solutions. Increases in intracellular Ca2+ concentrations were evoked by the depolarization through calcium channels. The type of calcium channel was identified as l‐type by the sensitivity to dihydropyridines. The Ca2+ response was completely blocked by 10 μM nifedipine, whereas it was remarkably enhanced by 5 μM Bay K 8644. Then we sought a factor to activate the calcium channel and found that GABA could activate it by membrane depolarization at the E3 chick retina. Puff application of 100 μM GABA raised intracellular Ca2+ concentrations, and this Ca2+ response to GABA was also sensitive to the two dihydropyridines. Intracellular potential recordings verified clear depolarization by bath‐applied 100 μM GABA. The Ca2+ response to GABA was mediated by GABAA receptors, since the GABA response was blocked by 10 μgM bicuculline or 50 μM picrotoxin, and mimicked by muscimol but not by baclofen. Neither glutamate, kainate, nor glycine evoked any Ca2+ response. We conclude that l‐type calcium channels and GABAA receptors are already are already expressed before differentiation of retinal cells and synapse formation in the chick retina. A possibility is proposed that GABA might act as a trophic factor by activating l‐type calcium channels via GABAA receptors during the early period of retinal neurogenesis. © 1993 John Wiley & Sons, Inc.
Laryngeal muscle and motor neuron plasticity in Xenopus laevis: Testicular masculinization of a developing neuromuscular system
Authors: Watson James T. , Robertson John , Sachdev Ulka , Kelley Darcy B.
Published: January 2005

In Xenopus laevis, the sexual differentiation of the neuromuscular system responsible for courtship song is controlled by testicular androgen secretion. To explore the sensitivity of this system to androgenic stimulation, male and female frogs were gonadectectomized and given testis transplants at seven different developmental stages between the end of metamorphosis and adulthood, grown to sexual maturity, and the laryngeal muscle fibers and motor axons were counted. Muscle fiber and axon numbers in males were not affected by the testicular transplant at any stage. In females, testicular transplants at all developmental stages increased muscle fiber numbers in adulthood. Values attained were, however, significantly less than those of adult intact or testis‐transplanted males. Testis transplantation increased laryngeal axon numbers in females to levels equivalent to those of intact males; this effect was obtained at every stage of postmetamorphic development including adulthood. To further explore androgen regulation in adults, males and females were gonadectomized and implanted with silicone tubes containing testosterone propionate for 1.5–3 years and laryngeal muscle fibers and axon numbers compared to those of gonadectomized or sham‐operated adult controls. Neither treatment with exogenous androgen nor gonadectomy had any effect on laryngeal muscle fiber or axon number in either males or females; values did not differ from those of sham‐operated controls. We conclude that testicular secretions can induce laryngeal muscle fiber and axon addition in females throughout postmetamorphic life. This degree of plasticity, exhibited after the period when adult values are normally attained, stands in contrast to the effects of administration of synthetic androgen and suggests that the degree of plasticity in adult females may be underestimated if exogenous hormones rather than testicular transplants are provided. © 1993 John Wiley & Sons, Inc.
Axonal outgrowth within the abnormal scaffold of brain tracts in a zebrafish mutant
Authors: Patel Chetan K. , Rodriguez Luis C. , Kuwada John Y.
Published: January 2005

The role of specific axonal tracts for the guidance of growth cones was investigated by examining axonal outgrowth within the abnormal brain tracts of zebrafish cyclops mutants. Normally, the earliest differentiating neurons in the zebrafish brain establish a simple scaffold of axonal tracts. Later‐developing axons follow cell‐specific pathways within this axonal scaffold. In Cyclops embryos, this scaffold is perturbed due to the deletion of some ventromedial neurons that establish parts of the axonal scaffold and the development of an abnormal crease in the brain. In these mutant embryos, the growth cones projected by the neurons of the nucleus of the posterior commissure (nur PC) are deprived of the two tracts of axons that they sequentially follow to first extend ventrally, then posteriorly. These growth cones respond to the abnormal scaffold in several interesting ways. First, nuc PC growth cones initially always extend ventrally as in wild‐type embryos. This suggests that for the first portion of their pathway the axons they normally follow are not required for proper navigation. Second, approximately half of the nuc PC growth cones follow aberrant longitudinal pathways after the first portion of their pathway. This suggests that for the longitudinal portion of the pathway, specific growth cone/axon interactions are important for guiding growth cones. Third, although approximately half of the nuc PC growth cones follow aberrant longitudinal pathways, the rest follow normal pathways despite the absence of the axons that they normally follow. This suggests that cues independent of these axons may be capable of guiding nuc PC growth cones as well. These results suggest that different guidance cues or combinations of cues guide specific growth cones along different portions of their pathway. 1994 John Wiley & Sons, Inc.
Proposed pathways for vocal self‐stimulation: Met‐enkephalinergic projections linking the mibrain vocal nucleus, auditory‐responsive thalamic vocal nucleus, auditory‐responsive thalamic regions and neurosecretory hypothalamus
Authors: Cheng Mei‐Fang , Zuo Mingxue
Published: January 2005

In this study, we have investigated the neuroanatomical pathways that may underlie the influence of a female bird's vocal behavior upon her own reproductive endocrine response. We traced the ascending efferent projections of the midbrain vocal control nucleus, the intercollicularis (ICo), using an anterograde tracer, PHAL, delivered by iontophoretic application. We found labelled terminal fields in the anterior regions of the hypothalamus that contained luteinizing hormone releasing hormone‐ (LHRH) immunoreactive neurons. We injected into the LHRH‐rich anterior medial hypothalamus (AM) the retrograde tracer, fluorogold, to verify the results of PHAL anterograde tracing and exmine whether retrogradely labelled neurons in the ICo can be stained with met‐enkephalin antiserum by the immunohistochemical method. Of the retrogradely labelled neurons in the medial division of ICo (mICo), between 5% and 15% were found to be met‐enkephalin‐immunoreactive positive perikarya. Our data suggest that axonal projections into the anterior medial hypothalamus may arise in part from enkephalin‐immunoreactive neurons in the medial ICo. The mICo neurons distributed along the medial border of the midbrain auditory nucleus give rise to projections into the posterior medial hypothalamus (PMH) via synapses within the shell region of thalamic auditory nucleus, ovoidalis (Ov).

We conclude that in the ring dove, the medial division of the vocal control nucleus, by virtue of its connection with the auditory thalamus and neurosecretory hypothalamus, is in a position to exert influence on endocrine response partly through enkephalinergic systems. Implications of similar connections in other species are discussed. 1994 John Wiley & Sons, Inc.
Neurotrophic regulation of mouse muscle β‐amyloid protein precursor and α1‐antichymotrypsin as revealed by axotomy
Authors: Akaaboune Mohammed , Ma Jianxin , Festoff Barry W. , Greenberg Barry D. , Hantaï Daniel
Published: January 2005

Kunitz‐inhibitor containing forms of the β‐amyloid precursor protein (βAPP), known also as protease nexin II (PNII), and α1‐antichymotrypsin (α1‐ACT), a serpin, are important components of the serine protease and inhibitor balance in many tissues. In the nervous system, this balance may have trophic or growth factor activity at different stages of development, after injury and in disease states. In the current study, using immunocytochemistry and Western blotting with antibodies against the human homologues, we analyzed whether denervation affected the localization of βAPP and α1‐ACT in adult mouse muscle following axotomy. In mouse muscle, antitive band and anti‐human βAPP antibody a band at 92 kD in both normal and denervated extracts. βAPP was present in normal mouse muscle at both neuromuscular junctions and within intramuscular nerves. α1‐ACT was also detected at neuromuscular junctions, on the perineruim and endothelial cell surfaces. Following axotomy, both βAPP and α1‐ACT disappeared from intramuscular nerves simultaneously. However, at the neuromuscular junction, α1‐ACT decreased more rapidly with βAPP lingering before disappearing. Since both α1‐ACT as well as βAPP are present within senile plaques in Alzheimer's disease brains such experiments with the nicotinic, cholinergic neuromuscular synapse in denervated muscle may help to focus experiments on the mechanism of synapse loss as well as plaque deposition in this disease. © 1994 John Wiley & Sons, Inc.
Growth behavior of retinotectal axons in live zebrafish embryos under TTX‐induced neural impulse blockade
Authors: Kaethner Rolf J. , Stuermer Claud A. O.
Published: January 2005

The growth dynamics of individual DiO‐labeled retinal axons deprived of normal neural impulse activity by TTXZ was monitored in the tectum of living zebrafish embryos with time‐lapse video microscopy and compared with normal active axons. Growth cones of TTX‐blocked axons advance intermittently with an average velocity similar to normal axons. While exploring their local environment, they are broadened and bear ruffling lamellipodia and filopodia, but become streamlined when advancing. The activity‐deprived axons grow directly towards their retinotopic target sites in the tectum as do their normal counterparts and very rarely extend branches en route. Much like normal axons, TTX‐blocked axons begin to branch and develop their terminal arbors only at their retinotopic target area. They emit and retract numerous short side branches over a period of several hours. Thearea they contact (the “exploration field”) is of similar dimension as that of active axons, covering from 1% to 7.4% of the tectal neuropil surface, but the final arbor, cover an area only one‐half to one‐sixth as large. TTX arbors are as small as arbors of normal active axons and retinotopically correct. Thus, the typical exploratory growth behavior of developing retinal axons in the tectum, the dynamics of terminal arbor formation at retinotopically correct sites, the dimension of the exploration field, and the shaping of the arbors in zebrafish embryos are unaffected by TTX‐induced neural impulse blockade. 1994 John Wiley & Sons, Inc.