bluuebunny/crossref_metadata_2025_split huggingface dataset:
Neuron‐specific modulation by serotonin of regenerative outgrowth and intracellular calcium within the CNS of Helisoma trivolvis
Authors: Murrain Michelle , Murphy A. Don , Mills Linda R. , Kater Stanley B. 
Published: January 2005

AbstractWe have investigated the cell‐specific effect of serotonin (5‐HT) on regenerating neurons within the adult central nervous system of the pond snail, Helisoma trivolvis. In culture, 5‐HT arrests outgrowth of buccal neurons B19 but not neurons B5 (Haydon, McCobb, and Kater, 1984). After axotomy, neurons within the Helisoma nervous system typically exhibit profuse regenerative outgrowth. This study, on neurons within the CNS, shows that 5‐HT selectively inhibits the outgrowth of specific identified neurons, and also causes significant elevations in intracellular calcium concentrations as measured by the calcium indicator dye, Fura‐2. The outgrowth of neurons B19 and C1 was selectively inhibited when ganglia were incubated in 5 × 10−5M 5‐HT. The outgrowth of buccal neurons B5, however, was not affected. Moreover, 5‐HT caused significant transient elevations of calcium concentrations in neurons B19 over 30 minutes, but neurons B5 did not show any increases in calcium concentrations with the addition of 5‐HT. These results suggest that the effect of 5‐HT upon outgrowth of regenerating neurons may be due to an increase in the intracellular calcium concentration.
Ontogeny of the sexually dimorphic male nucleus in the preoptic / anterior hypothalamus of ferrets and its manipulation by gonadal steroids
Authors: Cherry James A. , Basham Mark E. , Weaver Charles E. , Krohmer Randolph W. , Baum Michael J. 
Published: January 2005

AbstractA sexually dimorphic nucleus exists in the dorsal region of the ferret preoptic / anterior hypothalamic area (POA / AH), and is called the male nucleus of the POA / AH (MN‐POA / AH) because it is found only in males. Development of the MN‐POA / AH was studied in male ferrets, and for comparison a sexually nondimorphic ventral POA / AH nucleus was studied in both sexes. The MN‐POA / AH was conspicuous in males as early as embryonic day 37 (E37) of a 41‐day gestation, and its volume increased until postnatal day 56 (P56). No nucleus was present in the dorsal POA / AH of females at any age. The densities and average somal areas of cells in the dorsal POA / AH were similar in males and females at E33, before the MN‐POA / AH could be visualized. However, at E37 and E41 dorsal cells were greater in density and / or somal area in males than in females, accounting for the appearance of a nucleus in males at these ages. To insure that the dorsal POA / AH necleus seen in males at E37 andE41 was the presumptive MN‐POA / AH present in adult males, pregnant ferrets were given progesterone and either implanted subcutaneously (s.c.) with testosterone (T) or ovariectomized and implanted s.c. with the aromatase inhibitor, 1,4,6‐androstatriene‐3,17‐dione (ATD), on day 30 of gestation. As predicted from previous studies in which subjects were sacrificed in adulthood, formation of a dorsal POA / AH nucleus was promoted in female ferrets by T, and blocked in males by maternal ovariectomy and ATD treatment for animals sacrificed at E41. Much evidence suggests that behavioral sexual differentiation is accomplished in the male ferret between age E28 and P20. The MN‐POA / AH is present and potentially functional in males during a considerable portion of this perinatal period.
Neurometamorphosis
Authors: Harris William A. 
Published: January 2005

AbstractThis article introduces this special issue of the Journal of Neurobiology by reviewing several basic issues in metamorphosis as they specifically relate to the nervous system. It promotes the idea that metamorphic changes in the nervous system (neurometamorphosis) represent adaptive restructurings rather than recapitulations of evolutionary transitions. It introduces, but leaves unresolved, the question of whether neurometamorphosis is achieved primarily as a delayed phase of embryonic neurogenesis or as a special neurogenic period. It points out that respecification of old neurons and the addition of new neurons are the main contributory pathway of neural restructuring at metamorphosis, that respecification can be dramatic and seems to be preferred over the elimination and replacement of particular neurons. It also highlights the question of how much the central rewiring during metamorphosis is driven by trophic interactions with the changing body of the metamorphic animal and to what extent neurometamorphosis is driven by the direct action of metamorphic hormones on the neural elements themselves. Finally, this article introduces the question of the cellular and molecular pathways of neurometamorphosis, from the role of the nervous system in triggering the event to the receptor mediated changes in gene expression. Further details on all of these issues are to be found in the articles that make up the rest of this special issue.
Metamorphosis of the amphibian eye
Authors: Hoskins Sally G. 
Published: January 2005

AbstractFor many metamorphosing amphibians, the visual system must remain functional as the animal changes from an aquatic to a terrestrial habitat. Thyroid hormone, the trigger for metamorphosis, brings about changes at all levels of the animal, and profoundly alters the visual system, from cellular changes within the eye to new central connections subserving the binoculr vision that develops during metamorphosis in some species. I will survey the alterations in the visual system in the metamorphosis of several Amphibian groups, and consider the role of thyroid hormone in bringing about these transformations through action at the molecular level.
Mesencephalic fifth nucleus cell responses to thyroid hormone: One population or two?
Authors: Kollros Jerry J. , Bovbjerg Ann M. 
Published: January 2005

AbstractHypophysectomized Rana pipiens tadpoles 3–6 months old were placed in dl‐thyroxine (T4) solutions of 4 to 200 μg/l for 1–18 days and fixed 1 day after removal from the hormone solution. Exposure times varied inversely with T4 concentration. Mesencephalic fifth nucleus (M‐V) cells were counted on both sides, and cell and nuclear sizes were drawn and measured for each tadpole. Changes in M‐V cell characteristics correlated well with T4 exposure times and concentrations, as did changes in external tadpole morphology. All T4 concentrations were effective. Cells and nuclei were distinctly larger in all T4‐treated groups. The changes were greatest for cell sizes, less for nuclear dimensions, and still less for nucleo‐cytoplasmic ratios. Significant changes were seen for minimum and maximum sizes as well as for the mean values. The greatest mean changes were seen at dosages of 50 μg/l for 7–9 days.Mean M‐V cell numbers are significantly smaller in hypophysectomized tadpoles than in controls (about 420 vs. 650). Thyroid hormone treatment of the hypophysectomized animals abolishes much of the deficit, though M‐V cell deaths at the higher concentrations and longer treatment times reduce the apparent increase in numbers. Are the additional cells obtained through cell division, or do they represent a preexisting subpopulation of prospective M‐V cells that require stimulation by thyroid hormone for their full differentiation?
The gastropod nervous system in metamorphosis
Authors: Marois Rene , Carew Thomas J. 
Published: January 2005

AbstractMany gastropods, including the sea hare Aplysia californica, undergo metamorphosis in passing from the larval to the juvenile phases of their life cycle. During metamorphosis, the gastropod nervous system is affected by both progressive and regressive neuronal events. In addition to this metamorphic reorganization, the nervous system appears to be centrally involved in initiating metamorphosis. We propose that gastropods not only possess temprally distinct neuronal adaptations for the specific needs of the larval and juvenile phases, but also another transient neuronal adaptation specialized to subserve the metamorphic episode.
Metamorphic‐like changes in the nervous system of the nematode Caenorhabditis elegans
Authors: Walthall W. W. 
Published: January 2005

AbstractDuring postembryonic development of the nematode Caenorhabditis elegans, one class of embryonic motoneurons, the DD cells, respecifies its pattern of synaptic connections. At the same time, a closely related set of postembryonic motoneurons, the VD cells, complete differentiation and assume a pattern of connections equivalent to the original pattern of the DD cells. These types of changes are reminiscent of changes observed in the nervous systems of animals as they undergo metamorphosis. The DD and VD neurons arise through different lineage mechanisms and in the adult, receive different synaptic inputs and make different outputs. The embryonic DD motoneurons are clonally related to one another; whereas the postembryonic VD motoneurons are produced by a repeated sublineage in which each stem cell generates four or five cell types in addition to the VD cells. In spite of these differences, it has been possible to identify only one gene by mutation that effects one of the two motoneuronal classes. Mutations in the gene unc‐55 (unc meaning uncoordinated) cause the VD cells to become essentially identical to the DD cells; thus the unc‐55 gene product appears necessary and sufficient to transform homeotically the pattern of synaptic connections of an entire class of motoneuron.
The developing visual system and metamorphosis in the lamprey
Authors: Rubinson Kalman 
Published: January 2005

AbstractMetamorphosis of the sea lamprey, Petromyzon marinus, is a true metamorphosis. The larval lamprey is a filter‐feeder who dwells in the silt of freshwater streams and the adult is an active predator found in large lakes or the sea. The transformation usually occurs in the fifth or sixth year of life. Enlargement of the eye has been long accepted as a distinctive indication of metamorphosis in the sea lamprey, but it had been thought that this was because eye development in the larva was arrested after the formation of only the small central region. Recent studies indicate that all of the retina begins its development in the larva and that ganglion, amacrine, and horizontal cells differentiate in the peripheral retina of the larva. Retinal development is arrested during the premetamorphic period, to be resumed during metamorphosis. Metamorphic contributions include the differentiation of photoreceptor and bipolar cells. With the early appearance of ganglion cells, retinal pathways to the thalamus and tectum are established in larvae, as is a centripetal pathway. Tectal development spans the larval period but a spurt in tectal growth and differentiation is correlated with the completion of the retinal circuitry late in metamorphosis. The metamorphic changes in retina and tectum complete the functional development of the visual system and provide for the adult lamprey's predatory and reproductive behavior.
Developmental expression of the GABAA receptor α1 subunit mRNA in the rat brain
Authors: Gambarana Carla , Pittman Robin , Siegel Ruth E. 
Published: January 2005

AbstractRecent studies have suggested that the GABAA, receptor complex, the site of action of the inhibitory neurotransmitter gamma amino‐butyric acid (GABAA) and the anxiolytic benzodiazepines, is heterogeneous. Moreover, its composition may change during development. To better understand the molecular basis of receptor heterogeneity, the levels and distribution of the mRNA encoding the α1 receptor subunit were examined in the developing and adult rat brain with quantitative in situ hybridization histochemistry. Our studies demonstrate that α1 subunit mRNA expression changes during ontogeny. At late embryonic stages and in the first postnatal week, low levels of the mRNA were detected in the cortex, inferior colliculus, and hippocampus. The mRNA levels in these regions increased during the second and third postnatal weeks. Furthermore, a dramatic change in the distribution of the α1 subunit mRNA was seen in the second postnatal week when the message first became detectable in the cerebellar cortex. During subsequent development and in the mature brain, the α1 subunit mRNA was most abundant in the cerebellum, olfactory bulb, and inferior colliculus, although the absolute levels of mRNA varied by as much as sixfold in selected brain regions. The mature distribution of α1 subunit mRNA, along with its temporal appearance in the cerebellum, suggests that this subunit is a constituent of the Type 1 benzodiazepine site of the GABAA receptor complex. Furthermore, the onset of α1 subunit mRNA expression in the cerebellar cortex coincides with a period of extensive synapse formation, raising the possibility that synaptic interactions modulate the appearance of this GABAA receptor subunit in the cerebellum.
Elevated levels of polyneuronal innervation persist for as long as two years in reinnervated frog neuromuscular junctions
Authors: Werle Michael J. , Herrera Albert A. 
Published: January 2005

AbstractWhen the nerve to an adult frog sartorius muscle is crushed, and axons are allowed to regenerate, the level of polyneuronal innervation at reinnervated neuromuscular junctions is higher than normal. With time, much of this polyneuronal innervation is reduced by the process of synapse elimination (Werle and Herrera, 1988). Using intracellular recording, we estimated the level of polyneuronal innervation in adult frog (Rana pipiens) sartorius muscles 2 years (range: 1.7–2.4 years) after crushing the sartorius nerve. We found that 27% (S.E. = 1.4%) of the junctions in muscles 2 years after reinnervation were polyneuronally innervated, whereas only 10% (S.E. = 1.2%) of the junctions in normal frog muscles were polyneuronally innervated. Thus, the synapse elimination that occurs following reinnervation does not restore the normal level of polyneuronal innervation. Histological comparisons of junctional structure between muscles 2 years after reinnervation and normal muscles revealed substantial differences. Reinnervated junctions had a greater length of synaptic gutter apposed by nerve terminal processes, more axonal inputs, more empty synaptic gutter, more instances of single synaptic gutters innervated by more than one axon, and longer lengths of nerve terminal processes that connect synaptic gutters within a junction. On the basis of this physiological and anatomical evidence, we conclude that nerve injury causes persistent changes in the pattern of muscle innervation.
Using fluorescence photoablation to study the regeneration of singly cut leech axons
Authors: Camhi Jeffrey M. , Macagno Eduardo 
Published: January 2005

AbstractThe regeneration of the axons of leech Retzius cells was compared following two different methods of axonal severing: (1) a crush of the whole connective that includes the Retzius axon; and (2) photoablation of a small segment of only the Retzius axon. The photoablation was carried out after filling the Retzius cell with Lucifer Yellow (LY). Several tests were carried out to determine whether the photoablation actually severed the axon. These included (1) using the lipophilic membrane probe Dil as an indicator of membrane severance [Fig. 4 (A)]; (2) electron microscopic examination of the photoablated axon after filling it with horseradish peroxidase (HRP) (Fig. 7); and (3) filling the Retzius cell first with HRP, then photoablating, and looking for the disappearance of the HRP in the photoablated region (Figs. 5,6). These and other observations indicated that the photoablated axon was actually severed. Two differences were seen in the regeneration of the Retzius axon after crush versus after photoablation. First, the sprouting following crush was far more disorganized, and included significantly more lateral spread. Second, after photoablation, over 70% of the axons, upon refilling with LY after 3 days or more, showed the newly introduced LY suddenly extending far down the distal segment, indicating that the proximal and distal segments had become reconnected (Figs. 8,9). This was never seen following a crush (Fig. 1). The photoablated axons did not pass HRP into the distal segment, suggesting that the reconnection was not by fusion, but perhaps by a gap junction. The results show that axonal regeneration can take a dramatically different from than it does following a standard crush procedure if, instead, the axon is severed in a way that preserves the structural integrity of the surrounding tissue.
Nonspiking pathways antagonize the resistance reflex in the thoraco‐coxal joint of stick insects
Authors: Büschges Ansgar , Schmitz Josef 
Published: January 2005

AbstractIn the stick insect (Carausius morosus) imposed forward and backward movements of the coxa of the middle leg induce resistance reflexes in the retractor or protractor coxae muscles, depending on the direction of movement. The hairs of the ventral coxal hairplate (cxHPv) function as the primary transducer of the retractor part of the underlying feedback loop: bending of the hairs of the cxHPv during an imposed forward movement of the coxa leads to a reflex activation of the retractor motoneurones, whereas releasing of the hairs causes an inhibition of these motoneurones. Local nonspiking interneurones were investigated, which transmit information from the cxHPv onto the retractor motoneurones: (1) they are depolarized during bending of the hair sensilla of the cxHPv and (2) they decrease the activities of retractor motoneurones. In addition, four of the interneurones drive a protractor motoneurone, when they are depolarized. As bending stimuli at the cxHPv (mimicking an imposed forward movement of the leg) induce reflex activation of the retractor motoneurones and reflex inhibition of the protractor motoneurones, the physiology of the recorded interneurones appears to antagonize the resistance reflex in the thoraco‐coxal joint. The results indicate that these nonspiking interneurones take part in the shaping of the reflex response and that furthermore these interneurones are involved in the organization of the motor output to the two antagonistic sets of motoneurones. The possible role of these interneurones might be the adjustment of the gain and of the time constant in the thoraco‐coxal feedback loop.
Light‐adapting migration of the screening‐pigment in crayfish photoreceptors is a two‐stage movement comprising an all‐or‐nothing initial phase
Authors: Frixione Eugenio , Pérez‐Olvera Ofelia 
Published: January 2005

AbstractThe light‐adapting response of the screening‐pigment in crayfish retinal photoreceptors, previously described as a monophasic movement, was found to consist of two stages with different properties: (1) a rapid initial expansion that once started proceeds for at least half of the full distance, and (2) a slower and more variable continuation of the movement. The two components were resolved in isolated eyes stimulated under conditions expected to restrict Na+ influx into the photoreceptors. Only the second stage of the response to light was inhibited when Na+ was substituted with choline, or if the normal saline contained amiloride, a diuretic that hinders Na+ entry across many cell membranes. Amiloride in a medium without Na+ delayed, but did not curb, the first stage, whereas the rest of the movement was markedly restrained. Partial replacement of Na+ with Li+ blocked the second stage without affecting the rapid initial shift triggered by light. Exposure of dark‐adapted eyes to high Na+ levels or to ouabain in the presence of Na+ in the dark also elicited a two‐staged pigment dispersion to the light‐adapted position. Low Na+ concentrations or amiloride affected the latency, but not the rate or extent, of the first stage of migration in ouabain‐treated eyes. Consistent though less significant results were obtained with cyanide and the Na+ ionophore monensin. These observations suggest a differential control of pigment position over two defined domains along the photoreceptors, probably to integrate a double mechanism of light‐adaptation: an all‐or‐nothing partial shift of the pigment screen as a safety factor against overexposure, followed by a regulated adjustment according to stimulation intensity.
Glycoconjugates are stage‐ and position‐specific cell surface molecules in the developing olfactory system, 2: Unique carbohydrate antigens are topographic markers for selective projection patterns of olfactory axons
Authors: Schwarting Gerald A. , Deutsch Gail , Gattey Devin M. , Crandall James E. 
Published: January 2005

AbstractThree monoclonal antibodies specific for different carbohydrate antigens were used to analyze the development of the olfactory system in rats. CC2 antibodies react with a subset of main olfactory neurons, their axons, and terminals in the olfactory bulb. CC2 antigens are expressed on dorsomedial neurons in the olfactory epithelium (OE) from embryonic (E) day 15 to adults. In the olfactory bulb (OB), only dorsomedially located glomeruli express CC2 glycoconjugates from postnatal day (P) 2 to adults. Thus CC2 defines a dorsomedially organized projection that is established early in embryonic development and continues in adults. P‐Path antibodies react with antigens that are expressed on the olfactory nerve in embryos, and are also detected on cell bodies in the neuroepithelium and in glomeruli of the OB at P2. At P14, P‐Path staining is weaker, but remains present on many cells in the epithelium and in many glomeruli in the bulb. Postnatally, P‐Path immunostaining continues to decrease in most regions of the OE and OB. At P35 and afterwards, only a few P‐Path‐positive neuronal cells can be detected in the OE. Furthermore, after P35 only two groups of glomeruli in the OB are P‐Path immunoreactive. One is situated adjacent to the accessory olfactory bulb (AOB) at the dorsocaudal surface of the OB. The other is adjacent to the AOB at the ventrocaudal surface of the OB. Thus, in adults, P‐Path glycoconjugates are expressed in neurons and axons that project only to a specific subset of caudal glomeruli of the OB. Monoclonal antibody 1B2, reacts with β‐galactose‐terminating glycolipids and glycoproteins. At P2, 1B2 immunoreactivity is seen on a subset of cell bodies that are distributed throughout the OE and is expressed in most glomeruli in the OB at this age. By P35 and in adults, 1B2 continues to be expressed on a subset of neurons in the OE that project to only a small subset of glomeruli in the OB. Unlike CC2 and P‐Path antigens that define specific groups of glomeruli, 1B2‐immunoreactive glomeruli do not have a detectable spatial pattern. It is more likely that 1B2 antigens define a specific stage in the maturation of connections between the OE and OB.
Inhibition of tyrosine phosphorylation potentiates substrate‐induced neurite growth
Authors: Bixby John L. , Jhabvala Perseus 
Published: January 2005

AbstractProtein tyrosine kinases (PTKs) have major roles in signal transduction and growth control. There are several lines of evidence implicating PTKs in the regulation of axon growth, and this has led to the suggestion that they are centrally involved in the transduction of neuronal growth signals. To test this idea, we assayed the effect of the compounds genistein and lavendustin, specific inhibitors of PTKs, on neurite growth. We find that genistein greatly reduces phosphotyrosine in neurons, as expected from its action on other cells. Surprisingly, administration of genistein or lavendustin potentiated substrate‐induced neurite growth in at least several different neuronal types. Stimulation of neurite growth by genistein was abolished by vanadate, providing additional evidence that inhibition of PTKs is responsible for this effect. The potentiation of growth is rather general, in that it occurs on several different extracellular matrix substrates and on two different cell adhesion molecules. Both the initiation of neurite growth and the rate of neurite elongation appear to be potentiated. Our results do not provide evidence for models of substrate‐induced signal transduction that involve PTKs asa positive and necessary step, but suggest that such kinases play aregulatory role in neurite elongation. © 1992 John Wiley & Sons, Inc.