bluuebunny/crossref_metadata_2025_split huggingface dataset:
Eliminating afferent impulse activity does not alter the dendritic branching of the amphibian mauthner cell
Authors: Goodman Linda A. , Model Pat G. 
Published: January 2005

AbstractIn the developing amphibian, the formation of extra vestibular contacts on the Mauthner cell (M‐cell) enhances dendritic branching, while deprivation reduces it (Good‐man and Model, 1988a). The mechanism underlying the interaction between afferent fibers and developing dendritic branches is not known; neural activity may be an essential component of the stimulating effect. We examined the role of afferent impulse activity in the regulation of M‐cell dendritic branching in the axolotl (Ambystoma mexicanum) embryo. M‐cells occur as a pair of large, uniquely identifiable neurons in the axolotl medulla. Synapses from the ipsilateral vestibular nerve (nVIII) are restricted to a highly branched region of the M‐cell lateral dendrite. We varied the amount of nVIII innervation and eliminated neural activity. First, unilateral transplantation of a vestibular primordium deprived some M‐cells of nVIII innervation and superinnervated others. Second, surgical fusion of axolotls to TTX‐harboring California newt (Taricha torosa) embryos paralyzed the Ambystoma twin: voltage‐sensitive Na+ channel blockade by TTX eliminated action potential propgation. Reconstruction of M‐cells in 18 mm larvae revealed that dendritic growth was influenced by ingrowing axons even in the absence of incoming impulses: impulse blockade had no effect on the stimulation of dendritic growth by the afferent fibers.
The evolution of metamorphosis in amphibians
Authors: Fritzsch Bernd 
Published: January 2005

AbstractA survey is provided of the external transformations that coincide with metamorphosis or a water‐to‐land transition, and of transformations during water‐to‐land transition in the retinal projection, the brain stem, the lateral‐line system, and the inner ear of amphibians. Among the three orders of amphibians, the frogs are characterized by more pronounced transformations during the water‐to‐land transition than are the other two orders. Some of the progressive and regressive changes in the sensory and nervous system are presented and a scenario is suggested for the evolution of these transformations among amphibians. Suggestions that metamorphosis in frogs can recapitulate the water‐to‐land transition of ancestral amniotic vertebrates are refuted.
Contributions of syringeal muscles to respiration and vocalization in the zebra finch
Authors: Vicario David S. 
Published: January 2005

AbstractAcute and chronic electormyographic (EMG) recordings from individual syringeal muscles were used to study syringeal participation in respiration and vocalization. In anesthetized birds, all syringeal muscles recorded were active to some degree during the expiratory phase of respiration, following activity in the abdominal musculature and preceding the emergence of breath from the nostril. In awake birds, the ventralis (V) muscle fired a strong, consistent burst, but the dorsalis (D) was variable both in strenght and timing. Denervation of V is sufficient to produce the wheezing respiration originally seen in birds with complete bilateral section of the tracheosyringeal nerve. Complete syringeal denervation also removed almost all the acoustic features that distinguish individual song syllables, but had a minor effect on the temporal structure of song. When activity in V and D was recorded in awake, vocalizing birds, D was active before and during sound production, and V showed a small burst before sound onset and a vigorous burst timed to the termination of sound. During song, V was consistently active at sound offset, but also participated during sound for narrow bandwidth syllables. For some syllables (simple harmonic stacks), neither muscle was active. These data suggest that V contributes to syllable termination during vocalization and may silence the syrinx during normal respiration. D contributes to the acoustic structure of most syllables, and V may contribute to a special subset of syllables. In summary, the syringeal muscles show different activity patterns during respiration and vocalization and can be independently activated during vocalization, depending on the syllable produced.
Cortisol reduces plasticity in the kitten visual cortex
Authors: Daw N. W. , Sato H. , Fox K. , Carmichael T. , Gingerich R. 
Published: January 2005

AbstractWe investigated the effect of elevated levels of cortisol on plasticity in the visual cortex of the cat. Animals were given daily injections of cortisol i.m. for 20 days starting around 35 days of age. After 10 days they were monocularly deprived, and after an additional 10 days recordings were made from the visual cortex to construct an ocular dominance histogram. The results were compared with those from normal animals of the same age, and with animals monocularly deprived for the same period but not treated with cortisol. Cortisol reduced the ocular dominance shift in a dose‐dependent manner, but did not totally abolish it even at the highest doses used. Two other series of animals were recorded, one slightly later in the critical period and one slightly earlier, with care taken to give cortisol before the animals were exposed to light in the morning. In both cases, cortisol reduced the ocular dominance shift but did not abolish it. To interpret these results, we measured levels of plasma cortisol in normal cats of various ages. Average levels were fairly constant between birth and 12 months of age (0.5–1 μg/dl), and increased slightly after that, but there was a large variation between animals. Thus elevated levels of cortisol can have a substantial effect on plasticity in the visual cortex of the cat, but the decline of the critical period for plasticity between 6 weeks and 3–5 months of age does not seem to be due to a rise in cortisol levels during this time.
Physiological properties of newly formed synapses between sympathetic preganglionic neurons and sympathetic ganglion neurons
Authors: Hume Richard I. , Honig Marcia G. 
Published: January 2005

AbstractWe have examined the physiological properties of transmission at newly formed synapses between sympathetic preganglionic neurons and sympathetic ganglion neurons in vitro. Chick neurons were labeled with fluorescent carbocyanine dyes before they were placed into culture (Honig and Hume, 1986), and were studied by making intracellular recordings during the first 2 weeks of coculture. Evoked monosynaptic excitatory postsynaptic potentials (EPSPs) were not observed until 48 h of coculture. Beyond this time, the frequency with which connected pairs could be found did not vary greatly with time.With repetitive stimulation, the evoked monosynaptic EPSPs fluctuated in amplitude from trial to trial and showed depression at frequencies as low as 1 Hz. To gain further information about the quantitative properties of transmission at newly formed synapses, we analyzed the pattern of fluctuations of delayed release EPSPs. In mature systems, delayed release EPSPs are known to represent responses to single quanta, or to the synchronous release of a small number of quanta. For more than half of the connections we studied, the histograms of delayed release EPSPs were extremely broad. This result suggested that either quantal reponses are drawn from a continuous distribution that has a large coefficient of variation or that there are several distinct size classes of quantal responses. The pattern of fluctuation of monosynaptic EPSPs was consistent with both of these possibilities, and was inconsistent with the possibility that monosynaptic EPSPs are composed of quantal subunits with very little intrinsic variation. Although variation in the size of responses to single quanta might arise in a number of ways, one attractive explanation for our results is that the density and type of acetylcholine receptors varies among the different synaptic sites on the surface of developing sympathetic ganglion neurons.
Development and modulation of endogenous bursting in identified neuron R15 of juvenile Aplysia
Authors: Marcus Emilie A. , Carew Thomas J. 
Published: January 2005

AbstractEvidence from a variety of both vertebrate and invertebrate preparations has demonstrated that modulation of the intrinsic firing patterns of individual neurons can have a dramatic effect on the functional output of a neural circuit. Although the mechanisms underlying the production and modulation of intrinsic firing patterns have been extensively studied in adult nervous systems, relatively little is known about how these two features of intrinsically active neurons develop. To address these issues, we have examined the development of endogenous bursting and its modulation by neuropeptides in the identified cell R15 of juvenile Aplysia. Confirming Ohmori (1981), we found that the mature parabolic bursting pattern of R15 is absent in early juvenile stages and develops only gradually over the last stage of juvenile development. We have then analyzed the modulatory effects of extracts made from the neurosecretory bag cells of Aplysia on the immature firing pattern of juvenile R15 cells. In the adult, neuroactive peptides released from the bag cells are known to intensify bursting. In juveniles, we have found that bag cell extract (BCE) can induce bursting prematurely as well as intensify immature bursts, whereas control extracts have no effect on the firing pattern of R15. These results show that the ionic currents necessary for the generation of endogenous bursting in R15 are present and can be modulated before the normal developmental expression of the burst pattern.
A neurite‐promting factor from muscle supports the survival of cultured chicken spinal motor neurons
Authors: Jeong Soo J. , Oh Tae H. , Markelonis George J. 
Published: January 2005

AbstractDuring embryonic development, spinal motor neurons require muscle‐derived trophic factors for their survival and growth. We have recently isolated a protein from muscle that is not laminin but that still stimulates neurite outgrowth from embryonic neurons in culture. In the present study, we investigated whether this protein, which we refer to as muscle‐derived neurite‐promoting factor (NPF), could also promote the survival and growth of motor neurons in culture. Spinal motor neurons were isolated from 6‐day‐old chicken embryos by a metrizamide step‐gradient centrifugation protocol. Most large cells (putative motor neurons) were found in the upper metrizamide fraction (0%–6.8% interface; fraction I). Motor neurons were identified by increased specific activity of choline acetyltransferase (CAT) and by their propensity to transport retrogradely either wheat germ agglutininhorseradish peroxidase or the fluorescent dye, 1,1′‐dioctadecyl‐3,3,3′,3′‐tetramethylindocarbocyanine per chlorate (diI), when those substances were injected into the target field. Labeled motor neurons were 2.6‐fold enriched in fraction I and the specific CAT activity was 4.4‐fold increased in fraction I as compared to unfractionated cells. When motor neurons were grown on muscle‐derived NPF, the protein supported the survival of at least 21% of the neurons for as long as 6 days in culture. The protein showed no significant effect on either CAT specific activity or on high‐affinity choline uptake by neurons. There was a substantial increase from 21% to 38% of the survival of motor neurons when a combination of muscle‐derived NPF also promoted the survival of sensory neurons and sympathetic neurons in culture. Our results demonstrate that a neurite‐promoting protein derived from muscle promotes both the survival and the outgrowth of neurites from cultured spinal motor neurons as well as from sensory and sympathetic neurons.
Testosterone and the incidence of hormone target cells in song‐control nuclei of adult canaries
Authors: Bottjer Sarah W. , Maier Elke 
Published: January 2005

AbstractAdult male canaries learn to produce high‐amplitude complex courtship songs each breeding season, whereas females do not, and brain nuclei involved with the production of song behavior are much larger in breeding males than in nonbreeding males or females (Nottebohm, 1980, 1981). However, treatment of adult females with testosterone (T) causes them to produce male‐like song and stimulates pronounced growth of some song‐control brain nuclei such as the caudal nucleus of the ventral hyperstriatum (HVc). We reexamined the effects of T on song‐control nuclei in deafened birds. In order to examine whether the pattern of hormone accumulation varies as a function of circulating testosterone levels we described the distribution of testosterone‐concentrating cells in HVc and the magnocellular nucleus of the anterior neostriatum (MAN) in hearing adult male, female, and T‐treated female canaries, as well as in deaf T‐treated and untreated females. In contrast to our previous findings (Bottjer, Schoonmaker, and Arnold, 1986a), we observed no tendency in this study for testosterone‐induced growth of HVc to be attenuated in deafened birds. There was no difference between deaf and hearing birds in the incidence of labeled cells within HVc. We also observed no sex or hormone‐induced differences in the percentage of hormone‐concentrating cells in HVc: normal females have approximately the same proportion of hormone target cells as do males and T‐treated females. However, males normally have many more neurons in HVc than do control females, and systemic exposure to testosterone induces a pronounced increase in the number of HVc neurons of adult females. Therefore, the absolute number of hormone target cells in HVc is likely to be much greater in males and T‐treated females than in normal females. As in HVc, there were no differences among groups in the proportion of labeled cells within lateral MAN (IMAN), a nucleus that has been implicated in song learning (Bottjer, Miesner and Arnold, 1984). In contrast, the incidence of hormone target cells in medial MAN (mMAN) did vary as a function of hormonal condition: although mMAN of normal females is rarely visible in Nissl‐stained sections and cells in this region are not hormone labeled, mMAN is clearly visible in Nisslstained sections of males and T‐treated females and contains many hormone‐labeled cells. This testosterone‐induced change in the phenotype of mMAN cells suggests a possible role for mMAN in learned song behavior.
Expression of the Raf‐1 protein in rat brain during development and its hormonal regulation in hypothalamus
Authors: Whorf R. C. , Tobet S. A. 
Published: January 2005

AbstractTo study mechanisms involved in the sexual differentiation of the rat brain, the expression of the protein product of the proto‐oncogene c‐raf‐1 (Raf‐1) was examined. Biochemical and immunocytochemical analyses localized Raf‐1 in embryonic rat brain regions and demonstrated hormonally induced changes in Raf‐1 expression. For this study an affinity‐purified anti‐peptide antiserum specific for Raf‐1 (NH‐44) was used. Western blots revealed an approximately 77 kD polypeptide isolated in the cytosol of developing rat brains. Raf‐1 levels were highest in the embryonic (E) day 22 female hypothalamus (HYP), and approximately twofold higher than levels detected in male HYP at E22 as determined by quantitative protein dot blot and semiquantitative Western blot analyses. Raf‐1 levels in HYP were greater than those in either brain stem (BS) or cortex. Immunocytochemical analysis revealed high levels of Raf‐1 in selective brain regions (e.g., the ventromedial nucleus in the HYP, the mitral cell layers in the main and accessory olfactory bulbs (OB), and the locus coeruleus) at E22 and postnatal (P) day I. Lower levels of immunoreactivity were observed in many areas of the perinatal neuraxis. To test hormonal regulation of Raf‐1, testosterone propionate (TP) was administered to pregnant rats on E17; male and female fetuses were examined on E22. This treatment significantly decreased Raf‐1 levels in female HYP, but not in male HYP, as determined by Western blot analysis. No significant sex difference or response to prenatal hormone treatments were observed in either brain stem or cortex. No significant sex difference was noted postnatally, and administration of TP 3 h after birth did not change Raf‐1 levels examined 24 h later. In summary, Raf‐1 was localized within selective regions of the rat brain, and its expression was altered by exogenous prenatal hormonal stimulation. One role for Raf‐1 in signal transduction may be to delimit hormonal critical periods in sexual differentiation of the brain.
Glycoconjugates are stage‐ and position‐specific cell surface molecules in the developing olfactory system, 1: The CC1 immunoreactive glycolipid defines a rostrocaudal gradient in the rat vomeronasal system
Authors: Schwarting Gerald A. , Deutsch Gail , Gattey Devin M. , Crandall James E. 
Published: January 2005

AbstractPrimary sensory neurons in the vomeronasal organ (VNO) project axons to the glomeruli of the accessory olfactory bulb (AOB) where they form connections with mitral cell dendrites. We demonstrate here that monoclonal antibodies to specific carbohydrate antigens define stage‐ and position‐specific events during the development of the vomeronasal system (VN). CC1 monoclonal antibodies react with specific N‐acetyl galactosamine containing glycolipids. In the embryo, CC1 antigens are expressed throughout the VNO and on vomeronasal nerves. Beginning approximately at birth and continuing into adults, CC1 expression is spatially restricted in the VNO to centrally located cell bodies. In the postnatal AOB, CC1 is expressed in the nerve layer and glomeruli, but only in the rostral half of the AOB. These data suggest that CC1 antigens may participate in the targeting of axons from centrally located VNO neurons to rostral glomeruli in the AOB. In contrast, CC2 monoclonal antibodies, which recognize complex α‐galactosyl and α‐fucosyl glycoproteins and glycolipids, react with all VNO cell bodies and VN nerves from embryonic (E) day 15 to adults. CC2 antibodies do not distinguish rostral from caudal regions of the AOB, nor are the CC2 glycoconjugates developmentally regulated. P‐Path monoclonal antibodies, which recognize 9‐O‐acetyl sialic acid, react with cell bodies in the VNO and nerve fibers from E13 to postnatal (P) day 2. P‐Path immunoreactivity disappears from the VNO system almost completely by P14, when only a few P‐Path reactive nerve fibers can be seen. These studies suggest that specific cell surface glycoconjugates may participate in spatially and temporally selective cell–cell interactions during development and maintenance of vomeronasal connections.
Evidence for a driving role of ingrowing axons for the shifting of older retinal terminals in the tectum of fish
Authors: Wilm Claudia , Fritzsch Bernd 
Published: January 2005

AbstractIn amphibians and teleosts, retina and tectum grow incongruently. In order to maintain the retinotopy of the retinotectal projection, Gaze, Keating, and Chung (1974) postulated a shifting of terminals throughout growth. In order to test the possibility that ingrowing retinal fibers are the driving force for this shifting, we induced a permanent retinal projection into the ipsilateral tectum in juveniles of the cichlid fish Haplochromis burtoni. The surface of the tectum had increased (11–18 months later) 2.5–5.8 times, and the surface of the retina 8.6–14 times. Filling of ganglion cells with horseradish peroxidase (HRP) retrogradely from the tectum showed ipsilaterally regenerating ganglion cells only in the center of the retina. The position of ganglion cells indicated that the ipsilateral projection derived only from axotomized and regenerating retinal ganglion cells but not from those newly born. Ipsilaterally projecting retinal fibers showed terminals only in the rostral half of the tectum. Comparison of area of terminations of ipsilaterally projecting ganglion cells at various times after the crush provided no evidence for expansion or a shift into caudal tectal areas throughout the period of growth. These findings are compatible with the idea that newly ingrowing fibers induce older terminals to move caudally.
Regulation of hemicholinium binding sites in isolated nerve terminals
Authors: Knipper M. , Kahle C. , Breer H. 
Published: January 2005

AbstractHigh‐affinity uptake of choline, the rate‐limiting, regulatory step for the synthesis of acetylcholine is regulated via presynaptic auto‐ and heteroreceptors. Binding studies using tritiated hemicholinium‐3 ([3H]HCh‐3) as the specific ligand for the choline carrier revealed that the number of hemicholinium binding sites in nerve terminals isolated from insect brain changes corresponding to the activity of synaptosomal kinase A and kinase C. Activation of kinase A apparently increases the total number of hemicholinium binding sites by recruiting additional occult carriers, whereas the effect of kinase C activity is most appropriately explained by preventing a down‐regulation of carrier proteins. The kinase‐mediated regulation of choline transporters is obviously due to a phosphorylation of the carrier protein itself.
Estradiol pulses induce progestin receptors selectively in substance P‐immunoreactive neurons in the ventrolateral hypothalamus of female guinea pigs
Authors: Olster Deborah H. , Blaustein Jeffrey D. 
Published: January 2005

AbstractLow doses of estradiol, administered as pulses, are as effective as higher doses for priming ovariectomized (OVX) guinea pigs to display progesterone‐facilitated lordosis. High doses of estradiol, administered by constant‐release implants, induce progestin receptors in many substance P‐immunoreactive (SP‐IR) neurons in the ventrolateral hypothalamus (VLH), a site at which estradiol primes OVX guinea pigs to respond behaviorally to progesterone. To test the hypothesis that behaviorally effective estradiol pulses induce progestin receptors selectively in substance P‐containing neurons in the VLH, OVX females received estradiol implants 1 week prior to perfusion, or two pulses of estradiol‐ 17β, injected 39 and 11 h before perfusion. Colchicine was administered intracerebroventricularly prior to perfusion. No significant differences were observed in the total number of progestin receptor‐immunoreactive (PR‐IR) or substance P‐immunoreactive cells in the VLH and VLH/ventromedial hypothalamus (VMH), respectively, of females receiving the two estradiol treatments. However, the percentage of PR‐IR cells in the VLH also immunoreactive for SP was significantly higher in the estradiol pulse‐treated (53%), than in the estradiol capsule‐implanted animals (36%). These data suggest that behaviorally effective estradiol pulses induce progestin receptors selectively in substance P‐containing neurons in the VLH and are consistent with the hypothesis that substance P is involved in progesterone‐facilitated lordosis in guinea pigs.