bluuebunny/crossref_metadata_2025 huggingface dataset:
Respecification of larval proleg motoneurons during metamorphosis of the tobacco hornworm, Manduca sexta: Segmental dependence and hormonal regulation
Authors: Weeks Janis C. , Ernst‐Utzschneider Kristina
Published: January 2005

The principal locomotory appendages of the Manduca sexta caterpillar, the prolegs, are present on the third through sixth abdominal segments (anal prolegs located on the terminal segment were not included in this study). Previous studies have characterized some of the proleg retractor muscles and their motoneurons. In the present study we identified additional proleg motoneurons and their putative homologs in the non‐proleg‐bearing segments. One of the motoneurons present in the proleg‐bearing segments is absent in the non‐proleg‐bearing segments. At pupation the prolegs are lost, their muscles degenerate, and some of their motoneurons regress structurally. Subsequently, subsets of the proleg motoneurons and their homologs in other segments die in a segment‐specific pattern. This is the first report of segment‐specific motoneurons, and of segment‐specific death of identified motoneurons, in Manduca. During adult development the surviving proleg motoneurons innervate the tergosternal muscle (TSM) and grow bilateral dendritic arbors. Dendritic growth is completed by about the 12th of the 18 days of adult development. Following adult emergence all but one of the respecified proleg motoneurons dies. The hormonal dependence of dendritic outgrowth was tested by isolating abdomens to eliminate the ecdysteroid‐secreting glands in the thorax. Between the second and fifth days after pupation the motoneurons became progressively more competent to undergo dendritic outgrowth following abdomen isolation. The extent of dendritic outgrowth paralleled the degree of morphological development attained by isolated abdomens. It is concluded that ecdysteroids are required for motoneuron outgrowth, but our findings suggest that, unless an abdominal source of ecdysteroids exists in pupae, a relatively small exposure may be sufficient.
Cell death during development of a forebrain nucleus involved with vocal learning in zebra finches
Authors: Bottjer Sarah W. , Sengelaub Dale R.
Published: January 2005

Lateral MAN (magnocellular nucleus of the anterior neostriatum) is a forebrain nucleus that is known to be importantly involved with vocal learning in juvenile male zebra finches only during a restricted period of the learning process: lesions of lMAN completely disrupt song behavior in zebra finches prior to 50 days of age but have little or no effect in older juvenile or adult birds. The development of lMAN, as of other song‐control regions, is delayed until the time that song behavior is being learned. Lateral MAN undergoes a substantial loss of neurons between 25 and 55 days of age, a time that encompasses initial stages of vocal production as well as the interval during which lMAN lesions become ineffective. In this study, we measured both the time course of neuronal loss and the incidence of pyknotic cells within lMAN during the period of cell loss. There is a pronounced loss of neurons from lMAN between 20 and 35 days, after which the adult number of neurons is established. The incidence of pyknosis is greatest at 20 days, around the time when the loss of live cells is also most pronounced, suggesting that the loss of neurons from lMAN is attributable to cell death. The loss of neurons occurs well before lesions of lMAN become ineffective in disrupting vocal behavior. Thus the neurons remaining in lMAN after the period of cell loss apparently undergo a substantial change in function at the time lesions lose effectiveness (about 55–60 days).
A temporal analysis of testosterone‐induced changes in electric organs and electric organ discharges of mormyrid fishes
Authors: Freedman E. G. , Olyarchuk J. , Marchaterre M. A. , Bass A. H.
Published: January 2005

The electric organ discharge (EOD) of several species of mormyrid fishes within the genus Brienomyrus is sexually dimorphic during the breeding season: the duration of the male's EOD is much longer than the duration of the female's (for a review see Hopkins, 1986). The mormyrid used here, Brienomyrus sp., exhibits similar alterations in the duration of the triphasic EOD after treatment with testosterone, as do other members of this genus (for reviews see Bass, 1986a,b). In this experiment, animals were intraperitoneally implanted with pellets of either 11‐ketotestosterone or 17 a‐methyltestosterone, and the time course of the changes in the duration of each of the three phases of the EOD were quantified. Additionally, the time course of changes in the morphology of the electric organ, after testosterone treatment, was also quantified using electron microscopic techniques. The results suggest that the change in the duration of the first phase of the EOD is due exclusively to the change in the thickness of the electrocyte body: this is consistent with a model proposed by Bennett and Grundfest (1961) for the electrogenesis of a triphasic EOD. Changes in the duration of the second and third phases of the EOD are highly correlated with changes in the surface area of the posterior and anterior faces of the electrocyte, respectively. The results support the hypothesis that gonadal steroid hormone‐induced changes in the EOD are due to structural changes in the electrocyte's membranes, and that all of the observed changes in the discharge of this system can be explained by the action of steroid hormones on the peripheral target cells (electrocytes).
Ocular dominance stripe formation by regenerated isogenic double temporal retina in Xenopus laevis
Authors: Coletti Steven M. , Ide Charles F. , Blankenau Andrew J. , Meyer Ronald L.
Published: January 2005

In lower vertebrates such as frogs and fish, long ocular dominance stripes with anterior‐posterior (A‐P) orientation can be produced by causing both eyes to innervate one optic tectum during the course of development. Similar experiments on adult animals usually produce patches rather than stripes. During development, new retinal fibers from the nasal retina segregate into appropriate stripes at the growing edge of the posterior (P) tectum while new temporal fibers segregate at the nongrowing anterior (A) tectal edge. Fiber segregation into long A‐P oriented stripes might depend upon a template produced by new nasal fibers initiating stripe orientation in the vicinity of new tectal cells; new nasal fibers would orient to the nascent (posterior) edge of the template while temporal fibers would orient to the anterior (nongrowing) end of the template. To test the dependence of stripe formation on the matching of nascent retinal cells with nascent tectal cells, we compared stripe orientation in animals with isogenic double nasal innervation and isogenic double temporal innervation of the tectum. In double nasal innervation, the oldest retinal cells innervate the anterior tectum; new fibers from the entire retinal periphery always innervate the newest tectal cells at the posterior tectum. Stripes are oriented A‐P, consistent with a maturation front model. In contrast, the oldest retinal cells innervate the newest (posterior) tectal cells in double temporal innervation of the tectum; the growing retinal periphery innervates the non‐growing anterior tectum. Stripes are also oriented A‐P, indicating that the production of long stripes does not depend upon maturation front matching of nascent retinal fibers and nascent tectal cells.
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

In 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

A 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

Acute 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

We 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

We 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

Evidence 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

During 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

Adult 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

To 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

Primary 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

In 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

High‐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

Low 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.
Mechanism of agrin‐induced acetylcholine receptor aggregation
Authors: Wallace Bruce G.
Published: January 2005

Agrin induces the formation of specializations on chick myotubes in culture at which several components of the postsynaptic apparatus accumulate, including acetylcholine receptors (AChRs). Agrin also induces AChR phosphorylation. Several lines of evidence suggest that agrininduced phosphorylation of tyrosine residues in the β subunit of the AChR is an early step in receptor aggregation: agrin‐induced phosphorylation and aggregation have the same dose dependence; treatments that prevent aggregation block phosphorylation; phosphorylation begins before any detectable change in receptor distribution, reaches a maximum hours before aggregation is complete, and declines slowly together with the disappearance of aggregates after agrin is withdrawn; agrin slows the rate at which receptors are solubilized from intact myotubes by detergent extraction; and the change in receptor extractability parallels the change in phosphorylation. A model for agrin‐induced AChR aggregation is presented in which phosphorylation of AChRs by an agrin‐activated protein tyrosine kinase causes receptors to become attached to the cytoskeleton, which reduces their mobility and detergent extractability, and leads to the accumulation of receptors in the vicinity of the activated kinase, forming an aggregate. © 1992 John Wiley & Sons, Inc.
An antigen present in the Drosophila central nervous system only during embryonic and metamorphic stages
Authors: Go Masahiro J. , Hotta Yoshiki
Published: January 2005

We report here about an antigen that is expressed in the central nervous system (CNS) of Drosophila only during the embryonic and metamorphic stages. In Drosophila, axonogenesis and synaptogenesis occur twice during the development: first in the embryonic and second in the metamorphic stages. We generated monoclonal antibodies (MAbs) in order to obtain molecular probes for analyzing axonogenesis or synaptogenesis in the CNS on the assumption that good candidates for molecules responsible for such phenomena must be present in the neuropil during those stages exclusively. As a result, we found MAb 66B2 whose intense immunoreactivity in the neuropil of the CNS was observed exclusively in the embryo and pupa, and not in the larva and adult. Immunoblot analyses showed that MAb 66B2 binds specifically to a protein with an apparent molecular weight of 350 K and neutral pl in the prepupal CNS. A significant amount of the antigen was isolated in forms that were soluble without detergent. Results of immunohistochemistry with MAb 66B2 in a primary culture of embryos showed that some live cells in the ganglion‐like cluster were stained, and that neuronal cell bodies and neurites emanating from there were negative. These results strongly suggest that the 66B2 antigen observed in the CNS is an extracellular matrix component secreted from nonneuronal cells. These developmental changes in the 66B2 immuno‐reactivity in the CNS presumably reflect dynamic changes of an extracellular matrix in the CNS that are accompanied by axonogenesis or synaptogenesis. © 1992 John Wiley & Sons, Inc.
Environmental influences on neural crest cell migration
Authors: Bronner‐Fraser Marianne
Published: January 2005

Neural crest cells migrate extensively and interact with numerous tissues and extracellular matrix components during their movement. Cell marking techniques have shown that neural crest cells in the trunk of the avian embryo migrate through the anterior, but not posterior, half of each sclerotome and avoid the region around the notochord. A possible mechanism to account for this migratory pattern is that neural crest cells may be inhibited from entering the posterior sclerotome and the perinotochordal space. Thus, interactions with other tissue may prescribe the pattern of neural crest cell migration in the trunk. In contrast, interactions between neural crest cells and the extracellular matrix may mediate the primary interactions controlling neural crest cells migration in the head region. © 1993 John Wiley & Sons, Inc.
Symmetrical segregation of potassium channels at cytokinesis
Authors: Lenzi David , Radke Kathryn , Wilson Martin
Published: January 2005

To determine how voltage‐gated ion channels segregate between sibling cells at cytokinesis, we used a whole‐cell patch clamp to measure the electrophysiological phenotypes of siblings within 45 min of division. Recently born siblings in an immortalized line of embryonic retinal cells were identified as pairs of spherical cells adhering to one another. All siblings were electrically coupled when cells were simultaneously voltage clamped, whereas nonsiblings were not coupled. Twelve paris of siblings were electrically isolated by mechanical separation so that their phenotypes could be measured independently. Cells expressed two principal membrane conductances, delayed rectifier‐like (IK) and inward rectifier (IK(IR)) potassium currents. Despite qualitative and quantitative variability in IK and IK(IR) expression within the population, each cell of a given pair expressed similar steady‐state current densities between –110 and +50 mV. We estimated IK(IR) slope conductance by blocking the current specifically with 5 mM Cs and calculated IK(IR) ratios in siblings and nonsiblings. Three pairs of siblings expressed IK(IR) ratios of approximately 1.2, while ratios in three pairs of adhered nonsiblings varied between 1.6 and 5.4. When currents were sampled continuously through cytokinesis by using the perforated‐patch recording mode, current amplitude showed no net change within 30 min of division. Because channel number did not appear to change in siblings during this interval, parental channels were inherited by each daughter in proportion to the area of membrane received. Heterogeneity therefore arises after siblings reenter interphase and is not due to the asymmetrical segregation of channels at cytokinesis. © 1993 John Wiley & Sons, Inc.
Synaptic repression at crayfish neuromuscular junctions. II. Evidence for calcium involvement
Authors: Gupta Anuj , Smith Edward , Vélez Samuel J.
Published: January 2005

The inability of synaptic junctions to generate normalsized postsynaptic potentials under normal physiological conditions was studied at crayfish neuromuscular synapses. Synaptic repression in the superficial flexor muscle system of the crayfish was induced by surgery: the nerve was cut in the middle of the target field, and the lateral muscle fibers were removed. After this surgery, the remaining medial synapses were unable to generate normal‐sized junction potentials (jp) over the medial muscle population. In an attempt to study the mechanism underlying this response, we varied the extracellular calcium concentration of the Ringers solution bathing the preparation, in both repressed and control animals, while monitoring the size of the same junction potential. The junction potential generated by the spontaneous activity of the nerve increased in size with increasing calcium concentrations in control animals, but failed to do so in repressed animals, that is, changes in external calcium concentrations did not affect repressed synapses. However, in the presence of the calcium ionophore A23187, control and repressed synapses both show an increase in the junction potential sizes they generate. Our data suggest that calcium is involved in the mechanisms that underlie synaptic repression in this crustacean neuromuscular system. © 1993 John Wiley & Sons, Inc.
Cues intrinsic to the retina induce nAchR gene expression during development
Authors: Hankin M. H. , Hoover F. , Goldman D.
Published: January 2005

Recent studies of optic nerve regeneration in goldfish have indicated that the optic tectum plays an important role in modulating the induction of nicotinic acetylcholine receptor (nAChR) gene expression in regenerating retinal ganglion cells (Hieber, Agranoff, and Goldman, 1992, J. Neurochem. 58:1009–1015). These observations suggest that induction of these genes is regulated by brain target regions. The appearance of nAChR mRNA in the developing rat retina coincides with a time when ganglion cells are sending axons to their brain targets (Hoover and Goldman, 1992, Exp. Eye Res. 54:561–571). Might a mechanism similar to that seen during goldfish optic nerve regenerationalso mediate induction of nAChR gene expression during development of the mammalian retina? This possibility was tested by either transplanting embryonic rat retina to different brain regions, or explanting it to organ culture and assaying for nAChR gene expression. These studies showed that induction of the nAChR genes in developing rat retina is independent of the environment in which the retina develops. These results indicate that either the retinal microenvironment or a signal intrinsic to the retinal ganglion cell is responsible for this induction. © 1993 John Wiley & Sons, Inc.
Effects of development and altered gravity conditions on cytochrome oxidase activity in a vestibular nucleus of the larval teleost brain: A quantitative electronmicroscopical study
Authors: Paulus Ulrike , Körtje Karl‐Heinz , Rahmann Hinrich
Published: January 2005

The mitochondrial enzyme, cytochrome oxidase, was localized cytochemically in the nucleus magnocellularis, a primary relay nucleus of vestibular information within the area octavolateralis in the fish brain. Larvae of the cichlid fish Oreochromis mossambicus were analyzed at different developmental stages (4, 10, and 35 days posthatching) and after long‐term exposure (8 days) to increased gravity (2–4 g). Quantification of highly reactive, moderately reactive, and nonreactive mitochondria reveals differences in the cytochrome oxidase activity of various cellular structures, for example, perikarya of neurons, presynaptic terminals, and myelinated and nonmyelinated cell profiles. Cytochrome oxidase activity in the mitochondria of neuronal perikarya increases during development which parallels the differentiation of the area octavolateralis. This possibly reflects the increasing energy demand during maturation and innervation of the magnocellular nucleus. Hyper‐g‐exposure of the larvae for 8 days (centrifuge) caused a further augmentation of cytochrome oxidase activity in the perikarya within the nucleus magnocellularis. This may reflect an increased oxidative metabolism resulting from the need for compensation of altered inputs from gravity‐sensitive epithelia in the inner ear. Another possibility is that acceleration within a centrifuge causes physiological stress for the animals and, therefore, influences the cytochrome oxidase activity in neurons. © 1993 John Wiley & Sons, Inc.
Different forms of the neurotrophin receptor TrkB mRNA predominate in rat retina and optic nerve
Authors: Jelsma Tony N. , Friedman Hana Hyman , Berkelaar Michelle , Bray Garth M. , Aguayo Albert J.
Published: January 2005

The expression of TrkB mRNAs was investigated in rat retina and optic nerve. A 11.5 kb transcript that encodes full‐length TRKB was found to predominate in Northern blots of retinal RNA. By in situ hybridization, this trkB expression was concentrated in the ganglion cell and inner nuclear layers. Furthermore, an antibody to the full‐length TRKB immunostained retinal ganglion cells and their axons. In contrast, Northern blots of optic nerve RNA showed a prominent 9.5 kb band that encoded a form of the TRKB receptor lacking the tyrosine kinase domain. This species was also detected in both the sciatic nerve and cultured astrocytes and C6 glioma cells. These results suggest that neurons express the full‐length TRKB containing the tyrosine kinase domain, while non‐neuronal cells express the truncated form of the receptor. These two classes of TRKB may mediate different neurotrophic actions in the retina and optic nerve. © 1993 John Wiley & Sons, Inc.
Position, guidance, and mapping in the developing visual system
Authors: Holt Christine E. , Harris William A.
Published: January 2005

Positional identity in the visual system affects the topographic projection of the retina onto its central targets. In this review we discuss gradients and positional information in the retina, when and how they arise, and their functional significance in development. When the axons of retinal ganglion cells leave the eye, they navigate through territory in the central nervous system that is rich in positional information. We review studies that explore the navigational cues that the growth cones of retinal axons use to orient towards their target and organize themselves as they make this journey. Finally, these axons arrive at their central targets and make a precise topographic map of visual space that is crucial for adaptive visual behavior. In the last section of this review, we examine the topographic cues in the tectum, what they are, when, and how they arise, and how retinal axons respond to them. We also touch on the role of neural activity in the refinement of this topography. © 1993 John Wiley & Sons, Inc.
Fiber pathways and positional changes in efferent perikarya of 2.5‐to 7‐day chick embryos as revealed with dil and dextran amiens
Authors: Fritzsch B. , Christensen M. A. , Nichols D. H.
Published: January 2005

The differentiation of facial motoneurons and inner ear (octaval) efferents was examined in chicken embryos by applying Dil or dextran amines to the cut VII/VIII nerve (peripheral label) or to the basal/floor plate of rhombomeres 4/5 (central label). Central labeling found axons of these efferent neurons to leave the brain as early as 2.5 days of incubation. Peripheral labeling identified cell bodies ipsilaterally in rhombomeres 4 and 5 at 2.5 days. Central labeling at 3.5 days showed these fibers to have fully segregated into separate pathways to the facial nerve and the inner ear and that the octaval efferent axons had reached the otocyst wall. By 3.5 days many peripherally labeled octaval efferent somata were found in the floor plate and by 5 days they were found bilaterally. At 6 days, selective peripheral labeling of either the VIIth or VIIIthe nerve showed that the contralateral population consisted of octaval efferents and central label applied to the floor plate of rhombomeres 4/5 identified fibers that entered the octaval nerve via the facial root and entered the vestibular sensory epithelia. To gether these data suggest an initial mingling of two different motoneuron populations (facial and octaval) in rhombomeres 4/5 and a subsequent segregation by differential migration. Our data also find a much earlier arrival of octaval efferent axons at the otic vesicle than previously described and suggest a contralateral migration of many octaval efferents beginning shortly after their axons reach the facial nerve root. © 1993 John Wiley & Sons, Inc.
Distinct mode of microtubule‐associated protein 2 expression in the neuroblastoma/glioma cell line 108CC15/NG108‐15
Authors: Beaman‐Hall C. M. , Vallano M. L.
Published: January 2005

The properties of microtubule‐associated protein‐2 (MAP‐2) expression were examined in a transformed cell line, and compared to neurons from rodent brain where evidence supports both transcriptional and nontranscriptional regulation of MAP‐2 synthesis. A monoclonal antibody that recognizes a common epitope in the adult (HMW MAP‐2) and juvenile (MAP‐2c) forms was used in an immunoblotting assay to assess the protein levels in actively dividing and differentiated neuroblastoma/glioma (108CC15, also designated NG108‐15) cells. Multiply‐phosphorylated MAP‐2c was the predominant form in actively dividing cells, whereas HMW MAP‐2 predominated in differentiated cells, which exhibited several other neuronal‐like properties. A progressive increase in the levels of immunoreactive HMW MAP‐2 was observed with increasing days of cell differentiation using dBcAMP as the inducing agent. However, the absolute levels of both HMW MAP‐2 and MAP‐2c in NG108‐15 cells were significantly lower (at least 10‐fold) than levels measured in rodent brain. To assess whether there are correspondingly lower levels of HMW MAP‐2 and MAP‐2c mRNAs in NG108‐15 cells, relative to rodent brain, a highly sensitive RNA amplification assay (reverse transcription‐polymerase chain reaction; RT‐PCR) was developed. Oligonucleotide primers were designed to specify either HMW MAP‐2 mRNA or MAP‐2c mRNA, and whole tissue RNA extracted from adult and neonatal rodent brain was used to verify the reliability of the RT‐PCR assay. Accordingly, PCR products of the predicted size, specificity, and abundance were obtained, with similar levels of HMW MAP‐2 mRNA and proportionately higher levels of MAP‐2c mRNA in neonatal brain, relative to adult brain. MAP‐2c mRNA was the predominant transcript in actively dividing NG108‐15 cells, and the amount of HMW MAP‐2 mRNA gradually increased and became the predominant transcript in cells exposed to dBcAMP for 6–9 days. Thus, the observed changes in MAP‐2‐specific mRNAs during differentiation paralleled changes in expressed protein, suggesting that MAP‐2 synthesis in NG108y15 cells is transcriptionally controlled. However, the levels of both MAP‐2 mRNAs in NG108‐15 cells were comparable to levels in rodent brain, despite the fact that MAP‐2 protein levels are at least 10‐fold lower in NG108‐15 cells. These data suggest that the low levels of HMW MAP‐2 and MAP‐2c protein expression in NG108‐15 cells are not due to correspondingly lower levels of MAP‐2 mRNAs, and that transformed neuronal cell lines demostrate a unique mode of MAP‐2 regulation. © 1993 John Wiley & Sons, Inc.