bluuebunny/crossref_metadata_2025 huggingface dataset:
Vasopressin‐induced neurotrophism in cultured hippocampal neurons via V1 receptor activation
Authors: Brinton Roberta Diaz , Monreal Alex W. , Fernandez Judivick G.
Published: January 2005

Structural enhancement of nerve cell morphology has been postulated to be an integral step in the cellular process leading to information storage in the nervous system. To investigate this postulate, we determined whether vasopressin (AVP), a neural peptide that can enhance memory function, would enhance the cytoarchitectural features of hippocampal neurons in culture. Results of these studies demonstrated that in the presence of serum, vasopressin (1 μM), induced a significant in crease in the number of neurites, in neuritic length, and in neurite diameter following 48 h of exposure. Morphological complexity was also enhanced following vasopressin exposure as indicated by a significant increase in the number of filopodia/branches, in the sum of branch lengths, and in the number of branch bifurcation points. The number of microspikes decorating neuritic branches was also significantly increased following vasopressin exposure. To determine whether the neurotrophic effects of vasopressin was dependent upon factors present in serum, hippocampal nerve cells were cultured in serum‐free media and exposed to 100–1000 nM AVP. Results of these studies demonstrated that in the absence of serum, AVP induced significant enhancement of hippocampal nerve cell growth and that the minimally effective concentration was reduced from 1 μM, as required in the presence serum, to 100 nM. In addition, the time required for a significant increase in nerve cell growth to become apparent decreased from 48 to 24 h. These results demonstrate that AVP‐induced neurotrophism is not dependent upon unidentified factors in serum. AVP‐induced neurotrophism was found to be mediated by V1 receptor activation. Significant enhancement of nerve cell growth occurred following exposure to V1 receptor agonist (100–1000 nM), whereas exposure to V2 receptor agonist (100–1000 nM) did not increase any of the morphological parameters measured. Considered together, these data indicate that vasopressin can exert a significant neurotrophic effect upon hippocampal nerve cells in culture. Moreover, AVP‐induced neurotrophism is a direct effect and not dependent upon unidentified factors present in serum. Enhancement of hippocampal nerve cell growth occurred in the presence of a specific V1 receptor agonist and not following exposure to a V2 agonist, suggesting that activation of the phosphatidyl inositol pathway via V1 receptor activation mediates AVP‐induced neurotrophism. Results of these studies are discussed with respect to their implications for understanding vasopressin involvement during neural development and induction of cytoarchitectual modifications associated with memory formation. 1994 John Wiley & Sons, Inc.
Spatiotemporal pattern of expression of tenascin‐like molecules in a developing insect olfactory system
Authors: Krull Catherine E. , Morton David B. , Faissner Andreas , Schachner Melitta , Tolbert Leslie P.
Published: January 2005

During the development of the olfactory (antennal)l lobe of the moth Manduca sexta, olfactory sensory axons induce glamerular branching patterns in their target neurons. Glial cells, by surrounding the developing glomerular template, are thought to mediate the developmental influence of olfactory axons on these branching patterns. Previous studies have demonstrated that, in the absence of glia, neurons in the antennal lobe branch in an aglomerular fashino, even in the presence of competent antennal axosn (Oland and Tolbert, 1988, J. Comp. Neurol. 278:377–387; Oland et al., 1988, J. Neurosci. 8:353–367). We have begun to explore the molecular basis by which glial cells could influence patterns of neurite branching. For this work, we have utilized immonocytochemical techniques and a partial biochemical analysis to demonstrate that molecules antigenically similar and comparable in size to mammalian tenascin are localized on the neuropil‐associated glial cells that form borders aroudn glomeruli in the developig antennal lobe. These tenascin‐like molecules associated with neuropilar glia are present at critical stages of glomerulus development; tenascin‐like immunoreactivity declines after glomeruli form and become stabilized. Neither the arrival nor the absence of antennal axons in the lobe induces changes in either the molecular forms or the amounts of tenascin‐like molecules. The spatiotemporal pattern of expression to tenascin‐like molecules suggests that they are in a position to participate in the formation of a glomerular neuropil and could form a molecular barrier that constrains neurite outgrowth strictly to glomeruli. © 1994 John Wiley & Sons, Inc.
Characterization and localization of D1 dopamine receptors in the sexually dimorphic vocal control nucleus, area X, and the basal ganglia of european starlings
Authors: Casto Joseph M. , Ball Gregory F.
Published: January 2005

D1 dopamine receptors were pharmacologically characterized and localized by quantitative autoradiography in the basal ganglia of male and female European starlings (Sturnus vulgaris). The D1 selective antagonist SCH 23390 was used to label this receptor subtype. Starlings are songbirds and possess a neural circuit implicated in the learning and production of song. This circuit includes a sexually dimorphic nucleus, area X, that is a subregion of the parolfactory lobe of the basal ganglia and is known from work on zebra finches to receive dopaminergic input from the area ventralis of Tsai. We focused our investigation on the D1‐like receptor subtype because they are abundant in the basal ganglia. Competition studies indicate that a variety of dopaminergic ligands compete with [3H] SCH 23390 for the binding site in an order of potency characteristic of a D1‐like receptor. Autoradiographic studies of the basal ganglia revealed high D1 receptor densities in the avian homologues of the caudate‐putamen and relatively low‐receptor densities were observed in the avian homologue of the globus pallidus. In male starlings, area X could be reliably discerned on the autoradiograms by the higher density of D1 receptors compared to the surrounding parolfactory lobe (LPO). This was also true for females, though nt as reliably as in males. When we compared the mean D1 receptor density in area X for males and females we did not find a significant sex difference. However, we also analyzed the data by comparing sex differences in the degree to which area X has a higher receptor density in comparison with the surrounding LPO. When we normalized D1 receptor density in area X relative to the LPO, we did find a significant sex difference. This sex difference in relative receptor density represents another neural sex difference in the song circuit that may mediate sex differences in the learning and production of song in starlings and other songbirds. 1994 John Wiley & Sons, Inc.
The molecular cloning and characterization of potential chick DM‐GRASP homologs in zebrafish and mouse
Authors: Kanki John P. , Chang Susannah , Kuwada John Y.
Published: January 2005

A full‐length zebrafish cDNA clone and a partial mouse cDNA clone similar to chick DM‐GRASPwere isolated and analyzed. The nucleotide sequence of the full‐length zebrafish clone shares 54% identity, and predicts 39% amino acid identity, with chick DM‐GRASP. The partial mouse clone shares 76% nucleotide identity, and predicts 76% amino acid identity, with chick DM‐GRASP. The predicted proteins encoded by both of these clones exhibit conserved structural domains that are characteristic of the chick protein. These features may identify them as a distinct subfamily within the immunoglobulin superfamily of cell adhesion molecules. Express of the zebrafish DM‐GRASP protein is similar to chick DM‐GRASP and is principally restricted to a small subset of developing sensory and motor neurons during axonogenesis. Zebrafish DM‐GRASP expression was temporally regulated and limited to specific axon domains. This regional expression correlated with fasciculated axon domains. These results suggest that the zebrafish and mouse cDNA clones represent the respective fish and mammalian homologs of thick DM‐GRASP. The highly selective expression of zebrafish DM‐GRASP suggests that it is involved in the selective fasciculation and guidance of axons along their normal pathways. 1994 John Wiley & Sons, Inc.
Neurotrophin‐4/5 (NT‐4/5) increases adult rat retinal ganglion cell survival and neurite outgrowth in vitro
Authors: Cohen A. , Bray G. M. , Aguayo A. J.
Published: January 2005

Retinal ganglion cell (RGC) survival and neurite outgrowth were investigated in retinal explants from adult rats. Neutrotrophin‐4/5 (NT‐4/5) caused dose‐dependent increases in neurite outgrowth with one‐half maximal effects at approximately 0.5 ng/ml and maximal effects at 5 ng/ml. In explants treated for 7 days, the actions of NT‐4/5 were similar to those of brain‐derived neurotrophic factor (BDNF); with either neurotrophin, nearly twice as many RGCs survived and there was a two‐ to threefold increase in the number of neurites formed by RGCs. Combinations of saturating concentrations of NT‐4/5 and BDNF did not enhance these in vitro effects, implying that both neurotrophins share a common signaling pathway. In contrast, nerve growth factor (NGF), neurotrophin‐3 (NT‐3), or ciliary nuerotrophic factor (CNTF) appeared to exert minimal influences on RGC survival or neurite outgrowth. 1994 John Wiley & Sons, Inc.
Reciprocal regulation of estrogen and NGF receptors by their ligands in PC12 cells
Authors: Sohrabji Farida , Greene Lloyd A. , Miranda Rajesh C. , Toran‐Allerand C. Dominique
Published: January 2005

Recent work has shown that estrogen receptor mRNA and protein co‐localize with neurotrophin receptor systems in the developing basal forebrain. In the present study we examined the potential for reciprocal regulation of estrogen and neurotrophin receptor systems by their ligands in a prototypical neurotrophin target, the PC12 cell. using in situ hybridization histochemistry, RT‐PCR and a modified nuclear exchange assay, we found both estrogen receptor mRNA and estrogen binding in PC12 cells. Moreover, while estrogen binding was relatively low in naive PC12 cells, long‐term exposure to NGF enhanced estrogen binding in these cells by sixfold. Furthermore, concurrent exposure to estrogen and NGF receptor mRNAs deifferentially regulated the expression of the two NGF receptor mRNAs. The expression of trkA mRNA was up‐regulated, while p75NGFR mRNA was down‐regulated transiently. The present data indicate that NGF may increase neuronal sensitivity to estrogen, and that estrogen, by differentially regulating p75NGFR and trkA mRNA, may alter the ratio fo the two NGF receptors, and, conseuqnetly, neurotrophin responsivity. In view of the widespread co‐localization of estrogen and neurotrophin receptor systems in the developing CNS, the reciprocal regulation of these receptor systems by NGF and estrogen may have important implications for processes governing neural maturation and the maintenance of neural funciton. 1994 John Wiley & Sons, Inc.
Response of thoracic interneurons to tactile stimulation in the cockroach, Periplaneta americana
Authors: Ritzmann Roy E. , Pollack Alan J.
Published: January 2005

Receåfindings indicate that cockroaches escape in response to tactile stimulation as well as they do in response to the classic wind puff stimulus. The thoracic interneurons that receive inputs from ventral giant interneurons also respond to tactile stimulation and therefore, represent a potential site of convergence between wind and tactile stimulation as well as other sensory modalities. In this article, we characterize the tactile response of these interneurons, which are referred to as type‐A thoracic interneurons (TIAs). In response to tactile stimulation of the body cuticle, TIAs typically respond with a short latency biphasic depolarization which often passes threshold for action potentials. The biphasic response is not typical of responses to wind stimulation nor of tactile stimulation of the antennae. It is also not seen in tactile responses of thoracic interneurons that are not part of the TIA group. The responses of individual TIAs to stimulation of various body locations were mapped. The left‐right directional properties of TIAs are consistent with their responses to wind puffs from various different directions. Cells that respond equally well to wind from the left and right side also respond equally well to tactile stimuli on the left and right side of the animal's body. In contrast, cells that are biased to wind on one side are also biased to tactile stimulation on the same side. In general, tactile responses directed at body cuticle are phasic rather than tonic, occurring both when the tactile stimulator is depressed and released. The response reflects stimulus strength and follows repeated stimulation quite well. However, the first phase of the biphasic response is more robust during high‐frequency stimulation than the second phase. TIAs also respond to antennal stimulation. However, here the response characteristics are complicated by the fact that movement of either antenna evokes descending activity in both left and right thoracic connectives. The data suggest that the TIAs make up a multimodal site of sensory convergence that is capable of generating an oriental escape turn in response to any one of several sensory cues. 1994 John Wiley & Sons, Inc.
Neuronal responses to purinoceptor agonists in the leech central nervous system
Authors: Backus Kurt H. , Braum Susanne , Lohner Frank , Deitmer Joachim W.
Published: January 2005

Exracellular nucleotides like ATP and its derivatives are possible chemical messengers in vertebrate nervous systems. In invertebrate nervous systems, however, little is known about their role in neurotransmission. We have studied the reponse of identified neurones of the leech Hirudo medicinalis to the purinoceptor agonist ATP, ADP, AMP, and adenosine using conventional intracellular microelectrodes and whole‐cell patch‐clamp recording. Bath application of the agoinsts depolarized the different neurons, but not neuropil glial cells. The most effective responses (up to 10 mV) were observed with ATP (100 μM) or ADP (100 μM) in the noxious and touch cells. In most neurons the nonhydrolyzable ATP derivative ATP‐γ‐S (5 μM) induced larger depolarizations that 100 μM ATP, indicating that most of the potency of ATP is lost presumably due to its degradation by ectonucleotidases. In medial noxios cells, ATP (100 μM) induced an inward current of 1.7 ± 1.1 nA at a holding potential of −60 mV. The ATP‐induced current‐voltage relationship showed an inward rectification and a reversal potential close to 0 m V. In a Na+‐free extracellular solution, the ATP‐induced inward current decreased and in a Na+‐ and Ca2+‐free saline only a small residual current persisted. The possible P2 purinoceptor antagonist suramin did not antagonize the ATP‐induced current, but itself evoked an inward current and a conductance increase. We conclude that ATP activates nonselective cation channels in medial noxious cells of the leech with the order of potency of purinoceptor agonists ATP ≥ ADP > AMP. The results suggest that these cells express purinoceptors of the P2 type. 1994 John Wiley & Sons, Inc.
The role of neurotrophins in the developing nervous system
Authors: Davies Alun M.
Published: January 2005

Neurotrophins were originally identified by their ability to promote the survival of developing neurons. However, recent work on these proteins indicates that they may also influence the proliferation and differentiation of neuron progenitor cells and regular several differentiated traits of neurons throughout life. Moreover, the effects of neurotrophins on survival have turned out to be more complex than originally thought. Some neurons switch their survival requirements from one set of neurotrophins to another during development, and several neurotrophins may be involved in regulating the survival of a population of neurons at any one time. Much of our understanding of the developmental physiology of neurotrophins has come from studying neurons of the peripheral nervous system. Because these neurons and their progenitors are segregated into anatomically discrete sites, it has been possible to obtain these cell for in vitro experimental studies from the earliest stage of their development. The recent generation of mice having null mutations in the neurotrophin and neurotrophin receptor genes has opened up an unparalleled opportunity to assess the physiological relevance of the wealth of data obtained from these in vitro studies. Here I provide a chronological account of the effects of members of the NGF family of neurotrophins on cells of the neural lineage with special reference to the peripheral nervous system. 1994 John Wiley & Sons, Inc.
Neurotrophin signal transduction by the Trk receptor
Authors: Kaplan David R. , Stephens Robert M.
Published: January 2005

The initial event in the neuronal differentiation of PC12 cells is the binding of the neurotrophin nerve growth factor (NGF) to the Trk receptor. This interaction stimulates the intrinsic tyrosine kinase activity of TRk, initiating a signalling cascade involving the phosphorylation of intracellular proteins on tyrosine, serine, and threonine residues. These signals are then in turn propagated to other messengers, ultimately leading to differentiation, neurotrophin‐dependent survival and the loss of proliferative capacity. To transmit NGF signals, NGF‐activated Trk rapidly associated with the cytoplasmic proteins, SHC, PI‐3 kinase, and PLC‐γ1. These proteins are involved in stimulating the formation of various second messenger molecules and activating the Ras signal transduction pathway. Studies with Trk mutants indicate that the acivation of the Ras pathway is necessary for complete differentiation of PC12‐derived cells and for the maintenance of the differentiated phenotype. Trk also induces the tyrosine phosphorylation of SNT, a specific target of neurotrophic factor activity in neuronal cells. This review will discuss the potential roles of Trk and the proteins of the Trk signalling pathways in NGF function, and summarize our attempts to understand the mechanisms used by Trk to generate dthe many phenotypic responses of PC12 cells to NGF. 1994 John Wiley & Sons, Inc.
Ciliary neurotrophic factor
Authors: Sendtner M. , Carrol P. , Holtmann B. , Hughes R. A. , Thoenen H.
Published: January 2005

Ciliary neurotrophic factor (CNTF) was first identified and partially purified from embryonic chick eye tissues. Subsequently, it was shown that CNTF is also present in large amounts in sciatic nerves of adult rats and rabbits, which led to its final purification and cloning. CNTF is not secreted by the classical secretory pathway involving the endoplasmatic reticulum and Golgi complex, but can be detected in high quantities within the cytoplasm of myelinating Schwann cells and astrocytes using immunohistochemistry. CNTF supports survival and / or differentiation of a variety of neuronal cell types including sensory, sympathetic and motoneurons. Also, nonneuroanl cells, such as oligodendrocytes, microglial cells, liver cells, and skeletal muscle cells, respond to exogenously administered CNTF, both in vitro and in vivo. During development, expression of CNTF is very low, if indeed it is expressed at all, and the phenotype of mice lacking endogenous CNTF, suggesting that CNTF after inactivation of the CNTF gene by homologous recombination suggests that CNTF does not play a crucial role for responsive cells during embryonic development. However, motoneurons are lost postnatally in mice lacking endogenous CNTF, suggesting that CNTF acts physiologically on the maintenance of these cells. The ability of exogenous CNTF to protect against motoneuron loss following lesion or in other animal models indicates that CNTF might be useful in the treatment of human motoneuron disorders, provided appropriate means of administration can be found. 1994 John Wiley & Sons, Inc.
The growth of PC‐12 neurites is biased towards the anode of an applied electrical field
Authors: Cork R. J. , McGinnis M. E. , Tsai J. , Robinson K. R.
Published: January 2005

We have exposed cultures of PC12 cells to uniform DC electric fields following the addition of NGF. The success of these experiments relied upon the design of new chambers enabling fields to be applied to mammalian cell cultures. After 48 h of field application, the distribution of neurite outgrowths was biased towards the anode. More neurites faced the anode than would be expected if growth was uniform. The magnitude of this bias was strongly correlated with field strenght, with a threshold value of about 1 mV/mm. At field strengths above 30 mV/mm, the neurites growing towards the cathode were shorter than those growing towards the anode or perpendicular to the field. This response was not correlated with field strenght. This report confirms that mammalian neurons respond to electrical fields and supports the notion that neurites are influenced by endogenous electrical fields during development. As far as we are aware, this is the only report the documents a response towards the anode. 1994 John Wiley & Sons, Inc.
GABAA receptor subunit polypeptides increase in parallel but exhibit distinct distributions in the developing rat cerebellum
Authors: Nadler Laurie S. , Guirguis Eman R. , Siegel Ruth E.
Published: January 2005

The GABAA receptor, a multisubunit ligand‐gated ion channel, plays a central role in cell–cell communication in the developing and adult nervous system. Although the developmental expression of mRNAs encoding many subunit isoforms has been extensively characterized throughout the central nervous system, little is known concerning the relationship between subunit mRNA and polypeptide expression. To address this issue, we examined the developmental expression of the α1, β2/3, and γ2 subunit polypeptides, subunits that are thought to coassemble in many brain regions. Western blot analysis using subunit‐specific antibodies revealed that the levels of these polypeptides in both the cerebral cortex and cerebellum increased severalfold during the second postnatal week. Whereas polypeptide expression in the cerebellum paralleled that of the corresponding subunit mRNAs, increase in β2/3 and γ2 polypeptide expression in the cerebral cortex occurred in the absence of detectable changes in the mRNA levels. To determine whether the increases in subunit polypeptide expression in the cerebellum were accompanied by changes in distribution, immunohistochemistry was performed. These studies demonstrated that the subunits exhibited different but partially overlapping distributions that remained constant throughout postnatal development. Our findings suggest that although GABAA receptor subunit polypeptide expression may be regulated primarily at the level of the mRNA, additional regulatory mechanisms may play role. Furthermore, the observation that subunit distribution remains constant in the cell bodies of cerebellar Purkinje neurons, which express the α1, β2, β3, and γ2 subunit mRNAs exclusively, suggests that GABAA receptor subunit composition in this cell population does not change during postnatal maturation. 1994 John Wiley & Sons, Inc.
Long‐term survival followed by degradation of neurofilament proteins in severed Mauthner axons of goldfish
Authors: Moehlenbruck Jeffrey W. , Cummings Jennifer A. , Bittner George D.
Published: January 2005

The morphology and protein composition of intact and severed Mauthner axons (M‐axons) from goldfish were examined on electron micrographs, sodium dodecyl sulfate gels, and immunoblots. Neurofilaments were the most common cytoskeletal element on electron micrographs, and neurofilament proteins (NFPs) were the most intensely silver‐stained bands in M‐axoplasm microdissected from control M‐axons. NFPs at about 235, 145, 123, 105, 80, and 60 kD in M‐axoplasm were identified with four monoclonal and three polyclonal antibodies. Similar immunoblots of samples of the M‐axon myelin sheath (M‐sheath) showed no reactivity to antibodies against NFPs. For up to 62 days following spinal cord severance in goldfish maintained at 15°C, the ultrastructure, protein banding pattern, and anti‐NFP immunoreactivity of severed distal segments of M‐axons did not change compared with control M‐axons. At 62 to 81 days after severance, novel bands appeared in many silver‐stained gels and anti‐NFP immunoblots of distal M‐axons. NFP bands completely disappeared from distal M‐axon segments of some M‐axons as early as 72 days after severance. However, NFP bands persisted in some distal segments for up to 81 days after severance. The degradation of NFPs occurred equally along the entire length of a distal M‐axon segment, that is, there was no indication of a proximal‐to‐distal or distal‐to‐proximal sequence of NFP degradation in distal segments of severed M‐axons. These biochemical data were consistent with morphological data that showed little change in the diameter or ultra‐structure of severed M‐axons held at 15°C for about 2 months followed by a rapid collapse of the entire distal segment at 72 to 85 days postseverance. 1994 John Wiley & Sons, Inc.
Differential estrogen accumulation among populations of projection neurons in the higher vocal center of male canaries
Authors: Johnson Frank , Bottjer Sarah W.
Published: January 2005

The higher vocal center (HVC) of adult male canries undergoes a seasonal change in volume that corresponds to seasonal modifications of vocal behavior: HVC is large when birds produce stereotyped song (spring) and is small when birds produce plastic song and add new song syllables into their vocal repertoires (fall). We reported previously that systemic exposure to testosterone (T) produces an increase in the volume of HVC similar to that observed with long‐day photoperiods. T‐induced growth of HVC occured regardless of wheter the borders of HVC were defined by Nissl‐staining, the distribution of androgen‐concentrating cells, or the distribution of projection neurons [separate neuronal populations within HVC project to the robust nucleus of the archistriatum (RA) and to Area X of the avian striatum (X)]. In the present study we used steroid autoradiography to determine whether T can influence the distribution of HVC cells that bind estrogen, and we combined estrogen autoradiography with retrograde labeling to determine whether HVC neurons that project to RA versus X differ in their ability to accumulate estrogen. Results showed that T increased the volume of Nissl‐defined HVC and although HVC contained a low density of estrogen‐concentrating cells, T increased the spatial distribution of these cells to match the Nissl borders of HVC. We also identified a region containing a high density of estrogenconcentrating cells located medial to HVC [we call this region paraHVC (pHVC)], and T also increased the volume of pHVC. pHVC also contained numerous X‐projecting neurons, but few if any RA‐projecting neurons. Double‐labeling analysis revealed the RA‐projecting neurons did not accumulate estrogen, a small percentage of X‐projecting neurons in HVC accumulated estrogen, and the majority of X‐projecting neurons in pHVC showed heavy accumulation of estrogen. The data reported here and in our previous article suggest distinct roles for gonadal steroids within the HVC‐pHVC complex: estrogens are concentrated by neurons that project to a striatal region that influences vocal production during song learning (X), whereas androgens are concentrated primarily by neurons that project to a motor region that is involved in vocal production during both song learning and the recitation of already‐learned song (RA). © 1995 John Wiley & Sons, Inc.
Embryonic fibronectins are up‐regulated following peripheral nerve injury in rats
Authors: Mathews Greta A. , Ffrench‐Constant Charles
Published: January 2005

Fibronectin mRNAs that include the alternatively spliced exons EIIIA, EIIIB, and V are prevalent during embryogenesis, and EIIIA and EIIIB reappear during wound healing. Using ribonuclease protection analyses, we found an up‐regulation of V120 (containing the α4β1 integrin binding site), as well as EIIIA, and EIIIB in fibronectin mRNAs in the crush‐injured adult rat sciatic nerve. In situ hybridization using splice variant‐specific probes revealed that cells within endoneurial tubes of the injured nerve synthesize these embryonic forms of fibronectin. Our results suggest that embryonic fibronectins synthesized within the nerve contribute to the permissiveness of the peripheral nervous system to axon regrowth and a mechanism by which alternative splicing of the V region in fibronectin mRNA could enhance nervous system regeneration. © 1995 John Wiley & Sons, Inc.
Suppression of programmed neuronal death by a thapsigargin‐induced Ca2+ influx
Authors: Lampe Patricia A. , Cornbrooks Ellen B. , Juhasz Anna , Johnson Eugene M. , Franklin James L.
Published: January 2005

Rat sympathetic neurons undergo programmed cell death (PCD) in vitro and in vivo when they are deprived of nerve growth factor (NGF). Chronic depolarization of these neurons in cell culture with elevated concentrations of extracellular potassium ([K+]o) prevents this death. The effect of prolonged depolarization on neuronal survival is thought to be mediated by a rise of intracellular calcium concentration ([Ca2+]i) caused by Ca2+ influx through voltage‐gated channels. In this report we investigate the effects of chronic treatment of rat sympathetic neurons with thapsigargin, an inhibitor of intracellular Ca2+ sequestration. In medium containing a normal concentration of extracellular Ca2+ ([Ca2+]o), thapsigargin caused a sustained rise of intracellular Ca2+ concentration and partially blocked death of NGF‐deprived cells. Elevating [Ca2+]o in the presence of thapsigargin further increased [Ca2+]i, suggesting that the sustained rise of [Ca2+]i was caused by a thapsigargin‐induced Ca2+ influx. This treatment potentiated the effect of thapsigargin on survival. The dihydropyridine Ca2+ channel antagonist, nifedipine, blocked both a sustained elevation of [Ca2+]i and enhanced survival caused by depolarization with elevated [K+]o, suggesting that these effects are mediated by Ca2+ influx through L‐type channels. Nifedipine did not block the sustained rise of [Ca2+]i or enhanced survival caused by thapsigargin treatment, indicating that these effects were not mediated by influx of Ca2+ through L‐type channels. These results provide additional evidence that increased [Ca2+]i can suppress neuronal PCD and identify a novel method for chronically raising neuronal [Ca2+]i for investigation of this and other Ca2+‐dependent phenomena. © 1995 John Wiley & Sons, Inc.
The Ca2+ influx induced by β‐amyloid peptide 25–35 in cultured hippocampal neurons results from network excitation
Authors: Brorson James R. , Bindokas Vytautas P. , Iwama Toshi , Marcuccilli Charles J. , Chisholm Jane C. , Miller Richard J.
Published: January 2005

Although a neurotoxic role has been postulated for the β‐amyloid protein (βAP), which accumulates in brain tissues in Alzheimer's disease, a precise mechanism underlying this toxicity has not been identified. The peptide fragment consisting of amino acid residues 25 through 35 (βAP25‐35), in particular, has been reported to be toxic in cultured neurons. We report that βAP25‐35, applied to rat hippocampal neurons in culture, caused reversible and repeatable increases in the intracellular Ca2+ concentration ([Ca2+]i), as measured by fura 2 fluorimetry. Furthermore, βAP25‐35 induced bursts of excitatory potentials and action potential firing in individual neurons studied with whole cell current clamp recordings. The βAP25‐35–induced [Ca2+]i elevations and electrical activity were enhanced by removal of extracellular Mg2+, and they could be blocked by tetrodotoxin, by non‐N‐methyl‐D‐aspartate (NMDA) and NMDA glutamate receptor antagonists, and by the L‐type Ca2+ channel antagonist nimodipine. Similar responses of bursts of action potentials and [Ca2+]i increases were evoked by βAP1‐40. Responses to βAP25‐35 were not prevented by pretreatment with pertussis toxin. Excitatory responses and [Ca2+]i elevations were not observed in cerebellar neuron cultures in which inhibitory synapses predominate. Although the effects of βAP25‐35 depended on the activation of glutamatergic synapses, there was no enhancement of kainate‐ or NMDA‐induced currents by βAP25‐35 in voltage‐clamp studies. We conclude that βAP25‐35 enhances excitatory activity in glutamatergic synaptic networks, causing excitatory potentials and Ca2+ influx. This property may explain the toxicity of βAP25–35. © 1995 John Wiley & Sons, Inc.
Cell death, gliosis, and synaptic remodeling in the hippocampus of epileptic rats
Authors: Represa Alfonso , Niquet Jérôme , Pollard Hélène , Ben‐Ari Yehezkel
Published: January 2005

Seizures set in motion complex molecular and morphological changes in vulnerable structures, such as the hippocampal complex. A number of these changes are responsible for neuronal death of CA3 and hilar cells, which involves necrotic and apoptotic mechanisms. In surviving dentate granule cells seizures induce an increased expression of tubulin subunits and microtubule‐associated proteins, suggesting that an overproduction of tubulin polymers would lead to a remodeling of mossy fibers (the axons of granule cells). In fact, these fibers sprout in the dentate gyrus to innervate granule cell dendrites, creating recurrent excitatory circuits. In contrast, terminal mossy fibers do not sprout in the CA3 field. Navigation of mossy fiber's growth cones may be facilitated by astrocytes, which would exert differential effects by producing and excreting cell adhesion and substrate molecules. In the light of the results discussed here, we suggest that in adult brain activated‐resident astrocytes (nonproliferating, tenascin‐negative, neuronal cell‐adhesion molecule‐positive astrocytes) could contribute to the process of axonal outgrowth and synaptogenesis in the dentate gyrus, while proliferating astrocytes, tenascin‐positive, could impede any axonal rearrangement in CA3. © 1995 John Wiley & Sons, Inc.
Molecular correlates between reactive and developmental plasticity in the rat hippocampus
Authors: Khrestchatisky Michel , Ferhat Lotfi , Charton Gérard , Bernard Anne , Pollard Hélène , Represa Alfonso , Ben‐Ari Yehezkel
Published: January 2005

Area CA3 of the hippocampus is the most epileptogenic structure of the brain. Various studies have shown that kainate‐induced experimental epilepsy in rats and human cases of epilepsy are associated with sprouting of the mossy fibers of the dentate granule neurons and selective loss of pyramidal neurons, notably in the CA3‐CA4 areas of Ammon's horn. In experimental models of epilepsy, brief seizure activity initiates a cascade of molecular alterations that will contribute to changes in the expression of numerous genes, which can last several weeks. The products of some of these genes will contribute to the permanent state of enhanced synaptic efficiency, to the sprouting and formation of novel excitatory synapses, and possibly to neuronal cell loss. The expression of genes encoding transcription factors and numerous growth factors is rapidly altered following seizure episodes. Based on observations in vivo and in vitro in cultured hippocampal neurons, it is hypothesized that an interplay between transcription and growth factors, because of their pleiotropic effects on the regulation of effector genes, may be instrumental in coupling transient extracellular stimuli to irreversible cellular alterations. © 1995 John Wiley & Sons, Inc.
mRNA distribution within dendrites: Relationship to afferent innervation
Authors: Steward Oswald , Wallace Christopher S.
Published: January 2005

The majority of neuronal mRNAs are confined to cell bodies, but a few mRNAs are present at high levels in dendrites. Here we report an initial analysis of the relationship between afferent innervation and the distribution of mRNA within dendritic fields. In situ hybridization techniques were used to compare the subcellular distribution of dendritic mRNAs in principal neurons of the hippocampal formation in vivo. The mRNA encoding the α subunit of calcium/calmodulin dependent protein kinase II (CAMII kinase) was present at high levels throughout the layers that contain the dendrites of hippocampal pyramidal cells and dentate granule cells. In contrast, the mRNA encoding the high molecular weight microtubule‐associated protein MAP2 had a more limited distribution. In the dentate gyrus, labeling for MAP2 was present in a discrete band in the lamina containing proximal dendrites and decreased to low levels in laminae containing distal dendrites. This laminar pattern resembles the distinct terminations of the commissural/associational projection (high MAP2 labeling) and the entorhinal projection (lower MAP2 labeling) upon dendrites of granule cells. To determine if the differential distribution of dendritic mRNAs was regulated by either the presence or activity of afferents, we evaluated mRNA distribution in the dentate molecular layer following (1) removal of the entorhinal input by lesions of the entorhinal cortex or (2) prolonged delivery of potentiating stimulation to entorhinal afferents. Denervation led to modest decreases in the levels of mRNAs for both CAMII and MAP2 but did not lead to detectable alterations in mRNA distribution. Also, prolonged stimulation did not lead to detectable alterations in MAP2 or CAMII mRNA distribution, although such stimulation clearly elevated the expression of mRNA for glial fibrillary acidic protein (GFAP). © 1995 John Wiley & Sons, Inc.
A motoneuron spared from steroid‐activated developmental death by removal of descending neural inputs exhibits stable electrophysiological properties and morphology
Authors: Fahrbach Susan E. , DeLorme Andre W. , Klukas Kathleen A. , Mesce Karen A.
Published: January 2005

Neurons die during the development of nervous systems. The death of specific, idenified motoneuros during metamorphosis of the tobacco hornworm, Manduca sexta, provides an accessible model system in which to study the regulation of postembryonic neuronal death. Hormones and descending neural inputs have been shown toinfluence the survival of abdominal motoneurons during the first few days of adult life in this insect. Motoneurons prevented from undergoing the normal process of developmental degeneration by removal of neural inputs were examined at the physiological and structural levels using several cell imaging techniques. Although these neurons lost their muscle targets and experienced the endocrine cue that normally triggers death, they showed no overt electrophysiological or morphological signs of degeneration. Thus, by appropriate intervention, the MN‐12 motoneuron can be spared from developmental neuronal death and remain as a functioning supernumerary element in the mature nervous system. © 1995 John Wiley & Sons, Inc.
Agrin mRNA variants are differentially regulated in developing chick embryo spinal cord and sensory ganglia
Authors: Ma Enbo , Morgan Rodney , Godfrey Earl W.
Published: January 2005

Agrin is a synapse‐organizing protein synthesized and externalized by motor neurons in the spinal cord, which organizes the postsynaptic apparatus of the developing neuromuscular jucntion. Agin mRNA in the nervous system consists of several alternatively spliced variants. Splicing of agrin gene transcripts at the major site of variability results in four variants: encoding 8 (B8) or 11 (B11) amino acid inserts, both (B19), or a predominant variant (B0) without inserts. The insert‐containing variants are neuron specific and encode agrin proteins with greater synapse‐organizing activity than the B0 variant. Here, we report the localization and developmental regulation of agrin mRNA variants in chick embryo spinal cord and dorsal root ganglia. In situ hybridization using antisense oligodeoxynucleotide (ODN) probes specific for the B8 and B11 sequences shows that the neuorn‐specific variants are concentrated in ventrolateral cells of the chick embryo spinal cord, presumably motor neurons, begining at embryonic day 4 (E4). By E14, the insert‐containing mRNAs are found almost exclusively in presumptive motor neurons. These variants are also found in dorsal root ganglia and sympathetic ganglia, but not in non‐neural tissues. Analysis by polymerase chain reaction showed that the B11 and B19 mRNA variatns appeared in spinal cord at E4, whereas the B8 variant was first seen at E14. During development, B11 decreased and disappeared by E20, whereas B8 increased from E14 to E20. A similar time course was seen in dorsal root ganglia. The greatest acetylcholine receptor‐aggregating activity in the spinal cord was seen from E6 to E10, coincident with the highest proportion of B11‐containing transcripts and with the peak of synaptogenesis in limb muscles. These data provide the first evidence linking appearance of the neuron‐specific agrin mRNA variants with expression of the functional protien. The B11 and B19 variants appeared in E2 (stage 15) neural tubes cultured for 2 days with or without notochord and trunk tissues, indicating that there is no peripheral signal required to induce these agrin mRNA variants in developing motor neurons. © 1995 John Wiley & Sons, Inc.
Changes in the macrophage population of the rat superior cervical ganglion after postganglionic nerve injury
Authors: Schreiber R. C. , Shadiack A. M. , Bennett T. A. , Sedwick C. E. , Zigmond R. E.
Published: January 2005

Following peripheral nerve transection, a series of biochemical changes occurs in axons and Schwann cells both at the site of lesion and distal to it. Macrophages differentiated from monocytes that invade the area in response to transection (elicited macrophages) and, perhaps, also macrophages normally present in the tissue (resident macrophages) play important roles in these changes. In addition, nerve transection produces changes in the cell bodies of axotomized neurons and their surrounding glial cells, located at some distance from the lesion. To determine whether macrophages might play a role in the changes occurring in the superior cervical ganglion (SCG) after axotomy, we examined the presence of macrophages before and after axonal damage. The monoclonal antibodies ED1, ED2, and OX6 were used, each of which recognizes a somewhat different population of macrophages. Ganglia from normal rats contained a population of resident cells that were ED2+ but very few that were ED1+. Within 2 days after the postganglionic nerves were transected, the number of ED1+ cells increased substantially, with little change in immunostaining for ED2. These data, in combination with published studies on other tissues, suggest that ED1 in the SCG is selective for elicited macrophages and ED2 for resident macrophages. OX6 immunostaining was prominent in normal ganglia but also increased significantly after axotomy, suggesting that it reflects both macrophage populations. Systemic administration of 6‐hydroxydopamine, a neurotoxin that causes the destruction of sympathetic nerve endings, also produced an increase in ED1 immunostaining. Thus, the change in ED1 immunostaining in the SCG does not require surgery, with the attendant servering of local blood vessels and connective tissue, but rather only the disconnection of sympathetic neurons from their end organs. The time course of the invasion of monocytes after axotomy indicates that this process is not required to trigger the biochemical changes occurring in the ganglion within the first 24 h. On the other hand, the existence of a resident population of macrophages raises the possibility that changes in those cells might be involved. © 1995 John Wiley & Sons, Inc.
Aromatase and 5β‐reductase activity in cultures of developing zebra finch brain: An investigation of sex and regional differences
Authors: Wade Juli , Schlinger Barney A. , Arnold Arthur P.
Published: January 2005

Estrogen treatment of hatchling female zebra finches causes the masculine development of singing behavior and of the telencephalic brain regions involved in the control of song. However, early estrogen treatment of males also blocks masculine development of copulatory behavior, presumably controlled by diencephalic regions. In an effort to determine whether the differences in estrogen action are related to sex and regional differences in androgen metabolism (estrogen synthesis or androgen inactivation), we measured aromatase and 5β‐reductase activity in dissociated‐cell cultures made separately from the telencephalon, diencephalon, and also cerebellum of hatching zebra finches under a variety of conditions. Cultures from all three brain regions express high levels of aromatase and 5β‐reductase activity. Comparisons between telencephalic and diencephalic cultures of the activity and kinetics of aromatase suggest that the telencephalic cultures convert androgen to estrogen more efficiently than diencephalic cultures, which might be important in the differential action of estrogen in the two brain regions. However, the activity of neither aromatase nor 5β‐reductase was significantly different between the sexes in either telencephalic or diencephalic cultures. Thus, comparisons between the sexes do not support the idea that differences in posthatching aromatase or 5β‐reductase activity account for the pattern of sexual differentiation of the song and copulatory systems. © 1995 John Wiley & Sons, Inc.
Regulated expression of neurofibromin in migrating neural crest cells of avian embryos
Authors: Stocker Kate M. , Baizer Lawrence , Coston Tiffani , Sherman Larry , Ciment Gary
Published: January 2005

Neurofibromatosis type 1 (NF1) is a common human genetic disease involving various neural crest (NC)‐derived cell types, in particular, Schwann cells and melanocytes. The gene responsible for NF1 encodes the protein neurofibromin, which contains a domain with amino acid sequence homology to the ras‐guanosine triphosphatase activating protein, suggesting that neurofibromin may play a role in intracellular signaling pathways regulating cellular proliferation or differentiation, or both. To determine whether neurofibromin plays a role in NC cell development, we used antibodies raised against human neurofibromin fusion proteins in western blot and immunocytochemical studies of early avian embryos. These antibodies specifically recognized the 235 kD chicken neurofibromin protein, which was expressed in migrating trunk and cranial NC cells of early embryos (E1.5 to E2), as well as in endothelial and smooth muscle cells of blood vessels and in a subpopulation of non‐NC‐derived cells in the dermamyotome. At slightly later stages (E3 to E5), neurofibromin immunostaining was observed in various NC derivatives, including dorsal root ganglia and peripheral nerves, as well as non‐NC‐derived cell types, including heart, skeletal muscle, and kidney. At still later stages (E7 to E9), neurofibromin immunoreactivity was found in almost all tissues in vivo. To determine whether the levels of neurofibromin changed during melanocyte and Schwann cell development, tissue culture experiments were performed. Cultured NC cells were found to express neurofibromin at early time points in culture, but the levels of immunoreactivity decreased as the cells underwent pigmentation. Schwann cells, on the other hand, continued to express neurofibromin in culture. These data suggest, therefore, that neurofibromin may play a role in the development of both NC cells and a variety of non‐NC‐derived tissues. © 1995 John Wiley & Sons, Inc.