bluuebunny/crossref_metadata_2025 huggingface dataset:
Glutamate receptor-induced 45Ca2+ accumulation in cortical cell culture correlates with subsequent neuronal degeneration
Authors: Hartley DM , Kurth MC , Bjerkness L , Weiss JH , Choi DW
Published: March 2018

Murine neuronal and glial cell cultures exposed briefly to glutamate accumulated large amounts of 45Ca2+ from the extracellular medium during the exposure. Most of the accumulation likely reflected influx into neurons, as little accumulation was observed in similarly treated glial cultures. When the concentration of glutamate was varied between 10 and 1000 microM, or exposure duration was varied between 0 and 10 min, the amount of 45Ca2+ accumulation correlated closely with the amount of neuronal death 24 hr later. Both 45Ca2+ accumulation and cell death could be attenuated in a dose-dependent manner by the competitive NMDA antagonist D-aminophosphonovalerate or the noncompetitive antagonist dextrorphan, with IC50 values of approximately 100 microM and 15 microM, respectively. In contrast, neither 45Ca2+ accumulation nor cell death was blocked by the alpha-amino-3-hydroxy-5-methyl-4- isoxazole propionic acid (AMPA)/kainate antagonist 6-cyano-7- nitroquinoxaline-2,3-dione (CNQX) in the presence of high glycine. With brief exposure, high concentrations of AMPA, kainate, or K+ produced much less death or 45Ca2+ accumulation than produced by glutamate, especially if 10 microM MK-801 was included in the exposure medium to block NMDA receptor activation. Kainate- or AMPA-induced 45Ca2+ accumulation or neuronal cell death was blocked with CNQX. However, high K(+)-triggered 45Ca2+ accumulation was only partially blocked with CNQX plus MK-801, consistent with mediation by voltage-gated Ca2+ channels. In addition to measuring the accumulation of 45Ca2+ occurring during agonist exposure, we also assessed accumulation during the 30 min immediately following completion of a 3–5 min exposure to 500 microM NMDA.(ABSTRACT TRUNCATED AT 250 WORDS)
Differential localization of phosphoinositide-linked metabotropic glutamate receptor (mGluR1) and the inositol 1,4,5-trisphosphate receptor in rat brain
Authors: Fotuhi M , Sharp AH , Glatt CE , Hwang PM , von Krosigk M , Snyder SH , Dawson TM
Published: March 2018

The type 1 metabotropic glutamate receptor (mGluR1) is through to act via the phosphoinositide (PI) system with the associated formation of inositol 1,4,5-trisphosphate (IP3) and Ca2+ release. Utilizing immunohistochemistry and in situ hybridization, we have localized protein and mRNA, respectively, for the mGluR1 and the IP3 receptor (IP3R). We have also localized glutamate-linked PI turnover by autoradiography with 3H-cytidine. We observe a striking contrast in localizations of mGluR1 and IP3R both for protein and mRNA. For instance, mGluR1 occurs in the apparent absence of IP3R in neurons of the stratum oriens of the CA1 hippocampus, islands of Calleja, anterodorsal nucleus of thalamus, lateral nucleus of hypothalamus, and the granular cell layer and the deep nuclei of cerebellum. mGluR1 actions in these brain regions may primarily be mediated through the protein kinase C limb of the PI system, as they contain moderate amounts of 3H-phorbol ester binding. The subthalamic nucleus, red nucleus, and Darkshevich's nucleus, which possess high levels of mGluR1, are devoid of both IP3R immunoreactivity and 3H-phorbol ester binding. These reciprocal localizations suggest that mGluR1 actions in many brain areas may not primarily involve IP3, reflecting instead influences on protein kinase C or other second messengers.
Glutathione S-transferase isoenzymes in rat brain neurons and glia
Authors: Johnson JA , el Barbary A , Kornguth SE , Brugge JF , Siegel FL
Published: March 2018

The glutathione S-transferases (GSTs) constitute a family of cytosolic isoenzymes and a structurally unrelated microsomal enzyme that is involved in the detoxication of electrophilic xenobiotics. These enzymes also participate in the intracellular binding and transport of a broad range of lipophilic compounds including bilirubin, and hormones such as the glucocorticoids and thyroid hormones. The present investigation demonstrates that GSTs are present in neurons of the brainstem, forebrain, and cerebellum. An isoenzyme-specific distribution of GSTs was found in cytoplasm, nuclei, and nucleoli. The regional and cellular distribution of cytosolic GSTs in the brain was studied by immunohistochemistry, spectrophotometric enzyme assay, and reverse-phase HPLC. Polyclonal antibody against microsomal GST was strongly reactive with Purkinje cells throughout the cerebellar cortex, and with neurons in the brainstem and hippocampus. Nuclei of Purkinje cells and of neurons in the brainstem, hippocampus, and cerebral cortex were immunopositive for alpha-class GST 1–1 (YaYa), whereas alpha-class GST 2–2 (YcYc) antibody was consistently immunoreactive with the nucleolus, but not with the nucleus or soma. All alpha-class GST antibodies studied were reactive, to various degrees, with astrocytes and choroid plexus; however, ependymal cells of the subventricular zones were immunonegative. alpha-class GST 8–8 (YkYk) immunoreactivity was specifically localized to endothelial cells and/or astrocytic end feet associated with blood vessels. Reverse-phase HPLC indicated that there were also substantial regional differences in the pattern of alpha-, mu-, and pi-class GST subunit expression. For example, the thalamus/hypothalamus had the highest GST activity and greatest concentration of total GST protein and mu-class GST subunit 6 (Yb3), whereas the brainstem had the greatest concentration of pi-class GST subunit (Yp). This regional variation in GST expression may be reflective of regional differences in cell populations. In cerebellar cortex, the concentration of mu-class GST subunit 4 (Yb2) was greatest in the flocculus and lowest in the vermis. This is of clinical interest because the pattern of expression of mu-class GST subunit 4 (Yb2) in the cerebellum coincides with the known regional susceptibility of this structure to degeneration after exposure to toxic or metabolic insults. The vermis is most susceptible to these insults, whereas the lateral lobes and flocculus are most resistant.(ABSTRACT TRUNCATED AT 400 WORDS)
Neurogenesis in adult canary telencephalon is independent of gonadal hormone levels
Authors: Brown SD , Johnson F , Bottjer SW
Published: March 2018

Neurons generated in adulthood are found throughout the canary telencephalon. We are interested in the factors that control the rate of proliferation of stem cells that give rise to these new neurons. The rate of incorporation of newly generated neurons into vocal-control regions varies seasonally. This difference could reflect a higher rate of neurogenesis, a lower rate of cell death, or an altered migration. We examined the incidence of thymidine-labeled cells in the telencephalic ventricular zone of adult canaries as a function of variations in gonadal hormone levels. Adult female canaries maintained on a short-day photoperiod were anesthetized and gonadectomized. Four separate groups of birds received systemic exposure to either testosterone, estradiol, a combination of an anti-androgen and an inhibitor of estrogen synthesis, or nothing. All birds were also implanted with an osmotic minipump that released 3H-thymidine for 3 d and were killed 4 or 7 d following the onset of treatment. Analysis of autoradiograms revealed no differences between groups in the incidence of labeling within the ventricular zone either at the level of the anterior commissure or directly adjacent to the vocal-control nucleus HVC (higher vocal center). These results suggest that sex steroids do not regulate the rate of cell division in the ventricular zone. Seasonal differences in the incorporation of labeled cells into HVC may therefore be due to regulation of neurogenesis by photoperiodic factors other than gonadal steroids or to some other cellular mechanism, such as differential migration or survival of neurons.
Sodium channels, GABAA receptors, and glutamate receptors develop sequentially on embryonic rat spinal cord cells
Authors: Walton MK , Schaffner AE , Barker JL
Published: March 2018

It is not well understood when during embryonic development the elements of a cell's responsiveness first appear, nor the factors controlling their appearance. A strategy to approach this issue is to determine which aspects of neuronal development are highly stereotyped in presence, timing, or pattern across a variety of cell types, and which are more diversified by cell type, region, or other parameters. We have used a fluorescent potentiometric oxonol dye in conjunction with a digital video imaging system to record the emergence and distribution of specific forms of excitability in dissociated embryonic rat spinal cord cells. We studied the expression of responses to veratridine, a sodium channel activator; muscimol, a GABAA receptor agonist; and kainic acid, an agonist at a class of glutamate receptors. Responses were consistently detectable in a percentage of cells dissociated from the earliest age examined, embryonic day 13, and increased progressively in later ages. Cells were examined from four regions, with cervical-lumbosacral and ventrodorsal distinctions. In the population of cells from each region, functional sodium channels appeared prior to GABAA receptors, which in turn emerged prior to kainate-activated glutamate receptors. This pattern was common to all spinal cord regions and revealed ventrodorsal and rostrocaudal gradients reflecting the known pattern of spinal cord neurogenesis. Analysis of the individual cell responses indicated that the stereotypical pattern of sequential channel development occurs individually on most cells in each region.
Source specificity of early calcium neurotoxicity in cultured embryonic spinal neurons
Authors: Tymianski M , Charlton MP , Carlen PL , Tator CH
Published: March 2018

To examine the role of Ca2+ in early neuronal death, we studied the impact of free intracellular calcium concentration ([Ca2+]i) on survivability in populations of cultured mouse spinal neurons. We asked whether early neurotoxicity was triggered by Ca2+ influx, whether elevated [Ca2+]i was a predictive indicator of impending neuronal death, and whether factors other than [Ca2+]i increases influenced Ca2+ neurotoxicity. We found that when neurons were lethally challenged with excitatory amino acids or high K+, they experienced a biphasic [Ca2+]i increase characterized by a primary [Ca2+]i transient that decayed within minutes, followed by a secondary, sustained, and irreversible [Ca2+]i rise that indicated imminent cell death. We showed that in the case of glutamate-triggered neurotoxicity, processes triggering eventual cell death required Ca2+ influx, and that neurotoxicity was a function of the transmembrane Ca2+ gradient. Fura-2 Ca2+ imaging revealed a “ceiling” on measurable changes in [Ca2+]i that contributed to the difficulty in relating [Ca2+]i to neurotoxicity. We found, by evoking Ca2+ influx into neurons through different pathways, that the chief determinants of Ca2+ neurotoxicity were the Ca2+ source and the duration of the Ca2+ challenge. When Ca2+ source and challenge duration were taken into account, a statistically significant relationship between measured [Ca2+]i and cell death was uncovered, although the likelihood of neuronal death depended much more on Ca2+ source than on the magnitude of the measured [Ca2+]i increase. Thus, neurotoxicity evoked by glutamate far exceeded that evoked by membrane depolarization with high K+ when [Ca2+]i was made to increase equally in both groups. The neurotoxicity of glutamate was triggered primarily by Ca2+ influx through NMDA receptor channels, and exceeded that triggered by non-NMDA receptors and Ca2+ channels when [Ca2+]i was made to rise equally through these separate pathways. The greater neurotoxicity triggered by NMDA receptors was related to some attribute other than an ability to trigger greater [Ca2+]i increases as compared with other Ca2+ sources. We hypothesize that this represents a physical colocalization of NMDA receptors with Ca(2+)-dependent rate-limiting processes that trigger early neuronal degeneration.
Number, distribution, and morphology of retinal ganglion cells with axons regenerated into peripheral nerve graft in adult cats
Authors: Watanabe M , Sawai H , Fukuda Y
Published: March 2018

The optic nerve of adult cats was transected and an autologous peripheral nerve was transplanted to the stump. Two months later retinal ganglion cells (RGCs) that had regenerated their axons were retrogradely labeled with fluorescent dye injected into the graft. The more than 4000 labeled cells, which were 3.0–4.3% of total ganglion cell number in the intact retina, were distributed in a high-density area elongating horizontally, in a pattern similar to that observed in the intact retina. The dendritic morphology of RGCs with regenerated axons was examined after intracellular injections of HRP or Lucifer yellow in vitro. The morphology of alpha- and gamma-cells appeared comparable to normal, whereas the dendrites of some beta-cells seemed to degenerate. Some “unclassified” cells could not be identified as alpha-, beta-, or gamma-cells. The main dendrites of most unclassified cells were thin and less ramified than alpha- and beta-cells. Some unclassified cells had a vacant area in their dendritic fields, suggesting degenerative change in dendrites. The distal dendrites of some unclassified and gamma-cells had many fine processes that probably regrew during axonal regeneration. The proportion of alpha-, beta-, and other cells including gamma- and unclassified cells in the regenerating cell population was evaluated by examining all of the Lucifer yellow- injected cells in local patches. The average proportion of alpha-cells was 23.9%, about six times higher than in intact retinas. The average proportion of beta-cells was 50.3%, slightly higher than in intact retinas. The remaining cells (25.7%) could not be categorized as alpha or beta; this proportion is about half that found in intact retinas. These findings suggest that alpha-cells have the highest capacity to regenerate their axons into nerve grafts, rather than all types equally regenerating their axons.
Functional uncoupling of inhibitory interneurons plays an important role in short-term sensitization of Aplysia gill and siphon withdrawal reflex
Authors: Trudeau LE , Castellucci VF
Published: March 2018

Attempts to explain learning-associated potentiation of synaptic transmission in model systems such as withdrawal reflexes in the mollusk Aplysia or the hippocampus of vertebrates have focused on the mechanisms by which transmitter release is increased in the principal elements of the circuit. Increased transmission in neuronal networks such as the gill and siphon withdrawal reflex (GSWR) of Aplysia may, however, also be caused by a decrease of transmitter release by inhibitory interneurons. The importance and function of cholinergic inhibitory transmission in the GSWR network were investigated. Central application of the nicotinic cholinergic antagonist d-tubocurarine (d- TC) considerably potentiated gill contractions, evoked either by nerve stimulation or by tactile stimulation of the siphon. Compound EPSPs evoked in motoneurons upon siphon nerve stimulation were also significantly prolonged following application of d-TC, but were unaffected by hexamethonium, a blocker of excitatory ACh receptors in Aplysia. Recordings from excitatory interneurons showed that they received excitation followed by powerful inhibitory input upon stimulation of the siphon nerve. Application of d-TC completely blocked this rapid inhibition, thus prolonging the compound EPSPs evoked in the interneurons. These effects were obtained at a concentration of d-TC (100 microM) that almost totally blocked fast inhibitory cholinergic transmission, but was without effect on monosynaptic connections between sensory neurons and motoneurons of the reflex. Facilitation of (1) compound EPSCs in motoneurons and (2) evoked excitatory interneuronal firing was reduced in preparations already disinhibited by pretreatment with d-TC. Facilitation of sensory-motor synapses, however, was not reduced in the presence of d-TC, indicating that facilitatory interneurons are still activated under cholinergic blockade. These data show that transmission through the GSWR neuronal network is gated by a feedback inhibitory mechanism. They also suggest that a reduction of cholinergic inhibition onto excitatory interneurons may be a mechanism through which transmission within the GSWR network is increased during various forms of learning, such as sensitization. These data place new emphasis on the important role of inhibitory interneurons in determining the plastic properties of neuronal networks, in both invertebrates and vertebrates.
Nerve growth factor-induced hyperalgesia in the neonatal and adult rat
Authors: Lewin GR , Ritter AM , Mendell LM
Published: March 2018

Recently, we have shown that the interaction between NGF and sensory neurons in early postnatal periods is restricted to nociceptive afferents (Ritter et al., 1991; Lewin et al., 1992a; Ritter and Mendell, 1992). Here we show that administration of excess NGF to neonatal or mature animals can lead to a profound behavioral hyperalgesia. Neonatal NGF treatment (postnatal day 0–14) resulted in a profound mechanical hyperalgesia that persisted until the animals had reached maturity (6 weeks of age). This hyperalgesia could be explained by an NGF-mediated sensitization of A delta nociceptive afferents to mechanical stimuli. This peripheral sensitization wore off with a time course similar to that of the behavior hyperalgesia. Treatment of animals from the second postnatal week until 5 weeks of age (juveniles) led to a very similar behavioral hyperalgesia; however, there was no corresponding sensitization of A delta nociceptors to mechanical stimuli. Finally, one group of adult animals (5 weeks old) was treated daily with single injections of NGF for between 1 and 4 d. Within 24 hr after the first NGF injection these animals developed a mechanical hyperalgesia of the same magnitude seen after neonatal and juvenile NGF treatments. No sensitization of A delta nociceptive afferents was observed in these animals. In addition to the mechanical hyperalgesia, the animals also developed a heat hyperalgesia after one injection of NGF. The heat hyperalgesia was apparent within 15 min after the injection; however, signs of mechanical hyperalgesia were not seen until 6 hr after the injection. In conclusion, it appears that the NGF- induced mechanical hyperalgesia is brought about by different mechanisms in neonatal and adult rats. Furthermore, in adult animals the NGF-induced mechanical and heat hyperalgesia also appear to be attributable to two different mechanisms. The mechanical hyperalgesia may be due to central changes (see Lewin et al., 1992b), whereas the heat hyperalgesia is likely to result at least in part from the sensitization of peripheral receptors to heat.
Gonadotropin-releasing hormone (GnRH)-immunoreactive terminal nerve cells have intrinsic rhythmicity and project widely in the brain
Authors: Oka Y , Matsushima T
Published: March 2018

Modulation of ionic channel properties and synaptic functions by neurotransmitters and hormones is called neuro-modulation and may be the basis for many long-lasting changes in animal behavior, for example, changes in the arousal or motivational states. We have previously shown in a teleost, the dwarf gourami, that the terminal nerve (TN) cells are a major component of the gonadotropin-releasing hormone (GnRH) system and are structurally independent from the preoptic/hypophysial-GnRH system, which projects to the pituitary and facilitates gonadotropin release from the gonadotropes. While GnRH fibers originating from TN cells are distributed widely throughout the brain, they do not project to the pituitary. Thus, TN-GnRH system does not function as a hypophysiotropic hormone but probably as a neuro- modulator, capable of affecting widespread regions of the brain. In the present study, we used a whole-brain in vitro preparation to examine the spontaneous electrical activities of TN-GnRH cells and to determine the morphology of individual cells by intracellular injections of either neurobiotin or biocytin. The recorded cells were clearly identified as GnRH-immunoreactive TN cells by using combined intracellular injection and GnRH immunocytochemistry. Most of the TN cells showed endogenous slow (1–7 Hz), regular beating discharges. The intrinsic nature of this activity was demonstrated by the voltage dependency of the beating frequency, rhythm resetting, and persistence of rhythmicity after synaptic isolation. Only a small number of TN cells showed either irregular or bursting discharge patterns. Anatomical observation of intracellularly labeled cells showed that, regardless of discharge patterns, all the TN cells had multiple axonal branches that project to those areas where we had previously demonstrated dense GnRH-immunoreactive fibers. From the present results, we propose a hypothesis that may be relevant to the peptidergic and monoaminergic neuromodulatory systems in general. The modulator neurons have endogenous rhythmic activities that vary according to the animal's hormonal or environmental conditions, and they regulate the excitability of target neurons in a wide variety of brain regions simultaneously via multiple axonal branches.
An invertebrate calcium-binding protein of the calbindin subfamily: protein structure, genomic organization, and expression pattern of the calbindin-32 gene of Drosophila
Authors: Reifegerste R , Grimm S , Albert S , Lipski N , Heimbeck G , Hofbauer A , Pflugfelder GO , Quack D , Reichmuth C , Schug B
Published: March 2018

Antisera against vertebrate calcium-binding proteins cross-react with Drosophila nervous and muscle tissue. We have used an antiserum against carp parvalbumin to isolate from a Drosophila head cDNA library immunopositive expression clones. Tissue in situ hybridization identified a clone that labeled specific neurons and muscles similar to the parvalbumin-like immunohistochemical staining pattern. Five independent cDNAs derive from an mRNA whose open reading frame codes for a 310 amino acid polypeptide. Sequence analysis identifies six EF- hand calcium-binding domains and reveals 42% and 37% homology to chicken calretinin and calbindin D-28k, respectively. Since the positions of 9 out of 10 introns within the ORF are conserved from the Drosophila gene to both vertebrate genes, we conclude that we have identified the first invertebrate member of the calbindin sub-family of calcium-binding protein genes of the EF-hand homolog family. The calbindin-32 gene (cbn) maps to 53E on the second chromosome. It is expressed through most of ontogenesis with a selective distribution in the nervous system and in a few small adult thoracic muscles. The cloning of a Drosophila homolog to vertebrate neuronal Ca(2+)-binding proteins opens new routes to study the so far largely elusive function of these brain molecules.
Control of firing mode of corticotectal and corticopontine layer V burst-generating neurons by norepinephrine, acetylcholine, and 1S,3R- ACPD
Authors: Wang Z , McCormick DA
Published: March 2018

The ionic mechanisms by which the firing mode of layer V burst- generating neurons is modulated by noradrenergic, cholinergic, and glutamate metabotropic receptors were investigated with intracellular and extracellular recordings obtained in slices of guinea pig sensorimotor and primary visual cortices maintained in vitro. Extracellular and intracellular recordings revealed that a subset of layer V cells spontaneously generated bursts of three to six action potentials with an interburst frequency of 0.2–4 Hz. Depolarization of these cells with the intracellular injection of current inhibited burst firing and switched the cells to the tonic, single-spike mode of action potential generation. Intracellular recording from retrogradely labeled layer V pyramidal cells that project to either the superior colliculus or pontine nuclei revealed that a substantial portion of these are burst-generating cells. Application of norepinephrine (NE), the glutamate metabotropic receptor agonist 1S,3R-aminocyclopentane-1,3- dicarboxylic acid (ACPD), or ACh to layer V burst-generating cells resulted in depolarization and a subsequent shift in firing pattern from spontaneously bursting to single-spike activity. Pharmacological analysis of these responses indicated that they are mediated by the alpha 1-adrenoceptor for NE and the muscarinic subtype for ACh. Thus, the NE response was mimicked by the alpha-agonist phenylephrine but not by the beta-agonist isoprenaline, and was completely blocked by the alpha 1-antagonist prazosin but not by the alpha 2-antagonist yohimbine or the beta-antagonist propranolol. Finally, the ACh effect could be mimicked by the muscarinic agonist acetyl-beta-methylcholine (MCh) and was blocked by the muscarinic antagonist scopolamine. Intracellular recordings revealed that the NE-, MCh-, and ACPD-induced responses in bursting neurons are due to the direct activation of receptors on these cells, since block of synaptic transmission with local application of TTX or bath application of low [Ca2+]o and raised [Mg2+]o did not block the postsynaptic responses. Voltage-clamp analysis of the currents involved in the depolarizing responses of bursting cells revealed that activation of alpha 1-adrenergic, muscarinic, or glutamate metabotropic receptors resulted in a decrease in a potassium conductance that consisted of both a voltage-independent component and a voltage- and Ca(2+)-sensitive component. These results suggest that increased activity in noradrenergic, cholinergic, and glutamatergic pathways may control the firing mode of layer V corticotectal and corticopontine pyramidal cells by determining the resting membrane potential through modulation of both voltage-dependent and voltage-independent K+ conductances.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of frontal cortical lesions on mouse striatum: reorganization of cell recognition molecule, glial fiber, and synaptic protein expression in the dorsomedial striatum
Authors: Poltorak M , Herranz AS , Williams J , Lauretti L , Freed WJ
Published: March 2018

Brain injury induces trophic effects within adjacent tissue through an unknown molecular mechanism. One model of this lesion effect involves the enhanced outgrowth of neuronal processes from transplanted substantia nigra in animals with cerebral cortex lesions. Since cell recognition molecules are involved in the molecular mechanisms of contact between cells and surrounding extracellular matrix components, and are important in plasticity of the nervous system, we investigated changes in L1, N-CAM, and tenascin, as well as synapse-associated proteins and gliosis, in the striatum of mice with cortical lesions. The removal of somato-sensory and motor cortex would be expected to produce changes predominantly in the dorsal striatum. Lesioned mice, however, showed a significant enhancement of both L1 and N-CAM immunostaining intensity only within the most medial-periventricular and dorsomedial parts of the striatum, as compared to the nonlesioned side. Tenascin expression was significantly decreased, but only in the most medial part of the striatum. The changes in intensity of immunostaining with L1, N-CAM, and tenascin did not diminish with time after lesioning. These changes in cell recognition molecule expression indicate a possible molecular basis of lesion-induced plasticity in neuronal circuits within the dorsomedial striatum. These changes were accompanied by decreased synapsin and synaptophysin expression, but without any significant change in neurofilament expression. In contrast, glial fibrillary acidic protein and vimentin immunoreactivities were increased in almost the entire striatum on the lesioned side. Therefore, the areas of changes in cell recognition molecule expression did not simply correlate to the increased astrogliosis or neuronal fiber damage. We postulate that the periventricular dorsomedial striatum is relatively sensitive to disturbances of corticostriatonigral circuits and, simultaneously, this striatal area has a unique ability to support and promote neurite growth.
G(olf) and Gs in rat basal ganglia: possible involvement of G(olf) in the coupling of dopamine D1 receptor with adenylyl cyclase
Authors: Herve D , Levi-Strauss M , Marey-Semper I , Verney C , Tassin JP , Glowinski J , Girault JA
Published: March 2018

Using specific antibodies and cDNA probes, we have investigated, in rat basal ganglia, the distribution and the regulation of the expression of the alpha subunits of Gs and G(olf), two GTP-binding proteins (G- proteins) that stimulate adenylyl cyclase. We confirmed that G(olf) alpha is highly expressed in caudate-putamen, nucleus accumbens, and olfactory tubercle, whereas Gs alpha is less abundant in these areas than in the other brain regions. Intrastriatal injections of quinolinic acid decreased dramatically the levels of G(olf) alpha protein in the striatum and the substantia nigra, and those of G(olf) alpha mRNA in the striatum. Retrograde lesions of striatonigral neurons with volkensin reduced markedly the levels of D1 dopamine (DA) binding sites, as well as those of G(olf) alpha protein and mRNA in the striatum, without altering D2 binding sites. In contrast, both types of lesions increased the levels of Gs alpha protein in the striatum and substantia nigra. Immunocytochemistry showed the presence of G(olf) alpha protein in striatal medium-sized neurons and in several other neuronal populations. These results demonstrate that striatonigral neurons contain high levels of G(olf) alpha and little, if any, Gs alpha, suggesting that the coupling of D1 receptor to adenylyl cyclase is provided by G(olf) alpha. The levels of G(olf) alpha were five- to sixfold higher in the striatum than in the substantia nigra, indicating a preferential localization of G(olf) alpha in the somatodendritic region of striatonigral neurons and providing a basis for the low efficiency of D1 receptor coupling in the substantia nigra. Six weeks after 6-hydroxydopamine lesions of DA neurons, an increase in G(olf) alpha (+53%) and Gs alpha (+64%) proteins was observed in the striatum. This increase in G(olf) alpha levels may account for the DA-activated adenylyl cyclase supersensitivity, without change in D1 receptors density, that follows destruction of DA neurons. Fine regulation of the levels of G(olf) alpha in physiological or pathological situations may be a critical parameter for the efficiency of DA neurotransmission.
Attenuation of hippocampal long-term potentiation by ethanol: a patch- clamp analysis of glutamatergic and GABAergic mechanisms
Authors: Morrisett RA , Swartzwelder HS
Published: March 2018

Long-term potentiation of synpatic transmission (LTP) of the perforant path--dentate gyrus synapse is induced by 5 Hz, theta-like stimulation patterns. Such stimuli induce plasticity that is most likely driven by a decrease in synaptic inhibition (disinhibition) mediated by GABAB autoreceptors. In the present study, we demonstrate that LTP induced in this manner is completely antagonized by ethanol. In order to determine the site of ethanol inhibition of LTP induced by theta-like stimulation, we combined slice patch recordings with pharmacologic isolation of the individual glutamatergic and GABAergic synaptic currents. The present experiments revealed that ethanol inhibited NMDA receptor-mediated synaptic currents without potentiation of GABAA currents or attenuation of GABAB-mediated fading of GABAA synaptic currents. These observations with ethanol contrasted with the actions of the water-soluble benzodiazepine midazolam, which strongly potentiated GABAA synaptic currents, reversed the effect of GABAB- mediated fading of GABAA synaptic currents, and therefore blocked the resulting NMDA synaptic currents. These data indicate that the effects of ethanol on long-term changes in synaptic strength in the rat hippocampal formation are due primarily to an action at the NMDA receptor-channel complex.
How independent are the messages carried by adjacent inferior temporal cortical neurons?
Authors: Gawne TJ , Richmond BJ
Published: March 2018

There are at least three possibilities for encoding information in a small area of cortex. First, neurons could have identical characteristics, thus conveying redundant information; second, neurons could give different responses to the same stimuli, thus conveying independent information; or third, neurons could cooperate with each other to encode more information jointly than they do separately, that is, synergistically. We recorded from 28 pairs of neurons in inferior temporal cortex of behaving rhesus monkeys. Each pair was recorded from a single microelectrode. Both the magnitude and the temporal modulation of the responses were quantified. We separated the responses into signal (average response to each stimulus) and noise (deviation of each response from the average). Linear regression showed that an average of only 18.7% of the magnitude of the signal carried by one neuron could be predicted from the magnitude of the other, and only 22.0% could be predicted by including the temporal modulation. For the noise, the figures were 5.5% and 6.3%, respectively, even less than for the signal. Information theoretic analysis shows that the pairs of neurons we studied carried an average of 20% redundant information. However, even this relatively small amount of redundancy places a severe upper limit on the information that can be transmitted by a neuronal pool. A pool of neurons for which each pair is mutually redundant to extent y can only carry a maximum of 1/y, here five times, as much information as one neuron alone. Information theoretic analysis gave no evidence for the presence of information as a function of both neurons considered together, that is, synergistic codes. Cross-correlation showed that at least 61% of the neuronal pairs shared connections in some manner. Given these shared connections, if adjacent neurons had had identical characteristics, then the noise on the outputs of these neurons would have been highly correlated, and it would not be possible to separate the signal and noise. The severe impact of correlated noise and information redundancy leads us to propose that the processing carried out by these neurons evolved both to provide a rich description of many stimulus properties and simultaneously to minimize the redundancy in a local group of neurons. These two principles appear to be a major constraint on the organization of inferior temporal, and possibly all, cortex.
Changes of synaptic density in the primary visual cortex of the macaque monkey from fetal to adult stage
Authors: Bourgeois JP , Rakic P
Published: March 2018

The kinetics of synaptogenesis in the primary visual cortex (Brodmann's area 17) were analyzed by electron microscopy in 33 rhesus monkeys, ranging in age from the 50th embryonic day (E50) to 20 years. A series of overlapping electron micrographs (vertical probes) were examined at each age on sections of the upper bank of the calcarine fissure. Synaptic contacts were first observed in the E50 specimen in the subplate and marginal zone (prospective layer I). In the cortical plate itself, synapses appear between E65 and E89 starting in the prospective layer VI. By E112, after all cortical neurons have assumed their laminar positions, synapses situated predominantly on dendritic shafts were present at a low density throughout the full thickness of the cortical plate. Thereafter, synapses accumulate more rapidly on dendritic spines and by E144 an equal number of contacts are found on both spines and shafts. The density of synapses continues to increase exponentially in all layers and reaches the mean maximum density of about 90 synapses per 100 microns 3 of neuropil by the third postnatal month. During the next 2 postnatal years the density of synaptic contacts decreases only slightly to a mean of 80/100 microns 3 of neuropil. Around the time of puberty, however, synaptic density decreases more rapidly to reach the adult level of about 40–50/100 microns 3 of neuropil. The 40% decrease in the density of synaptic contacts occurring between 2.7 and 5 years represents a loss of about 5000 synapses per second in the primary visual cortex of the two hemispheres, due primarily to the loss of asymmetric synapses situated on dendritic spines. The transient phase of high density of synaptic contacts located on dendrospines is shorter in thalamo-recipient layer IV than in either supra- or intragranular layers and is completed within the first postnatal year. It ends earlier in sublayer IVC than in layers IVAB and II-III, for example, reflecting biochemical and functional maturation of the different visual subsystems.
Ultrastructural localization of 5'AMP odorant receptor sites on the dendrites of olfactory receptor neurons of the spiny lobster
Authors: Blaustein DN , Simmons RB , Burgess MF , Derby CD , Nishikawa M , Olson KS
Published: March 2018

A unique probe--biotinylated adenosine-5′-monophosphate (5′AMP-biotin)-- was used in transmission electron microscopic (TEM) studies to localize 5′AMP odorant binding sites on the dendrites of olfactory receptor neurons in the aesthetasc sensilla of the spiny lobster, Panulirus argus. This probe is capable of both binding to and exciting 5′AMP- sensitive olfactory receptor neurons, as revealed through biochemical and electrophysiological assays. TEM studies showed that 5′AMP-biotin binding sites are distributed along the entire dendritic region that is exposed to odorants, including the transitional zone (between the inner and outer dendritic segments, including the ciliary segment) and all of the outer dendritic segment. The density of 5′AMP binding sites per micron2 of membrane is similar along the length of the olfactory dendrite. However, the relative number of 5′AMP-biotin binding sites per micron2 of sensillar area diminishes in the distal 30% of the aesthetasc due to a decrease in the amount of dendritic membrane in that region. The distribution of these 5′AMP binding sites is therefore much more extensive than that of enzymes that inactivate 5′AMP-- 5′ectonucleotidase/phosphatase--which are restricted to the transitional zone (Gleeson et al., 1991). Taken together, these results suggest that 5′AMP-biotin is labeling 5′AMP-specific olfactory receptor sites that are located along the entire outer dendritic segment and that can be coupled to olfactory transduction. This study represents the first in situ localization of specific olfactory receptor sites using a specific, functionally defined ligand.
Parallel pathways mediating both sound localization and gaze control in the forebrain and midbrain of the barn owl
Authors: Knudsen EI , Knudsen PF , Masino T
Published: March 2018

The hypothesis that sound localization and gaze control are mediated in parallel in the midbrain and forebrain was tested in the barn owl. The midbrain pathway for gaze control was interrupted by reversible inactivation (muscimol injection) or lesion of the optic tectum. Auditory input to the forebrain was disrupted by reversible inactivation or lesion of the primary thalamic auditory nucleus, nucleus ovoidalis (homolog of the medial geniculate nucleus). Barn owls were trained to orient their gaze toward auditory or visual stimuli presented from random locations in a darkened sound chamber. Auditory and visual test stimuli were brief so that the stimulus was over before the orienting response was completed. The accuracy and kinetics of the orienting responses were measured with a search coil attached to the head. Unilateral inactivation of the optic tectum had immediate and long-lasting effects on auditory orienting behavior. The owls failed to respond on a high percentage of trials when the auditory test stimulus was located on the side contralateral to the inactivated tectum. When they did respond, the response was usually (but not always) short of the target, and the latency of the response was abnormally long. When the auditory stimulus was located on the side ipsilateral to the inactivated tectum, responses were reliable and accurate, and the latency of responses was shorter than normal. In a tectally lesioned animal, response probability and latency to contralateral sounds returned to normal within 2 weeks, but the increase in response error (due to undershooting) persisted for at least 12 weeks. Despite abnormalities in the response, all of the owls were capable of localizing and orienting to contralateral auditory stimuli on some trials with the optic tectum inactivated or lesioned. This was not true for contralateral visual stimuli. Immediately following tectal inactivation, the owls exhibited complete neglect for visual stimuli located more than 20 degrees to the contralateral side (i.e., beyond the edge of the visual field of the ipsilateral eye). In the tectally lesioned animal, this neglect diminished with time. Unilateral inactivation of nucleus ovoidalis had different effects in three owls. Response error to contralateral sound sources increased for one owl and decreased for two; response error to ipsilateral sources did not change significantly for any. The probability of response to ipsilateral (but not contralateral) stimuli decreased for one owl. The latency of response to ipsilateral (but not contralateral) stimuli increased for one and decreased for another. All of the owls, however, routinely localized and oriented toward ipsilateral and contralateral auditory stimuli with nucleus ovoidalis inactivated.(ABSTRACT TRUNCATED AT 400 WORDS)
Immunological relationships of NGF, BDNF, and NT-3: recognition and functional inhibition by antibodies to NGF
Authors: Murphy RA , Acheson A , Hodges R , Haskins J , Richards C , Reklow E , Chlumecky V , Barker PA , Alderson RF , Lindsay RM
Published: March 2018

Polyclonal antibodies raised against mouse 2.5S NGF (mNGF) and against synthetic peptides made from hydrophilic portions of mNGF have been used to compare the immunological properties of mNGF, human recombinant brain-derived neurotrophic factor (hrBDNF), and human recombinant neurotrophin-3 (hrNT-3). Affinity-isolated antibodies raised against intact mNGF reacted with all three neurotrophins when tested by ELISA and totally or partially blocked the bioactivities of the proteins in survival assays of embryonic chicken sensory and sympathetic neurons. On Western blots, mNGF antibodies reacted with all three neurotrophins but less well with hrBDNF and hrNT-3 than with mNGF. Antibodies to hydrophilic peptides within NGF (amino acids 23–35, 59–67, 69–79, and 91–100) showed partial reactivity with some but not all of the neurotrophins when tested by ELISA and on Western blots. The peptide antibodies were also selectively effective in reducing the survival- promoting activity of the neurotrophins on sensory neurons. Results show that mNGF, hrBDNF, and hrNT-3 are immunologically related proteins and that mNGF antibodies react also with other members of the neurotrophin family.
Voltage- and transmitter-gated currents of all-amacrine cells in a slice preparation of the rat retina
Authors: Boos R , Schneider H , Wassle H
Published: March 2018

All-amacrine cells are crucial interneurons in the rod pathway of the mammalian retina. They receive input synapses from rod bipolar cells and make electrical output synapses into the ON-pathway and glycinergic chemical synapses into the OFF-pathway. Whole-cell currents from more than 50 voltage-clamped All-amacrine cells were recorded in a slice preparation of the rat retina. The recorded cells were identified by intracellular staining with Lucifer yellow. Spike-like potentials could be elicited upon depolarization by current injection. A voltage- activated, fast, TTX-sensitive, inward Na+ current was identified. A prominent outward K+ current could be suppressed by tetraethylammonium. GABA as well as glycine activated Cl- channels, which could be blocked by bicuculline and strychnine, respectively. Four agonists of excitatory amino acid receptors--kainate (KA), AMPA, 2-amino-4- phosphonobutyrate (APB), and NMDA--were tested. Inward currents at holding potentials of VH = -70 mV were found by application of KA and AMPA but not by application of APB and NMDA. These currents could be blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). ACh did not evoke any current responses.
Differential expression of correlates of classical conditioning in identified medial and lateral type A photoreceptors of Hermissenda
Authors: Frysztak RJ , Crow T
Published: March 2018

Classical conditioning of Hermissenda produces neurophysiological correlates in the primary sensory neurons of the pathway mediating the conditioned stimulus (CS), the type B and type A photoreceptors. Biophysical and biochemical changes intrinsic to the type B photoreceptors have been studied extensively in conditioned animals. A second site for intrinsic modification with learning has been recently identified in type A photoreceptors. We have recorded from identified medial and lateral type A photoreceptors in conditioned animals and animals that received pseudorandom presentations of light (CS) and rotation (unconditioned stimulus). Here we report that conditioning produces differential effects upon CS-elicited spike frequency and intrinsic excitability detected in identified lateral and medial type A photoreceptors. Lateral type A photoreceptors from conditioned animals exhibited significant increases in spike frequency elicited by the CS as compared to pseudorandom controls. In contrast, CS-elicited spike frequency recorded in medial type A photoreceptors was not significantly different from random controls. The amplitude of the peak and plateau phases of the generator potential of medial and lateral type A photoreceptors was decreased in conditioned animals as compared to random controls. In addition, only lateral type A photoreceptors exhibited enhanced cellular excitability as expressed by increased spike discharges produced by the injection of extrinsic depolarizing current pulses. Conditioning also decreased spike frequency accommodation in lateral type A photoreceptors. In normal controls, medial type B photoreceptors produced stronger synaptic inhibition of medial type A photoreceptors than the lateral type B photoreceptors inhibition of lateral type A photoreceptors.(ABSTRACT TRUNCATED AT 250 WORDS)
Dihydropyridine-sensitive calcium current mediates neurotransmitter release from bipolar cells of the goldfish retina
Authors: Tachibana M , Okada T , Arimura T , Kobayashi K , Piccolino M
Published: March 2018

The release of neurotransmitter is evoked by activation of the Ca current (ICa) at presynaptic terminals. Though multiple types of ICa have been reported in various cells, little is known about the properties of presynaptic ICa in the vertebrate CNS. The aim of this article is to identify the type of ICa involved in the release of neurotransmitter from retinal bipolar cells. Bipolar cells with a large axon terminal were isolated enzymatically from the goldfish retina, and studied by the following techniques: (1) recordings of ICa in the whole- cell recording configuration, (2) visualization of intracellular free Ca2+ concentration ([Ca2+]i) with the Fura-2 imaging system, and (3) real-time electrophysiological bioassay of released excitatory amino acid transmitter by a voltage-clamped horizontal cell isolated from the catfish retina. The only ICa found in bipolar cells was the high- voltage-activated, dihydropyridine-sensitive type. This result supports the recent study by Heidelberger and Matthews (1992). When ICa was activated by a short depolarizing pulse, a rapid increase of [Ca2+]i was restricted to the axon terminal. A much slower and smaller increase of [Ca2+]i was sometimes observed at the cell body, probably due to the diffusion of intracellular free Ca2+ from the axon terminal. The increase of [Ca2+]i was completely suppressed by nicardipine, suggesting that Ca2+ entered through dihydropyridine-sensitive Ca channels located mainly at the axon terminal. Activating ICa of the bipolar cell evoked a transmitter-induced current in the excitatory amino acid probe (i.e., the catfish horizontal cell). Both currents were suppressed concomitantly by nifedipine but not by omega- conotoxin.(ABSTRACT TRUNCATED AT 250 WORDS)