bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibitory actions of delta 1-, delta 2-, and mu-opioid receptor agonists on excitatory transmission in lamina II neurons of adult rat spinal cord
Authors: Glaum SR , Miller RJ , Hammond DL
Published: April 2018

This study examined the electrophysiological consequences of selective activation of delta 1-, delta 2-, or mu-opioid receptors using whole- cell recordings made from visually identified lamina II neurons in thin transverse slices of young adult rat lumbar spinal cord. Excitatory postsynaptic currents (EPSCs) or potentials (EPSPs) were evoked electrically at the ipsilateral dorsal root entry zone after blocking inhibitory inputs with bicuculline and strychnine, and NMDA receptors with D-2-amino-5-phosphonopentanoic acid. Bath application of the mu receptor agonist [D-Ala2, N-MePhe4, Gly5-ol]enkephalin (DAMGO) or the delta 1 receptor agonist [D-Pen2, D-Pen5]enkephalin (DPDPE) produced a long-linear, concentration-dependent reduction in the amplitude of the evoked EPSP/EPSC. By comparison, the delta 2 receptor agonist [D- Ala2,Glu4]deltorphin (DELT) was unable to reduce the evoked EPSP/EPSC by more than 50% at 100 microM, the highest concentration tested. At concentrations that reduced evoked EPSP/EPSCs by 40–60%, neither DAMGO, DPDPE, nor DELT decreased the amplitude of the postsynaptic current produced by brief pressure ejection of (S)-alpha-amino-3-hydroxy-5- methyl-4-isoxazole-propionic acid, suggesting a presynaptic site of action of these opioid receptor agonists. Bath application of 200 nM naltriben (NTB), a delta 2 receptor antagonist, competitively increased the EC75 of DELT by 15.3-fold, but did not antagonize either DPDPE or DAMGO. The EC75 of DELT was further increased by 169.7-fold in the presence of 1 microM NTB. However, this high concentration of NTB also increased the EC50 of DPDPE by about threefold in a noncompetitive manner and antagonized DAMGO in a noncompetitive manner.(ABSTRACT TRUNCATED AT 250 WORDS)
Prostaglandin E2 enhances bradykinin-stimulated release of neuropeptides from rat sensory neurons in culture
Authors: Vasko MR , Campbell WB , Waite KJ
Published: April 2018

Prostaglandins are known to enhance the inflammatory and nociceptive actions of other chemical mediators of inflammation such as bradykinin. One possible mechanism for this sensitizing action is that prostanoids augment the release of neuroactive substances from sensory neurons. To initially test this hypothesis, we examined whether selected prostaglandins could enhance the resting or bradykinin-evoked release of immunoreactive substance P (iSP) and/or immunoreactive calcitonin gene-related peptide (iCGRP) from sensory neurons in culture. Bradykinin alone causes a concentration-dependent increase in the release of iSP and iCGRP from isolated sensory neurons, and this action is abolished in the absence of extracellular calcium. Pretreating the neurons with PGE2 (10 nM to 1 microM) potentiates the bradykinin-evoked release of both iSP and iCGRP by approximately two-to fourfold. At these concentrations, PGE2 alone did not significantly alter peptide release. Exposing the cultures to 1 microM PGF2 alpha is ineffective in altering either resting or bradykinin-evoked peptide release. Sensory neurons in culture contain cyclooxygenase-like immunoreactivity suggesting that the enzyme that converts arachidonic acid to prostaglandins is present. In addition, pretreating cultures with 14C- arachidonic acid yields radiolabeled eicosanoids that cochromatograph with known prostaglandin standards. Preexposing cultures to indomethacin abolishes the production of prostaglandins and attenuates the bradykinin-stimulated release of iSP and iCGRP. This implies that the synthesis of prostaglandins contributes to the bradykinin-evoked release of peptides. The augmentation of bradykinin-induced release of iSP and iCGRP by PGE2 may be one mechanism to account for the inflammatory and hyperalgesic actions of this eicosanoid.
Cell adhesion molecules regulating neurite growth from amacrine and rod photoreceptor cells [published erratum appears in J Neurosci 1994 Oct;14(10):following table of contents]
Authors: Kljavin IJ , Lagenaur C , Bixby JL , Reh TA
Published: April 2018

A great deal is now known about the cell adhesion molecules (CAMs) that are responsible for promoting the growth of ganglion cell axons as they project out of the retina through the optic nerve and finally to distant targets in the brain. However, the CAMs important for regulating axon outgrowth from nonprojection neurons, such as amacrine cells and rods, are not known. Such local circuit neurons extend their neurites rather short distances on cellular surfaces not normally encountered by the ganglion cell axons. To study the mechanisms regulating axon or dendrite growth from local circuit neurons, neurite outgrowth from amacrine cells and rod photoreceptor cells derived from the rat was examined in vitro on immunopurified forms of NCAM, L1, and N-cadherin, three well-characterized adhesive molecules found in the developing retina. Either early (P3) or late (P10) postnatal amacrine cells grew neurites on all three CAMs, but there were significant differences in the percentage of the amacrine cells that responded to each CAM. None of the CAMs supported neurite outgrowth from early postnatal rods, but, surprisingly, NCAM stimulated vigorous neurite extension from rods isolated at postnatal day 10. Postnatal ganglion cells were also examined for comparison and were found not to grow neurites on NCAM, but did grow extensive processes on L1 and N- cadherin. These results show that NCAM, L1, and N-cadherin can promote neurite outgrowth from local circuit neurons, but that the effectiveness of any particular CAM is dependent on the cell type and the developmental period.
Extracellular glucose concentration in mammalian brain: continuous monitoring of changes during increased neuronal activity and upon limitation in oxygen supply in normo-, hypo-, and hyperglycemic animals
Authors: Silver IA , Erecinska M
Published: April 2018

The concentration of extracellular glucose in anesthetized rat brain was measured continuously with two types of substrate-specific microelectrodes in a number of physiological and pathological conditions. Extracellular glucose level increased in hyperglycemia and decreased in hypoglycemia, paralleling the changes in blood sugar. Increased neuronal activity and in particular spreading depression, evoked triphasic alterations in extracellular glucose concentration: an initial rapid fall was followed by an equally swift overshoot above the baseline and a subsequent return to it. Limitation in O2 supply led to a decline in extracellular content of glucose: respiration with 5% O2 reduced the level by 7–20% and that with 3% O2 by 75–85%. Decreases to undetectable concentrations were seen in ischemia despite the use of an oxygen-insensitive microglucose sensor. Restoration of oxygen supply to the brain was accompanied by increases in extracellular glucose content above the original normoxic level, which returned to baseline values after 10–15 min. In hyperglycemic animals ischemia-induced leakage of K+ was delayed while the rate of recovery to control levels after restitution of blood flow was enhanced. It is concluded that continuous monitoring of glucose with glucose-specific microelectrodes provides a new and important insight into brain energy metabolism.
Dendritic pathology of granule cells in Alzheimer's disease is unrelated to neuritic plaques
Authors: Einstein G , Buranosky R , Crain BJ
Published: April 2018

Neuritic plaques are the histologic hallmark of Alzheimer's disease (AD); however, the extent to which they are injurious to neurons is unclear. In order to investigate this problem, we intracellularly filled human dentate granule cells with Lucifer yellow in a lightly fixed slice preparation and studied the relationships between their dendrites and neuritic plaques. After counterstaining for plaques and drawing the filled granule cell dendrites, we found that there were significant differences in the morphology of dendrites in control and AD cases; granule cell dendrites from Alzheimer's cases were generally shorter, branched less profusely, and had fewer spines than those from age matched controls. Surprisingly, when dendrites traveled into plaques, they still bore spines and their morphology was distinct from that of the amyloid-stained dystrophic neurites surrounding them. Furthermore, within AD cases we found no significant differences between dendrites that were located directly beneath or passing through plaques and those that were located in plaque-free regions. We conclude that granule cell dendrites are not an integral component of plaques within their dendritic fields and that neuritic plaques have no direct effect on granule cells in the dentate gyrus.
Activity of descending propriospinal axons in the turtle hindlimb enlargement during two forms of fictive scratching: phase analyses
Authors: Berkowitz A , Stein PS
Published: April 2018

In the preceding companion article (Berkowitz and Stein, 1994b), we showed that many descending propriospinal neurons in the turtle were rhythmically activated during two different motor patterns, fictive rostral scratching and fictive pocket scratching. In this article, we present phase analyses of the activity of each such neuron during fictive scratching. Each neuron's activity was concentrated in a particular phase of the ipsilateral hip flexor muscle nerve (VP-HP) activity cycle; each had a distinct "preferred phase." Each neuron's preferred phase during fictive rostral scratching was similar to its preferred phase during fictive pocket scratching. This result is consistent with the idea that some descending propriospinal neurons may contribute to the generation of both rostral scratching and pocket scratching. Many descending propriospinal neurons were rhythmically activated during fictive scratching evoked on either side of the body. This activity may contribute to production of bilateral hindlimb movements during scratching. It is also possible that synaptic interactions between the two sides of the spinal cord may be important in generating the motor patterns for movement of a single hindlimb. In addition, we present a model which illustrates that a population of propriospinal neurons, each of which is broadly tuned to a region of the body surface and is rhythmically activated in a constant phase of the hip control cycle, could mediate the selection and generation of rostral scratching and pocket scratching. Thus, the selection of an appropriate motor pattern and the production of the required knee-hip synergy may each be distributed over a diverse population of spinal cord neurons. This model requires that each such neuron project to both knee muscle and hip muscle motoneurons. According to this model, the process of selecting a motor pattern would not be completed until knee muscle motoneurons integrate overlapping excitatory and inhibitory inputs.
Target dependence of adult neurons: pattern of terminal arborizations
Authors: Marty S , Weinitz JM , Peschanski M
Published: April 2018

During development, the survival of neurons in the CNS depends critically on interactions with postsynaptic target cells. The role of target cells on the maintenance of afferent neurons in the adult, however, is a matter of controversy. Morphological alterations of target-deprived neurons, such as axonal retraction or pruning, may occur. We have therefore undertaken an analysis of target-deprived neurons over time after an excitotoxic lesion in order to investigate these potential changes. Dorsal column nuclei (DCN) neurons were deprived of their target neurons in adult rats by the injection of kainic acid into the ventrobasal thalamic complex. Anterogradely transported wheat germ agglutinin conjugated to HRP from the DCN showed a progressive decrease of the density of afferent terminals during the first month after lesion. Density stabilized thereafter through the longest time studied (8 months). In contrast, the extent of the area occupied by DCN projections did not change up to 1 month and then shrank over time. These results indicated a continuous decrease in the number of axonal elements in the lesion, which is the strongest during the first month postlesion. To interpret these data, we then studied axonal morphology. Diffusion-filled lemniscal axons were labeled by WGA- HRP injections aimed at the medial lemniscus. There was no conspicuous alteration of axonal stems in the medial lemniscus. Terminal axonal arborizations and swellings dramatically decreased in number over the first month after the kainate injection, and large axonal varicosities were formed over the same period of time. These morphological data suggest that the decrease in number of axons in an excitotoxic lesion is related, at least during the first month, to a loss of axonal terminal arborizations rather than to a retraction of axonal stems. The pattern of terminal arborizations in the adult CNS may therefore depend critically on interactions of afferents with their target neurons, while the maintenance of the axonal stems does not.
Oligodendrocyte precursor quantitation and localization in perinatal brain using a retrospective bioassay
Authors: Gonye GE , Warrington AE , DeVito JA , Pfeiffer SE
Published: April 2018

Several late stages of the oligodendrocyte (OL) developmental lineage can be identified immunologically in the newborn rat brain. However, OL lineage-specific markers are not available for the detection of the less mature, yet determined, OL precursors. We have developed a retrospective bioassay, combining limiting dilution analysis with a novel culture system, that quantitatively assesses the developmental potential in vivo of phenotypically undefined OL precursors in order to (1) demonstrate their existence, (2) estimate their total number in the premyelinated rat brain, and (3) demonstrate their presence in regions distal to germinal zones at times previously predicted to be devoid of such cells. Between embryonic day (E) 21 and postnatal day (P) 0, cells determined to become oligodendrocytes increase in frequency approximately 5-fold in the whole brain (from one precursor for every 365 cells to 1 in 74), and approximately 2.5-fold in the telencephalon (from 1 in 298 to 1 in 115). From these data it is calculated that a pool of approximately 10(6) phenotypically undefined cells are present in the newborn brain that are able to differentiate into OL in vitro. Further, by applying this assay to tissue samples of subdomains of the developing cerebellum, we have demonstrated that such cells are present in large numbers as early as E20 in regions sparsely populated with cells expressing the blastic neural cell marker ganglioside GD3, suggesting that they migrated to this position as a pre-GD3-expressing cell. These results significantly change the predicted ontogeny of the oligodendrocyte lineage and should fuel the ongoing search for these early OL precursors.
Patterns of brain vasopressin receptor distribution associated with social organization in microtine rodents
Authors: Insel TR , Wang ZX , Ferris CF
Published: April 2018

Central vasopressin pathways have been implicated in the mediation of paternal behavior, selective aggression, and affiliation in monogamous prairie voles. Here we demonstrate markedly different patterns of brain vasopressin receptor binding in the monogamous prairie vole and the congeneric nonmonogamous (promiscuous) montane vole. Vasopressin binding was assessed with both 3H-vasopressin and 125I-sarc-AVP using receptor autoradiography. The specificity of binding was consistent with a V1a receptor, the saturation kinetics were similar in the two species, and neither species showed evidence of sexual dimorphisms. In the prairie vole, highest specific binding was observed in the accessory olfactory bulb, diagonal band, laterodorsal thalamus, and superior colliculus. In the montane vole, specific binding was observed in the accessory olfactory bulb and superior colliculus as well, but in several other regions with high levels of binding in the prairie vole, binding was low or undetectable in the montane vole. In this nonmonogamous species, specific binding was high in lateral septum. Functional studies demonstrated the induction of phosphoinositol by AVP in the septum of the montane vole but not in the prairie vole. The pattern of 125I-sarc-AVP binding to lateral septum may reflect the social organization of these two species, as similar differences in AVP receptor distribution in the lateral septum were also observed in two related species, pine voles and meadow voles, which are monogamous and nonmonogamous, respectively. These results, along with earlier studies of AVP's effects on pair bonding, suggest the importance of this neuropeptide for the mediation of behaviors related to social organization.
Entrainment of the fetal hamster circadian pacemaker by prenatal injections of the dopamine agonist SKF 38393
Authors: Viswanathan N , Weaver DR , Reppert SM , Davis FC
Published: April 2018

Prenatal treatment with the D1-dopamine receptor agonist SKF 38393 or cocaine induces expression of the immediate-early gene c-fos in the fetal rat suprachiasmatic nucleus (SCN) (Weaver et al., 1992). Because the induction of c-fos gene expression in the SCN has been implicated in the entrainment of circadian rhythms by light in mature animals, the present study investigated whether prenatal dopaminergic activation entrains the fetal circadian pacemaker. Injections of SKF 38393 (8 mg/kg) were given to pregnant, SCN-lesioned hamsters during the last 5 d of gestation and the phases of the offspring's wheel-running activity rhythms were measured on postnatal day 20. Pregnant hamsters were each given two injections/day 12 hr apart, but only one of the injections each day contained SKF 38393. One group of hamsters received the drug at 0800 hr while another group received the drug at 2000 hr. The offspring from these treatment groups showed average phases that differed by 11.3 hr, demonstrating that prenatal SKF 38393 set the phase of the offspring's circadian rhythms. These results suggest that the fetal circadian pacemaker can be entrained by dopaminergic activation. In situ hybridization using cRNA probes demonstrated that a single injection of SKF 38393 on the last day of gestation induced c- fos gene expression in the fetal hamster SCN and that mRNA for the D1- dopamine receptor was present in the SCN at that time. It is possible that maternal entrainment of the fetal circadian pacemaker, which normally occurs during development, is mediated by dopaminergic activation within the fetal hypothalamus.
Distinctive patterns of GABAA receptor subunit mRNAs in 13 cell lines
Authors: Tyndale RF , Hales TG , Olsen RW , Tobin AJ
Published: April 2018

We have investigated the GABAA receptor mRNA composition in 13 cell lines, using 13 subunit-specific oligo-primers (alpha 1–6, beta 1–3, gamma 1–3, and delta) and reverse transcriptase PCR amplification. Cell lines (B35, B65, B103, B104, RINm5F, Rat1, PC12, C6, C17, C27, beta TC3, NB41A3, AtT-20), derived from diverse tissue origins, were investigated in order to identify homogeneous cellular sources with distinctive GABAA receptor subunits. Fifteen GABAA receptor subunits have been cloned from mammalian tissue (those listed above plus the retinal subunits rho 1 and rho 2). This multiplicity of GABAA receptor subunits underlies the diverse pharmacology of the GABAA receptor. Attempts to understand the regulation and pharmacology of individual subunits and of the heterooligomeric receptor combinations have been impeded by a lack of pure populations of cells expressing GABAA receptor subunits. Permanent cell lines provide such a resource. Each GABAA receptor subunit mRNA, alpha 1–5, beta 1–3, gamma 1–3, and delta, was detected in at least one cell line. All cell lines examined contained detectable levels of at least one GABAA receptor subunit mRNA. Each cell line contained distinctive combinations of subunit mRNAs. None of the cell lines examined contained detectable amounts of alpha 6 mRNA. These cell lines, which transcribe GABAA receptor subunit mRNAs, provide useful cellular sources for transcriptional and pharmacological studies. Our data also suggest that endogenous GABAA receptor subunit mRNAs may be present in cells that are routinely used for transfection studies, and that this expression might confound interpretation of the studies. In the following companion article, we have looked for functional GABAA receptor Cl- ion channels in these cell lines, using the patch-clamp technique (Hales and Tyndale, 1994).
Gustatory, olfactory, and visual convergence within the primate orbitofrontal cortex
Authors: Rolls ET , Baylis LL
Published: April 2018

Behavioral and perceptual responses to food depend on a convergence between gustatory, olfactory, and visual information. In previous studies a secondary cortical taste area has been found in the caudolateral orbitofrontal cortex of the primate. Furthermore, neurons with olfactory responses have been recorded in a more medial part of the orbitofrontal cortex, and visual inputs have been shown to influence neurons in an intermediate region. These studies suggest that the orbitofrontal cortex may act as a region for convergence of multiple sensory modalities including chemosensation. In the present study neurons throughout the caudal two-thirds of the orbitofrontal cortex of the macaque were tested to gustatory, to olfactory, and to visual stimulation to investigate whether convergence occurs. Neurons in this region of cortex were found that responded to stimulation of the taste, olfactory, or visual system. In addition, some neurons were found with bimodal responses, responding for example to both taste and olfactory, or taste and visual stimuli. Since these multimodal neurons were found in very close proximity to unimodal neurons, and the unimodal sensory neurons were intermingled, it is possible that the orbitofrontal cortex represents the first cortical area of convergence for these three modalities in primates.
Intrathalamic rhythmicity studied in vitro: nominal T-current modulation causes robust antioscillatory effects
Authors: Huguenard JR , Prince DA
Published: April 2018

Thalamocortical oscillations mediate both physiological and pathophysiological behaviors including sleep and generalized absence epilepsy (GA). Reciprocal intrathalamic circuitry and robust burst firing, dependent on underlying transient Ca current (IT) in thalamic neurons, support generation of such rhythms. In order to study the regulation of intrathalamic rhythm generation and the effects of GA anticonvulsants previously shown to reduce IT in acutely isolated thalamic neurons, we developed an in vitro rat thalamic slice preparation that retains sufficient intrathalamic circuitry to support evoked oscillations (range = 2.0–4.6 Hz, average = 2.7, n = 38), associated with burst firing in the thalamic reticular nucleus (nRt) and thalamic relay neurons. Extracellular stimulation of nRt evoked in relay neurons a biphasic inhibitory response with prominent GABAA and GABAB receptor-mediated components. The GABAA component was picrotoxin sensitive, outwardly rectifying and Cl- dependent, with a very negative reversal potential (-94 mV), indicating that an active extrusion mechanism exists in these cells to keep [Cl-]i < 5 mM. The GABAB component had a linear conductance, a reversal potential of -103 mV, and was quite long lasting (about 300 msec) so that rebound bursts often were generated on its decay phase, presumably leading to reexcitation of nRt through known excitatory connections. GABAB- mediated responses thus provide a timing mechanism for promoting slow intrathalamic oscillations. Reduction of IT (30–40%) by succinimides slightly increased the threshold for burst generation in relay and nRt cells, but there was little effect on either number of spikes/burst or intraburst frequency, and there were no other direct effects on other measures of cellular excitability. Intrathalamic oscillations were significantly reduced by these agents through a slight decrease in burst probability of thalamic neurons. We conclude that interactions between the intrinsic properties of thalamic neurons and intrathalamic circuitry lead to generation of slow oscillations. A similar mechanism may underlie the pathophysiological 3 Hz spike and wave EEG activity that characterizes GA. Furthermore, anti-GA drugs such as ethosuximide probably exert their action by reducing the burst-firing probability of neurons within populations of reciprocally interconnected relay and nRt neurons, thus producing a desynchronization of the thalamic circuit that prevents spike/wave generation.
Quantitative measurement of calcium flux through muscle and neuronal nicotinic acetylcholine receptors
Authors: Vernino S , Rogers M , Radcliffe KA , Dani JA
Published: April 2018

A new approach was developed to determine quantitatively the fraction of current carried by Ca2+ through an ion channel under physiological conditions. This approach entails the simultaneous measurement of membrane current and intracellular Ca2+ for single cells. Whole-cell patch-clamp techniques were used to measure current, and intracellular Ca2+ was monitored with the fluorescent indicator fura-2. To obtain a quantitative measure of the fraction of current carried by Ca2+, a cell- by-cell calibration method was devised to account for differences among cells in such factors as cellular volume and Ca2+ buffering. The method was used to evaluate the Ca2+ flux through muscle and neuronal nicotinic ACh receptors (nAChRs). In a solution containing 2.5 mM Ca2+ at a holding potential of -50 mV, Ca2+ carries 2.0% of the inward current through muscle nAChRs from BC3H1 cells and 4.1% of the inward current through neuronal nAChRs from adrenal chromaffin cells. The Ca2+ flux through neuronal nAChRs of adrenal chromaffin cells is insensitive to alpha-bungarotoxin. The influx of Ca2+ is voltage dependent, and because of the Ca2+ concentration difference across the cellular membrane, there is Ca2+ influx into the cell even when there is a large net outward current. At both muscle and neuronal cholinergic synapses, activity-dependent Ca2+ influx through nicotinic receptors produces intracellular signals that may have important roles in synaptic development, maintenance, and plasticity.
Properties and function of low- and high-voltage-activated Ca2+ channels in hypoglossal motoneurons
Authors: Umemiya M , Berger AJ
Published: April 2018

Calcium influx through voltage-gated Ca2+ channels plays an important role in neuronal function. In a thin-slice preparation of neonatal rat hypoglossal motoneurons (HMs) we recorded Ba2+ currents through voltage- gated Ca2+ channels using the whole-cell configuration of the patch- clamp technique. We found that HMs have low-voltage-activated (LVA) and at least three types of high-voltage-activated (HVA) Ca2+ channels (omega-Aga-IVA sensitive, omega CgTx sensitive, and dihydropyridine sensitive), based on pharmacological and voltage-dependent properties. Of the Ca2+ current activated at 0 mV from a holding potential of -70 mV, approximately one-half was omega-Aga-IVA (200 nM) sensitive, one- third was omega-CgTx (3 microM) sensitive, whereas only 6% was DHP (nimodipine; 10 microM) sensitive. The residual current, after applying these three antagonists, had characteristics of LVA Ca2+ currents. Based on this pharmacology we found that Ca2+ entry during a single action potential (AP) through LVA Ca2+ channels has a different role from CA2+ entry through HVA Ca2+ channels. Ca2+ influx through omega- Aga-IVA-sensitive and omega-CgTx-sensitive HVA Ca2+ channels activates Ca(2+)-activated K+ channels responsible for the AP afterhyperpolarization. On the other hand, Ca2+ entry through LVA Ca2+ channels is responsible for spike afterdepolarization and provides Ca2+ for the Ca(2+)-activated K+ channels that contribute to AP repolarization.
Heat shock proteins protect against stress-related phosphorylation of tau in neuronal PC12 cells that have acquired thermotolerance
Authors: Kirby BA , Merril CR , Ghanbari H , Wallace WC
Published: April 2018

A68, or PHF-tau, is an abnormally phosphorylated form of the microtubule-associated protein tau, which is a primary protein constituent of paired helical filaments (PHFs) and, ultimately, of Alzheimer's disease-associated neurofibrillary tangles (NFTs). Previously, we have shown that in heat-shocked neuronal PC12 cells, tau is hyperphosphorylated and transformed to an A68-like state as determined by immunologic and biochemical criteria. In the present study, we investigated the role of heat shock protein of 72 kDa (hsp72) in the protection of tau against hyperphosphorylation during heat shock. Neuronal PC12 cells were exposed either directly to a heat shock (45 degrees C for 30 min) or to a conditioning heat stress (43 degrees C for 90 min followed by a 4 hr recovery at 37 degrees C) followed by the heat shock. Hsp72 was maximally induced immediately after heat shock in conditioned (acquired thermotolerant, ATT) cells, while unconditioned (nonacquired thermotolerant, non-ATT) cells required 9 hr of recovery to exhibit maximal hsp72 induction. The differential time course of hsp72 induction during recovery of ATT and non-ATT cells correlated with the presence of normal tau. Immediately after the heat shock, when hsps were maximally induced, ATT cells exhibited the normal form of tau. With longer recovery times, the levels of hsp72 were reduced and tau was hyperphosphorylated. A similar correlation was observed in non-ATT cells. In the presence of L-azetidyl 2-carboxylic acid, ATT cells synthesized nonfunctional hsp72, as exhibited by the inability of the cells to recover from the effects of heat shock.(ABSTRACT TRUNCATED AT 250 WORDS)
Otx1 and Otx2 define layers and regions in developing cerebral cortex and cerebellum
Authors: Frantz GD , Weimann JM , Levin ME , McConnell SK
Published: April 2018

Within the cerebral and cerebellar cortices, neurons are organized in layers that segregate neurons with distinctive morphologies and axonal connections, and areas or regions that correspond to distinct functional domains. To explore the molecular underpinnings of pattern formation in layered regions of the CNS, we have characterized the patterns of expression of two homeodomain genes, Otx1 and Otx2, by in situ hybridization during embryonic and postnatal development in the rat. Otx1 and Otx2 are vertebrate homologs of the Drosophila gap gene orthodenticle, and are expressed during the development of the murine CNS (Simeone et al., 1992). Here we report that Otx1 mRNA is expressed in a subpopulation of neurons within cortical layers 5 and 6 during postnatal and adult life. This gene is also expressed by the precursors of deep-layer neurons within the developing cerebral ventricular zone, but is apparently downregulated by the progenitors of upper-layer neurons; Otx1 is never expressed by the neurons of layers 1–4. The spatial and temporal patterns suggest that Otx1 may play a role in the specification or differentiation of neurons in the deep layers of the cerebral cortex. Within the cerebellum, mRNAs for Otx1 and Otx2 are found within the external granular layer (EGL), but in three spatially distinct domains. During postnatal development, Otx1 is expressed within anterior cerebellar lobules; Otx2 mRNA is localized posteriorly, and a region of overlap in mid-cerebellum defines a third domain in which both genes are expressed. The boundaries of Otx1 and Otx2 expression correspond to the major functional boundaries of the cerebellum, and define the vestibulocerebellum, spinocerebellum, and pontocerebellum, respectively. Spatially restricted patterns of hybridization are observed early in postnatal life, at times that correspond roughly to the invasion of spinal and pontine afferents into the cerebellum (Arsenio-Nunes and Sotelo, 1985; Mason, 1987). These results raise the possibility that Otx1 and Otx2 play a role in cerebellar regionalization during early development.
Intracellular sorting of neuromodulin (GAP-43) mutants modified in the membrane targeting domain
Authors: Liu Y , Fisher DA , Storm DR
Published: April 2018

Neuromodulin (GAP-43) is a neurospecific calmodulin binding protein that is targeted to neuronal growth cones via fast axonal transport by an undefined mechanism. The protein is associated with membranes by palmitoylation of cys-3 and cys-4. The objective of this study was to examine the intracellular localization of neuromodulin and neuromodulin mutants modified in the membrane targeting domain of the protein in neurons and non-neuronal cells. The N-terminal palmitoylation domain of neuromodulin was found to be sufficient for membrane and Golgi targeting as well as neurite transport. A fusion protein consisting of the N-terminal 20 amino acids of neuromodulin and beta-galactosidase accumulated in neurite endings demonstrating that this sequence is sufficient for targeting to growth cone membranes. Mutations in the palmitoylation domain of neuromodulin that abolished its acylation and membrane association diminished its Golgi localization. Mutations that prevented Golgi accumulation of neuromodulin-beta-galactosidase fusion proteins also interfered with neurite transport of the fusion proteins. These data demonstrate a correlation between membrane targeting, Golgi localization, and neurite transport of neuromodulin.
A quantitative measurement of the dependence of short-term synaptic enhancement on presynaptic residual calcium
Authors: Delaney KR , Tank DW
Published: April 2018

We simultaneously measured presynaptic free calcium ion concentration ([Ca2+]i) and synaptic strength at the crayfish claw opener neuromuscular junction (nmj) under a variety of experimental conditions. Our experiments were designed both to test the hypothesis that elevated [Ca2+]i is necessary and sufficient for the induction of a form of synaptic enhancement that persists for several seconds after tetanic stimulation--augmentation--and to determine the quantitative relationship between elevated [Ca2+]i and this enhancement. Action potential trains increased [Ca2+]i and enhanced transmission. During the decay phase of synaptic enhancement known as augmentation (time constant of decay approximately 7 sec at 20 degrees C with < 200 microM fura-2 in terminals), [Ca2+]i was elevated 700 nM or less above rest and an essentially linear relationship between [Ca2+]i and enhancement was observed. Introduction of exogenous Ca2+ buffers into the presynaptic terminal slowed the buildup and recovery kinetics of both [Ca2+]i and the component of synaptic enhancement corresponding to augmentation. The slope of the relationship relating delta [Ca2+]i to augmentation was not changed. The time course of augmentation and recovery of [Ca2+]i remained correlated as the temperature of the preparation was changed from about 10 degrees C to 20 degrees C, but the quantitative relationship of enhancement to [Ca2+]i was increased more than two- to threefold. During moderate frequency trains of action potentials, a slowly developing component of the total synaptic enhancement was approximately linearly related to residual [Ca2+]i measured with fura-2. The quantitative relationship between [Ca2+]i and this component of synaptic enhancement during trains was the same as that during synaptic augmentation after trains.(ABSTRACT TRUNCATED AT 250 WORDS)
Reorganization of neural peptidergic systems in the median eminence after hypophysectomy
Authors: Villar MJ , Meister B , Hokfelt T
Published: April 2018

Earlier studies have shown the formation of a novel neural lobe after hypophysectomy, an experimental manipulation that causes transection of neurohypophyseal nerve fibers and removal of pituitary hormones. The mechanisms that underly this regenerative process are poorly understood. The localization and number of peptide-immunoreactive (-IR) fibers in the median eminence were studied in normal rats and in rats at different times of survival after hypophysectomy using indirect immunofluorescence histochemistry. The number of vasopressin (VP)-IR fibers increased in the external layer of the median eminence in 5 d hypophysectomized rats. Oxytocin (OXY)-IR fibers decreased in the internal layer and progressively extended into the external layer. At long survival times (9 and 16 months) both VP- and OXY-IR fibers had a bilayered distribution occupying both the external and internal layers. Double-labeling experiments combining VP and tyrosine hydroxylase antisera as well as OXY and growth hormone-releasing factor antisera showed that injured neurosecretory fibers growing into the external layer displaced fibers from parvocellular cells originally located there. As a result, there was essentially an inversion in the distribution of these fibers within the median eminence. Galanin (GAL)- and cholecystokinin (CCK)-IR fibers exhibited a similar pattern of distribution after the lesion. Thus, after 5 d there was an increase in GAL- and CCK-IR fibers in the internal layer. At 14 and 30 d, the number of GAL- and CCK-IR fibers progressively decreased, but after longer survivals (9 and 16 months) there was a dramatic reappearance. Dynorphin (DYN)-LI showed a dramatic increase at all levels of the median eminence at short survival times after hypophysectomy, followed by a subsequent decrease to a final stage of a few, strongly immunoreactive fibers in the external layer at longer survival times. Vasoactive intestinal polypeptide (VIP)- and peptide histidine- isoleucine (PHI)-IR fibers in hypophysectomized animals had already contacted portal vessels 5 d after hypophysectomy, and from then on progressively increased in numbers. Finally, most of the peptide fibers described above formed dense innervation patterns around the large blood vessels along the lateral borders of the median eminence. The present results show that hypophysectomy induces a wide variety of changes in hypothalamic neurosecretory fibers. Not only is the expression of several peptides in these fibers modified following different survival times, but a reorganization of the distribution of immunoreactive fibers within the median eminence is demonstrated. The hypothesis is raised that regeneration of injured neurosecretory fibers may be dependent on changes in the expression of peptides possessing trophic actions.
Acoustically responsive fibers in the vestibular nerve of the cat
Authors: McCue MP , Guinan JJ
Published: April 2018

Recordings were made from single afferent fibers in the inferior vestibular nerve, which innervates the saccule and posterior semicircular canal. A substantial portion of the fibers with irregular background activity increased their firing in response to moderately intense clicks and tones. In responsive fibers, acoustic clicks evoked action potentials with minimum latencies of < or = 1.0 msec. Fibers fell into two classes, with the shortest latency either to condensation clicks (PUSH fibers) or to rarefaction clicks (PULL fibers). Low- frequency (800 Hz) tone bursts at moderately high sound levels (> 80 dB SPL) caused synchronization of spikes to preferred phases of the tone cycle. PUSH and PULL fibers had preferred response phases approximately 180 degrees apart. These two response classes are consistent with fibers that innervate hair cells having opposite morphological polarizations, an arrangement found in the saccule. With low-frequency tone bursts, sound levels of > or = 90 dB SPL evoked increases in mean spike rate. Spike rates increased monotonically with sound level without saturating at levels < or = 115 dB SPL. Contraction of the middle-ear muscles decreased responses to sound, consistent with the sound transmission path being through the middle ear. Several fibers were labeled with biocytin and traced. All labeled fibers had bipolar cell bodies in the inferior vestibular ganglion with peripheral processes extending toward the saccular nerve and central processes in the vestibular nerve. Two fibers were traced to the saccular epithelium. One fiber was traced centrally and arborized extensively in vestibular nuclei and a region ventromedial to the cochlear nucleus. Our results confirm and extend previous suggestions that the mammalian saccule responds to sound at frequencies and levels within the normal range of human hearing. We suggest a number of auditory roles that these fibers may play in the everyday life of mammals.
Individual locomotor response to novelty predicts selective alterations in D1 and D2 receptors and mRNAs
Authors: Hooks MS , Juncos JL , Justice JB , Meiergerd SM , Povlock SL , Schenk JO , Kalivas PW
Published: April 2018

Rats that have a greater locomotor response to novelty (high responders, HR) have differences in measures of presynaptic dopamine transmission compared to low responders (LR) to a novel environment, including altered dopamine release and behavioral response to indirect dopamine agonists. This study examined the role of three dopamine terminal fields, the nucleus accumbens, striatum, and medial prefrontal cortex, in differences between HR and LR. In the first experiment, dopamine was infused directly into the nucleus accumbens (0, 3, 10, and 30 micrograms/side) or the striatum (0, 10, 30, and 100 micrograms/side). HR showed a greater behavioral response to both the 3 and 30 micrograms/side doses infused into the nucleus accumbens compared to LR. No differences between HR and LR were revealed by dopamine infusion into the striatum. In the second experiment, radioligand binding assays were performed to determine if differences exist between high and low responder rats in the Bmax and/or KD of radiolabeled antagonist ligands for the dopamine D1 and/or D2 receptors. There were fewer D2 binding sites in the nucleus accumbens and fewer sites in the striatum in HR compared to LR. High responders showed a greater Bmax for D1 binding sites in the nucleus accumbens than LR. No differences in number of binding sites for D1 receptors were observed between HR and LR in the striatum. No differences between HR and LR in D2 or D1 receptor binding were observed in the medial prefrontal cortex. There were no differences in KD for any of the dopamine receptors in the regions examined.(ABSTRACT TRUNCATED AT 250 WORDS)
IL-2 induces vasopressin release from the hypothalamus and the amygdala: role of nitric oxide-mediated signaling
Authors: Raber J , Bloom FE
Published: April 2018

The neuropeptide arginine vasopressin (AVP) can replace the cytokine interleukin 2 (IL-2) as a T-cell mitogen for the induction of interferon gamma (IFN gamma) expression in splenic cultures. IL-2-like and IL-2 receptor immunoreactivity have been reported in different brain regions, under normal and pathophysiological conditions. Regulatory functions for IL-2 in the CNS have been suggested. In addition to the spleen, AVP might also mediate some IL-2 effects centrally. In the present study, we evaluated the effect of IL-2 on the in vitro release of AVP from the hypothalamus and amygdala. In addition, we used these release systems to study the possible involvement of NO-mediated signaling in AVP release, based on the reported detection of nitric oxide synthase (NOS) in the hypothalamus and amygdala. IL-2 rapidly stimulates AVP release in both regions, in a calcium- and dose-dependent manner. In addition, nitroprusside also induces AVP release. Norepinephrine also induces AVP release from both the hypothalamus, as well as the amygdala. The norepinephrine-induced AVP release is antagonized by phentolamine, but not by propranolol, suggesting an alpha-adrenergic receptor-mediated AVP response in both brain regions. The IL-2- and acetylcholine-induced AVP release is antagonized by Ng-methyl-L-arginine, indicating a role for NO in this AVP release. Ng-methyl-L-arginine does not affect the norepinephrine- induced AVP release. A stimulatory effect of IL-2 on hypothalamic CRF release and plasma ACTH has already been reported. Our results suggest that in addition to CRF, AVP may also mediate the IL-2 stimulation of ACTH secretion. These data further suggest that in addition to the hypothalamus, the amygdala may also play a role in the bidirectional communication between neuroendocrine and immune systems. Understanding the mode of interaction between IL-2 with AVP could clarify the pathophysiologic or toxic effects of high brain levels of IL-2.
The extent of adaptation in bullfrog saccular hair cells
Authors: Shepherd GM , Corey DP
Published: April 2018

Positive deflection of the sensory hair bundle of a vertebrate hair cell opens transduction channels to depolarize the cell. In bullfrog saccular hair cells, there is a subsequent adaptation process, whereby the proportion of transduction channels that are open, and thus the receptor current, declines toward the resting value. This occurs because the sensitivity curve, relating open probability to bundle deflection, shifts along the deflection axis in response to bundle deflections, in a manner consistent with a relaxation of mechanical tension on transduction channels. In this study we determined the extent of adaptation, measured as the shift of the sensitivity curve following deflection of the hair bundle. The shift was determined both by comparison of the receptor current in the adapted state to the resting sensitivity curve, and by comparison of pre- and postadapted sensitivity curves. The adaptive shift approached steady state with a time constant of 20–30 msec, and was at steady state within 150 msec. For all positive and for small negative deflections, both methods showed a shift that was approximately 80% of the deflection. For larger negative deflections, the shift reached a fixed limit that was 100–500 nm negative to the freestanding bundle position. The limited extent of adaptation confers a time-dependent sensitivity: the cell has an instantaneous or phasic sensitivity curve that is steep, and steady- state or tonic sensitivity curve that is about five times broader. It also suggests the existence of two additional structural elements within the transduction apparatus. A revised quantitative theory accommodates these elements.