bluuebunny/crossref_metadata_2025 huggingface dataset:
Controlled Aqueous Synthesis of CdSe Quantum Dots using Double-Hydrophilic Block Copolymers as Stabilizers
Authors: Runge Denis , Cölfen Helmut
Published: April 2018

We present a simple experimental procedure to obtain CdSe quantum dots from aqueous solution with a controllable size. Double-hydrophilic block copolymers consisting of a poly(ethylene glycol) block and a block of either poly(ethylene imine) or polylysine are used as stabilizers. UV/VIS absorption spectroscopy, analytical ultracentrifugation and transmission electron microscopy are used to examine the resulting quantum dots. The particle size can be simply controlled by adjusting the polymer concentration during synthesis for both block copolymers.
GEOGRAFIA ESCOLAR NO ENSINO FUNDAMENTAL: ANÁLISE DO CONTEXTO DA PRÁTICA DA POLÍTICA EDUCACIONAL PARA JOVENS E ADULTOS / SCHOOL GEOGRAPHY IN FUNDAMENTAL TEACHING: ANALYSIS OF THE CONTEXT OF THE PRACTICE OF EDUCATIONAL POLICY FOR YOUTH ANLD ADULTS
Authors: Dal Molin Adriana , Dias Liz Cristiane , Tessmann Jéssica Moara Da Cunha
Published: April 2018

Esse artigo traz para discussão a Geografia Escolar no Ensino Fundamental a partir da análise do contexto da prática da política educacional para Jovens e Adultos. Nosso objetivo é ampliar o debate acerca do tema à luz da contribuição teórica de Stephen Ball sobre o ciclo de políticas educacionais. Para tanto, adotamos como metodologia a abordagem qualitativa com ênfase na observação. O cotidiano escolar é permeado por diferentes concepções de educação e os limites entre o texto legal de uma política e a prática escolar podem ser demarcados pela ação dos profissionais responsáveis pela educação em diferentes espaços e tempos. Por fim, evidenciamos certa distância entre o proposto pela macro política educacional e o contexto da prática no cotidiano da escola deixando em aberto a discussão e a tomada de decisões e ações para que a oferta da modalidade seja efetivamente uma oportunidade para aquelas pessoas que não tiveram acesso em idade regular ou precisaram abandonar a escola precocemente.Abstract:This article brings to the discussion the School Geography in Elementary School from the analysis of the context of the practice of the educational policy for Young people and Adults. Our aim is to broaden the debate on the subject in light of Stephen Ball's theoretical contribution to the educational policy cycle. To do so, we adopted as methodology the qualitative approach with emphasis on observation. The daily school life is permeated by different conceptions of education and the limits between the legal text of a policy and the school practice can be demarcated by the action of professionals responsible for education in different spaces and times. Finally, we show a certain distance between the proposed by the macro educational policy and the context of the practice in the daily school, leaving open discussion and decision making and actions so that the offer of the modality is effectively an opportunity for those who have not had access or had to leave school early.Keywords: Youth and Adult Education. Policy Cycle. Geography.
LEVANTAMENTO DE SOLOS NO BRASIL: MÉTODOS, PRÁTICAS E DIFICULDADES
Authors: Flach Cláudia Werner , Corrêa Edvania Aparecida
Published: April 2018

Os levantamentos de solos no Brasil são realizados a muitas décadas. Ao longo desse período, diferentes métodos e técnicas de levantamentos foram sendo utilizados, a fim de atender as demandas vigentes ou os recursos disponíveis, destacando-se o mapeamento convencional de solos, o mapeamento digital de solos e mapeamento de solos por determinação espectral. Apesar do grande número de levantamentos realizados, ainda há uma carência de informações, principalmente de informações de solos em escala de detalhe.
Leis, Costumes e Valores de Conduta Moral: Sistemas de Regulamentação entre Comunidades de Pescadores Artesanais na Lagoa Mirim, Rio Grande do Sul
Authors: Nunes Pieve Stella Maris , Korting Matheus Sehn
Published: April 2018

O presente artigo tem como objetivo apresentar uma discussão acerca dos sistemas de regulamentação vigentes entre comunidades de pescadores da Lagoa Mirim, Rio Grande do Sul. A partir da experiência etnográfica em três municípios, Arroio Grande, Jaguarão e Santa Vitória do Palmar, a proposta é entender e analisar de que maneira “regras internas” e “regras externas” acerca das práticas do cotidiano, dos costumes, da conduta moral e da honra se articulam nos casamentos locais, nas cooperações de trabalho e na implementação da legislação ambiental. O que podemos perceber ao observar o sistema normativo a partir de diversos prismas são as lacunas formadas entre a intencionalidade da lei e da autoridade e a prática dos costumes, destacando as possibilidades, mas não totalidade das formas de regulamentação.
High affinity choline uptake and calcium-dependent acetylcholine release in proteoliposomes derived from rat cortical synaptosomes
Authors: Meyer EM , Cooper JR
Published: April 2018

Proteoliposomes were prepared from rat cortical synaptic plasma membranes that retained high and low affinity choline transport. High affinity transport was inhibited by hemicholinium-3 in a competitive manner and was apparently dependent on membrane potential or ion gradients. Proteoliposomes supplemented with an acetylcholine- generating system were able to synthesize [3H]ACh de novo from [3H]choline taken up by high or low affinity transport; however, we were able to specifically load proteoliposomes derived from cholinergic membranes by using a low choline concentration. [3H]ACh, but not [3H]choline, was subsequently released in a calcium-dependent manner by K+ depolarization. This preparation offers a simplified membrane system for studying functional high affinity choline transport and nonvesicular ACh release.
Regenerated hair cells can originate from supporting cell progeny: evidence from phototoxicity and laser ablation experiments in the lateral line system
Authors: Balak KJ , Corwin JT , Jones JE
Published: April 2018

The mechanisms that lead to the production of sensory hair cells during regeneration have been investigated by using 2 different procedures to ablate preexisting hair cells in individual neuromast sensory epithelia of the lateral line in the tails of salamanders, then monitoring the responses of surviving cells. In one series of experiments, fluorescent excitation was used to cause the phototoxic death of hair cells that selectively take up the pyridinium dye DASPEI. In the other experiments, the ultraviolet output of a pulsed neodymium-YAG laser was focused to a microbeam through a quartz objective lens in epi- illumination mode and used to selectively kill individual unlabeled hair cells while the cells were simultaneously imaged by transmitted light DIC microscopy. Through observation of the treated neuromasts in vivo, these experiments demonstrated that mature sensory epithelia that have been completely depleted of hair cells can still generate new hair cells. Preexisting hair cells are not necessary for regeneration. Immediately after the ablations the only resident cells in the sensory epithelia were supporting cells. These cells were observed to divide at rates that were increased over control values, and eventually those cell divisions gave rise to progeny that differentiated as hair cells, replacing those that had been killed. Macrophages were active in these epithelia, and their phagocytic activity had a significant influence on the standing population of cells. The first new hair cells appeared 3–5 d after the treatments, and additional hair cells usually appeared every 1–2 d for at least 2 weeks. We conclude that the fate of the progeny produced by supporting cell divisions is plastic to a degree, in that these progeny can differentiate either as supporting cells or as hair cells in epithelia where hair cells are missing or depleted.
Neuronal activities in brain-stem cholinergic nuclei related to tonic activation processes in thalamocortical systems
Authors: Steriade M , Datta S , Pare D , Oakson G , Curro Dossi RC
Published: April 2018

This study was performed to examine the hypothesis that thalamic- projecting neurons of mesopontine cholinergic nuclei display activity patterns that are compatible with their role in inducing and maintaining activation processes in thalamocortical systems during the states of waking (W) and rapid-eye-movement (REM) sleep associated with desynchronization of the electroencephalogram (EEG). A sample of 780 neurons located in the peribrachial (PB) area of the pedunculopontine tegmental nucleus and in the laterodorsal tegmental (LDT) nucleus were recorded extracellularly in unanesthetized, chronically implanted cats. Of those neurons, 82 were antidromically invaded from medial, intralaminar, and lateral thalamic nuclei: 570 were orthodromically driven at short latencies from various thalamic sites: and 45 of the latter elements are also part of the 82 cell group, as they were activated both antidromically and synaptically from the thalamus. There were no statistically significant differences between firing rates in the PB and LDT neuronal samples. Rate analyses in 2 distinct groups of PB/LDT neurons, with fast (greater than 10 Hz) and slow (less than 2 Hz) discharge rates in W, indicated that (1) the fast-discharging cell group had higher firing rates in W and REM sleep compared to EEG- synchronized sleep (S), the differences between all states being significant (p less than 0.0005); (2) the slow-discharging cell group increased firing rates from W to S and further to REM sleep, with significant difference between W and S (p less than 0.01), as well as between W or S and REM sleep (p less than 0.0005). Interspike interval histograms of PB and LDT neurons showed that 75% of them have tonic firing patterns, with virtually no high-frequency spike bursts in any state of the wake-sleep cycle. We found 22 PB cells that discharged rhythmic spike trains with recurring periods of 0.8–1 sec. Autocorrelograms revealed that this oscillatory behavior disappeared when their firing rate increased during REM sleep. Dynamic analyses of sequential firing rates throughout the waking-sleep cycle showed that none of the full-blown states of vigilance is associated with a uniform level of spontaneous firing rate. Signs of decreased discharge frequencies of mesopontine neurons appeared toward the end of quiet W, preceding by about 10–20 sec the most precocious signs of EEG synchronization heralding the sleep onset. During transition from S to W, rates of spontaneous discharges increased 20 sec before the onset of EEG desynchronization.(ABSTRACT TRUNCATED AT 400 WORDS)
Electroconvulsive shock differentially increases binding to alpha-1 adrenergic receptor subtypes in discrete regions of rat brain
Authors: Blendy JA , Grimm LJ , Perry DC , West-Johnsrud L , Kellar KJ
Published: April 2018

Quantitative in vitro autoradiographic methods were used to examine for the effect of repeated administration of electroconvulsive shock (ECS) on binding to subtypes of the alpha-1 receptor in rat brain. Rats were treated once daily for 10 d with ECS or sham ECS, then killed, and brains were removed and sectioned for autoradiographic analysis. Total alpha-1 binding (including both alpha-1a and alpha-1b subtypes) was assessed with [3H]prazosin; alpha-1b binding was assessed with [3H]prazosin in the presence of 10 nM WB4 101 to mask alpha-1a binding; and alpha-1a binding was assessed with [3H]WB4 101. ECS caused a significant increase in [3H]prazosin binding in most cortical regions: this increase was confined to a band corresponding to cortical laminae I-III. Subtype analysis indicated that the increase in cortical binding was due to an increase in binding to the alpha-1b subtype. Dense alpha- 1 binding was detected in most thalamic nuclei: however, only 1 small area, the parafascicular nucleus, showed a significant increase in alpha-1 binding following repeated ECS. The only other region where ECS was shown to significantly affect alpha-1 binding was the amygdala. Binding to all regions of the amygdala except the central nuclei was increased by ECS: in the lateral amygdala, this was due primarily to an increase in alpha-1b binding, while in the remaining regions the increase was primarily an alpha-1a phenomenon. Thus the effect of repeated ECS on alpha-1 binding in rat brain was found to be confined to several specific regions of the cortex, thalamus, and amygdala. Furthermore, in each of these regions, the ECS effect was limited to 1 or the other of the 2 subtypes of the alpha-1 receptor.
Evidence for two calcium-dependent potassium conductances in lizard motor nerve terminals
Authors: Morita K , Barrett EF
Published: April 2018

Action potentials and afterpotentials were recorded with a microelectrode inserted into lizard motor axons within a few millimeters of their motor terminals. In the presence of 1 mM 4- aminopyridine (4-AP), the duration of the action potential recorded near motor terminals was Ca-sensitive: repolarization was more rapid when bath [Ca] was elevated, and became slower when bath [Ca] was removed or when 0.1–1 mM Mn was added. Repolarization was also slowed following addition of 3–10 nM charybdotoxin or 100–300 microM tetraethylammonium (TEA) to the bath, and following intra-axonal injection of the Ca buffer BAPTA. These results, in agreement with published extracellular recordings, indicate that the motor nerve terminal membrane contains rapidly activating, Ca-activated K channels. When these (and other) K channels were blocked by 10 mM TEA, the action potential recorded near motor terminals was followed by Ca-dependent depolarizing afterpotentials, followed in turn by a slow hyperpolarizing afterpotential (h.a.p.) that lasted several seconds. This slow h.a.p. was also Ca-sensitive: it became larger with increasing bath [Ca] and was abolished by removal of bath [Ca] and by addition of 1 mM Mn. Intra-axonal injection of BAPTA reduced the amplitude of the slow h.a.p., and prolonged injections promoted repetitive discharge. The slow h.a.p. following single action potentials was observed in 100 microM ouabain and in K-free solutions and thus is pharmacologically distinct from the hyperpolarization that follows tetanic stimulation. The slow h.a.p. was selectively inhibited by 100 nM apamin, but persisted in 100 nM charybdotoxin. This afterpotential was enhanced by 0.1–1 mM 4-AP and by the dihydropyridine Bay K 8644 (0.1–1 microM). These results suggest that the slow h.a.p. in lizard motor nerve terminals is mediated by Ca-activated K channels that can be activated near the resting potential and are pharmacologically distinct from the Ca-activated K channels that contribute to action potential repolarization. The slow h.a.p. was enhanced by 0.1–1 mM caffeine and inhibited by 100 microM procaine, raising the possibility that this afterpotential may be activated not only by Ca entering via the plasma membrane, but also by Ca released from intra-terminal stores.
Differential effects of NGF, FGF, EGF, cAMP, and dexamethasone on neurite outgrowth and sodium channel expression in PC12 cells
Authors: Pollock JD , Krempin M , Rudy B
Published: April 2018

PC12 cells are a pheochromocytoma cell line that can be made to differentiate into sympatheticlike neurons by nerve growth factor (NGF). An essential component of the NGF-induced differentiation is the development of action potentials and sodium channels. Using whole-cell clamp we have confirmed that NGF produces a 5- to 6-fold increase in sodium channel density. The sodium channels induced by NGF are not different from those in cells not treated with NGF and are similar to those in other cell types. Basic fibroblast growth factor (FGF), another growth factor that causes PC12 cells to differentiate into sympathetic-like neurons, also produces a 5- to 6-fold increase in sodium current density with channels indistinguishable from those in PC12 cells treated and not treated with NGF. Basic FGF produces the same or somewhat larger increase in sodium channel density but much less neurite outgrowth. In contrast, epidermal growth factor does not produce neurite outgrowth but induces a small, reproducible increase in sodium channel density. Cyclic AMP produces spike-like processes but not neurites and results in a decrease in sodium current and sodium current density. Dexamethasone, a synthetic glucocorticoid, inhibits the increase in sodium current and sodium current density but does not antagonize the neurite outgrowth induced by NGF. Thus, although the increase in sodium channel expression induced by NGF and basic FGF parallels the changes in morphology that lead to neurite outgrowth, it clearly does not depend on them. The results show that different aspects of neuronal differentiation might be independently regulated by the microenvironment.
Biometric analyses of vibrissal tactile discrimination in the rat
Authors: Carvell GE , Simons DJ
Published: April 2018

Blindfolded rats were trained to stretch across a gap to palpate rough or smooth surfaces with their mystacial vibrissae. Animals learned to discriminate reliably a smooth surface from a rough surface having shallow (approximately 30 microns) grooves spaced at 90 microns intervals. Field-by-field video analyses confirmed that rats used only their vibrissae to contact the discriminanda. The whiskers swept across the surfaces at 696 degrees/sec during forward movements and 1106 degrees/sec for retracting movements. Mean amplitudes, which were 32 degrees, were considerably smaller than the total arc through which whiskers can move. Rats maintained whisker contact with discriminanda for several hundreds of msec, during which time the animals repetitively swept their vibrissae across the surface at a dominant frequency of 8 Hz. The range extended from 1 to 20 Hz, and the frequencies utilized varied within and among subjects. Whiskers contacted the discriminanda along the hair shaft, not at the whisker tips. The hair shafts were bent continually but to varying degrees as an animal palpated the surface, and more than one of the large caudal whiskers were almost always in contact with it. Thus, whiskers are not used independently as rigid levers. Results indicate that the capacity of the rodent whisker system to distinguish a smooth surface from a rough one is comparable to that of primates using their fingertips and suggest common strategies for active touch in the mammalian somatomotor system.
Electron microscopic localization of immunoreactive enkephalinase (EC 3.4.24.11) in the neostriatum of the rat
Authors: Marcel D , Pollard H , Verroust P , Schwartz JC , Beaudet A
Published: April 2018

The fine structural distribution of the enzyme-neutral endopeptidase EC 3.4.24.11 (enkephalinase) was examined by immunoradioautography (using an iodinated monoclonal antibody) and peroxidase immunocytochemistry (using the same probe in nonradioactive form) in the neostriatum of the rat. At the light microscopic level, both techniques revealed a heterogeneous distribution of immunoreactive enkephalinase in the caudoputamen, characterized by the presence of patches of intense immunolabeling prominent against a relatively strong immunoreactive matrix, a pattern reminiscent of mu opioid receptors radioautographically labeled in the same region. Pilot experiments indicated that fixation of the brain with a mixture of 4% paraformaldehyde, 0.05% glutaraldehyde, and 0.2% picric acid did not modify the distribution and only slightly reduced the intensity of striatal enkephalinase antigenicity, provided that the post-fixation period did not exceed 1 hr. In the neostriatum of animals fixed according to this protocol, enkephalinase immunoreactivity was found by electron microscopic immunoradioautography to be exclusively confined to neuronal and glial membrane interfaces. Immunoperoxidase cytochemistry confirmed the association of immunoreactive enkephalinase with the plasma membrane of neurons and, to a lesser extent, of astrocytes and oligodendrocytes. Both immunoradioautographic and immunoperoxidase techniques revealed a predominant association of the enzyme with neuronal perikarya and dendrites. The morphological features of the labeled perikarya, together with the presence of immunoreactive dendritic spines, suggested that some of these neurons corresponded to striatofugal medium spiny neurons. Immunoreactive enkephalinase was also detected at the level of myelinated and unmyelinated axons and axon terminals. These axons could potentially have originated from intrinsic striatal neurons or from the substantia nigra. Statistical analysis of silver grain distribution in electron microscopic immunoradioautographs indicated that immunoreactive enkephalinase was not preferentially concentrated at the level of specific membrane interfaces, but rather, was more or less uniformly distributed on the surface of neurons and/or glial cells. A similarly diffuse localization of the enzyme was apparent in peroxidase-reacted material, though the latter technique also revealed a microheterogeneity in the deposition of the reaction product along the labeled membranes. Finally, quantitative analysis of immunoradioautographs clearly indicated an absence of enkephalinase enrichment at the level of synaptic junctions. The similarity between the light and electron microscopic distribution of enkephalinase observed in the present study, and that previously reported for mu opioid receptors, lends support to the concept that this ectoenzyme may be involved in the inactivation of endogenous opioids in the mammalian neostriatum.
The effect of depolarization on expression of the human proenkephalin gene is synergistic with cAMP and dependent upon a cAMP-inducible enhancer
Authors: Van Nguyen T , Kobierski L , Comb M , Hyman SE
Published: April 2018

Membrane depolarization is a critical component of neural signaling; in recent years there also has been a great deal of evidence that membrane depolarization can regulate neural gene expression. Therefore, excitatory neurotransmission may be an important mechanism of neural plasticity. We have investigated the intracellular pathways and DNA regulatory elements through which membrane depolarization activates expression of the neural gene encoding human proenkephalin. In PC12 and C6-glioma cells, depolarization-induced expression of a transfected proenkephalin fusion gene was proportional to extracellular calcium concentration and was inhibited by verapamil. Activation of the gene by KCl-induced depolarization or the calcium ionophore A23187 was dependent upon and synergistic with cAMP in PC12 and C6-glioma cells, but neither depolarization nor treatment with A23187 affected cAMP levels. Trifluoperazine and W7 inhibited depolarization-induced gene expression but did not affect expression induced by the adenylyl cyclase activator forskolin. At the level of the DNA, depolarization- induced activation is conferred on the proenkephalin gene by a previously characterized cAMP-inducible enhancer. Multiple copies of a single component element of that enhancer, containing the CGTCA sequence motif characteristic of cAMP regulatory elements, can reconstitute the entire repertoire of responses to both cAMP and depolarization. These data suggest a model in which membrane depolarization activates gene expression through a calcium-dependent pathway, potentially involving calmodulin, and in which the transcriptional responses to both cAMP and calcium are transduced by the same DNA element.
The neurotrophic effects of fibroblast growth factors on dopaminergic neurons in vitro are mediated by mesencephalic glia [published erratum appears in J Neurosci 1992 Mar;12(3):685]
Authors: Engele J , Bohn MC
Published: April 2018

Neurotrophic support is generally believed to result from a direct action of growth factors on developing neurons. However, there is increasing evidence that growth factors can indirectly affect neuronal development by glial-mediated processes. To investigate a possible role of glia in mediating neurotrophic effects on dopaminergic neurons, four purified growth factors were screened for dual effects on the survival and differentiation of dopaminergic neurons and on the proliferation of mesencephalic glial cells in vitro. Dissociated embryonic day 14.5 rat mesencephalon was grown at low cell density without serum, conditions under which both glial growth and neuronal survival are not optimal. Treatment of these cultures with acidic fibroblast growth factor (aFGF) or basic fibroblast growth factor (bFGF) increased the number of surviving tyrosine hydroxylase-immunoreactive (TH-IR) neurons by 90- 110% [corrected] at 8 d in vitro in a dose-dependent manner. The effects of these factors were not additive. High-affinity dopamine uptake was increased by bFGF, but not by aFGF. Length of TH-IR neurites was not affected by either aFGF or bFGF. Both growth factors induced proliferation of mesencephalic astrocytes as demonstrated by autoradiographic labeling with 3H-thymidine combined with immunocytochemistry for glial fibrillary acidic protein (GFAP). In contrast, platelet-derived growth factor (PDGF) and interleukin-1 had no effect on the survival or differentiation of dopaminergic neurons or the proliferation of mesencephalic astrocytes. Inhibition of glial proliferation abolished the neurotrophic effects exerted by aFGF or bFGF on dopaminergic neurons. Moreover, conditioned medium derived from mesencephalic glial cultures replated in the virtual absence of neurons also contained neurotrophic activity.(ABSTRACT TRUNCATED AT 250 WORDS)
Membrane resealing in cultured rat septal neurons after neurite transection: evidence for enhancement by Ca(2+)-triggered protease activity and cytoskeletal disassembly
Authors: Xie XY , Barrett JN
Published: April 2018

Neurites of cultured septal neurons were transected with a laser under sterile conditions, and the subsequent membrane resealing was assayed using a dye exclusion method. In agreement with findings in other preparations, Ca2+ enhanced resealing: in normal culture medium the percentage of lesioned neurons that resealed within 20-30 min after transection increased with increasing bath [Ca2+] over the range 10(-7) to 2 x 10(-3) M; about 75% of cells resealed in 2 mM Ca2+. Mn2+ and Sr2+ also enhanced resealing, but Mg2+ inhibited it. The percentage of resealing neurons was sensitive to agents known to alter the stability of cytoskeletal components. Agents that tend to disassemble microtubules and/or neurofilaments (e.g., colchicine, low-ionic- strength media) strongly promoted resealing, whereas treatments that tend to stabilize microtubules (taxol, Mg2+) inhibited resealing. Addition of exogenous proteases (papain, trypsin, or dispase) enhanced resealing, whereas inhibitors of cysteine proteases (including a specific inhibitor of calpain, a Ca-activated neutral protease) strongly inhibited resealing. Calmodulin inhibitors inhibited resealing, consistent with reports that calmodulin facilitates calpain- mediated proteolysis of fodrin, a component of the cortical cytoskeleton. Based on these results, we hypothesize that one of the major mechanisms involved in resealing is activation of endogenous proteases by Ca2+ entry into the injured neurite. The resulting changes in the cellular cytoskeleton might promote fusion and resealing of the cut ends of the plasma membrane by enhancing membrane mobility and/or by removing structures that normally prevent membrane-membrane contact.
6-Hydroxydopamine lesions of the prefrontal cortex in monkeys enhance performance on an analog of the Wisconsin Card Sort Test: possible interactions with subcortical dopamine
Authors: Roberts AC , De Salvia MA , Wilkinson LS , Collins P , Muir JL , Everitt BJ , Robbins TW
Published: April 2018

The effects of 6-hydroxydopamine lesions of the prefrontal cortex in monkeys were investigated on two cognitive tests of prefrontal function, spatial delayed response, and attentional set shifting. The latter test provided a componential analysis of the Wisconsin Card Sort Test, a commonly used clinical test of frontal lobe function in man. Acquisition of a visual compound discrimination requiring a shift of attention from one dimension to another (extradimensional shift), for example, shapes to lines, was significantly improved. This enhancement was behaviorally specific in that there were no effects on acquisition of a discrimination that required the continued maintenance of an attentional set toward one particular dimension (intradimensional shift), nor any effects on a series of visual or spatial discrimination reversals that involved the repeated shifting of responding between two exemplars from the same dimension. In contrast, spatial delayed response performance was impaired, in agreement with previous results. Neurochemical measures showed a marked depletion of dopamine limited to the prefrontal cortex and a smaller loss of prefrontal noradrenaline. This was accompanied by a long-term adaptive change in the striatum such that extracellular dopamine in the caudate nucleus, as measured by in vivo microdialysis, was elevated in response to potassium stimulation as long as 18 months postsurgery. It is proposed that attentional set shifting is mediated by a balanced interaction between prefrontal and striatal dopamine, and that elevated dopamine contributes to the improvement in attentional set-shifting ability. This interpretation is consistent with the impairment in attentional set-shifting ability observed in patients with Parkinson's disease or with damage to the frontal lobes using the same test as used here for infrahuman primates.
Involvement of auditory cortical and hippocampal neurons in auditory working memory and reference memory in the rat
Authors: Sakurai Y
Published: April 2018

The goal of the present study was to see whether one neuron is involved exclusively in one type of memory or in different types of memory. Single-unit activity was recorded from rat hippocampal CA1, CA3, dentate gyrus, and auditory cortex (AC) during performances of auditory working memory (WM) and reference memory (RM) tasks. Both the memory tasks employed identical apparatus and stimuli and differed only in the type of memory required for correct performance. Around 10% and 43% of the units from the four brain regions showed sensory correlates (differences in activity due to the type of sensory stimulus) only in the WM or RM task, respectively. Only the AC had units showing different kinds of sensory correlates between the WM and RM tasks. About 30% of the units from the four regions had sensory-retention correlates (sustained differential activity during the delay) only in the RM task, whereas the AC had units with sensory-retention correlates only in the WM task or in both the WM and RM tasks. Approximately 35% of the units from the hippocampal regions showed motor correlates (increments of activity immediately prior to responses) only in the WM task. Another 30% of the hippocampal units showed such correlates both in the WM and RM tasks. About 22% of the hippocampal CA1 and CA3 units showed comparison-motor correlates (increases of activity prior to correct responses) only in the WM task. These results indicate that some neurons are involved solely in WM or RM, whereas other neurons are involved in both WM and RM. The results also suggest that more neurons are involved in sensory and retention processing for RM than for WM, and that the AC alone has flexible neurons involved in the processes for both types of memory. More hippocampal neurons are involved in the motor and comparison processes for WM than for RM.
Postnatal development and plasticity of corticocortical projections from area 17 to area 18 in the cat's visual cortex
Authors: Price DJ , Ferrer JM , Blakemore C , Kato N
Published: April 2018

We used retrogradely transported fluorescent tracers to study the development of projections from area 17 to area 18 in normal and monocularly deprived kittens. In newborn animals, cells in area 17 that were labeled from small, discrete injections in area 18 were concentrated around the retinotopically corresponding zone, but distributed with lower density over a very wide surrounding area. Hence, the total convergence and divergence of the projection were initially enormous, but they decreased dramatically, mainly during the first postnatal month, through elimination of the sparse, widespread distribution of projections. Injections of two different tracers close together in area 18 produced very few double-labeled cells in area 17 at any age, implying that most individual axons arborize over very small territories even at birth. In normal kittens the peak density of association cells in the upper layers, corrected for the overall expansion of the cortex, doubled over the first postnatal month and then declined gradually over the following several months, presumably because of continuing selection and elimination. As shown in previous work (Price and Blakemore, 1985a), area 17 to 18 cells in newborn kittens were distributed in two continuous bands in supragranular and infragranular layers. During normal maturation, elimination of projections results in the formation of distinct clusters; these lie preferentially in the upper layers above patches of ipsilateral eye input to layer 4 (Price et al., 1994). Monocular deprivation, which causes the terminal patches representing the deprived eye to become much smaller than normal, did not stop the normal decrease in overall convergence/divergence or the appearance of clusters of association cells, but the clusters were distinctly larger than normal in both hemispheres. Monocular deprivation also prevented the normal reduction in density of association cells within clusters after 1 month of age. Comparison with results from binocularly deprived animals, where clusters also form but association cell density is low, suggests that the size of clusters and the density of association cells retained depend on the overall level of cortical activity.
Distribution of agrin mRNAs in the chick embryo nervous system
Authors: Ma E , Morgan R , Godfrey EW
Published: April 2018

Agrin is a synapse-organizing protein likely to mediate nerve-induced aggregation of acetylcholine receptors and other postsynaptic components at the neuromuscular junction. We used in situ hybridization and polymerase chain reaction (PCR) to define the localization of agrin mRNA and its alternatively spliced forms in the chick embryo nervous system. Agrin cRNA probes intensely labeled motor neurons, dorsal root ganglia, cerebellar Purkinje neurons, and retinal ganglion cells. Neuronal layers in optic tectum and ventricular regions were also labeled. Analysis by PCR showed that all parts of the nervous system at embryonic day 10 contained three major forms of agrin mRNA. Our results raise the possibility that agrin isoforms play a role in synapse formation or other aspects of neuronal development in the central nervous system.
Odorant-induced oscillations in the mushroom bodies of the locust
Authors: Laurent G , Naraghi M
Published: April 2018

Kenyon cells are the intrinsic interneurons of the mushroom bodies in the insect brain, a center for olfactory and multimodal processing and associative learning. These neurons are small (3–8 microns soma diameter) and numerous (340,000 and 400,000 in the bee and cockroach brains, respectively). In Drosophila, Kenyon cells are the dominant site of expression of the dunce, DC0, and rutabaga gene products, enzymes in the cAMP cascade whose absence leads to specific defects in olfactory learning. In honeybees, the volume of the mushroom body neurophils may depend on the age or social status of the individual. Although the anatomy of these neurons has been known for nearly a century, their physiological properties and the principles of information processing in the circuits that they form are totally unknown. This article provides a first such characterization. The activity of Kenyon cells was recorded in vivo from locust brains with intracellular and local field potential electrodes during olfactory processing. Kenyon cells had a high input impedance (approximately 1 G omega at the soma). They produced action potentials upon depolarization, and consistently showed spike adaptation during long depolarizing current pulses. They generally displayed a low resting level of spike activity in the absence of sensory stimulation, despite a large background of spontaneous synaptic activity, and showed no intrinsic bursting behavior. Presentation of an airborne odor, but not air alone, to an antenna evoked spatially coherent field potential oscillations in the ipsilateral mushroom body, with a frequency of approximately 20 Hz. The frequency of these oscillations was independent of the nature of the odorant. Short bouts of oscillations sometimes occurred spontaneously, that is, in the absence of odorant stimulation. Autocorrelograms of the local field potentials in the absence of olfactory stimulation revealed small peaks at +/- 50 msec, suggesting an intrinsic tendency of the mushroom body networks to oscillate at 20 Hz. Such oscillatory behavior could not be seen from local field potential recordings in the antennal lobes, and may thus be generated in the mushroom body, or via feedback interactions with downstream neurons in the protocerebrum. During the odor-induced oscillations, the membrane potential of Kenyon cells oscillated around the resting level, under the influence of excitatory inputs phase- locked to the field activity. Each phasic wave of depolarization in a Kenyon cell could be amplified by intrinsic excitable properties of the dendritic membrane, and sometimes led to one action potential, whose timing was phase-locked to the population oscillations.(ABSTRACT TRUNCATED AT 400 WORDS)
Desensitization of the neuronal 5-HT carrier following its long-term blockade
Authors: Pineyro G , Blier P , Dennis T , de Montigny C
Published: April 2018

In vivo extracellular unitary recordings, in vitro 3H-5-hydroxy- tryptamine (5-HT) uptake, and 3H-paroxetine binding assays were used to assess the effect of acute and long-term administration of the 5-HT reuptake inhibitor paroxetine on the neuronal 5-HT transporter in the rat dorsal hippocampus. Recovery time of the firing activity of CA3 hippocampus pyramidal neurons following microiontophoretic application of 5-HT was used as an index of in vivo reuptake activity. In a first series of experiments, the acute intravenous administration of paroxetine and 5-HT denervation with the neurotoxin 5,7- dihydroxytryptamine produced a marked prolongation of the suppressant effect of 5-HT, indicating that reuptake into 5-HT terminals plays a significant role in terminating the action of microiontophoretically applied 5-HT. In a second series of experiments, rats were treated with paroxetine (10 mg/kg/d, s.c.) for 2 or 21 d. In both treatment groups, there was a marked prolongation of the effect of microiontophoretically applied 5-HT; however, in rats treated for 2 d, the prolongation was significantly greater than that observed in rats treated for 21 d. After the 21 d treatment with paroxetine and a 48 hr washout, the prolongation of the effect of microiontophoretically applied 5-HT by acute intravenous paroxetine was significantly reduced, suggesting a decrease in the number of 5-HT carriers. In keeping with this interpretation, following the same treatment regimen, there was a 50% and 60% reduction of the in vitro 3H-5-HT uptake in hippocampal and dorsal raphe slices, respectively, and a reduced effectiveness of paroxetine in blocking 3H-5-HT uptake in both regions. The determination of the binding parameters of 3H-paroxetine revealed that, in rats treated for 21 d with paroxetine (10 mg/kg/d, s.c.), following a 48 hr washout Kd values were unchanged but Bmax values were reduced by 70% and 60% in hippocampal and cortical membranes, respectively.
In vivo infusion of NGF induces the organotypic regrowth of perivascular nerves following their atrophy in aged rats
Authors: Andrews TJ , Cowen T
Published: April 2018

The aim of this study was to investigate whether NGF could reverse the nerve fiber atrophy exhibited by some neurons in old age. We used quantitative immunohistochemical techniques to investigate how the autonomic nerves that supply different blood vessels are affected by aging. Age changes in the nerve plexus were not widespread but were specific to particular vascular targets. Furthermore, where nerve fiber atrophy did occur, it affected different populations of nerves; specifically, sympathetic nerve fibers were lost from the middle cerebral artery while nonsympathetic nerves were lost from the tail vein. Peripheral target tissues have been shown to have a trophic influence on the pattern and density of their innervation, which declines in old age (Gavazzi et al., 1992), possibly as a result of decreased availability of neurotrophic factors such as NGF. Consequently, in an attempt to reverse nerve fiber atrophy, we used miniosmotic pumps to infuse NGF for 2 weeks over involuting nerve fibers in the middle cerebral artery of freely moving aged rats. Our results show that exogenous NGF can induce organotypic neurite outgrowth from aged neurons undergoing nerve fiber atrophy. Moreover, NGF can induce a change in the pattern of the old nerve plexus to one similar to that seen in young animals. NGF had different effects on the extent and manner of neurite outgrowth in young and aged nerves. NGF induced greater nerve growth in old compared to young nerves, causing old nerves to grow within existing nerve bundles and to sprout new nerve fibers, in contrast to young nerves, which tended to grow only within existing nerve bundles. In conclusion, this study shows the potential of exogenous NGF to reverse age-related changes in neuronal morphology.
Photomechanical movements of cultured embryonic photoreceptors: regulation by exogenous neuromodulators and by a regulable source of endogenous dopamine
Authors: Stenkamp DL , Iuvone PM , Adler R
Published: April 2018

In the retina of nonmammalian vertebrates, light regulates photoreceptor morphology by causing rod photoreceptor elongation and cone photoreceptor contraction. The opposite photomechanical movements occur in the dark, and proceed with a circadian rhythm in many species in vivo. Using dissociated cultures of embryonic chick retina cells, we have recently demonstrated that photoreceptor cells that differentiate in vitro acquire the capacity of responding to light/dark cycles with photomechanical movements (Stenkamp and Adler, 1993). Here we report that the putative neuromodulators melatonin and dopamine can mimic the effects of darkness and light, respectively, on in vitro photomechanical movement. Pharmacological studies showed that dopamine appears to function by means of a D2-type receptor negatively coupled to adenylate cyclase. The effects of light on the cultured photoreceptors were inhibited by dopamine D2 receptor antagonists, and were attenuated by the dopaminergic neurotoxin 6-hydroxydopamine and by the dopamine synthesis inhibitor alpha-methyl-p-tyrosine. The possible existence of an endogenous source of dopamine in the cultures was also suggested by the presence of tyrosine hydroxylase-like immunoreactivity, and of an Na(+)-dependent mechanism for the accumulation of 3H-dopamine, which was predominantly associated with nonphotoreceptor cells. Additionally, 3H-dopamine release occurred in vitro through a Ca(2+)-dependent mechanism, as well as through reverse function of a nomifensine-sensitive dopamine transporter. Both of these putative release mechanisms appeared to be regulated by light and by melatonin, suggesting a mechanism whereby the putative dopaminergic cells may interact with other cells present in the cultures. These studies suggest that complex paracrine neuromodulatory mechanisms can differentiate in low-density embryonic cell culture, that dopaminergic activities exist in vitro, and that they are important for mediating photomechanical movements.
The ACTH(4-9) analog Org2766 modulates the behavioral changes induced by NMDA and the NMDA receptor antagonist AP5
Authors: Spruijt BM , Josephy M , Van Rijzingen I , Maaswinkel H
Published: April 2018

In studies on aged and brain-lesioned rats the chronic administration of the ACTH(4–9) analog Org2766 has been demonstrated to improve the behavioral performance. Those results suggest that maintenance of hippocampal functioning in senescence and facilitation of functional recovery after brain damage are not due to facilitated reinnervation of denervated structures as suggested in previous studies concerning regeneration of the PNS. Alternative explanations may refer to either the neuroprotective properties of the peptide as demonstrated when chronic treatment immediately follows the damage, or a peptide-induced general change in attention that indirectly may contribute to functional recovery. The behavioral effects after acute treatment with ACTH-like peptides have been previously associated with sustained attention by enhanced neuronal excitability of limbic structures. Now, a hypothesis accounting for both neuroprotection and enhanced attention is forwarded by supposing that the peptide exerts its influence by modulation of NMDA receptor activation. Therefore, the acute effects and interactions between the peptide and the NMDA receptor antagonist AP5 (D,L-2-amino-5-phosphonopentanoic acid), and the peptide and NMDA were studied in a water maze and an open field. Impaired water maze performance induced by an acute intracerebroventricular administration of AP5 was counteracted by the ACTH(4–9) analog Org2766, whereas the peptide alone did not affect spatial orientation. NMDA induced extreme locomotor activity at the periphery of the open field. Interestingly, the ACTH(4–9) analog strongly suppressed NMDA-induced enhanced locomotor activity and normalized the pattern of exploratory behavior.
Neuritic deposition of agrin on culture substrate: implications for nerve-muscle synaptogenesis
Authors: Cohen MW , Moody-Corbett F , Godfrey EW
Published: April 2018

Recent experiments have indicated that neural agrin is deposited at newly forming nerve-muscle synapses and has a primary synaptogenic role there. As a step toward assessing how the spatial arrangement of new synaptic sites is regulated, we compared the pattern of agrin deposition by Xenopus neurites on culture substrate and on muscle cells. The neurons were grown on a substrate that bound their externalized agrin so tightly that it remained bound even when the neurites retracted spontaneously or were eliminated experimentally. By contrast, the neural cell adhesion molecule, NCAM, was not left behind on the substrate when the neurites were eliminated. Agrin, visualized by immunofluorescent staining, was deposited on the culture substrate in a continuous fashion along virtually the entire neuritic arbor of many spinal cord (SC) neurites. The pattern of agrin deposition by the same neurites changed from continuous to discontinuous when the neurites contacted muscle cells, and it became continuous again when the neurites returned to the culture substrate. The sites of agrin deposition on muscle cells were also sites of accumulation of ACh receptors (AChRs). Dorsal root ganglion (DRG) neurons and some SC neurons did not deposit agrin along their neuritic outgrowth, either on the culture substrate or on the muscle cells, and did not induce AChR accumulation at sites of contact with muscle cells. Besides adding to the evidence in support of agrin's synaptogenic role, the findings indicate that muscle cells significantly influence how neural agrin and synaptic sites become distributed along paths of neurite-muscle contact.