bluuebunny/crossref_metadata_2025 huggingface dataset:
A radialization factor in normal cortical plate restores disorganized radial glia and disrupted migration in a model of cortical dysplasia
Authors: Hasling Thomas A. , Gierdalski Marcin , Jablonska Beata , Juliano Sharon L.
Published: March 2003

Treatment of pregnant ferrets on embryonic day 24 (E24) with the antimitotic methylazoxy methanol (MAM) leads to a specific constellation of effects in newborn kits, which include a very thin and poorly laminated neocortex, disruption of radial glial cell morphology with early differentiation into astrocytes, and abnormal positioning of Cajal–Retzius cells. We suggest that MAM treatment on E24 results in this model of cortical dysplasia by eliminating a population of cells that produce a factor capable of maintaining radial glia in their normal morphology. The abnormal radial glia, either alone or in combination with other abnormal features, are likely to prevent proper migration into the cortical plate. To test the possibility that normal cortex can provide the missing substance that influences radial glia, slices of E24 MAM‐treated cortex were removed at postnatal day 0 (P0) and cultured adjacent to explants of P0 normal cortical plate. By labelling a small number of cells with injections of fluorescent dextrans into the cultured slices, we found that abnormal radial glia in MAM treated slices cocultured adjacent to normal cortical plate were restored toward normal, in comparison to E24 MAM treated slices cultured alone and in other control conditions. We also found that abnormally positioned Cajal–Retzius cells move into the marginal zone and that neurons are able to migrate into the cortical plate more effectively in the coculture condition. These data indicate that normal cortical plate of ferrets contains a factor causing radial glia to maintain their elongated morphology; the improved position of radial glia encourages repositioning of Cajal–Retzius cells and improved neuronal migration into the cortical plate.
Time course of striatal ΔFosB‐like immunoreactivity and prodynorphin mRNA levels after discontinuation of chronic dopaminomimetic treatment
Authors: Andersson M. , Westin J. E. , Cenci M. A.
Published: March 2003

ΔFosB‐like proteins are particularly stable transcription factors that accumulate in the brain in response to chronic perturbations. In this study we have compared the time‐course of striatal FosB/ΔFosB‐like immunoreactivity and prodynorphin mRNA expression after discontinuation of chronic cocaine treatment to intact rats and chronic L‐DOPA treatment to unilaterally 6‐hydroxydopamine (6‐OHDA) lesioned rats. The animals were killed between 3 h and 16 days after the last drug injection. In both treatment paradigms, the drug‐induced FosB/ΔFosB immunoreactivity remained significantly elevated in the caudate putamen even at the longest withdrawal period examined. The concomitant upregulation of prodynorphin mRNA, a target of ΔFosB, paralleled the time‐course of ΔFosB‐like immunoreactivity in the 6‐OHDA‐lesion/L‐DOPA model, but was more transient in animals treated with cocaine. These results suggest that ΔFosB‐like proteins have exceptional in vivo stability. In the dopamine‐denervated striatum, these proteins may exert sustained effects on the expression of their target genes long after discontinuation of L‐DOPA pharmacotherapy.
Intrathecally applied flurbiprofen produces an endocannabinoid‐dependent antinociception in the rat formalin test
Authors: Ates Mehmet , Hamza May , Seidel Kay , Kotalla Carolin E. , Ledent Catherine , Gühring Hans
Published: March 2003

It is generally accepted that the phospholipase‐A2‐cyclooxygenase‐prostanoids‐cascade mediates spinal sensitization and hyperalgesia. However, some observations are not in line with this hypothesis. The aim of the present work was to investigate whether different components of this cascade exhibit nociceptive or antinociceptive effects in the rat formalin test. Intrathecal (i.th.) injection of prostaglandin E2 (PGE2) induced a dose‐dependent antinociceptive effect on the formalin‐induced nociception. Furthermore, thimerosal, which inhibits the reacylation of arachidonic acid thereby enhancing arachidonic acid levels, had an antinociceptive effect rather than the expected pronociceptive effect when given i.th. While the phospholipase A2 inhibitor methyl arachidonyl fluorophosphonate (MAFP; i.th.) had a significant antinociceptive effect, its analogue palmitoyl trifluoromethyl ketone (PTFMK; i.th.) had no significant effect on the formalin‐induced nociception. However, MAFP, but not PTFMK, showed a cannabinoid CB1 agonistic effect as shown by the inhibition of electrically evoked contractions of the vas deferens isolated from CB1 wild‐type mice but not of that from CB1 knockout mice. The antinociceptive effect of MAFP was completely reversed by the CB1 receptor antagonist AM‐251 (i.th.), thus attributing such effect to its CB1 agonistic effect. Moreover, the antinociceptive effect of the cyclooxygenase inhibitor, flurbiprofen (i.th.) was reversed by the co‐administration of AM‐251, but not by PGE2. Finally. the combination of phenylmethylsulfonyl fluoride (PMSF; intraperitoneal), which inhibits the degradation of anandamide through the inhibition of fatty acid amidohydrolase, with thimerosal (i.th.) produced a profound CB1‐dependent antinociception. The present results show that endocannabinoids play a major role in mediating flurbiprofen‐induced antinociception at the spinal level.
Differential galanin receptor‐1 and galanin expression by 5‐HT neurons in dorsal raphé nucleus of rat and mouse: evidence for species‐dependent modulation of serotonin transmission
Authors: Larm Jari A. , Shen Pei‐Juan , Gundlach Andrew L.
Published: March 2003

Galanin and galanin receptors are widely expressed by neurons in rat brain that either synthesize/release and/or are responsive to, classical transmitters such as γ‐aminobutyric acid, acetylcholine, noradrenaline, histamine, dopamine and serotonin (5‐hydroxytryptamine, 5‐HT). The dorsal raphé nucleus (DRN) contains ≈ 50% of the 5‐HT neurons in the rat brain and a high percentage of these cells coexpress galanin and are responsive to exogenous galanin in vitro. However, the precise identity of the galanin receptor(s) present on these 5‐HT neurons has not been previously established. Thus, the current study used a polyclonal antibody for the galanin receptor‐1 (GalR1) to examine the possible expression of this receptor within the DRN of the rat and for comparative purposes also in the mouse. In the rat, intense GalR1‐immunoreactivity (IR) was detected in a substantial population of 5‐HT‐immunoreactive neurons in the DRN, with prominent receptor immunostaining associated with soma and proximal dendrites. GalR1‐IR was also observed in many cells within the adjacent median raphé nucleus. In mouse DRN, neurons exhibited similar levels and distribution of 5‐HT‐IR to that in the rat, but GalR1‐IR was undetectable. Consistent with this, galanin and GalR1 mRNA were also undetectable in mouse DRN by in situ hybridization histochemistry, despite the detection of GalR1 mRNA (and GalR1‐IR) in adjacent cells in the periaqueductal grey and other midbrain areas. 5‐HT neuron activity in the DRN is primarily regulated via 5‐HT1A autoreceptors, via inhibition of adenylate cyclase and activation of inward‐rectifying K+ channels. Notably, the GalR1 receptor subtype signals via identical mechanisms and our findings establish that galanin modulates 5‐HT neuron activity in the DRN of the rat via GalR1 (auto)receptors. However, these studies also identify important species differences in the relationship between midbrain galanin and 5‐HT systems, which should prompt further investigations in relation to comparative human neurochemistry and which have implications for studies of animal models of relevant neurological conditions such as stress, anxiety and depression.
Differential routing of coexisting neuropeptides in vasopressin neurons
Authors: Landry Marc , Vila‐Porcile Evelyne , Hökfelt Tomas , Calas André
Published: March 2003

The functional implications of intraneuronal coexistence of different neuropeptides depend on their respective targeting to release sites. In the rat hypothalamic magnocellular neurons, we investigated a possible differential routing of the coexpressed galanin and vasopressin. The respective location of proteins and messengers was assessed with double immunogold and in situ hybridization combining confocal and electron microscope analysis. The various populations of labelled granules were quantitatively compared in three subcellular compartments: perikarya, local processes and posthypophyseal nerve endings. Three subpopulations of granules were detected in all three compartments, but their respective amount showed significant differences. Galanin alone was immunolocalized in some secretory granules, vasopressin alone in others, and both peptides in a third subpopulation of granules. The major part of the granules containing vasopressin, either alone or in association with galanin, is found in neurohypophyseal nerve endings. In contrast, galanin single‐labelled granules represent the most abundant population in dendritic processes, while double‐labelled granules are more numerous in perikarya. This indicates a preferential distribution of the two peptides in the different compartments of magnocellular neurons. Furthermore, galanin and vasopressin messenger RNAs were detected at different domains of the endoplasmic reticulum, suggesting that translation might also occur at different locations, thus leading to partial segregation of galanin and vasopressin cargoes between two populations of secretory granules. The present study provides, for the first time in mammals, evidence suggesting that galanin and vasopressin are only partly copackaged and undergo a preferential targeting toward dendrites or neurohypophysis, suggesting different functions, autocrine/paracrine and endocrine, respectively.
Rat strain differences in peripheral and central serotonin transporter protein expression and function
Authors: Fernandez Francesca , Sarre Sophie , Launay Jean‐Marie , Aguerre Sylvie , Guyonnet‐Dupérat Véronique , Moisan Marie‐Pierre , Ebinger Guy , Michotte Yvette , Mormède Pierre , Chaouloff Francis
Published: March 2003

Female Fischer 344 (F344) rats have been shown to display increased serotonin transporter (5‐HTT) gene expression in the dorsal raphe, compared to female Lewis (LEW) rats. Herein, we explored, by means of synaptosomal preparations and in vivo microdialysis, whether central, but also peripheral, 5‐HTT protein expression/function differ between strains. Midbrain and hippocampal [3H]paroxetine binding at the 5‐HTT and hippocampal [3H]serotonin (5‐HT) reuptake were increased in male and female F344 rats, compared to their LEW counterparts, these strain differences being observed both in rats of commercial origin and in homebred rats. Moreover, in homebred rats, it was found that these strain differences extended to blood platelet 5‐HTT protein expression and function. Saturation studies of midbrain and hippocampal [3H]paroxetine binding at the 5‐HTT, and hippocampal and blood platelet [3H]5‐HT reuptake, also revealed significant strain differences in Bmax and Vmax values. Although F344 and LEW rats differ in the activity of the hypothalamo‐pituitary‐adrenal (HPA) axis, manipulations of that axis revealed that the strain differences in hippocampal [3H]paroxetine binding at 5‐HTTs and [3H]5‐HT reuptake were not accounted for by corticosteroids. Hippocampal extracellular 5‐HT levels were reduced in F344 rats, compared to LEW rats, with the relative, but not the absolute, increase in extracellular 5‐HT elicited by the local administration of citalopram being larger in F344 rats. Because the aforementioned strain differences did not lie in the coding sequences of the 5‐HTT gene, our results open the promising hypothesis that F344 and LEW strains model functional polymorphisms in the promoter region of the human 5‐HTT gene.
Cognitive control processes during an anticipated switch of task
Authors: Wylie G. R. , Javitt D. C. , Foxe J. J.
Published: March 2003

For successful negotiation of our environment, humans must be readily able to switch from one task to another. This ability relies on ‘executive control’ processes and despite extensive efforts to detail the nature of these processes, there is little consensus as to how the brain achieves this critical function. Behavioural studies show that as subjects are given more time to prepare to switch task, performance improves; yet even with the longest preparation intervals, there remains an ineradicable performance cost on switch trials. As such, some elements of the switching process must wait until the stimulus to be acted upon has actually been presented. Here, using the methods of high‐density mapping of brain potentials, we show that early visual processes are substantially different on switch trials than on later trials. Our data show that while there is clearly a degree of preparatory processing that occurs prior to a predictable switch of task, some elements of switching are only achieved after the switch stimulus has been presented. Our findings are discussed in the context of a new model of executive control processes that suggests that preparing to switch task may not be a separate (control) processper se, but rather, the beginning of a competition between the potentially relevant tasks, a competition that is ultimately resolved during the switch trial.
Impairments in visual discrimination after perirhinal cortex lesions: testing ‘declarative’ vs. ‘perceptual‐mnemonic’ views of perirhinal cortex function
Authors: Bussey Timothy J. , Saksida Lisa M. , Murray Elisabeth A.
Published: March 2003

Two experiments tested the predictions of ‘declarative’ vs. ‘perceptual‐mnemonic’ views of perirhinal cortex function. The former view predicts that perirhinal cortex lesions should impair rapidly learned, but not more slowly learned, visual discriminations, whereas the latter view predicts that impairments should be related not to speed of learning but to perceptual factors. It was found that monkeys with perirhinal cortex lesions were impaired in the acquisition and performance of slowly learned, perceptually difficult greyscale picture discriminations, but were not impaired in the acquisition of rapidly learned, perceptually easier discriminations. In addition, these same monkeys were not impaired in the acquisition or performance of difficult colour or size discriminations, indicating that the observed pattern of impairments was not due to ceiling effects or difficultyper se. These findings, taken together, are consistent with the ‘perceptual‐mnemonic’ view that the perirhinal cortex is involved in both perception and memory, but are not consistent with the ‘declarative’ view that the perirhinal cortex is important exclusively for declarative memory, having little or no role in perception. Moreover, the results are consistent with the more specific proposal that the perirhinal cortex contributes to the solution of complex visual discriminations with a high degree of ‘feature ambiguity’, a property of visual discrimination problems that can emerge when features of an object are rewarded when part of one object, but not when part of another. These and other recent findings suggest the need for a revision of prevailing views regarding the neural organization of perception and memory.
Prefrontal and agranular cingulate projections to the dorsal premotor areas F2 and F7 in the macaque monkey
Authors: Luppino Giuseppe , Rozzi Stefano , Calzavara Roberta , Matelli Massimo
Published: March 2003

The superior sector of Brodmann area 6 (dorsal premotor cortex, PMd) of the macaque monkey consists of a rostral and a caudal architectonic area referred to as F7 and F2, respectively. The aim of this study was to define the origin of prefrontal and agranular cingulate afferents to F7 and F2, in the light of functional and hodological evidence showing that these areas do not appear to be functionally homogeneous. Different sectors of F7 and F2 were injected with neural tracers in seven monkeys and the retrograde labelling was qualitatively and quantitatively analysed. The dorsorostral part of F7 (supplementary eye field, F7‐SEF) was found to be a target of strong afferents from the frontal eye field (FEF), from the dorsolateral prefrontal regions located dorsally (DLPFd) and ventrally (DLPFv) to the principal sulcus and from cingulate areas 24a, 24b and 24c. In contrast, the remaining part of F7 (F7‐non SEF) is only a target of the strong afferents from DLPFd. Finally, the ventrorostral part of F2 (F2vr), but not the F2 sector located around the superior precentral dimple (F2d), receives a minor, but significant, input from DLPFd and a relatively strong input from the cingulate gyrus (areas 24a and 24b) and area 24d. Present data provide strong hodological support in favour of the idea that areas F7 and F2 are formed by two functionally distinct sectors.
AMPA/kainate and NMDA‐like glutamate receptors at the chromatophore neuromuscular junction of the squid: role in synaptic transmission and skin patterning
Authors: Lima Pedro A. , Nardi Giovanna , Brown Euan R.
Published: March 2003

Glutamate receptor types were examined at the chromatophore synapses of the squids Alloteuthis subulata and Loligo vulgaris, where nerve‐induced muscle contraction causes chromatophore expansion. Immunoblotting with antibody raised against a squid AMPA receptor (sGluR) demonstrated that AMPA/kainate receptors are present in squid skin. Application of l‐glutamate evoked chromatophore muscle contractions in both ventral and dorsal skins, while NMDA was only active on a subpopulation of dorsal chromatophores. In dorsal skin, neurotransmission was partly blocked by either AMPA/kainate receptor antagonists (CNQX and DNQX) or NMDA receptor antagonists (AP‐5 and MK‐801) or completely blocked by simultaneous application of both classes of antagonists. In isolated muscle fibres, ionophoretic application of l‐glutamate evoked fast inward CNQX‐ and DNQX‐sensitive currents with reversal potentials around +14 mV and a high conductance to Na+. In fibres from dorsal skin only, a slower outward glutamate‐sensitive current appeared at positive holding potentials. At negative potentials, currents were potentiated by glycine or by removing external Mg2+ and were blocked by AP‐5 and MK‐801. Glutamate caused a fast, followed by a slow, transient increase in cytoplasmic Ca2+. The slow component was increased in amplitude and duration by glycine or by lowering external Mg2+ and decreased by AP‐5 and MK‐801. In cells from ventral skin, no ‘NMDA‐like responses’ were detected. Thus, while AMPA/kainate receptors mediated fast excitatory synaptic transmission and rapid colour change over the whole skin, activation of both AMPA/kainate and NMDA‐like receptors in a subpopulation of dorsal chromatophores prolonged the postsynaptically evoked Ca2+ elevation causing temporally extended colour displays with behavioural significance.
Modulation of spontaneous and evoked EPSCs and IPSCs in optic lobe neurons of cuttlefish Sepia officinalis by the neuropeptide FMRF‐amide
Authors: Chrachri Abdesslam , Williamson Roddy
Published: March 2003

The effects of the neuropeptide FMRFa on spontaneous excitatory postsynaptic currents (sEPSCs) and inhibitory postsynaptic currents (sIPSCs), as well as on evoked EPSCs and IPSCs, in two types of neurons within the central optic lobe of cuttlefish were examined using the whole‐cell voltage‐clamp technique. FMRFa (1–10 µm) did not affect cell membrane resting potentials, but reversibly reduced both the frequency and amplitude of sEPSCs in neurons within the medulla region of the optic lobe while increasing the frequency and amplitude of their sIPSCs. For centrifugal neurons in the inner granule cell layer of the optic lobe, FMRFa (1–10 µm) decreased both the frequency and amplitude of sEPSCs. In the presence of tetrodotoxin (0.5 µm), neither the interevent interval, nor amplitude distributions of the miniature EPSCs or the miniature IPSCs, were affected by FMRFa, implying a presynaptic action of FMRFa on the optic lobe neurons. Bath application of the neuropeptide also abolished or reduced in amplitude the evoked EPSCs and increased the amplitude of evoked IPSCs in optic lobe neurons, showing that FMRFa induced similar effects on evoked as on spontaneous postsynaptic currents. These results demonstrate the complex range of modulatory effects FMRFa can have within central nervous system circuits.
Sex differences in anxiety, sensorimotor gating and expression of the α4 subunit of the GABAAreceptor in the amygdala after progesterone withdrawal
Authors: Gulinello M. , Orman R. , Smith S. S.
Published: March 2003

In a progesterone withdrawal (PWD) model of premenstrual anxiety, we have previously demonstrated that increased hippocampal expression of the α4 subunit of the GABAAreceptor (GABAA‐R) is closely associated with higher anxiety levels in the elevated plus maze. However, several studies indicate that sex differences in regulation of the GABAA‐R in specific brain regions may be an important factor in the observed gender differences in mood disorders. Thus, we investigated possible sex differences in GABAA‐R subunit expression and anxiety during PWD. To this end, we utilized the acoustic startle response (ASR) to assess anxiety levels in male and female rats undergoing PWD as the ASR is also applicable to the assessment of human anxiety responses. We also investigated GABAA‐R α4 subunit expression in the amygdala, as the amygdala directly regulates the primary startle circuit. Female rats exhibited a greater ASR during PWD than controls, indicating higher levels of anxiety and arousal. In contrast, male rats undergoing PWD did not demonstrate an increased ASR. The sex differences in the ASR were paralleled by sex differences in the expression of the GABAA‐R α4 subunit in the amygdala such that α4 subunit expression was up‐regulated in females during PWD whereas α4 levels in males undergoing PWD were not altered relative to controls. These findings might have implications regarding gender differences in human mood disorders and the aetiology of premenstrual anxiety.
Disabled‐1 mRNA and protein expression in developing human cortex
Authors: Meyer Gundela , De Rouvroit Catherine Lambert , Goffinet Andre M. , Wahle Petra
Published: March 2003

Disabled‐1 (Dab1) forms part of the Reelin–Dab1 signalling pathway that controls neuronal positioning during brain development; Dab1 deficiency gives rise to a reeler‐like inversion of cortical layers. To establish a timetable of Dab1 expression in developing human brain, Dab1 mRNA and protein expression were studied in prenatal human cortex. The earliest Dab1 signal was detected at 7 gestational weeks (GW), the stage of transition from preplate to cortical plate, suggesting a role of the Reelin–Dab1 signalling pathway in preplate partition. From 12 to 20 GW, the period of maximum cortical migration, Dab1 expression was prominent in the upper tiers of the cortical plate, to decline after midgestation. Radially orientated apical dendrites of Dab1‐expressing neurons indicated a predominant pyramidal phenotype. Pyramidal cells in hippocampus and entorhinal cortex displayed a more protracted time of Dab1 expression compared to neocortex. In addition, at later stages (18–25 GW), Dab1 was also expressed in large neurons scattered throughout intermediate zone and subplate. From 14 to 22 GW, particularly high levels of Dab1 mRNA and protein were observed in cells of the ventricular/subventricular zone displaying the morphology of radial glia. The partial colocalization of vimentin and Dab1 in cells of the ventricular zone supported a radial glia phenotype. The concentration of Dab1 protein in ventricular endfeet and initial portions of radial processes of ventricular‐zone cells points to a possible involvement of Dab1 in neurogenesis. Furthermore, a subset of Cajal–Retzius cells in the marginal zone colocalized Dab1 and Reelin, and may thus represent a novel target of the Reelin–Dab1 signalling pathway.
Potentiation of glycine responses by dideoxyforskolin and tamoxifen in rat spinal neurons
Authors: Chesnoy‐Marchais Dominique
Published: March 2003

Dideoxyforskolin, a forskolin analogue unable to stimulate adenylate cyclase, and tamoxifen, an antioestrogen widely used against breast cancer, are both known to block some Cl− channels. Their effects on Cl− responses to glycine or GABA have been tested here by using whole‐cell recording from cultured spinal neurons. Dideoxyforskolin (4 or 16 µm) and tamoxifen (0.2–5 µm) both potentiate responses to low glycine concentrations. They also induce blocking effects, predominant at high glycine concentrations. At 5 µm, tamoxifen increased responses to 15 µm glycine by a factor >4.5, reaching 20 in some neurons. Potentiation by extracellular dideoxyforskolin or tamoxifen persisted after intracellular application of the modulator and was not due to Zn2+ contamination. Potentiation by tamoxifen also persisted in a Ca2+‐free extracellular solution, after intracellular Ca2+ buffering and protein kinase C blockade. Thus, the critical sites of action are not intracellular. The EC50 for glycine was lowered 6.6‐fold by 5 µm tamoxifen. The kinetics and voltage‐dependence of the effects of tamoxifen on glycine responses support the idea that this hydrophobic drug may act from a site located within the membrane. Tamoxifen (5 µm) also increased responses to 2 µm GABA by a factor of 3.5, but barely affected peak responses to 20 µm GABA. The demonstration that tamoxifen affects some of the main inhibitory receptors should be useful for better evaluating its neurological effects. Furthermore, the results identify a new class of molecules that potentiate glycine receptor function.
Acute antinociceptive responses in single and combinatorial opioid receptor knockout mice: distinct mu, delta and kappa tones
Authors: Martin Miquel , Matifas Audrey , Maldonado Rafael , Kieffer Brigitte L.
Published: March 2003

We have examined responses of mice lacking mu, delta and kappa opioid receptor (MOR, DOR and KOR, respectively) genes, as well as combinatorial mutants, in several pain models. This is the first truly comparative study of all three opioid receptor‐deficient mice, with genotypes and gender analysis using mice on the hybrid 50% 129/SV : 50% C57BL/6 genetic background. In the tail‐immersion test, only KOR−/− females showed decreased withdrawal latencies. This modification was also found in MOR/KOR and MOR/DOR/KOR, but not MOR/DOR mutants. The hotplate test revealed increased nociceptive sensitivity for MOR−/−, a phenotype which was also observed in double mutants involving the MOR deletion, and in the triple mutants. The tail‐pressure test showed increased response for both MOR−/− and DOR−/− mutants, a modification which was enhanced in the triple‐mutant mice. In the formalin test, MOR−/− and DOR−/− mice showed increased responses in the early and late phases, respectively, while the triple mutant tended to show enhanced nociception in both phases. Finally, the enhanced response of KOR−/− mice in the writhing test, which we have demonstrated previously, was confirmed in double MOR/KOR‐ and triple‐mutant mice. Together, the data support the existence of an antinociceptive opioid tone. Each receptor presents a distinct pattern of activities, with mu receptors influencing responses to mechanical, chemical and thermal nociception at a supraspinal level, kappa receptors involved in spinally mediated thermal nociception and chemical visceral pain, and delta receptors modulating mechanical nociception and inflammatory pain. Phenotypes of mutant mice were subtle, suggesting a low endogenous opioid tone in the regulation of physiological pain.
Potentiation of intracellular Ca2+ mobilization by hypoxia‐induced NO generation in rat brain striatal slices and human astrocytoma U‐373 MG cells and its involvement in tissue damage
Authors: Meini Antonella , Benocci Alberto , Frosini Maria , Sgaragli Gian Pietro , Garcia Julian Blanco , Pessina Gian Paolo , Aldinucci Carlo , Palmi Mitri
Published: March 2003

The relationship between nitric oxide (NO) and intracellular Ca2+ in hypoxic–ischemic brain damage is not known in detail. Here we used rat striatal slices perfused under low‐oxygen and Ca2+‐free conditions and cultured human astrocytoma cells incubated under similar conditions as models to study the dynamics of intracellular NO and Ca2+ in hypoxia‐induced tissue damage. Exposure of rat striatal slices for 70 min to low oxygen tension elicited a delayed and sustained increase in the release of 45Ca2+. This was potentiated by the NO donors sodium nitroprusside (SNP) and spermine–NO and inhibited by N‐ω‐nitro‐L‐arginine methyl ester (L‐NAME) or by the NO scavenger 2‐phenyl‐4,4,5,5 tetramethylimidazoline‐1‐oxyl‐3‐oxide (PTIO). A membrane‐permeant form of heparin in combination with either ruthenium red (RR) or ryanodine (RY) also inhibited 45Ca2+ release. In human astrocytoma U‐373 MG cells, hypoxia increased intracellular Ca2+ concentration ([Ca2+]i) by 67.2 ± 13.1% compared to normoxic controls and this effect was inhibited by L‐NAME, PTIO or heparin plus RR. In striatal tissue, hypoxia increased NO production and LDH release and both effects were antagonized by L‐NAME. Although heparin plus RR or RY antagonized hypoxia‐induced increase in LDH release they failed to counteract increased NO production. These data therefore indicate that NO contributes to hypoxic damage through increased intracellular Ca2+ mobilization from endoplasmic reticulum and suggest that the NO–Ca2+ signalling might be a potential therapeutic target in hypoxia‐induced neuronal degeneration.
Neurons with distinctive firing patterns, morphology and distribution in laminae V–VII of the neonatal rat lumbar spinal cord
Authors: Szûcs Péter , Odeh Francis , Szokol Karolina , Antal Miklós
Published: March 2003

It is generally accepted that neurons in the ventral spinal grey matter, a substantial proportion of which can be regarded as constituents of the spinal motor apparatus, receive and integrate synaptic inputs arising from various peripheral, spinal and supraspinal sources. Thus, a profound knowledge concerning the integrative properties of interneurons in the spinal ventral grey matter appears to be essential for a fair understanding of operational principles of spinal motor neural assemblies. Using the whole cell patch clamp configuration in a correlative physiological and morphological experimental approach, here we demonstrate that the intrinsic membrane properties of neurons vary widely in laminae V–VII of the ventral grey matter of the neonatal rat lumbar spinal cord. Based on their firing patterns in response to depolarizing current steps, we have classified the recorded neurons into four categories: ‘phasic’, ‘repetitive’, ‘single’ and ‘slow’. Neurons with firing properties characteristic of the ‘phasic’, ‘repetitive’ and ‘single’ cells have previously been reported also in the superficial and deep spinal dorsal horn, but this is the first account in the literature in which ‘slow’ neurons have been recovered and described in the spinal cord. The physiological heterogeneity in conjunction with the morphological correlation and distribution of neurons argues that different components of motor neural assemblies in the spinal ventral grey matter possess different signal processing characteristics.
The eye of the african mole‐ratCryptomys anselli: to see or not to see?
Authors: Cernuda‐Cernuda Rafael , García‐Fernández José M. , Gordijn Marijke C. M. , Bovee‐Geurts Petra H. M. , DeGrip Willem J.
Published: March 2003

In an attempt to clarify its possible physiological role, we studied the eye of the Zambian mole ratCryptomys anselliby light, electron and confocal microscopy using conventional staining as well as immunolabelling with rod and cone cell markers. The small eyes ofCryptomysare located superficially and display all features typical of sighted animals: iris, pupil and well‐developed lens, separating the anterior chamber and the vitreous. The retina shows a well stratified organization and the folds described in blind subterranean or nocturnal mammals were not observed. The major population of the photoreceptor cells in theCryptomysretina consists of rod cells, again with a morphology quite similar to that found in sighted animals. The relatively short outer segments contain numerous well‐stacked disks and show a strong rod‐opsin as well as transducin immunoreaction. Synapses were evident in the spherules, the round basal processes of the rod cell, but they lacked the precise organization reported for sighted mammals. Cone cells were present as well, as indicated by peanut lectin staining, but no immunolabelling with polyclonal M/L‐opsin antisera was detectable. The presence of cone cells was also suggested by some basal processes at the outer plexiform layer which displayed several synaptic active sites and irregular contours. While the other retinal layers also showed an organization typical of sighted mammals, there were signs of less tightly preserved morphology as well. Displaced rods and amacrine and/or ganglion cells were observed, and some sparse rod spherules penetrated into the inner nuclear layer. A major reduction was observed in the number of ganglion cells, estimated from the number of axons in the optic nerve, that was very low (≈1000 per retina on average) relative to sighted mammals. The data we have suggest a slow, ongoing loss of cells with ageing. Apoptotic nuclei, mainly corresponding to photoreceptor cells and ganglion cells, were detected in young individuals, and an overall reduction in the thickness of the retina was observed in older animals. The morphological data presented here allow some first speculations on the physiological role of theCryptomyseye and will hopefully trigger detailed studies on the chronobiology and the anatomy of the retinal projections and of the visual cortex of this remarkable species.
Effects of insulin‐like growth factor I on climbing fibre synapse elimination during cerebellar development
Authors: Kakizawa Sho , Yamada Kazuyuki , Iino Masamitsu , Watanabe Masahiko , Kano Masanobu
Published: March 2003

Functional neural circuit formation includes the process by which redundant synaptic connections formed earlier during development are subsequently eliminated. We report that insulin‐like growth factor I (IGF‐I) is a candidate factor that influences the developmental transition from multiple to mono innervation of cerebellar Purkinje cells (PCs) by climbing fibres (CFs). Continuous local application of exogenous IGF‐I to the mouse cerebellum by means of ethylene‐vinyl acetate copolymer (Elvax) significantly increased the degree of multiple CF innervation, when the IGF‐I containing Elvax was implanted at postnatal day 8 (P8). In contrast, the IGF‐I application starting at P12 had no effect on CF innervation. Conversely, continuous local application of antisera against IGF‐I and its receptor significantly decreased the degree of multiple CF innervation when the application started at P8. We found that chronic treatment of exogenous IGF‐I from P8 significantly enhanced the CF‐mediated excitatory postsynaptic currents (CF‐EPSCs). This effect was manifest for the smaller CF‐EPSCs but not for the largest CF‐EPSC of the multiple‐innervated PCs. Conversely, chronic application of antisera from P8 caused attenuation of the largest CF‐EPSCs. Other parameters for basic synaptic functions and cerebellar morphology were largely normal after the IGF‐I or antisera treatment. These results suggest that IGF‐I enhances the strength of developing CF synapses and may promote their survival, whereas the shortage of IGF‐I impairs the development of CF synapses and, as a result, may facilitate their elimination. Thus, IGF‐I is a potentially important factor among various signalling molecules that can influence CF synapse elimination during cerebellar development.
A hVIPR transgene as a novel tool for the analysis of circadian function in the mouse suprachiasmatic nucleus
Authors: King V. M. , Chahad‐Ehlers S. , Shen S. , Harmar A. J. , Maywood E. S. , Hastings M. H.
Published: March 2003

A mouse bearing a novel transgene encoding the human VPAC2 receptor (hVIPR; Shen et al. (2000) PNAS, 97, 11575–11580) was used to investigate circadian function in the hypothalamic suprachiasmatic nuclei (SCN). Neurons expressing hVPAC2R, detected by a beta‐galactosidase (β‐GAL) tag, have a distinct distribution within the SCN, closely matching that of neurophysin (NP) neurons and extending into the region of peptide histidine isoleucine (PHI) cells. In common with NP and PHI cells, neurons expressing hVPAC2R are circadian in nature, as revealed by synchronous rhythmic expression of mPERIOD (mPER) proteins. A population of SCN cells not expressing PHI, NP or hVPAC2R exhibited circadian PER expression antiphasic with the rest of the SCN. Nocturnal light exposure induced mPER1 in the ventral SCN and mPER2 widely across the nucleus. Induction of nuclear mPER2 in hVPAC2R cells confirmed their photic responsiveness. Having established their circadian properties, we tested the utility of SCN neurons expressing the hVIPR transgene as functionally and anatomically explicit markers for SCN tissue grafts. Prenatal SCN tissue from hVIPR transgenic pups survived transplantation into adult CD1 mice, and expressed β‐GAL, PER and PHI. Over a series of studies, hVIPR transgenic SCN grafts restored circadian activity rhythms to 17 of 72 arrhythmic SCN lesioned recipients (23.6%). By using heterozygous hVIPR transgenic grafts on a heterozygous Clock mutant background we confirmed that restored activity rhythms were conferred by the donor tissue. We conclude that the hVIPR transgene is a powerful and flexible tool for examination of circadian function in the mouse SCN.
The small conductance Ca2+‐activated K+ channel SK3 is localized in nerve terminals of excitatory synapses of cultured mouse hippocampal neurons
Authors: Obermair Gerald J. , Kaufmann Walter A. , Knaus Hans‐Günther , Flucher Bernhard E.
Published: March 2003

In the central nervous system small conductance Ca2+‐activated K+ (SK) channels are important for generating the medium/slow afterhyperpolarization seen after single or trains of action potentials. Three SK channel isoforms (SK1,‐2,‐3) are differentially distributed throughout the brain, but little is known about their specific expression in particular neuronal compartments. In the hippocampus SK3 was found in the neuropil, predominantly in the terminal field of the mossy fibres and in fine varicose fibres, but excluded from the pyramidal and granule cell layers. Because this expression pattern suggested a presynaptic localization, we examined the subcellular distribution of SK3 in cultured hippocampal neurons using high‐resolution immunofluorescence analysis. SK3 was localized in a punctate, synaptic pattern. The SK3 clusters were precisely colocalized with the presynaptic marker synapsin and at close range (0.4–0.5 µm) from NMDA‐receptors and PSD‐95. This arrangement is consistent with a localization of SK3 in the presynaptic nerve terminal, but not restricted to the synaptic membrane proper. In agreement with the increasing expression of SK3 during early postnatal development in vivo, the fraction of synapses containing SK3 increased from 14% to 57% over a six‐week culture period. SK3‐containing synapses were equally observed on spiny, glutamatergic and smooth GABAergic neurons. In contrast to its close association with NMDA‐receptors and PSD‐95, SK3 was rarely associated with GABAA‐receptor clusters. Thus, SK3 is a presynaptic channel in excitatory hippocampal synapses, with no preference for glutamatergic or GABAergic postsynaptic neurons, and is probably involved in regulating neurotransmitter release.
Saccadic eye movements evoked by microstimulation of striate cortex
Authors: Tehovnik Edward J. , Slocum Warren M. , Schiller Peter H.
Published: March 2003

Experiments were performed to assess the excitability of neural elements activated while inducing saccadic eye movements electrically from different cortical layers of striate cortex (area V1) in rhesus monkeys. Excitability was assessed by measuring current thresholds, saccadic latencies, chronaxies, and the effectiveness of anode‐first vs. cathode‐first pulses. Minimum current thresholds for the evocation of saccades (i.e. less than 5 µA) were observed when the deepest layers of V1 were stimulated. The shortest saccadic latencies were also observed at these depths. The shortest latency at 10 times the threshold current was 49 ms on average. The chronaxies of the elements mediating saccades were less in deep V1 (i.e. 0.17 ms) than in superficial V1 (i.e. 0.23 ms). Anode‐first pulses were more effective at evoking saccades from superficial V1, whereas cathode‐first pulses were more effective at evoking saccades from deep V1. These results indicate that the excitability properties of superficial and deep V1 are distinct for the generation of saccades. Moreover, the excitability of elements mediating saccades in V1 of monkeys is comparable to that of elements mediating phosphenes in human V1.
Presynaptic inhibition of Schaffer collateral synapses by stimulation of hippocampal cholinergic afferent fibres
Authors: Fernández de Sevilla David , Buño Washington
Published: March 2003

It has been known for decades that muscarinic agonists presynaptically inhibit Schaffer collateral synapses contacting hippocampal CA1 pyramidal neurons. However, a demonstration of the inhibition of Schaffer collateral synapses induced by acetylcholine released by cholinergic hippocampal afferents is lacking. We present original results showing that electrical stimulation at the stratum oriens/alveus with brief stimulus trains inhibited excitatory postsynaptic currents evoked by stimulation of Schaffer collaterals in CA1 pyramidal neurons of rat hippocampal slices. The increased paired‐pulse facilitation and the changes in the variance of excitatory postsynaptic current amplitude that paralleled the inhibition suggest that it was mediated presynaptically. The effects of oriens/alveus stimulation were inhibited by atropine, and blocking nicotinic receptors with methyllycaconitine was ineffective, suggesting that the inhibition was mediated via the activation of presynaptic muscarinic receptors. The results provide a novel demonstration of the presynaptic inhibition of glutamatergic neurotransmission by cholinergic fibres in the hippocampus, implying that afferent cholinergic fibres regulate the strength of excitatory synaptic transmission.
Behavioural sensitization and enhanced dopamine response in the nucleus accumbens after intravenous cocaine self‐administration in mice
Authors: Zapata Agustin , Chefer Vladimir I. , Ator Robert , Shippenberg Toni S. , Rocha Beatriz A.
Published: March 2003

The behavioural effects of cocaine are enhanced in animals with a prior history of repeated cocaine administration. This phenomenon, referred to as sensitization, is also associated with an increase in cocaine‐evoked extracellular dopamine levels in the nucleus accumbens. Behavioural and neurochemical sensitization has been demonstrated in rats with a prior history of cocaine self‐administration and in those that had received experimenter‐administered cocaine. Although it is clear that the repeated non‐contingent administration also results in behavioural sensitization in the mouse, the issue of whether behavioural and neurochemical sensitization also occur in this species following intravenous cocaine self‐administration has not been assessed. The present study used the technique of in vivo microdialysis in conjunction with operant self‐administration to characterize cocaine‐evoked locomotor activity and dopamine levels in the nucleus accumbens in mice with a prior history of intravenous cocaine self‐administration or those that had received yoked infusions of cocaine. Mice that had received contingent or non‐contingent infusions of cocaine exhibited an enhanced behavioural response to cocaine and increased cocaine‐evoked dopamine levels in the nucleus accumbens. There was no difference between groups in the magnitude of this effect. Prior exposure to cocaine did not modify baseline dopamine levels in the nucleus accumbens. These data demonstrate that mice with previous cocaine self‐administration experience show an enhanced behavioural and dopamine response to cocaine in the nucleus accumbens. Furthermore, control over cocaine infusion does not significantly alter the magnitude of the sensitized behavioural and presynaptic dopamine responses observed in response to a challenge dose of cocaine.
Modulatory action of acetylcholine on striatal neurons: microiontophoretic study in awake, unrestrained rats
Authors: Windels François , Kiyatkin Eugene A.
Published: March 2003

Cholinergic interneurons innervate virtually all medium spiny striatal cells, but the relevance of this input in regulating the activity and afferent responsiveness of these cells remains unclear. Studies in anaesthetized animals and slice preparations have shown that iontophoretic acetylcholine (ACh) either weakly excites or inhibits striatal neurons. These differential responses may reflect cholinergic receptor heterogeneity but may be also related to the different activity states of recorded units and different afferent inputs specific in each preparation. Single‐unit recording was combined with iontophoresis in awake, unrestrained rats to examine the effects of ACh and selective muscarinic (oxotremorine M or Oxo‐M) and nicotinic agonists (nicotine or NIC) on dorsal and ventral striatal neurons. These effects were tested on naturally silent, spontaneously active and glutamate‐stimulated units. We found that iontophoretic ACh primarily inhibited spontaneously active and glutamate‐stimulated units; the direction of the ACh response, however, was dependent on the firing rate. The effects of ACh were generally mimicked by Oxo‐M and, surprisingly, by NIC, which is known to excite units in most central structures, including striatal neurons in anaesthetized preparation. Given that NIC receptors are absent on striatal cells but located primarily on dopamine terminals, we assessed the effects of NIC after complete blockade of dopamine receptors induced by systemic administration of a mixture of D1 and D2 antagonists. During dopamine receptor blockade the number of NIC‐induced inhibitions dramatically decreased and NIC had mainly excitatory effects on striatal neurons. Thus, our data suggest that under physiologically relevant conditions ACh acts as a state‐dependent neuromodulator, and its action involves not only postsynaptic but also presynaptic cholinoreceptors located on dopamine‐ and glutamate‐containing terminals.
Repeated, non‐habituating stress suppresses inflammatory plasma extravasation by a novel, sympathoadrenal dependent mechanism
Authors: Strausbaugh Holly J. , Green Paul G. , Dallman Mary F. , Levine Jon D.
Published: March 2003

The mechanism by which chronic stress affects the course of inflammatory diseases is still not well understood. We have evaluated the effect of two types of nonhabituating stress on a major component of the inflammatory response, synovial plasma extravasation, induced by perfusion of the potent inflammatory mediator, bradykinin and evaluated the underlying neuroendocrine mechanism in the rat. Chronic intermittent noise or ether stress induced profound inhibition of bradykinin‐induced plasma extravasation, which is associated with increased adjuvant‐arthritis severity. This inhibition, however, took 24 h to fully develop after the last exposure to stress and persisted for at least 48 h. The inhibition could be reversed by an additional exposure to the stressor, just prior to measuring the inflammatory response, suggesting that the delay is due to stress‐induced release of a factor that acutely masks the inhibition of the inflammatory response. This novel, unexpected feature of the effect of nonhabituating stress on inflammation may help explain variability in effects of stress in patients with inflammatory disease. The effect of nonhabituating stress on inflammation was dependent on the sympathoadrenal axis with no detectable contribution by the hypothalamic–pituitary–adrenal axis.