bluuebunny/crossref_metadata_2025 huggingface dataset:
Basic and acidic fibroblast growth factors protect spinal motor neurones in vivo after experimental spinal cord injury
Authors: Teng Yang Dong , Mocchetti Italo , Wrathall Jean R.
Published: March 2003

We studied the effect of a single focal injection of recombinant basic (FGF2) or acidic (FGF1) fibroblast growth factor on the survival of spinal motor neurones at 24 h after a standardized spinal cord contusion injury (SCI) in the rat. Both FGF2 and FGF1 (3 μg), microinjected into the injury site at 5 min post‐injury (p.i.), protected at least two functionally important classes of spinal motor neurones, autonomic preganglionic neurones in the intermediolateral (IML) column and somatic motor neurones in the ventral horn (VH). Moreover, there was enhanced choline acetyltransferase (ChAT) immunoreactivity in surviving VH and IML neurones, suggesting an improved functional status. Thus, neurotrophic factors such as FGF2 and FGF1 may contribute to an overall strategy to treat acute SCI and improve recovery of function.
Temporal limits of spatial working memory in humans
Authors: Ploner Christoph J. , Gaymard Bertrand , Rivaud Sophie , Agid Yves , Pierrot‐Deseilligny Charles
Published: March 2003

An essential feature attributed to working memory is the labile and transient nature of its representations. Using an oculomotor task, we examined the stability of spatial working memory in 16 normal human subjects. Eye movements towards remembered spatial cues (memory‐guided saccades) were electro‐oculographically recorded after memorization delays that varied unpredictably between 0.5 and 30 s. A peaked time‐course of saccadic targeting errors, with maximal errors around 20 s delay, was found, showing that delay‐dependent decay of spatial information in working memory occurs, but is time‐limited and reverts significantly beyond delays of about 20 s. These data (i) indicate temporal limits of spatial working memory and (ii) provide the first behavioural evidence for the existence of two parallely generated mental representations of space that successively control memory‐guided behaviour in humans.
Spectral envelope coding in cat primary auditory cortex: linear and non‐linear effects of stimulus characteristics
Authors: Calhoun Barbara M. , Schreiner Christoph E.
Published: March 2003

Electrophysiological studies in mammal primary auditory cortex have demonstrated neuronal tuning and cortical spatial organization based upon spectral and temporal qualities of the stimulus including: its frequency, intensity, amplitude modulation and frequency modulation. Although communication and other behaviourally relevant sounds are usually complex, most response characterizations have used tonal stimuli. To better understand the mechanisms necessary to process complex sounds, we investigated neuronal responses to a specific class of broadband stimuli, auditory gratings or ripple stimuli, and compared the responses with single tone responses. Ripple stimuli consisted of 150–200 frequency components with the intensity of each component adjusted such that the envelope of the frequency spectrum is sinusoidal. It has been demonstrated that neurons are tuned to specific characteristics of those ripple stimulus including the intensity, the spacing of the peaks, and the location of the peaks and valleys (C. E. Schreiner and B. M. Calhoun, Auditory Neurosci. 1994; 1: 39–61). Although previous results showed that neuronal response strength varied with the intensity and the fundamental frequency of the stimulus, it is shown here that the relative response to different ripple spacings remains essentially constant with changes in the intensity and the fundamental frequency. These findings support a close relationship between pure‐tone receptive fields and ripple transfer functions. However, variations of other stimulus characteristics, such as spectral modulation depth, result in non‐linear alterations in the ripple transformation. The processing between the basilar membrane and the primary auditory cortex of broadband stimuli appears generally to be non‐linear, although specific stimulus qualities, including the phase of the spectral envelope, are processed in a nearly linear manner.
Opioid withdrawal activates MAP kinase in locus coeruleus neurons in morphine‐dependent rats in vivo
Authors: Schulz Stefan , Höllt Volker
Published: March 2003

Opioid dependence is widely believed to result from neuroadaptations in specific brain regions. However, the precise molecular mechanisms underlying these adaptations are not yet clear. Our aim was to explore the role of mitogen‐activated protein kinase (MAPK) in μ opioid receptor signalling in vivo. Using anti‐phospho MAPK antibodies, activated MAPK was detected in cortical neurons (layers II/III), median eminence, amygdaloid and hypothalamic nuclei in untreated animals. Dense nuclear and cytoplasmic staining was observed resulting in full visualization of processes in these cells. Chronic, but not acute, administration of morphine greatly diminished this staining pattern while μ opioid receptor levels and levels of MAPkinase as detected with a phosphorylation state‐independent antibody were unchanged. When opioid withdrawal was precipitated with naloxone a dramatic increase in MAPkinase phosphorylation was observed in somata and fibres of locus coeruleus, solitary tract and hypothalamic neurons. Thus, the differential activation state of MAPK could have important implications for understanding the mechanisms underlying opioid tolerance and dependence.
Glutamate‐induced Co2+uptake in rat auditory brainstem neurons reveals developmental changes in Ca2+permeability of glutamate receptors
Authors: Caicedo Alejandro , Kungel Martin , Pujol Rémy , Friauf Eckhard
Published: March 2003

Ca2+influx through glutamate receptors (GluRs) is thought to play a crucial part in developmental processes and neuronal plasticity. Here we have examined the spatiotemporal distribution of Ca2+‐permeable GluRs in auditory brainstem neurons of the rat from birth to adulthood, using the cobalt‐staining technique of Pruss and collaborators. In slices of young adult rats, 1 mmglutamate evoked intense cobalt uptake in subsets of neurons in the ventral cochlear nuclei, the medial nucleus of the trapezoid body, the lateral and the medial superior olive, and the lateral lemniscal nuclei. Neurones in the central nucleus of the inferior colliculus, and thalamic auditory nuclei appear to express few, if any, Ca2+‐permeable GluRs. Thus, in adults, Ca2+‐permeable GluRs are present in neurons of almost all main relay stations of the auditory brainstem. During development, cobalt‐stained cells first appeared at about hearing onset (at postnatal day 12 [P12]). At P16, staining levels were highest and the pattern of distribution was already adult‐like. The staining intensity slightly declined during the fourth postnatal week. In contrast, Ca2+‐permeable receptors were detected in the external cortex of the inferior colliculus as early as P4. Our results show that auditory neurons, characterized by a high temporal precision in neuronal activity, display Ca2+‐permeable GluRs. Because Ca2+permeability appears at about the onset of hearing and is highest during the following 2 weeks, Ca2+influx through GluRs is likely to be implicated in remodelling processes occurring during this ontogenetic period.
Different patterns of induction of FGF‐2, FGF‐1 and BDNF mRNAs during kindling epileptogenesis in the rat
Authors: Simonato Michele , Molteni Raffaella , Bregola Gianni , Muzzolini Anna , Piffanelli Maddalena , Beani Lorenzo , Racagni Giorgio , Riva Marco
Published: March 2003

Neurotrophic factors (NTF) play important roles in the developing and in the adult brain. NTF involvement in neuronal plasticity is suggested by the modulation of NTF expression patterns in different physiological and pathological situations and by the effects they produce in the adult brain (e.g. axonal sprouting induction and neuroprotection). We used the RNAase protection assay to investigate the expression patterns of some NTFs during amygdala kindling, an animal model of epilepsy in which ‘pathological’ neuronal plasticity appears to occur. After a single kindling stimulation, fibroblast growth factor‐2 (FGF‐2) mRNA levels were increased in the hippocampus, the cortex and the hypothalamus, whereas they were not significantly altered in the thalamus and the striatum. A single stimulation did not alter fibroblast growth factor‐1 (FGF‐1) and brain‐derived neurotrophic factor (BDNF) gene expression. Fully kindled animals, left unstimulated for a week, did not exhibit any alteration in the mRNA levels for any of the NTFs examined. However, in contrast with the effect of a single stimulation, amygdala stimulation of kindled animals (evoking a generalized tonic‐clonic seizure) produced a great increase in hippocampal and cortical BDNF mRNA levels, but FGF‐1 mRNA levels were not altered, and FGF‐2 mRNA levels were significantly increased only in the cortex. These results suggest that different NTFs can be recruited at different stages of kindling epileptogenesis and, accordingly, may play different parts in the adaptive changes taking place in this experimental paradigm.
Electrophysiological evidence that noradrenergic neurons of the rat locus coeruleus are tonically inhibited by GABA during sleep
Authors: Gervasoni D. , Darracq L. , Fort P. , Soulière F. , Chouvet G. , Luppi P‐H.
Published: March 2003

It is well known that noradrenergic locus coeruleus (LC) neurons decrease their activity during slow wave sleep (SWS) and are virtually quiescent during paradoxical sleep (PS). It has been proposed that a GABAergic input could be directly responsible for this sleep‐dependent neuronal inactivation. To test this hypothesis, we used a new method combining polygraphic recordings, microiontophoresis and single‐unit extracellular recordings in unanaesthetized head‐restrained rats. We found that iontophoretic application of bicuculline, a specific GABAA‐receptor antagonist, during PS and SWS restore a tonic firing in the LC noradrenergic neurons. We further observed that the application of bicuculline during wakefulness (W) induced an increase of the discharge rate. Of particular importance for the interpretation of these results, using the microdialysis technique, Nitz and Siegel (Neuroscience 1997; 78: 795) recently found an increase of the GABA release in the cat LC during SWS and PS as compared with waking values. Based on these and our results, we therefore propose that during W, the LC cells are under a GABAergic inhibitory tone which progressively increases at the entrance and during SWS and PS and is responsible for the inactivation of these neurons during these states.
Potassium depolarization of mammalian vestibular sensory cells increases [Ca2+]i through voltage‐sensitive calcium channels
Authors: Boyer C. , Lehouelleur J. , Sans A.
Published: March 2003

The existence of voltage‐sensitive Ca2+ channels in type I vestibular hair cells of mammals has not been conclusively proven. Furthermore, Ca2+ channels present in type II vestibular hair cells of mammals have not been pharmacologically identified. Fura‐2 fluorescence was used to estimate, in both cell types, intracellular Ca2+ concentration ([Ca2+]i) variations induced by K+ depolarization and modified by specific Ca2+ channel agonists and antagonists. At rest, [Ca2+]i was 90 ± 20 nm in both cell types. Microperifusion of high‐K+ solution (50 mm) for 1 s increased [Ca2+]i to 290 ± 50 nm in type I (n = 20) and to 440 ± 50 nm in type II cells (n = 10). In Ca2+‐free medium, K+ did not alter [Ca2+]i. The specific L‐type Ca2+ channel agonist, Bay K, and antagonist, nitrendipine, modified in a dose‐dependent manner the K+‐induced [Ca2+]i increase in both cell types with maximum effect at 2 μm and 400 nm, respectively. Ni2+, a T‐type Ca2+ channel blocker, reduced K+‐evoked Ca2+ responses in a dose‐dependent manner. For elevated Ni2+ concentrations, the response was differently affected by Ni2+ alone, or combined to nitrendipine (500 nm). In optimal conditions, nitrendipine and Ni2+ strongly depressed by 95% the [Ca2+]i increases. By contrast, neither ω‐agatoxin IVA (1 μm), a specific P‐ and Q‐type blocker, nor ω‐conotoxin GVIA (1 μm), a specific N‐type blocker, affected K+‐evoked Ca2+i responses. These results provide the first direct evidence that L‐ and probably T‐type channels control the K+‐induced Ca2+ influx in both types of sensory cells.
Motor discoordination and increased susceptibility to cerebellar injury in GLAST mutant mice
Authors: Watase Kei , Hashimoto Kouichi , Kano Masanobu , Yamada Keiko , Watanabe Masahiko , Inoue Yoshiro , Okuyama Shigeru , Sakagawa Takashi , Ogawa Shin‐ichi , Kawashima Naoya , Hori Seiji , Takimoto Misato , Wada Keiji , Tanaka Kohichi
Published: March 2003

To study the function of GLAST, a glutamate transporter highly expressed in the cerebellar Bergmann astrocytes, the mouse GLAST gene was inactivated. GLAST‐deficient mice developed normally and could manage simple coordinated tasks, such as staying on a stationary or a slowly rotating rod, but failed more challenging task such as staying on a quickly rotating rod. Electrophysiological examination revealed that Purkinje cells in the mutant mice remained to be multiply innervated by climbing fibres even at the adult stage. We also found that oedema volumes in the mutant mice increased significantly after cerebellar injury. These results indicate that GLAST plays active roles both in the cerebellar climbing fibre synapse formation and in preventing excitotoxic cerebellar damage after acute brain injury.
Regulation of cell‐type specific expression of lacZ by the 5′‐flanking region of mouse GAD67 gene in the central nervous system of transgenic mice
Authors: Katarova Zoya , Mugnaini Enrico , Sekerková Gabriela , Mann Jeffrey R. , Aszódi Attila , Bösze Zsuzsanna , Greenspan Ralph , Szabó Gábor
Published: March 2003

The transcriptional regulation of the murine gene encoding the 67‐kDa form of glutamic acid decarboxylase (GAD67) was studied by β‐galactosidase histochemistry in transgenic mice carrying fusion genes between progressively longer portions of the 5′‐upstream regulatory region of GAD67 and E. coli lacZ. No expression was detected in brains of mice carrying 1.3 kb of upstream sequences including a housekeeping and two conventional promoters, and two negative regulatory elements with homology to known silencers. In mice carrying the same portion of the promoter region plus the first intron, lacZ expression in the adult central nervous system was found in few, exclusively neuronal sites. The number of correctly stained GABAergic centres increased dramatically with increasing the length of the 5′‐upstream region included in the construct which suggests that multiple putative spatial enhancers are located in this region. Their action is influenced by epigenetic mechanisms that may be due to site‐of‐integration and transgene copy‐number effects. Additional cis‐acting elements are needed to obtain fully correct expression in all GABAergic neurons of the adult central nervous system.
Different cell surface areas of polarized radial glia having opposite effects on axonal outgrowth
Authors: Stier Heike , Schlosshauer Burkhard
Published: March 2003

During neuronal development neurites are likely to be specifically guided to their targets. Within the chicken retina, ganglion cell axons are extended exclusively into the optic fibre layer, but not into the outer retina. We investigated, whether radial glial cells having endfeet at the optic fibre layer and somata in the outer retina, might be involved in neurite guidance. In order to analyse distinct cell surface areas, endfeet and somata of these glial cells were purified. Glial endfeet were isolated from flat mounted retina by a specific detachment procedure. Glial somata were purified by negative selection using a monoclonal antibody/complement mediated cytolysis of all non‐glial cells. Retinal tissue strips were explanted either onto pure glial endfeet or onto glial somata. As revealed by scanning and fluorescence microscopy, essentially no ganglion cell axons were evident on glial somata, whereas axonal outgrowth was abundant on glial endfeet. However, when glial somata were heat treated and employed thereafter as the substratum, axon extension was significantly increased. Time‐lapse video recording studies indicated that purified cell membranes of glial somata but not of endfeet induced collapse of growth cones. Collapsing activity was destroyed by heat treatment of glial membranes. The collapsing activity of retinal glia was found to be specific for retinal ganglion cell neurites, because growth cones from dorsal root ganglia remained unaffected. Employing four different kinase inhibitors revealed that the investigated protein kinase types were unlikely to be involved in the collapse reaction. The data show for the first time that radial glial cells are functionally polarized having permissive endfeet and inhibitory somata with regard to outgrowing axons. This finding underscores the pivotal role of radial glia in structuring developing nervous systems.
The perforant path projection from the medial entorhinal cortex layer III to the subiculum in the rat combined hippocampal–entorhinal cortex slice
Authors: Behr J. , Gloveli T. , Heinemann U.
Published: March 2003

Intracellular recordings were performed to examine the perforant path projection from layer III of the entorhinal cortex to the subiculum in rat combined hippocampal–entorhinal cortex slices. Electrical stimulation in the medial entorhinal cortex layer III caused short latency combined excitatory and inhibitory synaptic responses in subicular cells.

In the presence of the GABAA antagonist bicuculline and the GABAB antagonist CGP‐55845 A inhibition was blocked and isolated AMPA‐ or NMDA receptor‐mediated EPSPs could be elicited. After application of the non‐NMDA antagonist NBQX and the NMDA antagonist APV excitatory responses were completely blocked indicating a glutamatergic input from the neurons of the medial entorhinal cortex layer III. By stimulation from a close (< 0.2 mm) position in the presence of NBQX and APV and either CGP‐55845 A or bicuculline we could record monosynaptic fast GABAA or slow GABAB receptor‐mediated IPSPs, respectively.

We compared synaptic responses in subicular cells induced by stimulation in the medial entorhinal cortex layer III with responses elicited by stimulation of afferent fibres in the alveus. The EPSPs of subicular cells induced by stimulation of alvear fibres could be significantly augmented by simultaneous activation of perforant path fibres originating in the medial entorhinal cortex layer III, while delayed activation of alvear fibres after stimulation of the perforant path resulted in a weak inhibition of the alveus evoked EPSPs.

Thus, the perforant path projection activates monosynaptic excitation of subicular neurons. Therefore the entorhinal cortex does not only function as an important input structure of the hippocampal formation but is also able to modulate the hippocampal output via the entorhinal–subicular circuit.
The neural processing of 3‐D visual information: evidence from eye movements
Authors: Miles F.A.
Published: March 2003

Primates have several reflexes that generate eye movements to compensate for bodily movements that would otherwise disturb their gaze and undermine their ability to process visual information. Two vestibulo‐ocular reflexes compensate selectively for rotational and translational disturbances of the head, and each has visual backups that operate as negative feedback tracking mechanisms to deal with any residual disturbances of gaze. Of particular interest here are three recently discovered visual tracking mechanisms that specifically address translational disturbances and operate in machine‐like fashion with ultra‐short latencies (< 60 ms in monkeys, < 85 ms in humans). These visual reflexes deal with motions in all three dimensions and operate as automatic servos, using preattentive parallel processing to provide signals that initiate eye movements before the observer is even aware that there has been a disturbance. This processing is accomplished by visual filters each tuned to a different feature of the binocular images located in the immediate vicinity of the plane of fixation. Two of the reflexes use binocular stereo cues and the third is tuned to particular patterns of optic flow associated with the observer's forward motion. Some stereoanomalous subjects show tracking deficits that can be attributed to a lack of just one subtype of cortical cell encoding motion in one particular direction in a narrow depth plane centred on fixation. Despite their rapid, reflex nature, all three mechanisms rely on cortical processing and evidence from monkeys supports the hypothesis that all are mediated by the medial superior temporal (MST) area of cortex. Remarkably, MST seems to represent the first stage in cortical motion processing at which the visual error signals driving each of the three reflexes are fully elaborated at the level of individual cells.
Stimuli which entrain the circadian clock of the neonatal Syrian hamster in vivo regulate the phosphorylation of the transcription factor CREB in the suprachiasmatic nucleus in vitro
Authors: McNulty S. , Schurov I.L. , Sloper P.J. , Hastings M.H.
Published: March 2003

Photic resetting of the adult mammalian circadian clock in vivo is associated with phosphorylation of the Ser133 residue of the calcium/cyclic AMP response‐element binding‐protein (CREB) in the retinorecipient region of the suprachiasmatic nucleus (SCN). Western blotting and immunocytochemistry were used to investigate whether agonists known to reset the clock of neonatal hamsters in vivo are also able to influence the phosphorylation of CREB in the suprachiasmatic hypothalamus in vitro. Antisera raised against synthetic CREB peptide sequences were used to differentiate between total CREB and the Ser133 phosphorylated form of CREB (pCREB). Western blot analysis of proteins isolated from suprachiasmatic tissue of 1‐day‐old Syrian hamsters revealed bands at ≈ 45 kDa corresponding to total CREB and pCREB. Treatment of the tissue with a mixture of glutamatergic agonists [N‐methyl‐d‐aspartate (NMDA), amino‐methyl proprionic acid (AMPA) and kainate, all at 1 μm], or native glutamate (1 μm) had no effect on the total CREB signal, but increased the pCREB signal, indicative of agonist‐stimulated phosphorylation of CREB on Ser133. A similar effect was seen following treatment of the suprachiasmatic blocks with either dopamine (1 μm) or forskolin (1 μm). Simultaneous treatment with melatonin (1 μm) significantly attenuated stimulation by forskolin. The effect of the agonists on nuclear pCREB‐immunoreactivity (‐ir) was investigated in primary cultures which contained a mixture of cell types characteristic of the suprachiasmatic nuclei in vivo. Basal expression of nuclear total CREB‐ir was high, whereas expression of pCREB‐ir was low. Treatment with glutamate (1 μm) or dopamine (1 μm) had no effect on total CREB‐ir, but increased pCREB‐ir in ≈ 50 and 30% of cells, respectively, whereas forskolin (1 μm) increased pCREB‐ir in almost all cells (> 90%). The effects of all three agonists were rapid (< 15 min), and dose and time dependent. Melatonin reversed the effects of forskolin in mixed cultures, but not in pure astrocyte cultures. Dual‐immunocytochemistry (ICC) revealed that glutamate (1 μm) increased nuclear pCREB‐ir in cells immunoreactive for microtubule‐associated protein II (MAP II‐ir), but not other cells, indicating an effect predominantly on neurons. This occurred equally in γ‐amino butyric acid (GABA)‐ir and non‐GABA‐ir neurons. Dopamine (1 μm) was more selective, increasing pCREB‐ir only in GABA‐ir neurons, whereas forskolin increased pCREB‐ir in all cells. The specific stimulation of pCREB‐ir in GABA‐ir neurons by dopamine was reversed by melatonin, but melatonin had no effect on the increase in pCREB‐ir induced in GABA‐ir neurons by glutamate. These results demonstrate that agonists known to entrain the circadian clock in vivo modulate phosphorylation of CREB in GABA‐ir neurons derived from the neonatal suprachiasmatic nuclei.
Functional heterogeneity of periglomerular cells in the rat olfactory bulb
Authors: Puopolo Michelino , Belluzzi Ottorino
Published: March 2003

The periglomerular cells of the rat olfactory bulb, a virtually unknown population of interneurons, have been studied applying the whole‐cell patch‐clamp technique to thin slices. A prominent result, obtained under current‐clamp conditions, is that these cells appear to be functionally heterogeneous, and show distinct excitability profiles. Voltage‐clamp analysis allows the identification of the ionic basis of these differences and suggests a division into at least two classes, based on the characteristics of the K+ conductances. The first group displays two K+ conductances (delayed rectifier, gKV, and fast transient, gA) of similar amplitude, and under current‐clamp conditions shows the usual outward rectifying behaviour at depolarized potentials. The second group has a large gA, and a small or absent gKV. Consequently, following sustained depolarizations under current‐clamp conditions leading to inactivation of gA, these neurons do not show any sign of outward rectification and behave as ohmic elements, as normally observed only at hyperpolarized potentials. The transition ion zinc (10–300 μm) affects gA but not gKV. The inactivation process (steady‐state curve and rate constant) is strongly altered by Zn2+, the activation process less so; open‐channel conductance is not affected. The Zn2+ effect is unlikely to be due to surface charge screening or to a mechanism involving channel block. In view of the substantial presence of zinc ions in the olfactory nerve terminals, its actions on the A‐current could be of some relevance for physiological function.
Lesion‐induced transneuronal plasticity of the cholinergic innervation in the adult rat entorhinal cortex
Authors: De Lacalle Sonsoles , Kulkarni Sunita , Wiley Ronald G.
Published: March 2003

The present experiments were designed to determine the effect that lesions of the basal forebrain cholinergic system exert on cholinergic interneurons within the entorhinal cortex (EC) in the rat. Unilateral infusion of 192 IgG‐saporin into the nucleus of the horizontal diagonal band of Broca (HDB) decreased the number of ipsilateral choline acetyltransferase immunoreactive (ChAT‐ir) neurons by 54%. Two–four weeks after the lesion, the ipsilateral EC exhibited a moderate but significant loss of ChAT‐ir fibres and interneurons. Adjacent sections revealed a parallel loss of vasoactive intestinal polypeptide (VIP) immunoreactivity. Cell counts in the cingulate cortex were unaffected, suggesting that this effect was indeed specific to the main target area for HDB neurons. Ibotenic acid lesions also induced a significant 36% decrease in the number of cholinergic neurons in the ipsilateral HDB, and disappearance of ChAT terminals in the EC, whereas the number of ChAT‐ir neurons in the EC was unchanged. Since ibotenic acid affects all cells and not only cholinergic ones, our results suggest that the specific degeneration of cholinergic neurons in the HDB after 192 IgG‐saporin treatment could be inducing transsynaptic effects on their targets. Injections of 192 IgG‐saporin directly into the EC also lesioned the cholinergic projection from the HDB, but had no effect on the intrinsic population.

Eight weeks after immunolesion, the number of interneurons immunoreactive for ChAT and VIP in the EC had returned to normal values, and persisted for as long as 6 months after the lesion. By contrast, ChAT‐ir neurons in the HDB were permanently lost.

Our results suggest that the transient down‐regulation of the cholinergic phenotype in entorhinal cortex interneurons could be a manifestation of activity‐dependent plasticity, and that the loss of cholinergic innervation from the basal forebrain could be responsible for these effects through an imbalance of inputs. We hypothesize that the recovery of the phenotypic expression of entorhinal interneurons could be due to a recovery in their innervation, perhaps from sprouting axons in the same fields, belonging to surviving cholinergic neurons in the basal forebrain.
A rat G protein‐coupled receptor selectively expressed in myelin‐forming cells
Authors: Allard J. , Barrón S. , Diaz J. , Lubetzki C. , Zalc B. , Schwartz J. ‐C. , Sokoloff P.
Published: March 2003

By screening an olfactory bulb cDNA library using dopamine receptor probes, we isolated the cDNA coding for the rat counterpart of an orphan receptor known as Edg‐2, homologous to G protein‐coupled receptors. In situ hybridization analysis showed that Edg‐2 mRNA expression is restricted to myelinated structures, e.g. corpus callosum or peripheral nerves. A weaker expression in various peripheral organs was also detected in newborns. A 3.8‐kb transcript was found at high levels in highly myelinated brain structures and sciatic nerve, and, at lower levels, in poorly myelinated peripheral organs, consistent with its occurrence in Schwann cells in the peripheral nervous system. One hundred percent of Edg‐2 mRNA‐containing cells in the brain also expressed mRNA encoding myelin‐basic‐protein, a marker of oligodendrocytes. This restricted olygodendrocytes localization was confirmed by the absence of cellular colocalization of Edg‐2 and glial fibrillary acidic protein, an astrocytic marker. During prenatal development, Edg‐2 mRNA expression was high in the cortical neuroepithelium and meningeal layer at E16, extended later to other neuroepithelia, and disappeared shortly after birth. During brain postnatal development, Edg‐2 mRNA expression in myelinated structures followed a caudo‐rostral gradient, similar to that of myelination. Thus, Edg‐2 is the first G protein‐coupled receptor found to be selectively expressed in myelin‐forming cells in the nervous system and its temporal expression pattern is consistent with a dual role (i) in neurogenesis, during embryonic development, and (ii) in myelination and myelin maintenance, during postnatal life.
Growth of pyramidal, but not non‐pyramidal, dendrites in long‐term organotypic explants of neonatal rat neocortex chronically exposed to neurotrophin‐3
Authors: Baker R.E. , Dijkhuizen P.A. , Van Pelt J. , Verhaagen J.
Published: March 2003

The present study was undertaken to determine the effects of neurotrophin‐3 (NT3) and spontaneous bioelectric activity (SBA) on dendritic elongation and branching in long‐term isolated organotypic explants of rat neocortex. Viral vector‐directed expression of NT3 was used as an effective means to ensure a continuous, local production of the neurotrophic factor. Quantitative light microscopic measurement of dendritic branching patterns was carried out on Golgi‐stained materials. Explants were exposed to an adenoviral vector encoding the genetic sequence for neurotrophin‐3 (Ad‐NT3), or to exogenous additions of the neuropeptide NT3. In order to test for activity‐dependent growth effects under control and experimental conditions, explants were exposed to glutamatergic blockade using a cocktail of APV and DNQX. Both Ad‐NT3 and NT3 peptide potently promoted apical and basal dendritic growth (elongation and branching) in pyramidal neurons. This growth was observed to be significant in layers II–IV and V. These growth effects were also not activity dependent, inasmuch as they were elicited from explants in which spontaneous bioelectric activity had been suppressed. Non‐pyramidal neurons, throughout the neocortical slice, showed no significant dendritic responses to the prolonged presence of NT3. These findings show that pyramidal dendritic growth in long‐term neocortical explants responds to at least one neurotrophic growth factor, NT3, and is independent of intrinsic bioelectric activity. The use of viral vectors in delivering a continuous high level of neurotrophic factor within developing neural tissues demonstrates its potential application to in vivo tissues during development, or in the stimulation of neuritogenesis and neuroregeneration following injuries.
Dissociations in dopamine release in medial prefrontal cortex and ventral striatum during the acquisition and extinction of classical aversive conditioning in the rat
Authors: Wilkinson L.S. , Humby T. , Killcross A.S. , Torres E.M. , Everitt B.J. , Robbins T.W.
Published: March 2003

Dual perfusion in vivo brain microdialysis was used to monitor extracellular levels of dopamine in the medial prefrontal cortex and ventral striatum during the acquisition and extinction of a classical aversive conditioning paradigm in rats. The main finding was a dissociation in the pattern of release in the two brain areas. The first stimulus–footshock pairing elicited large increases in cortical dopamine over baseline levels that were much greater than the increases elicited by different stimuli of equivalent salience that were unpaired with footshock. In contrast, dopamine levels in ventral striatum were unchanged under these conditions. Over the next two pairings, there was a decline in the cortical response and an increase in the response in ventral striatum. The first presentation of the aversive conditioned stimulus in a separate context elicited the largest response in ventral striatum. Post‐conditioning, the cortical response to the conditioned stimulus was smaller than that elicited by the initial stimulus–footshock pairing and was equivalent in magnitude to that elicited by stimuli unpaired with footshock. Over the final two conditioned stimuli presentations, in the absence of the footshock reinforcer (extinction), responses declined in both brain areas. Simultaneous monitoring of behaviour indicated that the neurochemical events were accompanied by effective aversive learning, as indexed by conditioned freezing responses. The data are discussed in terms of the hypothesis that medial prefrontal cortex is especially engaged during novel circumstances which may, potentially, require new learning, whilst ventral striatal dopamine more closely follows the expression of conditioned responding during learning and extinction.
The onset of parvalbumin‐expression in interneurons of the rat parietal cortex depends upon extrinsic factor(s)
Authors: Weisenhorn D. M. Vogt , Celio M.R. , Rickmann M.
Published: March 2003

Parvalbumin (PV) belongs to the large family of EF‐hand calcium‐binding proteins and is an excellent marker for a subpopulation of GABAergic neocortical interneurons. During cortical development, PV first appears on postnatal day (P)8, in the infragranular layers; after P14, it also becomes apparent within the supragranular layers. However, nothing is known about the factors controlling its expression, which could involve functional activity, neuronal connectivity and/or neurotrophic factors. It being difficult to manipulate these parameters in vivo, their role may be more readily assessed in organotypic cultures, which are deprived of their subcortical afferents and efferents, and hence of subcortically derived neurotrophic factors and extrinsic functional activity. We prepared slices of the rat brain on P3, P5, P7 and P9, maintained them in culture for 2–5 weeks, and compared the temporal and spatial distribution pattern of PV‐immunoreactivity within these slices with the in vivo situation. We found, first, that during late postnatal in vivo development and ageing, the number of PV‐immunoreactive neurons in the parietal cortex decreases significantly, and second, that the expression of PV‐immunoreactivity in the parietal cortex was markedly influenced by the phase of postnatal development at which slice cultures were explanted. In those removed on P7 and P9, the number of PV‐immunoreactive cells, as well as the temporal and spatial distribution pattern of PV‐immunoreactivity corresponded to the in vivo situation, but in explants obtained on P3 or P5, PV‐immunoreactivity remained confined to layer V of the cortex, reminiscent of the expression profile manifested at the end of the second postnatal week in vivo. Also, the number of PV‐immunoreactive cells in these cultures was significantly lower than in explants at the later stages. Our results indicate that the onset of PV‐expression in the parietal cortex depends upon extrinsic cortical factors subsisting prior to P7. Once the production of this protein has been initiated, such influences are no longer required.
Synaptic loss reflected by secretoneurin‐like immunoreactivity in the human hippocampus in Alzheimer's disease
Authors: Kaufmann W.A. , Barnas U. , Humpel C. , Nowakowski K. , DeCol C. , Gurka P. , Ransmayr G. , Hinterhuber H. , Winkler H. , Marksteiner J.
Published: March 2003

Secretoneurin is a recently described peptide derived by endoproteolytic processing from secretogranin II, previously named chromogranin C. In this study, we have investigated the distribution of secretoneurin‐like immunoreactivity in the human hippocampus in controls and in Alzheimer's disease patients, and compared the staining pattern to that of calretinin. Secretoneurin‐like immunoreactivity is present throughout the hippocampal formation. At the border of the dentate molecular layer and the granule cell layer, a band of dense secretoneurin immunostaining appeared. In this part, as in the area of the CA2 sector, the high density of secretoneurin‐immunoreactivity coincided with calretinin‐like immunoreactivity. The mossy fibre system displayed a moderate density of secretoneurin‐immunoreactivity. In the entorhinal cortex, a particularly high density of secretoneurin‐immunoreactivity was observed. The density of secretoneurin‐like immunoreactivity was significantly reduced in the innermost part of the molecular layer and in the outer molecular layer of the dentate gyrus in Alzheimer's disease. For calretinin‐like immunoreactivity, a less pronounced decrease was found in the innermost part of the molecular layer. About 40–60% of neuritic plaques were secretoneurin‐immunopositive.

This study shows that secretoneurin is distinctly distributed in the human hippocampus and that significant changes of secretoneurin‐like immunoreactivity occur in Alzheimer's disease, reflecting synaptic loss.
The cortical somatotopic map and phantom phenomena in subjects with congenital limb atrophy and traumatic amputees with phantom limb pain
Authors: Montoya Pedro , Ritter Karin , Huse Ellena , Larbig Wolfgang , Braun Christoph , Töpfner Stephanie , Lutzenberger Werner , Grodd Wolfgang , Flor Herta , Birbaumer Niels
Published: March 2003

The extent of the cortical somatotopic map and its relationship to phantom phenomena was tested in five subjects with congenital absence of an upper limb, four traumatic amputees with phantom limb pain and five healthy controls. Cortical maps of the first and fifth digit of the intact hand, the lower lip and the first toe (bilaterally) were obtained using neuroelectric source imaging. The subjects with congenital upper limb atrophy showed symmetric positions of the left and right side of the lower lip and the first toe, whereas the traumatic amputees with pain showed a significant shift (about 2.4 cm) of the cortical representation of the lower lip towards the hand region contralateral to the amputation side but no shift for the toe representation. In healthy controls, no significant hemispheric differences between the cortical representation of the digits, lower lip or first toe were found. Phantom phenomena were absent in the congenital but extensive in the traumatic amputees. These data confirm the assumption that congenital absence of a limb does not lead to cortical reorganization or phantom limbs whereas traumatic amputations that are accompanied by phantom limb pain show shifts of the cortical areas adjacent to the amputation zone towards the representation of the deafferented body part.
Relations between cortical and thalamic cellular activities during absence seizures in rats
Authors: Seidenbecher Thomas , Staak Rainer , Pape Hans‐Christian
Published: March 2003

In a rat model of generalized absence epilepsies (Genetic Absence Epilepsy Rats from Strasbourg, GAERS), multiunit activity was recorded simultaneously at different sites of the thalamocortical system under neurolept anaesthesia (fentanyl‐droperidol). Under these conditions, bilaterally synchronized spike‐and‐wave‐discharges (SWDs) occurred spontaneously on the electroencephalogram (EEG) that were in principle identical to those reported earlier from unanaesthetized preparations. The generation of SWDs on the EEG was associated with spike‐concurrent, rhythmic burst‐like activity in (mono‐)synaptically connected regions of specific (somatosensory) thalamic regions and layers IV/V of the somatosensory cortex, and the reticular thalamic nucleus. Precursor activity was typically recorded in cortical units, concomitant with ‘embryonic’ SW seizures on the EEG, before the paroxysm was evident on the gross EEG and in the thalamus. On average, SWD‐correlated activity in layers IV/V of the somatosensory cortex started significantly earlier than correlated burst‐like firing in reticular and in ventrobasal thalamic neurons. Cellular peak firing in thalamus and cortex during bilaterally synchronized SWDs was related to the spike component on the gross EEG with the temporal rank order ventroposteromedial > ventrolateral ≥ ventroposterolateral thalamic > > rostral reticular thalamic nuclei ≥ cortex (layers IV/V) = caudal reticular thalamic nucleus. A spike‐related depression and wave‐related increase in firing was recorded in anteroventral ventrolateral thalamic areas, presumably reflecting their peculiar anatomical arrangement within the thalamus. These results from an in vivo preparation with intact synaptic connections that spontaneously produces SWDs indicate that SWDs spread within the thalamocortical network, involving short and long delays. The order of concurrent rhythmic firing observed in thalamocortical circuits during SW seizures are supportive of the hypothesis that the processes of rhythmogenesis recruit local thalamic networks, while cortical mechanisms appear to synchronize rhythmic activities on a larger spatiotemporal scale, thereby providing an important contribution to the generalization of epileptiform activity and expression of SWDs on the EEG.
The relation between dopamine oxidation currents in the nucleus accumbens and conditioned increases in motor activity in rats following repeated administration of d‐amphetamine or cocaine
Authors: Di Ciano Patricia , Blaha Charles D. , Phillips Anthony G.
Published: March 2003

Chronoamperometric recording techniques were used to monitor extracellular dopamine efflux in the nucleus accumbens associated with unconditioned and conditioned increases in motor activity in rats, following the intravenous administration of either d‐amphetamine (0.63 mg/kg) or cocaine (3 mg/kg), or the presentation of a conditioned stimulus paired repeatedly with one of these psychostimulants. Each drug was administered daily for 7 days, either in the home cage or an environment in which a compound stimulus (light offset, odour) was presented. Rats in control groups received saline instead of drug in the distinctive test environment. On day 7 of training, significant increases in unconditioned motor activity were observed in the 30 min session following infusions of either d‐amphetamine or cocaine. Associated dopamine oxidation currents in the nucleus accumbens increased immediately following administration of either drug and remained significantly elevated above baseline during the entire 30 min recording period. On the test day, presentation of the conditioned stimulus with vehicle infusions, in the distinct environment, was accompanied by an increase in dopamine oxidation currents and a conditioned increase in motor activity, only in the groups in which these stimuli had been paired with d‐amphetamine or cocaine. Neither the magnitude or duration of the conditioned motor activity matched the corresponding change in extracellular dopamine efflux in the nucleus accumbens. Accordingly, it is argued that the increase in dopamine concentration serves as a neurochemical correlate of the unconditioned and conditioned stimuli. The change in motor activity constitutes the unconditioned and conditioned responses that are subserved by the neural systems activated by the initial rise in extracellullar dopamine.
Conditioned changes in dopamine oxidation currents in the nucleus accumbens of rats by stimuli paired with self‐administration or yoked‐administration of d‐amphetamine
Authors: Di Ciano Patricia , Blaha Charles D. , Phillips Anthony G.
Published: March 2003

In vivo chronoamperometry was used to monitor changes in dopamine oxidation currents corresponding to dopamine efflux in the nucleus accumbens of rats after presentation of a conditioned light stimulus repeatedly paired with either yoked‐ or self‐administered intravenous injections of the psychostimulant d‐amphetamine. Daily conditioning trials began with a non‐contingent drug injection, paired with a conditioned stimulus consisting of a 5 s flashing light and 30 s lights out, after which a house light was illuminated during the 3 h session, signalling drug availability. Each subsequent injection of d‐amphetamine was paired with the conditioned stimulus. Electrochemical measures were taken on conditioning trials 4–7, and on each trial, intravenous

d‐amphetamine (0.25 mg/kg per injection) self‐administration produced a significant maximal increase in mean dopamine oxidation currents of ≈ 8 nA above baseline. Dopamine oxidation currents in rats receiving yoked

d‐amphetamine were ≈ 5 nA above baseline by the fourth day of drug administration and reached ≈ 8 nA on the seventh and final day of drug administration. On day 9 the first presentation of the vehicle injection and conditioned stimulus, in combination with illumination of the house lights, induced an immediate increase in nucleus accumbens dopamine oxidation currents in all rats that had previously received d‐amphetamine. Subsequent presentations of the conditioned stimulus at 30 min intervals induced further increases in extracellular dopamine oxidation currents in both drug‐treated groups. By the end of the 3 h session, both groups had similar maximal conditioned increases in dopamine oxidation currents of ≈ 6 nA. These data are discussed with relation to the neurochemistry of drug craving.
Spatiotemporal distribution of a late synchronized activity in olfactory pathways following stimulation of the olfactory bulb in rats
Authors: Mouly Anne‐Marie , Litaudon Philippe , Chabaud Pascal , Ravel Nadine , Gervais Rémi
Published: March 2003

The evoked potential recorded in the rat piriform cortex in response to electrical stimulation of the olfactory bulb is composed of an early component occasionally followed by a late component (60–70 ms). We previously showed that the late component occurrence was enhanced following an olfactory learning. In the present study carried out in naive rats, we investigated the precise conditions of induction of this late component, and its spatiotemporal distribution along the olfactory pathways. In the anaesthetized rat, a stimulating electrode was implanted in the olfactory bulb. Four recording electrodes were positioned, respectively, in the olfactory bulb, the anterior and posterior parts of the piriform cortex, and the entorhinal cortex. Simultaneous recording of signals evoked in the four sampled structures in response to stimulation of the olfactory bulb revealed that the late component was detected in anterior and posterior piriform cortex as well as in entorhinal cortex, but not in the olfactory bulb. The late component occurred reliably for a narrow range of low intensities of stimulation delivered at frequencies not exceeding 1 Hz. Comparison of late component amplitude and latency across the different recorded sites showed that this component appeared first and with the greatest amplitude in the posterior piriform cortex. In addition to showing a functional dissociation between anterior and posterior parts of the piriform cortex, these data suggest that the posterior piriform cortex could be the locus of generation of this late high amplitude synchronized activity, which would then propagate to the neighbouring regions.