bluuebunny/crossref_metadata_2025 huggingface dataset:
Involvement of a c‐fos‐Dependent Mechanism in Caffeine‐Induced Expression of the Preprotachykinin A and Neurotensin/Neuromedin N Genes in Rat Striatum
Authors: Svenningsson Per , Georgieva Jeanette , Kontnyi Ewa , Heilig Markus , Fredholm Bertil B.
Published: April 2006

Striatal c‐fos induction was blocked by local administration of phosphorothioated c‐fos antisense oligonucleotides (AS‐ODN) to examine the possible role of caffeine‐induced c‐fos expression in transcriptional regulation of striatal preproenkephalin, prodynorphin, preprotachykinin A and neurotensin/neuromedin N. Caffeine (100 mg/kg i.p.) induced both c‐fos mRNA and Fos‐protein, and this induction was significantly attenuated by intrastriatal injection of 4 (but not 1) nmol c‐fos AS‐ODN. This suggests that, in addition to translational arrest, other mechanisms may be involved in the mediation of antisense action. The action of the AS‐ODN was sequence specific. The antisense blockade of c‐fos reduced the effect of caffeine on the expression of mRNAs for preprotachykinin A and neurotensin/neuromedin N in the ventrolateral caudate–putamen. Levels of preproenkephalin and prodynorphin transcripts were unaffected. Thus caffeine induction of striatal preprotachykinin A mRNA and neurotensin/neuromedin N mRNA, but not of preproenkephalin mRNA or prodynorphin mRNA, may at least in part be mediated by a pathway involving Fos protein. The findings illustrate the utility of blockade of gene expression with antisense oligonucleotides for in vivo studies of drug actions.
The Primate Striatum: Neuronal Activity in Relation to Spatial Attention Versus Motor Preparation
Authors: Boussaoud Driss , Kermadi Imane
Published: April 2006

The primate basal ganglia are known to be involved in the initiation and control of visually guided movements. However, the precise role of these structures is not clear, partly because most neurophysiological studies have not dissociated neuronal activity related to visuomotor processing from that reflecting other aspects of behaviour, such as shifts of spatial attention. Moreover, the way the basal ganglia function together with the frontal cortex during movement initiation and execution is still a matter of debate. In an effort to clarify these issues, we recorded single neurons from the striatum (caudate nucleus and putamen) in two rhesus monkeys trained to perform a conditional visuomotor task, and compared their properties with those of the frontal cortex. The experimental paradigm was designed to distinguish neuronal activity associated with shifts of attention from that reflecting motor preparation. In a given trial, an identical visual stimulus could serve as a cue for the reorientation of spatial attention or as a cue for establishing a motor set depending on when it occurred during that trial. Additional aspects of the paradigm were designed to identify neurons whose activity differed when various stimulus configurations instructed the same action (stimulus effect), as well as neurons whose activity differed when two different actions were instructed by the same stimulus (movement effect). The majority of cells (60%) were preferentially active after instructional cues, 38% discharged preferentially after attentional cues, and the remaining 2% of cells discharged equally after both types of cue. Neurons active after instructional cues were further analysed for stimulus and movement effects. During movement preparation, the activity of the vast majority of striatal cells (putamen, 81%; caudate, 76%) varied significantly when different stimuli instructed the same action. Likewise, when different movements were instructed by the same stimulus, preparatory activity of a majority of cells (putamen, 92%; caudate, 82%) changed. Consequently, a substantial proportion of cells showed combined stimulus and movement effects. Comparison of these neuronal properties with those of the dorsal premotor cortex showed significantly higher proportions of cells in the striatum whose activity reflected sensory or sensorimotor processing. These results suggest that the basal ganglia are involved in shifting attentional set and in high‐order processes of movement initiation, including the linking of sensory information with behavioural responses.
Somatotopy in the Human Motor Cortex Hand Area. A High‐Resolution Functional MRI Study
Authors: Kleinschmidt Andreas , Nitschke Matthias F. , Frahm Jens
Published: April 2006

Fine‐scale somatotopic encoding in brain areas devoted to sensorimotor processing has recently been questioned by functional neuroimaging studies which suggested its absence within the hand area of the human primary motor cortex. We re‐examined this issue by addressing somatotopy both in terms of functional segregation and of cortical response preference using oxygenation‐sensitive magnetic resonance imaging at high spatial resolution. In a first step, spatial representations of self‐paced isolated finger movements were mapped by using motor rest as a control state. A subsequent experimental design studied the predominance of individual finger movements by using contrasting finger movements as the control task. While the first approach confirmed previous reports of extensive overlap in spatial representations, the second approach revealed foci of differential activation which displayed an orderly mediolateral progression in accordance with the classical cortical motor homunculus. We conclude that somatotopy within the hand area of the primary motor cortex does not present as qualitative functional segregation but as quantitative predominance of certain movement or digit representation embedded in an overall joint hand area.
Differential Modulation of the Uptake Currents by Redox Interconversion of Cysteine Residues in the Human Neuronal Glutamate Transporter EAAC1
Authors: Trotti Davide , Nussberger Stephan , Volterra Andrea , Hedger Matthias A.
Published: April 2006

Control of extrasynaptic glutamate concentration in the central nervous system is an important determinant of neurotransmission and excitotoxicity. Mechanisms that modulate glutamate transporter function are therefore critical factors in these processes. The redox modulation of glutamate uptake was examined by measuring transporter‐mediated electrical currents and radiolabelled amino acid influx in voltage‐clamped Xenopus oocytes expressing the human neuronal glutamate transporter EAAC1. Up and down changes of the glutamate uptake currents in response to treatment with dithiothreitol and 5,5′‐dithio‐bis‐(2‐nitrobenzoic) acid (DTNB) were observed in oocytes clamped at ‐60 mV. The redox interconversion of cysteines induced by dithiothreitol/DTNB influenced the Vmax (Imax) of transport, while the apparent affinity for glutamate was not affected. Formation or breakdown of disulphide groups did not affect the pre‐steady‐state currents, suggesting that these manipulations do not interfere with the Na+ binding/unbinding and/or the charge distribution on the transporter molecule. The glutamate‐evoked net uptake current of EAAC1 was composed of the inward current from electrogenic glutamate transport and the current arising from the glutamate‐activated CI‐ conductance. The structural rearrangement produced by the formation or breakdown of disulphide groups only affected the current from electrogenic giutamate transport. The electrogenic currents of EAAC1 were significantly reduced by peroxynitrite, an endogenously occurring oxidant formed in certain pathological brain processes, and the mechanism of inhibition partially depended on the formation of disulphide groups.
Complexities in the Thalamocortical and Corticothalamic Pathways
Authors: Adams Niels C. , Lozsádi Dora A. , Guillery R. W.
Published: April 2006

It is now a century since Kölliker (Handbuch der Gewebelehre des Menschen. Nervensystemen des Menschen und der Thiere, Vol. 2, 6th edn. Engelmann, Leipzig, 1896) described the thalamic reticular nucleus as the ‘Gitterkern’ or lattice nucleus on the basis of the fibrous latticework that is the characteristic feature of this part of the ventral thalamus and adjacent parts of the internal capsule. We suggest that the fibre reorganization produced in this lattice is a fundamental requirement for linking orderly maps in the thalamus to corresponding cortical maps by two‐way thalamocortical and corticothalamic connections; these connections involve divergence, convergence and mirror reversals, which all have to occur between the thalamus and the cortex. Apart from the thalamic reticular nucleus, two transient groups of cells, the perireticular nucleus (located in the internal capsule lateral to the reticular nucleus) and the cells of the cortical subplate, are prominent along the course of axons linking the cortex and thalamus early in development. The functions of these two cell groups are not known. However, since early in development complex patterns of reorganization, defasciculation and crossings occur in the regions of these cells, it is likely that they play a role in creating the latticework of the adult. The latticework that characterizes the thalamic reticular nucleus of mammals can also be identified in the ventral thalamus of non‐mammalian brains, formed along the course of the fibres that join the dorsal thalamus to the telencephalon. We suggest that the ubiquitous presence of such a zone of fibre reorganization is integral to the functioning of the thalamocortical pathways, and that the complexity of thalamic connections produced in the lattice has been central to the evolutionary success of the thalamotelencephalic system.
Infusions of Tyrosine Hydroxylase Antisense Oligodeoxynucleotide into Substantia Nigra of the Rat: Effects on Tyrosine Hydroxylase mRNA and Protein Content, Striatal Dopamine Release and Behaviour
Authors: Skutella Thomas , Schwarting Rainer K. W. , Huston Joseph P. , Sillaber Lnge , Probst Joseph C. , Holsboer Florian , Spanagel Rainer
Published: April 2006

Modulation of the transcriptional message of tyrosine hydroxylase was investigated in vivo in the rat nigrostriatal dopamine system with unmodified antisense oligodeoxynucleotide, mismatch oligodeoxynucleotide or vehicle controls. Oligodeoxynucleotide was infused (0.5 μg/0.5 μl/h) unilaterally into the substantia nigra by an osmotic minipump system over 14 days. The presence of oligodeoxynucleotide in the brain was verified by in situ hybridization and fluorescence labelling. Animals treated with unmodified antisense oligodeoxynucleotide showed ipsilateral turning behaviour when challenged systemically with the indirect dopamine agonist amphetamine, whereas mismatch‐ and vehicle‐infused rats showed no such behavioural asymmetries. In the substantia nigra, antisense treatment had no effects on tyrosine hydroxylase mRNA, but it led to a reduction in tyrosine hydroxylase protein content. Tissue levels of dopamine, measured in postmortem tissue punches of the neostriatum and substantia nigra, were reduced in the oligodeoxynucleotide‐treated hemisphere. Furthermore, basal extracellular levels of dopamine, monitored by in vivo microdialysis, were also lower in the neostriatum ipsilateral to antisense infusion and showed a weaker response to an amphetamine challenge when compared with the contralateral side. These effects were not observed after infusion of mismatch oligodeoxynucleotide or vehicle into the substantia nigra. Finally, the GABAergic enzyme glutamate decarboxylase was not affected in the antisense‐treated substantia nigra, indicating that non‐specific damage in this area was not caused by this treatment. Our results indicate that antisense oligodeoxynucleotide treatment against tyrosine hydroxylase in the substantia nigra has behavioural and neurochemical effects that are comparable with known actions of dopamine neurotoxins, which are conventional pharmacological tools for the depletion of dopamine. Furthermore, our data show the potential of antisense targetting to reveal new relationships between neurotransmitter‐related enzymes and behavioural parameters, because the possibility of selectively and discretely manipulating tyrosine hydroxylase function is likely to produce new insights into the physiological and behavioural functions of the dopaminergic nigrostriatal system.
Organization of Pyramidal Cell Apical Dendrites and Composition of Dendritic Clusters in the Mouse: Emphasis on Primary Motor Cortex
Authors: Lev Dmitri L. , White Edward L.
Published: April 2006

It has been proposed that neurons in sensory cortices are organized into modules that centre on clusters of apical dendrites belonging to layer V pyramidal neurons. In the present study, sections reacted for microtubule‐associated protein (MAPP) were examined in order to determine the three‐dimensional inter‐relationships of pyramidal cell dendrites in mouse primary motor cortex (MsI) cortex. Results indicate that pyramidal cell dendrites in MsI cortex can be interpreted to be arranged in a modular fashion, and that these modules are organized similarly to those in the sensory areas of the cortex. Also included in the present study are experiments designed to determine if the clusters of apical dendrites, around which the modules are centred, are composed of dendrites belonging to one or to more than one type of projection cell. Callosal neurons in MsI cortex were labelled by the retrograde transport of horseradish peroxidase deposited onto severed callosal fibres in the contralateral hemisphere. Examination of tangential thin sections through layer IV of MsI cortex shows clusters of apical dendrites in which every dendrite is labelled with horseradish peroxidase. Adjacent clusters are composed of unlabelled dendrites, suggesting that the apical dendrites of callosal neurons aggregate to form clusters that are composed exclusively of dendrites belonging to this type of projection cell. These findings suggest a hitherto unsuspected degree of specificity in the cellular composition of cortical modules.
Corticotropin‐releasing Factor in the Caudal Pontine Reticular Nucleus Mediates the Expression of Fear‐potentiated Startle in the Rat
Authors: Fendt Markus , Koch Michael , Schnitzler Hans‐Ulrich
Published: April 2006

The fear‐potentiated startle paradigm is a valuable model for the investigation of the neuronal basis of fear. Previous studies have demonstrated that the neuropeptide corticotropin‐releasing factor (CRF) plays an important role in fear‐related processes, notably in the potentiation of the acoustic startle response. The present study investigated the role in fear‐potentiated startle of CRF in the caudal pontine reticular nucleus, a brain nucleus that mediates the acoustic startle response. First, we showed that the central nucleus of the amygdala gives rise to a CRFergic projection to the caudal pontine reticular nucleus. In the second experiment, we iontophoretically applied CRF to caudal pontine reticular nucleus neurons and extracellularly recorded the activity of these neurons. CRF had a mainly excitatory effect on the tone‐evoked activity of the neurons. In our third experiment, we injected the CRF antagonist α‐helical CRF into the caudal pontine reticular nucleus of awake rats. Here, α‐helical CRF dose‐dependently blocked fear‐potentiated startle, but had no effect on the baseline startle amplitude. The present results show that CRF‐containing neurons which project from the central nucleus to the caudal pontine reticular nucleus are important for the enhancement of startle by fear, and further characterize the hypothetical neuronal circuitry underlying the expression of fear‐potentiated startle.
GP55 Inhibits both Cell Adhesion and Growth of Neurons, but not Non‐neuronal Cells, via a G‐protein‐coupled Receptor
Authors: Clarke G. A. , Moss D. J.
Published: April 2006

There is compelling evidence for the role of inhibitory molecules in guiding neurons to their appropriate targets. Furthermore, continued expression of these molecules in the adult could explain why there is little regeneration of neurons in the central nervous system. We have previously identified a family of glycosyl phosphatidylinositol‐linked glycoproteins (GP55) from adult chicken brain that has been shown to inhibit neurite outgrowth from dorsal root ganglion and forebrain neurons. GP55 consists of two or more glycoproteins and belongs to a subgroup of the Ig superfamily which contains OBCAM, LAMP, neurotrimin and CEPU‐1. We now show that GP55 is anti‐adhesive, blocking the adhesion of neurons to normally adhesive substrata in a concentration dependent manner. The anti‐adhesive effect can be blocked using antiserum raised against GP55 and pertussis toxin (PTX) but not the β oligomer alone. In contrast, the adhesion of fibroblasts and Schwann cells to the substrata is not affected by GP55. Indeed, non‐neuronal cells spread and grow normally. These results would suggest that both the anti‐adhesive effect and the inhibition of outgrowth by GP55 is specific to neurons and is mediated by a PTX sensitive, G‐protein‐coupled receptor.
Differential Effects of Acetylcholine on Neuronal Activity and Interactions in the Auditory Cortex of the Guinea‐pig
Authors: Shulz Daniel E. , Cohen Shuki , Haidarliu Sebastian , Ahissar Ehud
Published: April 2006

During normal brain operations, cortical neurons are subjected to continuous cholinergic modulations. In vitro studies have indicated that, in addition to affecting general cellular excitability, acetylcholine also modulates synaptic transmission. Whether these cholinergic mechanisms lead to a modulation of functional connectivity in vivo is not yet known. Herein, the effects were studied of an iontophoretic application of acetylcholine and of the muscarinic agonist, carbachol, on the ongoing activity and co‐activity of neurons simultaneously recorded in the auditory cortex of the anaesthetized guinea‐pig. Iontophoresis of cholinergic agonists mainly affected the spontaneous firing rates of auditory neurons, affected autocorrelations less (in most cases their central peak areas were reduced), and rarely affected cross‐correlations. These findings are consistent with cholinergic agonists primarily affecting the excitability of cortical neurons rather than the strength of cortical connections. However, when changes of cross‐correlations occurred, they were usually not correlated with concomitant changes in average firing rates nor with changes in autocorrelations, which suggests a secondary cholinergic effect on specific cortico‐cortical or thalamo‐cortical connections.
Regulation of Quantal Transmitter Secretion by ATP and Protein Kinases at Developing Neuromuscular Synapses
Authors: Fu W. M. , Chen Y. H. , Lee K. F. , Liou J. C.
Published: April 2006

The effects of endogenously released ATP on the maturation of developing neuromuscular synapses were investigated in Xenopus nerve‐muscle co‐cultures. The potentiating action of ATP (1 mM) on spontaneous acetylcholine release was inhibited by P2‐purinoceptor antagonists suramin (0.3 mM) and reactive blue 2 (RB‐2, 3 μM) in day 1 cultures. Bath application of suramin (10 μM) or RB‐2 in day 1 cultures and prolonged treatment for 2 days dramatically decreased the amplitude of both spontaneous synaptic currents (SSCs) and evoked synaptic currents (ESCs) in the same cultures on day 3. Chronic treatment with 8‐cyclopentyltheophylline (4 μM) or 6‐cyano‐2, 3‐dihydroxy‐7‐nitroquinoxaline (CNQX, 10 μM), P1‐purinoceptor and glutamate receptor antagonists respectively, did not exert such an inhibitory effect. Chronic treatment with suramin or RB‐2 for 2 days had no significant effect on the amplitude of either iontophoretic acetylcholine‐induced whole‐cell currents or single acetylcholine channel measurements in 3‐day‐old cultured myocytes. In addition, prolonged treatment for 2 days with various kinase inhibitors such as H‐8 (10 μM), KN‐62 (5 μM) and H‐7 (10 μM) also decreased the amplitudes of both spontaneous and evoked synaptic currents in natural synapses, but not those of iontophoretic acetylcholine‐induced currents. Furthermore, suramin and these protein kinase inhibitors also decreased the amplitude of spontaneous synaptic currents in manipulated synapses of ‘vacated’ nerve terminals. The results suggest that endogenously released ATP, acting in concert with various protein kinases, is involved in the maintenance and/or development of the quantum size of synaptic vesicles at embryonic neuromuscular synapses.
Activation by Cutaneous or Visceral Noxious Stimulation of Spinal Neurons Projecting to the Medullary Dorsal Reticular Nucleus in the Rat: A c‐fos Study
Authors: Almeida Armando , Lima Deolinda
Published: April 2006

The involvement of spinal neurons in the transmission of cutaneous and visceral nociceptive input to the medullary dorsal reticular nucleus was studied. Rats were injected with cholera toxin subunit B in the left dorsal reticular nucleus and subjected 4 days later to noxious mechanical, thermal or chemical stimulation of the proximal internal aspect of the left thigh, or to chemical stimulation of the urinary bladder. Sections of spinal segments T13‐L3 were processed immunocytochemically for cholera toxin subunit B and Fos protein. The percentage of double‐labelled cells in the population of Fos‐positive cells was higher in lamina I (1–4%) than in deeper laminae (0–0.7%) following all stimuli. The percentage of double‐labelled cells in the population of retrogradely labelled cells was 30–53% in lamina I and 0–5% in laminae III—X. Visceral stimulation activated more retrogradely labelled lamina I cells than any kind of cutaneous stimulation. Pyramidal cells were activated in higher numbers than multipolar and flattened cells after thermal cutaneous or visceral stimulation, and in lower numbers than multipolar cells after mechanical stimulation. These results suggest that, in the experimental conditions used, spinal cord cells conveying noxious input to the dorsal reticular nucleus are concentrated in lamina I. They further indicate that the spinaldorsal reticular nucleus pathway plays a major role in the transmission of nociceptive visceral input, and point to the preferential involvement of pyramidal cells in cutaneous thermal and visceral processing.
Locomotor‐Related Presynaptic Modulation of Primary Afferents in the Lamprey
Authors: El Manira A. , Tegner J. , Grillner S.
Published: April 2006

Presynaptic modulation of sensory afferent transmission during rhythmic motor activity was investigated in the lamprey spinal cord in vitro. Intracellular recordings were performed from the somata and axons of the glutamatergic sensory neurons from the skin (dorsal cells) during locomotor activity induced by N‐methyl‐D‐aspartate (NMDA). Dorsal cells were phasically depolarized during each ipsilateral ventral root burst. In some soma recordings no or only small amplitude depolarizations were seen, although intracellular recording of their axons revealed the existence of large depolarizations, suggesting that the input synapses are located on the axons. The amplitude of the depolarizations increased during intracellular injection of hyperpolarizing current. The amplitude of the depolarizations increased when the frequency of the locomotor rhythm was increased by elevating the NMDA concentration. The depolarizations were not blocked by specific GABAA (bicuculline) or GABAB (phaclofen and saclofen) antagonists. To investigate whether the phasic depolarization may influence the monosynaptic excitatory transmission to giant interneurons, the amplitude of the monosynaptic excitatory postsynaptic potential (EPSP) was compared between the onset of the ipsilateral locomotor burst and the burst mid‐point. The compound monosynaptic EPSP evoked from dorsal column was significantly smaller during the peak depolarization than at burst onset. The reduction of the amplitude of the EPSPs was not associated with any change of the membrane potential or input resistance of the giant interneurons, suggesting that this effect is mediated by a presynaptic mechanism. Phase‐dependent effects were also seen on burst and cycle duration following dorsal column stimulation. Thus, the locomotor‐related depolarizations in dorsal cell axons may represent a mechanism for a phasic gain control of sensory transmission during fictive locomotion.
Analysis of the Ion Channel Complement of the Rat Oligodendrocyte Progenitor in a Commonly Studied In vitro Preparation
Authors: Williamson A. V. , Compston D. A. S. , Randall A. D.
Published: April 2006

We have analysed the ion channel complement of the oligodendrocyte‐type 2 astrocyte (O‐2A) glial cell progenitor obtained from the commonly studied neonatal rat mixed brain preparation. Ionic currents, in O‐2A progenitors identified on both morphological and immunological grounds, were recorded using the whole‐cell variant of the patch‐clamp technique. The cells had an average resting membrane potential close to ‐50 mV and fired single action potentials in response to suprathreshold current injections. Using voltage‐clamp methods we were able to identify and characterize a voltage‐activated TTX‐sensitive Na+ current, two classes of voltage‐activated outward K+ currents, an inactivating inwardly rectifying K+ current, a voltage‐activated Cl‐ current and at least three classes of Ca2+ current.
Serpins Inhibit the Toxicity of Amyloid Peptides
Authors: Schubert David
Published: April 2006

The amyloid plaque in Alzheimer's disease (AD) contains numerous proteins, some of which may be relevant to the pathogenesis of the disease. The serine protease inhibitor α1‐antichymotrypsin is specifically localized in AD plaques. It is shown here that α1‐antichymotrypsin and several other serine protease inhibitors (serpins) inhibit the toxicity of amyloid peptides on primary cortical nerve cell cultures as well as a clonal cell line. This inhibition of toxicity is not mediated via the serpin enzyme complex receptor, the transferrin receptor, or by interference with the polymerization of amyloid fibrils. Since a variety of synthetic serine protease inhibitors mimic the effects of serpins on amyloid toxicity, it is likely that the antiprotease activities of serpins are responsible for their biological effects.
Evidence That Spinal Interneurons Undergo Programmed Cell Death Postnatally in the Rat
Authors: Lawson S. J. , Davies H. J. , Bennett J. P. , Lowrie M. B.
Published: April 2006

Programmed cell death has been demonstrated in several specific neuronal populations as a mechanism for modulating the population size following differentiation, but its applicability to all neuronal types is unclear. Evidence for programmed cell death in some populations such as the numerous spinal interneurons has been lacking. We have studied the incidence of apoptosis in the rat spinal cord with three different methods and found a previously undocumented wave of apoptosis occurring in spinal grey matter shortly after birth. The apoptotic morphology was confirmed ultrastructurally. Dying cells were identified as neurons by immunocytochemical labelling for neuronal markers and had an anatomical distribution which indicated that most of the apoptotic cells were interneurons not motoneurons. This wave of apoptosis has the characteristics of a discrete developmental process and occurs later than that of either ventral horn motoneurons or dorsal root ganglion cells, to which most spinal interneurons are connected. These findings indicate that interneurons do undergo programmed cell death, and we suggest that this occurs in response to the earlier reduction in size of their main synaptic targets.
Microinfusion of the Metabotropic Glutamate Receptor Agonist 1S, 3R–1‐Aminocyclopentane‐1, 3‐dicarboxylic Acid Into the Nucleus Accumbens Induces Dopamine‐dependent Locomotor Activation in the Rat
Authors: Attarian Shahram , Amalric Marianne
Published: April 2006

Although the striatum has one of the highest densities of metabotropic glutamate receptor (mGluR) binding sites in the brain, little is known about their physiological role. In this study we characterized the contribution of mGluRs located in the ventral part of the striatum (the nucleus accumbens) to the control of extrapyramidal motor function. Activation of mGluRs by local infusion of the selective agonist 1S, 3R–1‐aminocyclopentane‐1, 3‐dicarboxylic acid (1 S, 3R‐ACPD; 25, 50 and 100 nmol/0.5 μl) into the nucleus accumbens induced a dose‐dependent increase in locomotor activity in rats. Intra‐accumbens infusion of a selective antagonist of mGluRs, a‐methyl‐4‐carboxyphenylglycine (MCPG) did not modify spontaneous locomotion but decreased the locomotor response to 1S, 3R‐ACPD. This effect appeared to be mediated by dopamine, since blockade of dopamine receptors with haloperidol (0.05 and 0.1 mg/kg i.p.) dose‐dependently reduced 1 S3R‐ACPD‐induced locomotor activation. Furthermore, D‐amphetamine (0.5 mg/kg, i.p.) combined with intra‐accumbens infusion of 1S, 3R‐ACPD (100 nmol) potentiated the locomotor hyperactivity response to a higher level than that seen with a single treatment with either drug. In contrast, D‐amphetamine‐induced hypermotility was abolished by infusion of MCPG (100 nmol) into the nucleus accumbens. These results demonstrate that glutamate may control extrapyramidal motor function through metabotropic receptors. Furthermore, activation of metabotropic glutamate receptors appears to act in synergy with the dopamine system at the level of the nucleus accumbens to produce a motor stimulant response.
Development of G Protein‐mediated Ca2+ Channel Regulation in Mouse Embryonic Stem Cell‐derived Neurons
Authors: Strübing Carsten , Rohwedel Jürgen , Ahnert‐Hilger Gudrun , Wiedenmann Bertram , Hescheler Jürgen , Wobus Anna M.
Published: April 2006

Besides other mechanisms, the influx of Ca2+ into embryonic neurons controls growth and differentiation processes. To study the expression and regulation of voltage‐gated Ca2+ channels during early neurogenesis, we measured whole‐cell Ca2+ currents (Ica) in neurons developing from pluripotent embryonic stem cells. Various receptor agonists, including somatostatin and baclofen, reversibly inhibited ICa in embryonic stem cell‐derived neurons. The effects of somatostatin and baclofen were abolished by pretreatment of cells with pertussis toxin and mimicked by intracellular infusion of guanosine 5′‐O‐(3‐thiotriphosphate), suggesting the involvement of pertussis toxin‐sensitive G proteins in Ica inhibition. Investigations at different stages of neuronal differentiation showed that somatostatin efficiently suppressed L‐ and N‐type Ca2+ channels in immature as well as mature neurons. In contrast, inhibition of L‐ and N‐type channels by baclofen was rarely observed at the early stage. In terminally differentiated neurons, responses to baclofen were as prominent as those to somatostatin but were confined to N‐type Ca2+ channels. The stage‐dependent sensitivity of voltage‐gated Ca2+ channels to somatostatin and baclofen was not due to differential expression of Gαo isoforms, as revealed by reverse transcription‐polymerase chain reaction and immunofluorescence microscopy. These findings demonstrate that specific neurotransmitters such as somatostatin regulate voltage‐gated Ca2+ channels via G proteins during the early stages of neurogenesis, thus providing a mechanism for the epigenetic control of neuronal differentiation.
Stimulation of the Ventral Subiculum of the Hippocampus Evokes Glutamate Receptor‐mediated Changes in Dopamine Efflux in the Rat Nucleus Accumbens
Authors: Blaha Charles D. , Yang Charles R. , Floresco Stan B. , Barr Alasdair M. , Phillips Anthony G.
Published: April 2006

The effects of electrical stimulation of the ventral subiculum/CA1 region of the hippocampus on changes in dopamine oxidation current (corresponding to dopamine efflux) in the nucleus accumbens were examined using in vivo chronoamperometry with stearate‐graphite paste electrodes in urethane‐anaesthetized rats. Burst‐patterned monophasic pulses (10–100 Hz/burst delivered at 0.84 Hz) evoked a three‐component change in dopamine efflux in the nucleus accumbens with an initial transient increase in the dopamine signal above baseline, followed by an immediate decrease below baseline, and thereafter by a prolonged increase in the dopamine signal above baseline. 6–Hydroxydopamine lesions of the mesoaccumbens dopamine pathway or transection of the fimbria‐fornix blocked all of the evoked changes in the dopamine signal. Both the first and third components of enhanced dopamine efflux were blocked by microinfusion into the nucleus accumbens of the ionotropic glutamate receptor antagonists (±)‐2‐amino‐5‐phosphonopentanoic acid, 6,7‐dinitroquinoxaline‐2,3‐dione and kynurenate. Burst stimulation‐evoked decreases in the dopamine signal were abolished following microinfusions into the nucleus accumbens of the metabotropic glutamate receptor antagonist (+)‐α‐methyl‐4‐carboxyphenylglycine. These results suggest that ventral subiculum/CA1 glutamatergic inputs to the nucleus accumbens may presynaptically modulate dopamine efflux by synaptic activation of both ionotropic and metabotropic glutamate receptors in the nucleus accumbens. These glutamate‐dopamine interactions may constitute part of the mechanisms by which hippocampal signals are integrated through selective modulation of dopamine release in the nucleus accumbens in both physiological and pathological conditions.
Contribution of Area 17 to Cell Responses in the Striate‐recipient Zone of the Cat's Lateral Posterior‐Pulvinar Complex
Authors: Casanova C. , Savard T. , Darveau S.
Published: April 2006

The cat's lateral posterior‐pulvinar complex (LP‐pulvinar) contains three main representations of the visual field. The lateral part of the LP nucleus (LPI or striate‐recipient zone) is the only region of these extrageniculate nuclei which receives afferents from the primary visual cortex. We investigated the contribution of area 17 to the response properties (orientation and spatial frequency tuning functions) of LPI neurons by cooling or lesioning the visual cortex. Responses of 40 LPI cells were studied before, during and after the reversible cooling of the striate cortex. When tested for orientation, a total of 10 units out of 28 was affected (36%). For most of these cells (eight of lo), cooling the visual cortex yielded a reduction of the cells’ visual responses without altering their orientation‐selectivity (there was no significant change in the orientation tuning width). For only two cells, inactivation led to an increase in the response amplitude. Also, blocking the visual cortex never modified the direction‐selectivity of LPI cells. When tested for spatial frequency, 12 neurons out of 33 were affected (36%) by the experimental protocol. In most cases, we observed a reduction in the responses at each spatial frequency tested, with no change in tuning bandwidth. For only three LPI cells, the effects of inactivation of the visual cortex were restricted to specific spatial frequencies, altering the profile of the spatial frequency tuning function. In five cats, removing area 17 reduced the proportion of visual neurons in LPI and the spared visually evoked responses were noticeably depressed. Despite the reduction in responsiveness, a few LPI receptive fields within the cortical scotoma were still sensitive to the orientation and/or direction of a moving stimulus. This last observation suggests that some properties in LPI could be generated either by circuits intrinsic to the LPI or by afferents from extrastriate cortical areas. Overall, these results indicate that projections from the visual cortex to the striate‐recipient zone of the LP‐pulvinar complex are mainly excitatory. Despite the strong impact of the area 17 projections, our data suggest that the extrastriate cortex could also play a role in the establishment of response properties in the cat's LPI.
Tachykinin Actions on Deep Dorsal Horn Neurons In Wm: An Electrophysiological and Morphological Study in the Immature Rat
Authors: King A. E. , Slack J. R. , Lopez‐Garcia J. A. , Ackley M. A.
Published: April 2006

To assess whether functional neurokinin receptors exist in the deep dorsal horn of the rat, the actions of the selective neurokinin‐1 receptor (NK1R) agonist [Sar9,Met(O2)11]substance P [Sar9,Met(O2)11]]SP), the neurokinin‐2 receptor (NK2R) agonists [β‐Ala8]NKA4‐10 and GR64349 and the neurokinin‐3 receptor (NK3R) agonist senktide were examined intracellularly in vitro. [Sar9,Met(O2)11]]SP (1–4 μM) and senktide (1‐2 μM) elicited slow depolarizations (40 mV) associated with increased synaptic activity and cell firing. [β‐Ala8]NKA4‐10 (10‐20 μM) and GR64349 (0.25‐10 μM) caused small depolarizations (<2.0 mV) and no firing. Neurons were categorized as either ‘tonic’ or ‘phasic’ depending on their firing response to direct current step depolarizations. Tonic neurons, which, unlike phasic neurons, display no spike firing accommodation, generated a significantly larger depolarization to the NK1R and NK3R agonists. The putative contribution of these receptors to primary afferent‐mediated synaptic transmission was assessed by testing the NKIR antagonist GR82334 (1 μM), the NK2R antagonist MEN10,376 (1 μM) and the NK3R antagonist [Trp7,β‐Ala8]NKA4‐10 (1 μM) against the dorsal root‐evoked excitatory postsynaptic potential (DR‐EPSP). GR82334 and [Trp7,β‐Ala8]NKA4‐10 significantly reduced (P ≤ 0.05) the duration but not the amplitude of the DR‐EPSP. MEN10,376 (1 μM) had no effect on DR‐EPSP amplitude or duration. Morphological detail was obtained for seven biocytin‐filled deep dorsal horn neurons tested with [Sar9,Met(O2)11]SP. Five neurons responded to the NKIR agonist, and two of these had dorsally directed dendrites into the substantia gelatinosa. The other three [Sar9,Met(O2)11]SP‐sensitive neurons had dendrites within deeper laminae. These data support the existence of functional NK1Rs and NK3Rs in the deep dorsal horn which may be involved in mediating sensory afferent inputs from nociceptors.
Synaptic Plasticity in Dissociated Hippocampal Cultures: Pre‐ and Postsynaptic Contributions
Authors: Vogt Kaspar , Streit Jürg , Dityatev Alexander , Lüscher Hans‐Rudolf
Published: April 2006

The distinction between pre‐ or postsynaptic expression of synaptic plasticity is difficult to make, unless the postsynaptic receptors can be investigated in isolation. We have studied single synaptic contacts in dissociated cultures of rat hippocampus. The reaction of postsynaptic receptor assemblies to the induction of synaptic plasticity was measured and compared with changes in the rate of spontaneous miniature excitatory postsynaptic currents (mEPSCs), which can reflect changes in the transmitter release mechanism. The response of a receptor assembly to locally applied exogenous glutamate was measured before and after synchronized application of glutamate and a train of postsynaptic depolarizations (‘pairing’). Pairing induced a variety of changes: (i) the majority of the receptor assemblies showed no change in their response to glutamate before and after pairing; (ii) the postsynaptic current due to exogenous glutamate showed a rapid increase in five out of 26 cases. This was not due to changes in the single channel conductance; (iii) the rate of mEPSCs increased, if it had previously been below 25 Hz; (iv) the rate of mEPSCs decreased, if it had previously been above 25 Hz. Effects 2 and 3 were blocked by antagonists of NMDA receptors. These findings provide direct evidence for an increase of the number of glutamate receptors at a subset of the investigated postsynaptic sites during synaptic potentiation.
Nerve Growth Factor Treatment Increases Stimulus‐evoked Release of Sensory Neuropeptides in the Rat Spinal Cord
Authors: Malcangio Marzia , Garrett Neil E. , Tomlinson David R.
Published: April 2006

In the adult rat, nerve growth factor (NGF) upregulates the nociceptive peptide substance P (SP) and calcitonin gene‐related peptide (CGRP) in neuronal cell bodies of C fibres but the effects of NGF on release of these neuropeptides from the central afferent terminals have not been reported. Thus, this study compared rats treated with six doses of NGF over 2 weeks with controls and measured the release of the neuropeptides, SP and CGRP from the dorsum of the lumbar spinal cord in vitro. NGF (1.0 mg/kg s.c.) greatly increased basal and stimulus‐evoked SP and CGRP release; at 0.1 mg/kg, NGF did not affect SP release but significantly increased CGRP basal outflow and evoked release. In a different set of experiments, topical application of NGF (100 ng/ml) to cords from naive rats did not increase stimulus‐evoked release of SP or CGRP. These findings show marked stimulation by NGF treatment in vivo of release of sensory neuropeptides during stimulation of dorsal roots, albeit at relatively large doses of the neurotrophin.
Responses of Cortical EEG‐related Basal Forebrain Neurons to Brainstem and Sensory Stimulation in Urethane‐anaesthetized Rats
Authors: Détári László , Semba Kazue , Rasmusson Douglas D.
Published: April 2006

The basal forebrain can be considered to be a rostral extension of the ascending reticular activating system. A large number of neurons in the basal forebrain have been shown to display higher firing rates when low‐voltage fast activity is present in the cortical EEG as opposed to states characterized by large slow waves in both unanaesthetized and anaesthetized animals. However, a smaller number of cells with increased discharge rate during slow waves was also observed in most of these studies. While it is likely that these two types of neurons have opposite roles in the regulation of cortical activation, it is not known how they respond to inputs from the brainstem or the periphery. In the present study, extracellular recordings were made in the basal forebrain of urethane‐anaesthetized rats. A total of 52 neurons were studied in which the firing rate was significantly higher during fast cortical EEG waves (F‐cells), and 14 neurons in which activity was significantly greater during slow waves (S‐cells). The two cell types responded differently to stimulation of the pedunculopontine tegmental nucleus (PPT) and dorsal raphe nucleus (DRN) with short (0.5–1 s) trains of pulses and to noxious sensory stimuli (tail pinch). These stimulations excited most F‐cells (80–96%) and inhibited the majority of S‐cells (55–67%). In the few F‐cells that were inhibited by stimulation, the response varied with the background firing rate of the cell: the higher the firing rate at the time of stimulation, the higher the probability of observing an inhibitory response. In contrast, single electrical pulses delivered to the PPT and DRN excited the majority (72%) of both F‐ and S‐cells. Previous in vitro studies have shown that the application of acetylcholine or serotonin has predominantly inhibitory effects on basal forebrain cholinergic neurons. The predominantly excitatory effect of noxious, PPT and DRN stimulation on F‐cells therefore suggests that glutamatergic or other excitatory afferents play a more dominant role in regulating basal forebrain neurons. We have previously shown that F‐cells are more prevalent than S‐cells. In combination, these findings suggest that basal forebrain neurons, and F‐cells in particular, are important in mediating the ascending excitatory drive from the brainstem to the cerebral cortex.
GX/Z Is Regulated by μ But Not δ Opioid Receptors in the Stimulation of the Low Km GTPase Activity in Mouse Periaqueductal Grey Matter
Authors: Garzón Javier , Martinez‐Peña Yolanda , Sánchez‐Blázquez Pilar
Published: April 2006

High affinity low Km GTPase activity was measured in membrane preparations of adult mouse mesencephalic periaqueductal grey matter (PAG). Opioids displaying selectivity towards μ‐ or δ‐opioid receptors (OR) activated the enzyme in a concentration‐dependent manner. Antibodies to μ‐OR greatly impaired the potential of μ‐agonists, [D‐Ala2,N‐MePhe4,Gly‐ol5]‐enkephalin (DAMGO) and morphine, to increase hydrolysis of GTP. The same antibodies had little effect on [D‐Pen2,5]enkephalin (DPDPE) and [D‐Ala2]deltorphin II, both agonists at δ‐OR. Stimulation of GTPase by DPDPE and [D‐Ala2]deltorphin II ‐ but not by morphine or DAMGO ‐ was diminished by antibodies to δ‐OR. The blockade of Gi2α subunits by specific antibodies impaired the activation of Gα‐related GTPase by all opioids. Antibodies in vitro, and oligodeoxynucleotides in vivo, prepared against Gx/zα subunits, reduced the release of Pi promoted by DAMGO and morphine. The impairment of Gx/z proteins also slightly reduced the effect of the δ2 agonist [D‐Ala2]deltorphin II. At δ1 receptors, DPDPE fully expressed its activation of GTPase. These results indicate that in the PAG, μ‐OR and δ‐OR couple with Gi2 transducer proteins. Notably, μ‐OR also regulates the pertussis toxin‐insensitive G‐protein Gx/z, an effect poorly exhibited by δ‐OR in this tissue.
The Whole Nucleotide Sequence and Chromosomal Localization of the Gene for Human Metabotropic Glutamate Receptor Subtype 6
Authors: Hashimoto Takao , Inazawa Johji , Okamoto Naoyuki , Tagawa Yoshiaki , Bessho Asumasa , Honda Yoshihito , Nakanishi Shigetada
Published: April 2006

Metabotropic glutamate receptor subtype 6 (mGluR6) is restrictedly expressed in the retinal ON bipolar cells and ablation of mouse mGluR6 by gene targeting results in a loss of ON responses to light stimulus and impairs the detection of visual contrasts. We have isolated genomic clones containing the human mGluR6 gene and determined the whole nucleotide sequence of the mGluR6 gene. The transcription initiation site of the human mGluR6 gene has been identified using primer extension analysis in combination with reverse transcriptase‐mediated polymerase chain reaction analysis of human retinal RNA, while the termination of the mGluR6 mRNA has been assigned by the analysis of rapid amplification of 3′‐cDNA ends. The human mGluR6 gene consists of 16 742 base pairs with 10 exons separated by nine introns. The human mGluR6 is composed of 877 amino acid residues with a signal peptide of 24 amino acid residues and the mature protein shows a 94.6% homology with the rat counterpart. A CpG‐rich island is present at exon 1 and its preceding putative promoter region and this unusual sequence, like several tissue‐specific genes, may be important for a specific expression of the mGluR6 gene in the retinal bipolar cells. The human mGluR6 gene has been mapped to chromosome 5q35 by the analyses of blot hybridization of a DNA panel of human/mouse/hamster somatic cell hybrids and fluorescence in situ hybridization of human chromosomes. This study should provide the genetic basis for not only better understanding the molecular mechanism underlying a tissue‐specific expression of the mGluR6 gene but also exploring a potential defect in human mGluR6 in a certain inherited eye disease.
Figure‐Ground Segregation at Contours: a Neural Mechanism in the Visual Cortex of the Alert Monkey
Authors: Baumann R. , van der Zwan R. , Peterhans E.
Published: April 2006

An important task of vision is the segregation of figure and ground in situations of spatial occlusion. Psychophysical evidence suggests that the depth order at contours is defined early in visual processing. We have analysed this process in the visual cortex of the alert monkey. The animals were trained on a visual fixation task which reinforced foveal viewing. During periods of active visual fixation, we recorded the responses of single neurons in striate and prestriate cortex (areas V1, V2, and V3/V3A). The stimuli mimicked situations of spatial occlusion, usually a uniform light (or dark) rectangle overlaying a grating texture of opposite contrast. The direction of figure and ground at the borders of these rectangles was defined by the direction of the terminating grating lines (occlusion cues). Neuronal responses were analysed with respect to figure‐ground direction and contrast polarity at such contours. Striate neurons often failed to respond to such stimuli, or were selective for contrast polarity; others were non‐selective. Some neurons preferred a certain combination of figure‐ground direction and contrast polarity. These neurons were rare both in striate and prestriate cortex. The majority of neurons signalled figure‐ground direction independent of contrast polarity. These neurons were only found in prestriate cortex. We explain these responses in terms of a model which also explains neuronal signals of illusory contours. These results suggest that occlusion cues are used at an early level of processing to segregate figure and ground at contours.