bluuebunny/crossref_metadata_2025 huggingface dataset:
Olfactory Bulb Repetitive Stimulations Reveal Non‐homogeneous Distribution of the Inhibitory Processes in the Rat Piriform Cortex
Authors: Litaudon P. , Cattarelli M.
Published: April 2006

Optical signals were recorded in the in vivo rat piriform cortex in response to a burst of seven electrical stimulations (100 ms interval) delivered in the olfactory bulb. Based on the recorded responses, three types of signal could be identified according to the relative amplitude of their monosynaptic and disynaptic components. The disynaptic component had a larger (type 1) or an equal amplitude (type 2) compared with the monosynaptic one. Type 3 exhibited only the monosynaptic component. Type 1 represented 96% of the first response. The second response was characterized by an increase in type 3 signals (39%). The remaining type 1 signals were lower in amplitude when compared with the first response. The responses to the last five stimulations did not differ from one another but were different from the first two (type 1, 74%; type 2, 7.8%; type 3, 18.2% on average). The spatial distribution of these three types of signal was analysed by dividing the piriform cortex into several areas. These areas were not homogeneous in the percentage of each signal type: the percentage of type 3 signals was highest (˜30%) in the area near the lateral olfactory tract and <10% in the most posterodorsal area. Thus the level of inhibition remained high in some piriform areas whereas it decreased rapidly in others, suggesting that the inhibitory processes were not homogeneously distributed in the whole piriform cortex. Functional implications are discussed.
Responses of Neurons of the Nucleus of the Optic Tract and the Dorsal Terminal Nucleus of the Accessory Optic Tract in the Awake Monkey
Authors: Ilg Uwe J. , Hoffmann Klaus‐Peter
Published: April 2006

The nucleus of the optic tract (NOT) and the dorsal terminal nucleus of the accessory optic tract (DTN) are essential nuclei for the generation of slow‐phase eye movements during horizontal optokinetic nystagmus. We recorded from 101 neurons (all directionally selective) in four NOT/DTN of three trained and behaving rhesus monkeys. Neuronal activity increased when stimuli moved ipsiversively with respect to the recording site and decreased below spontaneous activity when stimuli moved contraversively. While the monkey fixated a small spot, some NOT/DTN neurons did not respond at all to the retinal image slip of a whole‐field random dot pattern; others showed a monotonic increase of activity to increasing velocities of that stimulus. The velocity range tested was up to 100°/s. During the execution of optokinetic nystagmus, 39 of 73 cells tested showed a velocity‐tuned response with an average optimum at 21°/s retinal image slip. Following saccades during optokinetic nystagmus (quick phases), the NOT/DTN neuronal activity briefly attained the level of spontaneous activity, as predicted from the velocity selectivity during optokinetic nystagmus. Immediately upon cessation of optokinetic stimulation in the preferred direction, NOT/DTN activity returned to the spontaneous level and did not reflect the ongoing optokinetic afternystagmus in darkness. Most NOT/DTN neurons displayed direction selectivity also during smooth pursuit. Twenty‐one of 50 cells tested (42%) always responded to the retinal slip of the target (target velocity cells), 16 cells (32%) responded to the retinal slip of the background (background velocity cells), and 13 cells (26%) did not respond at all during smooth pursuit. We conclude from our results that the NOT/DTN is an essential structure for the processing of the direction and speed of retinal image slip. This information is then used for the generation and maintenance of slow eye movements, preferentially during horizontal optokinetic nystagmus but also during pursuit eye movements.
Mechanisms for Synchronous Calcium Oscillations in Cultured Rat Cerebellar Neurons
Authors: Nuñez Lucia , Sanchez Ana , Fonteriz Rosalba I. , Garcia‐Sancho Javier
Published: April 2006

Removal of Mg2+ caused oscillations of the cytosolic Ca2+ concentration ([Ca2+]i) and the membrane potential in cultured cerebellar granule neurons. Oscillations of [Ca2+]i were synchronous in all the cells, and were restricted to the neurons (immunocytochemically identified) that responded to exogenous N‐methyl‐D‐aspartate (NMDA). Oscillations were blocked by Ca2+ removal, nickel, NMDA receptor antagonists, ω‐agatoxin IVA, tetrodotoxin, sodium removal and γ‐aminobutyric acid, but not by dihydropyridines, ω‐conotoxin M VIIA or by emptying the intracellular Ca2+ stores with thapsigargin or ionomycin. The upstroke of the [Ca2+]i oscillations coincided in time with an increase in manganese permeability of the plasma membrane. Propagation of the [Ca2+]i wave followed more than one pathway and the spatiotemporal pattern changed with time. Membrane potential oscillations consisted of transient slow depolarizations of ˜20 mV with faster phasic activity superimposed. We propose that the synchronous [Ca2+]i oscillations are the expression of irradiation of random excitation through a neuronal network requiring generation of action potentials and functional glutamatergic synapses. Oscillations of [Ca2+]i are due to cyclic Ca2+ entry through NMDA receptor channels activated by synaptic release of glutamate, which requires Ca2+ entry through P‐type Ca2+ channels activated by action potentials at the presynaptic terminal.
TGF‐β Rescues Target‐deprived Preganglionic Sympathetic Neurons in the Spinal Cord
Authors: Blottner Dieter , Wolf Nicole , Lachmund Astrid , Flanders Kathleen C. , Unsicker Klaus
Published: April 2006

Transforming growth factors β (TGF‐β), a family of pleiotropic cytokines, are widely distributed in the developing and adult nervous system. In order to further determine the neural functions of TGF‐β, we have localized the TGF‐β isoforms 1, 2 and 3 in the adult rat adrenal medulla and studied the neuroprotective capacity of one representative family member, TGF‐β2, for those spinal cord neurons which innervate adrenal chromaffin cells and which die after destruction of the adrenal medulla. Unilateral electrothermal destruction of the adrenal medulla led to the disappearance of 25% of sympathetic preganglionic neurons, which are located in the intermediolateral (IML) column of thoracic spinal cord segments 7–10 and can be selectively marked by NADPH‐diaphorase. The neurons which disappeared following adrenomedullectomy constitute the full set of neurons that innervate the adrenal medulla. Implantation of gelfoam soaked with 0.5 μg TGF‐β2 into the adrenal wound cavity rescued all spinal cord neurons in the IML ipsilaterally to the lesioned side. Cytochrome c was not effective. Injections of [125l]TGF‐β2 into the adrenal medulla did not result in retrograde transport and subsequent labelling of spinal cord neurons, suggesting that TGF‐β may exert its neuroprotective actions by indirect mechanisms. TGF‐β applied to cultured adrenocortical cells did not overtly increase the amount of mRNA for fibroblast growth factor‐2, an established trophic molecule for sympathetic preganglionic spinal cord neurons. The mechanisms by which TGF‐β exerts its neurotrophic effect are therefore unclear. Even so, our data provide the first evidence that TGF‐β may play an important role in vivo in the control of maintenance of a population of spinal cord neurons.
Cholinergic Modulation of the Action Potential in Rat Hippocampal Neurons
Authors: Figenschou Anne , Hu Guo‐Yuan , Storm Johan F.
Published: April 2006

The cholinergic input to the hippocampus from the medial septum is important for modulating hippocampal activity and functions, including theta rhythm and spatial learning. Neuromodulation by transmitters in central nervous system neurons usually affects cell excitability by modifying the membrane potential, discharge pattern and spike frequency. Here we describe another type of neuromodulation: changing the action potential waveform. During intracellular recordings from CA1 pyramidal cells in hippocampal slices from rats, the cholinergic agonist carbachol caused several reversible changes in the action potential: low doses (2 μM) caused an increase in spike duration; high doses (10–40 μM) or long‐lasting applications also reduced the spike amplitude and rate of rise, and raised the spike threshold. These effects are similar to those of metabotropic glutamate receptor agonists or phorbol esters, both of which activate protein kinase C. The effects were blocked by the muscarinic antagonist atropine, and were prevented by Ca2+‐free medium and by Ca2+‐channel blockers. However, the cholinergic spike modulation was not occluded or mimicked by blocking the Ca2+‐dependent K+ currents Ic or IAHP, suggesting that these K+ currents are not involved in the modulation.
Differential Localization of AMPA Glutamate Receptor Subunits in the Two Segments of the Globus Pallidus and the Substantia Nigra Pars Reticulata in the Squirrel Monkey
Authors: Paquet Maryse , Smith Yoland
Published: April 2006

The subthalamic nucleus has long been known as the main source of glutamatergic afferents to the pallidum and the substantia nigra in primates. Recent findings showed that the excitatory effects induced by the subthalamic nucleus in pallidal cells are mediated through the activation of non‐NMDA receptors in the rat. The objective of the present study was to analyse the distribution of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole‐propionate (AMPA) glutamate receptor subunits in the external pallidum (GPe), the internal pallidum (GPi) and the substantia nigra pars reticulata (SNr) in squirrel monkeys (Saimiri sciureus). This was achieved by means of immunohistochemistry using antibodies raised against the GluR1 and the GluR2/3 subunits of the AMPA receptor. Our results show that all neuronal perikarya in GPe and GPi display immunoreactivity for GluR2/3 subunits whereas GluR1 is confined exclusively to cells in the GPe. The proportion of GluR1‐immunoreactive neurons is not uniform throughout the rostrocaudal extent of GPe; in the rostral third all GPe cells display GluR1 immunoreactivity, whereas in the caudal third the proportion of GluR1‐positive cells decreases to 50%. The intensity of GluR1 immunostaining associated with GPe cells is lower than that associated with neighbouring large‐sized neurons in the nucleus basalis of Meynert. In contrast to GPi cells, the neurons in the SNr display immunoreactivity for both GluR1 and GluR2/3 subunits. In conclusion, our results provide the first evidence for a different distribution of the GluR1 subunit of the AMPA receptors in the two segments of the globus pallidus in monkeys. These findings imply that the control of the basal activity of GPe and GPi cells by the subthalamic nucleus is exerted via the activation of AMPA receptors composed of different subunits. These data reinforce the view that the two segments of the globus pallidus are different entities that possess their own functional characteristics in primates.
A Critique of a New Analysis Proposed for Functional Neuroimaging
Authors: Frackowiak R. S. J. , Zeki S. , Poline J.‐B. , Friston K. J.
Published: April 2006

Methods for analysing functional imaging data have evolved rapidly over the last ten years. Standardized techniques based on formal mathematical and statistical theory and rigorous empirical validation have been proposed to facilitate comparisons of biological results between laboratories. This paper examines an image analysis technique that appears to identify unexpectedly large numbers of activated brain areas for the data collected. It concludes that the method may not adequately control for false positives, rendering interpretation of the functional anatomy difficult.
Modulation of Cerebral Blood Flow in the Human Auditory Cortex During Speech: Role of Motor‐to‐sensory Discharges
Authors: Paus Tomáš , Perry David W. , Zatorre Robert J. , Worsley Keith J. , Evans Alan C.
Published: April 2006

To investigate mechanisms of audio‐vocal interactions in the human brain, we studied the effect of speech output on modulation of neuronal activity in the auditory cortex. The modulation was assessed indirectly by measuring changes in cerebral blood flow (CBF) during unvoiced speech (whispering). Using positron emission tomography (PET), CBF was measured in eight volunteers as they uttered syllables at each of seven rates (30, 50, 70, 90, 110, 130 or 150/min) during each of the seven 60–s PET scans. Low‐intensity white noise was used throughout scanning to mask auditory input contingent on the whispering. We found that, as a function of the increasing syllable rate, CBF increased in the left primary face area, the upper pons, the left planum temporale and the left posterior perisylvian cortex. The latter two regions contain secondary auditory cortex and previously have been implicated in the processing of speech sounds. We conclude that, in the absence of speech‐contingent auditory input, the modulation of CBF in the auditory cortex is mediated by motor‐to‐sensory discharges. As such, it extends our previous findings of oculomotor corollary discharges to the audio‐vocal domain.
Differential Temporal Evolution of Post‐Training Changes in Regional Brain Glucose Metabolism Induced by Repeated Spatial Discrimination Training in Mice: Visualization of the Memory Consolidation Process?
Authors: Bontempi B. , Jaffard R. , Destrade C.
Published: April 2006

The present study analyses the effects of the stage of learning on the spatial patterns and time‐course of [14C] glucose uptake in BALB/c mice brain regions produced by spatial discrimination training in an eight‐arm radial maze. Our particular approach was designed to follow, during the post‐training period, the level of functional activity in individual brain areas which may underlie the memory consolidation process. Regional mapping of relative [14C] glucose uptake was assessed at three post‐training time intervals (5 min, 1 and 3 h) after either the first (Day 1), the fourth (Day 4) or the last (Day 9) daily training session of the discrimination task and compared with sham‐conditioned animals placed in the same experimental environment. The results indicated that numerous subcortical and cortical brain regions exhibit metabolic alterations following the acquisition of the spatial discrimination task. These alterations, which were specifically related to learning since they did not appear in sham‐conditioned animals, were functions both of the post‐training interval studied and of the degree of mastery of the task. On Day 1, a progressive, time‐dependent and sequential increase in labelling was found from subcortical (5 min post‐training) to cortical regions (3 h post‐training). On Day 4, a peak of cortical metabolic activation was identified at 1 h post‐training. In contrast, on Day 9, maximum labelling was found 5 min post‐training in all subcortical and cortical regions followed by a general monotonic decline at 1 and 3 h post‐training. These findings, which show widely distributed changes of metabolic activity in the brain, are consistent with the hypothesis that learning involves distributed neural networks. The sequential activation from subcortical to cortical regions seems to indicate a general mechanism whose function would ultimately be to store cortical memory representations. The acquisition‐dependent shifts in the patterns of post‐training metabolic labelling observed as a function of task mastery may be taken to represent a visualization of the spatio‐temporal evolution of the networks of brain structures actively engaged in the memory consolidation process. In particular, the present data suggest that the duration of post‐acquisition memory processing is a function of the quantity of new information which has to be dealt with by the central nervous system.
Neuronal Nicotinic Receptor a6 Subunit mRNA is Selectively Concentrated in Catecholaminergic Nuclei of the Rat Brain
Authors: Le Novere Nicolas , Zoli Michele , Changeux Jean‐Pierre
Published: April 2006

Although the neuronal nicotinic receptor a6 subunit was cloned several years ago, its functional significance remains to be investigated. Here we describe an in situ hybridization study of the mRNA for this subunit in the adult rat central nervous system using oligonucleotide probes. Specific a6 mRNA labelling was restricted to a few nuclei throughout the brain; it was particularly high in several catecholaminergic nuclei [the locus coeruleus (A6), the ventral tegmental area (A10) and the substantia nigra (A9)] at levels significantly higher than those found for any other known nicotinic receptor subunit mRNA. Labelling for a6 mRNA was also detected at lower levels in the reticular thalamic nucleus, the supramammillary nucleus and the mesencephalic V nucleus. Some cells of the medial habenula (medioventral part) and of the interpeduncular nucleus (central and lateral parts) were also labelled. The distribution of a6 mRNA was compared with the distribution of the other known nicotinic acetylcholine receptor subunit mRNAs. In several nuclei, the expression of a6 was complementary to those of other a subunits. Moreover, some of the cell groups (such as the substantia nigra, the ventral tegmental area and the locus coeruleus) previously thought to contain mainly a3 mRNA in fact were found to contain high levels of α6 mRNA. Finally, we found extensive colocalization of α6 and p3, indicating the possible existence of nicotinic receptor hetero‐oligomers containing both subunits. The present results show that a6 is the major nicotinic acetylcholine receptor a subunit expressed in dopaminergic cell groups of the mesencephalon and noradrenergic cells of the locus coeruleus. This suggests the involvement of the a6 subunit in some of the major functions of central nicotinic circuits, including the modulation of locomotor behaviour and reward.
The Role of Spinal Neurokinin‐2 Receptors in the Processing of Nociceptive Information from the Joint and in the Generation and Maintenance of Inflammation‐evoked Hyperexcitability of Dorsal Horn Neurons in the Rat
Authors: Neugebauer V. , Rümenapp P. , Schaible H.‐G.
Published: April 2006

In spinal cord neurons in anesthetized rats, the role of neurokinin A and neurokinin‐2 receptors in the processing of nociceptive information from the knee joint was studied. The specific non‐peptide antagonist at the neurokinin‐2 receptor, SR48968, its inactive R‐enantiomer, SR48965, neurokinin A, substance P and (R, S)‐α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid (AMPA), were administered ionophoretically close to neurons with input from the knee joint. SR48968 reduced the effects of exogenous neurokinin A, but not those of exogenous substance P and AMPA, indicating selective blockade of neurokinin‐2 receptors. In most neurons with input from the normal knee joint, SR48968 reduced dose‐dependently the responses to noxious pressure applied to the knee, and in ˜50% of the neurons the responses to innocuous pressure. The administration of SR48968 during the induction of an experimental joint inflammation markedly attenuated the development of inflammation‐evoked hyperexcitability. In hyperexcitable neurons with input from the inflamed joint, SR48968 reduced the responses to noxious and innocuous pressure. The relative reduction of the responses was more pronounced than in neurons with input from the normal joint. None of the effects of SR48968 was mimicked by SR48965. These data show that neurokinin‐2 receptors are involved in the spinal processing of nociceptive information from the normal joint. Furthermore, neurokinin‐2 receptors must be coactivated at an early stage of inflammation, to allow the generation of hyperexcitability. Finally, neurokinin‐2 receptors are involved in the maintenance of hyperexcitability during inflammation. In summary, spinal neurokinin‐2 receptors are important in the generation of pain in the normal and inflamed joint.
Neurotrophin‐4/5 Maintains the Cholinergic Phenotype of Axotomized Septal Neurons
Authors: Alderson Ralph F. , Wiegand Stanley J. , Anderson Keith D. , Cai Ning , Cho Jae‐Young , Lindsay Ronald M. , Altar C. Anthony
Published: April 2006

We examined the effect of intraseptal or intracerebroventricular (i.c.v.) infusions of NT‐4/5 or intraseptal infusions of NGF on the level of immunohistochemical staining of choline acetyltransferase (ChAT) and the low‐affinity nerve growth factor receptor (LNGFR) in the rat medial septum following unilateral transection of the fimbria. The extent of cell loss in the septum ipsilateral to the lesion, determined by cell counts of ChAT‐immunopositive neurons and expressed as a ratio comparing the lesioned to the intact sides, was 0.28 in animals that received an infusion of phosphate‐buffered saline (PBS). The ratios were 0.97 and 1.07 in animals that received an infusion of NT‐4/5 into the ipsilateral ventricle and septum respectively. Septal infusions of NGF produced a ratio of ChAT‐immunopositive cells of 1.03. The ratios of LNGFR‐immunopositive neurons increased from 0.50 in PBS‐infused animals to 0.79 and 0.83 in animals infused with NT‐4/5 via the i.c.v. and septal routes respectively, and to 0.89 with NGF via the septal route. Transection of the fimbria also reduced the expression of TrkA in the ipsilateral medial septum and vertical limb of the diagonal band of Broca in PBS‐infused animals. The loss of TrkA was ameliorated by either i.c.v. infusion of NT‐4/5 or septal infusion of NT‐4/5 or NGF. As determined by immunohistochemical staining, NT‐4/5 infused into the lateral ventricle was detected in the periventricular portions of the forebrain ipsilateral to the infusion, while NT‐4/5 or NGF infused intraseptally was detected in much of the septum, bilaterally. Furthermore, exogenous NT‐4/5 or NGF was detected in numerous neuronal perikarya in the medial septal and diagonal band nuclei. These data demonstrate that, as with NGF, i.c.v. as well as septal infusions of NT‐4/5 can maintain the phenotype of basal forebrain cholinergic neurons following axotomy.
Leukaemia Inhibitory Factor or Related Factors Promote the Differentiation of Neuronal and Astrocytic Precursors within the Developing Murine Spinal Cord
Authors: Richards Linda J. , Kilpatrick Trevor J. , Dutton Renee , Tan Seong‐Seng , Gearing David P. , Bartlett Perry F. , Murphy Mark
Published: April 2006

Previously we have shown that leukaemia inhibitory factor (LIF) potentiates the development of murine spinal cord neurons in vitro, suggesting that it, or related factors, may play an important regulatory role in neuronal development. We have further investigated this role and show here that the generation of neurons in cultures of embryonic day 10 spinal cord cells is inhibited by antibodies to the β subunit of the LIF receptor. Since there are more undifferentiated precursors in antibody‐treated cultures than in control and LIF‐treated cultures, it is concluded that the primary action of LIF, or related molecules, is to promote neuronal differentiation, not precursor survival. In addition, the failure of LIF to support neuronal survival in the period immediately following differentiation suggests that the increased numbers of neurons generated with LIF are not attributable to its neurotrophic action. By selecting neuronal precursors on the basis of their inability to express class I major histocompatibility complex molecules, it was shown that LIF acted directly upon these cells and not via an intermediary cell. LIF also appears to be involved in regulating the differentiation of astrocytes, since it increases the number of glial fibrillary protein (GFAP)‐positive cells present in the cultures and since the spontaneous production of GFAP‐positive cells is blocked by antibodies to the LIF β receptor. These findings suggest that LIF or related factors promote the differentiation of neural precursors in the spinal cord, but that they are not involved in preferentially promoting precursors down a specific differentiation pathway.
Effects of Repeated Sensory Stimulation (Electro‐acupuncture) and Physical Exercise (Running) on Open‐field Behaviour and Concentrations of Neuropeptides in the Hippocampus in WKY and SHR rats
Authors: Bucinskaite Violeta , Theodorsson Elvar , Crumpton Kevin , Stenfors Carina , Ekblom Anders , Lundeberg Thomas
Published: April 2006

The effects of repeated sensory stimulation (electro‐acupuncture) and physical exercise (running) on open‐field behaviour and on hippocampal concentrations of neuropeptide Y, neurokinin A, substance P, galanin and vasoactive intestinal peptide (VIP)‐like immunoreactivities were studied in WKY (Wistar‐Kyoto) and SHR (spontaneously hypertensive) rats. Significantly higher concentrations of substance P‐like immunoreactivity, neurokinin A‐like immunoreactivity and neuropeptide Y‐like immunoreactivity were found in the hippocampus immediately after 3 weeks of treatment (electro‐acupuncture and running), but not 1 week after the last (tenth) intervention. No changes in galanin‐like immunoreactivity and VIP‐like immunoreactivity were found. The changes in neuropeptide concentrations were similar in the two rat strains. Open‐field behaviour was significantly reduced during the treatment period in both strains. There were significant negative correlations between behaviour and neuropeptide concentrations in SHR rats, suggesting interdependency with sympathetic activity. It is proposed that the effects of electro‐acupuncture and physical exercise in rats are related to increases in neuropeptide Y, neurokinin A and substance P in the hippocampus.
Acquisition of Conditioned Inhibition in Rats is Impaired by Ablation of Serotoninergic Pathways
Authors: Lister Sarah , Pearce John M. , Butcher Steven P. , Collard Keith J. , Foster George A.
Published: April 2006

The effects of chronically ablating the serotoninergic inputs to various regions of the rat brain on the ability to solve a feature‐negative discrimination was measured. After intracerebroventricular administration of the specific neurotoxin 5, 7‐dihydroxytryptamine, the rats exhibited an impaired capacity to solve such a discrimination, irrespective of whether auditory or visual stimuli were used. Further behavioural analysis revealed that this effect was not due to a reduced capacity to form excitatory associations, since both groups responded equally to reinforced stimuli. By contrast, the lesion more likely resulted in a failure to endow the non‐reinforced stimuli with inhibitory properties. This suggestion was supported by the observation that, in a retardation test, the conditioned inhibitor aroused less inhibition in the lesioned group than in vehicle‐injected controls. Furthermore, the conditioned inhibitor failed to pass a summation test in lesioned animals, again indicating that their hampered ability to master the discrimination was the result of an impairment in the formation of inhibitory associations. It is concluded that destruction of central 5‐hydroxytryptamine‐containing pathways impairs the functioning of brain areas underlying inhibitory associative learning.
Comparative Patch‐clamp Studies with Freshly Dissociated Rat Hippocampal and Striatal Neurons on the NMDA Receptor Antagonistic Effects of Amantadine and Memantine
Authors: Parsons C. G. , Panchenko V. A. , Pinchenko V. O. , Tsyndrenko A. Y. , Krishtal O. A.
Published: April 2006

Patch‐ and concentration‐clamp techniques were used to compare the effects of the uncompetitive N‐methyl‐D‐aspartate (NMDA) receptor antagonists (+)‐MK‐801 (dizocilpine, (+)‐5‐methyl‐10, 11‐dihydro‐5H‐dibenzo‐cyclohepten‐5, 10‐imine maleate), ketamine, memantine (1‐amino‐3, 5‐dimethyladamantane) and amantadine (1‐amino‐adamantane) on agonist‐induced inward currents in freshly dissociated rat hippocampal and striatal neurons. In hippocampal neurons, ketamine (5 μM), memantine (10 μM) and amantadine (100 μM) selectively antagonized inward current responses to NMDA (500 μM plus glycine 5 μM) in a voltage‐dependent manner without affecting responses to (s)‐α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazoleproprionic acid (100 μM) or γ‐aminobutyric acid (10 μM). The NMDA receptor antagonistic effect of all four agents was typical of open channel blockade. The kinetics of blockade/unblockade was inversely related to antagonist affinity. In hippocampal neurons amantadine was the least potent NMDA receptor antagonist (IC50 18.6 ± 0.9 μM) and showed the fastest blocking kinetics, whereas (+)‐MK‐801 was the most potent (IC50 0.12 ± 0.01 μM) and showed the slowest blocking kinetics. Memantine (IC50 1.04 ± 0.26 μM) and ketamine (IC50 0.43 ± 0.10 μM) were almost equipotent and had similar, intermediate blocking kinetics. In striatal neurons recorded under identical conditions (+)‐MK‐801, ketamine and memantine were 3‐ to 4‐fold less potent whereas amantadine was somewhat more potent than on hippocampal neurons. This could offer an explanation for the better clinical profile of amantadine in Parkinson's disease, as therapeutically relevant concentrations of amantadine are likely to be more active in the striatum whereas memantine is likely to be more active in other structures.
Triiodothyronine Exerts a Trophic Action on Rat Sensory Neuron Survival and Neurite Outgrowth through Different Pathways
Authors: Walter I. Barakat
Published: April 2006

Apart from several growth factors which play a crucial role in the survival and development of the central and peripheral nervous systems, thyroid hormones can affect different processes involved in the differentiation and maturation of neurons. The present study was initiated to determine whether triiodothyronine (T3) affects the survival and neurite outgrowth of primary sensory neurons in vitro. Dorsal root ganglia (DRG) from 19‐day‐old embryos or newborn rats were plated in explant or dissociated cell cultures. The effect of T3 on neuron survival was tested, either in mixed DRG cell cultures, where neurons grow with non‐neuronal cells, or in neuron‐enriched cultures where non‐neuronal cells were eliminated at the outset. T3, in physiological concentrations, promoted the growth of neurons in mixed DRG cell cultures as well as in neuron‐enriched cultures without added nerve growth factor (NGF). Since neuron survival in neuron‐enriched cultures cannot be promoted by endogenous neurotrophic factors synthesized by non‐neuronal cells, the increased number of surviving neurons was due to a direct trophic action of T3. Another trophic effect was revealed in this study: T3 sustained the neurite outgrowth of sensory neurons in DRG explants. The stimulatory effect of T3 on nerve fibre outgrowth was considerably reduced when non‐neuronal cell proliferation was inhibited by the antimitotic agent cytosine arabinoside, and was completely suppressed when the great majority of non‐neuronal cells were eliminated in neuron‐enriched cultures. These results indicate that the stimulatory effect of T3 on neurite outgrowth is mediated through non‐neuronal cells. It is conceivable that T3 up‐regulates Schwann cell expression of a neurotrophic factor, which in turn stimulates axon growth of sensory neurons. Together, these results demonstrate that T3 promotes both survival and neurite outgrowth of primary sensory neurons in DRG cell cultures. The trophic actions of T3 on neuron survival and neurite outgrowth operate under two different pathways.
Calcium Channels in Neuroblastoma Cell Growth Cones
Authors: Zimprich Fritz , Bolsover Stephen R.
Published: April 2006

The concentration of free calcium ions in the cytosol has been shown to influence many components of growth cone behaviour, including the extension of filopodia and veils, the addition of new membrane to the plasmalemma, the retraction and disappearance of filopodia, and gross collapse and retraction of the growth cone. A spatially localized modulation of these processes by very local calcium changes has been proposed to underlie the steering of growth cones by gradients of neurotransmitters, voltage and cell adhesion molecules. Such local control can be studied in mouse neuroblastoma cells, where depolarization causes calcium to rise in a limited number of spatially restricted hotspots, triggering a localized advance. We have studied the simple, club‐shaped growth cones that are characteristically found on advancing neurites. Depolarization caused calcium to increase most at the distal, leading tip. Agents that disrupt calcium‐induced calcium release do not affect growth cone calcium dynamics, ruling out a local release of calcium at the tip as a cause of the gradient. Using cell‐attached patch recording, we find that L‐type calcium channels are present at a higher density at the distal tip than in the proximal growth cone. Our results show that the calcium gradients seen in depolarized growth cones are a direct consequence of a gradient of calcium channel density.
Decreased Expression of TrkB and TrkC mRNAs in Spinal Motoneurons of Aged Rats
Authors: Johnson Hans , Hökfelt Tomas , Ulfhake Brun
Published: April 2006

Several studies have indicated that a decrease in availability and/or responsiveness to neurotrophin(s) may be of importance in ageing and disease‐related neurodegeneration. Using in situ hybridization we have studied the mRNA expression of the full‐length neurotrophin receptors TrkB and TrkC in spinal cord motoneurons of aged rats (30 months old) with symptoms of hindlimb incapacity and in young adult rats (2–3 months old). The labelling intensity for TrkB of the individual cell profile was decreased by 25% (P < 0.001) in both the cervical and lumbar motor nuclei of aged rats. In thoracic motoneurons of aged and young adult rats the difference in expression of TrkB mRNA was smaller (down by 15%; P < 0.05). The labelling for TrkC mRNA was much weaker than that for TrkB in both aged and young adult rats, but TrkC mRNA expression also seemed to decrease. Comparison of the different motor nuclei along the spinal cord axis revealed that the motoneurons of the L6/S1 nuclei showed the strongest hybridization signal for the two Trk receptors in both aged and young adult rats. The possibility that a decrease in TrkB mRNA may contribute to age‐related motor disturbances is discussed.
Biochemical and Functional Characterization of Basal Lamina‐bound Agrin in the Chick Central Nervous System
Authors: Kröger Stephan , Mann Sabine
Published: April 2006

Agrin is a high‐molecular weight extracellular matrix molecule, initially purified from the electric organ of the marine ray Torpedo californica, which induces on the surface of cultured myotubes the formation of postsynaptic specializations similar to those found at the neuromuscular junction. Agrin immunoreactivity is highly concentrated in the basal lamina of the synaptic cleft but is also found in a number of other tissues where its function is not known. We characterized agrin associated with two basal laminae from the central nervous system, the inner limiting membrane of the retina and the mesencephalic external limiting membrane. A major broad band with an apparent molecular weight of <300 kDa was identified in immunoblots of isolated basal laminae from retina, mesencephalon, kidney and muscle, showing that basal lamina‐bound agrin from the central nervous system and that from non‐neural tissues have similar molecular sizes. Agrin is stably but not covalently bound to the inner limiting membrane and could be completely removed only with strong detergents. Agrin could be partially extracted with buffers that are also able to partially release acetylcholine receptor aggregation activity from the neuromuscular junction or from the electric organ. Despite these immunological and biochemical similarities, agrin from both central nervous system‐derived basal laminae was not able to induce acetylcholine receptor aggregation on cultured myotubes. This shows that functionally different agrin isoforms are associated with basal laminae in the central nervous system compared to the neuromuscular junction or the electric organ.
Ciliary Neurotrophic Factor Constitutively Expressed in the Nervous System of Transgenic Mice Protects Embryonic Dorsal Root Ganglion Neurons from Apoptosis
Authors: Tolosano Emanuela , Cutufia Miguel Angel , Hirsch Emilio , Stefanuto Guglielmo , Voyron Samuele , Fasolo Aldo , Silengo Lorenzo , Altruda Fiorella
Published: April 2006

Ciliary neurotrophic factor (CNTF) is a potent survival factor for several neuronal populations. It is expressed postnatally by Schwann cells in the peripheral nervous system and by some glial and neuronal cells in the central nervous system. We used the promoter of the neurofilament light chain gene to produce transgenic mice that express CNTF in neurons from the beginning of neuronal differentiation. These transgenic animals may represent a suitable model to identify neuronal cell types responsive to CNTF in vivo and to study the mechanism of action of this neurotrophic factor. We show that dorsal root ganglion neurons of transgenic mice expressing CNTF in neurons are protected from apoptosis during embryonic development: 40% of these cells undergo apoptosis between embryonic day 12.5 and postnatal day 5 in transgenic mice whereas 60% do so in control animals. However, protection from apoptosis does not result in an increase in the total number of neurons at the end of development. We discuss our results with regard to CNTF potentialities in vivo and the significance of programmed cell death during development.
A Quantitative Study of Electroencephalography, Eye Movements and Neck Electromyography Characterizing the Sleep—Wake Cycle of the Guinea‐pig
Authors: Escudero M. , Vidal P. P.
Published: April 2006

The qualitative and quantitative characteristics of cerebral cortex electrical activity, ocular motility and muscular activity were studied in six head‐restrained guinea‐pigs during wakefulness, slow‐wave and paradoxical sleep. Animals were chronically implanted with bipolar electrodes in the obliquus capitis muscle for electromyographic recordings and epidurally through the parietal bones for electroencephalographic (EEG) recordings. Eye movements were recorded using the scleral search‐coil technique. After postoperative recovery and a short period of habituation to immobilization, head‐restrained animals exhibited a polyphasic sleep–wake cycle similar to what has already been described in the unrestrained guinea‐pig. Paradoxical sleep periods of mean duration 110 ± 42 s occurred at a mean interval of 32.2 ± 7.2 min. Amplitude and frequency components of EEG activity were different for each state of vigilance. EEG amplitude was highest and frequency range lowest—with two well‐defined peaks at 4 and 10 Hz—during slow‐wave sleep. During paradoxical sleep, frequencies were higher and amplitudes lower than during wakefulness. Three types of eye movement intermingled with periods of ocular fixation were recorded: saccadic movements during wakefulness and paradoxical sleep, slow drifts during slow‐wave sleep and paradoxical sleep, and a new type of eye movement—bursts of high‐velocity eye oscillations during paradoxical sleep. Saccadic eye movements during paradoxical sleep were more frequent and showed higher velocities and amplitudes than during wakefulness. During paradoxical sleep the episodes of eye oscillation (8–14 Hz) occurred quite regularly every 1.6 s and had a mean duration of 1.4 s. During wakefulness, the obliquus muscle activity displayed a burst‐tonic pattern. Bursting components were closely related to saccadic eye movements directed to the side of the recorded muscle. The muscle activity was predominantly tonic during slow‐wave sleep and was completely absent during paradoxical sleep except for small bursts or twitches. These twitches were tightly synchronized with the occurrence of the rapid eye movements oriented towards the side of the recorded obliquus muscle, as during wakefulness. These results strongly suggest that paradoxical sleep is characterized by the oscillatory discharge of at least two neuronal populations: the brainstem saccadic generators and the tecto‐reticular spinal network which underlies gaze‐orienting behaviour during wakefulness. The occurrence of rhythmic discharges at ˜11 Hz may explain the spinal motoneurons’ inhibition during paradoxical sleep in order to avoid anarchic motor behaviour. Whether these neuronal oscillations are simply an epiphenomenon or have functional implications remains to be determined.
Synaptically Activated Low‐threshold Muscarinic Inward Current Sustains Tonic Firing in Rabbit Prevertebral Sympathetic Neurons
Authors: Niel J.‐P. , Delmas P. , Gola M.
Published: April 2006

Whole‐cell patch‐clamp experiments were performed on non‐dissociated rabbit coeliac sympathetic neurons in the presence of nicotinic blockers. Coeliac neurons were classified as either silent or spontaneously active (pacemaker) cells. Under voltage‐clamp conditions, pacemaker cells exhibited a steady‐state N‐shaped current‐voltage relationship due to the presence of a persistent voltage‐dependent inward current in the potential range of ‐100 to —20 mV. This inward current sustained the regular firing activity of pacemaker cells and was absent from quiescent neurons. It disappeared in the presence of tetrodotoxin and in low Ca2+‐high Mg2+ external solutions and was enhanced by eserine. Splanchnic nerve stimulation induced slow regenerative depolarizations and firing discharges in silent neurons by activating a low‐threshold voltage‐sensitive inward current. The synaptic current had a U‐shaped voltage‐dependence from —96 to —20 mV and exhibited the dynamic properties of the muscarinic voltage‐dependent inward current lNa, M. It gave the current‐voltage relationship an N shape similar to that observed in spontaneously active cells. The muscarinic antagonists atropine and pirenzepine abolished the inward current present in pacemaker cells and that induced by nerve stimulation in silent neurons. These data provide evidence that both spontaneous firing activity and nerve‐evoked depolarizing responses in coeliac neurons are sustained by the activation of the muscarinic Na, M current. The tonic activation of lNa, M in spontaneously firing cells results from a sustained Ca2+‐dependent tetrodotoxin‐sensitive release of acetylcholine. This study provides evidence that the role of the muscarinic receptors is not purely a neuromodulatory one, but that these receptors are directly involved in ganglionic neurotransmission.
A Decrease in [Ca2+]c but not in cAMP Mediates L‐AP4 Inhibition of Glutamate Release: PKC‐mediated Suppression of this Inhibitory Pathway
Authors: Herrero Inmaculada , Vázquez Elena , Miras‐Portugal M. Teresa , Sánchez‐Prieto José
Published: April 2006

We investigated the mechanism of the inhibition of glutamate release by L‐2‐amino‐4‐phosphonobutyrate (L‐AP4) in cerebrocortical nerve terminals from young rats (3 weeks of age). The Ca2+‐dependent release of glutamate was reduced by L‐AP4 in a concentration‐dependent manner. This inhibitory effect was prevented by pertussis toxin, insensitive to staurosporine and associated with a reduction both in the depolarization‐evoked increase in the cytoplasmic free Ca2+ concentration ([Ca2+]c) and in forskolin‐stimulated cAMP formation. However, the reduction in [Ca2+]c but not in cAMP seemed to be responsible for the decrease in release, since inhibition by L‐AP4 can also be observed in the absence of detectable changes in CAMP. The inhibitory modulation by L‐AP4 was suppressed by the activation of protein kinase C with phorbol esters. The nerve terminals from young rats also exhibited a facilitatory pathway of glutamate release which was mediated by protein kinase C. Interestingly, stimulation of this pathway with the glutamate agonist (1 S,3R)‐1‐aminocyclopentane‐1,3‐dicarboxylate in the presence of arachidonic acid also abolished the inhibitory action of L‐AP4. The dominance of the facilitatory pathway in its interaction with the L‐AP4‐mediated inhibitory control may provide some clues to understand the presynaptic changes during synaptic plasticity.
Ex Vivo Gene Transfer of Brain‐derived Neurotrophic Factor to the Intact Rat Forebrain: Neurotrophic Effects on Cholinergic Neurons
Authors: Martinez‐Serrano Alberto , Hantzopoulos Petros A. , Björklund Anders
Published: April 2006

Neurotrophic effects of human brain‐derived neurotrophic factor (hBDNF) on forebrain cholinergic neurons were addressed after ex vivo gene transfer to the intact adult rat brain, using a conditionally immortalized neural progenitor cell line (CINP) engineered to secrete the neurotrophin (2.8 ng/h/106 cells). This cell line was derived by repeated retroviral infection of the parental neural precursor line HiB5 followed by subcloning. The cells survived well in the host brain for long periods of time (up to 4 weeks), and induced a hypertrophic response of cholinergic neurons (positive for acetylcholinesterase, choline acetyltransferase or low‐affinity nerve growth factor receptor) in the nucleus basalis magnocellularis and striatum. We conclude that these cholinergic cell groups are responsive to a low‐level supply (nanograms per day) of BDNF in vivo when the neurotrophin is administered locally in the vicinity of the cell bodies.
Selective Excitatory Amino Acid Uptake in Glutamatergic Nerve Terminals and in Glia in the Rat Striatum: Quantitative Electron Microscopic Immunocytochemistry of Exogenous D‐Aspartate and Endogenous Glutamate and GABA
Authors: Gundersen Vidar , Ottersen Ole Petter , Storm‐Mathisen Jon
Published: April 2006

To characterize glutamate/aspartate uptake activity in various cellular and subcellular elements in the striatum, rat striatal slices were exposed to 10 and 50 μM exogenous D‐aspartate. After fixation with glutaraldehyde/ formaldehyde the distribution of D‐aspartate was analysed by postembedding immunocytochemistry and the ultrastructural distribution was compared with the distributions of endogenous glutamate and GABA. Light microscopically, D‐aspartate‐like immunoreactivity was localized in conspicuous dots along very weakly labelled dendritic profiles and neuron cell bodies. At the electron microscope level gold particles signalling D‐aspartate occurred at highest density in nerve terminals making asymmetrical contacts with postsynaptic spines (i.e. resembling synapses of cortical afferents). Astrocytic processes also contained gold particles, but at a lower density than nerve endings. In contrast, dendritic spines were only weakly D‐aspartate–positive. The difference in labelling at 10 and 50 μM D‐aspartate was consistent with‘high‐affinity’uptake. Neighbouring sections processed with other antibodies showed that the D‐aspartate labelling occurred in nerve terminals strongly immunoreactive for glutamate, rather than in terminals very weakly glutamate‐immunopositive or in nerve endings immunoreactive for GABA. Glutamate labelling of perfusion‐fixed striatum confirmed that terminals forming asymmetrical synaptic contacts with spines were enriched with gold particles, suggesting that these terminals use glutamate as a transmitter. This study demonstrates that high‐affinity uptake sites for excitatory amino acids in the striatum are most strongly expressed on presumed glutamatergic nerve terminals and on astrocytes.