bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential Distribution of Syntaxin Isoforms 1A and 1B in the Rat Central Nervous System
Authors: Ruiz‐Montasell B. , Aguado F. , Majó G. , Chapman E. R. , Canals J. M. , Marsal J. , Blasi J.
Published: April 2006

Syntaxin 1 binds to several proteins of the synaptic terminal and is a central component in the pathway of protein–protein interactions that underlies docking and fusion of synaptic vesicles. Molecular studies revealed the occurrence of two isoforms, syntaxin 1A and syntaxin 1B, which coexpress in neural tissues. However, they display differential expression patterns in endocrine cell types. We generated isoform‐specific antibodies that were used in Western blotting and immunocytochemical studies. First, we confirmed the sole presence of syntaxin 1A in endocrine pituitary cells. Second, we found distinctive immunolabelling patterns of each isoform in the rat olfactory system, hippocampus, striatum, thalamus and spinal cord. In addition, the principal white matter commissures displayed distinct immunoreactivity for each isoform. This report shows, for the first time, major differences between the distributions of syntaxin 1A and syntaxin 1B isoforms in the rat central nervous system.
Identification of a Determinant of Acetylcholine Receptor Gating Kinetics in the Extracellular Portion of the γ Subunit
Authors: Fucile Sergio , Mileo Anna M. , Grassi Francesca , Salvatore Anna M. , Alemà Stefano , Eusebi Fabrizio
Published: April 2006

A large body of structure‐function studies has identified many of the functional motifs underlying ion permeation through acetylcholine receptor (AChR) channels. The structural basis of channel gating kinetics is, however, incompletely understood. We have previously identified a novel shorter form of the AChR γ subunit, which lacks the 52 amino acids within the extracellular amino‐terminal half, encoded by exon 5. To define the contribution of the missing domain to AChR channel function, we have transiently coexpressed the mouse short γ subunit (γs) with α, β and δ subunits in human cells and recorded single‐channel currents from the resulting AChRs. Our findings show that replacement of the γ by the γs subunit confers a long duration characteristic to AChR channel openings without altering unitary conductance sizes or receptor affinity for the transmitter. We also show that βγδSδ AChR channels exhibit a peculiar voltage sensitivity characterized by a short opening duration when the membrane potential is hyperpolarized. Together, these findings indicate that the domain in the extracellular amino‐terminal half of the γ subunit that encompasses a conserved disulphide loop and a critical tyrosine residue implicated in receptor oligomerization and insertion at the cell surface is a functional motif that also modulates AChR channel gating kinetics. The results also provide a molecular explanation of the functional diversity exhibited by skeletal muscle AChRs during development.
Neuronal Control of MHC Class II Inducibility in Rat Astrocytes and Microglia
Authors: Neumann H. , Boucraut J. , Hahnel C. , Misgeld T. , Wekerle H.
Published: April 2006

We analysed the inducibility of major histocompatibility complex (MHC) class II molecules of astrocytes and microglia in organotypic hippocampus slice cultures of Lewis rats. Treatment with interferon‐γ (IFN‐γ) resulted in the induction of MHC class II molecules on microglia preferentially in the injured marginal zones of the slice culture, but only sporadically in areas containing intact neuronal architecture. In astrocytes, inducibility of MHC class II molecules was even more strictly controlled. IFN‐γ treatment induced MHC class II expression only in the slice culture zones containing degenerated neurons, and not in the presence of functional neurons. After suppression of spontaneous neuronal activity of the slice culture by the sodium channel blocker tetrodotoxin, MHC class II molecules on astrocytes could be induced by IFN‐γ in areas with intact neuronal architecture, and microglia cells exhibited a higher level of expression. These data suggest that loss of neurons could result in MHC class II inducibility of glial cells, and thus in increased immune reactivity of nervous tissue.
Phenylglycines can Evoke Quisqualate‐primed Depolarizations in Rat Cingulate Cortex: An Effect Associated with [3H]DL‐AP4 Uptake
Authors: Sheardown Malcolm J. , Thomsen Christian
Published: April 2006

Depolarization could be evoked in slices of rat cingulate cortex by the normally non‐excitatory compound L‐2‐amino‐4‐phosphonobutyrate (l‐AP4) if the slices had been sensitized by exposure to quisqualate. The magnitude of the response to l‐AP4 was dependent on the concentrations of both l‐AP4 and quisqualate and was inhibited by α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionate receptor antagonism. A series of phenylglycine analogues were capable of evoking similar dose‐dependent depolarizations in the rat cingulate cortex following quisqualate sensitization, the most potent being (S)‐4‐carboxy‐3‐hydroxyphenylglycine. If the superfusate collected during application of (S)‐4‐carboxy‐3‐hydroxyphenylglycine to a quisqualate‐sensitized slice was administered to a slice not previously exposed to quisqualate, a small depolarization was obtained. All the compounds shown to be capable of evoking the quisqualate‐sensitized response showed affinity for the l‐AP4 uptake site whilst having no affinity at ionotropic glutamate receptors and different profiles of activity at metabotropic glutamate receptors. None of the compounds was active at the metabotropic glutamate 4a receptor. There was a statistically significant correlation between a compound's effectiveness in inhibiting [3H]DL‐AP4 uptake into rat cortical synaptosomes and its potency in evoking quisqualate‐sensitized depolarization. It is concluded that this response may be the result of hetero‐exchange between L‐AP4 ligands and quisqualate.
NMDA and Kainate‐evoked Release of Nitric Oxide and Classical Transmitters in the Rat Striatum: In Vivo Evidence that Nitric Oxide May Play a Neuroprotective Role
Authors: Kendrick Keith M. , Guevara‐Guzman Rosalinda , de la Riva Carlos , Christensen Jakob , Østergaard K. , Emson Piers C.
Published: April 2006

The effects of N‐methy‐d‐aspartate (NMDA), kainate, S‐α‐amino‐3‐hydroxyd‐5‐methyl‐4‐isoxazole propionate (AMPA) and KCI on striatal nitric oxide (NO), acetylcholine (ACh), dopamine (DA), serotonin (5‐HT), aspartate (ASP), glutamate (GLU) and γ‐aminobutyric acid (GABA) release were measured in anaesthetized rats in vivo by microdialysis and in vitro in organotypic slice cultures. Local NMDA (1–100 μM) infusion by retrodialysis dose‐dependently increased levels of classical transmitters, NO2‐, NO3‐, ctrulline and arginine at similar thresholds (10 γM) Similar patterns of NMDA‐evoked (50 μM) release were seen in striatal cultures. NMDA‐evoked changes were all calcium‐dependent and blocked by NMDA (APV or MK‐801) but not AMPN/kainate (DNQX) receptor antagonists, excepting DA which could be prevented by both. In vivo, kainate increased NO2‐, NO3‐, CIT and ARG levels at 50 and 100 μM but was less potent than NMDA. Kainate also evoked significant Ach1 DA and GLU release dose‐dependently starting at 1–10 μM whereas 5‐HT, ASP and GABA required 50 or 100 μM doses. Kainate effects were inhibited by DNQX, but not by APV, and were calcium‐dependent. AMPA failed to alter NO2‐, NO3‐, CIT or ARG levels at 50 or 100 μM doses but dose‐dependently increased ACh and DA. Similar results were seen with kainate (50 μM) and AMPA (50 μM) in vitro KCI evoked NO2‐, NO3‐, CIT and ARG release as well as that of the classical transmitters in vivo and in vitro. In vivo administration of the NO synthase inhibitor L‐nitroarginine (L‐NARG; 100 μM) significantly reduced NO2‐, NO3‐ and CIT levels and prevented NMDA, kainate or KCI‐evoked increases. It also potentiated ACh, ASP, GLU and GABA release and reduced that of DA in response to 50 μM NMDA whereas treatment with an NO‐donor (SNAP; 10 μM) significantly reduced evoked ACh, ASP and GLU release. The NO synthase inhibitor L‐NARG potentiated kainate‐evoked ACh release and reduced that of DA, although less potently than NMDA, but it had no effect on KCI‐evoked transmitter release. Overall, these results show that both NMDA and kainate increase striatal NO release at similar dose‐thresholds as for classical transmitter release suggesting that NO is dynamically released under physiological and not just pathological conditions. Reduction of striatal NO levels also potentiates calcium‐dependent transmitter release in response to NMDA and, to a lesser extent, kainate, whereas increasing them reduces it. This is consistent with a role for NO as a neuroprotective agent in this region acting to desensitize NMDA receptors.
Protein Kinases in the Rat Nucleus Accumbens are Involved in the Aversive Component of Opiate Withdrawal
Authors: Valverde Olga , Tzavara Eleni , Hanoune Jacques , Roques Bernard P. , Maldonado Rafael
Published: April 2006

The specific participation of protein kinases in the expression of the somatic signs of morphine withdrawal has been previously demonstrated, suggesting that changes in intracellular signalling systems are involved in opioid addiction. In the present study, the involvement of protein kinases in the aversive/dysphoric effects of morphine abstinence has been investigated in the nucleus accumbens, because of the critical role played by the mesolimbic system in the rewarding effects of opioids. Rats were chronically treated with morphine, twice a day for 5 days, with doses progressively increased from 5 to 30 mg/kg (i‐p.). In addition, microinjections into the nucleus accumbens of the serine‐threonine kinase inhibitors H7 or H8 (1 or 10 nmol per side) or saline once daily were also given, both in control and in morphine‐treated animals. After these chronic treatments, withdrawal syndrome was induced by naloxone administration (0.1 mg/kg, s. c.), and the motivational component of morphine abstinence was studied using the place aversion paradigm. When administered at the highest dose (10 nmol), H7 and H8 strongly reduced the place aversion induced by naloxone in morphine dependent animals. Protein kinase inhibitors did not induce significant behavioural responses in non‐dependent animals. Chronic morphine treatment induced a selective up‐regulation of adenylate cyclase activity in the amygdala, without affecting other brain regions. The morphine‐increased adenylate cyclase activity in amygdala was reversed by the chronic intra‐accumbens microinjection of H7 or H8. These results suggest that serine‐threonine kinases in the nucleus accumbens play an important role in the emotional/dysphoric properties which characterize opiate withdrawal.
The Cerebral Cortex and Parafascicular Thalamic Nucleus Facilitate In vivo Acetylcholine Release in the Rat Striatum through Distinct Glutamate Receptor Subtypes
Authors: Consolo Silvana , Baldi Gianni , Giorgi Susanna , Nannini Luca
Published: April 2006

Electrical stimulation (ten pulses of 0.5 ms, 10 V applied over 10 s at 10 Hz, 140 pA) delivered bilaterally to the prefrontal cortex or the parafascicular thalamic nucleus of freely moving rats facilitated acetylcholine release in dorsal striata, assessed by trans‐striatal microdialysis. The facilitatory effects were blocked by coperfusion with 5 μM tetrodotoxin, suggesting that the release was of neuronal origin. The response of the striatal cholinergic neurons to prefrontal cortical stimulation was short‐lived and required a longer period of stimulation (20 min) than the response to thalamic stimulation (4 min) to reach maximal effect. The α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid (AMPA)/kainate glutamatergic receptor antagonist 6,7‐dinitroquinoxaline‐2,3‐dione [DNQX; 12 nmol per side, intracerebroventricularly (i.c.v.)] and the AMPA antagonist 6‐nitro‐7‐sulphamoylbenzo(f)quinoxaline‐2,3‐dione (NBQX; 12 nmol per side, i.c.v. or 12.8 μM infused into the striatum), but not the NMDA‐type receptor antagonist MK‐801 (0.2 mg/kg, i.p.), abolished the facilitatory effect on striatal acetylcholine release evoked by stimulation of the prefrontal cortex. By contrast, DNQX or NBQX did not prevent the increase in striatal acetylcholine release evoked by parafascicular nucleus stimulation, but MK‐801, in accordance with previous results, did so. MK‐801 by itself lowered striatal acetylcholine output while DNQX and NBQX did not. The results provide in vivo evidence that the cerebral cortex facilitates cholinergic activity in the dorsal striatum apparently through the non‐tonic activation of AMPA‐type glutamatergic receptors while the parafascicular nucleus does this through tonic activation of NMDA receptors. Both glutamate receptor types are probably located in the striatum. The overall results suggest that the two pathways operate independently to regulate striatal cholinergic activity through distinct mechanisms.
Localization of the Serotonin Transporter in Rat Spinal Cord
Authors: Sur Cyrille , Betz Heinrich , Schloss Patrick
Published: April 2006

The spinal cord is richly innervated by serotoninergic fibres originating from the raphe nuclei. The localization of the terminating component of serotoninergic neurotransmission, the serotonin transporter SERT1, was found in both the dorsal and ventral horns, especially at the level of the cervical and lumbar segments. Within the thoracic region, we observed a heavily labelled bundle in the intermediolateral nucleus of lamina VII. A low density of stained fibres was encountered in the sacral spinal cord. In contrast to homogeneous staining of motor nuclei, a differential labelling of laminae was seen in the dorsal horn, with laminae I, III and IV exhibiting a higher density of immunopositive terminals than the medial part of lamina II. High magnification revealed a preferential accumulation of serotonin transporter staining within nerve endings and varicosities of thin fibres. Double immunofluorescence staining demonstrated a co‐localization of serotonin and its uptake system within these varicosities. These results show that the serotonin transporter is highly expressed in the rat spinal cord and that its distribution parallels the serotoninergic innervation. They also reinforce the view that varicosities are important neuronal structures, which modulate the function of dorsal and ventral horn neurons by releasing serotonin.
Hippocampal Lesions Cause Forgetting in a Spatial Response Task
Authors: Baylis Gordon C. , Moore Beth O.
Published: April 2006

Monkeys with lesions to the hippocampus and overlying cortex were impaired in making a spatially selective response on the basis of a spatial cue. Their impairment was even more severe on a task in which they were required to make spatial responses on the basis of cues which are not spatially distinct. A second experiment showed that once lesioned monkeys had been trained on a task with spatially distinct stimuli, they were initially able to perform accurately if the spatial distinctiveness of the cue was reduced. However, their performance declined to chance over four to six trials. These results suggest that lesions to the hippocampus and overlying cortex may cause impairments in memory for the arrangement of visual scenes, including the spatial location of responses.
Synaptic Connections Between Spiny Neurons of the Direct and Indirect Pathways in the Neostriatum of the Rat: Evidence from Dopamine Receptor and Neuropeptide Immunostaining
Authors: Yung K. K. L. , Smith A. D. , Levey A. I. , Bolam J. P.
Published: April 2006

The flow of cortical information through the basal ganglia occurs through the so‐called ‘direct pathway’ and ‘indirect pathways’. The object of the present work was to attempt to determine whether spiny neurons in the neostriatum that give rise to the direct pathway (i.e. the striatonigral/entopeduncular pathway) and those giving rise to the indirect pathways (i.e. striatopallidal pathway) are synaptically interconnected. The approach was to carry out double immunocytochemistry at the electron microscopic level using antibodies against peptides or dopamine receptor subtypes that are selectively associated with the neurons that give rise to the direct (substance P or D1 receptors) and indirect pathways (enkephalin or D2 receptors). Sections of perfuse‐fixed rat neostriatum were immunostained to reveal both substance P immunoreactivity and D2 receptor immunoreactivity or enkephalin and D1 receptor immunoreactivity, respectively. Double peroxidase methods were employed using different chromogens that were distinguishable at both the light and electron microscopic levels. In the electron microscope substance P‐immunoreactive terminals were seen in synaptic contact with dendritic structures that displayed immunoreactivity for D2 receptor. Similarly, enkephalin‐immunoreactive terminals were seen in synaptic contact with D1‐immunoreactive dendritic structures. Thus, axon collaterals of neurons giving rise to the direct pathway form synaptic contacts with neurons that give rise to the indirect pathway and axon collaterals of neurons giving rise to the indirect pathway form synaptic contact with neurons that give rise to the direct pathway. These results indicate that the two pathways of information flow through the basal ganglia are synaptically linked at the level of the neostriatum.
Neuronal Differentiation in the Rat Hippocampus Involves a Stage‐specific Reorganization of Subnuclear Structure both In Vivo and In Vitro
Authors: Santama Niovi , Dotti Carlos G. , Lamond Angus I.
Published: April 2006

Pyramidal neurons from the hippocampus undergo a well characterized programme of differentiation in vitro involving five distinct stages (1–5). While some important aspects of the dynamic organization of cell cytoplasmic structure that underlie neuronal polarization have been elucidated, little is known about corresponding changes in nuclear organization. Here we identify major changes affecting nuclear structure and gene expression during late stages of differentiation. At stage 4 a sustained increase in global transcriptional activity occurs. This is followed at stage 5 by proliferation of coiled bodies, i.e. subnuclear organelles containing splicing factors, which form a novel domain around the nucleolus that we refer to as the rosette. Both the morphology and timing of rosette formation are identical in neurons in vitro and in situ in the developing hippocampus in rat brain. Long‐term synaptic inhibition in vitro or growth at low density does not prevent either nuclear reorganization, enhanced transcriptional activity or the formation of pre‐synaptic specializations. These data indicate that stage‐specific changes in nuclear structure and function, similar to distinct rearrangements of cytoplasmic components, are pre‐programmed aspects of the neuronal differentiation pathway in the hippocampus.
Chronic Dizocilpine Maleate (MK‐801) Treatment Suppresses the Effects of Nigrostriatal Dopamine Deafferentation on Enkephalin but not on Substance P Expression in the Rat Striatum
Authors: Hajji Moulay Driss , Salin Pascal , Goff Lydia Kerkerian‐Le
Published: April 2006

The present study examined the effects of chronic treatment with dizocilpine maleate (0.2 mg/kg i.p., twice a day for 8 days) alone or in combination with unilateral 6‐hydroxydopamine‐induced lesion of the nigrostriatal dopaminergic neurons on substance P and enkephalin expression in the rat striatum. This was done by means of quantitative in situ hybridization histochemistry and immunocytochemistry. As reported previously, the unilateral dopaminergic lesion resulted in marked decreases in substance P mRNA expression and immunoreactivity in the ipsilateral striatum, while enkephalin mRNA expression and Met‐enkephalin immunoreactivity were considerably increased in this structure. Blockade of NMDA receptors by chronic dizocilpine maleate treatment alone resulted in decreased levels of striatal substance P mRNA without significant change in substance P immunoreactivity versus controls. Enkephalin mRNA levels were also decreased in the striatum, matched by parallel reductions in Met‐enkephalin immunoreactivity. These observations indicate that NMDA receptor activity may exert tonic excitatory effects on substance P and enkephalin expression in the striatum. The same chronic treatment with dizocilpine maleate started 12 days after the 6‐hydroxydopamine injection suppressed the lesion‐induced up‐regulation of enkephalin expression without significantly affecting the down‐regulation of substance P expression. These data provide evidence that NMDA receptor‐mediated mechanisms contribute to the alteration of striatal enkephalin expression associated with dopaminergic depletion in hemiparkinsonian rat models.
Contrasting Effects of Chronic Clozapine, SeroquelTM (ICI 204,636) and Haloperidol Administration on ΔFosB‐like Immunoreactivity in the Rodent Forebrain
Authors: Vahid‐Ansari F. , Nakabeppu Y. , Robertson G. S.
Published: April 2006

We have recently demonstrated that specific neuroanatomical patterns of Fos‐like immunoreactivity are predictive of atypical antipsychotic activity. However, the fact that neuroleptics must be administered chronically in order to generate both extrapyramidal side effects and an optimal therapeutic response calls into question the relevance of acute changes in Fos‐like immunoreactivity for these slowly developing events. Fos‐like immunoreactivity cannot be used to identify neurons activated by chronic neuroleptic administration because the increase in Fos‐like immunoreactivity produced by an acute antipsychotic injection is dramatically reduced following repeated neuroleptic administration. In contrast, expression of the immediate‐early gene product ΔFosB is persistently elevated in the striatum by chronic haloperidol administration. This suggests that ΔFosB‐like immunoreactivity may be used to identify neurons activated by chronic antipsychotic administration. Since typical and atypical neuroleptics elevate Fos‐like immunoreactivity in different regions of the forebrain acutely, the purpose of the present study was to determine whether typical (haloperidol) and atypical (clozapine, ICI 204,636) antipsychotics produce distinct patterns of elevated ΔFosB‐like immunoreactivity in the forebrain after chronic administration. Administration of haloperidol (2 mg/kg/day) to rats for 19 days induced a homogeneous elevation of neurons which displayed ΔFosB‐like immunoreactivity in the ventral, medial and dorsolateral aspects of the striatum. Chronic haloperidol administration did not enhance ΔFosB‐like immunoreactivity in the prefrontal cortex and lateral septal nucleus. Repeated administration of clozapine (20 mg/kg/day) and ICI 204,636 (20 mg/kg/day) for 19 days elevated ΔFosB‐like immunoreactivity not only in the ventral striatum but also in the prefrontal cortex and lateral septal nucleus. However, these compounds had weak effects on ΔFosB‐like immunoreactivity in the dorsolateral striatum. These results suggest that a preferential action on limbic structures such as the prefrontal cortex, ventral striatum and lateral septal nucleus may account for the ability of chronic clozapine and ICI 204,636 administration to reduce the symptoms of schizophrenia without generating extrapyramidal side effects.
Brain Rhythms of Language: Nouns Versus Verbs
Authors: Pulvermüller Friedemann , Preissl Hubert , Lutzenberger Werner , Birbaumer Niels
Published: April 2006

Electrocortical activity was recorded from scalps of human subjects reading nouns and verbs. Current source density analysis of EEG signals and calculation of spectral responses revealed differences between word categories in the 30 Hz range. Verbs elicited stronger 30 Hz activity at recording sites over the motor cortices, while nouns elicited stronger responses at sites over visual cortices in the occipital lobes. Behavioural testing indicated that, at the cognitive level, this double dissociation corresponds to motor and visual associations prompted by verbal stimuli. These results suggest that local high‐frequency brain responses can be indicators of conscious processing of motor and visual associations of verbal material. Furthermore, the results provide additional evidence that nouns and verbs have distinct neuronal generators in the intact human brain.
Synaptogenesis in the Occipital Cortex of Macaque Monkey Devoid of Retinal Input From Early Embryonic Stages
Authors: Bourgeois Jean‐Pierre , Rakic Pasko
Published: April 2006

The role of input from the retina on the development of synaptic organization in the primate striate cortex was examined in macaque monkeys enucleated at embryonic (E) day 67 and E59. Both the prenatally operated animals and their age‐matched controls were delivered at term (E165) and killed either at 3 months (at the end of the rapid phase of synaptogenesis) or 3 years (at the end of the plateau phase of synaptogenesis). As expected, in the operated animals the striate cortex had a smaller surface area but a normal thickness and complement of layers. The present study revealed that the mean densities of synaptic contacts per unit area and volume of neuropil in the striate cortex of the two operated animals were similar to those of age‐matched controls (∼30/100 μm2 or 100/100 μm3 of neuropil). Thus, the absence of retinal input via the lateral geniculate nucleus did not affect the schedule and magnitude of synaptogenesis. Likewise, the ratio of symmetrical versus asymmetrical synapses and mean lengths of synaptic junctions were within the normal range of variation in both group of animals. The proportions of synaptic contacts situated on dendritic spines and shafts were also similar in supra‐ and infragranular cortical layers of normal and enucleated animals. However, the ratio of synapses situated on dendritic spines and shafts in the sublayers IVAB and IVC, which normally become reversed during late adolescence, were not reversed in the enucleates. Therefore, our study indicates that certain parameters of synaptic development, such as the density of contacts per unit volume of neuropil and the proportion of basic types and their size, in the supra‐ and infragranular layers of the striate cortex develop to an optimal normal level in the absence of both retinae from early embryonic stages. However, in the thalamorecipient sublayers the details of the synaptic circuits, such as their localization on dendritic spines or shafts, fail to mature properly in the absence of normal functional input from the periphery.
Involvement of Na+–Ca2+ Exchanger in Reperfusion‐induced Delayed Cell Death of Cultured Rat Astrocytes
Authors: Matsuda Toshio , Takuma Kazuhiro , Nishiguchi Emi , Asano Shoichi , Hashimoto Hitoshi , Azuma Junichi , Baba Akemichi
Published: April 2006

In some cells, Ca2+ depletion induces an increase in intracellular Ca2+ ([Ca2+]i) after reperfusion with Ca2+‐containing solution, but the mechanism for the reperfusion injury is not fully elucidated. Using an antisense strategy we studied the role of the Na+‐Ca2+ exchanger in reperfusion injury in cultured rat astrocytes. When astrocytes were perfused in Ca2+‐free medium for 15–60 min, a persistent increase in [Ca2+]i was observed immediately after reperfusion with Ca2+‐containing medium, and the number of surviving cells decreased 3–5 days latter. The increase in [Ca2+]i was enhanced by low extracellular Na+ ([Na+]o) during reperfusion and blocked by the inhibitors of the Na+‐Ca2+ exchanger amiloride and 3,4‐dichlorobenzamil, but not by the Ca2+ channel antagonists nifedipine, Cd2+ and Ni2+. Treatment of astrocytes with antisense, but not sense, oligodeoxynucleotide to the Na+‐Ca2+ exchanger decreased Na+–Ca2+ exchanger protein level and exchange activity. The antisense oligomer attenuated reperfusion‐induced increase in [Ca2+]i and cell toxicity. The Na+‐Ca2+ exchange inhibitors 3,4‐dichlorobenzamil and ascorbic acid protected astrocytes from reperfusion injury partially, while the stimulators sodium nitroprusside and 8‐bromo‐cyclic GMP and low [Na+]o exacerbated the injury. Pretreatment of astrocytes with ouabain and monensin caused similar delayed glial cell death. These findings suggest that Ca2+ entry via the Na+–Ca2+ exchanger plays an important role in reperfusion‐induced delayed glial cell death.
Activation of Meningeal 5‐HT2B Receptors: An Early Step in the Generation of Migraine Headache?
Authors: Schmuck Karin , Ullmer Christoph , Kalkman Hans O. , Probst Alphonse , Lübbert Hermann
Published: April 2006

Several pharmaceuticals are frequently dispensed to prevent or reduce the occurrence of migraine attacks. The prophylactic effect of these drugs has been suggested to be caused through blockade of serotonin (5‐HT) receptors of type 5‐HT2B or 5‐HT2C. To elucidate which of these receptors is involved, we first used radioligand binding assays to determine the pharmacological profile of the human and rat 5‐HT2B receptor. Furthermore, the potency of drugs used in migraine prophylaxis to stimulate or inhibit 5‐HT2B or 5‐HT2C receptor‐mediated phosphatidyl inositol hydrolysis was measured. All these drugs were found to block both human receptors. Correlation of the receptor affinities with the potencies used in migraine prophylaxis showed significant correlations, which were better for the 5‐HT2B (P= 0.001) than for the 5‐HT2C receptor (P= 0.005). Migraine headache is thought to be transmitted by the trigeminal nerve from the meninges and their blood vessels. Using the reverse transcription–polymerase chain reaction, the expression patterns of all cloned G‐protein‐coupled serotonin receptors were analysed in various human meningeal tissues. All tissues expressed 5‐HT1Dβ, 5‐HT2A, 5‐HT2B, 5‐HT4 and 5‐HT7 mRNAs. Only trace amounts of 5‐HT2C receptor mRNA were found. With organ bath experiments we showed that the 5‐HT2B receptor stimulated the relaxation of the pig cerebral artery via the release of nitric oxide. Our data support the hypothesis that 5‐HT2B receptors located on endothelial cells of meningeal blood vessels trigger migraine headache through the formation of nitric oxide.
Origin of Aspartate‐induced Responses in Rat Cerebellar Purkinje Cells
Authors: Renard A. , Crépel F.
Published: April 2006

The effects of glutamate, aspartate and N‐methyl‐d‐aspartate (NMDA) on Purkinje cells and interneurons were investigated in cerebellar slice cultures using the whole‐cell configuration of the patch‐clamp technique. l‐Glutamate and l‐aspartate induced inward currents in Purkinje cells voltage‐clamped at ‐60 mV. In standard external solution, the amplitude of the responses induced by these two amino‐acids was a linear function of the membrane potential. l‐Aspartate‐induced currents were inhibited by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX), a selective antagonist of non‐NMDA receptors. NMDA, a selective agonist of NMDA receptors, had no effect of its own on the excitability of Purkinje cells, but was effective in blocking the responses induced by aspartate in Purkinje cells in a voltage‐independent manner. In contrast, d‐(–)‐2‐amino‐5‐phosphonovaleric acid (d‐APV), a selective antagonist of NMDA receptors, had no effect on aspartate‐induced responses. d‐Aspartate also induced responses in Purkinje cells, and the amplitude of these responses was a linear function of the membrane potential. Currents induced by l‐ and d‐aspartate were inhibited by dihydrokainate, a glutamate uptake blocker. In sodium‐free external solution, glutamate still induced outward currents in Purkinje cells, whereas l‐ and d‐aspartate no longer evoked any current. When sodium was replaced by lithium in the external medium, no change in the holding current could be detected in Purkinje cells maintained at ‐60 mV; moreover, in this bathing medium l‐aspartate no longer evoked any current whereas glutamate‐induced responses were still present. In contrast, interneurons were sensitive to both NMDA and aspartate applications, and these responses were antagonized by d‐APV. In addition, aspartate still induced an outward current in sodium‐free external solution. This study presents rather direct evidence in favour of l‐aspartate as being a very selective NMDA receptor agonist in the cerebellum. l‐Aspartate‐induced currents in Purkinje cells are not due to activation of mixed NMDA/non‐NMDA receptors, but are probably due to the release of l‐glutamate induced by aspartate through glutamate uptake.
Chromogranin mRNA Levels in the Brain as a Marker for Acute and Chronic Changes in Neuronal Activity: Effect of Treatments Including Seizures, Osmotic Stimulation and Axotomy in the Rat
Authors: Shen P.‐J. , Gundlach A. L.
Published: April 2006

Chromogranin/secretogranins are a family of acidic, soluble proteins with a widespread distribution in secretory vesicles of endocrine and nervous tissues. The effects of experimental stimuli of differing duration and intensity on chromogranin B and secretogranin II mRNA levels in relevant areas of the rat brain were examined by in situ hybridization histochemistry using 35S‐labelled oligonucleotides. Effects of two ‘chronic stimulation’ paradigms were studied—the effect of 4 days of water or food deprivation on mRNA levels in the hypothalamus and the effect of unilateral cervical vagotomy on transcript levels in the dorsal vagal complex 1, 2 and 7 days after surgery. After 4 days of water deprivation secretogranin II mRNA was significantly increased in the supraoptic nucleus (366 ± 21% of control, P < 0.01), the magnocellular paraventricular nucleus (209 ± 20% of control, P < 0.01) and the parvocellular paraventricular nucleus (147 ± 6% of control, P < 0.01). Conversely, the level of secretogranin II mRNA in the supraoptic nucleus was decreased (61 ± 13% of control, P < 0.05) after 4 days of food deprivation. Seven days after unilateral cervical vagotomy, secretogranin II and chromogranin B mRNA levels were markedly decreased in the ipsilateral dorsal motor nucleus of the vagus (25 ± 4 and 47 ± 8% of contralateral values respectively, P < 0.01). Rapid changes in chromogranin mRNA were also detected following shorter duration ‘acute stimulation’—in the hypothalamus after hypertonic saline injection, in the hippocampus after electrical stimulation‐induced kindled seizures, and in the cerebral cortex after unilateral craniotomy. A large increase in secretogranin II mRNA was detected in the supraoptic nucleus (202 ± 25% of control, P < 0.01) and the magnocellular paraventricular nucleus (168 ± 29% of control, P < 0.05) 3 h after a single intraperitoneal injection of hypertonic (1.8 M) saline. Markedly increased levels of secretogranin II (125–160% of control) and chromogranin B (140–230% of control) mRNA were observed in granule cells of the dentate gyrus 0.5–2 h after amygdaloid stimulation‐induced seizures. A moderate increase in secretogranin II mRNA (144 ± 11% of contralateral side, P < 0.01) was found in the underlying cerebral cortex 2.5 h after unilateral craniotomy. These results indicate that measurement of changes in chromogranin mRNA, particularly secretogranin II, is a useful means of assessing both rapid and long‐lasting increases and decreases in neuronal activity and, in contrast to immediate early gene mRNA levels, may better reflect specific changes in neuronal secretory activity associated with transmitter/peptide release.
Differential Frequency Conditioning Enhances Spectral Contrast Sensitivity of Units in Auditory Cortex (Field Al) of the Alert Mongolian Gerbil
Authors: Ohl Frank W. , Scheich Henning
Published: April 2006

Differential aversive auditory conditioning in the awake Mongolian gerbil was performed during single‐ and multi‐unit recording in field Al of the primary auditory cortex. Presentations of pure tone stimuli of a given frequency (reinforced conditioned stimulus; CS+) paired with electrocutaneous stimulation (unconditioned stimulus) were combined with several other non‐reinforced tone stimuli (non‐reinforced conditioned stimulus; CS‐). Stimulus presentation during training and testing was optimized for constancy of the probability of occurrence of both the CS+ and the CS‐ stimulus. The paradigm led to a reorganization of both the spectral and temporal response characteristics of auditory cortical neurons with the following basic results. First, tone‐evoked responses of Al neurons recorded after multiple acoustic stimulation under these conditions varied statistically around a mean value (stationarity). Conditioning produced a shift in mean values of evoked responses. The altered tone responses were also stationary (stability of the plastic effects). Second, the frequency‐receptive fields (FRFs) of neurons were reorganized in a frequency‐specific way such that the CS+ frequency became located in a local minimum of the FRF after training. This resulted from a training‐induced increase in the responses to frequencies adjacent to the CS+ frequency in the FRF relative to the CS+ response. The effect can be interpreted as an enhancement of the ‘spectral contrast’ sensitivity of the unit in the CS+ neighbourhood. Third, apart from this frequency‐specific plastic effect, responses to other frequencies also underwent changes during training. The non‐frequency‐specific changes were not generally predictable but the post‐trial responses were stationary. Fourth, the analysis of the long‐term behaviour of FRF reorganization revealed the stability of plastic effects under retention training and the gradual re‐establishment of the pretrial FRF during extinction training. Fifth, not only the spectral characteristics but also the temporal structure of the tone‐evoked responses could be affected by the training. In most cases the training‐induced changes measured within the first tens of milliseconds of the response corresponded to the response changes obtained by integration over the total response period. There were some cases, however, in which the direction of the response change varied with time, indicating that excitatory and inhibitory influences on the temporal response pattern were differently affected by training.
Increased Expression of BDNF and trkB mRNA in Rat Facial Motoneurons after Axotomy
Authors: Kobayashi Nao R. , Bedard Annie M. , Hincke Maxwell T. , Tetzlaff Wolfram
Published: April 2006

Motoneurons of the adult survive after axotomy even though they are deprived of putative target derived trophic factors. Alternative sources of trophic support may substitute. In this study we test the hypothesis that the immediate environment of the motoneuronal cell body or the cell body itself increases the production of trophic factors after axonal injury. Using in situ hybridization (ISH) and reverse transcription–polymerase chain reaction (RT‐PCR), we report that after axotomy, rat facial motoneurons increase the expression of mRNA for brainderived neurotrophic factor (BDNF) and its receptor trkB. After transection of the facial nerve, we measured a 2‐to 4‐fold increase in BDNF mRNA expression which had its onset between 3 and 8 h after injury. The BDNF mRNA levels peaked at ∼1–2 days and gradually declined thereafter to return to contralateral levels within 7 days of injury. Western blotting revealed a several‐fold increase in BDNF as early as 24 h, which subsequently reached a maximum in ∼5–7 days and was still sustained at 2 weeks post‐axotomy. Using exon‐specific primers, we determined that the increase in BDNF mRNA is largely due to an increased expression from the promoters of exons IV and III, and to a lesser extent from exons I and II. Analysing the mRNA expression for the BDNF receptor, trkB, we found a 2‐ to 3‐fold increase in full‐length trkB mRNA expression starting 2 days after axotomy which lasted for 2–3 weeks. These findings suggest that BDNF might act locally on axotomized motoneurons in an autocrine fashion, providing support for axotomized motoneurons during the first weeks after axotomy.
Effects of Substance P on Medial Vestibular Nucleus Neurons in Guinea‐pig Brainstem Slices
Authors: Vibert Nicolas , Serafin Maura , Vidal Pierre‐Paul , Mühlethaler Michel
Published: April 2006

The undecapeptide substance P (SP) has been recently implicated in the control of vestibular function. In particular, it seems to be co‐localized with glutamate in approximately half of the primary vestibular afferents in mammals. Using intracellular recordings in guinea‐pig brainstem slices, we have investigated the effects of SP and of several agonists of the three known tachykinin receptor subtypes (NK1, NK2 and NK3) on the three main types (A, B and B+LTS) of guinea‐pig medial vestibular nucleus neurons (MVNn) that we had previously described. SP could induce two distinct kinds of effects on all types of MVNn. Whereas around half of them were depolarized and had their membrane resistance increased by SP, ∼ 10% of all MVNn were in contrast hyperpolarized and inhibited while their membrane resistance was decreased. Both responses persisted under conditions of blockade of synaptic transmission, and were thus due to the activation of postsynaptic binding sites. The SP‐induced membrane depolarization could not be reproduced with any one of the specific agonists of the three tachykinin receptor subtypes, nor was it blocked by the specific NK1 receptor antagonists GR 82334 and CP 99994. This effect might therefore be due to the activation of a new, pharmacologically distinct, ‘NK1‐like’ receptor. Only the hyperpolarizing effects, which were in contrast mimicked by the specific NK1 receptor agonists GR 73632 and [Sar9, Met (O2)11]‐SP, would be mediated by the few typical NK1 receptors which have been demonstrated in the medial vestibular nucleus.
Evidence for Direct Connections between the Hand Region of the Supplementary Motor Area and Cervical Motoneurons in the Macaque Monkey
Authors: Rouiller Eric M. , Moret Véronique , Tanné Judith , Boussaoud Driss
Published: April 2006

In primates the corticospinal neurons of the hand representation of the primary motor cortex (M1) give rise to direct contacts with the cervical motoneurons that control distal forelimb muscles. We investigated, at the light‐microscopy level, whether corticospinal cells present in the hand area of the supplementary motor area (SMA) also establish direct connections with cervical motoneurons, particularly those innervating hand and finger muscles. The hand representation of the M1 (two monkeys) or SMA (two monkeys) was located using intracortical microstimulation and injected with the anterograde tracer biotinylated dextran amine to label corticospinal terminals. Forearm muscles acting on the wrist and hand as well as hand muscles acting on the thumb and index finger, thus including those activated by intracortical stimulation, were injected with the retrograde tracer cholera‐toxin B subunit, in order to label the motoneurons. A consistent zone of overlap between the two markers was found in the cervical cord. Close appositions between corticospinal axonal terminals and the somata or dendrites of motoneurons were found after injection in the M1, confirming previous observations. The new finding is the observation of similar close appositions after injection in the SMA, suggesting its control of hand movements in parallel with the M1.
Chronic NMDA Receptor Antagonism During Retinotopic Map Formation Depresses CaM Kinase II Differentiation in Rat Superior Colliculus
Authors: Scheetz A. J. , Prusky Glen T. , Constantine‐Paton Martha
Published: April 2006

We examined the effects of chronic NMDA receptor antagonism on the normal postnatal differentiation of calcium‐ and calmodulin‐dependent kinase II (CaM kinase II) in the rat superior colliculus. At postnatal day (P) zero, most CaM kinase II protein, as well as CaM kinase II activity, was detected in the soluble fraction. In vitro phosphorylation of P0 superior colliculus revealed several prominent substrates in both the particulate and soluble fractions. At P19 there was more particulate enzyme than soluble enzyme, and CaM kinase II activity in the particulate fraction was higher than in P0 particulate tissue. Additionally, in vitro phosphorylation of P19 superior colliculus revealed many more CaM kinase II substrates. Chronic NMDA receptor antagonism with 2‐amino‐5‐phosphonovalerate (DL‐AP5) caused CaM kinase II to retain many of the characteristics of the enzyme found in P0 untreated superior colliculus. In P19 superior colliculus treated with DL‐AP5 from birth, most of the protein was in the soluble fraction, CaM kinase II activity was largely restricted to the soluble fraction, and only a few substrates were observed by in vitro phosphorylation. These effects were not observed in tissue treated with the inactive isomer, L‐AP5. These results suggest that synaptic maturation is slowed by antagonism of NMDA receptors during retinotopic map formation.
Interactions between Associative Synaptic Potentials in the Piriform Cortex of the In Vitro Isolated Guinea Pig Brain
Authors: Biella Gerardo , Panzica Ferruccio , de Curtis Marco
Published: April 2006

The interaction between synaptic potentials generated by the activation of separate sets of associative fibres was investigated in the piriform cortex of an in vitro isolated guinea pig brain preparation. Restricted regions of the piriform cortex served by separate contingents of afferent fibres of the lateral olfactory tract were isolated surgically. The activity generated by these patches of cortex in response to afferent stimulation propagates to remote cortical regions along cortico‐cortical associative fibres. Current source density (CSD) analysis of field potential laminar profiles evoked by lateral olfactory tract stimulation confirmed that the synaptic sinks induced by distinct associative fibre contingents converge on the apical dendrites of piriform cortex neurons in the superficial lb layer. Pairing between potentials evoked by activation of two separate sets of associative fibres resulted in an almost linear summation when the two responses coincided. For interstimulus intervals of <100 ms, heterosynaptic pairing of independent associative inputs induced a facilitation of the conditioned associative potential, which correlated with an increase in the associative sink located in layer lb, as demonstrated by CSD analysis. The evaluation of the pairing intervals suggests that the heterosynaptic facilitation of the conditioned associative potentials may be due to the summation of local and remote associative synaptic events. It is concluded that separate associative inputs converge on the apical dendrites of piriform cortex pyramidal neurons to generate synaptic potentials through the activation of spatially close but independent synapses. The role of associative synaptic integration in the functional organization of the olfactory cortex is discussed.
Cortical Networks for Visual Reaching: Intrinsic Frontal Lobe Connectivity
Authors: Johnson Paul B. , Ferraina Stefano
Published: April 2006

The anatomical substrates of reaching to visual targets were studied in monkeys (Macaca nemestrina) by combining behavioural neurophysiology and neuroanatomy. An instructed‐delay reaching task was used to characterize the arm‐related regions of the dorsolateral frontal cortex. This task revealed gradients of signal‐, set‐, movement‐ and position‐related activity along the rostrocaudal extent of the frontal lobe. The frontal mesial projections to these physiologically defined gradients were studied through anatomical methods based on the retrograde transport of distinguishable tracers. The tangential distribution of the cells of origin of these projections displayed a gradient‐like arrangement similar to that defined physiologically in their terminal territory. These mesial projections to the dorsolateral frontal cortex may therefore be considered part of a cortical network wherein connections make only a limited contribution to the integration of different sources of information for the control of reaching movements. Further combination of such information must occur within each given cortical region by intrinsic local connections