bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of GABAergic agonists and antagonists on oscillatory signal propagation in the guinea‐pig accessory olfactory bulb slice revealed by optical recording
Authors: Sugai Tokio , Sugitani Michio , Onoda Norihiko
Published: March 2003

To investigate the action of GABAergic agents on oscillatory signal propagation induced by electrical stimulation of the vomeronasal nerve layer, optical and electrophysiological recordings were carried out in slice preparations of the guinea‐pig accessory olfactory bulb. In response to electrical stimuli, characteristic optical signals appeared in each layer: in the vomeronasal nerve layer, a transient presynaptic response; in the glomerular layer, pre‐ and postsynaptic responses; in the external plexiform, mitral cell and granule cell layers, a damped oscillatory response. Application of the GABAergic agonists, that is, GABA, muscimol (a GABAA receptor agonist) and baclofen (a GABAB receptor agonist), suggested that the GABAB action existed mainly in the glomeruli, whereas the GABAA action was present in both the glomeruli and the external plexiform layer. Bicuculline (a GABAA receptor antagonist) produced long‐lasting but nonoscillating excitation in the external plexiform and mitral cell layers, indicating that the GABAA action contributes to the formation of oscillatory responses. When double‐pulse stimulation was applied to the vomeronasal nerve layer, the test responses in the glomerular layer and external plexiform and mitral cell layers were depressed, but those in the vomeronasal nerve layer were not. Application of 2‐hydroxysaclofen (a GABAB receptor antagonist) mostly blocked paired‐pulse depression occurring in the glomerular layer and restored the reduced transmission to mitral cells, but had only a small effect on the depressed oscillatory response in the external plexiform and mitral cell layers. These observations suggest that GABAB action in the glomerular layer might, at least, regulate information flow from vomeronasal afferents to apical dendrites of mitral cells, like a gate inhibition. However, actions other than GABAB could also be involved in the depression of the oscillation in the external plexiform and mitral cell layers.
The pH response of rat cutaneous nociceptors correlates with extracellular [Na+] and is increased under amiloride
Authors: Steen Kay H. , Wegner Holger , Reeh Peter W.
Published: March 2003

Excess hydrogen ions induce sustained nociceptor excitation as well as pain, and this has been suggested, with evidence from sensory ganglion cells, to result from gating a slowly inactivating sodium/calcium inward current. In the rat skin‐nerve preparation, isolated receptive fields of pH‐sensitive C‐fibre terminals were exposed to low‐pH solutions of various sodium concentrations. The pH responses showed a good correlation with log [Na+]e, which supports the above model. Amiloride has previously been shown to block a pH‐induced Na+ current involved in sensory transduction in hamster taste cells; however, it has been shown to act differently in cutaneous nociceptors. Amiloride induced a dose‐dependent increase in and prolongation of the nociceptive pH responses, with a prominent acceleration of the onset. The latter could be mimicked by replacing external sodium with sucrose, thus impeding sodium‐proton antiport. Together, the findings indicate functional expression of amiloride‐sensitive Na+/H+‐antiporters, which enable the nociceptive nerve endings to extrude invading H+. Intracellular acidification may thus compete with Na+/H+ exchange, and pHi may be decisive in the transduction of nociception and pain from tissue acidosis.
Cocaine self‐administration increases the incentive motivational properties of the drug in rats
Authors: Deroche Véronique , Le Moal Michel , Piazza Pier Vincenzo
Published: March 2003

A progressive increase in the frequency and intensity of drug use is one of the major behavioural phenomena characterizing the development of addiction. The nature of the drug‐induced adaptations involved in this escalating drug intake remains unknown. Some theories propose that this escalation is due to a progressive decrease (tolerance) in the reinforcing or incentive effects of the drug. Alternative views posit that with chronic use the reinforcing or incentive effects of drugs increase, by a sensitization or a learning mechanism. In this report, we address the question of whether escalating cocaine intake is paralleled by an increase or a decrease in the reinforcing and incentive effects of the drug. Using the experimental model of intravenous drug self‐administration with a within‐session dose–response paradigm, we first studied the course of cocaine intake over 14 sessions in rats. After acquisition of cocaine self‐administration, cocaine intake progressively increased at each dose tested. Then rats, previously allowed to self‐administer cocaine during either six or 29 sessions, were compared in three different tests of the incentive and reinforcing effects of cocaine: cocaine‐induced reinstatement of self‐administration, cocaine‐induced runway and cocaine‐induced place conditioning. As compared with rats briefly exposed to cocaine self‐administration (six sessions), rats with the longer experience (29 sessions) exhibited a higher intake of cocaine paralleled by a higher responsiveness in the cocaine‐induced reinstatement and runway tests. Both groups of rats were similarly sensitive to the rewarding effects of the drug as evaluated by the threshold dose of cocaine inducing place conditioning. Our results demonstrate that escalating cocaine intake is paralleled by an increase in the motivational properties of the drug in the absence of apparent signs of tolerance to the reinforcing or incentive effects of cocaine.
Astrocytes are required for the oscillatory activity in cultured hippocampal neurons
Authors: Verderio Claudia , Bacci Alberto , Coco Silvia , Pravettoni Elena , Fumagalli Guido , Matteoli Michela
Published: March 2003

Synchronous oscillations of intracellular calcium concentration ([Ca2+]i) and of membrane potential occurred in a limited population of glutamatergic hippocampal neurons grown in primary cultures. The oscillatory activity occurred in synaptically connected cells only when they were in the presence of astrocytes. Microcultures containing only one or a few neurons also displayed oscillatory activity, provided that glial cells participated in the network. The glutamate‐transporter inhibitors L‐trans‐pyrrolidine‐2,4‐dicarboxylic acid (PDC) and dihydrokainate, which produce an accumulation of glutamate in the synaptic microenvironment, impaired the oscillatory activity. Moreover, in neurons not spontaneously oscillating, though in the presence of astrocytes, oscillations were induced by exogenous l‐glutamate, but not by the stereoisomer d‐glutamate, which is not taken up by glutamate transporters. These data demonstrate that astrocytes are essential for neuronal oscillatory activity and provide evidence that removal of glutamate from the synaptic environment is one of the major mechanisms by which glial cells allow the repetitive excitation of the postsynaptic cell.
Accumulation of murine amyloidβ42 in a gene‐dosage‐dependent manner in PS1 ‘knock‐in’ mice
Authors: Nakano Yuka , Kondoh Gen , Kudo Takashi , Imaizumi Kazunori , Kato Masaya , Miyazaki Jun‐ichi , Tohyama Masaya , Takeda Junji , Takeda Masatoshi
Published: March 2003

The establishment of an animal model with a missense mutation of presenilin‐1 (PS1) is an initial step toward understanding the molecular pathogenesis of familial Alzheimer’s disease (FAD) and developing therapeutic strategies for the disease. We previously described a Japanese family with FAD caused by the I213T mutation of PS1, in which typical signs and symptoms of Alzheimer’s disease were observed at the age of 45 ± 4.2 years [Hardy, J. (1997) Trends. Neurosci., 20, 154–159; Kamino, K et al. (1996) Neurosci. Lett., 208, 195–198]. Here, we report the establishment of ‘knock‐in’ mice with the I213T PS1 missense mutation. Northern blot and reverse transcription polymerase chain reaction (RT‐PCR) analyses showed that the mutated PS1 allele was expressed at the same level as the endogenous PS1 allele, demonstrating that the PS1 missense mutation was successfully introduced into the mouse PS1 locus, and therefore that the situation mimics that in FAD patients bearing PS1 missense mutations. Amyloid beta (Aβ) 42(43) peptide, but not Aβ40 peptide, accumulated in ‘knock‐in’ mice at the age of 16–20 weeks. A clear gene‐dosage effect on the increase of Aβ42(43) was observed in ‘knock‐in’ mice: the percentage increase of Aβ42(43) in mice with mutations in both alleles was twice as high as that in mice with a single allele. These results indicate that the level of the mutated PS1 gene expression is likely to be critically involved in the production of highly amyloidogenic Aβ42(43), and confirm that PS1 mutation has an important effect on amyloid precursor protein (APP) processing, in proportion to the level of the expression of the mutant gene.
Ectopic expression of the bHLH gene Math1 disturbs neural development
Authors: Isaka Fumiaki , Ishibashi Makoto , Taki Waro , Hashimoto Nobuo , Nakanishi Shigetada , Kageyama Ryoichiro
Published: March 2003

The basic helix–loop–helix gene Math1, a positive regulator of neuronal differentiation, is specifically expressed in the dorsal part of the developing nervous system. To determine the effects of ectopic expression of Math1, we generated two transgenic mouse lines; One carried the Cre recombinase gene under the control of the nestin promoter and enhancer, which direct expression in neural precursor cells, and the other carried the Math1 gene, the expression of which was regulated by the cytomegalovirus (CMV) promoter but interrupted by the stop cassette flanked by loxP sites. In F1 embryos that carried the two transgenes, the stop cassette was removed by Cre recombinase in the developing nervous system, and Math1 expression was ectopically directed from the CMV promoter. We found that these embryos exhibited abnormal morphology of the brain and extensive cell death in the nervous system. These results suggest that ectopic expression of Math1 is toxic to neurons and leads to apoptosis.
Interocular temporal delay sensitivity in the visual cortex of the awake monkey
Authors: Perez Rogelio , Gonzalez Francisco , Justo Maria S. , Ulibarrena Carlos
Published: March 2003

Due to the separation of the eyes, temporal retinal disparities are created during binocular stimulation and they have been proposed to be the basis of several stereo‐visual effects. This paper studies the sensitivity of cortical neurons from area V1 to interocular temporal delay in the awake monkey (Macaca mulatta). Forty‐four cells were included in this study. Temporal delay sensitivity was observed in 59% of them. About half of these temporal‐delay‐sensitive cells were also sensitive to the stimulation sequence of the eyes. The cells that preferred one eye to be stimulated first were termed asymmetrical (46%); those which were not sensitive to the eye sequence of stimulation were termed symmetrical (54%). No clear differences were observed in the distribution of delay‐sensitive cells according to their eye dominance. Fifty‐six percent of balanced cells and 65% of unbalanced cells were sensitive to interocular delay. These data underline the importance of temporal cues for depth perception.
Visuospatial attentional functioning in mice: interactions between cholinergic manipulations and genotype
Authors: Humby Trevor , Laird Fiona M. , Davies William , Wilkinson Lawrence S.
Published: March 2003

Attentional functioning in mice was assessed in an analogue of the five‐choice serial reaction time task in which the requirement was to detect brief visual stimuli presented across five spatial locations. Two hybrid strains of mice were assessed; F1 C57Bl/6xDBA/2 and C57Bl/6x129sv. Both strains acquired the task to high levels of performance with, in particular, no problems due to premature responding. At performance, systematic manipulation of the task parameters indicated a pattern of effects consistent with the task, taxing aspects of visuospatial attention. There were some differential effects of task manipulations at baseline across strain. However, the pattern of effects suggested these were likely to be the result of effects on factors other than attentional functioning per se, such as behavioural reactivity and inhibition. There was evidence in both strains of specific, centrally mediated effects of scopolamine on attentional functioning, with the C57Bl/6xDBA/2 hybrid showing greater sensitivity to the drug manipulation. Specific effects on discriminative accuracy were observed at doses of 0.02 and 0.2 mg/kg scopolamine. At the 2 mg/kg dose, large reductions in accuracy were associated with large effects on other measures, including omissions and response latencies, suggestive of nonspecific effects on task performance. These data indicate, for the first time, the utility of operant methods in assessing visuospatial attentional functioning in mice. They confirm the importance of cholinergic mechanisms in attentional processes across species, and suggest interactions between cholinergic mechanisms and genotype in the expression of attentional phenotypes.
Acidic calponin immunoreactivity in postnatal rat brain and cultures: subcellular localization in growth cones, under the plasma membrane and along actin and glial filaments
Authors: Plantier Marc , Fattoum Abdellatif , Menn Bénédicte , Ben‐Ari Yehezkel , Der Terrossian and Elisabeth , Represa Alfonso
Published: March 2003

Acidic calponin, an F‐actin‐binding protein, is particularly enriched in brain, where calponin protein and mRNA are mainly expressed by neurons. The presence of calponin immunoreactivity in cultured astroglial cells has been reported, but the presence of acidic calponin in astrocytes in vivo appears equivocal. For the present study, we raised a specific polyclonal antibody against the 16‐residue synthetic peptide covering the sequence E311‐Q326 (EYPDEYPREYQYGDDQ) situated at the carboxy‐terminal end of rat acidic calponin, and we investigated the cellular and subcellular localization of the protein in the developing central nervous system. Our results show that acidic calponin is particularly enriched in: (i) growth cones and submembranous fields of maturing cerebellar and cortical cells, where it codistributes with microfilaments and (ii) glial cells in vivo, including radial glia, glia limitans, Bergmann glia and mature astrocytes, and ex vivo, where acidic calponin strongly colocalizes with intermediate glial fibrillary acidic protein (GFAP) and vimentin filaments. Finally, up to four acidic calponin subtypes with different isoelectric point (pI) values were identified by two‐dimensional gel electrophoresis of cerebellar and hippocampal extracts. The more acidic isoforms were developmentally regulated. As only one single mRNA for acidic calponin has been identified, these isoforms must reflect postsynthesis changes probably related to the particular functions of acidic calponin in maturing cells. Although brain acidic calponin's exact role remains uncertain, the present data suggest that it is involved in neuronal and glial plasticity.
Expression of functional α7 nicotinic acetylcholine receptor during mammalian muscle development and denervation
Authors: Fischer Uwe , Reinhardt Sigrid , Albuquerque Edson X. , Maelicke Alfred
Published: March 2003

We have studied, on the transcriptional, protein and functional level, the expression of α7 nicotinic acetylcholine receptors (nAChR) in the course of rat muscle development, denervation and renervation. At foetal day 13, α7 nAChR expression was observed in somites and developing muscles of the back, but not yet in migrating myoblasts. Two days later, concomitant with myoblast aggregation, the α7 isoform began to be expressed in isolated myoblasts, with the highest level of expression in the frontal zone of the migrating wave. On foetal day 18, a time when the myoblasts in the upper hindleg have fused, α7 nAChR expression was most prominent in the outer layer of muscle tissue. The highest level of expression was observed in the first postnatal week, when practically all muscle cells stained positively for α7 protein. During the following weeks, α7 nAChR expression slowly decreased and practically disappeared in adult hindleg muscle. Following chronic denervation of adult Soleus muscle fibres, expression of α7 nAChR returned within 2–4 weeks.

Electrophysiological measurements showed that the α7 nAChR of chronically denervated soleus muscle fibres were functional and, in particular, that they could be activated by choline. The presence of the α7 nAChR in developing and denervated muscle suggests a role for this nicotinic receptor in neuronal pathfinding and/or endplate stabilization.
Alternative splicing generates a novel isoform of the rat metabotropic GABABR1 receptor
Authors: Pfaff Torsten , Malitschek Barbara , Kaupmann Klemens , Prézeau Laurent , Pin Jean‐Philippe , Bettler Bernhard , Karschin Andreas
Published: March 2003

Here we present a novel isoform of the metabotropic G‐protein‐coupled receptor for γ‐aminobutyric acid (GABA). The isoform, termed GABABR1c (R1c), differs from the recently identified R1a and R1b receptors by an in‐frame insertion of 31 amino acids between the second extracellular loop and the fifth transmembrane region. Analysis of the rat GABABR1 gene demonstrates that the insertion is the result of an alternative splicing event within a 567‐bp intron between exons 16 and 17. In situ hybridization in the rat brain shows a wide distribution of R1c transcripts and an overlap with the R1a and R1b transcripts. The highest mRNA levels are found in cerebellar Purkinje cells, cerebral cortex, thalamus and hippocampal CA1 and CA3 regions. Western blots and immunodetection of recombinant epitope‐tagged receptors as well as [125I]CGP71872 photoaffinity labelling of cell membranes demonstrate that R1c is correctly expressed, although at a lower level than the previously identified isoforms. When coexpressed with the newly characterized GABABR2, R1c functionally couples to G‐protein‐activated Kir3.1/3.2 channels in Xenopus oocytes and to PLC‐activating chimeric Gαqo subunits in HEK‐293 cells with a similar EC50 for agonists. These data suggest that the R1c isoform represents a functional GABABR in the rat brain.
Long‐term effects of prenatal stress and postnatal handling on age‐related glucocorticoid secretion and cognitive performance: a longitudinal study in the rat
Authors: Vallée Monique , Maccari Stefania , Dellu Françoise , Simon Hervé , Le Moal Michel , Mayo Willy
Published: March 2003

There is growing evidence that stress during prenatal and postnatal periods of life can modify adaptive capacities in adulthoods. The hypothalamo–pituitary–adrenal axis may mediate an animal's responses to perinatal stressful events and thus serve as a neurobiological substrate of the behavioural consequences of these early events. However, little is known about the long‐term effects of prenatal stressors throughout the entire life of the animals. The focus of the present study was to examine the long‐term influences of a prenatal and postnatal stress on glucocorticoid secretion and cognitive performance. Prenatal stress of rat dams during the last week of pregnancy and postnatal daily handling of rat pups during the first 3 weeks of life were used as stressors. The long‐term effects of these manipulations were analysed using a longitudinal approach throughout the entire life of the animals, and were repeatedly tested in adulthood (4–7 months), middle age (13–16 months) and in later life (20–24 months). The study demonstrated that prenatal stress and postnatal handling induced opposite effects on both glucocorticoid secretion and cognitive performance. Prenatal stress accelerated the age‐related hypothalamo–pituitary–adrenal axis dysfunctions; indeed, circulating glucocorticoids levels of prenatally stressed middle‐aged animals are similar to old control ones, and also induced cognitive impairments. In contrast, postnatal handling protected from the age‐related neuroendocrine and behavioural alterations. These results show that the altered glucocorticoid secretion induced by early environmental manipulations is primary to the cognitive alterations observed only later in life and could be one cause of age‐related memory deficits.
Expression of potassium channels during postnatal differentiation of rabbit Müller glial cells
Authors: Bringmann A. , Biedermann B. , Reichenbach A.
Published: March 2003

The postnatal maturation of Müller glial cells from immature radial glial cells is accompanied by specific changes in the activity of distinct types of K+ channels, as shown by whole‐cell and cell‐attached records on freshly isolated cells from retinae of young (postnatal days 1–30, P1–P30) and adult rabbits. (i) The density of inwardly rectifying currents, providing the main K+ conductance in adult Müller cells, was very low (0.8 pA/pF) from P1 to P6 but increased rapidly thereafter until a relatively stable level of 11.0 pA/pF was established at P17. (ii) Transient (A‐type) K+ currents were expressed in all immature cells at a high density (9.6 pA/pF). After P12, both the percentage of cells with A‐type currents and the peak amplitudes of the currents (2.8 pA/pF) declined. (iii) Delayed rectifying K+ currents developed slowly until after P30. (iv) The postnatal maturation of radial glial cells was accompanied by a strong decrease in the activity of large‐conductance, Ca2+‐activated K+ channels, the open probability of which (measured at the resting membrane potential) decreased from 0.69 at P2–4 to 0.06 at P13–14. The developmental decrease of the activity of Ca2+‐activated K+ channels is assumed to be mainly caused by alteration of the resting membrane potential which developed from low values (–49 mV) at P1–6 to high adult values (–84 mV) after P13. The activity of each distinct type of K+ channel investigated is differently modulated by developmental regulation. This may reflect different functional requirements of immature and mature Müller cells.
Different types of calcium channels and secretion from bovine chromaffin cells
Authors: Lukyanetz E. A. , Neher E.
Published: March 2003

Bovine chromaffin cells possess several types of Ca2+ channels, and influx of Ca2+ is known to trigger secretion. However, discrepant information about the relative importance of the individual subtypes in secretion has been reported. We used whole‐cell patch‐clamp measurements in isolated cells in culture combined with fura‐2 microfluorimetry and pharmacological manipulation to determine the dependence of secretion on different types of Ca2+ channels. We stimulated cells with relatively long depolarizing voltage‐clamp pulses in a medium containing 60 mm CaCl2. We found that, within a certain range of pulse parameters, secretion as measured by membrane capacitance changes was mainly determined by the total cumulative charge of Ca2+ inflow and the basal [Ca2+] level preceding a stimulus. Blocking or reducing the contribution of specific types of Ca2+ channels using either 20 μm nifedipine plus 10 μm nimodipine or 1 μmωCTxGVIA (omega‐conotoxin GVIA) or 2 μmωCTxMVIIC (omega‐conotoxin MVIIC) reduced secretion in proportion to Ca2+ charge, irrespective of the toxin used. We conclude that for long‐duration stimuli, which release a large fraction of the readily releasable pool of vesicles, it is not so important through which type of channels Ca2+ enters the cell. Release is determined by the total amount of Ca2+ entering and by the filling state of the readily releasable pool, which depends on basal [Ca2+] before the stimulus. This result does not preclude that other stimulation patterns may lead to responses in which subtype specificity of Ca2+ channels matters.
A pre‐ and postsynaptic modulatory action of 5‐HT and the 5‐HT2A, 2C receptor agonist DOB on NMDA‐evoked responses in the rat medial prefrontal cortex
Authors: Arvanov Viktor L. , Liang Xiaofu , Magro Pellegrino , Roberts Roy , Wang Rex Y.
Published: March 2003

Intracellular recordings were made from pyramidal neurons in layers V and VI of the rat medial prefrontal cortex in slice preparations to investigate the effect of the serotonin 5‐HT2A,2C receptor agonist (–)‐1‐2,5‐dimethoxy‐4‐bromophenol‐2‐aminopropane (DOB) and 5‐hydroxytryptamine (5‐HT) on N‐methyl‐d‐aspartate (NMDA)‐induced responses. Bath application of either DOB or 5‐HT [in the presence of antagonists to 5‐HT1A, 5‐HT3 and γ‐aminobutytric acid (GABA) receptors] produced a concentration‐dependent biphasic modulation of the NMDA responses. They facilitated and inhibited NMDA responses at low (≤ 1 μm DOB and ≤ 50 μm 5‐HT) and higher concentrations, respectively. Both the facilitating and inhibitory action were blocked by the highly selective 5‐HT2A receptor antagonist r‐(+)‐α‐(2,3‐dimethoxyphenil)‐1‐[4‐fluorophenylethyl]‐4‐piperidinemethanol (M100907) and the 5‐HT2 receptor antagonist ketanserin, thus indicating that both facilitation and inhibition were mediated by the activation of the 5‐HT2A receptor subtype. However, the facilitating, but not inhibitory, action of DOB showed a marked desensitization, suggesting that the facilitation and inhibition of NMDA responses resulted from activation of different 5‐HT2A receptor subtypes and/or signal‐transduction pathways. Indeed, the selective PKC inhibitor chelerythrine and the Ca2+/CaM‐KII inhibitor KN‐93 prevented the facilitating and inhibitory action of DOB, respectively. We have generated several lines of evidence to indicate the following scenario. Low concentrations of DOB, at presynaptic nerve terminals, markedly enhance NMDA‐induced release of excitatory amino acids (EAAs), which then act upon both NMDA and non‐NMDA receptors to elicit inward current. The massive inward current masks the postsynaptic inhibitory action of DOB. At higher concentrations, DOB inhibits the release of EAAs and discloses the postsynaptic inhibitory action.
Subunit‐selective modulation of GABAA receptors by the non‐steroidal anti‐inflammatory agent, mefenamic acid
Authors: Halliwell R. F. , Thomas P. , Patten D. , James C. H. , Martinez‐Torres A. , Miledi R. , Smart T. G.
Published: March 2003

Mefenamic acid (MFA) has anti‐convulsant and pro‐convulsant effects in vivo, and has been shown to potentiate and inhibit GABAA (γ‐aminobutyric acid) receptors in vitro. In this study, whole‐cell currents were recorded from Xenopus oocytes and human embryonic kidney (HEK) cells expressing human recombinant GABAA receptors to resolve the molecular mechanisms by which MFA modulates GABAA receptor function. We demonstrate that MFA potentiated GABA‐activated currents for α1β2 γ2S (EC50 = 3.2 ± 0.5 μm), but not for α1β1 γ2S receptors. MFA also enhanced GABA‐activated responses and directly activated α1β2/β3 GABAA receptors, but inhibited responses to GABA on α1β1 constructs (IC50 = 40 ± 7.2 μm). A comparison of β1, β2 and β3 subunits suggested that the positive modulatory action of MFA involved asparagine (N) 290 in the second transmembrane domain (TM2) of the β2 and β3 subunits. Mutation of N290 to serine (S) markedly reduced modulation by MFA in α1β2(N290S)γ2S receptors, whereas α1β1(S290N)γ2S constructs revealed potentiated responses to GABA (EC50 = 7.8 ± 1.7 μm) and direct activation by MFA. The potentiation by MFA displayed voltage sensitivity. The direct activation, potentiation and inhibitory aspects of MFA action were predominantly conferred by the β subunits as the spontaneously active homomeric β1 and β3 receptors were susceptible to modulation by MFA. Molecular comparisons of MFA, loreclezole and etomidate, agents which exhibit similar selectivity for GABAA receptors, revealed their ability to adopt similar structural conformations. This study indicates that N290 in TM2 of β2 and β3 subunits is important for the regulation of GABAA receptor function by MFA. Our data provide a potential molecular mechanism for the complex central effects of MFA in vivo.
Increased glutathione levels in neurochemically identified fibre systems in the aged rat lumbar motor nuclei
Authors: Ramírez‐León Vania , Kullberg Susanna , Hjelle Ole Petter , Ottersen Ole Petter , Ulfhake Brun
Published: March 2003

The spinal cord motor nuclei have been the focus of a number of investigations exploring neurodegenerative mechanisms, e.g. excitotoxicity mediated by glutamate and oxidative stress. Here, high‐resolution quantitative post‐embedding immunocytochemistry with antibodies to oxidized and reduced glutathione (GSH), an ubiquitously expressed scavenger of free radicals, was used to examine if GSH synthesis is upregulated pre‐ and/or postsynaptically in the lumbar motor nuclei of aged (30 month old) rats. The purpose was, moreover, to resolve the extent of correlation between GSH expression, transmitter identity and degenerative changes. Tissue from young adult rats was co‐processed for comparison. The quantitative immunogold analysis revealed an increase in GSH‐immunoreactivity in both pre‐ and postsynaptic compartments in the lumbar motor nuclei of aged rats. Presynaptically, the enrichment of GSH‐immunoreactivity was seen in axonal boutons of normal appearance, and was furthermore restricted to the extra‐mitochondrial compartment. Postsynaptically, the aged rats disclosed, in comparison with young adults, higher values for GSH‐immunoreactivity both over mitochondria (+49%) and cytoplasmic matrix (+130%). When analysing the transmitter identity of the bouton profiles, it turned out that close to 50% of all glutamate‐immunoreactive boutons in the aged rats contained very high levels (> 40 gold particles/μm2) of GSH‐immunoreactivity. Strong GSH‐immunoreactivity was also a typical feature of a subset of axon terminal‐ and axon fibre‐like profiles in the aged rat that showed signs of axon dystrophy and degeneration. When comparing with normally appearing axon fibre profiles located in close vicinity, the population of aberrant axons had higher average levels of glutamate‐immunoreactivity (+93%), and lower average levels of glycine‐immunoreactivity (–88%). No difference was seen regarding the levels of GABA. The results of this study lend support to the idea that aging in the spinal cord motor nuclei is associated with an increased oxidative stress and indicate that different transmitter systems are differentially affected by the degenerative process.
Distribution of the voltage‐dependent calcium channel α1G subunit mRNA and protein throughout the mature rat brain
Authors: Craig P. J. , Beattie R. E. , Folly E. A. , Reeves M. B. , Priestley J. V. , Carney S. L. , Sher E. , Perez‐Reyes E. , Volsen S. G.
Published: March 2003

The molecular identity of a gene which encodes the pore‐forming subunit (α1G) of a member of the family of low‐voltage‐activated, T‐type, voltage‐dependent calcium channels has been described recently. Although northern mRNA analyses have shown α1G to be expressed predominantly in the brain, the detailed cellular distribution of this protein in the central nervous system (CNS) has not yet been reported. The current study describes the preparation of a subunit specific α1G riboprobe and antiserum which have been used in parallel in situ mRNA hybridization and immunohistochemical studies to localize α1G in the mature rat brain. Both α1G mRNA and protein were widely distributed throughout the brain, but variations were observed in the relative level of expression in discrete nuclei. Immunoreactivity for α1G was typically localized in both the soma and dendrites of many neurons. Whilst α1G protein and mRNA expression were often observed in cells known to exhibit T‐type current activity, some was also noted in regions, e.g. cerebellar granule cells, in which T‐type activity has not been described. These observations may reflect differences between the subcellular distribution of channels that can be identified by immunohistochemical methods compared with electrophysiological techniques.
Clonal expansion and cell dispersion in the developing mouse retina
Authors: Reese B. E. , Necessary B. D. , Tam P. P. L. , Faulkner‐Jones B. , Tan S. ‐S.
Published: March 2003

The present study has used two different approaches for labelling progenitor cells at the optic vesicle stage in order to examine patterns of clonal expansion and cellular dispersion within the developing retina. X‐inactivation transgenic mice and chimeric mice expressing the lacZ reporter transgene were examined during development and in adulthood to study the radial and tangential dispersion of proliferating neuroepithelial cells and postmitotic retinal cells of known identities. Chimeric retinas were used to measure tangential dispersion distances, while transgenic retinas were used to assess the frequency of tangential dispersion for individual populations of retinal neurons. Tangential dispersion is shown to be a universal feature of particular retinal cell types, being contrasted with the strictly radial dispersion of other cells. Tangential dispersion is a relatively short‐distance phenomenon, with distinct dispersion distances characteristic for cone, horizontal, amacrine and ganglion cells. Embryonic and postnatal retinas show that tangential dispersion occurs at different times for these distinct cell types, associated with their times of differentiation rather than their neurogenetic periods. These developmental results rule out the possibility that tangential dispersion is due to a passive displacement produced by the proliferation of later‐born cells, or to the lateral dispersion of a dividing sibling; rather, they are consistent with the hypothesis that tangential dispersion plays a role in the establishment of the orderly spatial distribution of retinal mosaics.
Filial imprinting in domestic chicks is associated with spine pruning in the associative area, dorsocaudal neostriatum
Authors: Bock Jörg , Braun Katharina
Published: March 2003

Juvenile emotionally modulated learning events are fundamental for the normal development of socio‐emotional competence and intellectual capabilities. Filial imprinting in the domestic chick provides a suitable model to investigate the neural mechanisms underlying such juvenile learning events. The forebrain area dorsocaudal neostriatum (Ndc), a multimodal integration area and presumed equivalent to mammalian parietotemporal association cortices, has been shown to be critically involved in this learning process. We investigated whether filial imprinting is associated with changes of synaptic connectivity in the Ndc. Quantitative measurements of spine densities of a large neuron type in the Ndc revealed a massive pruning of spine synapses after filial imprinting. Compared with 7‐day‐old naive control chicks, imprinted chicks displayed significantly lower spine frequencies on all dendritic segments. Since the average length of the dendritic segments did not change during imprinting, these results can be interpreted as a reduction of the absolute number of spine synapses on this neuron type. In a control region, the primary sensory forebrain area ectostriatum, spine density and dendritic length remained unchanged. These results indicate that synaptic pruning may represent a mechanism of selective synaptic reorganization in higher associative forebrain areas as a fundamental feature of juvenile learning events.
Differential coupling of G‐protein‐linked receptors to Ca2+ mobilization through inositol(1,4,5)trisphosphate or ryanodine receptors in cerebellar granule cells in primary culture
Authors: Del Río E. , Mclaughlin Mark , Downes C. P. , Nicholls D. G.
Published: March 2003

Rat cerebellar granule cells in primary culture possess muscarinic, metabotropic glutamatergic, histaminergic and α‐adrenergic receptors which couple to phosphoinositide‐specific phospholipase C. We have determined the ability of these receptors to elevate inositol(1,4,5)trisphosphate and to release intracellular calcium, in order to establish the correlation between these two responses. In resting cerebellar granule cells, only the muscarinic agonist carbachol evoked significant increases in both inositol(1,4,5)trisphosphate and cytoplasmic free Ca2+. Mild depolarization (20 mm KCl) enhanced inositol(1,4,5)trisphosphate elevation by carbachol and histamine, but not by noradrenaline or the metabotropic glutamate agonist 1S,3R ACPD. In contrast, Ca2+‐release responses were modified differently by 20 mm KCl‐depolarization: the responses to carbachol, histamine and 1S,3R ACPD, but not the responses to noradrenaline, were markedly enhanced. The contribution of ryanodine‐sensitive Ca2+‐release channels (ryanodine receptors) to the calcium release signal in depolarized cells was determined. Ryanodine (10 μm) inhibited most effectively the cytoplasmic Ca2+ elevation evoked by 1S,3R ACPD (> 90%), while Ca2+ release upon stimulation by carbachol and histamine was only inhibited by ≈ 60% and remained larger than in the absence of KCl. Our data are consistent with a specific coupling between metabotropic glutamate receptors and ryanodine‐sensitive Ca2+‐release channels which may not require generation of inositol(1,4,5)trisphosphate.
β‐Thymosin, a modulator of the actin cytoskeleton is increased in regenerating retinal ganglion cells
Authors: Roth Lukas W. A. , Bormann Peter , Wiederkehr Christa , Reinhard Eva
Published: March 2003

β‐Thymosins are actin monomer‐binding polypeptides that are expressed in a neuronal growth‐specific manner during embryonic development. Here, we show that regenerating retinal ganglion cells and non‐neuronal cells of the optic nerve transiently activate β‐thymosin transcription after optic nerve lesion in the zebrafish. In retinal cell cultures, β‐thymosin is found at highest concentration in growth cones, branching points and varicosities of neurite‐extending retinal ganglion cells. These places often exhibit reduced phalloidin staining, indicating that β‐thymosin promotes the disassembly of actin filaments. β‐Thymosin distribution within neurons in culture is distinct from actin, tubulin and the actin‐severing protein gelsolin. Ectopic expression of β‐thymosin in a central nervous system (CNS) catecholaminergic cell line leads to alterations in the shape of the cell bodies and neurites. β‐Thymosin‐positive cells spread more fully and exhibit an excessive degree of branching. We partially cloned two other actin‐binding proteins, profilin and gelsolin, and analysed their expression patterns. Profilin is constitutively expressed in virtually all cells. Gelsolin, like β‐thymosin, is selectively increased in regenerating retinal ganglion cells. During development, however, gelsolin mRNA is not detected in the nervous system. These findings indicate that distinct mechanisms control the actin cytoskeleton in embryonic and regenerating neurons, and that β‐thymosin may be a major regulator of actin dynamics in the zebrafish CNS.
The cellular and developmental expression of hrs‐2 in rat
Authors: Tsujimoto S. , Pelto‐Huikko M. , Aitola M. , Meister B. , Vik‐Mo E. O. , Davanger S. , Scheller R. H. , Bean A. J.
Published: March 2003

The molecular events underlying vesicular trafficking probably involve the formation and dissolution of protein complexes between integral components of the vesicle and its target membrane. SNAP‐25 is associated with the plasma membrane and is a component of a core protein complex thought to be essential for neurotransmitter release. We have previously characterized a protein, hrs‐2, that interacts with SNAP‐25 and inhibits secretion from permeabilized PC12 cells. The cellular localization and developmental expression patterns of a number of proteins involved in the secretion machinery have been documented. To understand more about the possible cellular role of hrs‐2, we have examined hrs‐2 distribution, developmental expression and subcellular localization in rat tissues and cell lines. We show herein that the distribution of hrs‐2 in brain and periphery parallels that of SNAP‐23/25, and that recombinant hrs‐2 binds to both SNAP‐23 and SNAP‐25. Hrs‐2 mRNA and protein are found almost ubiquitously in neurons in the brain. Hrs‐2 mRNA is expressed in the neural tube at E10 and thereafter mRNA and protein levels remain relatively constant in the whole brain through adulthood. In cultured PC12 cells, endogenous hrs‐2 is expressed in the cytoplasm and on the limiting membranes of multivesicular bodies. Overexpression of hrs‐2 in mammalian cells results in the appearance of large intracellular compartments that are labelled with hrs‐2 antibodies. The wide distribution, the interaction with SNAP‐23 and the localization on multivesicular body membranes suggest a general role for hrs‐2 in cellular machinery.
Effects of juvenile isolation and morphine treatment on social interactions and opioid receptors in adult rats: behavioural and autoradiographic studies
Authors: Van den Berg Caroline L. , Van Ree Jan M. , Spruijt Berry M. , Kitchen Ian
Published: March 2003

The consequences of juvenile isolation and morphine treatment during the isolation period on (social) behaviour and μ‐, δ‐ and κ‐opioid receptors in adulthood were investigated by using a social interaction test and in vitro autoradiography in rats. Juvenile isolation reduced social exploration in adults. Morphine treatment counteracted this reduction in isolated rats, but decreased social exploration in nonisolated rats. Self‐grooming and nonsocial exploration were enhanced after juvenile isolation. Morphine treatment had no effect on self‐grooming, but suppressed nonsocial exploration in isolated rats. With respect to the opioid receptors, juvenile isolation resulted in regiospecific increases in μ‐binding sites with a 58% increase in the basolateral amygdala and a 33% increase in the bed nucleus of stria terminalis. Morphine treatment in isolated rats reversed this upregulation in both areas. The number of δ‐binding sites did not differ between the experimental groups. A general upregulation of κ‐binding sites was observed after juvenile isolation, predominantly in the cortical regions, the hippocampus and the substantia nigra. Morphine treatment did not affect the upregulation of κ‐receptors. The results show that juvenile isolation during the play period causes long‐term effects on social and nonsocial behaviours and on the number of μ‐ and κ‐ but not δ‐opioid receptors in distinct brain areas. The number of μ‐receptors in the basolateral amygdala appears to be negatively correlated with the amount of social exploration in adult rats.
Morphology, morphometry and probability mapping of the pars opercularis of the inferior frontal gyrus: an in vivo MRI analysis
Authors: Tomaiuolo F. , MacDonald J. D. , Caramanos Z. , Posner G. , Chiavaras M. , Evans A. C. , Petrides M.
Published: March 2003

The pars opercularis occupies the posterior part of the inferior frontal gyrus. Electrical stimulation or damage of this region interferes with language production. The present study investigated the morphology and morphometry of the pars opercularis in 108 normal adult human cerebral hemispheres by means of magnetic resonance imaging. The brain images were transformed into a standardized proportional steoreotaxic space (i.e. that of Talairach and Tournoux) in order to minimize interindividual brain size variability. There was considerable variability in the shape and location of the pars opercularis across brains and between cerebral hemispheres. There was no significant difference or correlation between left and right hemisphere grey matter volumes. There was also no significant difference between sex and side of asymmetry of the pars opercularis. A probability map of the pars opercularis was constructed by averaging its location and extent in each individual normalized brain into Talairach space to aid in localization of activity changes in functional neuroimaging studies.
Calcium channel heterogeneity among cone photoreceptors in the tree shrew retina
Authors: Morgans Catherine W.
Published: March 2003

Retinal photoreceptors are depolarized in darkness and release neurotransmitter tonically. They respond to light by hyperpolarization and a concomitant reduction in transmitter release. The calcium‐dependent release of transmitter is coupled to graded changes in membrane potential by L‐type calcium channels in the photoreceptor terminals. This paper reports the immuno‐localization of an L‐type channel α1D subunit to most, but not all, synaptic terminals of cones in the tree shrew retina. Double labelling for the α1D subunit and the plasma membrane Ca2+‐ATPase, which has been shown to be present in all tree shrew cones, revealed a subpopulation of cone terminals that did not react with the α1D antibody. The nonimmunoreactive synaptic terminals represented ≈ 5.8% of the total and formed a highly regular array across the retina reminiscent of the blue cones. Double‐staining for the α1D subunit and blue cone opsin confirmed that these are the blue cones. The observed differences in calcium channel immunoreactivity between long and short wavelength cones points to previously unsuspected heterogeneity in the molecular machinery governing transmitter release from spectrally different cone types.
Partial denervation of the whiskerpad in adult mice: altered patterns of metabolic activity in barrel cortex
Authors: Bronchti Gilles , Corthésy Marc‐Etienne , Welker Egbert
Published: March 2003

One hundred days after unilateral C‐row nerve transection in the adult mouse whiskerpad, the caudal follicles of row C are reinnervated with ≈ 80 % of the original number of axons [Corthésy, M.‐E., Bronchti, G. & Welker, E. (1999) Eur. J. Neurosci., 11, 2835–2846]. To what extent is this reinnervation functional, and how does it interact with the enlargement of the functional representation of neighbouring rows subsequent to the denervation? Using the autoradiographic deoxyglucose method, we studied the whisker representation at the level of the barrel cortex 100 days post lesionem. We stimulated whiskers belonging to the denervated row C, the neighbouring rows B and D, or to all five rows A–E. The deoxyglucose uptake was measured in tangential sections through layer IV. The results indicate that, 100 days post lesionem, whiskers of row C reactivate their cortical barrels. However, (i) the magnitude of this cortical response was reduced; (ii) row C barrels were equivalently activated by the stimulation of the neighbouring rows; and (iii) when all whiskers were stimulated, we observed a significantly reduced deoxyglucose uptake over the representation of nonlesioned whiskers of rows D and E. Therefore, 100 days after the peripheral nerve lesion the reinnervation of the whiskerpad had not restored a normal pattern of activation at the level of the barrel cortex. We propose that this is due to a modified interaction between the representations of the various rows of follicles at the cortical level that does not return to normal.