bluuebunny/crossref_metadata_2025 huggingface dataset:
Dopaminergic signalling in the rodent neonatal suprachiasmatic nucleus identifies a role for protein kinase A and mitogen‐activated protein kinase in circadian entrainment
Authors: Schurov Irina L. , Hepworth Tracie J. , Hastings Michael H.
Published: March 2003

The circadian clock of the suprachiasmatic nuclei (SCN) of perinatal rodents is entrained by maternally derived cues. The SCN of neonatal Syrian hamsters express high‐affinity D1 dopamine receptors, and the circadian activity–rest cycle of pups can be entrained by maternal injection of dopaminergic agonists. The present study sought to characterize the intracellular pathways mediating dopaminergic signalling in neonatal rodent SCN. Both dopamine and the D1 agonist SKF81297 caused a dose‐dependent increase in phosphorylation of the transcriptional regulator Ca2+/cyclic AMP response element (CRE) binding protein (CREB) in suprachiasmatic GABA‐immunoreactive (‐IR) neurons held in primary culture. The D1 antagonist SCH23390 blocked this effect. Dopaminergic induction of pCREB‐IR in GABA‐IR neurons was also blocked by a protein kinase A (PKA) inhibitor, 5–24, and by the MAPK inhibitor, PD98059, whereas KN‐62, an inhibitor of Ca2+/calmodulin‐dependent (CAM) kinase II/IV was ineffective. Treatment with NMDA increased the level of intracellular Ca2+ in the cultured primary SCN neurons in Mg2+‐free medium, but SKF81297 did not. Blockade of CaM kinase II/IV with KN‐62 inhibited glutamatergic induction of pCREB‐IR in GABA‐IR neurons, whereas 5–24 was ineffective, confirming the independent action of Ca2+‐ and cAMP‐mediated inputs on pCREB. SKF81297 caused an increase in pERK‐IR in SCN cells, and this was blocked by 5–24, indicative of activation of MAPK via D1/cAMP. These results demonstrate that dopaminergic signalling in the neonatal SCN is mediated via the D1‐dependent activation of PKA and MAPK, and that this is independent of the glutamatergic regulation via Ca2+ and CaM kinase II/IV responsible for entrainment to the light/dark cycle.
The expression of Fos following kainic acid‐induced seizures is age‐dependent
Authors: Silveira Diosely C. , Sogawa Yoshimi , Holmes Gregory L.
Published: March 2003

The expression of limbic seizures following kainic acid (KA) administration starts at approximately postnatal day (P) 19 in rats. In this study we investigated whether the expression of Fos‐like immunoreactivity (Fos‐IR) in limbic regions occurs concomitantly with the behavioural expression of limbic seizures. Immunohistochemistry for c‐Fos protein was examined 1, 2, 4, 12 and 24 h following seizure onset (KA‐treated rats) or saline injections (controls) in immature and adult rats at P7, P13, P20 and P60. The expression of Fos‐IR in limbic structures following KA‐induced seizures is age‐dependent. There is a strong and selective induction of Fos‐IR in the CA3 region of the hippocampus following KA‐induced seizures in rats at P7. However, the expression of Fos‐IR in KA‐treated rats at P13, P20 and P60 involved other hippocampal structures in addition to CA3. Abundant induction of Fos‐IR was found in the CA1, CA3 and dentate gyrus (DG) in KA‐treated rats at P13, P20 and P60. While immature rats at P7 and P13 showed very few or no Fos‐IR neurons in most amygdala nuclei, rat pups at P20 showed strong induction of Fos‐IR in the amygdala. Our results demonstrated that the induction of Fos‐IR in most amygdala nuclei and the full expression of behavioural limbic seizures occur at the same developmental age, which is consistent with the idea that the amygdala may play a role in the modulation of limbic seizures.
The organization of visual object representations: a connectionist model of effects of lesions in perirhinal cortex
Authors: Bussey Timothy J. , Saksida Lisa M.
Published: March 2003

We have developed a simple connectionist model based on the idea that perirhinal cortex has properties similar to other regions in the ventral visual stream, or ‘what’ pathway. The model is based on the assumption that representations in the ventral visual stream are organized hierarchically, such that representations of simple features of objects are stored in caudal regions of the ventral visual stream, and representations of the conjunctions of these features are stored in more rostral regions. We propose that a function of these feature conjunction representations is to help to resolve ‘feature ambiguity’, a property of visual discrimination problems that can emerge when features of an object predict a given outcome (e.g. reward) when part of one object, but predict a different outcome when part of another object. Several recently reported effects of lesions of perirhinal cortex in monkeys have provided key insights into the functions of this region. In the present study these effects were simulated by comparing the performance of connectionist networks before and after removal of a layer of units corresponding to perirhinal cortex. The results of these simulations suggest that effects of lesions in perirhinal cortex on visual discrimination may be due not to the impairment of a specific type of learning or memory, such as declarative or procedural, but to compromising the representations of visual stimuli. Furthermore, we propose that attempting to classify perirhinal cortex function as either ‘perceptual’ or ‘mnemonic’ may be misguided, as it seems unlikely that these broad constructs will map neatly onto anatomically defined regions of the brain.
Perirhinal cortex resolves feature ambiguity in complex visual discriminations
Authors: Bussey, Timothy J. , Saksida Lisa M. , Murray Elisabeth A.
Published: March 2003

The present experiment tested predictions of a ‘perceptual–mnemonic/feature conjunction’ (PMFC) model of perirhinal cortex function. The model predicts that lesions of perirhinal cortex should disrupt complex visual discriminations with a high degree of ‘feature ambiguity’, a property of visual discrimination problems that can emerge when features of an object are rewarded when they are part of one object, but not when part of another. As feature ambiguity is thought to be the critical factor, such effects should be independent of the number of objects to be discriminated. This was tested directly, by assessing performance of control monkeys and monkeys with aspiration lesions of perirhinal cortex on a series of concurrent discriminations in which the number of object pairs was held constant, but the degree of feature ambiguity was varied systematically. Monkeys were tested in three conditions: Maximum Feature Ambiguity, in which all features were explicitly ambiguous (AB+, CD+, BC–, AD–; the biconditional problem); Minimum Feature Ambiguity, in which no features were explicitly ambiguous (AB+, CD+, EF–, GH–); and Intermediate Feature Ambiguity, in which half the features were explicitly ambiguous (AB+, CD+, CE–, AF–). The pattern of results closely matched that predicted by simulations using a connectionist network: monkeys with perirhinal cortex lesions were unimpaired in the Minimum Feature Ambiguity condition, mildly impaired in the Intermediate Feature Ambiguity condition and severely impaired in the Maximum Feature Ambiguity condition. These results confirm the predictions of the PMFC model, and force a reconsideration of prevailing views regarding perirhinal cortex function.
Opposing actions of neuropeptide Y and light on the expression of circadian clock genes in the mouse suprachiasmatic nuclei
Authors: Maywood Elizabeth S. , Okamura Hitoshi , Hastings Michael H.
Published: March 2003

The circadian clockwork of the hypothalamic suprachiasmatic nuclei (SCN) is synchronized by light and by nonphotic cues. The core timing mechanism is cell‐autonomous, based on an autoregulatory transcriptional/translational feedback loop of circadian genes and their products. This study investigated the effects of neuropeptide Y (NPY), a potent nonphotic resetting cue, and its interaction with light in regulating clock gene expression in the SCN in vivo. Injection of NPY adjacent to the SCN and transfer to darkness 7 h before scheduled lights out, shifted the circadian activity–rest cycle. Exposure to light for 1 h immediately after NPY infusion blocked this behavioural response. NPY‐induced shifts were accompanied by suppression of both mPer1 and mPer2 mRNA in the SCN, assessed 3 h after infusion. mPer mRNAs were not altered 1 h after infusion. Levels of mClock mRNA or mCLOCK immunoreactivity in the SCN were not affected by NPY at either time point. In parallel to the behavioural response, the NPY‐induced suppression of mPer genes in the SCN was attenuated when a light pulse was delivered immediately after the infusion. These results identify mPer1 and mPer2 as molecular targets for both photic and nonphotic (NPY‐induced) resetting of the clockwork, and support a synthetic model of circadian entrainment based upon convergent up‐ and downregulation of mPer expression.
Expression of CRABP I mRNA in fastigial cells of the developing cerebellum
Authors: Parenti Rosalba , Wassef Marion , Cicirata Federico
Published: March 2003

The expression of the cellular retinoic acid binding protein type I (CRABP I) was examined in the early phase of cerebellar development in the mouse. The CRABP I was expressed from embryonic day (E) 10.5 to E15.5 in the cerebellar plate. The expression was diffused at E10.5–E11.5 and thereafter localized in a small rostrodorsal area of the cerebellar territory of both sides. By using in situ hybridization and both immunohistochemistry and carbocyanine tracing procedures, we identified the fastigial cells as the population that expresses CRABP I in the cerebellum. The results suggest that these cells play a critical role in the early development of the cerebellum.
Postnatal maturation of Na+, K+, 2Cl– cotransporter expression and inhibitory synaptogenesis in the rat hippocampus: an immunocytochemical analysis
Authors: Marty Serge , Wehrlé Rosine , Alvarez‐Leefmans Francisco Javier , Gasnier Bruno , Sotelo Constantino
Published: March 2003

GABA, a major inhibitory neurotransmitter, depolarizes hippocampal pyramidal neurons during the first postnatal week. These depolarizations result from an efflux of Cl– through GABAA‐gated anion channels. The outward Cl– gradient that provides the driving force for Cl– efflux might be generated and maintained by the Na+, K+, 2Cl– cotransporter (NKCC) that keeps intracellular Cl– concentration above electrochemical equilibrium. The developmental pattern of expression of the cotransporter in the hippocampus is not known. We studied the postnatal distribution pattern of NKCC in the hippocampus using a monoclonal antibody (T4) against a conserved epitope in the C‐terminus of the cotransporter molecule. We also examined the temporal relationships between the developmental pattern of NKCC expression and the formation of perisomatic GABAergic synapses. This study was aimed at determining, with antivesicular inhibitory amino acid transporter (VIAAT) antibodies, whether perisomatic GABAergic synapses are formed preferentially at the time when GABA is depolarizing. During the first postnatal week, NKCC immunolabelling was restricted to cell bodies in the pyramidal cell layer and in the strata oriens and radiatum. In contrast, at postnatal day 21 (P21) and in adult animals little or no labelling occurred in cell bodies; instead, a prominent dendritic labelling appeared in both pyramidal and nonpyramidal neurons. The ultrastructural immunogold study in P21 rat hippocampi corroborated the light‐microscopy results. In addition, this study revealed that a portion of the silver‐intensified colloidal gold particles were located on neuronal plasmalemma, as expected for a functional cotransporter. The formation of inhibitory synapses on perikarya of the pyramidal cell layer was a late process. The density of VIAAT‐immunoreactive puncta in the stratum pyramidale at P21 reached four times the P7 value in CA3, and six times the P7 value in CA1. Electron microscopy revealed that the number of synapses per neuronal perikaryal profile in the stratum pyramidale of the CA3 area at P21 was three times higher than at P7, even if a concomitant 20% increase in the area of these neuronal perikaryal profiles occurred. It is concluded that, in hippocampal pyramidal cells, there is a developmental shift in the NKCC localization from a predominantly somatic to a predominantly dendritic location. The presence of NKCC during the first postnatal week is consistent with the hypothesis that this transporter might be involved in the depolarizing effects of GABA. The depolarizing effects of GABA may not be required for the establishment of the majority of GABAergic synapses in the stratum pyramidale, because their number increases after the first postnatal week, when GABA action becomes hyperpolarizing.
Distinct localization of GABAB receptors relative to synaptic sites in the rat cerebellum and ventrobasal thalamus
Authors: Kulik Ákos , Nakadate Kazuhiko , Nyíri Gábor , Notomi Takuya , Malitschek Barbara , Bettler Bernhard , Shigemoto Ryuichi
Published: March 2003

Metabotropic γ‐aminobutyric acid receptors (GABABRs) are involved in modulation of synaptic transmission and activity of cerebellar and thalamic neurons. We used subtype‐specific antibodies in pre‐ and postembedding immunohistochemistry combined with three‐dimensional reconstruction of labelled profiles and quantification of immunoparticles to reveal the subcellular distribution of pre‐ and postsynaptic GABABR1a/b and GABABR2 in the rat cerebellum and ventrobasal thalamus. GABABR1a/b and R2 were extensively colocalized in most brain regions including the cerebellum and thalamus. In the cerebellum, immunoreactivity for both subtypes was prevalent in the molecular layer. The most intense immunoreactivity was found in Purkinje cell spines with a high density of immunoparticles at extrasynaptic sites peaking at around 240 nm from glutamatergic synapses between spines and parallel fibre varicosities. This is in contrast to dendrites at sites around GABAergic synapses where sparse and random distribution was found for both subtypes. In addition, more than one‐tenth of the synaptic membrane specialization of spine–parallel fibre synapses were labelled at pre‐ or postsynaptic sites. Weak immunolabelling for both subtypes was also seen in parallel fibres but only rarely in GABAergic axons. In the ventrobasal thalamus, immunolabelling for both receptor subtypes was intense over the dendritic field of thalamocortical cells. Electron microscopy demonstrated an extrasynaptic localization of GABABR1a/b and R2 exclusively in postsynaptic elements. Quantitative analysis further revealed the density of GABABR1a/b around GABAergic synapses was higher than glutamatergic synapses on thalamocortical cell dendrites. The distinct localization of GABABRs relative to synaptic sites in the cerebellum and ventrobasal thalamus suggests that GABABRs differentially regulate activity of different neuronal populations.
Brain catecholamine metabolism in catechol‐O‐methyltransferase (COMT)‐deficient mice
Authors: Huotari Marko , Gogos Joseph A. , Karayiorgou Maria , Koponen Olli , Forsberg Markus , Raasmaja Atso , Hyttinen Juha , Männistö Pekka T.
Published: March 2003

Catechol‐O‐methyltransferase (COMT) catalyses theO‐methylation of compounds having a catechol structure and its main function involves the elimination of biologically active or toxic catechols and their metabolites. By means of homologous recombination in embryonic stem cells, a strain of mice has been produced in which the gene encoding the COMT enzyme is disrupted. We report here the levels of catecholamines and their metabolites in striatal extracellular fluid in these mice as well as in homogenates from different parts of the brain, under normal conditions and after acute levodopa administration. In immunoblotting studies, COMT‐knockout mice had no COMT protein in brain or kidney tissues but the amounts of catecholamine synthesizing and other metabolizing enzyme proteins were normal. Under normal conditions, COMT deficiency does not appear to affect significantly brain dopamine and noradrenaline levels in spite of relevant changes in their metabolites. This finding is consistent with previous pharmacological studies with COMT inhibitors and confirms the pivotal role of synaptic reuptake processes and monoamine oxidase‐dependent metabolism in terminating the actions of catecholamines at nerve terminals. In contrast, when COMT‐deficient mice are challenged withl‐dihydroxyphenylalanine, they show an extensive accumulation of 3,4‐dihydroxyphenylacetic acid and dihydroxyphenylglycol and even dopamine, revealing an important role for COMT under such situations. Notably, in some cases these changes appear to beComtgene dosage‐dependent, brain‐region specific and sexually dimorphic. Our results may have implications for improving the treatment of Parkinson's disease and for understanding the contribution of the natural variation in COMT activity to psychiatric phenotypes.
Magnetic oscillatory responses to lateralization changes of natural and artificial sounds in humans
Authors: Kaiser Jochen , Birbaumer Niels , Lutzenberger Werner
Published: March 2003

Oscillatory signals in human magnetoencephalogram were investigated as correlates of cortical network activity in response to sound lateralization changes. Previously, we found lateralized presentations of a monosyllabic word to elicit posterior temporo‐parietal gamma‐band activity, possibly reflecting synchronization of neuronal assemblies in putative auditory dorsal stream areas. In addition, beta activity was decreased over sensorimotor regions, suggesting the activation of motor networks involved in orientating. The present study investigated responses to lateralization changes of both a barking dog sound and a distorted noise to test whether beta desynchronization would depend on the sound's relevance for orientating. Eighteen adults listened passively to 900 samples of each sound in separate location mismatch paradigms with midline standards and both right‐ and left‐lateralized deviants. Lateralized distorted noises were accompanied by enhanced spectral amplitude at 58–73 Hz over right temporo‐parietal cortex. Left‐lateralized barking dog sounds elicited right and right‐lateralized sounds elicited bilateral temporo‐parietal spectral amplitude increases at ≈ 77 Hz. This replicated the involvement of posterior temporo‐parietal areas in auditory spatial processing. Only barking dog sounds, but not distorted noises, gave rise to 30 Hz desynchronization over contralateral sensorimotor areas, parieto‐frontal gamma coherence increases and beta coherence reductions between sensorimotor and prefrontal sensors. Apparently passive listening to lateralized natural sounds with a potential biological relevance led to an activation of motor networks involved in the automatic preparation for orientating. Parieto‐frontal coherence increases may reflect enhanced coupling of networks involved in the integration of auditory spatial and motor processes.
Alterations in trkB mRNA in the human prefrontal cortex throughout the lifespan
Authors: Romanczyk T. B. , Weickert C. Shannon , Webster M. J. , Herman M. M. , Akil M. , Kleinman J. E.
Published: March 2003

Signalling through tyrosine kinase receptor B (trkB) influences neuronal survival, differentiation and synaptogenesis. trkB exists in a full‐length form (trkBTK+), which contains a catalytic tyrosine kinase (TK) domain, and a truncated form (trkBTK–), which lacks this domain. In the rodent brain, expression of trkBTK+ decreases and trkBTK– increases during postnatal life. We hypothesized that both forms of trkB receptor mRNA would be present in the human neocortex and that the developmental profile of trkB gene expression in human may be distinct from that in rodent. We detected both trkBTK+ and trkBTK– mRNA in RNA extracted from multiple human brain regions by Northern blot. Using in situ hybridization, we found trkBTK+ mRNA in all cortical layers, with highest expression in layer IV and intermediate‐to‐high expression in layers III and V of the human dorsolateral prefrontal cortex. trkBTK+ mRNA was present in neurons with both pyramidal and nonpyramidal shapes in the dorsolateral prefrontal cortex. trkBTK+ mRNA levels were significantly increased in layer III in young adults as compared with infants and the elderly. In the elderly, trkBTK+ mRNA levels were reduced markedly in all cortical layers. Unlike the mRNA encoding the full‐length form of trkB, trkBTK– mRNA was distributed homogeneously across the grey matter, and trkBTK– mRNA levels increased only slightly during postnatal life. The results suggest that neurons in the human dorsolateral prefrontal cortex are responsive to neurotrophins throughout postnatal life and that this responsiveness may be modulated during the human lifespan.
Orexin receptor‐1 (OX‐R1) immunoreactivity in chemically identified neurons of the hypothalamus: focus on orexin targets involved in control of food and water intake
Authors: Bäckberg Matilda , Hervieu Guillaume , Wilson Shelagh , Meister Björn
Published: March 2003

The neuropeptides orexin‐A and orexin‐B are produced in neurons of the lateral hypothalamic area and have been implicated to be involved in the regulation of food/water intake and sleep–wake control. The orexins act at two different G‐protein‐coupled orexin receptors (OX‐R1 and OX‐R2) that are derived from separate genes and expressed differentially throughout the central nervous system. In the present study, we have used a polyclonal antipeptide antiserum to analyse in detail the distribution of OX‐R1‐immunoreactive neurons in the rat hypothalamus. In order to identify the chemical mediators of orexin action in the hypothalamus, the OX‐R1‐containing neurons were characterized with regard to the content of peptides shown previously to affect ingestive and drinking behaviour. Neurons containing OX‐R1 immunoreactivity were widely distributed in the hypothalamus with cell bodies located in the suprachiasmatic, periventricular, paraventricular (both magno‐ and parvocellular division), supraoptic, arcuate, ventromedial, dorsomedial and tuberomammillary nuclei and the lateral hypothalamic area. In magnocellular neurons of the paraventricular and supraoptic nuclei, OX‐R1 immunoreactivity was seen in both vasopressin‐ and oxytocin‐containing neurons. OX‐R1 immunoreactivity was demonstrated in vasopressin and vasoactive intestinal polypeptide (VIP) neurons of the suprachiasmatic nucleus, in somatostatin neurons of the periventricular nucleus and in corticotropin‐releasing hormone (CRH) neurons of the parvocellular paraventricular nucleus. In the arcuate nucleus, OX‐R1 immunoreactivity was present in neuropeptide Y (NPY) and agouti‐related peptide (AGRP) neurons of the ventromedial part as well as in proopiomelanocortin (POMC) and cocaine‐ and amphetamine‐regulated transcript (CART) neurons of the ventrolateral division. In the lateral hypothalamic area, OX‐R1 immunoreactivity was demonstrated in melanin‐concentrating hormone (MCH)‐ and orexin‐containing neurons. In the hypothalamic tuberomammillary nucleus, OX‐R1‐immunoreactivity was shown in many histamine‐containing neurons. The results support the idea that orexins have important actions on hypothalamic neurons that control food intake and fluid balance, but also that orexins may regulate other neuroendocrine systems.
Mu and kappa opioid agonists modulate ventral tegmental area input to the ventral pallidum
Authors: Mitrovic Igor , Napier T. Celeste
Published: March 2003

The ventral pallidum (VP) is situated at the convergence of midbrain dopamine and accumbal opioid efferent projections. Using in vivo electrophysiological procedures in chloral hydrate‐anaesthetized rats, we examined whether discrete application of µ‐ [D‐Ala2,N‐Me‐Phe4,Gly‐ol5 (DAMGO)] or κ− (U50488) opioid receptor agonists could alter VP responses to electrical stimulation of ventral tegmental area. Rate suppressions occurred frequently following ventral tegmental area stimulation. Consistent with an involvement of dopamine in this effect, none of the 12 spontaneously active ventral pallidal neurons recorded in rats that had monoamines depleted by reserpine responded to electrical stimulation of ventral tegmental area. Moreover, in intact rats, the dopamine antagonist flupenthixol attenuated evoked suppression in 100% of the neurons tested; however, the GABAA antagonist bicuculline was able to slightly attenuate the response in 50% of the neurons tested. These observations concur with our previous studies in indicating that ventral tegmental area stimulation releases dopamine (and sometimes GABA) onto ventral pallidal neurons. Both DAMGO and U50488 decreased the inhibitory effects of ventral tegmental area stimulation. These effects on the endogenously released transmitter differed from those seen with exogenously applied dopamine, for DAMGO did not alter the efficacy or potency of microiontophoretically applied dopamine. Taken together, these observations suggest that the interaction between DAMGO and dopamine does not occur at a site that is immediately postsynaptic to the dopaminergic input within the VP, but rather that opioid modulation involves mechanisms governing presynaptically released dopamine. These modulatory processes would enable ventral pallidal opioids to gate the influence of ventral tegmental area dopamine transmission on limbic system outputs at the level of the VP.
Knocking out the glial glutamate transporter GLT‐1 reduces glutamate uptake but does not affect hippocampal glutamate dynamics in early simulated ischaemia
Authors: Hamann Martine , Rossi David J. , Marie Hélène , Attwell David
Published: March 2003

Glutamate release in ischaemia triggers neuronal death. The major glial glutamate transporter, GLT‐1, might protect against glutamate‐evoked death by removing extracellular glutamate, or contribute to death by reversing and releasing glutamate. Previous studies of the role of GLT‐1 in ischaemia have often used the GLT‐1 blocker dihydrokainate at concentrations that affect transporters other than GLT‐1 and which affect kainate, N‐methyl‐d‐aspartate (NMDA) and α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid (AMPA) receptors. In hippocampal slices from postnatal day 14 mice lacking GLT‐1, the current response of area CA1 pyramidal cells to superfused AMPA and NMDA (which are not taken up) was unaffected, whereas the response to 100 µm glutamate was more than doubled relative to that in wild‐type littermates, a finding consistent with a decrease in glutamate uptake. In response to a few minutes of simulated ischaemia, pyramidal cells in wild‐type mice showed a large and sudden inward glutamate‐evoked current [the anoxic depolarization (AD) current], which declined to a less inward plateau. In mice lacking GLT‐1, the time to the occurrence of the AD current, its amplitude, the size of the subsequent plateau current and the block of the plateau current by glutamate receptor blockers were all indistinguishable from those in wild‐type mice. We conclude that GLT‐1 does not contribute significantly to glutamate release or glutamate removal from the extracellular space in early simulated ischaemia. These data are consistent with glutamate release being by reversal of neuronal transporters, and with uptake into glia being compromised by the ischaemia‐evoked fall in the level of ATP needed to convert glutamate into glutamine.
A peripheral nervous system actin‐binding protein regulates neurite outgrowth
Authors: Ravenall Samantha J. , Gavazzi Isabella , Wood John N. , Akopian Armen N.
Published: March 2003

Difference cloning has identified a Villin‐like mRNA transcript expressed selectively in peripheral sensory and sympathetic neurons. Pervin, the encoded 820‐amino acid protein, has 60% identity with Villin and is the rat homologue of Advillin. Coimmunoprecipitation studies demonstrate that Pervin and actin interact in vivo. Transfection of COS‐7 epithelial cell lines demonstrates colocalization of epitope‐tagged Pervin with green fluorescent protein‐actin and results in an increase in process formation. This effect is abolished when the putative actin‐bundling headpiece of Pervin is deleted. Biolistic transfection of primary cultures of rat dorsal root ganglion sensory neurons also results in increased neurite outgrowth with FLAG‐tagged Pervin. Deletion of the actin‐bundling headpiece inhibits normal neurite growth. These data suggest that Pervin may play a significant role in regulating process outgrowth in peripheral neurons through a mechanism that involves the activity of an actin‐bundling domain.
Modulation by 5‐hydroxytryptamine of nicotinic acetylcholine responses recorded from an identified cockroach (Periplaneta americana) motoneuron
Authors: Butt Simon J. B. , Pitman Robert M.
Published: March 2003

Recordings from the soma of the cockroach (Periplaneta americana) fast coxal depressor motoneuron (Df) were made while acetylcholine (ACh) was regularly pressure‐applied locally from a micropipette. The modulatory effects upon these nicotinic ACh responses of bath‐applied 5‐hydroxytryptamine (5‐HT, serotonin), dopamine and octopamine were investigated under either current‐clamp or voltage‐clamp conditions. The biogenic amines reversibly suppressed, but never totally abolished, ACh responses, 5‐HT being the most potent, with a threshold near 10−6 m (EC50 = 5 × 10−5 m). Occlusion experiments indicate that the amines share a common mechanism at the level of either receptors or second messenger pathways. The amines also modulated responses to nicotine or carbachol (each of which resists hydrolysis by acetylcholinesterases), indicating that the amines did not act by accelerating ACh degradation. Pharmacological antagonists were used in an attempt to characterize the receptor responsible for amine‐mediated modulation. Although a number of antagonists mimicked the action of amines rather than producing blockade, the antagonistic actions of LSD and RS23597 pointed strongly to a receptor‐mediated mechanism, but did not allow receptor identification. The magnitude of the modulatory effect of 5‐HT was significantly reduced by intracellular guanosine‐5′‐O‐(2‐thiodiphosphate) (GDP‐β‐S), indicating involvement of a G‐protein. Intracellular injection of the calcium chelator BAPTA did not block the modulatory effect of 5‐HT, showing that the amines do not operate through the calcium‐dependent pathway by which muscarinic receptors act on nicotinic currents. The adenylate cyclase inhibitor dideoxyadenosine (DDA), on the other hand, did attenuate the action of 5‐HT, suggesting involvement of cyclic AMP.
Insulin‐like growth factor‐II/Mannose‐6‐phosphate receptor in the spinal cord and dorsal root ganglia of the adult rat
Authors: Hawkes C. , Kar S.
Published: March 2003

The insulin‐like growth factor‐II/mannose‐6‐phosphate (IGF‐II/M6P) receptor is a multifunctional transmembrane glycoprotein, which interacts with a number of molecules, including IGF‐II and M6P‐containing lysosomal enzymes. The receptor is widely distributed throughout the brain and is known to be involved in lysosomal enzyme trafficking, cell growth, internalization and degradation of IGF‐II. In the present study, using autoradiographic, Western blotting and immunocytochemical methods, we provide the first report that IGF‐II/M6P receptors are discretely distributed at all major segmental levels of the spinal cord and dorsal root ganglia of the adult rat. In the spinal cord, a high density of [125I]IGF‐II binding sites was evident in the ventral horn (lamina IX) and in areas around the central canal (lamina X), whereas intermediate grey matter and dorsal horn were associated with moderate receptor levels. The dorsal root ganglia exhibited rather high density of [125I]IGF‐II binding sites. Interestingly, meninges present around the spinal cord displayed highest density of [125I]IGF‐II binding compared to any given region of the spinal grey mater or the dorsal root ganglia. Western blot results indicated the presence of the IGF‐II/M6P receptor at all major levels of spinal cord and dorsal root ganglia, with little segmental variation. At the cellular level, spinal motorneurons demonstrated the most intense IGF‐II/M6P receptor immunoreactivity, followed by interneurons in the intermediate region and deeper dorsal horn. Some scattered IGF‐II/M6P immunoreactive fibers were found in the superficial laminae of the dorsal horn and dorsolateral funiculus. The meninges of the spinal cord also seemed to express IGF‐II receptor immunoreactivity. In the dorsal root ganglia, receptor immunoreactivity was evident primarily in a subset of neurons of all diameters. These results, taken together, provide anatomical evidence of a role for the IGF‐II/M6P receptor in general cellular functions such as transport of lysosomal enzymes and/or internalization followed by clearance of IGF‐II in the spinal cord and dorsal root ganglia.
Alpha‐adrenoreceptor activation modulates swimming via glycinergic and GABAergic inhibitory pathways in Xenopus laevis tadpoles
Authors: Merrywest Simon D. , Fischer Hanno , Sillar Keith T.
Published: March 2003

This study focuses upon the network pathways underlying the adrenoreceptor‐mediated modulation of fictive swimming in the immobilized Xenopus laevis tadpole. As shown recently, noradrenaline (NA) increases cycle periods while simultaneously reducing the rostrocaudal delay in head‐to‐tail firing and the duration of swimming episodes. Furthermore, both swimming frequency and duration are reduced by selective pharmacological activation of α1‐ and/or α2‐adrenoreceptors, while α1‐receptor activation also reduces rostrocaudal delays. We show that NA could still modulate aspects of swimming after blocking either glycine or GABAA receptors with strychnine and bicuculline, respectively. Furthermore, after prior application of NA, strychnine could counteract noradrenergic effects on cycle periods and rostrocaudal delays, while bicuculline could counteract effects on cycle periods, suggesting that these two fast inhibitory pathways are both involved in the NA modulation of swimming. In addition, blocking glycine receptors reduced the effects of α1‐receptors on cycle periods and delays, while blocking GABAA receptors had no effect. Blocking either glycine or GABAA receptors, however, lessened the reduction in swimming frequency by α2‐receptors. In addition, pre‐application of bicuculline prevented a reduction in episode durations by NA, α1‐ and α2‐receptors. Our findings suggest that the noradrenergic modulation of Xenopus swimming is mediated via α‐adrenoreceptors interacting with both glycinergic and GABAergic inhibitory pathways. Both α1‐ and α2‐receptor activation influences the GABAergic pathway controlling the duration of swimming episodes and is involved in the glycinergic modulation of the swimming rhythm and its longitudinal co‐ordination, with α2‐receptors additionally affecting swimming frequency through GABAergic pathways.
Bilateral overactivation of the sensorimotor cortex in the unilateral rodent model of Parkinson's disease – a functional magnetic resonance imaging study
Authors: Pelled Galit , Bergman Hagai , Goelman Gadi
Published: March 2003

Functional magnetic resonance imaging (fMRI) is used to investigate the basal ganglia (BG)–cortex circuit using a rat model of Parkinson's disease (PD). The model involves a unilateral destruction of the right substantia nigra by intranigral injection of the dopaminergic neurotoxin 6‐hydroxydopamine. Volume of cortical activity was measured by the blood oxygenation level‐dependent contrast method while applying electrical forepaw stimulation. The main findings are the following. (i) Contrary to the predictions of the classic model but in line with recent experimental results (positron emission tomography, fMRI and electrophysiology), an increased cortical activity in the sensorimotor cortex of PD rats compared with sham‐operated or normal rats was found. (ii) A diffuse neuronal activity at large cortical areas that were not related directly to the stimulation used, was observed. (iii) No difference was found between the lesion and the nonlesion hemispheres when the left or the right forepaw was stimulated; both cortices show significant overactivation of the sensorimotor cortices in addition to diffuse cortical activation. The last finding could be explained by either corticocortical connections or by bilateral BG–cortex connections. These finding suggest that the mutual influence of the two hemispheres is important in the pathophysiology of the BG–cortex circuit and might be crucial in predicting treatments.
NMDA antagonists exacerbate neuronal death caused by proteasome inhibition in cultured cortical and striatal neurons
Authors: Snider B. Joy , Tee Lee Y. , Canzoniero Lorella M. T. , Babcock Debra J. , Choi Dennis W.
Published: March 2003

The proteasome is involved in multiple cellular processes including control of the cell cycle, apoptosis and intracellular signalling; loss of proteasome function has been postulated to participate in the pathogenesis of triplet repeat diseases. We examined the vulnerability of central neurons to proteasome inhibition and tested the ability of anti‐excitotoxic and anti‐apoptotic treatments to attenuate proteasome inhibition‐induced neuronal death. Exposure of murine neocortical cultures to proteasome inhibitors (0.1–10 µmclasto‐lactacystin β‐lactone or MG‐132) for 48 h resulted in widespread neuronal death associated with a reduction in intracellular free calcium; higher inhibitor concentrations killed astrocytes. Cultured striatal neurons were more vulnerable than cortical neurons. Within each population, the NADPH diaphorase‐positive neuronal subpopulation was more vulnerable than the general neuronal population. Enhancing calcium entry with S(–)BayK8644 or kainate, or blocking apoptosis with cycloheximide, actinomycin D or Z‐VAD.FMK attenuated neuronal death, whereas, reducing calcium entry with NMDA antagonists or R(+)BayK8644 potentiated neuronal death. These findings suggest that proteasome inhibition can induce selective neuronal apoptosis associated with intracellular calcium starvation, and point to manipulation of intracellular calcium as a specific therapeutic strategy. In particular, concern is raised that glutamate receptor antagonists might exacerbate, rather than attenuate, proteasome inhibition‐induced neuronal death.
Brain macrophages inhibit gap junctional communication and downregulate connexin 43 expression in cultured astrocytes
Authors: Rouach N. , Calvo C.‐F. , Glowinski J. , Giaume C.
Published: March 2003

Astrocytes are typically interconnected by gap junction channels that allow, in vitro as well as in vivo, a high degree of intercellular communication between these glial cells. Using cocultures of astrocytes and neurons, we have demonstrated that gap junctional communication (GJC) and connexin 43 (Cx43) expression, the major junctional protein in astrocytes, are controlled by neuronal activity. Moreover, neuronal death downregulates these two parameters. Because in several brain pathologies neuronal loss is associated with an increase in brain macrophage (BM) density, we have now investigated whether coculture with BM affects astrocyte gap junctions. We report here that addition of BM for 24 h decreases the expression of GJC and Cx43 in astrocytes in a density‐dependent manner. In contrast, Cx43 is not detected in BM and no heterotypic coupling is observed between the two cell types. A soluble factor does not seem to be involved in these inhibitions because they are not observed either in the presence of BM conditioned media or in the absence of direct contact between the two cell types by using inserts. These observations could have pathophysiological relevance as neuronal death, microglial proliferation and astrocytic reactions occur in brain injuries and pathologies. Because astrocyte interactions with BM and dying neurons both result in the downregulation of Cx43 expression and in the inhibition of GJC, a critical consequence on astrocytic phenotype in those situations could be the inhibition of gap junctions.
Forced swimming triggers vasopressin release within the amygdala to modulate stress‐coping strategies in rats
Authors: Ebner Karl , Wotjak Carsten T. , Landgraf Rainer , Engelmann Mario
Published: March 2003

Previously, we have demonstrated that forced swimming triggers the release of arginine vasopressin (AVP) within the septum of rats, where AVP modulates stress‐coping strategies. The present study was designed to examine the effects of forced swimming on the release of AVP within the amygdala. Therefore, adult male Wistar rats were chronically implanted with a microdialysis probe aimed at the amygdala to monitor the local release of AVP under both resting and stress conditions. A 10‐min forced swimming session caused a significant increase in the extracellular AVP concentration (to 366 ± 90% of baseline; P < 0.05) within this brain area. In a subsequent experiment we investigated the physiological impact of the stressor‐induced release of AVP by administrating the AVP V1 receptor antagonist d(CH2)5Tyr(Me)AVP into the amygdala via inverse microdialysis. Bilateral antagonist treatment modulated the behavioural response acutely by increasing the time the animals spent struggling and by reducing the time the animals floated. Our results demonstrate a significant activation of the vasopressinergic system within the amygdala in response to forced swimming. AVP released within the amygdala seems to be involved in the generation of passive coping strategies in stressful situations. Taken together with previous findings the results of the present study suggest that AVP is released within septum and amygdala to balance the behavioural response during forced swimming.
The human startle reflex and pons activation: a regional cerebral blood flow study
Authors: Pissiota Anna , Frans Örjan , Fredrikson Mats , Långström Bengt , Flaten Magne Arve
Published: March 2003

Using positron emission tomographic measurements of regional cerebral blood flow, we report activation of a medial pons area in humans during acoustic startle stimulation. Eight healthy volunteers were scanned during rest and when presented startle‐eliciting stimuli. We performed a theory‐driven directed search for activity in the nucleus reticularis pontis caudalis, situated in the pons. Because habituation of cerebellar activity during acoustic startle repetition has been reported [Timmann, D., Musso, C., Kolb, F.P., Rijntjes, M., Juptner, M., Muller, S.P., Diener, H.C. & Weiller, C. (1998) J. Neurol. Neurosurg. Psychiatry65, 771–773], we also predicted habituation in the cerebellum and in the pons as a function of startle repetition. Measurements of eye electromyography validated the presence of a startle response and its habituation. Analysis of regional cerebral blood flow revealed higher neural activity during startle stimulation than at rest in a medial pons area consistent with the location of the pontine reticular nucleus. As a consequence of startle repetition, regional cerebral blood flow increased in the medial cerebellum, and habituated in the ventral cerebellum and in a ventral pons area separate from the pontine reticular nucleus. In the ventral pons, but not in the pontine reticular nucleus, regional cerebral blood flow and the startle reflex were positively correlated. In the cerebellum both positive and negative correlations with the startle reflex were observed. Thus we conclude that the neurofunctional correlates of the startle circuit and its habituation in humans are similar to that previously described in animals.
A single olfactory receptor specifically binds a set of odorant molecules
Authors: Gaillard Isabelle , Rouquier Sylvie , Pin Jean‐Philippe , Mollard Patrice , Richard Sylvain , Barnabé Cécile , Demaille Jacques , Giorgi Dominique
Published: March 2003

The sense of smell is mediated by the initiation of action potential in olfactory sensory neurons during odor stimulation. However, little is known about odorant‐olfactory receptor (OR) recognition mechanisms. In the present work, we identified the structural motifs of odorant molecules required to activate mouse OR912‐93 by detection of the odorant response using calcium measurement in cells transfected with OR and Gαq and Gα15 proteins. The use of sets of odorants led to the identification of ketones with an aliphatic carbon chain length ≥ four carbon atoms and a carbonyl group preferentially located in position C2 or C3. The threshold of detection of these odorants is as low as 10−6−10−8m. No other odorant ligand, out of 70 representatives of the odorant world, was active. The human ortholog of OR912‐93 is not functional, suggesting that apart from a stop‐mutation located at the 5′‐end that was corrected in the construct, it incurred other deleterious mutations during evolution.
Differential subcellular localization of the 5‐HT3‐As receptor subunit in the rat central nervous system
Authors: Miquel M.‐C. , Emerit M. B. , Nosjean A. , Simon A. , Rumajogee P. , Brisorgueil M.‐J. , Doucet E. , Hamon M. , Vergé D.
Published: March 2003

Following the cloning and sequencing of the A subunit of the 5‐HT3 receptor, two alternatively spliced isoforms, 5‐HT3‐AS and 5‐HT3‐AL, have been identified. In order to analyse the distribution of the receptor, a polyclonal antibody has been produced against the short form which is the most abundant in the central nervous system [Doucet et al. (2000) Neuroscience 95, 881–892]. As expected from the recognition of functional 5‐HT3 receptors, immunostaining by this anti‐5‐HT3‐R‐AS antibody matched the distribution of the high‐affinity 5‐HT3 binding sites in the rat brain and spinal cord. 5‐HT3‐AS‐like immunoreactivity was detected at low levels in the limbic system, particularly in the amygdala and the hippocampus, and in the frontal, piriform and entorhinal cortices. High levels of immunoreactivity were found in the brainstem, mainly in the nucleus tractus solitarius and the nucleus of the spinal tract of the trigeminal nerve, and in the dorsal horn of the spinal cord. At the ultrastructural level, immunostaining was generally found associated with axons and nerve terminals (70–80%) except in the hippocampus, where labelled dendrites were more abundant (56%). This preferential localization on nerve endings is consistent with the well‐documented physiological role of 5‐HT3 receptors in the control of neurotransmitter release. However, the different distribution in the hippocampus raises the question of whether differential addressing mechanisms exist for preferentially targeting 5‐HT3 receptors to postsynaptic dendritic sites as compared to presynaptic nerve endings, depending on the nature of the neurons bearing these receptors.
Speech listening specifically modulates the excitability of tongue muscles: a TMS study
Authors: Fadiga Luciano , Craighero Laila , Buccino Giovanni , Rizzolatti Giacomo
Published: March 2003

The precise neural mechanisms underlying speech perception are still to a large extent unknown. The most accepted view is that speech perception depends on auditory‐cognitive mechanisms specifically devoted to the analysis of speech sounds. An alternative view is that, crucial for speech perception, it is the activation of the articulatory (motor) gestures that generate these sounds. The listener understands the speaker when his/her articulatory gestures are activated (motor theory of speech perception). Here, by using transcranial magnetic stimulation (TMS), we demonstrate that, during speech listening, there is an increase of motor‐evoked potentials recorded from the listeners' tongue muscles when the presented words strongly involve, when pronounced, tongue movements. Although these data do not prove the motor theory of speech perception, they demonstrate for the first time that word listening produces a phoneme specific activation of speech motor centres.