bluuebunny/crossref_metadata_2025 huggingface dataset:
Late embryonic expression of AMPA receptor function in the CA1 region of the intact hippocampus in vitro
Authors: Diabira D. , Hennou S. , Chevassus‐au‐Louis N. , Ben‐Ari Y. , Gozlan H.
Published: March 2003

Studies in slices suggest that α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptor‐mediated synaptic currents are not present in CA1 (Cornu ammonis) pyramidal neurons at birth (P0). We have re‐examined this issue in the rat intact hippocampal formation (IHF) in vitro. Injections of biocytin or carbocyanine show that the temporo‐ammonic, commissural and Schaffer collateral pathways are present at birth in the marginal zone of CA1. Electrical stimulation of these pathways evoked field excitatory postsynaptic potentials (fEPSPs) in the marginal zone of CA1 from embryonic day 19 (E19) to postnatal day 9 (P9). These fEPSPs are mediated by synaptic AMPA receptors as they are reduced or completely blocked by: (i) tetrodotoxin; (ii) high divalent cation concentrations; (iii) the adenosine A1 receptor agonist CPA; (iv) anoxic episodes; (v) the selective AMPA receptor antagonist 1‐(4‐aminophenyl)‐3‐methylcarbamyl‐4‐methyl‐7,8‐methylenedioxy‐3,4‐dihydro‐5H‐2,3‐benzodiazepine (GYKI‐53655) or the mixed AMPA‐kainate receptor antagonists 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) and 6‐nitro‐7‐sulphamoylbenzo[f]quinoxaline‐2,3‐dione (NBQX). The amplitude of the fEPSPs is also reduced by d(–)‐2‐amino‐5‐phosphonopentanoic acid (D‐APV) and its duration is increased by bicuculline suggesting the participation of N‐methyl‐d‐aspartate (NMDA) and GABAA (γ‐aminobutyric acid) receptors. Finally, AMPA receptor‐mediated fEPSPs are also recorded in P0 slices, but they are smaller and more labile than in the IHF. Our results suggest that in embryonic CA1 neurons, glutamate acting on AMPA receptors already provides a substantial part of the excitatory drive and may play an important role in the activity‐dependent development of the hippocampus. Furthermore, the IHF may be a convenient preparation to investigate the properties of the developing hippocampus.
Analysis of neurotrophic effects of hepatocyte growth factor in the adult hypoglossal nerve axotomy model
Authors: Okura Yoshio , Arimoto Hirohiko , Tanuma Naoyuki , Matsumoto Kunio , Nakamura Toshikazu , Yamashima Tetsumori , Miyazawa Takahito , Matsumoto Yoh
Published: March 2003

Recent studies have shown that hepatocyte growth factor (HGF) promotes the survival of embryonic motor neurons. However, it remains unclear whether HGF has trophic effects on mature motor neurons. In the present study, we examined the effects of HGF on adult motoneurons using the hypoglossal nerve transection model. In adult rats, neurons in the hypoglossal nucleus show a dramatic loss of choline acetyltransferase (ChAT) protein and mRNA after the axotomy. This reduction of ChAT was markedly prevented when HGF was administered continuously at the cut end of the nerve using an osmotic pump. The HGF receptor, c‐met, protein and mRNA, which were faintly expressed in hypoglossal neurons under normal conditions, gradually increased and reached maximal levels 2 weeks after the axotomy. Administration of HGF reduced this c‐met upregulation almost to normal levels. We also quantified HGF mRNA in the tongue and hypoglossal nucleus. The tongue contained abundant HGF mRNA, whereas the nucleus contained only low levels. Interestingly, the HGF mRNA level in the nucleus did not increase after the axotomy. These findings suggest that HGF is principally produced in the tongue and contributes to maintain ChAT expression in the nucleus. HGF produced in the hypoglossal nucleus alone after disconnection from the tongue may not be sufficient for the maintenance of the motor neuron function. Thus, exogenously applied HGF was effective to prevent the downregulation of ChAT activities. These findings provide a strong rationale for the potential clinical use of HGF for the treatment of motor neuron degenerative disease.
Behavioural trait of reactivity to novelty is related to hippocampal neurogenesis
Authors: Lemaire V. , Aurousseau C. , Le Moal M. , Abrous D. N.
Published: March 2003

The hippocampal formation is one of the brain areas where neurogenesis persists during adulthood, with new neurons being continuously added to the population of dentate granule cells. However, the functional implications of this neurogenesis are unknown. On the other hand, the hippocampal formation is particularly concerned with the detection of novelty, and there are indications that dentate granule cells play a significant role in this function. Recently, the existence of inter‐individual differences in behavioural reactivity to novelty has been evidenced, related to differences in the reactivity of the hypothalamic–pituitary–adrenal axis (HPA). Rats that are highly reactive to novelty (HR) exhibit a prolonged corticosterone secretion in response to novelty and to stress when compared with low reactive rats (LR). Taking advantage of the existence of these inter‐individual differences, we investigated whether neurogenesis in the dentate gyrus is correlated with the behavioural trait of reactivity to novelty. Rats were first selected according to their locomotor reactivity to a novel environment. Two weeks later, cell proliferation, evaluated by the incorporation of 5‐bromo‐2′‐deoxyuridine (BrdU) in progenitors, was studied by immunohistochemistry. We found that cell proliferation in the dentate gyrus was negatively correlated with locomotor reactivity to novelty. Indeed, cell proliferation in LR rats was twice that observed in HR rats. In contrast, survival of nascent neurons was not influenced by the behavioural trait of reactivity to novelty. Using an unbiased stereology, we show that LR rats had more cells within the granule cell layer of the dentate gyrus than did HR rats. These results demonstrate the existence of inter‐individual differences in neurogenesis and total granule cell number within the dentate gyrus. These differences in hippocampal plasticity can be predicted by the behavioural trait of reactivity to novelty.
Functional heterogeneity of the rat medial prefrontal cortex: effects of discrete subarea‐specific lesions on drug‐induced conditioned place preference and behavioural sensitization
Authors: Tzschentke Thomas M. , Schmidt Werner J.
Published: March 2003

While the principal components of the brain reward system, the nucleus accumbens septi and the ventral tegmental area have received much attention, their efferent and afferent structures have not been investigated to the same degree. One major input to this system originates from the medial prefrontal cortex (mPFC) which is not a homogenous structure but can be divided into different subareas that can be distinguished on anatomical and possibly functional grounds. We examined the effects of discrete bilateral quinolinic acid lesions (45 nmol/0.5 μL) of each of the mPFC subareas, the infralimbic (il), prelimbic (pl) and the anterior cingulate (cg) mPFC, on the conditioned place preference (CPP) and psychomotor activation induced by several drugs. Lesions of the il mPFC blocked CPP induced by morphine (10 mg/kg) and CGP37849 [dl‐(E)‐2‐amino‐4‐methyl‐5‐phosphono‐3‐pentic acid, a competitive N‐methyl‐d‐aspartate receptor antagonist; 10 mg/kg]. Lesions of the pl mPFC blocked CPP induced by cocaine (15 mg/kg) and CGP37849, and lesions of the cg mPFC only blocked CGP37849‐induced CPP. Lesions of the whole mPFC blocked morphine‐, cocaine‐ and CGP37849‐induced CPP. None of the lesions affected dl‐amphetamine (4 mg/kg)‐induced CPP. During the conditioning period, none of the lesions affected amphetamine‐induced psychomotor activation and sensitization, whereas both phenomena were attenuated by pl and whole mPFC lesions in the case of cocaine, and by il and whole mPFC lesions in the case of morphine. These results show that the different mPFC subregions have distinct functional roles in the generation of behavioural effects produced by different classes of drugs. This heterogeneity should be taken into account in future studies addressing the role of the mPFC in drug reward and sensitization.
Perirhinal cortex input to the hippocampus in the rat: evidence for parallel pathways, both direct and indirect. A combined physiological and anatomical study
Authors: Naber P. A. , Witter M. P. , Da Silva F. H. Lopes
Published: March 2003

The possibility of a direct projection from the perirhinal cortex (PER) to areas CA1 and subiculum (SUB) in the hippocampus has been suggested on the basis of tracer studies, but this projection has not unequivocally been supported by physiological studies. The demonstration of such a functional pathway might be important to understand the functioning of the hippocampal memory system. Here we present physiological and further anatomical evidence for such a connection between PER and the hippocampus. Electrical stimulation of PER in vivo evoked field potentials (EFPs) at the border area of CA1/SUB, consisting of a short latency and a longer latency component. Current source density analysis revealed that the sink of the short latency component was situated in the molecular layer of area CA1/SUB, while the longer latency component had its sink in the outer molecular layer of the dentate gyrus (DG). Anterograde tracer injections in PER showed labelled fibres in the border area of CA1/SUB, but anatomical evidence for a projection of PER to DG was not found. When synaptic transmission in the entorhinal cortex was partly blocked, the amplitude of the longer latency component of the recorded EFPs in the hippocampus was decreased while the short latency component was not affected, which suggests that the indirect pathway originating in PER is mediated through a synaptic relay in the entorhinal cortex. From the present results we conclude that information originating in PER reaches area CA1/SUB by parallel, direct and indirect, routes. The existence of this parallel organization appears to form an essential feature for the proper function of the medial temporal lobe memory system.
The modulation of calcium current by GABA metabotropic receptors in a sub‐population of pallidal neurons
Authors: Stefani Alessandro , Spadoni Francesca , Giacomini Patrizia , Lavaroni Franco , Bernardi Giorgio
Published: March 2003

Globus pallidus (GP) receives an abundant GABAergic (γ‐aminobutyric acid) pathway from the corpus striatum. Several evidences suggested that alterations of this pathway might underlie the development of movement disorders. Classical models on Parkinsonism are centred on the increased excitability of GABAergic striatofugal neurons impinging GP and, therefore, on the presumed hypoactivity of GP neurons, but very few electrophysiological studies have addressed the activation of GABA receptors in mammalian GP. We have isolated calcium currents in GP neurons dissociated from the adult rat brain and analysed GABA‐mediated responses. In the presence of bicuculline, the fast, chloride‐mediated, ionotropic responses were obscured and GABA produced a large (≥ 35%) inhibition of calcium currents. The GABA‐induced inhibition of calcium currents strongly desensitized was mimicked by baclofen and prevented by hydroxy‐saclofen, supporting the involvement of GABAB receptors. The baclofen‐mediated modulation was: (i) associated with slowing of activation kinetics; (ii) relieved by prepulse facilitation; and (iii) G‐protein‐mediated. The response was slow in onset, requiring the mobilization of intracellular cAMP, and was abolished by the combination of N‐type and P‐type calcium channel blockers. The GABAB‐mediated effect, however, was confined to a particular subtype of GP neurons, identified by relatively small to medium soma. Differently, in cells characterized by larger somata and capacitance, the baclofen response was negligible. Intriguingly, these baclofen‐resistant, larger neurons manifested a consistent low‐voltage‐activated (LVA) calcium current, not detected in baclofen‐sensitive cells, at least when recorded in whole‐cell mode. This study demonstrates that GP neurons express functional GABAA and GABAB receptors. In a subset of GP neurons, the activation of GABAB receptors induces a large modulation of high‐voltage‐activated (HVA) calcium currents, which may strongly influence basal ganglia circuitry and partially explain some discrepancies of classical models of extrapyramidal disorders.
Synchronization of GABAergic interneuronal networks during seizure‐like activity in the rat horizontal hippocampal slice
Authors: Velazquez Jose L. Perez , Carlen Peter L.
Published: March 2003

We studied the contribution of GABAergic (γ‐aminobutyric acid) neurotransmission to epileptiform activity using the horizontal hippocampal rat brain slice. Seizure‐like (ictal) activity was evoked in the CA1 area by applying high‐frequency trains (80 Hz for 2 s) to the Schaffer collaterals. Whole‐cell recordings from stratum oriens‐alveus interneurons revealed burst firing with superimposed high‐frequency spiking which was synchronous with field events and pyramidal cell firing during ictal activity. On the other hand, interictal interneuronal bursts were synchronous with large‐amplitude inhibitory postsynaptic potentials (IPSPs) in pyramidal cells. Excitatory and inhibitory postsynaptic potentials were simultaneously received by pyramidal neurons during the ictal afterdischarge, and were synchronous with interneuronal bursting and field potential ictal events. The GABAA receptor antagonist bicuculline greatly reduced the duration of the ictal activity in the CA1 layer, and evoked rhythmic interictal synchronous bursting of interneurons and pyramidal cells. With intact GABAergic transmission, interictal field potential events were synchronous with large amplitude IPSPs (9.8 ± 2.4 mV) in CA1 pyramidal cells, and with interneuronal bursting. Simultaneous dual recordings revealed synchronous IPSPs received by widely separated pyramidal neurons during ictal and interictal periods, indicative of widespread interneuronal firing synchrony throughout the hippocampus. CA3 pyramidal neurons fired in synchrony with interictal field potential events recorded in the CA1 layer, and glutamate receptor antagonists abolished interictal interneuronal firing and synchronous large amplitude IPSPs received by CA1 pyramidal cells. These observations provide evidence that the interneuronal network may be entrained in hyperexcitable states by GABAergic and glutamatergic mechanisms.
Brain somatostatin: a candidate inhibitory role in seizures and epileptogenesis
Authors: Vezzani Annamaria , Hoyer Daniel
Published: March 2003

Recent evidence shows that neuropeptide expression in the CNS is markedly affected by seizure activity, particularly in the limbic system. Changes in neuropeptides in specific neuronal populations depend on the type and intensity of seizures and on their chronic sequelae (i.e. neurodegeneration and spontaneous convulsions). This paper reviews the effects of seizures on somatostatin‐containing neurons, somatostatin mRNA and immunoreactivity, the release of this peptide and its receptor subtypes in the CNS. Differences between kindling and status epilepticus in rats are emphasized and discussed in the light of an inhibitory role of somatostatin on hippocampal excitability. Pharmacological studies show that somatostatin affects electrophysiological properties of neurons, modulates classical neurotransmission and has anticonvulsant properties in experimental models of seizures. This peptidergic system may be an interesting target for pharmacological attempts to control pathological hyperactivity in neurons, thus providing new directions for the development of novel anticonvulsant treatments.
Hippocampal neuronal position selectivity remains fixed to room cues only in rats alternating between place navigation and beacon approach tasks
Authors: Trullier O. , Shibata R. , Mulder A. B. , Wiener S. I.
Published: March 2003

To study the relationship between brain representations and behaviour, we recorded hippocampal neuronal activity in rats repeatedly alternating between two different tasks on a circular platform with four reward boxes along the edge. In the beacon approach task, rewards were provided only at the pair of diametrically opposite boxes that was illuminated. In the place navigation task, rewards were available only at the boxes positioned near the north‐east and south‐west corners of the room. Performance levels were high and rats rapidly reoriented to changes in lamp cues in the beacon approach task. Neuropsychological studies show that rats with hippocampal lesions readily employ beacon approach strategies, while place navigation is severely impaired. Previous studies suggested that the neurons might change their behavioural correlates as the rat performed the respective tasks. However, of 34 hippocampal ‘place cells’ recorded, all showed position selectivity fixed with respect to room cues, even in the beacon approach task where coding the position of the rat in the room was of no use for locating rewards. Whether or not hippocampal signals are actually employed for ongoing behaviour would then be decided by structures downstream from the hippocampus. If this is the case, then the ‘counterproductive’ room referred place‐related discharges in the beacon approach task would be a background representation. This would provide support for proposals of multiple memory systems underlying different types of information processing and contrasts with the popular notion that local neuronal activity levels are selectively increased to the degree that the brain region is required for the ongoing function.
A mouse model of familial amyotrophic lateral sclerosis expressing a mutant superoxide dismutase 1 shows evidence of disordered transport in the vasopressin hypothalamo‐neurohypophysial axis
Authors: de Aguilar José‐Luis González , Gordon Jon W. , René Frédérique , Lutz‐Bucher Bernadette , Kienlen‐Campard Pascal , Loeffler Jean‐Philippe
Published: March 2003

Amyotrophic lateral sclerosis (ALS) is a fatal, paralytic disorder that primarily affects motoneurons. By combining physiological and morphological approaches, we examined the effect of a murine superoxide dismutase 1 (SOD1) mutation (G86R), which induces neurological disorders resembling human familial ALS (FALS), on the arginine vasopressin (AVP) hypothalamo‐neurohypophysial axis, an unmyelinated tract poor in neurofilaments. First, we observed that G86R mice progressively consumed more water than wild‐type littermates. Furthermore, levels of plasma AVP and neurohypophysial AVP content were decreased in the SOD1 mutant mice, whereas the amount of hypothalamic AVP increased in an age‐dependent manner. However, hypothalamic AVP mRNA levels were not significantly modified in these animals. At the ultrastructural level, we found that the neurohypophysis of G86R mice had a decreased number of neurosecretory axons. Conversely, the presence of large axon swellings was more pronounced in the SOD1 mutant mice. In addition, the size of neurosecretory granules was higher in G86R than in wild‐type animals. All these findings strongly suggest that the FALS‐associated SOD1 mutation injures the hypothalamo‐neurohypophysial axis by provoking early, progressive disturbances in the axonal transport of neurosecretory products from neuronal perikarya to nerve terminals. This blockade could ultimately result in degeneration of the tract, as proposed for the myelinated, neurofilament‐enriched motor axons affected by ALS.
Distinct kinetics of cloned T‐type Ca2 +  channels lead to differential Ca2 +  entry and frequency‐dependence during mock action potentials
Authors: Kozlov Andrei S. , McKenna Frank , Lee Jung‐Ha , Cribbs Leanne L. , Perez‐Reyes Edward , Feltz Anne , Lambert Régis C.
Published: March 2003

Voltage‐dependent activity around the resting potential is determinant in neuronal physiology and participates in the definition of the firing pattern. Low‐voltage‐activated T‐type Ca2 +  channels directly affect the membrane potential and control a number of secondary Ca2 + ‐dependent permeabilities. We have studied the ability of the cloned T‐type channels (α1G,H,I) to carry Ca2 +  currents in response to mock action potentials. The relationship between the spike duration and the current amplitude is specific for each of the T‐type channels, reflecting their individual kinetic properties. Typically the charge transfer increases with spike broadening, but the total Ca2 +  entry saturates at different spike durations according to the channel type: 4 ms for α1G; 7 ms for α1H; and >  10 ms for α1I channels. During bursts, currents are inhibited and/or transiently potentiated according to the α1 channel type, with larger effects at higher frequency. The inhibition may be induced by voltage‐independent transitions toward inactivated states and/or channel inactivation through intermediate closed states. The potentiation is explained by an acceleration in the channel activation kinetics. Relatively fast inactivation and slow recovery limit the ability of α1G and α1H channels to respond to high frequency stimulation ( >  20 Hz). In contrast, the slow inactivation of α1I subunits allows these channels to continue participating in high frequency bursts (100 Hz). The biophysical properties of α1G, H and I channels will therefore dramatically modulate the effect of neuronal activities on Ca2 +  signalling.
Manipulation of synaptic sign and strength with divalent cations in the vertebrate retina: pushing the limits of tonic, chemical neurotransmission
Authors: Piccolino Marco , Vellani Vittorio , Rakotobe Liramalala A. , Pignatelli Angela , Barnes S. , McNaughton Peter
Published: March 2003

At the first synaptic level of the vertebrate retina, photoreceptor light responses are transmitted to second order neurones through a chemical synapse based on a tonic release of neurotransmitter modulated by graded changes of presynaptic potential. The possibility that such synapses could work through a Ca2+‐independent process had been proposed by previous authors, based on the persistence of transmission process in low Ca2+ media containing Co2+ or Ni2+ ions. Recently, we were able to explain these results within the framework of the classical calcium‐hypothesis of synaptic transmission by taking into account the modifications of presynaptic surface potential brought about by changes of divalent cation concentrations. Here we report data showing how a surface‐charge hypothesis could account for several apparently paradoxical effects of divalent cation manipulations such as: the enhancement of neurotransmitter release induced by low Ca2+ media; the transmission "unblocking" effect of Zn2+, Co2+ and Ni2+; and the reversal of transmission polarity induced by application of low Ca2+ media containing Cd2+ or Mg2+ ions.
Modulation of feeding‐induced activation of mesolimbic dopamine transmission by appetitive stimuli and its relation to motivational state
Authors: Bassareo Valentina , Di Chiara Gaetano
Published: March 2003

We have previously shown in non‐deprived rats that feeding of an unfamiliar palatable food (Fonzies®) phasically stimulates in vivo dopamine (DA) transmission in the medial nucleus accumbens (NAc) and this effect undergoes habituation after a previous (24 h) Fonzies meal (Bassareo & Di Chiara 1997, J. Neurosci., 17, 851–861). The present study shows that an unfamiliar food (Kinder®) with a taste and composition (milk chocolate) different from that of Fonzies, also induces a release of DA in the NAc subjected to one‐trial habituation. Habituation was taste specific as no cross‐habituation was observed between Fonzies and Kinder. In undeprived rats, a 40‐min exposure to an intrinsic appetitive stimulus (food smell arising from a Fonzies‐filled plastic box) also prevented the increase in dialysate DA associated with Fonzies feeding, and this effect was partially reversed by food deprivation. Food deprivation also prevented habituation of Fonzies‐induced increase of dialysate DA in the NAc. Predictive association of an empty plastic box to Fonzies feeding resulted in the acquisition of appetitive properties by the box and in facilitation (rather than inhibition) of the phasic responsiveness of DA transmission to Fonzies feeding. A 10‐min pre‐exposure to appetitive olfactory stimuli intrinsic to Fonzies still prevented, like a 40‐min pre‐exposure, the NAc DA response to Fonzies feeding; however, a 5‐min pre‐exposure to these appetitive stimuli did not prevent the DA response in the NAc. These results show that the phasic responsiveness of NAc DA transmission to an unfamiliar palatable food is under strong modulatory control by primary (consummatory) and secondary (appetitive) stimuli, and that the sign and extent of this control depends on the nature of the appetitive stimulus, delay of reward and motivational state (deprivation).
Neurochemical gradients along monkey sensory cortical pathways: calbindin‐immunoreactive pyramidal neurons in layers II and III
Authors: Kondo Hideki , Tanaka Keiji , Hashikawa Tsutomu , Jones Edward G.
Published: March 2003

We examined the distribution of neurons containing immunoreactivity for three calcium‐binding proteins, calbindin, parvalbumin and calretinin, as well as nonphosphorylated neurofilament protein, in cortical areas along the ventral and dorsal cortical visual pathways, and in ventrally‐directed somatosensory and auditory cortical pathways. Calbindin‐immunoreactive pyramidal neurons showed the most prominent regional differences. They were largely restricted to layers II and III and their number monotonically increased from the primary sensory areas to the anteroventral areas along the ventral visual pathway and along the ventrally‐directed somatosensory and auditory pathways. The number of calbindin‐immunoreactive pyramidal neurons in layers II and III also increased along the dorsal visual pathway, but the number in the last recognized stage of the dorsal visual pathway (area 7a) was significantly smaller than that at the corresponding stage in the ventral visual pathway (TE). The number of calbindin‐immunoreactive pyramidal neurons was highest in layers II and III of areas 35/36, TG, and TF/TH, which represent terminal cortical regions of the pathways. These results show neurochemical differences between cortical areas located at early and late stages along serial corticocortical pathways, as well as confirming differences between pyramidal neurons in the supragranular and infragranular layers.
Induction of hypoxia‐inducible factor‐1 (HIF‐1) and its target genes following focal ischaemia in rat brain
Authors: Bergeron Marcelle , Yu Aimee Y. , Solway Karen E. , Semenza Gregg L. , Sharp Frank R.
Published: March 2003

HIF‐1 is a heterodimeric transcription factor, induced by hypoxia, that is composed of HIF‐1α and HIF‐1β protein subunits. It binds to promoter/enhancer elements and stimulates the transcription of hypoxia‐inducible target genes, including glucose transporter‐1 and the glycolytic enzymes. Because HIF‐1 activation might promote cell survival in hypoxic tissues, we studied the effect of permanent middle cerebral artery occlusion on the expression of HIF‐1α, HIF‐1β and several HIF‐1 target genes in adult rat brain. After focal ischaemia, mRNAs encoding HIF‐1α, glucose transporter‐1 and several glycolytic enzymes were up‐regulated in the peri‐infarct penumbra. This was observed by 7.5 h after the onset of ischaemia and increased further at 19 and 24 h. Regional cerebral blood flow was moderately decreased at 1 and 24 h after the ischaemia in areas of HIF‐1 and HIF‐1 target gene induction. Because hypoxia induces HIF‐1 in other tissues, systemic hypoxia (6% O2 for 4.5 h) was also shown to increase HIF‐1α protein expression in the adult rat brain. It is proposed that decreased blood flow to the penumbra decreases the supply of oxygen and that this induces HIF‐1 and its target genes. This is the first study to show induction of HIF‐1 after focal ischaemia in brain. Increased expression of HIF‐1 target genes as a result of HIF‐1 activation by hypoxia may contribute to tissue viability in the hypoxic/ischaemic penumbra by increasing glucose transport and glycolysis.
Encoding of target direction and speed during visual instruction and arm tracking in dorsal premotor and primary motor cortical neurons
Authors: Johnson M. T. V. , Coltz J. D. , Ebner T. J.
Published: March 2003

The encoding of direction and speed in the discharge of dorsal premotor (PMd) and primary motor (MI) neurons was studied during two‐dimensional visually‐instructed pursuit arm movements in which eight directions and four constant speeds were independently manipulated. Each trial consisted of equal durations of visual observation of target movement without hand movement (cue) and visual pursuit‐tracking of the target with the hand (track). A total of 240 neurons was recorded from PMd and MI in two Macaca mulatta monkeys. Two classes of regression analyses were used to relate neuronal firing during the cue and track periods to direction and speed. First, the average firing from each period was fitted to target direction or speed. Period‐averaged firing significantly correlated with direction more frequently in the track than in the cue period. Conversely, correlations with speed (with or without direction) were more common in the cue than in the track period. Secondly, a binwise regression evaluated the temporal evolution of firing correlations with direction and speed. Supporting the period‐based results, significant binwise correlations of the discharge with speed occurred preferentially during the cue period when there was no hand movement. Prior to movement, correlations of the firing with direction became significant and continued through the movement. Both analyses demonstrated a distinct tendency for neurons to be modulated by speed information early and by direction information later. This temporal parcellation reflects both the sequential demands of the task and constraints placed on the neural computations. The early representation of target speed is hypothesized to reflect the need to calculate a ‘go signal’ for the initiation of movement.
Expression of the cannabinoid receptor CB1 in distinct neuronal subpopulations in the adult mouse forebrain
Authors: Marsicano Giovanni , Lutz Beat
Published: March 2003

Cannabinoids can modulate motor behaviour, learning and memory, cognition and pain perception. These effects correlate with the expression of the cannabinoid receptor 1 (CB1) and with the presence of endogenous cannabinoids in the brain. In trying to obtain further insights into the mechanisms underlying the modulatory effects of cannabinoids, CB1‐positive neurons were determined in the murine forebrain at a single cell resolution. We performed a double in situ hybridization study to detect mRNA of CB1 in combination with mRNA of glutamic acid decarboxylase 65k, neuropeptide cholecystokinin (CCK), parvalbumin, calretinin and calbindin D28k, respectively. Our results revealed that CB1‐expressing cells can be divided into distinct neuronal subpopulations. There is a clear distinction between neurons containing CB1 mRNA either at high levels or low levels. The majority of high CB1‐expressing cells are GABAergic (γ‐aminobutyric acid) neurons belonging mainly to the cholecystokinin‐positive and parvalbumin‐negative type of interneurons (basket cells) and, to a lower extent, to the calbindin D28k‐positive mid‐proximal dendritic inhibitory interneurons. Only a fraction of low CB1‐expressing cells is GABAergic. In the hippocampus, amygdala and entorhinal cortex area, CB1 mRNA is present at low but significant levels in many non‐GABAergic cells that can be considered as projecting principal neurons. Thus, a complex mechanism appears to underlie the modulatory effects of cannabinoids. They might act on principal glutamatergic circuits as well as modulate local GABAergic inhibitory circuits. CB1 is very highly coexpressed with CCK. It is known that cannabinoids and CCK often have opposite effects on behaviour and physiology. Therefore, we suggest that a putative cross‐talk between cannabinoids and CCK might exist and will be relevant to better understanding of physiology and pharmacology of the cannabinoid system.
Expression, distribution and ultrastructural localization of the synapse‐organizing molecule agrin in the mature avian retina
Authors: Koulen Peter , Honig Lawrence S. , Fletcher Erica L. , Kröger Stephan
Published: March 2003

At the vertebrate neuromuscular junction the extracellular matrix molecule agrin is responsible for the formation, maintenance and regeneration of most if not all postsynaptic specializations. Several agrin isoforms are generated by alternative splicing which differ in their function and which are all expressed in the CNS. To analyse the role of agrin in the CNS, we investigated the expression and ultrastructural localization of agrin in the posthatched chick retina. In situ hybridization revealed the presence of agrin mRNA in all cellular layers of the mature retina, indicating that most if not all major retinal cell types synthesize agrin. Pan‐specific as well as isoform‐specific antiagrin antisera stained the optic fibre layer and the outer plexiform layer. However, only the pan‐specific antiserum additionally stained the inner limiting membrane. Immunoelectron microscopy showed that in the optic fibre layer agrin was associated with ganglion cell axons and that at least part of this agrin corresponds to a neuronal isoform of agrin. In the outer plexiform layer, agrin was localized in the cleft between the photoreceptor terminals and the invaginating horizontal and bipolar cell dendrites. In the synapse‐containing inner plexiform layer both antisera revealed punctate immunoreactivity. This staining corresponded to agrin concentrated in the synaptic cleft of conventional synapses as determined by preembedding immunoelectron microscopy. Agrin is thus concentrated at mature interneuronal synapses as it is at the neuromuscular junction, consistent with a role of agrin during formation and/or maintenance of synapses in the CNS.
Comparison of the Ca2 +  currents induced by expression of three cloned α1 subunits, α1G, α1H and α1I, of low‐voltage‐activated T‐type Ca2 +  channels
Authors: Klöckner Udo , Lee Jung‐Ha , Cribbs Leanne L. , Daud Asif , Hescheler Jürgen , Pereverzev Alexei , Perez‐Reyes Edward , Schneider Toni
Published: March 2003

Expression of rat α1G, human α1H and rat α1I subunits of voltage‐activated Ca2 +  channels in HEK‐293 cells yields robust Ca2 +  inward currents with 1.25 mm Ca2 +  as the charge carrier. Both similarities and marked differences are found between their biophysical properties. Currents induced by expression of α1G show the fastest activation and inactivation kinetics. The α1H and α1I currents activate and inactivate up to 1.5‐ and 5‐fold slower, respectively. No differences in the voltage dependence of steady state inactivation are detected. Currents induced by expression of α1G and α1H deactivate with time constants of up to 6 ms at a test potential of − 80 mV, but currents induced by α1I deactivate about three‐fold faster. Recovery from short‐term inactivation is more than three‐fold slower for currents induced by α1H and α1I in comparison to α1G. In contrast to these characteristics, reactivation after long‐term inactivation was fastest for currents arising from expression of α1I and slowest in cells expressing α1H calcium channels. The calcium inward current induced by expression of α1I is increased by positive prepulses while currents induced by α1H and α1G show little ( <  5%) or no facilitation. The data thus provide a characteristic fingerprint of each channel's activity, which may allow correlation of the α1G, α1H and α1I induced currents with their in vivo counterparts.
Apoptosis in Ca2 +  reperfusion injury of cultured astrocytes: roles of reactive oxygen species and NF‐κB activation
Authors: Takuma Kazuhiro , Lee Eibai , Kidawara Miyuki , Mori Koichi , Kimura Yuji , Baba Akemichi , Matsuda Toshio
Published: March 2003

We previously reported that incubation of cultured astrocytes in Ca2 + ‐containing medium after exposure to Ca2 + ‐free medium caused Ca2 +  influx followed by delayed cell death. Here, we studied the mechanisms underlying the Ca2 + ‐mediated injury of cultured astrocytes. Our results show that Ca2 +  reperfusion injury of astrocytes appears to be mediated by apoptosis, as demonstrated by DNA fragmentation and prevention of death by caspase‐3 inhibitors. Paradoxical Ca2 +  challenge stimulated rapidly reactive oxygen species (ROS) production. Ca2 +  reperfusion injury of astrocytes was influenced by several reagents which modified ROS production. When astrocytes were exposed to hydrogen peroxide (H2O2) for 30 min and then incubated without H2O2 for 1–5 days, cell toxicity including apoptosis was observed. Ca2 +  reperfusion injury induced by Ca2 +  depletion or H2O2 exposure was blocked by the iron chelator 1,10‐phenanthroline, the NF‐κB inhibitor pyrrolidinedithiocarbamate and the calcineurin inhibitor FK506. Incubation in normal medium after H2O2 exposure rapidly increased the level of nuclear NF‐κB p65 subunit, and the effect was blocked by 1,10‐phenanthroline, pyrrolidinedithiocarbamate and FK506. These findings indicate that Ca2 +  reperfusion‐induced apoptosis is mediated at least partly by ROS production and ROS cause NF‐κB activation in cultured astrocytes.
Characterization of AMPA receptors on isolated amacrine‐like cells in carp retina
Authors: Shen Ying , Zhou Yu , Yang Xiong‐Li
Published: March 2003

In amacrine‐like cells freshly dissociated from crucian carp (Carassius auratus) retina, we recorded whole‐cell responses to rapid application of glutamate and kainate. Currents induced by glutamate, but not kainate, usually showed extremely rapid desensitization, and the mean time constant for the decay of the responses to 10 mm glutamate was 2.77 ms. N‐methyl‐d‐aspartate (NMDA) failed to induce any current even with coapplication of glycine and removal of extracellular Mg2 + · 1‐(4‐aminophenyl)‐3‐Methylcarbamyl‐4‐methyl‐7,8‐methylenedioxy‐3,4‐dihydro‐5H‐2,3‐benzodiazepine (GYKI 53655), a selective α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid (AMPA) receptor antagonist, was found to completely block glutamate‐induced currents, suggesting that the glutamate receptors on these cells are AMPA preferring. The value of EC50 for glutamate and kainate was determined to be 2.73 mm and 97.5 μm, respectively. Noise analysis of fluctuation of whole‐cell currents induced by kainate of different concentrations indicated that the mean conductance of the AMPA receptor channels was 5.70 pS. Splice variant analysis of the AMPA receptors was also conducted by comparing the effects of cyclothiazide, a flip receptor‐preferring modulator and 4‐[2‐(phenylsulphonylamino)ethylthio]‐2,6‐difluoro‐phenoxyacetamide (PEPA), a flop receptor‐preferring modulator, on glutamate‐induced responses. PEPA was much more potent than cyclothiazide at these receptors with a EC50 of 17.3 μm. The mean ratio of the potentiation by PEPA versus cyclothiazide (P/C ratio) was 4.39. These modulatory effects of cyclothiazide and PEPA were rather similar to those obtained at AMPA receptors assembled from flop variants expressed in Xenopus oocytes, suggesting that the AMPA receptor of the carp amacrine cells may predominantly consist of the flop splice variants.
Morphological, immunophenotypical and electrophysiological properties of resting microglia in vitro
Authors: Eder Claudia , Schilling Tom , Heinemann Uwe , Haas Dorit , Hailer Nils , Nitsch Robert
Published: March 2003

Morphological, immunophenotypical and electrophysiological properties were investigated in isolated cultured murine microglia before and after exposure to astrocyte‐conditioned medium (ACM). Following application of ACM, microglial cells underwent a dramatic shape transformation from an amoeboid appearance to a ramified morphology. In parallel to morphological changes, a downregulation of macrophage surface antigens was observed in microglia exposed to ACM. Staining intensities for major histocompatibility complex (MHC) class II molecules and for the adhesion molecules leukocyte function‐associated antigen‐1 (LFA‐1) and intercellular adhesion molecule‐1 (ICAM‐1) were significantly decreased in ramified microglia 5 days after exposure to ACM. In microglial cells treated daily with ACM over a period of 5 days, the smallest staining intensities for all surface antigens as well as the smallest ramification index as a measure for the highest degree of ramification were determined. In addition, upregulation of delayed rectifier K +  currents was observed in microglia exposed to ACM for 1 day or treated daily with ACM for 5 days. In contrast, untreated amoeboid microglia or ramified microglia analysed 5 days after exposure to ACM did not express delayed rectifier K +  currents. Analyses of the resting membrane potential and expression levels and properties of inward rectifier K +  currents did not reveal any differences between untreated and ACM‐treated microglia. It is suggested that electrophysiological properties of microglia do not strongly correlate with the morphology or the immunophenotype of microglial cells.
Firing rate and theta‐phase coding by hippocampal pyramidal neurons during ‘space clamping’
Authors: Hirase Hajime , Czurkó András , Csicsvari Jozsef , Buzsáki György
Published: March 2003

In the hippocampus, spatial representation of the environment has been suggested to be coded by either the firing rate of pyramidal cell assemblies or the relative timing of the action potentials during the theta EEG cycle. Here, we used a behavioural ‘space clamp’ method, which involved the confinement of the actively running animal in a defined position in space (running wheel) to examine how ‘spatial’ and other inputs affect firing rate and timing of hippocampal CA1 pyramidal cells and interneurons. Nineteen per cent of the recorded CA1 pyramidal cells were selectively active while the rat was running in the wheel in a given direction (‘wheel’ cells). Spatial rotation of the apparatus showed that selective discharge of pyramidal cells in the wheel was under the combined influence of distal and apparatus cues. During steady running, both discharge rate and theta phase were constant. Rotation of the wheel apparatus resulted in a shift of both firing rate and preferred theta phase. The discharge frequency of ‘wheel’ cells increased threefold (on average) with increasing running velocity. In contrast, change in running speed had relatively little effect on the theta phase‐related discharge of ‘wheel’ cells. Our findings indicate that mechanisms that regulate rate and phase of spikes are overlapping but not necessarily identical.
Effects of aspiration versus neurotoxic lesions of the amygdala on emotional responses in monkeys
Authors: Meunier Martine , Bachevalier Jocelyne , Murray Elisabeth A. , Málková Ludiše , Mishkin Mortimer
Published: March 2003

All previous reports describing alterations in emotional reactivity after amygdala damage in monkeys were based on aspiration or radiofrequency lesions which likely disrupted fibres of passage coursing to and from adjacent ventral and medial temporal cortical areas. To determine whether this associated indirect damage was responsible for some or all of the changes described earlier, we compared the changes induced by aspiration of the amygdala with those induced by fibre‐sparing neurotoxic lesions. Four different stimuli, two with and two without a social component, were used to evaluate the expression of defence, aggression, submission and approach responses. In unoperated controls, defence and approach behaviours were elicited by all four stimuli, ‘social’ and inanimate alike, whereas aggression and submission responses occurred only in the presence of the two ‘social’ stimuli. Furthermore, all defence reactions were reduced with an attractive inanimate item, while freezing was selectively increased with an aversive one. Relative to controls, monkeys with neurotoxic amygdala lesions showed the same array of behavioural changes as those with aspiration lesions, i.e. reduced fear and aggression, increased submission, and excessive manual and oral exploration. Even partial neurotoxic lesions involving less than two‐thirds of the amygdala significantly altered fear and manual exploration. These findings convincingly demonstrate that the amygdala is crucial for the normal regulation of emotions in monkeys. Nevertheless, because some of the symptoms observed after neurotoxic lesions were less marked than those seen after aspiration lesions, the emotional disorders described earlier after amygdalectomy in monkeys were likely exacerbated by the attendant fibre damage.
Doc2α is an activity‐dependent modulator of excitatory synaptic transmission
Authors: Sakaguchi Gaku , Manabe Toshiya , Kobayashi Katsunori , Orita Satoshi , Sasaki Takuya , Naito Akira , Maeda Miki , Igarashi Hisanaga , Katsuura Goro , Nishioka Hideo , Mizoguchi Akira , Itohara Shigeyoshi , Takahashi Tomoyuki , Takai Yoshimi
Published: March 2003

Doc2α is a synaptic vesicle‐associated Ca2 + ‐binding protein. To study the role of Doc2α in synaptic transmission and modulation, we generated homozygous null Doc2α mutant mice. In the CA1 region of hippocampal slices in the mutant mice, excitatory synaptic responses evoked with prolonged 5 Hz stimulation showed a significantly larger frequency facilitation followed by a steeper depression than those in wild‐type mice, whereas there was no difference in synaptic transmission at lower frequencies or in paired‐pulse facilitation. These results suggest that Doc2α regulates synaptic transmission when high Ca2 +  concentrations in the presynaptic terminal are sustained. Furthermore, the mutant mice showed impairment in long‐term potentiation and passive avoidance task. Thus, Doc2α may regulate transmitter release during repetitive synaptic activation, thereby contributing to memory formation.
Activity‐dependent formation of perforated synapses in cultured hippocampal neurons
Authors: Neuhoff Henrike , Roeper Jochen , Schweizer Michaela
Published: March 2003

The study investigated the formation of perforated synapses in rat hippocampal cell cultures. Perforated synapses are defined by their discontinuous postsynaptic densities (PSDs) and are believed to occur in parallel with changes in synaptic activity and possibly also synaptic efficacy. Several in vivo studies have demonstrated an increase in the frequency of perforated synapses induced by development and environmental stimulation as well as long‐term potentiation (LTP). Also in in vitro brain slices, LTP was associated with an elevated number of perforated spine synapses. Our study demonstrated for the first time that the formation of perforated synapses can be induced by a short‐term increase in spontaneous neural activity in a hippocampal cell culture model. Stimulation with the GABAA‐antagonist picrotoxin (PTX) induced a significant increase in the percentage of perforated synapses. This strong increase was blocked when APV was added together with PTX, indicating that the formation of perforated synapses depended on the activation of NMDA receptors. We also showed that inhibition of the tissue type plasminogen activator (tPA‐stop/PAI‐1) significantly interfered with the activity‐induced increase in perforated synapses. This implies that the proteolytic activities of tPA might be involved in steps which are downstream from the NMDA receptor‐mediated synaptic plasticity leading to structural changes at synaptic contacts. In contrast, even long‐term inhibition of electrical network activity by tetrodotoxin had no effect on the number of perforated synapses, but almost completely abolished the formation of spine synapses. These results indicate that a short‐term increase in neural activity via NMDA receptors and a proteolytic cascade involving tPA lead to the formation of perforated synapses.