bluuebunny/crossref_metadata_2025 huggingface dataset:
Impairments in visual discrimination learning and recognition memory produced by neurotoxic lesions of rhinal cortex in rhesus monkeys
Authors: Baxter Mark G. , Murray Elisabeth A.
Published: March 2003

Much work on the cognitive functions of the primate rhinal (i.e. entorhinal plus perirhinal) cortex has been based on aspiration lesions of this structure, which might disrupt fibres passing nearby and through the rhinal cortex in addition to removing the cell bodies of the rhinal cortex itself. To determine whether damage limited to the cell bodies of the rhinal cortex is sufficient to impair visual learning and memory, four rhesus monkeys (Macaca mulatta) were preoperatively trained on a battery of visual learning and memory tasks, including single‐pair discrimination learning for primary reinforcement, single‐pair discrimination reversals, concurrent discrimination learning and reversal, and delayed matching‐to‐sample. Following acquisition of these tasks and a preoperative performance test, ibotenic acid was injected bilaterally into the rhinal cortex, and the monkeys were retested. Consistent with the results of studies using aspiration lesions, the monkeys were impaired on single‐pair discrimination learning as well as recognition memory performance postoperatively, although reliable reversal learning impairments were not observed. The magnitude of postoperative impairment in discrimination learning was not correlated with the magnitude of postoperative impairment in recognition memory, suggesting a possible dissociation between these functions within the rhinal cortex. The correspondence of behavioural deficits following aspiration and neurotoxic lesions of the rhinal cortex validates the attribution of various cognitive functions to this structure, based on the results of studies with aspiration lesions.
Social isolation after a single defeat reduces striatal dopamine transporter binding in rats
Authors: Isovich Eleonora , Engelmann Mario , Landgraf Rainer , Fuchs Eberhard
Published: March 2003

A single social defeat in male rats has long lasting physiological and behavioural consequences, which are similar to those seen in depressive patients. In addition, the housing conditions after social defeat appear to be crucial for the development of depression‐like symptoms. Because the dopaminergic system is thought to be altered in depressive illness, we investigated the impact of individual and group housing on the temporal development of changes of dopamine transporter (DAT) binding in male rats after a single social defeat. The number of striatal DAT binding sites was reduced in animals that remained isolated after being defeated. The isolation length after social defeat amplified this effect, indicating a temporal development of the changes on the striatal DAT. In animals which returned to the familiar group after social defeat the density of striatal DAT binding sites was not affected. We conclude that social isolation after a single defeat reduces the number of DAT binding sites. In contrast, a familiar environment after a single social defeat appears to prevent the stress‐induced alterations on the dopaminergic system. This finding suggests that housing conditions are critical when investigating the central nervous effects of social defeat in male rats.
Visual analysis and image motion in locomoting cats
Authors: Sherk Helen , Fowler Garth A.
Published: March 2003

During locomotion, observers see a characteristic pattern of motion referred to as an optic flow field. To investigate how they make use of this pattern, we have developed a paradigm for testing visual function during locomotion. Foot placement was recorded while cats walked down an alley cluttered with a high density of small objects; the task was to avoid stepping on any object. In the experiments reported here, motion cues were eliminated by the use of low‐frequency strobe lighting. In bright continuous light cats performed with great accuracy, and likewise at scotopic light levels. However, in strobe lighting their error rates increased more than threefold. This deterioration could not be attributed to lower acuity, since the cats' performance remained excellent when the light level was reduced well below that afforded by the strobe light. When very dim continuous light was combined with low‐frequency strobe lighting, performance was substantially better than under strobe light alone. We conclude that motion‐sensitive neurons make a major contribution to visual guidance of foot placement during locomotion. When strobe lighting is combined with very dim continuous light, even the minimal motion information available in the intervals between bright strobe flashes improves performance significantly. Cats were also trained to discriminate between complex patterns, and this discrimination was not affected by strobe lighting, suggesting that motion‐sensitive neurons are not critical for this analysis.
Cajal‐Retzius cells in early postnatal mouse cortex selectively express functional metabotropic glutamate receptors
Authors: Martínez‐Galán Juan Ramón , López‐Bendito Guillermina , Luján Rafael , Shigemoto Ryuichi , Fairén Alfonso , Valdeolmillos Miguel
Published: March 2003

Glutamate receptors have been linked to the regulation of several developmental events in the CNS. By using cortical slices of early postnatal mice, we show that in layer I cells, glutamate produces intracellular calcium ([Ca2+]i) elevations mediated by ionotropic and metabotropic glutamate receptors (mGluRs). The contribution of mGluRs to these responses was demonstrated by application of tACPD, an agonist to groups I and II mGluRs, which evoked [Ca2+]i increases that could be reversibly blocked by MCPG, an antagonist to groups I and II mGluRs. In the absence of extracellular Ca2+, repetitive applications of tACPD or quisqualate, an agonist to group I mGluRs, elicited decreasing [Ca2+]i responses that were restored by refilling a thapsigargin‐sensitive Ca2+ store. The use of specific group I mGluR agonists CHPG and DHPG indicated that the functional mGluR in layer I was of the mGluR1 subtype. Subtype specific antibodies confirmed the presence of mGlur1α, but not mGluR5, in Cajal‐Retzius (Reelin‐immunoreactive) neurons.
Oxygen modulates cell death in the proliferating retina
Authors: Semo Maayan , Bryce Jennifer , Jeffery Glen
Published: March 2003

Many factors probably regulate the process of natural cell death during development. It is present in both the early undifferentiated retina and later following differentiation. Melanin production plays a role in regulating retinal development and when it is absent, cell proliferation and death are enhanced. Here we examine the effects of hyperoxia on this process, as oxygen has been shown to reduce cell death among differentiated photoreceptors late in development. However, in this study we examine its effects much earlier in pigmented and albino pigmentation phenotypes, when most cells are still actively dividing and are not committed to a specific fate. Newborn mice were exposed to high oxygen levels for 24 h and then returned to normal air for varying periods and their retinae examined. Hyperoxia had a dramatic effect on the number of dying cells, reducing them by almost 60% in pigmented animals and by over 80% in albinos. Following the return to normal air there was a gradual increase in their number over 360 min back to normal levels in pigmented mice; however, in albinos there was a complete rebound in levels of cell death within 40 min, reflecting the increased metabolic stress present in albino retinae due to their abnormal levels of proliferation. These results highlight the important role played by oxygen during early natural cell death in the retina and reveal the different developmental conditions present in the retinae of the two pigmentation phenotypes examined.
Central monoamine and plasma corticosterone changes induced by a bacterial endotoxin: sensitization and cross‐sensitization effects
Authors: Hayley Shawn , Lacosta Susan , Merali Zul , Van Rooijen Nico , Anisman Hymie
Published: March 2003

Low doses of lipopolysaccharide, tumour necrosis factor‐alpha (TNF‐α), interleukin‐1β (IL‐1β), or exposure to a stressor (restraint) increased plasma corticosterone levels. In animals pretreated with lipopolysaccharide, a marked sensitization of the corticosterone response was evident upon subsequent exposure to lipopolysaccharide, TNF‐α, or restraint, 1 day later. As well, the sickness‐inducing effects of lipopolysaccharide, TNF‐α and IL‐1β were markedly increased in mice pretreated with lipopolysaccharide. The sensitization effects were marked when the second treatment was administered 1 day after lipopolysaccharide administration, but not when a 28‐day interval elapsed. In a second experiment, TNF‐α influenced monoamine functioning in the paraventricular nucleus of the hypothalamus and within extrahypothalamic regions, including the central amygdala, locus coeruleus, prefrontal cortex. Moreover, serotonin activity within the central amygdala, as well as dopamine activity within the prefrontal cortex, were subject to a sensitization effect in animals pretreated with lipopolysaccharide 1 day earlier. Macrophage depletion by a suspension of clodronate liposomes attenuated the plasma corticosterone changes induced by TNF‐α, but did not affect the sensitization. In contrast, the acute effects of TNF‐α on central neurotransmitters were unaffected by the liposome suspension, but this treatment prevented the sensitization. These data may be relevant to clinical situations in which individuals exposed to bacterial infections may be rendered more susceptible to the behavioural and neurochemical effects of subsequently encountered stressors and immunological challenges.
NMDA‐induced phosphorylation of the microtubule‐associated protein MAP‐2 is mediated by activation of nitric oxide synthase and MAP kinase
Authors: Llansola Marta , Sáez Rosana , Felipo Vicente
Published: March 2003

Microtubule‐associated protein MAP‐2 is a neuronal phosphoprotein which modulates microtubule stability and spatial organization of signal transduction pathways. The functions of MAP‐2 are modulated by phosphorylation. We studied the modulation of MAP‐2 phosphorylation using the N‐methyl‐d‐aspartate (NMDA) type of glutamate receptors and the signal transduction pathways mediating this modulation in primary cultures of rat cerebellar neurons. NMDA induced a rapid increase (330% of basal at 5 min) in MAP‐2 phosphorylation which was not prevented by KN‐62, indicating that it is not mediated by activation of Ca‐calmodulin‐dependent protein kinase. NMDA‐induced phosphorylation of MAP‐2 was inhibited by the nitric oxide synthase inhibitors nitroarginine and 7‐nitroindazole and by PD098059 (an inhibitor of MAP kinase kinase), but was only slightly reduced by calphostin C or U‐73122, inhibitors of protein kinase C and of phospholipase C, respectively. This indicates that the main pathway mediating NMDA‐induced phosphorylation of MAP‐2 is activation of nitric oxide synthase and subsequent activation of MAP kinase. We show that activation of NMDA receptors induces an activation of MAP kinase which is prevented by nitroarginine. The nitric oxide‐generating agent (±)‐S‐nitroso‐N‐acetylpenicillamine (SNAP) also induced activation of MAP kinase and increased phosphorylation of MAP‐2. Other nitric oxide‐generating agents (NOC‐18 and NOR‐3) also increased MAP‐2 phosphorylation. The interplay between NMDA receptors‐associated signal transduction pathways and MAP‐2 may be involved in the modulation of neuronal responses to extracellular signals and in the regulation of neuronal function.
Phorbol esters promote postsynaptic accumulation of Vesl‐1S/Homer‐1a protein
Authors: Kato Akihiko , Fukuda Takaichi , Fukazawa Yugo , Isojima Yasushi , Fujitani Kazuko , Inokuchi Kaoru , Sugiyama Hiroyuki
Published: March 2003

We examined effects of phorbol esters on the amount and the subcellular distribution of the activity‐regulated protein Vesl‐1S/Homer‐1a in cultured hippocampal neurons. Major Vesl‐1S immunoreactivity (IR) was detected throughout neuronal somata under control conditions. Bath application of phorbol esters, PMA and PDBu resulted in the increase in the amount of Vesl‐1S proteins and promoted punctate distribution of Vesl‐1S IR at the cortical regions of the neuronal somata. Immunofluorescent observations using antisynaptophysin and anti‐Vesl‐1S antibodies, and electron microscopic observations, revealed that Vesl‐1S accumulated at postsynaptic regions following PMA application. Membrane depolarization with high concentrations of external potassium also promoted the punctate distribution of Vesl‐1S IR. These results demonstrate that phorbol‐triggered reaction cascades result in the accumulation of Vesl‐1S protein at postsynaptic regions, and suggest that these phorbol effects may mimic those caused by synaptic activities.
Parallel fibre receptive fields of Purkinje cells and interneurons are climbing fibre‐specific
Authors: Ekerot Carl‐Fredrik , Jörntell Henrik
Published: March 2003

In cats decerebrated at the intercollicular level, the cutaneous parallel fibre receptive fields of Purkinje cells, molecular layer interneurons and Golgi cells in the cerebellar C3 zone were delineated by natural stimulation of the skin during extracellular unitary recordings. The locations of these receptive fields were compared with the climbing fibre receptive field of the local Purkinje cell and with the receptive fields of other neurons located along a beam of parallel fibres. The parallel fibre receptive fields of these neurons were highly specific to the local climbing fibre receptive field. In Purkinje cells, the parallel fibre receptive fields were located outside the climbing fibre receptive field of the same cell. In contrast, the parallel fibre receptive fields of interneurons were similar to the receptive field of the locally terminating climbing fibres. In both types of neurons, the parallel fibre receptive fields were small and had distinct borders. The location on the skin of the parallel fibre receptive fields differed conspicuously between neighbouring Purkinje cells and between neighbouring interneurons along a beam as well as between Purkinje cells and interneurons in the same electrode tracks. The remarkable specificity between the parallel fibre receptive fields in Purkinje cells and interneurons and the receptive field of the local climbing fibre is most easily explained by different forms of parallel fibre synaptic plasticity.
Neurotrophins act at presynaptic terminals to activate synapses among cultured hippocampal neurons
Authors: Collin Carlos , Vicario‐Abejon Carlos , Rubio Maria E. , Wenthold Robert J. , McKay Ronald D. G. , Segal Menahem
Published: March 2003

We have recently demonstrated that embryonic E16 hippocampal neurons grown in cultures are unable to form fast synaptic connections unless treated with BDNF or NT‐3. This experimental system offers an opportunity to define the roles of neurotrophins in processes leading to formation of functional synaptic connections. We have used ultrastructural and electrophysiological methods to explore the cellular locations underlying neurotrophin action on synaptic maturation. The rate of spontaneous miniature excitatory postsynaptic currents (mEPSCs) evoked by hyperosmotic stimulation was 7–16‐fold higher in neurotrophin‐treated cells than in controls. In addition, the potent neurotransmitter‐releasing drug α‐latrotoxin was virtually ineffective in the control cells while it stimulated synaptic events in neurotrophin‐treated cells. Likewise, the membrane‐bound dye FM1‐43 was taken up by terminals in neurotrophin‐treated cultures five‐fold more than in controls. Both the total number and the number of docked synaptic vesicles were increased by neurotrophin treatment. Activation of synaptic responses by neurotrophins occurred even when postsynaptic glutamate receptors and action potential discharges were pharmacologically blocked. These results are consistent with a presynaptic locus of action of neurotrophins to increase synaptic vesicle density which is critical for rapid synaptic transmission. They also suggest that neurotrophins can activate synapses in the absence of pre‐ and postsynaptic neuronal activity.
Nicotine regulates 5‐HT1A receptor gene expression in the cerebral cortex and dorsal hippocampus
Authors: Kenny Paul J. , File Sandra E. , Rattray Marcus
Published: March 2003

The 5‐HT1A receptor has previously been shown to be important in mediating the behavioural effects of nicotine. It is possible that nicotine administration might regulate the levels of 5‐HT receptors in limbic and cortical regions, and such regulations may underlie adaptive responses to nicotine in the central nervous system. The effects of acute and chronic systemic (–)‐nicotine administration on 5‐HT1A receptor gene expression were measured by in situ hybridization, in the rat cerebral cortex, dorsal hippocampus and lateral septum. In the cortex, acute nicotine (0.5 mg/kg i.p.) significantly increased the expression of 5‐HT1A receptor mRNA 2 h and 24 h after injection. Similarly, acute nicotine significantly increased 5‐HT1A receptor mRNA in the dentate gyrus (DG), CA3 and CA1 regions of the dorsal hippocampus 2 h and 24 h after injection. Acute nicotine was without effect in the lateral septum. Chronic nicotine (0.5 mg/kg i.p; twice daily for 7 days) significantly decreased 5‐HT1A receptor mRNA in the cortex 2 h after the final injection, but was without effect at 24 h or 72 h. Chronic nicotine caused no changes in 5‐HT1A mRNA in the lateral septum or dorsal hippocampus. These data demonstrate that nicotine regulates 5‐HT1A receptor gene expression in the cortex and hippocampus. The rapid regulation of expression of 5‐HT1A receptor mRNA leads to the hypothesis that nicotine‐induced 5‐HT release may alter the postsynaptic sensitivity to 5‐HT.
Induction of neonatal sodium channel II and III α‐isoform mRNAs in neurons and microglia after status epilepticus in the rat hippocampus
Authors: Aronica Eleonora , Yankaya Bulent , Troost Dirk , Van Vliet Erwin A. , Da Silva Fernando H. Lopes , Gorter Jan A.
Published: March 2003

Sodium channels (NaChs) regulate neuronal excitability in both physiological and pathological conditions, including epilepsy and are therefore an important target for antiepileptic drugs. In the present study, we examined the distribution of mRNAs encoding neonatal NaChs II and III α‐isoforms in control rat hippocampus and after electrically‐induced status epilepticus (SE), using nonradioactive in situ hybridization (ISH). Only weak expression of neonatal NaCh II and III mRNAs was observed in control hippocampus. By contrast, increased expression of neonatal NaCh II and III mRNAs was observed 4 h after the induction of SE in neurons of CA1–CA3 and the dentate granule cell layer. These changes were detected only in rats in which SE was successfully induced and persisted, although less intense, for up to 3 months, when rats display spontaneous seizures. Strong expression of neonatal NaCh α‐isoforms was observed 1 week after SE in microglial cells, as confirmed by double labelling, combining ISH with immunocytochemistry for microglia markers. The increased expression of neonatal isoforms of the NaCh in both neurons and microglial cells may represent a critical mechanism for modulation of neuronal excitability, glial function and pharmacological response to antiepileptic drugs in the course of epileptogenesis.
Brain extracellular glucose assessed by voltammetry throughout the rat sleep–wake cycle
Authors: Netchiporouk L. , Shram N. , Salvert D. , Cespuglio R.
Published: March 2003

In the present study, cortical extracellular levels of glucose were monitored for the first time throughout the sleep–wake states of the freely moving rat. For this purpose, polygraphic recordings (electroencephalogram of the fronto‐occipital cortices and electromyogram of the neck muscles) were achieved in combination with differential normal pulse voltammetry (DNPV) using a specific glucose sensor. Data obtained reveal that the basal extracellular glucose concentration in the conscious rat is 0.59 ± 0.3 mm while under chloral hydrate anaesthesia (0.4 g/kg, i.p.) it increases up to 180% of its basal concentration. Regarding the sleep–wake cycle, the existence of spontaneous significant variations in the mean glucose level during slow‐wave sleep (SWS = +13%) and paradoxical sleep (PS = −11%) compared with the waking state (100%) is also reported. It is to be noticed that during long periods of active waking, glucose level tends towards a decrease that becomes significant after 15 min (active waking = −32%). On the contrary, during long episodes of slow‐wave sleep, it tends towards an increase which becomes significant after 12 min (SWS = +28%). It is suggested that voltammetric techniques using enzymatic biosensors are useful tools allowing direct glucose measurements in the freely moving animal. On the whole, paradoxical sleep is pointed out as a state highly dependent on the availability of energy and slow‐wave sleep as a period of energy saving.
Ca2+ signalling and changes of mitochondrial function during low‐Mg2+‐induced epileptiform activity in organotypic hippocampal slice cultures
Authors: Kovacs R. , Schuchmann S. , Gabriel S. , Kardos J. , Heinemann U.
Published: March 2003

Several lines of evidence indicate that augmented neuronal activity is associated with increased mitochondrial function, however, the mechanisms of coupling are still unclear. In this study we used a low extracellular Mg2+ concentration and short stimulus trains to evoke neuronal hyperactivity in the form of seizure‐like events (SLE) in hippocampal slice cultures. Simultaneous microfluorimetric and electrophysiological techniques were applied to gain insight into changes of Ca2+ concentration in different compartments and into mitochondrial function. SLEs were associated with a large decrease of the extracellular Ca2+ concentration ([Ca2+]e), a spiking increase of the cytoplasmic and a smoothed elevation of the mitochondrial Ca2+ concentration (cytoplasmic concentration [Ca2+]i; intramitrochondrial concentration [Ca2+]m). Following an initial apparent decline in the mitochondrial membrane potential (ΔΨ) and NAD(P)H autofluorescence, mitochondria depolarized and NADH production was augmented. Furthermore, SLEs were associated with increased oxidation of dihydroethidine (HEt). Our data suggest that intramitochondrial Ca2+ accumulation stimulates NADH production and production of radical oxygen species (ROS). Interestingly, mitochondrial depolarization followed [Ca2+]i and [Ca2+]m changes with a delay implying that electrogenic extrusion of Ca2+ from the mitochondrial matrix might be responsible for the depolarization of the mitochondrial membrane.
BDNF reduces miniature inhibitory postsynaptic currents by rapid downregulation of GABAA receptor surface expression
Authors: Brünig Ina , Penschuck Silke , Berninger Benedikt , Benson Jack , Fritschy Jean‐Marc
Published: March 2003

Changes in neurotransmitter receptor density at the synapse have been proposed as a mechanism underlying synaptic plasticity. Neurotrophic factors are known to influence synaptic strength rapidly. In the present study, we found that brain‐derived neurotrophic factor (BDNF) acts postsynaptically to reduce γ‐aminobutyric acid (GABA)‐ergic function. Using primary cultures of rat hippocampal neurons, we investigated the effects of BDNF on GABAergic miniature inhibitory postsynaptic currents (mIPSCs) and on the localization of GABAA receptors. Application of BDNF (100 ng/mL) led within minutes to a marked reduction (33.5%) of mIPSC amplitudes in 50% of neurons, recorded in the whole‐cell patch‐clamp mode, leaving frequency and decay kinetics unaffected. This effect was blocked by the protein kinase inhibitor K252a, which binds with high affinity to trkB receptors. Immunofluorescence staining with an antibody against trkB revealed that about 70% of cultured hippocampal pyramidal cells express trkB. In dual labelling experiments, use of neurobiotin injections to label the recorded cells revealed that all cells responsive to BDNF were immunopositive for trkB. Treatment of cultures with BDNF reduced the immunoreactivity for the GABAA receptor subunits‐α2, ‐β2,3 and ‐γ2 in the majority of neurons. This effect was detectable after 15 min and lasted at least 12 h. Neurotrophin‐4 (NT‐4), but not neurotrophin‐3 (NT‐3), also reduced GABAA receptor immunoreactivity, supporting the proposal that this effect is mediated by trkB. Altogether the results suggest that exposure to BDNF induces a rapid reduction in postsynaptic GABAA receptor number that is responsible for the decline in GABAergic mIPSC amplitudes.
Retrograde response of the rat facial motor nucleus to muscle inflammation elicited by phytohaemagglutinin
Authors: Mariotti R. , Tongiorgi E. , Bressan C. , Armellin M. , Kristensson K. , Bentivoglio M.
Published: March 2003

To investigate whether motoneurons react to signals deriving from target inflammation, we studied the facial motor nucleus after injections of phytohaemagglutinin in the snout of adult rats. This plant lectin is a tool widely used to induce proliferation and activation of T lymphocytes, and we observed marked lymphocyte infiltration in the injected facial muscles. Retrograde labelling of motoneurons was not detected after peripheral injections of fluorochrome‐conjugated phytohaemagglutinin. Nitric oxide synthase, revealed by NADPH‐diaphorase histochemistry, OX‐42‐immunoreactive microglia, and expression of the cell death repressor gene bcl‐2, investigated with nonradioactive in situ hybridization and immunohistochemistry, were evaluated in the facial nucleus. Daily phytohaemagglutinin injections for 4 days, mimicking repeated muscle exposure to inflammatory stimuli, resulted after 2‐day survival in NADPH‐diaphorase induction in motoneurons and marked activation of the surrounding microglia. Quantitative image analysis of NADPH‐diaphorase staining, and OX‐42 immunoreactivity and microglial cell counts indicated highly significant increases with respect to saline‐injected control cases. The occurrence of a neuroprotective retrograde response was evaluated monitoring bcl‐2 expression. Following single phytohaemagglutinin administration, bcl‐2 mRNA was significantly upregulated at 6 h in facial motoneurons and returned to basal levels at 24 h. Bcl‐2 immunoreactivity was markedly upregulated at 24 h and was still significantly higher than in controls at 7 days, when concomitant NADPH‐diaphorase induction in motoneurons and microglia activation was also observed. No degenerative features were observed in motoneurons after phytohaemagglutinin injections at the examined time‐points. The data point out that local muscle inflammation retrogradely elicits gene activation in motoneurons and their microenvironment.
Kindling induces transient fast inhibition in the dentate gyrus–CA3 projection
Authors: Gutiérrez Rafael , Heinemann Uwe
Published: March 2003

The granule cells of the dentate gyrus (DG) send a strong glutamatergic projection, the mossy fibre tract, toward the hippocampal CA3 field, where it excites pyramidal cells and neighbouring inhibitory interneurons. Despite their excitatory nature, granule cells contain small amounts of GAD (glutamate decarboxylase), the main synthetic enzyme for the inhibitory transmitter GABA. Chronic temporal lobe epilepsy results in transient upregulation of GAD and GABA in granule cells, giving rise to the speculation that following overexcitation, mossy fibres exert an inhibitory effect by release of GABA. We therefore stimulated the DG and recorded synaptic potentials from CA3 pyramidal cells in brain slices from kindled and control rats. In both preparations, DG stimulation caused excitatory postsynaptic potential (EPSP)/inhibitory postsynaptic potential (IPSP) sequences. These potentials could be completely blocked by glutamate receptor antagonists in control rats, while in the kindled rats, a bicuculline‐sensitive fast IPSP remained, with an onset latency similar to that of the control EPSP. Interestingly, this IPSP disappeared 1 month after the last seizure. When synaptic responses were evoked by high‐frequency stimulation, EPSPs in normal rats readily summate to evoke action potentials. In slices from kindled rats, a summation of IPSPs overrides that of the EPSPs and reduces the probability of evoking action potentials. Our data show for the first time that kindling induces functionally relevant activity‐dependent expression of fast inhibition onto pyramidal cells, coming from the DG, that can limit CA3 excitation in a frequency‐dependent manner.
Temperature and PMA affect different phases of exocytosis in bovine chromaffin cells
Authors: Gil Anabel , Viniegra Salvador , Gutiérrez Luis M.
Published: March 2003

Amperometry was used to study secretory kinetics of single bovine chromaffin cells stimulated by transient depolarizations at different temperatures. The initial rate of release was moderately enhanced when the temperature was raised from 18 to 22 and 37 °C. Secretion increased drastically at a later period, 5–10 s after the initiation of stimulus. Interestingly, incubation of the cells with phorbol 12‐myristate 13‐acetate (PMA) clearly enhanced fast secretory components. In addition, the rate of secretion of the slower component recruited by prolonged depolarizations (t > 30 s) was unaffected at the range of temperatures normally used in secretory experiments (22–37 °C). A ‘counting events’ analysis of secretion, which avoids the influence of event charge changes, showed specific increases in a population of vesicles fusing between 7 and 12 s over the same range of temperatures, and a marked increase in vesicles fusing during the initial phase (1–5 s), of PMA‐treated cell secretion. An analysis of temperature influence on transient components released by high sucrose, the secretion elicited by cell permeabilization with digitonin, and studies of the individual characteristics of amperometric events, allow us to conclude that an increase in the size of a secondary‐released vesicle population is the main factor contributing to temperature‐dependent enhancement of secretion, in clear contrast to the enhancement of fast releasable pools caused by phorbol esters.
Corticotropin‐releasing factor triggers neurite outgrowth of a catecholaminergic immortalized neuron via cAMP and MAP kinase signalling pathways
Authors: Cibelli Giuseppe , Corsi Patriza , Diana Gennaro , Vitiello Francesco , Thiel Gerald
Published: March 2003

Corticotropin‐releasing factor (CRF), a neuropeptide of 41 amino acids, acts as the major physiological regulator of the basal and stress‐induced release of corticotropin (ACTH), β‐endorphin and other proopiomelanocortin‐derived peptides from the anterior pituitary gland. In addition to its endocrine activity, CRF displays extrahypophysiotropic effects, mainly as a regulator of stress responses. We show here that CRF may additionally function as a differentiating factor in immortalized noradrenergic neuronal CATH.a cells that express CRF receptor type I and resemble locus coeruleus‐derived neurons. CRF triggers morphological changes in CATH.a cells including the appearence of extended long, slender neurites with prominent growth cones. CRF‐treated CATH.a cells exhibit a morphology similar to locus coeruleus neurons in primary culture. CRF‐induced neurite outgrowth of CATH.a cells was blocked by addition of inhibitors for cAMP‐dependent protein kinase or extracellular signal‐regulated protein kinase (ERK), a subtype of the mitogen‐activated protein kinases. The participation of ERK within the CRF signalling cascade was further confirmed by Western blot experiments, with antibodies directed against the phosphorylated form of ERK, and also with transcription‐based assays. We conclude that CRF functions as a differentiating factor of CATH.a cells via the cAMP and the MAP kinase signalling pathways.
Reduction of metallothioneins promotes the disease expression of familial amyotrophic lateral sclerosis mice in a dose‐dependent manner
Authors: Nagano Seiichi , Satoh Masahiko , Sumi Hisae , Fujimura Harutoshi , Tohyama Chiharu , Yanagihara Takehiko , Sakoda Saburo
Published: March 2003

We previously reported that abnormal copper release from mutated Cu, Zn‐superoxide dismutase (SOD1) proteins might be a common toxic gain‐of‐function in the pathogenesis of familial amyotrophic lateral sclerosis (FALS) [Ogawa et al. (1997) Biochem. Biophys. Res. Commun., 241, 251–257.]. In the present study, we first examined metallothioneins (MTs), known to bind copper ions and decrease oxidative toxicity, and found a twofold increase in MTs in the spinal cord of the SOD1 transgenic mice with a FALS‐linked mutation (G93A), but not in the spinal cord of wild‐type SOD1 transgenic mice. We then investigated whether the clinical course of FALS mice could be modified by the reduced expression of MTs, by crossing the FALS mice with MT‐I‐ and MT‐II‐deficient mice. FALS mice clearly reached the onset of clinical signs and death significantly earlier in response to the reduction of protein expression. These results indicated that the copper‐mediated free radical generation derived from mutant SOD1 might be related to the degeneration of motor neurons in FALS and that MTs might play a protective role against the expression of the disease.
Perinatal changes of Ih in phrenic motoneurons
Authors: Di Pasquale Eric , Tell Fabien , Ptak Krzysztof , Monteau Roger , Hilaire Gérard
Published: March 2003

The hyperpolarization‐activated cationic current (Ih) was characterized and its maturation studied on phrenic motoneurons (PMNs), from reduced preparations of foetal (E18 and E21) and newborn (P0–P3) rats, using the whole‐cell patch‐clamp technique. In voltage‐clamp mode, 2‐s hyperpolarizing steps (5‐mV, −50 to −110 mV) elicited a noninactivating inward current, blocked by external application of Cs+ or ZD 7288. At −110 mV, Ih current density averaged 0.67 ± 0.41 pA/pF at E18, reached a transient peak at E21 (1.38 ± 0.11 pA/pF) and decreased at P0–P3 (0.77 ± 0.22 pA/pF). V1/2 was similar at E18 and E21 (−79 mV) but was significantly hyperpolarized at P0–P3 (−90 mV). The time constant of activation was voltage‐dependent, and significantly faster at E21. Reversal potential was similar at all ages when estimated by extrapolation or tail current procedures. It was positively shifted by 25 ± 6 mV when external potassium was raised from 3 to 10 mm, suggesting a similar sensitivity to K+ from E18 to P0–3. Cs+ or ZD 7288 applications on PMNs at rest in current‐clamp mode, in a partitioned chamber, induced a 10 ± 2 mV hyperpolarization at E18 and E21, and an 8 ± 2 mV hyperpolarization at P0–3. The area of the central respiratory drive potential or current was increased by 33 and 31%, respectively, at E21, but was not significantly modified at E18 and P0–3. Our data suggest a critical period during the perinatal maturation of Ih during which it is transiently upregulated and attenuates the influence of the central respiratory drive on PMNs just prior to birth.
Spontaneous GABAergic postsynaptic currents in Cajal–Retzius cells in neonatal rat cerebral cortex
Authors: Kilb Werner , Luhmann Heiko J.
Published: March 2003

Cajal–Retzius cells are among the first neurons appearing during corticogenesis, and play an important role in the establishment of cortical lamination. The variety of neurotransmitter receptors recently found on these cells imply that they are integrated in the neonatal cortical network. To investigate the presence and properties of spontaneous synaptic activity we performed whole‐cell patch‐clamp recordings from visually identified and biocytin‐labelled Cajal–Retzius cells in a tangential slice preparation of neonatal rat cerebral cortex (postnatal days P0–P5). Spontaneous postsynaptic currents (sPSCs) could be observed in about 23% of the cells using a pipette solution containing 136 mm Cl–. The sPSCs occurred at a low frequency (0.07 ± 0.07 Hz, n = 42 cells), had an average amplitude of 24.3 ± 12.4 pA (n = 415 events) and could not be divided in subpopulations according to their amplitude distribution or kinetic properties. The sPSCs were blocked by the GABAA antagonist bicuculline (100 µm), while the glutamatergic antagonists (±)‐2‐amino‐5‐phosphonopentatonic acid (APV, 30 µm) and 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX, 10 µm), as well as tetrodotoxin (1–2 µm), a blocker of voltage‐gated sodium‐currents, had no significant effect on sPSCs. The incidence rate of sPSCs declined within the age of the rats and no sPSCs could be observed after P4. These results suggest that Cajal–Retzius cells transiently receive action potential‐independent and GABAA receptor‐mediated spontaneous synaptic input, which may contribute to the refinement of cortical circuits.
Signals from cone photoreceptors to L‐type horizontal cells are differentially modulated by low calcium in carp retina
Authors: Xu Hong‐Ping , Luo Dong‐Gen , Yang Xiong‐Li
Published: March 2003

Ca2+ plays crucial roles in both phototransduction and calcium‐dependent glutamate release from the photoreceptor terminal. Modulation, by lowering extracellular Ca2+, of red‐sensitive (R‐) and short wavelength‐sensitive (S‐) cone‐driven light responses of L‐type horizontal cells (LHCs) was studied in the isolated superfused carp retina using intracellular recording techniques. Low Ca2+ (nominally Ca2+‐free) Ringer's reduced responses of LHCs to both green (500 nm) and red (680 nm) flashes in darkness, with the former being suppressed more substantially than the latter. This differential suppression became more significant when contribution of R‐cones to the green‐light‐induced responses was diminished by a moderate red (680 nm) background light. Application of IBMX, an inhibitor of phosphodiesterase (PDE), increased LHC responses to both red and green flashes equally, resembling the effect of low Ca2+ on phototransduction. In addition, photopic electroretinographic P III responses, reflecting the activity of cones, to red flashes were more potentiated by low Ca2+, compared to those to green flashes, whilst they were both equally potentiated by IBMX. Furthermore, low Ca2+ caused a more pronounced suppression of LHC responses to red flashes than those to green flashes in the presence of IBMX. It is postulated that reduction of LHC responses in low Ca2+ may be due to the ‘saturation suppression’ caused by the increased glutamate release from the photoreceptor terminal and the differential modulation may reflect a consequence of the dual action of low Ca2+ on the PDE activity in the photoreceptor outer segment and the synaptic strength between cones and LHCs.
PSA‐NCAM modulates BDNF‐dependent survival and differentiation of cortical neurons
Authors: Vutskits L. , Djebbara‐Hannas Z. , Zhang H. , Paccaud J.‐P. , Durbec P. , Rougon G. , Muller D. , Kiss J. Z.
Published: March 2003

We show that the loss or inactivation of the polysialic acid (PSA) tail of neural cell adhesion molecule (NCAM) on rat cortical neurons in culture leads to reduced differentiation and survival. The mechanism by which this negative effect is mediated appears to involve the neuronal response to brain‐derived neurotrophic factor (BDNF): (i) in the absence of PSA or in the presence of excess free PSA added to the culture medium, BDNF‐induced cell signalling is reduced; (ii) the addition of exogenous BDNF to the medium reverses the effect of PSA loss or inactivation. These data suggest that PSA‐NCAM, previously shown to modulate cell migration and plasticity, is needed for an adequate sensitivity of neurons to BDNF.
NMDA‐evoked calcium transients and currents in the suprachiasmatic nucleus: gating by the circadian system
Authors: Colwell Christopher S.
Published: March 2003

A variety of evidence suggests that the effects of light on the mammalian circadian system are mediated by glutamatergic mechanisms and that the N‐methyl‐d‐aspartate (NMDA) receptor plays an important role in this regulation. One of the fundamental features of circadian oscillators is that their response to environmental stimulation varies depending on the phase of the daily cycle when the stimuli are applied. For example, the same light treatment, which can produce phase shifts of the oscillator when applied during subjective night, has no effect when applied during the subjective day in animals held in constant darkness (DD). We examined the hypothesis that the effects of NMDA on neurons in the suprachiasmatic nucleus (SCN) also vary from day to night. Optical techniques were utilized to estimate NMDA‐induced calcium (Ca2+) changes in SCN cells. The resulting data indicate that there was a daily rhythm in the magnitude and duration of NMDA‐induced Ca2+ transients. The phase of this rhythm was determined by the light–dark cycle to which the rats were exposed with the Ca2+ transients peaking during the night. This rhythm continued when animals were held in DD. γ‐Aminobutyric acid (GABA)ergic mechanisms modulated the NMDA response but were not responsible for the rhythm. Finally, there was a rhythm in NMDA‐evoked currents in SCN neurons that also peaked during the night. This study provides the first evidence for a circadian oscillation in NMDA‐evoked Ca2+ transients in SCN cells. This rhythm may play an important role in determining the periodic sensitivity of the circadian systems response to light.
SB‐334867, a selective orexin‐1 receptor antagonist, enhances behavioural satiety and blocks the hyperphagic effect of orexin‐A in rats
Authors: Rodgers R. J. , Halford J. C. G. , Nunes de Souza R. L. , Canto de Souza A. L. , Piper D. C. , Arch J. R. S. , Upton N. , Porter R. A. , Johns A. , Blundell J. E.
Published: March 2003

Intracerebroventricular (i.c.v.) administration of the novel hypothalamic neuropeptide orexin‐A stimulates food intake in rats, and delays the onset of behavioural satiety (i.e. the natural transition from feeding to resting). Furthermore, preliminary findings with the selective orexin‐1 receptor antagonist, SB‐334867, suggest that orexin‐A regulation of food intake is mediated via the orexin‐1 receptor. At present, however, little is known about either the intrinsic effects of SB‐334867 on the normal structure of feeding behaviour, or its effects upon orexin‐A‐induced behavioural change. In the present study, we have employed a continuous monitoring technique to characterize the effects of SB‐334867 (3–30 mg/kg, i.p.) on the microstructure of rat behaviour during a 1‐h test with palatable wet mash. Administered alone, SB‐334867 (30 mg/kg, but not lower doses) significantly reduced food intake and most active behaviours (eating, grooming, sniffing, locomotion and rearing), while increasing resting. Although suggestive of a behaviourally nonselective (i.e. sedative) action, the structure of feeding behaviour was well‐preserved at this dose level, with the reduction in behavioural output clearly attributable to an earlier onset of behavioural satiety. As previously reported, orexin‐A (10 µg per rat i.c.v.) stimulated food intake, increased grooming and delayed the onset of behavioural satiety. Pretreatment with SB‐334867 dose‐dependently blocked these effects of orexin‐A, with significant antagonism evident at dose levels (3–10 mg/kg) below those required to produce intrinsic behavioural effects under present test conditions. Together, these findings strongly support the view that orexin‐A is involved in the regulation of feeding patterns and that this influence is mediated through the orexin‐1 receptor.
Laminar specific alterations of thalamocortical projections in organotypic cultures following layer 4 disruption in ferret somatosensory cortex
Authors: Palmer Sidney L. , Noctor Stephen C. , Jablonska Beata , Juliano Sharon L.
Published: March 2003

The developing neocortex influences the growth of thalamocortical projections. Layer 4 in particular receives the majority of input from the thalamus and is important in instructing thalamic afferents to terminate. Previous in vivo experiments demonstrated that disruption of layer 4 during corticogenesis in ferret somatosensory cortex by application of methylazoxy methanol acetate (MAM) prevents proper termination of thalamic afferents in appropriate cortical regions. To further explore the role of layer 4 in thalamocortical development, we prepared organotypic cocultures consisting of normal gestational day 0 (P0) ferret thalamus paired with normal, embryonic day 33 (E33), or E38 MAM‐treated cortex obtained from ferrets at either P0 or P7. Injection of MAM on E33 disrupts layer 4 formation, whereas similar injections on E38 interfere with layer 2 formation. The cocultures grew together for a number of days, then discrete injections of either fluorescent dextrans or 1,1’‐dioctadecyl‐3,3,3′,3′‐tetramethyl‐indocarbocyanine perchlorate (DiI) were made into the thalamic piece. The labeled thalamic afferents that grew into the cortical slice were analysed and the sites of their terminations quantified after 3, 5, or 7–10 days in culture (DIC). Our results varied somewhat with the amount of time in culture, but the preponderance of thalamic fibers in normal cortex terminated in layer 4, whereas their counterparts in E33 MAM‐treated cortex grew beyond the cortical plate and many fibers terminated inappropriately within lower cortical layers or white matter. Terminal distribution of thalamic fibers in E38 MAM‐treated cortex looked similar to normal. These results demonstrate that the cells of layer 4 provide thalamic afferents with important positional and termination cues.
Immunohistochemical characterisation of Fos‐positive cells in brainstem monoaminergic nuclei following intracranial self‐stimulation of the medial forebrain bundle in the rat
Authors: Ishida Yasushi , Nakamura Masato , Ebihara Kosuke , Hoshino Kaeko , Hashiguchi Hiroyuki , Mitsuyama Yoshio , Nishimori Toshikazu , Nakahara Daiichiro
Published: March 2003

Fos immunostaining was used as a marker of neuronal activity following intracranial self‐stimulation (ICSS) of the medial forebrain bundle (MFB) in the rat, and was combined with immunostaining for tyrosine hydroxylase (TH), serotonin (5‐HT), γ‐aminobutyric acid (GABA), or NR1 (one of the glutamate N‐methyl‐d‐aspartate receptor subunits) for purposes of neurochemical identification. ICSS induced a significant but different degree of increase in the number of Fos‐immunopositive (Fos+) cells in the six brainstem monoaminergic nuclei examined, which included the ventral tegmental area (VTA), substantia nigra pars compacta (SNc), dorsal raphe nucleus (DR), median raphe nucleus (MR), locus coeruleus (LC), and A7 noradrenaline cells. Densely labelled Fos+ cells were observed in the LC following ICSS, and many of these Fos+ cells were colocalized with TH. Similarly, many of Fos+ cells in the A7 and DR/MR were colocalized with TH and 5‐HT, respectively. By contrast, a smaller number of Fos+ cells was detected in the VTA and SNc following the ICSS, and in these regions the majority of Fos+ cells were not colocalized with TH. Although results among regions quantitatively differed, the ICSS induced a significant increase in the number of double‐labelled cells (GABA+/Fos+ or NR1+/Fos+) in all of the VTA, DR, and LC, in which the ICSS produced an ipsilaterally weighted increase in Fos‐like immunoreactivity. These results suggest that ICSS of the MFB induces differential Fos expression within monoaminergic and GABAergic neurons in brainstem monoaminergic nuclei under modulation by glutamatergic afferents.