bluuebunny/crossref_metadata_2025 huggingface dataset:
A role for protein kinase C in a form of metaplasticity that regulates the induction of long‐term potentiation at CA1 synapses of the adult rat hippocampus
Authors: Bortolotto Zuner A. , Collingridge Graham L.
Published: March 2003

The possibility that protein kinase C (PKC) is involved in the induction of N‐methyl‐ D‐aspartate (NMDA) receptor‐dependent long‐term potentiation (LTP) at CA1 synapses in the hippocampus has been the subject of considerable investigation. However, many of the conclusions have been drawn from the use of relatively nonspecific PKC inhibitors. In the present study we have examined the role of PKC in tetanus‐induced LTP of AMPA receptor‐mediated synaptic transmission in hippocampal slices obtained from adult rats. In particular, we have investigated the possible role of PKC in a molecular switch process that is triggered by the synaptic activation of metabotropic glutamate receptors and regulates the induction of LTP. We find that the three PKC inhibitors examined, chelerythrine, Ro‐31–8220 and Gö 6983, all block the setting of the molecular switch at concentrations consistent with inhibition of PKC. In contrast, these inhibitors are without affect on the induction of LTP, even when applied in very much higher concentrations. A PKA inhibitor, Rp‐cAMPS, had no effect on either process. We suggest that neither PKC nor PKA is required to induce LTP at this synapse. However, PKC is involved in the regulation of LTP induction, via the molecular switch process.
Distinct roles for GFRα1 and GFRα2 signalling in different cranial parasympathetic ganglia in vivo
Authors: Rossi Jari , Tomac Andreas , Saarma Mart , Airaksinen Matti S.
Published: March 2003

Neurturin (NRTN), signalling via the GDNF family receptor α2 (GFRα2) and Ret tyrosine kinase, has recently been identified as an essential target‐derived factor for many parasympathetic neurons. NRTN is expressed in salivary and lacrimal glands, while GFRα2 and Ret are expressed in the corresponding submandibular, otic and sphenopalatine ganglia. Here, we have characterized in more detail the role of GDNF and NRTN signalling in the development of cranial parasympathetic neurons and their target innervation. Gfra1 mRNA was expressed at E12 but not in newborn cranial parasympathetic ganglia, while Gfra2 mRNA and protein were strongly expressed in newborn and adult cranial parasympathetic neurons and their projections, respectively. In newborn GFRα1‐ or Ret‐deficient mice, where many submandibular ganglion neurons were still present, the otic and sphenopalatine ganglia were completely missing. In contrast, in newborn GFRα2‐deficient mice, most neurons in all these ganglia were present. In these mice, the loss and atrophy of the submandibular and otic neurons were amplified postnatally, accompanied by complete loss of innervation in some target regions and preservation in others. Surprisingly, GFRα2‐deficient sphenopalatine neurons, whose targets were completely uninnervated, were not reduced in number and only slightly atrophied. Thus, GDNF signalling via GFRα1/Ret is essential in the early gangliogenesis of some, but not all, cranial parasympathetic neurons, whereas NRTN signalling through GFRα2/Ret is essential for the development and maintenance of parasympathetic target innervation. These results indicate that GDNF and NRTN have distinct functions in developing parasympathetic neurons, and suggest heterogeneity among and within different parasympathetic ganglia.
Anatomy and physiology of a neural mechanism defining depth order and contrast polarity at illusory contours
Authors: Heider B. , Meskenaite V. , Peterhans E.
Published: March 2003

We studied the anatomy and physiology of neurons in monkey visual cortex, which contribute to mechanisms segregating figure and ground at contours based on information provided by occlusion cues. First, we defined the location of neurons sensitive to occluding (illusory) contours. These neurons were found most frequently in the pale cytochrome oxidase stripes of area V2 but rarely in V1. In area V2, they were found in all laminae and with similar frequencies. The few neurons recorded in area V1 concentrated in the upper laminae. Second, we studied the properties and anatomical location of neurons sensitive to occlusion cues (dark and light line‐ends, corners). These neurons had end‐stopped receptive fields and were found with similar frequencies in both areas. In area V1, they concentrated in the upper laminae. In area V2, they were found in all laminae and cytochrome oxidase stripes. These neurons responded to short stimuli of optimal length (bars, edges) and to stimuli terminating in their receptive field (line‐ends, corners). Overall, about half of these neurons detected the direction of such terminations and about 60% were selective for certain types of termination. In summary, our results suggest that in monkey visual cortex, occlusion cues are represented in areas V1 and V2, whereas grouping mechanisms detecting occluding contours concentrate in area V2.
β3, a novel auxiliary subunit for the voltage‐gated sodium channel, is expressed preferentially in sensory neurons and is upregulated in the chronic constriction injury model of neuropathic pain
Authors: Shah B. S. , Stevens E. B. , Gonzalez M. I. , Bramwell S. , Pinnock R. D. , Lee K. , Dixon A. K.
Published: March 2003

Adult dorsal root ganglia (DRG) have been shown to express a wide range of voltage‐gated sodium channel α‐subunits. However, of the auxiliary subunits, β1 is expressed preferentially in only large‐ and medium‐diameter neurons of the DRG while β2 is absent in all DRG cells. In view of this, we have compared the distribution of β1 in rat DRG and spinal cord with a novel, recently cloned β1‐like subunit, β3. In situ hybridization studies demonstrated high levels of β3 mRNA in small‐diameter c‐fibres, while β1 mRNA was virtually absent in these cell types but was expressed in 100% of large‐diameter neurons. In the spinal cord, β3 transcript was present specifically in layers I/II (substantia gelatinosa) and layer X, while β1 mRNA was expressed in all laminae throughout the grey matter. Since the pattern of β3 expression in DRG appears to correlate with the TTX‐resistant voltage‐gated sodium channel subunit PN3, we co‐expressed the two subunits in Xenopus oocytes. In this system, β3 caused a 5‐mV hyperpolarizing shift in the threshold of activation of PN3, and a threefold increase in the peak current amplitude when compared with PN3 expressed alone. On the basis of these results, we examined the expression of β‐subunits in the chronic constriction injury model of neuropathic pain. Results revealed a significant increase in β3 mRNA expression in small‐diameter sensory neurons of the ipsilateral DRG. These results show that β3 is the dominant auxiliary sodium channel subunit in small‐diameter neurons of the rat DRG and that it is significantly upregulated in a model of neuropathic pain.
Opioid tolerance induced by metamizol (dipyrone) microinjections into the periaqueductal grey of rats
Authors: Tortorici Víctor , Vanegas Horacio
Published: March 2003

Non‐opioid analgesics have been shown to elicit antinociception by an action upon central nervous system structures, in addition to their well known action upon peripheral tissues. Microinjection of metamizol (dipyrone), a widely used nonopioid analgesic, into the periaqueductal grey matter (PAG) of rats activates pain‐modulating systems in the nucleus raphe magnus and inhibits spinal nociceptive neurons and the tail‐flick reflex. Since these effects involve an activation of endogenous opioidergic systems, the possibility that metamizol induces opioid tolerance was investigated. Microinjection of metamizol into the ventrolateral PAG in awake rats induced antinociception, as demonstrated in the heat‐elicited tail flick and hot plate tests. When microinjected into the ventrolateral PAG twice daily for 2 days, metamizol induced tolerance, i.e. a progressive loss of its antinociceptive effect. In contrast to rats repeatedly microinjected with saline, metamizol‐tolerant rats were also tolerant to morphine microinjection into the same PAG site, and displayed signs of opioid withdrawal upon systemic administration of naloxone. These and other results suggest that metamizol activates endogenous opioid systems and that nonopioid analgesics may, by an action upon the central nervous system, lead to opioid tolerance and the risk of opioid withdrawal.
Effects of high frequency stimulation of subthalamic nucleus on extracellular glutamate and GABA in substantia nigra and globus pallidus in the normal rat
Authors: Windels François , Bruet Nicolas , Poupard Annie , Urbain Nadia , Chouvet Guy , Feuerstein Claude , Savasta Marc
Published: March 2003

High frequency stimulation (130 Hz) of the subthalamic nucleus has dramatic beneficial motor effects in severe parkinsonian patients. However, the mechanisms underlying these clinical results remain obscure. The objective of the present work was to study the neurochemical changes induced in rats by high frequency stimulation of the subthalamic nucleus by using intracerebral microdialysis within its target structures. Our results show that high frequency stimulation of the subthalamic nucleus induces a significant increase of extracellular glutamate levels in the ipsilateral globus pallidus and substantia nigra while GABA was augmented only in the substantia nigra. These data suggest that functional effects induced by high frequency stimulation of the subthalamic nucleus might imply distal mechanisms involving the synaptic relationships with the subthalamic efferences. They question the current view that the direct inhibition of the subthalamic neurons is induced by high frequency stimulation.
Reduced operant ethanol self‐administration and in vivo mesolimbic dopamine responses to ethanol inPKCε‐deficient mice
Authors: Olive M. Foster , Mehmert Kristin K. , Messing Robert O. , Hodge Clyde W.
Published: March 2003

There is increasing evidence that individual protein kinase C (PKC) isozymes mediate specific effects of ethanol on the nervous system. In addition, multiple lines of evidence suggest that the mesoaccumbens dopamine reward system is critically involved in the rewarding and reinforcing effects of ethanol. Yet little is known about the role of individual PKC isozymes in ethanol reinforcement processes or in regulation of mesolimbic systems. In this study, we report that mice lacking the epsilon isoform of PKC (PKCε) show reduced operant ethanol self‐administration and an absence of ethanol‐induced increase in extracellular dopamine levels in the nucleus accumbens. PKCε null mice exhibited a 53% decrease in alcohol‐reinforced operant responses under basal conditions, as well as following ethanol deprivation. Behavioural analysis revealed that while both genotypes had the same number of drinking bouts following deprivation, PKCε null mice demonstrated a 61% reduction in number of ethanol reinforcers per bout and a 57% reduction in ethanol‐reinforced response rate. In vivo microdialysis experiments showed that, in contrast to wild‐type mice, PKCε null mice exhibited no change in extracellular levels of dopamine in the nucleus accumbens following acute administration of ethanol (1 and 2 g/kg i.p.), while mesolimbic dopamine responses to cocaine (20 mg/kg i.p.) or high potassium (100 m m) in these mice were comparable with that of wild‐types. These data provide further evidence that increases in extracellular mesolimbic dopamine levels contribute to the reinforcing effects of ethanol, and indicate that pharmacological agents inhibiting PKCε may be useful in the treatment of alcohol dependence.
Influence of arm movements on saccades in humans
Authors: Lünenburger L. , Kutz D. F. , Hoffmann K. ‐P.
Published: March 2003

When reaching for an object we usually look at it before we touch it with the hand. This often unconscious eye movement prior to the arm movement allows guiding of the final part of the hand trajectory by visual feedback. We examined the temporal and spatial coordination of this control system by psychophysical measurements of eye and arm movements of naive human subjects looking or looking and pointing as fast as possible to visual targets in physical and virtual‐reality setups. The reaction times of saccades to a step‐displaced target were reduced, and the number of corrective saccades decreased, when the subject had to produce a corresponding simultaneous hand movement to the same target. The saccadic reaction time was increased when saccade and hand movement went in opposite directions. In a double‐step task the reaction time for the second saccade was longer than for the first. Co‐use of the hand leads to an additional increase of saccadic reaction time. Taken together this study shows an improvement in initial saccades if they are accompanied by hand movements to the same target. This effect might ensure that the reach target is foveated early and accurately enough to support the visual feedback control of the hand near the target. Longer reaction times for the second saccade to double‐step displaced targets might reflect a saccadic refractory time intensified by simultaneous arm movements. These results are discussed in the light of recent findings from our laboratory on saccade‐ and reach‐related neurons in the superior colliculus of macaque monkeys.
Effects of eletriptan on the peptidergic innervation of the cerebral dura mater and trigeminal ganglion, and on the expression of c‐fos and c‐jun in the trigeminal complex of the rat in an experimental migraine model
Authors: Knyihár‐Csillik Elizabeth , Tajti János , Csillik Anita E. , Chadaide Zoltán , Mihály András , Vécsei László
Published: March 2003

Nociceptive axons and terminals in the supratentorial cerebral dura mater display an intense calcitonin gene‐related peptide (CGRP) immunoreactivity. In an experimental migraine model, it has been shown that electrical stimulation of the rat trigeminal ganglion induced an increase in the lengths of CGRP‐immunoreactive axons, increased size and number of pleomorphic axonal varicosities in the dura mater, and an increased number of c‐jun and c‐fos protein‐expressing nerve cells in the trigeminal complex. We demonstrate the effect of the highly specific and moderately lipophilic serotonin agonist eletriptan (Pfizer) which prevents the effects of electrical stimulation in the dura mater. Eletriptan also affected the caudal trigeminal complex; it markedly reduced the numbers of the oncoprotein‐expressing cells, mainly after stimulation and to some extent also in nonstimulated animals. Eletriptan also affected expression of CGRP in perikarya of trigeminal ganglion cells, insofar as the number of small nerve cells exhibiting a compact CGRP immunoreaction was decreased to one quarter of the original value. In all these respects, eletriptan acted in a similar way to sumatriptan, with the notable exception that eletriptan also blocked the stimulation‐induced effects in the nucleus caudalis trigemini and the upper cervical spinal cord (trigeminal complex), whereas sumatriptan did not. It is concluded that eletriptan, acting on perikarya and both the peripheral and the central axon terminals of primary sensory neurons, exerts its antimigraine effect by an agonist action on 5‐HT1B/1D receptors throughout the entire trigeminal system, probably by passing the blood–brain‐barrier because of its lipophilic character.
A model of gamma‐frequency network oscillations induced in the rat CA3 region by carbachol in vitro
Authors: Traub Roger D. , Bibbig Andrea , Fisahn André , LeBeau Fiona E. N. , Whittington Miles A. , Buhl Eberhard H.
Published: March 2003

Carbachol (> 20 μm) and kainate (100 nm) induce, in the in vitro CA3 region, synchronized neuronal population oscillations at ≈ 40 Hz having distinctive features: (i) the oscillations persist for hours; (ii) interneurons in kainate fire at 5–20 Hz and their firing is tightly locked to field potential maxima (recorded in s. radiatum); (iii) in contrast, pyramidal cells, in both carbachol and kainate, fire at frequencies as low as 2 Hz, and their firing is less tightly locked to field potentials; (iv) the oscillations require GABAA receptors, AMPA receptors and gap junctions. Using a network of 3072 pyramidal cells and 384 interneurons (each multicompartmental and containing a segment of unmyelinated axon), we employed computer simulations to examine conditions under which network oscillations might occur with the experimentally determined properties. We found that such network oscillations could be generated, robustly, when gap junctions were located between pyramidal cell axons, as suggested to occur based on studies of spontaneous high‐frequency (> 100 Hz) network oscillations in the in vitro hippocampus. In the model, pyramidal cell somatic firing was not essential for the oscillations. Critical components of the model are (i) the plexus of pyramidal cell axons, randomly and sparsely interconnected by gap junctions; (ii) glutamate synapses onto interneurons; (iii) synaptic inhibition between interneurons and onto pyramidal cell axons and somata; (iv) a sufficiently high rate of spontaneous action potentials generated in pyramidal cell axons. This model explains the dependence of network oscillations on GABAA and AMPA receptors, as well as on gap junctions. Besides the existence of axon–axon gap junctions, the model predicts that many of the pyramidal cell action potentials, during sustained gamma oscillations, are initiated in axons.
Stimulation of the mesencephalic locomotor region elicits controlled swimming in semi‐intact lampreys
Authors: Sirota Mikhail G. , Di Prisco Gonzalo Viana , Dubuc Réjean
Published: March 2003

The role of the mesencephalic locomotor region (MLR) in initiating and controlling the power of swimming was studied in semi‐intact preparations of larval and adult sea lampreys. The brain and the rostral portion of the spinal cord were exposed in vitro, while the intact caudal two‐thirds of the body swam freely in the Ringer's‐containing chamber. Electrical microstimulation (2–10 Hz; 0.1–5.0 μA) within a small periventricular region in the caudal mesencephalon elicited well‐coordinated and controlled swimming that began within a few seconds after the onset of stimulation and lasted throughout the stimulation period. Swimming stopped several seconds after the end of stimulation. The power of swimming, expressed by the strength of the muscle contractions and the frequency and the amplitude of the lateral displacement of the body or tail, increased as the intensity or frequency of the stimulating current were increased. Micro‐injection of AMPA, an excitatory amino acid agonist, into the MLR also elicited active swimming. Electrical stimulation of the MLR elicited large EPSPs in reticulospinal neurons (RS) of the middle rhombencephalic reticular nucleus (MRRN), which also displayed rhythmic activity during swimming. The retrograde tracer cobalt‐lysine was injected into the MRRN and neurons (dia. 10–20 μm) were labelled in the MLR, indicating that this region projects to the rhombencephalic reticular formation. Taken together, the present results indicate that, as higher vertebrates, lampreys possess a specific mesencephalic region that controls locomotion, and the effects onto the spinal cord are relayed by brainstem RS neurons.
Light‐induced phase‐shifts in the circadian expression rhythm of mammalian Period genes in the mouse heart
Authors: Sakamoto Katsuhiko , Ishida Norio
Published: March 2003

To investigate the molecular mechanism that regulates circadian rhythms in mammalian peripheral tissues, we examined the phase shifts evoked by light exposure in the circadian mRNA expression rhythms of mammalian Period genes (mPer1, mPer2 and mPer3) and a clock‐controlled gene Dbp, in the mouse heart, by Northern blot analysis. The light pulse did not induce any acute mRNA expression of mPer in the heart, but the pulse gave rise to phase shifts in the circadian mRNA rhythms. On the first day after the exposure, only mPer1 mRNA showed a phase shift, whereas obvious phase shifts were not observed in the rhythms of mPer2, mPer3 and Dbp mRNAs. On the second day, phase shifts occurred to a similar extent in the mRNA rhythms of all four genes examined. The rhythm of mPer1 mRNA shifted fastest among those of the three mPers. Therefore mPer1 seems to play an important role in phase resetting of mammalian peripheral oscillators. Immediate responses to light pulses in mRNA expression of mPers may not be required for phase shifting of peripheral circadian oscillators. Our findings suggest that mammals require more than one day to have peripheral oscillators entrained to a new daily schedule.
Pressure‐induced depression of synaptic transmission in the cerebellar parallel fibre synapse involves suppression of presynaptic N‐type Ca2+ channels
Authors: Etzion Yoram , Grossman Yoram
Published: March 2003

High pressure induces CNS hyperexcitability while markedly depressing synaptic transmitter release. We studied the effect of pressure (up to 10.1 MPa) on the parallel fibre (PF) synaptic response in biplanar cerebellar slices of adult guinea pigs. Pressure mildly reduced the PF volley amplitude and to a greater extent depressed the excitatory field postsynaptic potential (fPSP). The depression of the PF volley was noted even at supramaximal stimulus intensities, indicating an effect of pressure on the amplitude of the action potential in each axon. Low concentrations of TTX mimicked the effects of pressure on the PF volley without affecting the fPSP. Application ω‐conotoxin GVIA (ω‐CgTx) reduced the synaptic efficacy by 34.3 ± 2.7%. However, in the presence of ω‐CgTx the synaptic depression at pressure was significantly reduced. Reduced Ca2+ entry by application of Cd2+ or low [Ca2+]o did not have a similar influence on the effects of pressure. Application of ω‐AGA IVA, ω‐AGA TK and Funnel‐web spider toxin did not affect the synaptic response in concentrations that usually block P‐type Ca2+ channels, whilst the N/P/Q‐type blocker ω‐conotoxin MVIIC reduced the response to 52.7 ± 5.0% indicating the involvement of Q‐type channels and R‐type channels in the non‐N‐type fraction of Ca2+ entry. The results demonstrate that N‐type Ca2+ channels play a crucial role in the induction of PF synaptic depression at pressure. This finding suggests a coherent mechanism for the induction of CNS hyperexcitability at pressure.
Changes in direct current (DC) potentials and infra‐slow EEG oscillations at the onset of the luteinizing hormone (LH) pulse
Authors: Marshall Lisa , Mölle Matthias , Fehm Horst L. , Born Jan
Published: March 2003

An essential function of the neuroendocrine system lies in the coordination of hypothalamo‐pituitary secretory activity with neocortical neuronal activity. Cortical direct current (DC) potential shifts and EEG were monitored in conjunction with the circulating concentration of luteinizing hormone (LH) in humans while asleep to assess a hypothalamic–neocortical interaction. The onset of an LH pulse was accompanied (i) at frontocortical locations by a transient positive DC potential shift of ≈ 3 min duration and peak amplitude 50 μV; (ii) at frontal and central locations by an increase in power of infra‐slow EEG oscillations for periodicities between 64 and 320 s. Results uniquely demonstrate a coupling of hypothalamo‐pituitary activity with regulation of neocortical excitability.
BDNF, NT‐3 and NGF induce distinct new Ca2+ channel synthesis in developing hippocampal neurons
Authors: Baldelli Pietro , Forni Paolo E. , Carbone Emilio
Published: March 2003

Neurotrophins exert short‐ and long‐term effects on synaptic transmission. The mechanism underlying these forms of synaptic plasticity is unknown although it is likely that intracellular Ca2+ and presynaptic Ca2+ channels play a critical role. Here we show that BDNF, NGF and NT‐3 (10–100 ng/mL) exhibit a selective long‐term up‐regulation of voltage‐gated Ca2+ current densities in developing hippocampal neurons of 6–20 days in culture. NGF and NT‐3 appear more effective in up‐regulating L‐currents, while BDNF predominantly acts on non‐L‐currents (N, P/Q and R). The effects of the three neurotrophins were time‐ and dose‐dependent. The EC50 was comparable for BDNF, NGF and NT‐3 (10–16 ng/mL) while the time of half‐maximal activation was significantly longer for NGF compared to BDNF (58 vs. 25 h). Despite the increased Ca2+ current density, the neurotrophins did not alter the voltage‐dependence of channel activation, the kinetics parameters or the elementary properties of Ca2+ channels (single‐channel conductance, probability of opening and mean open time). Neurotrophin effects were completely abolished by coincubation with the nonspecific Trk‐receptor inhibitor K252a, the protein synthesis blocker anisomycin and the MAP‐kinase inhibitor PD98059, while cotreatment with the PLC‐γ blocker, U73122, was without effect. Immunocytochemistry and Western blotting revealed that neurotrophins induced an increased MAP‐kinase phosphorylation and its translocation to the nucleus. The present findings suggest that on a long time scale different neurotrophins can selectively up‐regulate different Ca2+ channels. The action is mediated by Trk‐receptors/MAP‐kinase pathways and induces an increased density of newly available Ca2+ channels with unaltered gating activity.
Heme oxygenase1 (HSP‐32) is induced in myelin‐phagocytosing Schwann cells of injured sciatic nerves in the rat
Authors: Hirata Kazuho , He Jian‐wen , Kuraoka Akio , Omata Yoshiaki , Hirata Mizuki , Islam A. T. M. Shariful , Noguchi Masato , Kawabuchi Masaru
Published: March 2003

Schwann cells participate in myelin phagocytosis in the early stage of Wallerian degeneration, prior to the recruitment of macrophages. This is the first report that Schwann cells induce heme oxygenase‐1 (HO‐1), a 32‐kDa heat shock protein, only when they have transformed into myelin‐phagocytosing cells from myelinating cells (days 2–3) immediately after crush injury of rat sciatic nerves. Double immunofluorescent labelling for HO‐1 and transferrin receptors revealed that HO‐1‐immunoreactive Schwann cells also expressed transferrin receptors suggesting activation of iron metabolism. The transient induction of HO‐1 in Schwann cells may contribute to the adaptive function in an altered environment when the cells have lost contact with axons, and may play a crucial role in the ensuing regeneration.
Do neurons have a reserve of sodium channels for the generation of action potentials? A study on acutely isolated CA1 neurons from the guinea‐pig hippocampus
Authors: Madeja Michael
Published: March 2003

The density of voltage‐gated sodium channels is high in several regions of the neuronal membrane. It is unclear if this density of channels represents a reserve for the neuron, or if it fulfils a special role in action potential firing. This problem was addressed by studying sodium currents and action potentials in acutely isolated hippocampal CA1 neurons whose number of active sodium channels was acutely changed by applying the sodium channel blocker tetrodotoxin (TTX) at different concentrations. The results show that more than a third of the sodium channels can fail without affecting the single action potential. Thus, the neurons have a remarkable surplus of sodium channels. The surplus, however, is necessary for repetitive action potential firing, as every decrease in the fraction of sodium channels reduces the maximal frequency of action potentials that can be generated by the neuron.
Spatiotemporal profile of synaptic activation produced by the electrical and visual stimulation of retinal inputs to the optic tectum: a current source density analysis in the pigeon (Columba livia)
Authors: Letelier Juan Carlos , Mpodozis Jorge , Marin Gonzalo , Morales Daniver , Rozas Carlos , Madrid Carlos , Velasco Marcelo
Published: March 2003

The optic tectum of the pigeon is a highly organized, multilayered structure that receives a massive polystratified afference of at least five different populations of retinal ganglion cells and gives rise to various anatomically segregated efferent systems. The synaptic organization of retino‐tectal circuitry is, at present, mostly unknown. To investigate the spatiotemporal profile of synaptic activation produced by differential (electrical and visual) stimulation of the retinal inputs, we performed a high‐spatial‐resolution current source density analysis in the optic tectum of the anaesthetized pigeon. Electrical stimuli consisted of brief pulses of different durations applied to the optic nerve head, while visual stimuli consisted of light flashes of different intensities. Electrical stimulation generated sinks confined to retinorecipient layers. The temporal structure, spatial location and thresholds of these sinks indicated that they are all due to primary tectal synapses of retinal fibers with different conduction velocities. Sinks evoked by the fastest retinal axons were more superficially located than sinks produced by slower retinal fibers. Visual stimulation, on the other hand, resulted in a more complex pattern of current sinks, with various sinks located in the retinorecipient layers and also well below. Visual stimulation induced action potentials at superficial as well as deep tectal levels. We conclude that electrical stimulation activates most of the populations of ganglion cells as well as their primary tectal synapses, but is unable to elicit a significant activation of secondary tectal synapses. Visual stimulation, on the contrary, activates just some of the incoming retinal populations, but in a way that produces noticeable secondary activation of intratectal circuits. Laminar segregation of retinally evoked tectal activity, as reported here, has also been found in other vertebrates. Similarities and differences with previous studies are discussed.
Routes of zinc entry in mouse cortical neurons: role in zinc‐induced neurotoxicity
Authors: Marin Philippe , Israël Maurice , Glowinski Jacques , Prémont Joël
Published: March 2003

Exposure of central neurons to Zn2+ triggers neuronal death. The routes of Zn2+ entry were investigated in living cortical neurons from the mouse using the specific Zn2+ fluorescent dye N‐(6‐methoxy‐8‐quinolyl)‐p‐toluene sulphonamide (TSQ), which preferentially detects membrane‐bound Zn2+. Exposure of cortical neurons to increasing concentrations of Zn2+ (1–100 μm) induced a progressive increase in the fluorescence of TSQ. This fluorescence signal was not attenuated by the permeation of plasma membrane with digitonin. Accordingly, the major part of TSQ fluorescence (two‐thirds) was associated to the particulate fraction of cortical neurons exposed to Zn2+. These results suggest that Zn2+ detected with TSQ in neurons is mainly bound to membranes. TSQ fluorescence measured in neurons exposed to 3 μm Zn2+ was enhanced by Na+‐pyrithione, a Zn2+ ionophore, α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid (AMPA), N‐methyl‐d‐aspartate (NMDA) or KCl‐induced depolarization. However, in the absence of any treatment, TSQ labelling of neurons exposed to 3 μm Zn2+ was only decreased by NMDA receptor antagonists, whereas it remained unaltered in the presence of antagonists of AMPA receptors or L‐type voltage‐gated Ca2+ channels. Zn2+ entry through NMDA receptors did not contribute to Zn2+‐induced neuronal death, as it was prevented by antagonists of NMDA receptors only when they were added after the Zn2+ exposure. Finally, Zn2+ induced a delayed accumulation of extracellular glutamate which might be responsible for the delayed NMDA receptor activation that leads to neuronal death.
Differential regulation of the dopamine D1, D2 and D3 receptor gene expression and changes in the phenotype of the striatal neurons in mice lacking the dopamine transporter
Authors: Fauchey Valérie , Jaber Mohamed , Caron Marc G. , Bloch Bertrand , Le Moine Catherine
Published: March 2003

Mice with a genetic disruption of the dopamine transporter (DAT–/–) exhibit locomotor hyperactivity and profound alterations in the homeostasis of the nigrostriatal system, e.g. a dramatic increase in the extracellular dopamine level. Here, we investigated the adaptive changes in dopamine D1, D2 and D3 receptor gene expression in the caudate putamen and nucleus accumbens of DAT–/– mice. We used quantitative in situ hybridization and found that the constitutive hyperdopaminergia results in opposite regulations in the gene expression for the dopamine receptors. In DAT–/– mice, we observed increased mRNA levels encoding the D3 receptor (caudate putamen, +60–85%; nucleus accumbens, +40–107%), and decreased mRNA levels for both D1 (caudate putamen, −34%; nucleus accumbens, −45%) and D2 receptors (caudate putamen, −36%; nucleus accumbens, −33%). Furthermore, we assessed the phenotypical organization of the striatal efferent neurons by using double in situ hybridization. Our results show that in DAT+/+ mice, D1 and D2 receptor mRNAs are segregated in two different main populations corresponding to substance P and preproenkephalin A mRNA‐containing neurons, respectively. The phenotype of D1 or D2 mRNA‐containing neurons was unchanged in both the caudate putamen and nucleus accumbens of DAT–/– mice. Interestingly, we found an increased density of preproenkephalin A‐negative neurons that express the D3 receptor mRNA in the nucleus accumbens (core, +35%; shell, +46%) of DAT–/– mice. Our data further support the critical role for the D3 receptor in the regulation of D1–D2 interactions, an action being restricted to neurons coexpressing D1 and D3 receptors in the nucleus accumbens.
Transient neuromotor phenotype in transgenic spastic mice expressing low levels of glycine receptor β‐subunit: an animal model of startle disease
Authors: Becker Lore , Hartenstein Bettina , Schenkel Johannes , Kuhse Jochen , Betz Heinrich , Weiher Hans
Published: March 2003

Startle disease or hereditary hyperekplexia has been shown to result from mutations in the α1‐subunit gene of the inhibitory glycine receptor (GlyR). In hyperekplexia patients, neuromotor symptoms generally become apparent at birth, improve with age, and often disappear in adulthood. Loss‐of‐function mutations of GlyR α or β‐subunits in mice show rather severe neuromotor phenotypes. Here, we generated mutant mice with a transient neuromotor deficiency by introducing a GlyR β transgene into the spastic mouse (spa/spa), a recessive mutant carrying a transposon insertion within the GlyR β‐subunit gene. In spa/spa TG456 mice, one of three strains generated with this construct, which expressed very low levels of GlyR β transgene‐dependent mRNA and protein, the spastic phenotype was found to depend upon the transgene copy number. Notably, mice carrying two copies of the transgene showed an age‐dependent sensitivity to tremor induction, which peaked at ∼ 3–4 weeks postnatally. This closely resembles the development of symptoms in human hyperekplexia patients, where motor coordination significantly improves after adolescence. The spa/spa TG456 line thus may serve as an animal model of human startle disease.
Glucocorticoid receptor impairment alters CNS responses to a psychological stressor: an in vivo microdialysis study in transgenic mice
Authors: Linthorst Astrid C. E. , Flachskamm Cornelia , Barden Nicholas , Holsboer Florian , Reul Johannes M. H. M.
Published: March 2003

To study the consequences of impaired functioning of the glucocorticoid receptor (GR) for behavioural, neuroendocrine and neurochemical responses to a psychological stressor, a transgenic mouse expressing antisense RNA against GR was used. Previous studies on these transgenic mice have shown that impairment of GR evolves in disturbed neuroendocrine regulation and certain behavioural responses to stress. Here we investigated putative disturbances on the level of brain neurotransmission in GR‐impaired (GR‐i) mice using an in vivo microdialysis method. Through a microdialysis probe in the hippocampus, serotonin (5‐HT), 5‐hydroxyindoleacetic acid (5‐HIAA) and free corticosterone [as an index of hypothalamic–pituitary–adrenocortical (HPA) axis activity] were monitored. Moreover, specific behaviours (e.g. grooming, eating/drinking, sniffing, nest building and locomotion) displayed by the mice during collection of the dialysates were scored. Measurement of dialysate concentrations of corticosterone on days 1 and 3 after insertion of the microdialysis probe showed that the free levels of this glucocorticoid were significantly lower in GR‐i mice toward the evening. On day 2 after insertion of the microdialysis probe, baseline values of dialysate corticosterone, 5‐HT and 5‐HIAA were assessed, after which mice were exposed to a rat placed into their home cage. The rat and mouse were separated by a Plexiglas wall. A positive correlation between baseline hippocampal extracellular levels of 5‐HT and 5‐HIAA and the time spent performing active behaviours was observed in both genotypes. The main active behaviour performed at the baseline was grooming behaviour. During the rat exposure period, control mice remained mostly sitting and/or lying with their eyes fixed on the rat. Moreover, they showed a profound rise in free corticosterone levels. In contrast, GR‐i mice displayed significantly more activities along the separation wall and a trend toward more grooming behaviour, but no increase of free corticosterone. In both mouse lines, exposure to a rat increased hippocampal extracellular levels of 5‐HT and 5‐HIAA. The rise in 5‐HT was, however, more pronounced in the GR‐i mice. From these data it may be concluded that life‐long GR impairment has profound consequences for behavioural and neuroendocrine responses to a psychological stressor. Moreover, long‐term impaired functioning of GR evolves in hyper‐responsiveness of the raphe‐hippocampal serotonergic system.
Convergence of segregated pheromonal pathways from the accessory olfactory bulb to the cortex in the mouse
Authors: Von Campenhausen Harald , Mori Kensaku
Published: March 2003

The accessory olfactory system mediates intraspecies pheromonal communication. Two subsets of spatially segregated vomeronasal sensory neurons, presumably handling functionally and structurally different sets of ligand molecules, can be distinguished. The two subsets of sensory neurons project their axons to segregated zones of the accessory olfactory bulb (AOB) and connect with zonally separated mitral/tufted (M/T) cells, suggesting that the accessory olfactory system is divided into two distinct pathways up to the level of the AOB. To examine whether the segregation is maintained at the accessory olfactory cortical (AOC) regions, we selectively tracer‐labelled mitral/tufted cells located in the rostral, caudal or in both zones of the adult mouse AOB. The results demonstrate that the axonal projection patterns of rostral zone and caudal zone M/T cells were indistinguishable in the AOC regions. Mitral/tufted cell axons from either zone of the AOB covered the entire area of all four AOC regions: the bed nucleus of the accessory olfactory tract, the medial amygdaloid nucleus, the posteromedial cortical amygdaloid nucleus and the bed nucleus of the stria terminalis. Therefore, over the entire area of each AOC region, ensembles of cortical neurons receive input from both zonal subsets of M/T cells of the AOB. However, the present results do not rule out the possibility that individual cortical neurons sample information from M/T cells of a single zone. These results are consistent with the idea that the segregation of zonal pathways collapses in the AOC regions. Clusters of cortical neurons in each AOC region may combine information from both families of pheromone receptors and thus handle signals from structurally and functionally different categories of pheromone molecules.
Impaired cerebral autoregulation 24 h after induction of transient unilateral focal ischaemia in the rat
Authors: MacGregor D. G. , Carswell H. V. O. , Graham D. I. , McCulloch J. , Macrae I. M.
Published: March 2003

Cerebral blood flow (CBF) and cerebral autoregulation have been investigated 24 h after transient focal ischaemia in the rat. Cerebral blood flow was measured autoradiographically before and during a moderate hypotensive challenge, to test autoregulatory responses, using two CBF tracers, 99mTc‐d,l‐hexamethylproyleneamine oxide and 14C‐iodoantipyrine. Prior to induced hypotension, CBF was significantly reduced within areas of infarction; cortex (28 ± 20 compared with 109 ± 23 mL/100 g/min contralateral to ischaemic focus, P = 0.001) and caudate (57 ± 31 compared with 141 ± 32 mL/100 g/min contralaterally, P = 0.005). The hypotensive challenge (mean arterial pressure reduced to 60 mmHg by increasing halothane concentration) did not compromise grey matter autoregulation in the contralateral hemisphere; CBF data were not significantly different at normotension and during hypotension. However, in the ipsilateral hemisphere, a significant volume of cortex adjacent to the infarct, which exhibited normal flow at normotension, became oligaemic during the hypotensive challenge (e.g. frontal parietal cortex 109 ± 15% to 65 ± 15% of cerebellar flow, P < 0.01). This resulted in a 2.5‐fold increase in the volume of cortex which fell below 50% cerebellar flow (39 ± 34 to 97 ± 46 mm3, P = 0.003). Moderate hypotension induced a significant reduction in CBF in both ipsilateral and contralateral subcortical white matter (P < 0.01). In peri‐infarct caudate tissue, CBF was not significantly affected by hypotension. In conclusion, a significant volume of histologically normal cortex within the middle cerebral artery territory was found to have essentially normal levels of CBF but impaired autoregulatory function at 24 h post‐ischaemia.
Combined lesions of cholinergic and serotonergic neurons in the rat brain using 192 IgG‐saporin and 5,7‐dihydroxytryptamine: neurochemical and behavioural characterization
Authors: Lehmann Olivia , Jeltsch Hélène , Lehnardt Olivia , Pain Laure , Lazarus Christine , Cassel Jean‐Christophe
Published: March 2003

This study assessed behavioural and neurochemical effects of i.c.v. injections of both the cholinergic toxin 192 IgG‐saporin (2 μg) and the serotonergic toxin 5,7‐dihydroxytryptamine (5,7‐DHT; 150 μg) in Long–Evans female rats. Dependent behavioural variables were locomotor activity, forced T‐maze alternation, beam walking, Morris water‐maze (working and reference memory) and radial‐maze performances. After killing by microwave irradiation, the concentrations of acetylcholine, monoamines and 5‐hydroxyindoleacetic acid (5‐HIAA) were measured in the hippocampus, frontoparietal cortex and striatum. 192 IgG‐saporin reduced the concentration of acetylcholine by ∼ 40% in the frontoparietal cortex and hippocampus, but had no effect in the striatum. 5,7‐DHT lesions reduced the concentration of serotonin by 60% in the frontoparietal cortex and 80% in the hippocampus and striatum. Noradrenaline was unchanged in all structures except the ventral hippocampus where it was slightly increased in rats given 192 IgG‐saporin. Cholinergic lesions induced severe motor deficits but had no other effect. Serotonergic lesions produced diurnal and nocturnal hyperactivity but had no other effect. Rats with combined lesions were more active than those with only serotonergic lesions, showed motor dysfunctions similar to those found in rats with cholinergic lesions alone, and exhibited impaired performances in the T‐maze alternation test, the water‐maze working memory test and the radial‐maze. Taken together and although cholinergic lesions were not maximal, these data show that 192 IgG‐saporin and 5,7‐DHT lesions can be combined to selectively damage cholinergic and serotonergic neurons, and confirm that cholinergic–serotonergic interactions play an important role in some aspects of memory, particularly in spatial working memory.
Release of classical transmitters and nitric oxide in the rat olfactory bulb, evoked by vaginocervical stimulation and potassium, varies with the oestrus cycle
Authors: Guevara‐Guzmán Rosalinda , Barrera‐Mera Baltazar , De La Riva Carlos , Kendrick Keith M.
Published: March 2003

In vivo microdialysis was used to investigate the effects of ovariectomy and the oestrus cycle on vaginocervical stimulation‐evoked classical transmitter and nitric oxide release in the olfactory bulb of anaesthetized (urethane) and conscious rats. During pro‐oestrus/oestrus, vaginocervical stimulation (1 or 10 min) significantly increased concentrations of glutamate, aspartate, GABA, noradrenaline, dopamine and nitric oxide (citrulline) but failed to do so in met‐oestrus/di‐oestrus or following ovariectomy. Potassium chloride‐evoked GABA, noradrenaline and nitric oxide release in the olfactory bulb was also significantly enhanced during pro‐oestrus/oestrus. The effects of vaginocervical stimulation on olfactory bulb transmitter release during pro‐oestrus/oestrus were significantly reduced by pelvic or vagus nerve section. Basal concentrations of classical transmitters and nitric oxide in the olfactory bulb did not vary across the oestrus cycle although noradrenaline and dopamine levels were reduced following ovariectomy. These results confirm our previous electrophysiological data showing that the olfactory bulb mitral cells are only excited by vaginocervical stimulation during pro‐oestrus/oestrus. They also suggest that sex hormones acting primarily at the level of the olfactory bulb dramatically enhance the ability of vaginocervical stimulation to evoke release of both classical transmitters and nitric oxide in this region. Such alterations in neurochemical release in the olfactory bulb may be important for mediating plasticity changes underlying olfactory recognition of mates or offspring.
Distinct immunohistochemical localization of two isoforms of Ca2+/calmodulin‐dependent protein kinase kinases in the adult rat brain
Authors: Sakagami Hiroyuki , Umemiya Masashi , Saito Sachiko , Kondo Hisatake
Published: March 2003

Ca2+/calmodulin‐dependent protein kinase IV (CaM‐KIV) is thought to be involved in regulating gene expression by phosphorylating various transcriptional factors. CaM‐KIV as well as CaM‐KI are activated upon phosphorylation by two distinct isoforms of Ca2+/calmodulin‐dependent protein kinase kinases, CaM‐KKs α and β. In this study, we raised isoform‐specific monoclonal antibodies against CaM‐KKs and examined the immunohistochemical localization of CaM‐KKs in the rat brain, compared with that of CaM‐KIV. CaM‐KK α‐immunoreactivity was rather widely distributed in neurons throughout the brain, except cerebellar cortex. The highest levels of CaM‐KK α‐immunoreactivity were observed in the cerebral cortex, facial nucleus and motor neurons of the spinal cord. Moderate CaM‐KK α‐immunoreactivity was observed in the hippocampal formation, pontine nuclei and various brain stem nuclei including trigeminal, vestibular, cochlear and hypoglossal nuclei. In contrast, CaM‐KK β‐immunoreactivity was relatively restricted in some neuronal populations. The highest levels of CaM‐KK β‐immunoreactivity were observed in the cerebellar granule cell layer, and moderate immunoreactivity was observed in the cerebral cortex, hippocampal formation, caudate putamen, pontine nuclei, cochlear nucleus and molecular layer of the cerebellum. In contrast to the prominent nuclear localization of CaM‐KIV, both isoforms of CaM‐KKs were localized in the perikaryal cytoplasm, dendrites and nerve terminals, but not in the cell nuclei. The distinct localization of two isoforms of CaM‐KKs suggests that the complicated mechanisms for activation of CaM‐KIV by CaM‐KKs may be exerted in region‐specific manners as well as intracellularly.