bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of entorhinal cortex deep layer neurons projecting to the rat dentate gyrus
Authors: Gloveli Tengis , Dugladze Tamar , Schmitz Dietmar , Heinemann Uwe
Published: March 2003

Medial entorhinal cortex (EC) deep layer neurons projecting to the dentate gyrus (DG) were studied. Neurons, retrogradely‐labelled with rhodamine‐dextran‐amine were characterized electrophysiologically with the patch clamp technique and finally labelled with biocytin. Pyramidal and nonpyramidal neurons form projections from the deep layers of the EC to the molecular layer of the DG. In addition, both classes of projection neurons send ascending axon collaterals to the superficial layers of the EC. Both classes of neurons were characterized physiologically by regular action potential firing upon depolarizing current injection. While a substantial number of pyramidal projection cells showed intrinsic membrane potential oscillations, none of the studied nonpyramidal cells exhibited oscillations. Despite the morphological similarity of bipolar and multipolar cells to those of GABAergic interneurons in the EC, their electrophysiological characteristics were similar to those of principal neurons and immunocytochemistry for GABA was negative. We conclude, that neurons of the deep layers of the medial EC projecting to the DG may function as both local circuit and projecting neurons thereby contributing to synchronization between deep layers of the EC, superficial layers of the EC and the DG.
Corticosterone differentially modulates expression of corticotropin releasing factor and arginine vasopressin mRNA in the hypothalamic paraventricular nucleus following either acute or repeated restraint stress
Authors: Pinnock S. B. , Herbert J.
Published: March 2003

Exposing rats to repeated restraint stress induces well‐characterized adaptations in the expression of either corticotropin‐releasing factor (CRF) or arginine‐vasopressin (AVP) mRNA in the parvocellular neurons of the hypothalamic paraventricular nucleus (PVN). The effects of regulating corticosterone levels on this adaptation was studied in male rats. In intact rats, acute restraint stress increased the expression of CRF mRNA whilst AVP mRNA expression was no different to control. Repeated exposure resulted in habituation of CRF expression, whereas AVP mRNA increased above that seen in either non stressed or acutely stressed animals. In adrenalectomised rats with replacement pellets of corticosterone that replicated blood levels approximating to the daily trough (mean levels 37–65 ng/mL), basal CRF expression levels were raised, but the response to acute stress was still observed. However, the habituation seen in normal animals that had been repeatedly stressed was prevented, so that CRF mRNA levels continued to be raised after repeated stress. By contrast, the AVP response to both acute and repeated stress was unaltered in these low‐dose corticosterone‐treated rats compared with controls. Higher dose pellets, which resulted in blood levels around those of the daily maximum (mean 118–141 ng/mL) had the opposite effects. There was no change compared to intact rats in the expression of CRF mRNA following either acute or repeated stress, but the expected increase in AVP following repeated restraint was prevented. These experiments show that corticosterone has important modulating effects on the adaptive pattern of both CRF and AVP mRNA expression in the parvocellular PVN. The ‘set‐point’ of corticosterone differs; for CRF, experiencing higher levels is necessary for subsequent adaptation to repeated restraint to occur, whereas for AVP a return to lower levels is necessary to allow this peptide to respond to repeated stress.
Neuroprotection by estrogen via extracellular signal‐regulated kinase against quinolinic acid‐induced cell death in the rat hippocampus
Authors: Kuroki Yasutomi , Fukushima Kouji , Kanda Yasunari , Mizuno Katsushige , Watanabe Yasuhiro
Published: March 2003

Extracellular signal‐regulated kinase (ERK) belongs to the family of mitogen‐activated protein kinases (MAPKs), which are serine‐threonine kinases activated by phosphorylation in response to a variety of mitogenic signals. We previously reported that 17β‐estradiol rapidly activates ERK in the rat hippocampus. However, the physiological role of this rapid activation of ERK by estrogen in vivo has not yet been elucidated. This study investigated whether ERK may participate in mediating the neuroprotective effects of estrogen against quinolinic acid (QA) toxicity in the rat hippocampus in vivo. Injection of QA into the hippocampi of male rats produced a loss of Nissl‐stained neurons in the CA1 after 24 h. Prior administration of 17β‐estradiol (50 pmol/animal) to the ventricles prevented the QA‐induced decrease in Nissl‐stained neurons. Pretreatment with U0126, an inhibitor of MAPK/ERK kinase, inhibited the rapid activation of ERK by 17β‐estradiol in the rat hippocampus. Moreover, the neuroprotective effects of 17β‐estradiol against QA toxicity were blocked by the pretreatment with U0126. U0126 alone did not produce a loss of neurons. These results indicate that ERK mediates estrogen neuroprotection after QA toxicity in the rat hippocampus.
Distribution of transcripts for the brain‐specific GDP/GTP exchange factor collybistin in the developing mouse brain
Authors: Kneussel M. , Engelkamp D. , Betz H.
Published: March 2003

The dbl‐like GDP/GTP exchange factor, collybistin, binds to the receptor anchoring protein gephyrin and activates the Rho‐like GTPase Cdc42. Collybistin was found in two splice variants I and II, both of which share a tandem Dbl homology/pleckstrin homology (DH/PH) domain. In heterologous expression systems, collybistin II induces the formation of submembraneous gephyrin aggregates and therefore has been implicated in inhibitory synapse formation. Expression of collybistin is restricted to neuronal tissues and is predominantly found in brain. Here, we investigated the spatio‐temporal distribution of collybistin transcripts in the embryonic mouse brain and compared it to gephyrin and glycine receptor mRNA patterns. Our data show that collybistin expression is upregulated when neurons become postmitotic and start to differentiate.
LPS/IFN‐γ cytotoxicity in oligodendroglial cells: role of nitric oxide and protection by the anti‐inflammatory cytokine IL‐10
Authors: Molina‐Holgado Eduardo , Vela José Miguel , Arévalo‐Martín Angel , Guaza Carmen
Published: March 2003

Proinflammatory mediators have been implicated in demyelinating disorders, including multiple sclerosis, whereas it has been proposed that the anti‐inflammatory cytokines interleukin‐ (IL‐) 4 and IL‐10 participate in disease recovery. The present study analysed the effect of interferon‐γ (IFN‐γ) and bacterial endotoxin (lipopolysaccharide, LPS) on proliferation and survival of progenitors and differentiated oligodendrocytes. We also investigated the presence of receptors for IL‐4 and IL‐10 in oligodendroglial cells and explored a possible protective action of IL‐4 and IL‐10 in cultures following LPS/IFN‐γ. Finally, the role of endogenous nitric oxide (NO) on cell viability and the modulatory action of IL‐4 and IL‐10 on inducible nitric oxide synthase (iNOS) expression were also analysed. We report that LPS and/or IFN‐γ reduced proliferation and viability of oligodendroglial cells. Cell death, presumably by apoptosis as evidence by TUNEL and Annexin V binding, was observed following LPS/IFN‐γ, progenitors being more sensitive than differentiated cells. At both developmental stages, LPS/IFN‐γ‐treated cultures expressed iNOS protein and released micromolar concentrations of NO. In progenitors, LPS/IFN‐γ‐mediated cell damage was partially dependent on endogenous NO production, whereas NO was fundamental for cytotoxicity of differentiated oligodendrocytes. Both cell types expressed mRNA for IL‐4 and IL‐10 receptors and expression of IL‐10 receptors at the protein level was also demonstrated. Treatment with either cytokine inhibited the expression of iNOS resulting from the proinflammatory stimulation. IL‐10 was more effective than IL‐4 in suppressing iNOS expression and, interestingly, IL‐10 conferred protection against oligodendroglial death evoked by LPS/IFN‐γ. Our data raise the question of whether IL‐10 may play a protective role in demyelinating diseases, not only downregulating the function of inflammatory cells but also promoting survival of progenitors and differentiated oligodendrocytes.
Suppression of the induction of long‐term depression by carbon monoxide in rat cerebellar slices
Authors: Shibuki Katsuei , Kimura Shinji , Wakatsuki Hidemitsu
Published: March 2003

Carbon monoxide (CO) suppresses brain functions at doses lower than that suppressing oxygen (O2) supply to the brain, and the cerebellum is one of the sites most susceptible to the neurotoxic effects of CO. We investigated the effects of CO on the induction of cerebellar long‐term depression (LTD) in the synapses between parallel fibres (PFs) and Purkinje cells. CO, at concentrations between 8 nm and 5 µm, exhibited almost no effect on synaptic responses in Purkinje cells, O2 consumption and NO release from PFs in rat cerebellar slices. However, the induction of LTD was significantly suppressed by CO at concentrations between 40 and 200 nm. The suppressive effect of 40 nm CO was antagonized by 10 µm NOR3, an NO donor. In contrast, CO exhibited no clear effect on the induction of LTD at concentrations between 1 and 5 µm. The induction of LTD, suppressed by 10 µmNG‐nitro‐l‐arginine, an inhibitor of NO synthase, was not restored by 5 µm CO. CO is not only a neurotoxic substance but also a candidate for an intercellular messenger. δ‐Aminolevulinate (30 µm), a substance facilitating endogenous CO production, suppressed the induction of LTD, and the effect of δ‐aminolevulinate was antagonized by 10 µm NOR3. These findings suggest that CO may have a suppressive effect on the induction of cerebellar LTD at nanomolar concentrations, probably via its effects on NO/cGMP signalling.
The dorsomedial visual areas in New World and Old World monkeys: homology and function
Authors: Rosa Marcello G. P. , Tweedale Rowan
Published: March 2003

The extrastriate cortex near the dorsal midline has been described as part of an ‘express’ pathway that provides visual input to the premotor cortex. This pathway is considered important for the integration of sensory information about the visual field periphery and the skeletomotor system, especially in relation to the control of arm movements. However, a better understanding of the functional contributions of different parts of this complex has been hampered by the lack of data on the extent and boundaries of its constituent visual areas. Recent studies in macaques have provided the first detailed view of the topographical organization of this region in Old World monkeys. Despite differences in nomenclature, a comparison of the visuotopic organization, myeloarchitecture and connections of the relevant visual areas with those previously studied in New World monkeys reveals a remarkable degree of similarity and helps to clarify the subdivision of function between different areas of the dorsomedial complex. A caudal visual area, named DM or V6, appears to be important for the detection of coherent patterns of movement across wide regions of the visual field, such as those induced during self‐motion. A rostral area, named M or V6A, is more directly involved with visuomotor integration. This area receives projections both from DM/V6 and from a separate motion analysis channel, centred on the middle temporal visual area (or V5), which detects the movement of objects in extrapersonal space. These results support the suggestion, made earlier on the basis of more fragmentary evidence, that the areas rostral to the second visual area in dorsal cortex are homologous in all simian primates. Moreover, they emphasize the importance of determining the anatomical organization of the cortex as a prerequisite for elucidating the function of different cortical areas.
Stretch‐activated cation channels of leech neurons exhibit two activity modes
Authors: Pellegrini Monica , Menconi M. Carla , Pellegrino Mario
Published: March 2003

Single‐channel recordings were used to characterize two activity modes of stretch activated channels (SACs) in identified neurons of the leech. Clear‐cut differences in the activity pattern of SACs from freshly desheathed cell bodies and from cultured AP cells were observed. SACs of inside‐out patches, made by ‘gentle’ sealing and excised from cell bodies of freshly desheathed ganglia exhibited spike‐like (SL) activity, with a mean channel open time (MCOT) shorter than 10 ms. Fitting of dwell open‐time distributions revealed time constants shorter than 2 and 10 ms. This activity was characterized by a chord conductance of about 115 pS. SACs from cultured cells often displayed activity just after excision. MCOT exceeded 200 ms and the time constants of open‐time interval distributions were longer than 10 and 100 ms. Furthermore, this activity pattern was characterized by both sub‐ (about 80 and 40 pS) and super‐conductance (150 pS) levels, hence denoted as multiconductance (MC) mode. The percentage of open time spent at the main subconductance level (80 pS) was significantly higher in patches isolated from growth cones than in those from cell bodies of cultured neurons. The two activity modes (SL and MC) should belong to the same channel because both modes have a common main conductance value and exhibit outward rectification, stretch sensitivity and blockage by Gd3+ and gentamicin.

     Cytochalasin D applied to the cytoplasmic side induced activation of SACs or increased their ongoing activity. Thus, the observed differences in the expression of the two activity modes of SACs might be associated with different arrangements of the cortical cytoskeleton.
Nitric oxide induces cGMP immunoreactivity and modulates membrane conductance in identified central neurons of Aplysia
Authors: Koh H.‐Y. , Jacklet J. W.
Published: March 2003

Nitric oxide (NO) acts as an orthograde neurotransmitter in the central nervous system by stimulating guanylyl cyclase and increasing cGMP. We previously demonstrated this pathway for an identified synaptic follower neuron in the cerebral ganglion of the mollusc Aplysia californica. Here, we investigated the NO–cGMP pathway in other Aplysia central neurons using cGMP immunocytochemistry and intracellular recordings. NO‐induced cGMP immunoreactivity in a few neurons in the abdominal, pleural and buccal ganglia, including identified neurons L11 and R15 in the abdominal ganglion and neuron Bng in the buccal ganglion. NO depolarized all these neurons but none of the four nonimmunoreactive neurons tested. In neuron L11, NO‐induced depolarization, tonic spiking and a reduction in membrane conductance at resting potential. The NO effect was mimicked by applying the membrane permeable analogue, 8‐Br‐cGMP in L11. Neuron R15 was depolarized and its activity shifted from spike/bursts to tonic spiking. These NO effects were blocked by applying the guanylyl cyclase inhibitor ODQ and mimicked by 8‐Br‐cGMP. Neuron Bng was depolarized and produced spikes tonically. These results provide evidence that the NO–cGMP pathway is linked to membrane ionic channels in cGMP‐IR neurons, and the channels may be different in specific neurons.
Lowering the extracellular potassium concentration elicits epileptic activity in neocortical tissue of epileptic patients
Authors: Gorji Ali , Köhling Rüdiger , Straub Heidrun , Höhling Jörg‐Michael , Madeja Michael
Published: March 2003

The increase in the extracellular potassium concentration ([K+]o) is a well‐established model of epilepsy (the so‐called high potassium model). Therefore, it is generally accepted that for the prevention of abnormal excitability and seizure generation, increases of [K+]o must be avoided. In this paper, however, we show that on the contrary, a reduction of [K+]o also elicits epileptic activity in brain slices of man.
NMDA receptor antagonist treatment induces a long‐lasting increase in the number of proliferating cells, PSA‐NCAM‐immunoreactive granule neurons and radial glia in the adult rat dentate gyrus
Authors: Nacher Juan , Rosell Daniel R. , Alonso‐Llosa Gregori , McEwen Bruce S.
Published: March 2003

During adulthood, neural precursors located in the subgranular zone of the dentate gyrus continue to proliferate, leading to the generation of new granule neurons. These recently generated cells transiently express the polysialylated form of the neural cell adhesion molecule, PSA‐NCAM, and are supported by radial glia‐like cells that are likely to play a role in neuronal migration and differentiation, or even act as their precursors. Previous reports indicate that treatment with NMDA receptor antagonists stimulates adult neurogenesis in the dentate gyrus, and because of the potential therapeutic value of this approach, we were interested in further characterizing the consequences of pharmacologically modulating this process. We treated adult rats with the competitive NMDA receptor antagonist, CGP43487, and examined cell proliferation, PSA‐NCAM expression, and changes in the radial glia cell population in the subgranular zone at different time points. In addition, we sought to determine if this treatment led to changes in cell death or gliotic reactions. The number of proliferating cells in the subgranular region of the dentate gyrus was increased significantly 2 days after treatment and it remained elevated 7 days postinjection. PSA‐NCAM‐immunoreactive granule cells and nestin‐expressing radial glia‐like cells also increased in number 7 days after the treatment. In contrast, we did not observe any change in granule cell death, and we were unable to detect any microglial or astroglial reaction during the first 7 days after treatment. Thus, NMDA receptor antagonist treatment serves as a valuable tool to increase neurogenesis in the adult hippocampus without undesirable collateral deleterious effects.
Effects of substance P on excitability and ionic currents of normal and axotomized rat dorsal root ganglion neurons
Authors: Abdulla F. A. , Stebbing M. J. , Smith P. A.
Published: March 2003

Substance P (SP) may act within dorsal root ganglia (DRG) to modulate the transmission of nociceptive information. Because peripheral nerve injury (axotomy) alters the peptide content of sensory neurons, we used whole‐cell recording to examine the effects of sciatic nerve section on the sensitivity of rat lumbar DRG neurons to SP (0.3–1 µm). At 1 µm, SP increased the excitability of ‘small’, putative nociceptive neurons but had little effect on the excitability of ‘large’ neurons. Two‐four weeks after sciatic nerve section, however, the effect of SP on ‘large’ axotomized neurons was increased and its effect on ‘small’ neurons was decreased. SP did not affect Ca2+ channel currents in control or axotomized neurons. The effects of SP on the current‐voltage (I–V) relationship of 77% of neurons involved increased inward current at potentials below −30 mV and suppressed outward current at potentials above −20 mV. The effects of SP on the I–V relationship were similar in control and in axotomized neurons and the altered sensitivity of ‘small’ and ‘large’ cells could not be attributed to axotomy‐induced changes in input resistance or membrane potential. The possible relevance of alterations in sensitivity, of ‘large’ DRG neurons to SP, to the generation of neuropathic pain is discussed.
Characteristics of fast Na+ current of hypoglossal motoneurons in a rat brainstem slice preparation
Authors: Lape Remigijus , Nistri Andrea
Published: March 2003

Whole‐cell patch clamp recordings were performed on hypoglossal motoneurons in a brainstem slice preparation from the neonatal rat brain to study the characteristics of the fast Na+ current (INa) which has not been hitherto investigated in these cells. To aid voltage clamping of INa, cells were bathed in low Na+ solution, loaded intracellularly with Na+ (to reverse the Na+ gradient) or treated with a small dose (20 nm) of tetrodotoxin. In low extracellular Na+ solution (Na+ was replaced by choline or N‐methyl‐d‐glucamine) INa activated at membrane potentials positive to −45 mV and was half‐maximally activated at −30 mV. Similar data were obtained when the Na+ gradient was reversed or tetrodotoxin was applied. INa rapidly activated (1–3.5 ms time constant) and inactivated (1.6 ms time constant at 0 mV) during membrane depolarization. Inactivation was strongly voltage‐dependent (half inactivation at −44 mV) and developed mono‐exponentially. Recovery from inactivation was bi‐exponential with fast and slow time constants of 14 and 160 ms, respectively, at −58 mV. The rapid turning on of INa was presumably responsible for the upstroke of the fast action potential generated by these cells while the slow phase of recovery from inactivation might modulate the ability to fire repetitively at high rate.
Mismatch between BDNF mRNA and protein expression in the developing visual cortex: the role of visual experience
Authors: Tropea Daniela , Capsoni Simona , Tongiorgi Enrico , Giannotta Sabina , Cattaneo Antonino , Domenici Luciano
Published: March 2003

Brain‐derived neurotrophic factor (BDNF) messenger RNA (mRNA) expression in the rat visual cortex of young and postnatal day 90 (P90) animals is developmentally regulated and influenced by visual experience. In the present paper we compared the expression of BDNF mRNA to the actual changes of BDNF protein occurring during postnatal development and verified whether BDNF protein distribution is controlled by visual activity. To achieve this aim we analysed BDNF mRNA and/or BDNF protein cellular distribution in the rat visual cortex at different postnatal ages by using immunohistochemistry and highly sensitivein situhybridization. We found that before eye opening (P13), in all cortical layers a large number of visual cortical neurons contain BDNF mRNA with no detectable amount of BDNF protein. At later ages (P23 and P90), the number of BDNF‐immunostained cells increases; most neurons are double labelled for BDNF mRNA and protein, and a small group of neurons is labelled only for BDNF protein. The cellular increase of BDNF immunolabelling is blocked in animals deprived of visual experience from birth (dark rearing), with a large population of neurons containing BDNF mRNA but not BDNF protein. This is similar to what is observed before eye opening. Exposure of dark‐reared rats to a brief period (2 h) of light restores a good match between BDNF mRNA and BDNF protein cellular expression. We propose that visual experience controls the neuronal content of BDNF mRNA and BDNF protein in developing visual cortex.
Vasoactive intestinal polypeptide (VIP) phase‐shifts the rat suprachiasmatic nucleus clock in vitro
Authors: Reed Helen E. , Meyer‐Spasche Alert , Cutler David J. , Coen Clive W. , Piggins Hugh D.
Published: March 2003

In mammals, the principal circadian pacemaker is housed in the hypothalamic suprachiasmatic nuclei (SCN). The SCN exhibit high levels of vasoactive intestinal polypeptide (VIP) immunoreactivity and two of the three VIP receptors, VPAC2 and PAC1, are found in the rat SCN. However, the role of VIP in the SCN remains unclear. In this study, we examined the phase‐resetting actions of VIP and selective VIP receptor agonists on the electrical activity rhythm of rat SCN neurons in vitro. Application of VIP during the subjective day did not shift the peak in the firing rate rhythm. However, VIP treatment during the early or late subjective night evoked a small phase delay or a large phase advance, respectively. The phase‐advancing effect of VIP was reproduced by the novel VPAC2 receptor agonist RO 25‐1553, but not by pituitary adenylate cyclase‐activating peptide (a potent PAC1 receptor agonist), or by [K15,R16,L27]VIP(1‐7)/GRF(8‐27), a novel, selective VPAC1 receptor agonist. These data show that VIP phase‐dependently phase‐resets the rodent SCN pacemaker in vitro, presumably via the VPAC2 receptor. As the pattern of phase‐shifting evoked by VIP and RO 25‐1553 resembles the phase‐resetting actions of light on rodent behavioural rhythms, these data support a role for VIP and the VPAC2 receptor in photic entrainment of the rodent circadian pacemaker.
Differential daily expression of Per1 and Per2 mRNA in the suprachiasmatic nucleus of fetal and early postnatal mice
Authors: Shimomura Haruka , Moriya Takahiro , Sudo Motoki , Wakamatsu Hisanori , Akiyama Masashi , Miyake Yoshiaki , Shibata Shigenobu
Published: March 2003

It is well known that there are circadian rhythms of 2‐deoxyglucose uptake and neuronal firing in the rat suprachiasmatic nucleus (SCN) during fetal and early postnatal periods. A core clock mechanism in the mouse SCN appears to involve a transcriptional feedback loop in which CLOCK and BMAL1 function as positive regulators and three mPeriod (mPer) genes play a role in negative feedback. Per genes expression occurs not only in the adult SCN but also in the fetal SCN. However, the developmental change in these genes remains unclear. In this experiment, we examined the day–night pattern of expression of Per1 and Per2 mRNA in the mouse SCN and cerebral cortex on embryonic day 17, postnatal day 3, and in young adult mice under a light–dark cycle. Daily rhythms of mRNA content were observed in mPer1 but not mPer2 in the fetal SCN. Interestingly, the expression of mPer2 in the SCN was high throughout the entire day, and a significant daily rhythm of this gene was observed on postnatal day 6. The expression pattern of SCN mPer1 in constant darkness was similar to that seen in the light–dark cycle. The present results suggest that the daily oscillation of mPer1 but not of mPer2 in the SCN in fetal and early postnatal mice may be associated with the daily rhythms of 2‐deoxyglucose uptake and neuronal firing.
Neural cell adhesion molecule is endocytosed via a clathrin‐dependent pathway
Authors: Miñana R. , Duran J. M. , Tomas M. , Renau‐Piqueras J. , Guerri C.
Published: March 2003

Neural cell adhesion molecule (NCAM) constitutes a group of cell surface glycoproteins that regulate cell–cell interactions in the developing and adult brain. Endocytosis is a mechanism which dynamically controls the amount of cell surface NCAM expression and may involve the rapid changes occurring in NCAM expression under certain physiological or pathological conditions. However, the endocytic pathway of NCAM is presently unknown. Using astrocytes in culture and immunofluorescence we show that NCAM is internalized and that the immunolabelling presents a high degree of colocalization with clathrin, α‐adaptin and transferrin, suggesting that NCAM is endocytosed by a clathrin‐dependent pathway. Potassium depletion which disrupts clathrin‐mediated endocytosis, inhibited internalization of NCAM. Electron microscopy and immunogold studies also demonstrate that the surface of clathrin‐coated vesicles are also immunolabelled for both α‐adaptin and PSA‐NCAM, the highly sialylated isoform of NCAM. Furthermore, immunoprecipation studies demonstrate that NCAM is associated with both clathrin and α‐adaptin, a component of adaptor complex AP‐2, in brain, neurons and astrocytes. These findings indicate that NCAM is mainly endocytosed via clathrin‐coated vesicles, suggesting a possible mechanism that may contribute to the rapid changes in NCAM expression at the cell surface.
Swelling‐activated calcium signalling in cultured mouse primary sensory neurons
Authors: Viana Félix , De La Peña Elvira , Pecson Brian , Schmidt Robert F. , Belmonte Carlos
Published: March 2003

The effects of hypo‐osmotic membrane stretch on intracellular calcium concentration ([Ca2+]i), cell volume and cellular excitability were investigated in cultured mouse primary sensory trigeminal neurons. Hypotonic solutions (15–45%) led to rapid cell swelling in all neurons. Swelling was accompanied by dose‐dependent elevations in [Ca2+]i in a large fraction of neurons. Responses could be classified into three categories. (i) In 57% of the neurons [Ca2+]i responses had a slow rise time and were generally of small amplitude. (ii) In 21% of the neurons, responses had a faster rise and were larger in amplitude. (iii) The remaining cells (22%) did not show [Ca2+]i responses to hypo‐osmotic stretch. Slow and fast [Ca2+]i changes were observed in trigeminal neurons of different sizes with variable responses to capsaicin (0.5 µm). The swelling‐induced [Ca2+]i responses were not abolished after depletion of intracellular Ca2+ stores with cyclopiazonic acid or preincubation in thapsigargin, but were suppressed in the absence of external Ca2+. They were strongly attenuated by extracellular nickel and gadolinium. Hypotonic stimulation led to a decrease in input resistance and to membrane potential depolarization. Under voltage‐clamp, the [Ca2+]i elevation produced by hypotonic stimulation was accompanied by the development of an inward current and a conductance increase. The time course and amplitude of the [Ca2+]i response to hypo‐osmotic stimulation showed a close correlation with electrophysiological properties of the neurons. Fast [Ca2+]i responses were characteristic of trigeminal neurons with short duration action potentials and marked inward rectification. These findings suggest that hypo‐osmotic stimulation activates several Ca2+‐influx pathways, including Gd3+‐sensitive stretch‐activated ion channels, in a large fraction of trigeminal ganglion neurons. Opening of voltage‐gated Ca2+ channels also contributes to the response. The pattern and rate of Ca2+ influx may be correlated with functional subtypes of sensory neurons.
Corticonuclear projections of the cerebellum preserve both anteroposterior and mediolateral pairing patterns
Authors: Pantò M. R. , Zappalà A. , Parenti R. , Serapide M. F. , Cicirata F.
Published: March 2003

The aim of the present study was to establish whether a diverging arrangement of the corticonuclear cerebellar projections exists and, if so, what relation it has with the inferior olivary complex. Iontophoretic injections of a 1 : 1 mixture of tetramethylrhodamine dextran amine and byotinilated dextran amine into the cerebellar cortex orthogradely labelled fibre terminals in the cerebellar nuclei and retrogradely labelled cell bodies in the inferior olivary complex. The injections were into A, B, C2, C3, D1 and D2 bands. These injections showed diverging projections to the cerebellar nuclei, with ‘primary projections’ directed to the nuclear region previously reported to be specifically connected with the injected band and ‘secondary projections’ directed to other nuclear regions. Secondary projections from the A, C2 and C3 bands diverged to nuclear regions primarily controlled by cortical bands lateral to those injected. Secondary projections from the D1, and D2 bands diverged to nuclear regions primarily controlled by cortical bands medial to those injected. Moreover, injections distributed along the D1 and D2 bands showed similar sets of nuclear targets, while those distributed along the A, C2 and C3 bands showed two sets of nuclear targets in relation to the anteroposterior location of the injected area within these bands. The cortical areas that projected to the same set of nuclear targets were innervated from single olivary regions, while those that projected to different sets of nuclear targets were innervated from different subsets of single regions of the inferior olive. The results suggest that the olivary bands of the cerebellar cortex project to the cerebellar nuclei with a diverging pattern that is organized in both the mediolateral and the anteroposterior axes.
Dopamine D2receptors regulate tyrosine hydroxylase activity and phosphorylation at Ser40 in rat striatum
Authors: Lindgren Niklas , Xu Zhi‐Qing David , Herrera‐Marschitz Mario , Haycock John , Hökfelt Tomas , Fisone Gilberto
Published: March 2003

In the striatum, dopamine release is inhibited by activation of dopamine D2autoreceptors. Changes in dopamine release have been attributed to changes in the synthesis of dopamine, which is regulated via phosphorylation of tyrosine hydroxlase (TH), the rate‐limiting enzyme in the synthesis of catecholamines. Here, we have studied the involvement of dopamine D2receptors in the regulation of TH phosphorylation at distinct seryl residues, using phosphorylation site‐specific antibodies and a preparation of rat striatal slices. The D2receptor agonist, quinpirole, reduced basal TH phosphorylation at Ser40 but not at Ser19 or Ser31. Quinpirole was also able to reduce the increase in Ser40 phosphorylation caused by forskolin, an activator of adenylyl cyclase, without affecting the increase in Ser19 phosphorylation produced by the glutamate receptor agonist,N‐methyl‐d‐aspartate (NMDA). In addition, the dopamine D2receptor agonist reduced both basal and forskolin‐stimulated activity of TH, measured as 3,4‐dihydroxyphenylalanine (DOPA) accumulation. Quinpirole decreased phosphorylation of Ser40 induced by okadaic acid, an inhibitor of protein phoshatase 1 and 2A and Ro‐20‐1724, a phosphodiesterase inhibitor. In contrast, quinpirole did not affect the increase in Ser40 phosphorylation caused by the cAMP analogue, 8‐Br‐cAMP. These data indicate that, in the striatum, activation of dopamine D2receptors results in selective inhibition of TH phosphorylation at Ser40 via reduction of the activity of adenylyl cyclase. They also provide a molecular mechanism accounting for the ability of dopamine D2autoreceptors to inhibit dopamine synthesis and release from nigrostriatal nerve terminals.
RGS9 proteins facilitate acute tolerance to mu‐opioid effects
Authors: Garzón Javier , Rodríguez‐Díaz Marta , López‐Fando Almudena , Sánchez‐Blázquez Pilar
Published: March 2003

This paper reports that regulators of G‐protein signalling (RGS) proteins modulate the timing and amplitude of opioid signals by a push–pull mechanism. This is achieved without noticeable changes in the binding properties of opioids, e.g. β‐endorphin to mu‐opioid receptors. The expression of RGS proteins was reduced by blocking their mRNA with antisense oligodeoxynucleotides (ODN). Knock down of RGS2 or RGS3 diminished morphine and β‐endorphin analgesia, whereas that of RGS9 or RGS12 enhanced this activity. In mice with impaired RGS9, but not impaired RGS2, the potency and, in particular, the duration of opioid antinociception increased. Further, the animals did not exhibit acute tolerance generated by a single and efficacious dose of morphine, nor did they develop tolerance after a daily i.c.v. injection of the opioid for 4 days. In a model of sustained morphine treatment, the impairment of RGS9 proteins facilitated increases in the response to the delivered opioid. This was only effective for 2–3 h after the subcutaneous implantation of an oily morphine pellet; later, tolerance developed. To reduce the impact of the chronic morphine acting on opioid receptors, other RGS proteins presumably substitute the GTPase‐activating function of RGS9 on morphine‐activated Gα‐GTP subunits. The desensitization of mu‐opioid receptors appears to be a cell membrane‐limited process facilitated by RGS9′s sequestering of agonist‐segregated Gα subunits.
Gating of vagal inputs by sciatic afferents in nonspinally projecting neurons in the rat rostral ventrolateral medulla oblongata
Authors: Zagon A. , Hughes D. I.
Published: March 2003

Integration and coordination of somato‐visceral sensory information is crucial to achieve adaptive behavioural responses. We have recently shown that sensory vagal and somato‐sensory (sciatic nerve) inputs converge in neurons of the rostral ventrolateral medulla oblongata, which was implicated in adjusting visceral activities to changing somatic performances. In the present study, the neuronal mechanism of interaction between sciatic and vagal sensory inputs was examined in the rostral ventrolateral medulla oblongata using in vivo intracellular recording and labelling. Conditioning stimulation of the contralateral sciatic nerve (2 V) led to a time‐dependent inhibition of responses to vagal stimulation (100 µA) in each RVLM neuron that received convergent sciatic and vagal sensory inputs (n = 50). None of these neurons had direct spinal projections, and only 8% of them exhibited a visible response to stimulation of the aortic depressor nerve. A significant attenuation of the amplitude of vagal test responses was present for up to 800 ms of conditioning delay, although the duration of this sciatico‐vagal inhibition was greatly dependent on the intensity of both stimuli. The electrophysiological data indicated that sciatico‐vagal inhibition is mediated presynaptically, via activation of GABAB receptors. Morphological evidence of axo‐axonic interactions that may underlie sciatico‐vagal inhibition was subsequently found in the electron microscope. It is suggested that during movements of the hindleg, activation of sciatic sensory fibres leads to re‐patterning of neuronal activity in RVLM neurons via inhibition of visceral sensory inputs. Sciatico‐vagal inhibition is likely to affect the activity of those RVLM neurons that modulate higher neuronal activities via ascending projections.
In vitro effects of acetyl‐dl‐leucine (tanganil®) on central vestibular neurons and vestibulo‐ocular networks of the guinea‐pig
Authors: Vibert Nicolas , Vidal Pierre‐Paul
Published: March 2003

For 40 years, the amino acid acetyl‐dl‐leucine (or isoleucine/Tanganil®) has been used in clinical practice to reduce the imbalance and autonomic signs associated with acute vertigo crises. In animal models, acetyl‐dl‐leucine was shown to accelerate vestibular compensation following unilateral labyrinthectomy, while having only minor effects on normal vestibular function. However, the underlying mechanisms are unknown. In this study, the effect of acetyl‐dl‐leucine on the activity of central vestibular neurons of the medial vestibular nucleus (MVN) and/or the overall activity of vestibular‐related networks was electrophysiologically measured in brainstem slices and in the isolated, in vitro whole brain (IWB) of guinea‐pig. Only moderate effects were obtained in normal animals, where both excitatory and inhibitory actions of acetyl‐dl‐leucine were obtained. However, intracellular recordings from MVN neurons revealed that the nature of the response depended on the resting membrane potential. The neurons excited by acetyl‐dl‐leucine were significantly hyperpolarized compared to nonsensitive cells, whereas the neurons inhibited by this compound tended to display higher than normal membrane potentials. In accordance with these data, acetyl‐dl‐leucine reduced the prominent asymmetry characterizing the vestibular‐related networks of IWBs taken from previously labyrinthectomized animals, by decreasing the activity of the abnormally depolarized neurons on the hyperactive side. Altogether, our results suggest that acetyl‐dl‐leucine might act mainly on abnormally hyperpolarized and/or depolarized MVN neurons, by bringing back their membrane potential towards a mean value of −65 to −60 mV. Since in animal models, acute vestibular disorders are associated with asymmetrical spontaneous activities of MVN neurons, this study suggests how acetyl‐dl‐leucine may reduce acute, vestibular‐related imbalances in humans.
Novelty‐evoked elevations of nucleus accumbens dopamine: dependence on impulse flow from the ventral subiculum and glutamatergic neurotransmission in the ventral tegmental area
Authors: Legault Mark , Wise Roy A.
Published: March 2003

In vivomicrodialysis in freely moving rats was used to monitor novelty‐evoked elevations in extracellular dopamine in the nucleus accumbens septi (NAS) and to examine the role of the ventral subiculum of the hippocampus and glutamatergic transmission in the ventral tegmental area (VTA) on these elevations. Exposure to novel stimuli evoked investigatory activity and increased nucleus accumbens dopamine. Unilateral injections of the sodium channel blocker tetrodotoxin (0.16 ng/0.5 µL) into the ventral subiculum ipsilateral to the dialysed NAS abolished novelty‐evoked elevations in dopamine. Injections of tetrodotoxin into the contralateral VS did not prevent novelty‐evoked elevations in nucleus accumbens dopamine. Unilateral perfusion (via microdialysis) of the ionotropic glutamate receptor antagonists kynurenic acid (1 mm) into the ipsilateral but not the contralateral VTA blocked novelty‐evoked elevations in nucleus accumbens dopamine. Neither unilateral injections of tetrodotoxin nor unilateral perfusion of kynurenic acid disrupted investigatory behaviour. These data indicate that phasic elevations in nucleus accumbens dopamine evoked by exposure to unconditioned novel stimuli are dependent on impulse flow from the hippocampus and glutamatergic transmission in the VTA.
Immunocytochemical identification and analysis of the diffuse bipolar cell type DB6 in macaque monkey retina
Authors: Chan Tricia L. , Martin Paul R. , Grünert Ulrike
Published: March 2003

The distribution and morphology of CD15‐immunoreactive bipolar cells were studied in the retina of macaque monkey. Labelled cells have a large dendritic tree contacting several cones and a narrowly stratified axon terminal that ends deep in the inner plexiform layer, close to the ganglion cell layer. The morphology of the labelled cells corresponds to that of the diffuse bipolar cell type named DB6 by Boycott & Wässle (1991; Eur. J. Neurosci., 3,1069). We conclude that CD15 is a marker for DB6 bipolar cells, enabling the quantitative analysis of the distribution and connectivity of this diffuse bipolar cell type.
Defining the role of Drosophila lateral neurons in the control of circadian rhythms in motor activity and eclosion by targeted genetic ablation and PERIOD protein overexpression
Authors: Blanchardon Eric , Grima Brigitte , Klarsfeld André , Chélot Elisabeth , Hardin Paul E. , Préat Thomas , Rouyer François
Published: March 2003

The ventral lateral neurons (LNvs) of the Drosophila brain that express the period (per) and pigment dispersing factor (pdf) genes play a major role in the control of circadian activity rhythms. A new P‐gal4 enhancer trap line is described that is mostly expressed in the LNvs This P‐gal4 line was used to ablate the LNvs by using the pro‐apoptosis gene bax, to stop PER protein oscillations by overexpressing per and to block synaptic transmission with the tetanus toxin light chain (TeTxLC). Genetic ablation of these clock cells leads to the loss of robust 24‐h activity rhythms and reveals a phase advance in light–dark conditions as well as a weak short‐period rhythm in constant darkness. This behavioural phenotype is similar to that described for disconnected1 (disco1) mutants, in which we show that the majority of the individuals have a reduced number of dorsally projecting lateral neurons which, however, fail to express PER. In both LNv‐ablated and disco1 flies, PER cycles in the so‐called dorsal neurons (DNs) of the superior protocerebrum, suggesting that the weak short‐period rhythm could stem from these PDF‐negative cells. The overexpression of per in LNs suppresses PER protein oscillations and leads to the disruption of both activity and eclosion rhythms, indicating that PER cycling in these cells is required for both of these rhythmic behaviours. Interestingly, flies overexpressing PER in the LNs do not show any weak short‐period rhythms, although PER cycles in at least a fraction of the DNs, suggesting a dominant role of the LNs on the behavioural rhythms. Expression of TeTxLC in the LNvs does not impair activity rhythms, which indicates that the PDF‐expressing neurons do not use synaptobrevin‐dependent transmission to control these rhythms.
Developmental pattern of expression of the alpha chemokine stromal cell‐derived factor 1 in the rat central nervous system
Authors: Tham To Nam , Lazarini Françoise , Franceschini Isabelle Amiko , Lachapelle François , Amara Ali , Dubois‐Dalcq Monique
Published: March 2003

Stromal cell‐derived factor 1 (SDF‐1) is an alpha‐chemokine that stimulates migration of haematopoietic progenitor cells and development of the immune system. SDF‐1 is also abundantly and selectively expressed in the developing and mature CNS, as we show here. At embryonic day 15, SDF‐1 transcripts were detected in the germinal periventricular zone and in the deep layer of the forming cerebral cortex. At birth, granule cells in the cerebellum and glial cells of the olfactory bulb outer layer showed an SDF‐1 in situ hybridization signal that decreased progressively within the next 2 weeks. In other regions such as cortex, thalamus and hippocampus, SDF‐1 transcripts detected at birth progressively increased in abundance during the postnatal period. SDF‐1 protein was identified by immunoblot and/or immunocytochemistry in most brain regions where these transcripts were detected. SDF‐1 was selectively localized in some thalamic nuclei and neurons of the fifth cortical layer as well as in pontine and brainstem nuclei which relay the nociceptive response. The presence of SDF‐1 transcripts in cerebellar granule cells was correlated with their migration from the external to the inner granular layers with disappearance of the signal when migration was completed. In contrast, SDF1 mRNA signal increased during formation of the hippocampal dentate gyrus and stayed high in this region throughout life. The selective and regulated expression of SDF‐1 in these regions suggests a role in precursor migration, neurogenesis and, possibly, synaptogenesis. Thus this alpha chemokine may be as essential to nervous system function as it is to the immune system.
Neurochemical and electrophysiological evidence that 5‐HT4 receptors exert a state‐dependent facilitatory control in vivo on nigrostriatal, but not mesoaccumbal, dopaminergic function
Authors: Lucas Guillaume , Di Matteo Vincenzo , De Deurwaerdère Philippe , Porras Grégory , Martín‐Ruiz Raúl , Artigas Francesc , Esposito Ennio , Spampinato Umberto
Published: March 2003

In this study we investigated, using in vivo microdialysis and single unit recordings, the role of serotonin4 (5‐HT4) receptors in the control of nigrostriatal and mesoaccumbal dopaminergic (DA) pathway activity. In freely moving rats, the 5‐HT4 antagonist GR 125487 (1 mg/kg, i.p.), without effect on its own, significantly reduced the enhancement of striatal DA outflow induced by 0.01 (−35%) and 0.1 (−66%), but not 1 mg/kg, s.c. haloperidol (HAL). Intrastriatal infusion of GR 125487 (1 µm) had no influence on basal DA outflow, but attenuated (−49%) the effect of 0.01 mg/kg HAL. Systemic administration of GR 125487 modified neither basal nor 0.01 mg/kg HAL‐stimulated accumbal DA outflow. In halothane‐anaesthetized rats, 1 or 10 mg/kg GR 125487, without effect by itself, failed to modify the changes in accumbal and striatal DA outflow elicited by electrical stimulation (300 µA, 1 ms, 20 Hz, 15 min) of the dorsal raphe nucleus. Finally, GR 125487 (444 µg/kg, i.v.), whilst not affecting basal firing of DA neurons within either the substantia nigra or the ventral tegmental area, reduced HAL‐stimulated (1–300 µg/kg, i.v.) impulse flow of nigrostriatal DA neurons only. These results indicate that 5‐HT4 receptors exert a facilitatory control on both striatal DA release and nigral DA neuron impulse flow only when nigrostriatal DA transmission is under activated conditions. Furthermore, they indicate that the striatum constitutes a major site for the expression of the control exerted by 5‐HT4 receptors on DA release. In contrast, 5‐HT4 receptors have no influence on mesoaccumbal DA activity in either basal or activated conditions.