bluuebunny/crossref_metadata_2025 huggingface dataset:
Mitral cell loss following lateral olfactory tract transection increases proliferation density in rat olfactory epithelium
Authors: Weiler Elke , Farbman Albert I.
Published: March 2003

Olfactory sensory neurons are replaced throughout the life of vertebrates by proliferation of basal cells and differentiation of the new cells into neurons. Removal of their target, the olfactory bulb, increases proliferation twofold because sensory neurons die prematurely, suggesting that the olfactory bulb provides a trophic substance required for survival. We asked whether mitral cells, a major postsynaptic target of olfactory sensory neurons, are involved in their survival. We report here that depletion of mitral cells increases proliferation and cell death in the olfactory sensory neuron population. Mitral cell loss was induced unilaterally by transection of their axons in the lateral olfactory tract in 18‐day‐old rats. At all time points after surgery (3 weeks, 7 weeks, 3 months, 14 months) there was a 29% mean reduction in the number of mitral cells ipsilateral to the transection. The surviving mitral cells were smaller than controls and had less rough endoplasmic reticulum. In the olfactory epithelium, proliferation density (BrdU‐positive cells/mm epithelial length) in the progenitor basal cells was increased by an average of 20–25% at all time points, as was the number of TUNEL‐positive dying cells. The results are consistent with the notion that mitral cells, or the synaptic sites on them, are a source of trophic factor required for maintenance of the lives of olfactory sensory cells. The target field of postsynaptic neurons remaining after lateral olfactory tract transection is insufficient to maintain normal survival of all existing olfactory neurons. In unperturbed animals the proliferation density declines in an age‐dependent manner and interestingly the decline on the tractotomized side is parallel. This suggests that with age the sensory cells are less dependent on their targets.
Integrins at the neuromuscular junction are important for motoneuron survival
Authors: Wong K. C. K. , Meyer T. , Harding D. I. , Dick J. R. T. , Vrbová G. , Greensmith L.
Published: March 2003

During development motoneurons depend on target contact for their survival. Following injury to the sciatic nerve in neonatal rats, a large proportion of motoneurons die. However, the same injury inflicted at 5 days of age results in no loss of motoneurons. This critical period of postnatal development coincides with the time during which there is a significant increase in the release of transmitter from the nerve terminals at the neuromuscular junction. We have proposed that the role of the target muscle cell during this period is to induce this up‐regulation of transmitter release from motor nerve terminals. It has been shown that stretch‐induced increase in transmitter release from frog motor nerve terminals is accomplished via an integrin‐dependent mechanism. In this study we examined the role of integrins at the rat neuromuscular junction in motoneuron survival. We found that blocking integrin binding at the developing neuromuscular junction delayed the increase in choline acetyltransferase activity that normally takes place during the early postnatal period, and resulted in motoneuron death. Furthermore, the maturation of those motoneurons that survived was delayed so they remained susceptible to subsequent nerve injury. These results support the possibility that integrins, by their involvement in modulating transmitter release, can influence motoneuron survival.
Action of C‐type natriuretic peptide (CNP) on passive avoidance learning in rats: involvement of transmitters
Authors: Telegdy G. , Kokavszky K. , Nyerges A.
Published: March 2003

The action of C‐type of natriuretic peptide (CNP) was tested on one‐way passive avoidance learning in rats. The involvement of transmitters was investigated by pretreating the animals with different receptor blockers. CNP administered into the lateral brain ventricle caused a dose‐dependent facilitation of learning and consolidation of passive avoidance learning, but was ineffective on retrieval. Pretreatment of the animals with atropine, haloperidol or the nitric oxide synthase inhibitor nitro‐l‐arginine abolished the action of CNP. Phenoxybenzamine, naloxone, bicuculline, propranolol and methysergide were ineffective in modifying the action of CNP on consolidation. The results suggest that CNP is able to improve the learning and consolidation of learning in a passive avoidance paradigm, but is ineffective on retrieval processes. In the action of CNP, dopamine, acetylcholine and nitric oxide could be the mediating transmitters.
The effects of early prenatal monocular enucleation on the routing of uncrossed retinofugal axons and the cellular environment at the chiasm of mouse embryos
Authors: Chan S. ‐O. , Chung K. Y. , Taylor J. S. H.
Published: March 2003

Whereas it has been shown that early monocular enucleations produce a reduction in the uncrossed pathway from the surviving eye in rats and ferrets, similar evidence for binocular interactions in the development of the uncrossed component in mice is currently open to question. Using retrograde tracing, we have investigated the time course of changes in the uncrossed retinofugal pathway immediately after the early prenatal monocular enucleation in mouse embryos. Removal of one eye from C57 pigmented mice at embryonic day (E) 13 does not cause a reduction of the earliest uncrossed component from the central retina examined 1 day later at E14. However, a substantial reduction of the uncrossed pathway is seen at E15, the time when the major uncrossed projection first arises from the ventral temporal retina. This reduction is greater in E16 one‐eyed embryos, indicating that most retinal axons from the ventral temporal retina rely on a binocular interaction for their turning at the chiasm. Further, early removal of one eye at E13 does not produce any obvious changes in the cytoarchitecture of RC‐2‐immunopositive radial glia at the chiasm, nor of the stage‐specific antigen‐1 (SSEA‐1) ‐expressing neurons. This lack of changes in the cellular organization at the chiasm indicates that the reduction of the uncrossed pathway is probably produced by an elimination of binocular fibre interactions at the chiasm, rather than through a degenerative change of cellular elements at the chiasm as a consequence of the eye removal procedure.
Long‐term changes in connexin32 gap junction protein and mRNA expression following cocaine self‐administration in rats
Authors: Bennett Steffany A. L. , Arnold Jennifer M. , Chen Jiahua , Stenger Janet , Paul David L. , Roberts David C. S.
Published: March 2003

Considerable evidence indicates a critical role for dopamine in the reinforcing effects of cocaine. Because dopamine has been shown to be a critical modulator of gap junction communication in both eye and brain, we sought to examine whether extended intravenous cocaine self‐administration would affect the expression of gap junction channel‐forming proteins (connexins). Using ELISA, Western analysis, immunohistochemistry, semi‐quantitative reverse transcriptase polymerase chain reaction (RT‐PCR), and non‐radioactive in situ hybridization, we demonstrate that withdrawal from chronic cocaine self‐administration causes lasting changes in connexin32 (Cx32) expression in the nucleus accumbens and hippocampus at 2, 7 and 21 days after the last cocaine injection. A sustained decrease in Cx32 protein and mRNA levels is noted in areas that have been implicated in cocaine craving (i.e. nucleus accumbens and subfields of the hippocampal formation). A progressive increase in gap junction protein and mRNA expression is noted in areas that become hyperexcitable after chronic cocaine exposure (i.e. CA1 hippocampal neurons). We speculate that gap junction communication may be critically involved in reinforcement processes and neuroadaptive changes produced by drugs of abuse.
A fronto‐parietal circuit for object manipulation in man: evidence from an fMRI‐study
Authors: Binkofski F. , Buccino G. , Posse S. , Seitz R. J. , Rizzolatti G. , Freund H. ‐J.
Published: March 2003

Functional magnetic resonance imaging (fMRI) was used to localize brain areas active during manipulation of complex objects. In one experiment subjects were required to manipulate complex objects for exploring their macrogeometric features as compared to manipulation of a simple smooth object (a sphere). In a second experiment subjects were asked to manipulate complex objects and to silently name them upon recognition as compared to manipulation of complex not recognizable objects without covert naming. Manipulation of complex objects resulted in an activation of ventral premotor cortex [Brodmann's area (BA) 44], of a region in the intraparietal sulcus (most probably corresponding to the anterior intraparietal area in the monkey), of area SII and of a sector of the superior parietal lobule. When the objects were covertly named additional activations were found in the opercular part of BA 44 and in the pars triangularis of the inferior frontal gyrus (BA 45). We suggest that a fronto‐parietal circuit for manipulation of objects exists in humans and involves basically the same areas as in the monkey. It is proposed that area SII analyses the intrinsic object characteristics whilst the superior parietal lobule is related to kinaesthesia.
Axonal transport of synucleins is mediated by all rate components
Authors: Jensen Poul Henning , Li Jia‐Yi , Dahlström Annica , Dotti Carlos G.
Published: March 2003

Synucleins are abundant nerve terminal proteins of hitherto unknown function. In diseases with Lewy bodies, human α‐synuclein concentrates in these lesions in the cell body and mutations in α‐synuclein lead to heritable Parkinson's disease with Lewy bodies. This indicates that changes in the normal metabolism and axonal transport of α‐synuclein is perturbed in these diseases. To investigate the normal axonal transport of synucleins we studied the rat visual system by nerve crush operations and metabolic labelling of the retinal ganglion cells followed by immunoprecipitation of nerve segments. We found by immunofluorescence microscopy of the crush‐operated nerves that synucleins are transported by fast antero‐ and retrograde transport and colocalize with synaptophysin and SNAP‐25 around the lesion. The metabolic labelling studies demonstrated that synucleins were moved through the nerve with all the rate components, the fast component and the slow components a and b, with component b predominating. Two‐dimensional gel electrophoresis revealed that both α‐ and β‐synuclein migrate through the nerve by slow component b in a ratio of 2 : 1.
Neural activities of IL‐6‐type cytokines often depend on soluble cytokine receptors
Authors: März Pia , Otten Uwe , Rose‐John Stefan
Published: March 2003

Cytokines of the interleukin‐6 (IL‐6) family participate in regulatory and inflammatory processes within the nervous system. IL‐6, ciliary neurotrophic factor (CNTF) and IL‐11 act via specific membrane receptors which, together with their ligands, associate with signal‐transducing receptor subunits thereby initiating cytoplasmic signalling. Cells which only express signal‐transducing receptor subunits but no ligand binding subunits for IL‐6, CNTF and IL‐11 are refractory to these cytokines. An unusual feature of the IL‐6 cytokine family is that the soluble forms of the ligand binding receptor subunits generated by one cell type in complex with their ligands can directly stimulate the signal‐transducing receptor subunits on different cell types which lack ligand binding receptor subunits. This process has been named transsignalling. This article focuses on the importance of transsignalling events in neuronal differentiation and survival responses.
Growth responses of different subpopulations of adult sensory neurons to neurotrophic factors in vitro
Authors: Gavazzi Isabella , Kumar Robin D. C. , McMahon Stephen B. , Cohen James
Published: March 2003

Different subpopulations of adult primary sensory neurons in the dorsal root ganglia express receptors for different trophic factors, and are therefore potentially responsive to distinct trophic signals. We have compared the effect of the neurotrophins nerve growth factor (NGF), brain‐derived neurotrophic factor (BDNF) and NT‐3, and of glial cell line‐derived neurotrophic factor (GDNF) on neurite outgrowth in dissociated cultures of sensory neurons from the lumbar ganglia of young adult rats, and attempted to establish subset‐specific effects of these trophic factors. We analysed three parameters of neurite growth (percentage of process‐bearing neurons, length of longest neurite and total neurite length), which may correlate with particular types of axon growth in vivo, and may therefore respond differently to trophic factor presence. Our results showed that percentage of process‐bearing neurons and total neurite length were influenced by trophic factors, whilst the length of the longest neurite was trophic factor independent. Only NGF and GDNF were found to enhance significantly the proportion of process‐bearing neurons in vitro. GDNF was more effective than NGF on small, IB4– neurons, which are known to develop GDNF responsiveness early in postnatal development. NGF, and to a much lesser extent GDNF, enhanced the total length of the neurites produced by neurons in culture. BDNF exerted an inhibitory effect on growth, and both BDNF and NT‐3 could partially block some of the growth‐promoting effects of NGF on specific neuronal subpopulations.
Peripheral but not central axotomy promotes axonal outgrowth and induces alterations in neuropeptide synthesis in the nodose ganglion of the rat
Authors: Reimer Martina , Kanje Martin
Published: March 2003

We investigated the effects of central and peripheral axotomy of the sensory neurons in the nodose ganglion on neurite outgrowth and neuropeptide expression. Axonal outgrowth was studied in ganglia subjected to a conditioning lesion of the vagus nerve 6 days prior to in vitro explantation. In such cultures, a conditioning effect, i.e. a shorter initial delay and faster axonal outgrowth, was observed after peripheral axotomy, while central axotomy had no effect. Neuropeptide expression was measured by immunocytochemistry 3 days after axotomy. Peripheral axotomy induced an increase in the number of neurons expressing the C‐terminal flanking peptide of neuropeptide Y (C‐PON), galanin (GAL) and vasoactive intestinal peptide (VIP). In contrast, central axotomy did not affect neuropeptide expression. These results suggest that both axonal outgrowth and expression of neuropeptides in the sensory neurons of the nodose ganglion could be regulated by the contact of the cells with their peripheral, but not their central targets.
Potentiation of glutamatergic agonist‐induced inositol phosphate formation by basic fibroblast growth factor is related to developmental features in hippocampal cultures: neuronal survival and glial cell proliferation
Authors: Blanc Emmanuelle M. , Jallageas Monique , Recasens Max , Guiramand Janique
Published: March 2003

We investigated the modulation by growth factors of phospholipase C (PLC)‐linked glutamate receptors during in vitro development of hippocampal cultures. In defined medium, glial cells represent between 3 and 14% of total cell number. When we added basic fibroblast growth factor (bFGF) 2 h after plating, we found: (i) a neuroprotection from naturally occurring death for up to 5 days; (ii) a proliferation of glial cells from day 3; and (iii) a potentiation of quisqualate (QA)‐induced inositol phosphate (IP) formation from 1 to 10 days in vitro (DIV) and 1s,3r‐amino‐cyclopentane‐1,3‐dicarboxylate (ACPD) response from 3 to 10 DIV. The antimitotic cytosine‐β,d‐arabinofuranoside (AraC) blocked glial cell proliferation induced by bFGF, but not neuroprotection. Under these conditions, the early potentiation of the QA response (1–3 DIV) was not changed, while the ACPD and late QA response potentiations were prevented (5–10 DIV). Epidermal growth factor was not neuroprotective but it induced both glial cell proliferation and late QA or ACPD potentiation. Surprisingly, the early bFGF‐potentiated QA‐induced IP response was blocked by 6,7‐dinitro‐quinoxaline‐2,3‐dione (DNQX), suggesting the participation of ionotropic (rs)‐α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate (AMPA)/kainate (KA) receptors. The delayed bFGF‐potentiated ACPD‐induced IP response is inhibited by (s)‐α‐methyl‐4‐carboxyphenylglycine (MCPG), indicating possible activation of glial metabotropic receptors. These results suggest that, in hippocampal cultures, bFGF modulates AMPA and metabotropic glutamate receptors linked to the IP cascade, possibly in relation to the regulation of neuronal survival and glial cell proliferation, respectively.
Effects of microdialysis application of monoamines on the EEG and behavioural states in the cat mesopontine tegmentum
Authors: Crochet Sylvain , Sakai Kazuya
Published: March 2003

The peri‐locus coeruleus alpha (peri‐LCα) of the mediodorsal pontine tegmentum contains cholinergic and non‐cholinergic neurons, and is critically implicated in the regulation of both wakefulness and paradoxical sleep (PS). The peri‐LCα receives dense monoaminergic (adrenergic, noradrenergic, serotonergic, dopaminergic and histaminergic) afferent projections, but little is known about their exact roles in the control of sleep–wake cycles. We have therefore examined the in vivo effects of microdialysis application of monoamines to the peri‐LCα and adjacent cholinergic and non‐cholinergic tegmental structures on behavioural states and the electroencephalogram (EEG) in freely moving cats. Norepinephrine, epinephrine and dopamine selectively inhibited PS and induced PS without atonia when applied to the caudal part of the peri‐LCα, which mainly contains non‐cholinergic descending neurons, whereas histamine and serotonin had no effect at this site. In the rostral part of the peri‐LCα and the adjacent X area (nucleus tegmenti pedunculopontinus, pars compacta), which contain many ascending cholinergic neurons, norepinephrine and epinephrine suppressed PS with a significant increase in waking and a decrease in slow‐wave sleep, as expressed by a marked decrease in the power of the cortical and hippocampal delta (0.5–2.5 Hz) and cortical alpha (8–14 Hz) bands, and an increase in the cortical gamma (30–60 Hz) band. At these sites, histamine had similar waking and EEG‐desynchronizing effects, but never suppressed PS, while dopamine and serotonin had no effect. These findings indicate a special importance of the adrenergic, noradrenergic and dopaminergic systems in the inhibitory or permissive mechanisms of PS, and of the adrenergic, noradrenergic and histaminergic systems in the control of behavioural and EEG arousal.
Role of membrane conductances and protein synthesis in subjective day phase advances of the hamster circadian clock by neuropeptide Y
Authors: Hall Adam C. , Earle‐Cruikshanks Germaine , Harrington Mary E.
Published: March 2003

Neurons of the mammalian circadian pacemaker in the hypothalamic suprachiasmatic nuclei exhibit a rhythm in firing rate that can be reset by neuropeptide Y. We recorded the effects of neuropeptide Y on Na+ and K+ conductances of hamster suprachiasmatic nuclei neurons using whole‐cell, perforated‐patch and cell‐attached patch‐clamp recordings, both in dissociated and brain slice preparations. While neuropeptide Y had no effect on voltage‐gated Na+ currents, neuropeptide Y activated a leak K+ current. Neuropeptide Y phase advances in the suprachiasmatic nuclei brain slice preparation were blocked by a number of K+ channel blockers (tetraethylammonium chloride, dendrotoxin‐I, glybenclamide). However, a K+ ionophore, valinomycin, did not shift the rhythm. The inhibition by tetraethylammonium chloride did not persist in the presence of glutamatergic receptor blockers. We have previously shown that glutamate can oppose neuropeptide Y phase‐shifting actions, suggesting that K+ channel inhibition acts by inducing glutamate release. Protein synthesis inhibitors had no effect on clock phase when applied during the subjective day, and had no influence on neuropeptide Y‐induced phase shifts. On the other hand, glutamate's ability to inhibit neuropeptide Y shifts was abolished by protein synthesis inhibition. Thus, while neuropeptide Y phase shifts do not require protein synthesis, glutamate blocks neuropeptide Y shifts via increased gene expression during the subjective day, at a time when it does not reset the clock. These results indicate that neuropeptide Y phase shifts via a mechanism that does not involve changes in membrane conductance or protein synthesis.
Central effects of 5‐HT on respiratory rhythm in newborn rats in vivo
Authors: Khater‐Boidin J. , Rose D. , Glérant J. C. , Duron B.
Published: March 2003

The role of 5‐HT in inducing apnoeas (a major element in sudden infant death syndrome) is controversial because while 5‐HT is a respiratory depressant in vivo, it evokes respiratory analeptic effects when applied to the isolated brainstem of the newborn rat. In decerebrate newborn rats, the electrical activity of the diaphragm and that of a hypoglossally innervated tongue muscle, as well as the cardiac frequency (Fc), were recorded before and after the application of 5‐HT and related agents to the floor of the IVth ventricle. To assess the spontaneous variability in inspiratory frequency (Fi) and Fc, a sham group was studied. A decrease in Fi was observed in response to 5‐HT. This respiratory depressant effect was associated with an activation of the tongue muscle, but there was no change in Fc. Application of agonists elicited a small increase in Fi linked to activation of 5‐HT1A receptors, and decreases in both Fi and the activity of the tongue muscle resulting predominantly from activation of 5‐HT2 receptors. The decrease in Fi was much smaller in newborn rats than that reported in newborn kittens. Indeed, in newborn rats, we did not observe long‐lasting apnoeas. Our results differ from those obtained from the newborn rat in vitro, inasmuch as in vivo 5‐HT essentially depressed the respiratory rhythm generator. The role of the afferent system appears to be crucial in modulating the action of 5‐HT.
Spontaneous and evoked activity of intercalated amygdala neurons
Authors: Collins Dawn R. , Paré Denis
Published: March 2003

The intercalated cell masses are clusters of GABAergic neurons interposed between the basolateral and centromedial nuclear groups of the amygdala. Tract‐tracing studies have revealed that the main projection sites of intercalated neurons are the central amygdaloid nucleus and the basal forebrain. Through these projections, intercalated neurons could influence the activity of widespread regions of the central nervous system. However, no data are available regarding their physiological properties because of the paramount methodological difficulties raised by the small size of intercalated cell masses. Here, we have investigated the spontaneous and evoked activity of intercalated neurons in unanaesthetized, chronically implanted cats. Extracellular recording sites were identified using stringent histological criteria. The intercalated cell masses were found to contain a population of neurons firing at much higher rates than commonly observed in neighbouring amygdaloid nuclei. Individual intercalated neurons displayed state‐dependent changes in firing rates, but these varied from cell to cell. Most tested intercalated neurons displayed short‐latency orthodromic responses to cortical shocks and were responsive to a variety of auditory stimuli. Considering that the vast majority of intercalated neurons use γ‐aminobutyric acid (GABA) as a transmitter, the presence of neurons with high spontaneous firing rates within the intercalated cell masses suggests that these cell clusters may provide a tonic inhibitory input to their projection sites. Moreover, the fact that the firing probability of some intercalated neurons could be altered by the presentation of sensory stimuli suggests that this inhibitory input can be modulated as a function of environmental contingencies.
Differential regulation of tyrosine hydroxylase in the basal ganglia of mice lacking the dopamine transporter
Authors: Jaber Mohamed , Dumartin Brigitte , Sagné Corinne , Haycock John W. , Roubert Christine , Giros Bruno , Bloch Bertrand , Caron Marc G.
Published: March 2003

Mice lacking the dopamine transporter (DAT) display biochemical and behavioural dopaminergic hyperactivity despite dramatic alteration in dopamine homeostasis. In order to determine the anatomical and functional integrity of the dopaminergic system, we examined the expression of tyrosine hydroxylase (TH), the rate‐limiting enzyme of dopamine synthesis as well as DOPA decarboxylase and vesicular monoamine transporter. TH‐positive neurons in the substantia nigra were only slightly decreased (–27.6 ± 4.5%), which can not account for the dramatic decreases in the levels of TH and dopamine that we previously observed in the striatum. TH mRNA levels were decreased by 25% in the ventral midbrain with no modification in the ratio of TH mRNA levels per cell. However, TH protein levels were decreased by 90% in the striatum and 35% in the ventral midbrain. In the striatum, many dopaminergic projections had no detectable TH, while few projections maintained regular labelling as demonstrated using electron microscopy. DOPA decarboxylase levels were not modified and vesicular transporter levels were decreased by only 28.7% which suggests that the loss of TH labelling in the striatum is not due to loss of TH projections. Interestingly, we also observed sporadic TH‐positive cell bodies using immunohistochemistry and in situ hybridization in the striatum of homozygote mice, and to some extent that of wild‐type animals, which raises interesting possibilities as to their potential contribution to the dopamine hyperactivity and volume transmission previously reported in these animals. In conjunction with our previous findings, these results highlight the complex regulatory mechanisms controlling TH expression at the level of mRNA, protein, activity and distribution. The paradoxical hyperdopaminergia in the DAT KO mice despite a marked decrease in TH and dopamine levels suggests a parallel to Parkinson's disease implying that blockade of DAT may be beneficial in this condition.
Development of L‐type calcium channels and a nifedipine‐sensitive motor activity in the postnatal mouse spinal cord
Authors: Jiang Z. , Rempel J. , Li J. , Sawchuk M. A. , Carlin K. P. , Brownstone R. M.
Published: March 2003

Intrinsic membrane properties are important in the regulation of motoneuronal output during such behaviours as locomotion. A conductance through L‐type calcium channels has been implicated as an essential component in the transduction of motoneuronal input to output during locomotion. Given the developmental changes in calcium currents occurring postnatally in some neurons, and the increasing interest in the study of spinal locomotor output in neonatal preparations, experiments were conducted to investigate the postnatal development of L‐type calcium channels in mouse motoneurons. This was assessed both physiologically, using a chemically induced rhythmic motor output, and anatomically, using immunohistochemical methods. The electrophysiological data were obtained during rhythmic bursting produced by application of N‐methyl‐d‐aspartate (NMDA) and strychnine to the isolated spinal cord at various postnatal ages. The L‐type calcium channel blocker nifedipine has no effect on this ventral root bursting in postnatal day (P) P2–P5 animals, but reversibly reduced the amplitude and/or burst duration of this activity in animals greater than P7. The immunohistochemical evidence demonstrates a dramatic change in the cellular profile of both the α1C and α1D subunits of L‐type calcium channels during postnatal development; the labelling of both subunits increases with age, approximating the adult pattern by P18. These results demonstrate that in the spinal cord, the L‐type calcium channel profile develops both physiologically and anatomically in the early postnatal period. This development parallels the development of the mature functional behaviours of weight bearing and walking, and may be necessary for the production of complex motor behaviour in the mature mammal.
Induction of presynaptic differentiation in cultured neurons by extracellular matrix components
Authors: Son Young‐Jin , Patton Bruce L. , Sanes Joshua R.
Published: March 2003

Motoneurons reinnervating skeletal muscles form nerve terminals at sites of contact with a specialized basal lamina. To analyse the molecules and mechanisms that underly these responses, we introduce two systems in which basal lamina‐derived components induce presynaptic differentiation of cultured neurons from chick ciliary ganglia in the absence of a postsynaptic cell. In one, ciliary neurites that contact substrates coated with a recombinant laminin β2 fragment form varicosities that are rich in synaptic vesicle proteins, depleted of neurofilaments, and capable of depolarization‐dependent exocytosis and endocytosis. Thus, a single molecule can trigger a complex, coordinated program of presynaptic differentiation. In a second system, neurites growing on cryostat sections of adult kidney form vesicle‐rich, neurofilament‐poor arbors on glomeruli. Glomerular basal lamina, like synaptic basal lamina, is rich in laminin β2 and collagen (α3–5) IV. However, glomeruli from mutant mice lacking these proteins were capable of inducing differentiation, suggesting the glomerulus as a source of novel presynaptic organizing molecules.
Axotomy results in major changes in BDNF expression by dorsal root ganglion cells: BDNF expression in large trkB and trkC cells, in pericellular baskets, and in projections to deep dorsal horn and dorsal column nuclei
Authors: Michael G. J. , Averill S. , Shortland P. J. , Yan Q. , Priestley J. V.
Published: March 2003

Brain derived neurotrophic factor (BDNF) is normally expressed by a small number of predominantly trkA‐expressing dorsal root ganglion cells. Using immunocytochemistry and in situ hybridization, we have examined the effect of sciatic nerve section on the expression of BDNF in the adult rat. Following axotomy there was a long lasting (4‐week) increase in BDNF mRNA and protein in large‐diameter, trkB‐ and trkC‐expressing dorsal root ganglion cells. By 2 days postaxotomy, expression of BDNF mRNA had increased from 2% of trkB cells to 50%, and from 18% of trkC cells to 56%. In contrast, BDNF expression in most trkA cells was unchanged, although was increased in the small population of medium‐ and large‐sized trkA cells. Following axotomy, BDNF‐immunoreactive terminals appeared in the central axonal projections of large‐diameter cells, including the deep dorsal horn and gracile nucleus. Neuropeptide Y was also upregulated following axotomy and was coexpressed with BDNF in the cell bodies and central terminals of the large cells. Ultrastructural analysis in lamina IV of the spinal cord revealed that BDNF terminals in these central projections establish synaptic contacts. Immunoreactivity at 4 weeks was also observed in pericellular baskets that contained calcitonin gene‐related peptide (CGRP) and surrounded trkA‐ and trkB‐expressing cells in L4 and L5 lumbar ganglia. These baskets are likely to arise from local, highly immunoreactive, BDNF/CGRP/trkA‐expressing cells. Our results identify several novel targets for BDNF and imply that it acts locally in both autocrine and paracrine modes, as well as centrally in a synaptic mode, to modulate the response of somatosensory pathways in nerve injury.
Maturation of kainate‐induced epileptiform activities in interconnected intact neonatal limbic structures in vitro
Authors: Khalilov Ilgam , Dzhala Volodymyr , Medina Igor , Leinekugel Xavier , Melyan Zara , Lamsa Karri , Khazipov Roustem , Ben‐Ari Yehezkel
Published: March 2003

In vivo studies suggest that ontogenesis of limbic seizures is determined by the development of the limbic circuit. We have now used the newly‐developed in vitro intact interconnected neonatal rat limbic structures preparation to determine the developmental profile of kainate‐induced epileptiform activity in the hippocampus and its propagation to other limbic structures. We report gradual alterations in the effects of kainate during the first postnatal week on an almost daily basis; from no epileptiform activity at birth, through interictal seizures around postnatal day (P) 2 and ictal seizures by the end of the first week. The developmental profile of kainate‐induced hippocampal seizures is paralleled by the expression of postsynaptic kainate receptor‐mediated currents in CA3 pyramidal cells. Intralimbic propagation of the hippocampal seizures is also age‐dependent: whereas seizures readily propagate to the septum and to the contralateral hippocampus via the commissures on P2, propagation to the entorhinal cortex only takes place from P4 onwards. Finally, repeated brief applications of kainate to the hippocampus induce recurrent spontaneous glutamatergic ictal and interictal discharges which persist for several hours after the kainate is washed away and which replace the physiological pattern of network activity. Paroxysmal activities are thus generated by kainate in the hippocampus at an early developmental stage and are initially restricted to this structure. Before the end of the first week of postnatal life, kainate generates the epileptiform activities that may perturb activity‐dependent mechanisms that modulate neuronal development. Although at this stage neurons are relatively resistant to the pathological effects of kainate, the epileptiform activities that it generates will perturb activity‐dependent mechanisms that modulate neuronal development.
Chemical LTD in the CA1 field of the hippocampus from young and mature rats
Authors: Kamal Amer , Ramakers Geert M. J. , Urban Ivan J. A. , De Graan Pierre N. E. , Gispen Willem Hendrik
Published: March 2003

Within the hippocampal formation, two forms of long‐lasting synaptic plasticity, long‐term potentiation (LTP) and long‐term depression (LTD), can be induced which require the activation of NMDA receptors. Interestingly, it has been shown that both LTP and LTD are reduced in adult animals. Recently, a new chemical protocol has been described which elicits LTD in the CA1 field of the hippocampus. Application of 20 μm NMDA for 3 min results in a stable and long‐lasting decrease in the evoked synaptic responses. We used this protocol to induce LTD in hippocampal slices from young and adult rats and show that this form of LTD is AP5‐sensitive and can be blocked by the protein phosphatase inhibitor cyclosporin A in slices from adult animals. In contrast to electrical LTD (induced by prolonged low frequency stimulation), the extent of chemical LTD was not different between the young and adult rats. These findings indicate that the intracellular signal transduction cascades involved in long‐lasting synaptic depression are still intact in adult animals.
Correlations between neural discharges are related to receptive field properties in cat primary auditory cortex
Authors: Brosch Michael , Schreiner Christoph E.
Published: March 2003

The functional role of correlated neural activity in auditory cortex for the processing of sounds was explored by investigating whether and how cross‐correlation parameters are related to receptive field similarities of neurons. Multi‐unit activity was recorded simultaneously from several sites of isofrequency domains in primary auditory cortex. At each site various receptive field properties were determined. From the discharges of pairs of clusters, normalized cross‐correlation histograms (CCH) were calculated for extended periods of spontaneous activity and for periods with noise‐burst stimulation. In both conditions, most CCHs exhibited a symmetrical positivity near the origin of the CCH, a few to several tens of milliseconds wide. Cross‐correlation histograms were characterized with two parameters: the correlation strength, which was estimated from the peak correlation, and the correlation width, i.e. the time period of correlated firing, which was measured as the width of the positivity at half height. It was found that correlation strength increased and correlation width narrowed with increasing similarity of the receptive fields of two clusters. These relationships were observed both in the acoustically‐driven and spontaneous conditions. Specifically, correlation strength was most strongly associated with similarity in binaural interaction and in temporal response properties such as response onset, response offset and the temporal pattern of the response. Correlation width was predominantly associated with similarity in characteristic frequency, bandwidth and intensity threshold. Results suggest that correlated activity, reflecting potential mechanisms involved in the neural computation in auditory cortex, provides a means to evaluate the properties of the functional organization of auditory cortex. Systematic relationships were found between correlation properties and the receptive field‐based organization of cortical processing, suggesting that similar general mechanisms are utilized in many parts of the sensory cortex. In particular, the magnitude and/or the time period of synchronized firing of neurons is increased if the receptive field properties of the involved neurons are similar.
Disruption of the substance P receptor (neurokinin‐1) gene does not prevent upregulation of preprotachykinin‐A mRNA in the spinal cord of mice following peripheral inflammation
Authors: Palmer James A. , De Felipe Carmen , O'Brien John A. , Hunt Stephen P.
Published: March 2003

The neuropeptide substance P is thought to play an important role in nociception, although the function of the peptide remains controversial. Following peripheral inflammation there is a pronounced upregulation of substance P expression both in sensory neurons and in postsynaptic neurons within the spinal cord. We have examined the levels of expression of mRNA encoding substance P and dynorphin following the development of inflammatory hyperalgesia in mice in which the substance P receptor gene, also known as the neurokinin‐1 receptor gene, has been disrupted by homologous recombination. We show that inflammatory hyperalgesia following injection of complete Freund's adjuvant develops normally in animals that lack the neurokinin‐1 receptor and that expression of mRNAs encoding substance P and the neuropeptide dynorphin are upregulated regardless of the genotype of the mouse. This suggests that substance P activity is not required for the development and maintenance of inflammatory hyperalgesia and that the upregulation of substance P expression is mediated by neurotransmitters other than substance P.
Modulation of bistratified cell IPSPs and basket cell IPSPs by pentobarbitone sodium, diazepam and Zn2+: dual recordings in slices of adult rat hippocampus
Authors: Pawelzik Hannelore , Bannister A. Peter , Deuchars Jim , Ilia Maria , Thomson Alex M.
Published: March 2003

Simultaneous intracellular recordings from presynaptic Stratum pyramidale interneurons and postsynaptic pyramidal cells in adult rat hippocampal slices were performed to investigate the strength of the modulation of single‐axon inhibitory postsynaptic potentials (IPSPs) by the GABAA receptor modulators pentobarbitone, diazepam and zinc. The processing of biocytin‐filled interneurons for light microscopy revealed that these single‐axon IPSPs were generated by basket cells (n = 33), bistratified cells (n = 18) and axo‐axonic cells (n = 2). The IPSPs generated by these three groups of interneurons had amplitudes and widths at half amplitude with similar ranges, but when bistratified cell IPSPs were compared with basket cell IPSPs with similar half widths their rise times were slower. Pentobarbitone sodium (250 μm) powerfully enhanced 13 tested IPSPs generated by all three cell types. Amplitudes were enhanced by 82 ± 56%, 10–90% rise times by 150 ± 101% and the widths at half amplitude by 71 ± 29%. Diazepam (1–2 μm) also increased all IPSPs tested, although the changes were more moderate in basket cell IPSPs (amplitudes increased by 19 ± 11%, n = 8) than in bistratified cell IPSPs (amplitudes increased by 66 ± 48%, n = 5). Basket cell IPSP 10–90% rise times and widths at half amplitude were not significantly increased. Bistratified cell IPSP 10–90% rise times were increased by 44 ± 24% and the widths at half amplitude by 32 ± 35%. The one tested IPSP generated by an axo‐axonic cell was also diazepam‐sensitive. Zinc, 250 μm, decreased four out of 10 IPSPs generated by basket cells and four out of five IPSPs generated by bistratified cells. The one tested axo‐axonic cell IPSP was zinc‐insensitive. These data suggest that IPSPs generated in CA1 pyramidal cells by basket and bistratified cells display different pharmacologies and may be mediated by different receptors or receptor combinations.
CAMs and FGF cause a local submembrane calcium signal promoting axon outgrowth without a rise in bulk calcium concentration
Authors: Archer Fabienne R. , Doherty Patrick , Collins Dominic , Bolsover Stephen R.
Published: March 2003

Binding of basic fibroblast growth factor (bFGF) and cell adhesion molecules to the nerve cell membrane promotes axon outgrowth. This response can be blocked by antagonists of voltage‐gated calcium channels, yet no change of cytosolic calcium concentration in the growth cone can be detected upon binding of the growth factor bFGF or the cell adhesion molecule L1. Using barium as a charge carrier, we show that bFGF and L1 open a calcium influx pathway in growth cones of rat sensory neurons without changing the membrane voltage. L1 does not activate influx in cells expressing a dominant negative mutant of the fibroblast growth factor receptor (FGFR) tyrosine kinase. FGFR‐activated influx is blocked by specific antagonists of L‐ and N‐type voltage‐gated calcium channels and by an inhibitor of diacylglycerol lipase. We propose that both L1 and bFGF act via the FGFR to generate polyunsaturated fatty acids which in turn cause calcium channels to flicker open and shut. Short‐lived domains of raised calcium at the cytosolic mouth of open channels activate axon outgrowth without raising bulk cytosolic calcium concentration. In confirmation of this model, the rapidly‐acting calcium buffer BAPTA is significantly more effective at blocking FGF‐induced axon outgrowth when compared with the slower buffer EGTA. Generation of short‐lived calcium domains may provide a crucial mechanism for axon guidance during development and for promoting regeneration of damaged axons.
Immunocytochemical characterization of catecholaminergic neurons in the rat striatum following dopamine‐depleting lesions
Authors: Meredith G. E. , Farrell T. , Kellaghan P. , Tan Yun , Zahm D. S. , Totterdell S.
Published: March 2003

It is possible either permanently or transiently to deplete the rat striatum of dopamine. Following such depletions, striatal neurons immunoreactive for tyrosine hydroxylase (TH), aromaticl‐amino acid decarboxylase (AADC) or dopamine appear. The presence of dopamine‐producing neurons in the striatum has relevance for the treatment of Parkinson's disease, but whether these catecholaminergic phenotypes all produce dopamine is unclear. In the present study we establish that after unilateral 6‐hydroxydopamine lesions or methamphetamine administration, striatal TH‐immunoreactive neurons differ in size, morphology and location from those that are immunopositive for AADC or dopamine. The TH‐positive cells which were localized either to ventral parts of the striatum or to the central and dorsal areas of the caudate‐putamen generally have the morphological features of projection neurons, whereas those containing AADC or dopamine were confined to subcallosal positions in the dorsal medial quadrant of the caudate‐putamen and resemble small, local‐circuit neurons. The fact that AADC‐immunoreactive neurons overlap in size, morphology and location with the cells that produce dopamine suggests strongly that this population is dopaminergic. However, the simultaneous appearance of neurons that contain the TH enzyme but clearly do not make dopamine raises questions about the functional role of these cells and the cellular mechanisms responsible for their induction following striatal dopamine loss.
Voltage‐independent autocrine modulation of L‐type channels mediated by ATP, opioids and catecholamines in rat chromaffin cells
Authors: Hernández‐Guijo J. M. , Carabelli V. , Gandía L. , García A. G. , Carbone E.
Published: March 2003

The inhibition of L‐type channels induced by either bath application of ATP, opioids and catecholamines or by endogenously released neurotransmitters was investigated in rat chromaffin cells with whole‐cell recordings (5 mm Ba2+). In both cases, the L‐type current, isolated pharmacologically using ω‐toxin peptides and potentiated by Bay K 8644, was inhibited by ∼ 50% with nearly no changes to the activation–inactivation kinetics. Inhibition was voltage independent at a wide range of potentials (–20 to +50 mV) and insensitive to depolarizing prepulses (+100 mV, 50 ms). Onset and offset of the inhibition were fast (time constants: τon ∼ 0.9 s, τoff ∼ 3.6 s), indicating a rapid mechanism of channel modulation. Whether induced exogenously or from the released granules content in conditions of stopped cell superfusion, the neurotransmitter action was reversible and largely prevented by either intracellular GDP‐β‐S, cell treatment with pertussis toxin or simultaneous application of P2y,2x δ/μ‐opioidergic and α/β‐adrenergic antagonists. This suggests the existence of converging modulatory pathways by which autoreceptors‐activated G‐proteins reduce the activity of L‐type channels through fast interactions. The autocrine inhibition of L‐type currents, which was absent in superfused isolated cells, was effective on cell clusters, suggesting that L‐type channels may be potently inhibited by cell exocytosis under physiological conditions resembling the intact adrenal glands.
Acute desensitization of nociceptin/orphanin FQ inhibition of voltage‐gated calcium channels in freshly dissociated hippocampal neurons
Authors: Pu Lu , Bao Guo‐Bin , Ma Lan , Pei Gang
Published: March 2003

Nociceptin/orphanin FQ (N/OFQ), an endogenous ligand for opioid receptor‐like receptor, has been shown to inhibit high‐voltage‐gated calcium channels (VGCCs) in acutely dissociated rat hippocampal pyramidal cells [Knoflach, F., Reinscheid, R.K., Civelli, O. & Kemp, J.A. (1996), J. Neurosci., 16, 6657]. In this study, it was further demonstrated that N/OFQ inhibition of calcium channel current was blocked by its specific antagonist PGN, [Phe1‐ψ(CH2‐NH)‐Gly2]nociceptin (1‐13)‐NH2, and the EC50 of the N/OFQ inhibition was ∼ 10 nm, indicating that this effect was really mediated via the opioid receptor‐like receptor. The N/OFQ inhibition of the calcium channel current was significantly reduced, as the maximal inhibition decreased from 36 to 23%, by 1‐min pretreatment of freshly dissociated hippocampal neurons with the same peptide. The inhibition completely recovered from this acute desensitization in less than 20 min. The N/OFQ inhibition was also greatly attenuated by pretreatment of the neurons with the GABAB (γ‐aminobutyric acid) agonist baclofen while the baclofen inhibition of the calcium channel current was significantly reduced by N/OFQ pretreatment, revealing the agonist‐induced desensitization was heterologous in nature. This desensitization was blocked by pretreating the neurons with the sodium channel blocker, tetrodotoxin (TTX), or by removing the extracellular calcium, which indicates the necessity of membrane depolarization and extracellular calcium influx in the process. Furthermore, pretreatment of the neurons with the protein kinase C (PKC) activator, phorbol 12‐myristate 13‐acetate (PMA), attenuated the N/OFQ inhibition of the calcium channel current whereas the cAMP‐dependent kinase A activator, forskolin, showed no effect, suggesting the probable involvement of PKC in the N/OFQ‐induced desensitization.