摘要:

AbstractWe have investigated the anatomical distribution and postnatal development of D‐aspartate and D‐serine in the rat brain and periphery using HPLC techniques. D‐Serine was confined predominantly to the brain throughout postnatal life. At birth, a substantial quantity of D‐serine was observed throughout the brain areas. The cerebral D‐serine content increased from birth to postnatal week (PW) 3 and remained constant thereafter, whereas the cerebellar D‐serine content peaked at PW1. In contrast, the transient emergence of D‐aspartate was found in almost all brain and peripheral organs. A substantial quantity of D‐aspartate was also seen in all brain areas at birth, whereas the D‐aspartate content in the cerebrum and cerebellum decreased dramatically by PW1 and 7 respectively. Further, the D‐aspartate content and the ratio of D‐aspartate to total aspartate were highest in the adrenal at PW3 (608 ± 70 nmol/g, 45.9%) and in the testis at PW14 (221 ± 7 nmol/g, 57.8%) respectively. Because D‐serine potentiatesN‐methyl‐D‐aspartate receptor‐mediated transmission through the strychnine‐insensitive glycine site and because D‐serine exhibits anN‐methyl‐D‐aspartate receptor‐related distribution and development, D‐serine may be a tenable candidate for an intrinsic ligand for the glycine site. In contrast, because the periods of maximal emergence of D‐aspartate in the brain and periphery occur during critical periods of morphological and functional maturation of organs, D‐aspartate could participate in the re

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00687.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe anterior pituitary has recently been confirmed to be innervated by substance P‐immunoreactive nerve fibres in the monkey and human. The present study investigated the morphology of the nerve fibres and their relationship with anterior pituitary gland cells in the macaque by means of immunoelectron microscopy. Many substance P‐immunoreactive and unlabelled nerve fibres were distributed among the gland cells or formed nerve fibre bundles. These nerve fibres were unmyelinated and varicose, and contained a great many clear and/or large dense‐cored vesicles. Substance P‐immunoreactive cells were seen in the pars distalis of the anterior pituitary. Direct contacts between these nerve fibres and every cell type of the gland could be ascertained, including substance P‐immunoreactive cells. Synaptoid contacts were seen among the substance P‐immunoreactive varicosities and somatotropes, opiocortico‐melanotropes and folliculostellate cells. Typical synapses were identified in somatotropes and opiocortico

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00688.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractIn Huntington's disease neuronal degeneration mainly involves medium‐sized spiny neurons. It has been postulated that both excitotoxic mechanisms and energy metabolism failure are implicated in the neuronal degeneration observed in Huntington's disease. In central neurons,>40% of the energy released by respiration is used by Na+/K+ATPase to maintain ionic gradients. Considering that impairment of Na+/K+ATPase activity might alter postsynaptic responsivity to excitatory amino acids (EAAs), we investigated the effects of the Na+/K+ATPase inhibitors, ouabain and strophanthidin, on the responses to different agonists of EAA receptors in identified medium‐sized spiny neurons electrophysiologically recorded in the current‐ and voltage‐clamp modes. In most of the cells both ouabain and strophanthidin (1–3 μM) did not cause significant change in the membrane properties of the recorded neurons. Higher doses of either ouabain (30 μM) or strophanthidin (30 μM) induced,per se, an irreversible inward current coupled to an increase in conductance, leading to cell deterioration. Moreover, both ouabain (1–10 μM) and strophanthidin (1–10 μM) dramatically increased the membrane depolarization and the inward current produced by subcritical concentrations of glutamate, AMPA and NMDA. These concentrations of Na+/K+ATPase inhibitors also increased the membrane responses induced by repetitive cortical activation. In addition, since it had previously been proposed that dopamine mimics the effects of Na+/K+ATPase inhibitors and that dopamine agonists differentially regulate the postsynaptic responses to EAAs, we tested the possible modulation of EAA‐induced membrane depolarization and inward current by dopamine agonists. Neither dopamine nor selective dopamine agonists or antagonists affected the postsynaptic responses to EAAs. Our experiments show that impairment of the activity of Na+/K+ATPase may render striatal neurons more sensitive to the action of glutamate, lowering the threshold for the excitotoxic events. Our data support neither the role of dopamine as an ouabain‐like agent nor the differential modulatory action of dopamine receptors on the EAA‐induced r

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00689.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe most compelling evidence for a functional role of caffeine‐sensitive intracellular Ca2+reservoirs in nerve cells derives from experiments on peripheral neurons. However, the properties of their ryanodine receptor calcium release channels have not been studied. This work combines single‐cell fura‐2 microfluorometry, [3H]ryanodine binding and recording of Ca2+release channels to examine calcium release from these intracellular stores in rat sympathetic neurons from the superior cervical ganglion. Intracellular Ca2+measurements showed that these cells possess caffeine‐sensitive intracellular Ca2+stores capable of releasing the equivalent of 40% of the calcium that enters through voltage‐gated calcium channels. The efficiency of caffeine in releasing Ca2+showed a complex dependence on [Ca2+]i. Transient elevations of [Ca2+]iby 50–500 nM were facilitatory, but they became less facilitatory or depressing when [Ca2+]ireached higher levels. The caffeine‐induced Ca2+release and its dependence on [Ca2+]iwas further examined by [3H]ryanodine binding to ganglionic microsomal membranes. These membranes showed a high‐affinity binding site for ryanodine with a dissociation constant (KD= 10 nM) similar to that previously reported for brain microsomes. However, the density of [3H]ryanodine binding sites (Bmax= 2.06 pmol/mg protein) was at least three‐fold larger than the highest reported for brain tissue. [3H]Ryanodine binding showed a sigmoidal dependence on [Ca2+] in the range 0.1–10 μM that was further increased by caffeine. Caffeine‐dependent enhancement of [3H]ryanodine binding increased and then decreased as [Ca2+] rose, with an optimum at [Ca2+] between 100 and 500 nM and a 50% decrease between 1 and 10 μM. At 100 μM [Ca2+], caffeine and ATP enhanced [3H]ryanodine binding by 35 and 170% respectively, while binding was reduced by>90% with ruthenium red and MgCl2. High‐conductance (240 pS) Ca2+release channels present in ganglionic microsomal membranes were incorporated into planar phospholipid bilayers. These channels were activated by caffeine and by micromolar concentrations of Ca2+from the cytosolic side, and were blocked by Mg2+and ruthenium red. Ryanodine (2 μM) slowed channel gating and elicited a long‐lasting subconductance state while 10 mM ryanodine closed the channel with infrequent opening to the subconductance level. These results show that the properties of the ryanodine receptor/Ca2+release channels present in mammalian peripheral neurons can account for the properties of caffeine‐induced Ca2+release. Our data also suggest that the release of Ca2+by caffeine has a bell‐shaped dependence on Ca2+in the physiolo

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00690.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractIn contrast to the acute toxic effect of NMDA on mature cerebellar granule cells, chronic treatment with NMDA (140 μM from 1 to 9 daysin vitro) did not compromise cell survival. Such treatment markedly suppressed NMDA receptor activity: at 8 daysin vitroNMDA‐induced45Ca2+influx was reduced by ‐60% and acute exposure to NMDA (highest concentration tested, 1 mM) at 9 daysin vitrodid not cause detectable toxicity. The reduction in NMDA receptor activity was accompanied by a significant decrease (±80% at 9 daysin vitro) in the level of the NR1 and the NR2A NMDA receptor subunit protein, detected using the selective photoaffinity ligand [125I]CGP55802A. It seems, therefore, that the agonist‐induced decrease in NMDA receptor activity is due to receptor down‐regulation. In contrast to the marked influence of chronic NMDA exposure on the cellular content of the NMDA receptor subunit proteins, mRNA levels of the different subunits (NR1, NR2A, NR2B and NR2C) were not significantly affected. It seems, therefore, that agonist‐induced down‐regulation of the NMDA receptor involves critically mRNA translation and/or post‐translati

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00691.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractPrevious studies have indicated excitatory adrenergic effects on midbrain dopamine systems. To investigate the cellular mechanisms, intracellular recordings were made from neurons in perfused, oxygenated slices of male rat midbrain. Electrophysiological and pharmacological parameters were used to identify cells as principal (presumably dopaminergic) neurons as opposed to secondary (presumably GABAergic) neurons in the substantia nigra zona compacta and the ventral tegmental area. Noradrenalin (10–100 μM) hyperpolarized 57% of all principal cells and depolarized 36%. Sulpiride (100–1000 nM), a dopamine D2receptor antagonist, completely blocked noradrenalin‐induced hyperpolarizations (six of six cells). In sulpiride, noradrenalin depolarized 58% of all principal neurons and had no effect in 42%; this effect was mimicked by the α‐adrenergic agonist phenylephrine (10–30 μM) which depolarized 43 of 72 cells. The α1receptor antagonist prazosin (30–100 nM) completely blocked the membrane depolarization produced by either noradrenalin or phenylephrine in all cells tested, whereas α2‐ and β‐adrenergic agents had no effect. In voltage clamp, phenylephrine evoked an inward current (at ‐60 mV) and reduced cord conductance by 0.81 ± 0.14 nS (n= 4). Inward current evoked by phenylephrine became outward at ‐96 ± 8 mV, which is near the membrane reversal potential for potassium as predicted by the Nernst equation. Phenylephrine also depolarized secondary cells and increased the frequency of spontaneous GABAAreceptor‐mediated postsynaptic potentials recorded in both principal and secondary cells. We conclude that stimulation of α1‐adrenergic receptors depolarizes principal (dopamine) neurons by reducing membrane conductance for potassium, but this effect is modulated by the increase in frequency of spontaneous inhibitory postsynaptic potentials evoked by stimulation of α1‐adrenergic rece

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00692.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractQuail rhombomeres two to six (r2‐r6) were individually grafted homotopically into the hindbrain of chick embryos at 2 days of incubation. Nine to 10 days after the operation the chimeric embryos were fixed and processed for parallel cytoarchitectural and immunocytochemical study (with an anti‐quail antibody) in order to map the anatomical fate of the grafted tissue. Emphasis was placed on conventionally identified and distinct neuronal populations composing the sensory and motor longitudinal columns. Grafted rhombomeres consistently developed as complete transverse slices of the chimeric hindbrain. Interrhombomeric cell migration was either sparse or restricted to specific nuclei. The cranial nerve motor nuclei showed rhombomeric origins consistent with the patterns described in early embryos. Unexpectedly, alar r2 was found to form the auricular part of the cerebellum. As regards the cochlear nuclei, we found that nucleus angularis derives from r3 to r6, nucleus laminaris from r5 to r6, nucleus magnocellularis from r6 to r7 and nucleus olivaris superior from r5. The nuclei of the lateral lemniscus originated between r1 and r3. We also delimited the respective rhombomeric subdivisions of the sensory vestibular and trigeminal columns, both of which extend from r1 caudalwards throughout the hindbrain. There were consistently some interrhombomeric neuronal migrations inside the vestibular column, some motor nuclei and the reticular formation, involving only one rhombomere length. The pontine nuclei, which extended from r1 to r7, showed neuronal migrations that crossed several rhombomeres. On the whole, these results represent the first anatomical analysis of the mature avian hindbrain in terms of rhombomere‐derived do

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00693.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractIn this study, we have investigated the effect of fibroblast growth factors (bFGF and FGF‐5) and brain derived neurotrophic factor (BDNF) on the expression of calcitonin gene‐related peptide (CGRP) in rat motoneuronsin vivoandin vitro. Following sciatic nerve transection in adult rats, the levels of α‐CGRP and β‐CGRP mRNA were up‐ and down‐regulated respectively in axotomized motoneurons, revealed byin situhybridization histochemistry. Local administration of 1 μg bFGF was able to entirely abolish the up‐regulation of α‐CGRP mRNA, and to further down‐regulate β‐CGRP. These effects, albeit less pronounced, were still evident with 0.2 μg bFGF. In contrast, bFGF did not attenuate the lesion‐induced decrease of choline acetyltransferase (ChAT) mRNA. Administration of BDNF did not significantly alter the expression of CGRP or ChAT mRNA in axotomized motoneurons. Both α‐ and β‐CGRP mRNAs could be detected by PCR in enriched motoneuron cultures prepared from rat embryos at embryonic day 14–15. Comparing the amplification of α‐ and β‐CGRP mRNAs with that of mRNA encoding glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH) in parallel samples, we found that cultures treated with FGF‐5 had a lower ratio of α‐ and β‐CGRP mRNA to GAPDH mRNA, than did control or BDNF‐treated cultures. BDNF, on the other hand increased α‐CGRP and decreased β‐CGRP mRNA levels, though these effects were moderate compared with the effects of FGF‐5. The results obtained in this study suggest that members of the FGF family of growth factors influence the expression of CGRP in rat motoneurons, and that the increase of this neuropeptide induced by axotomy may, at least

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00694.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractIntracellular recordings were obtained from supragranular neurons in slices of the rat visual cortex. In ∼25% of the cells large (0.5–1.6 mV) excitatory postsynaptic potentials (EPSPs) of constant amplitude were observed after minimal, presumably single‐fibre stimulation. The amplitude variance of these large EPSPs was surprisingly small and within the range of the variance of the noise. These EPSPs could be reduced in amplitude by paired‐pulse and low‐frequency stimulation or by raising extracellular Mg2+concentration. Reduced EPSPs could either continue to behave as all‐or‐none responses, or they could fluctuate between several amplitude levels. Conversely, responses where the amplitude fluctuated from trial to trial under control conditions could be converted into large all‐or‐none responses by paired‐pulse facilitation. This indicates that the large all‐or‐none EPSPs were composed of several subunits, probably reflecting the action of several different release sites. It is concluded that these release sites are either independent and operate with a probability close to 1 or, if operating with a lower probability, are coordinated by a mechanism which synchronizes release. Several observations suggest that release probabilities can switch from values close to 1 to 0 with repetitive stimulation or high Mg2+concentration. Thus, a substantial fraction of single‐fibre inputs to supragranular cells possess synapses which operate with high synaptic efficiency and extremely low variance under control conditions but can undergo drastic changes in efficacy when release probabilities are interfered with. Such modifications of release probability could serve as an effective mechanism to regulate the gain

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00695.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractWe have shown previously that growth‐associated protein 43 (GAP‐43) is expressed by rat Schwann cells and is restricted to non‐myelin‐forming Schwann cellsin vivo.Here we examined the regulation of GAP‐43 using agents that are known to control Schwann cell differentiationin vitro.GAP‐43 protein and mRNA levels are decreased by forskolin and other agents that elevate intracellular cAMP (and promote expression of the myelinating Schwann cell phenotype). We also found that expression of GAP‐43 protein but not mRNA is down‐regulated by transforming growth factor betas (TGF‐βs). Moreover, TGF‐β treatment of Schwann cells results in cell clumping, process retraction and disappearance of GAP‐43 from the plasma membrane, revealing that GAP‐43 is associated with the Golgi apparatus. This association was confirmed by partial overlap of GAP‐43 with the trans‐Golgi network marker (23c) and the disruption of the Golgi with brefeldin A or monensin leading to altered GAP‐43 distribution. Golgi‐associated GAP‐43 appeared to have the same molecular weight as the plasma membrane‐associated GAP‐43. Thus these results show that GAP‐43 expression in Schwann cells is subject to regulation by both extracellular and intracellular signalling molecules and that Schwann cell GAP‐43 i

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00696.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY