摘要:

AbstractUsing two‐color immunoperoxidase staining combined with the retrograde transport of horseradish peroxidase injected into the rostral thoracic spinal cord, substance P‐immunoreactive (SPI) and serotonin‐immunoreactive (5HTI) variocosities have been observed in contiguity with medullary bulbospinal phenylethanolamine N‐methyl transferase‐immunoreactive (PNMTI) neurons of the C1, C2, and C3 cell groups. Since PNMTI terminals in the spinal cord are concentrated among sympathetic preganglionic neurons (SPGN) in the intermediolateral cell column, the close anatomical associations shown in the present study indicate that substance P‐ and serotonin‐containing pathways in the medulla likely affect activity of SPGN via adrenergic bulbos

ISSN:0887-4476    

DOI:10.1002/syn.890020602

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractTransient brain ischemia results in a selective destruction of cell bodies within the hippocampus and cortex. This cellular destruction appears to be mediated through a release of endogenous exictatory amino acids following the ischemic episode, since the neurotoxic effects of ischemia can be attenuated by compounds that have antagonist activity at N‐methyl‐D‐aspartate (NMDA) receptors. In the present study, the protective effects of a novel NMDA receptor antagonist, CGS 19755, were further evaluated by using quantitative autoradiography to characterize adenosine A1, NMDA, PCP, and benzodiazepine receptors in ischemic gerbil brain. Bilateral carotid artery occlusion (20 minutes) resulted in marked decreases (30–60%) in adenosine A1, NMDA, and PCP, but not benzodiazepine, receptors in gerbil forebrain. Postischemic treatment with CGS 19755 was found to completely block the ischemia‐induced decreases in brain adenosine and NMDA receptors. [3H]TCP binding in ischemic gerbil brain was also elevated by CGS 19755 treatment; significant differences remained, however, between the CGS 19755‐treated and control gerbils. These results indicate that transient brain ischemia produces significant and selective alterations in gerbil forebrain receptor systems. The observed decreases in radioligand binding are probably reflective of an ischemia‐induced destruction of forebrain structures. However, there is some evidence that transient ischemia can also cause long‐term changes in the affinity of some receptor systems. The postischemic efficacy of CGS 19755 appears to be due to its ability to block the neurotoxic effects of tra

ISSN:0887-4476    

DOI:10.1002/syn.890020603

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractIndirect immunofluorescence histochemistry was used to study the relation among GABAergic, catecholaminergic, cholinergic, and peptidergic neurons in the rat mediobasal hypothalamus. By employing a direct double‐labelling procedure using sheep antiserum against glutamic acid decarboxylase (GAD), mouse monoclonal and rabbit antibodies to neurotensin (NT) and rabbit antisera to tyrosine hydroxylase (TH),choline acetyltransferase (ChAT), galanin (GAL), growth hormone‐releasing factor (GRF), or somatostatin (SOM), it was demonstrated that GAD‐positive fibers and terminals in the external part of the median eminence co‐contained immunoreactivity for TH, NT, GAL or GRF, but not for SOM. In the internal part of the median eminence‐infundibular stalk, GAD‐positive/NT‐, GAL‐, and GRF‐negative and GAD‐Positive/TH‐positive fiber plexa were shown. When a recently developed direct triple‐labelling procedure with biotinconjugated mouse secondary antibodies in conjunction with diethylaminocoumarin (DAMC)‐conjugated avidin was employed, presence of GAD/GAL/NT‐ as well as GAD/GRF/NT‐containing varicosities could be demonstrated close to hypophysial portal vessels. In colchicine‐pretreated animals, GAD was shown to coexist with TH, NT, or GAL in cell bodies in both the dorsomedial and ventrolateral domains of the arcuate nucleus, but with GRF only in the ventrolateral division. ChAT‐positive neurons in the ventrolateral region were also TH‐positive. In the ventrolateral arcuate nucleus, triple‐labelling followed by elution‐restaining showed GAD/NT/GAL/TH‐immunoreactivities in the same cells. Similarly, double‐labelling with two following elution‐restaining steps showed several NT/GAL/GRF/TH‐containing cell bodies in this part of the arcuate nucleus. GAD‐positive cells in the anterior hypothalamic periventricular area and fibers in the pituitary neurointermediate lobe were also TH‐positive.The results demonstrate complex patterns of storage of chemical messengers in neurons of the arcuate nucleus‐median eminence complex. Possible neuroendocrine interactions of these systems in the control of

ISSN:0887-4476    

DOI:10.1002/syn.890020604

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractNeurons in the ectoderm of the perirhopalial tissue of the jellyfishCyanea capillatawere exposed and fixed for electron microscopy under conditions designed to minimize exocytosis of synaptic vesicles. The structure of the bidirectional chemical synapses that connect neurons was examined and the three‐dimensional organization of these synapses was determined from reconstructions of serial sections. Synapses were characterized by the accumulation of a relatively few, large synaptic vesicles. These lie in a single layer against the terminal membrane of each terminal. The cytoplasmic side of the vesicles in any one terminal was covered by a single, large, perforated cisternal sheet. In addition, there were numerous smaller, bulbous cisternae that intermingled with the vesicles in the terminal. The structure of any one terminal was mirrored by that of the opposite terminal of the pair. The organization of these synapses is discussed from the viewpoint of cnidarian synapses in genera

ISSN:0887-4476    

DOI:10.1002/syn.890020605

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractProtein kinase C and norepinephrine‐stimulated adenylate cyclase have been linked to formation of long‐term potentiation in the dentate gyrus. However, little is known about second messenger system interactions regulating synaptic transmission. In electrophysiological studies of the dentate gyrus, we observe synergistic interactions between norepinephrine and phorbol esters, activators of protein kinase C. Norepinephrine markedly potentiates the block of adenosine's inhibitory action by phorbol esters. Norepinephrine's action is mimicked by the β‐adrenoceptor agonist isoproterenol and blocked by the β‐adrenoceptor antagonists timolol and propranolol. Forskolin also mimicks norepinephrine's action. Accordingly, norepinephrine's potentiation of protein kinase C appears to be mediated by the cyclic AMP second messenger system. This mechanism may contribute to norepinephrine's facilitation of long‐term potentiation in the de

ISSN:0887-4476    

DOI:10.1002/syn.890020606

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractResponses to focal application of gamma‐aminobutyric acid (GABA) were compared to synaptic potentials elicited by afferent stimulation of rat visual cortical neurons, using a slice preparation and conventional intracellular recording techniques. GABA produced three types of responses: a brief hyperpolarization (mean reversal potential, −72 mV), brief depolarization (mean reversal potential, −50 mV), or a prolonged hyperpolarization (mean reversal potential, −80 mV). Synaptic potentials included simple or complex EPSPs and EPSPs followed by mono‐ or biphasic IPSPs. A comparison of the characteristics of the GABA responses and synaptic potentials indicated that GABA may mediate both phases of the IPSP in these cells. Our results suggest that despite differences in the circuitry of the visual cortex as opposed to other neocortical and allocortical (hippocampal) areas (Mountcastle and Poggio, 1968; Colonnier and Rossignol, 1969; Creutzfeldt, 1978; Kuhlenbeck, 1978), the inhibitory control of cortical pyramidal and nonpyramidal neurons by GABA is quit

ISSN:0887-4476    

DOI:10.1002/syn.890020607

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe inhibitory neurotransmitter γ‐aminobutyric acid (GABA) hyperpolarizes spinal neurons by activating bicuculline sensitive GABAAreceptors coupled to chloride permeable ionic channels in the cell membrane. Single channel measurements using outside‐out membrane patches from cultured mouse spinal neurons showed that there is a large excess of brief openings of these channels, compared to the number predicted from a simple, two‐state model of channel function. The cumulative open time distributions for channel openings were well fit by the sum of two exponential terms, a fast component with amplitude Nf and time constant TAUf, and a slow term with amplitude Ns and time constant TAUs. These kinetics could arise if monoliganded GABAAreceptors triggered an open state less stable than that induced by the biliganded receptor. A prediction of this hypothesis is that the ratio Nf/Ns should decline in an approximately linear fashion with increasing doses of GABA. This was found to be the case, as Nf/Ns declined by a factor of 4.8 on increasing the GABA dose from 0.5 μM to 5 μM. Application of 1.25 μM GABA produced an intermediate value of Nf/Ns, as predicted. In contrast the parameters TAUf and TAUs were not significantly influenced by GABA concentration. Spontaneous, bicuculline sensitive currents were seen in some patches. These events resembled currents triggered by low doses of exogenous GABA, with regard to the values of Nf/Ns, TAUf and TAUs. These results suggest that the spontaneous currents are triggered by endogenous GABA molecules, present in the culture environment at a concentration of 0.5

ISSN:0887-4476    

DOI:10.1002/syn.890020608

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractSingle‐unit activity was recorded in the rat neostriatum at different distances from the point of an infusion of either glutamate or serotonin. In each case, firing rate at the distant site (0.8–1.5 mm) was the mirror image of that at the near site (0.1–0.3 mm). These reciprocal changes were blocked by a subsequent injection of haloperidol, a dopamine antagonist. It appears that a lateral inhibitory network, intrinsic to the neostriatum and possibly modulated by dopamine, plays an important role in the operation of the neostr

ISSN:0887-4476    

DOI:10.1002/syn.890020609

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractElevation of extracellular potassium concentration ([K+]0) in cutaneous pectoris neuromuscular junction from 2 to 20 mM slowly increased the variability of the amplitudes of miniature end‐plate currents (AMEPC‐s), (coefficient of variation ofAMEPC‐sincreased by 73%). MeanAMEPC‐s, however, decreased but not markedly (by 14%). Comparable MEPC changes were observed when [K+] was raised in the presence of choline chloride (50 μM), arguing that MEPC changes were not primarily due to a lower and less uniform vesicular filling. Channel kinetics were not altered by high [K+]O, since the time constant of decay of miniature end‐plate currents (TMEPC‐s) did not change. Acetylcholine clearance from the synaptic cleft, however, appeared to be faster in high [K+Osince with cholinesterase blocked throughout,TMEPC‐swere shortened. The changes of spontaneous quantal discharge induced by high [K+]0] can be almost entirely explained by altered spatial distribution of vesicular release if, as recent reports suggest, at high [K+],0, exocytosis appears randomly not only at but also in between the active zones. However, relatively greater frequency of large MEPCssuggests that in high [K+]0some, and possibly all, quanta are filled above normal levels.High [Ca2+]0appears to counteract, although not always completely, all changes in spontaneous quantal secretion induced by high [K+]0. It is possible that high [Ca2+]0reverses the changes in the spatial distribution of vesicular release induced by high [K+]0. However, high [Ca2+]0also leads to other pre‐ and post

ISSN:0887-4476    

DOI:10.1002/syn.890020610

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractSpontaneous activity of 5‐hydroxytryptamine (5‐HT) neurons in the dorsal raphe nucleus (DRN) was recorded in adult rats that had undergone a bilateral locus coeruleus (LC) lesion during the neonatal period. The susceptibility of this neuronal firing to β‐adrenergic manipulation was tested. Microiontophoretic application of the β‐blockers d,l‐propranolol and acebutolol inhibited the firing of DRN cells in lesioned rats but not in control animals. This effect was specific to β‐receptors since the effects of pharmacological manipulation of other receptors—5‐HT, γ‐aminobutyric acid (GABA), γ‐adrenoceptors— were identical in lesioned and control animals. The present data demonstrate that a neonatal noradrenergic lesion allowed the persistence of a β‐regulation of DRN neuronal firing, which in young ra

ISSN:0887-4476    

DOI:10.1002/syn.890020611

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY