摘要:

AbstractIn the compound eye of the adult female flyMusca domestica, photoreceptors form populations of multiple‐contact output synapes, stereotypic in their architecture and in the identity of the four postsynaptic elements. Two postsynaptic elements, always, originating from monopolar interneurons L1 and L2, lie side by side beneath the elongated presynaptic bar. Beneath each end of the bar, a further postsynaptic contact is located. These contacts most often are two processes either of amacrine cells or of epithelial glial cells. Monopolar cell L3 may be postsynaptic as well, with either an amacrine or a glial process completing the tetrad.To learn more about the factors determining connectivity and synaptic architecture, a three‐dimensional reconstruction of serial electron microscopic sections was used to analyze a population of photoreceptor synapses at which one of the normally obligatory postsynaptic neurons, L1, was missing.In this abnormal case, the synapses make the normal four postsynaptic contacts in only 39% of the cases, otherwise making three (39%) or two (22%) contacts. Specificity of connectivity is preserved faithfully except that beta processes of T1 cells were postsynaptic at 2% of the synapses, where they do not normally contribute. In contrast to normal synapses, where amacrine and glial cell processes cell processes are mutual exclusive, such pairings could coexist in the aberrant synapse (27% of all synapses). All postsynaptic cells contributed the normal of processes to a synaptic site, except for three synapses each with a supernumerary amacrine cell process. The postsynaptic cells therefore may be involved in regulating the number of their contacts made to a synaptic s

ISSN:0887-4476    

DOI:10.1002/syn.890060302

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

年代:1990

数据来源: WILEY

摘要:

AbstractA double‐peroxidase procedure was used to study the ultrastructural relationship between terminals and fibers containing three putative neurotranasmitters and retrogradely identified sympathetic preganglionic neurons (SPNS) located in the intermediolateral cell column (IML) of the rat. SPNS with axons in the cervical sympathetic trunk were retrogradely labeled with horseradish peroxidase. In addition, terminals and fibers containing substance P, enkejphalin, and serotonin were detected using immunohistochemistry. Sections containing both retrogradely labeled SPNS and immunoreactive processes were processed for electron microscopy. Ultrastructural examination revealed synaptic contacts between terminals containing each of these three neurotransmitters and labeled dendrites from SPNS. Also, immunoreactive terminals were apposed to retrogradely labeled cell bodies. Therefore, these transmitters may alter sympathetic function by their direct action on SPN

ISSN:0887-4476    

DOI:10.1002/syn.890060303

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

年代:1990

数据来源: WILEY

摘要:

AbstractPerforated synapses are characterized by the appearance of one or more discontinuities in the postsynaptic density (PSD). These synapses are thought to represent intermediate stages in synaptic remodelling and turnover. To determine the dynamic level of these processes, the development of perforated synapses at different ages was examined in the neuropil of the ectostriatum, a visual projection area in birds. The overall number of perforated synapses per unit volume increases during development. Single and multeple perforated synapses, however, show a differnt developmental trend. Between 20 and 100 days, when the number of multiple perforated synapses decreases by 46%, single perforated synapses increase by 83% in number per unit volume. No significant changes in single or multiple perforated synapses can be observed at younger ages (i.e., 5 or 10 days). Various parameters increase between 10 and 20 days, followed by a reduction at 100 days: The relative frequency of perforations per synaptic contact, the length of the postsynaptic density including the size of the perforation, the length of the synaptic contact zone in perforated synapses excluding the size of the perforation, and the size of the perforation follow the same trend.

ISSN:0887-4476    

DOI:10.1002/syn.890060304

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe terminal projections of the descending 5‐hydroxytryptamine (5‐HT) bulbospinal pathway and the coexistence among 5‐HT‐, substance P (SP)‐, and thyrotropin‐releasing hormone (TRH)‐like immunoreactivities (LI) in fibers innervating the L7segement in the cat spinal cord were studied quantitively by use of the indirect double‐staining immunofluorescence technique. The content of 5‐HT, SP, and TRH in different parts of the spinal cord was determined by use of radioimmunoassay (RLA) (SP and TRH) and high‐performance liquid chromatography with electrochemical detection (HPLC‐ECD) (5‐HT).For all three substances studied, immunoreactive (IR) axon terminals were found in all parts of the gray matter, but with clear regional variation in the density of innervation. Thus, all three substances showed a dense innervation in the motor nucleus, particularly in the ventral part of the nucles, while the superficial dorsal horn was very densely innervated by SP‐IR fibers (laminae I and II) and TRH‐IR fibers (laminae II and III). In the motor nucleus, the studied substances coexisted to a very high degree, but some 5‐HT‐IR fibers (about 10%) lacked peptide‐LI and some SP‐IR fibers (about10%) lacked peptide‐LI and some SP‐IR fibers (about10%) lacked 5‐HT‐LI while virtually all TRH‐IR fibers also contained 5‐HT‐LI. In the superficial dorsal horn (laminae I‐III), no coexistence was detected, while other parts of the gray matter displayed various degrees of coexistence in between those found in the motor nucleus and laminae I‐III.The quantitative analyis of IR varicosities in the motor nucleus suggested that the unilateral L7motor nucleus is innerated by about 55–110 × 1065‐HT‐IR nerve trminals, which may indicate as many as 4,000 boutons per descending 5‐HT cell body in the brain stem only with this restricted projection. When combining these results with the biochemical data, it could be calculated that the concentration of 5‐HT in IR varicosities is about 3–6 × 10−3M, while the corresponding figures for SP and TRH was 0.3–0.5 × 10−3M and 0.1–0.2 ×10−3M, respectively.In cats subject to spinal cord transection at the lower thoracic level, all 5‐HT‐IR fibers in the L7segement had disapperared 44 days after the lesion, indicating a strict suprasegmental origion of 5‐HT‐IR fibers in this segment. A differential effect of the lesion was noticed, however, in that the dorsally projecting 5‐HT fibers without peptide‐LI had vanished already 74 days postoperatively, while a large part of the 5‐HT‐IR fibers to the motor nucleus with peptide‐LI still remained at this time interval. Furthermore, after the lesion increased numbers of SP‐IR cell bodies could be observed in the gray matter.Combined spinal cord transection and unilateral dorsal rhizotomy caused a transient decrease of the dense SP‐IR plexus in laminae I and II on the rhizotomized side, whereas in this part of the cord CGRP‐LI completely disappeared.It is concluded that the descending 5‐HT system constitutes a major innervation of the spinal cord and that it seems especially prominent in the motor nucleus, where it, in all probability, exerts direct effects on the motoneurons. The findings are discussed in relation to recent

ISSN:0887-4476    

DOI:10.1002/syn.890060305

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe manner in which the circuitry of the amygdala computes its suspected mnemonic has been a mystery, partly cellular analysis. Here we report in vitro methods and results that may help elucidate cellular learning mechanisms in amygdala neurons. The amygdala brain slice preparation was combined with the single‐electrode clamp (sEC) technique for intracellular analysis of membrane properties and synaptic responses. With respect to the active and passive membrane properties, we found considered diversity among the population of cells that were sampled in the lateral and basolateral nuclei (n = 85). Synaptic inputs to these neurons were studied by stimulating the external capsule (EC), which was shown to produce a complex response that typically consisted of an excitatory followed by an inhibitory component. Based on serval criteria, the excitatory component apperred to reflect a monosynaptic connection from the EC. One immediate goal was to discover whether the excitatory component displays the phenomenon of long‐term potentiation (LTP)–a persistent increase in synaptic stimulation. Indeed, we found that high‐frequency (100 Hz) stimulation of the EC induced LTP in 80% of the cells from which suitable recordings were obtained (n= 20). This finding of LTP in the amygdala is significant in regard to current effort to explore linkages between this use‐dependent form of synaptic plasticity and rapid kinds of associative

ISSN:0887-4476    

DOI:10.1002/syn.890060306

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

年代:1990

数据来源: WILEY

摘要:

AbstractInduction of long‐term potentiation (LTP) by burst stimulation patterned after the limbic system theta rhythm was studied in slices of piriform cortex. Monosynaptic responses were evoked by stimulation of afferent fibers of the lateral olfactory tract (LOT) or the intrinsic associational (ASSN) feedback system. LTP was difficult to elicit at LOT synapses in the presence of 2.5 mM extracellular Mg2+, and when it was induced potentiation increased for 20–30 min after burst stimulation before stabilizing. The probability of inducing LTP was increased when the extracellular Mg2+concentration was reduced to 50μM. In ASSN system LTP developed in about 1 min after burst stimulation and then remained stable. ASSN system LTP was more readily induced in slices from caudal than rostral piriform. Induction of LTP at both LOT and ASSN synapses was blocked by D‐2‐amino‐5‐phosphonopentanoate, indicating that NMDA receptor activation was required. Neither system exhibited the decremental short‐term potentiation effect observed after burst stimulation of inputs to the CA1 field

ISSN:0887-4476    

DOI:10.1002/syn.890060307

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

年代:1990

数据来源: WILEY

摘要:

AbstractA Fundamental question important to the undersanding of the neuro‐chemical organization of the central nervous system focuses on the relationships between the differential phenotypic expression of multiple neurotransmitter markers in individual neuronal populations and the factors that regulate their expression. The first approach in studying this phenomenon is the determination of specifcic relationships between neuro‐chemically distinct neuronal subpopulations and their efferent targets. The pontine nucleus locus coeruleus (LC) provides a useful model for adressing this question since the projections of LC neurons are topographically organized and several neuropeptides are expressed along with noradrenergic markers in subsets of these neurons. In these studies, we have focused on defining the efferent targets of LC neurons that contain neuropeptide tyrosine (NPY)‐like immunoreactivity. The has been accomplished by injecting the retrograde fluorescent tracer fluorogold into specifec cortical and hippocampal targets in adult rats and identifying the proportion of retrogradely labeled LC neurons that are positive for NPY‐like immunoreactivity. In agreement with other investgators, no preferential cortical projections of NPY‐positive LC neurons were observed. However, when fluorogold injections included or were limited to the entorhinal cortex, a discrete cluster of round or ovoid neurons in the dorsomedial portion of the LC approximately 9.8 mm posterior to bregma were found to contain NPY‐like immunoreactivity. This observation demonstrates that some topographic organization of NPY‐containing LC neurons does exist. In fact, these data indicate that morphologic and topographic organisation exists even within neurochemically distinct subsets of neurona

ISSN:0887-4476    

DOI:10.1002/syn.890060308

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe neurochemistry of autism, the most well‐validated childhood neuropsychiatric disorder, has been studied extensively over the past three decades. Autism is of interest neurochemically because it represents a relatively homogeneous disorder with a triad of social, communicative, and intellectual developmental disturbance. Because a sufficient animal model has been lacking and relatively few diagnosed people with autism have died, most investigation has been of peripheral fluids and tissues. The most consistent finding has been that over 25% of autistic children and adolescents are hyperserotonemic. However, after 29 years of investigation, the mechanism of hyperserotonemia has not been determined. Hyperserotonemia has been found to be familial. Elevated plasma norepinephrine has also been a replicated finding. Cerebrospinal fluid (CSF) opiate activity has been found to be elevated in two studies. Plasma cyclic adenosine monophosphate (cAMP) has been found to be elevated in autistic children. A high rate of nonsuppression after dexamethasone and blunted or delayed growth hormone response to L‐dopa have been found Abnormal cell‐mediated immunity has been replicated consistently in autism. Although several pharmacological trials have been conducted and shown promise in initial open trials, only “typical” antipsychotic drugs have shown replicable chronic ameliorating effects in double‐blind trials. However, chronic neurotoxicity (tardive dyskinesia) has also been revealed. Findings of morphological changes in the cerebellum have been replicated. Findings in need of replication include diminished platelet function, increased baseline CSF homovanillic acid, decreased nerve cell adhesion molecule serum fragment, blunted prolactin response to fenfluramine, amelioration of symptoms by naltrexone and bromocriptine, reduced electroretinographic (ERG) b‐wave amplitude, and morphological changes in the hippocampus, amygdala, and septal nuclei. In addition to refining and replicating past findings, future directions that may be fruitful include investigation of neurochemical aspects of platelet function, of interactions between monoaminergic systems, of phosphatidylinositides, and of pharmacological response to “atypical” antipsychotic agents and relatively selective serotonin receptor subtype agonis

ISSN:0887-4476    

DOI:10.1002/syn.890060309

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

年代:1990

数据来源: WILEY

ISSN:0887-4476    

DOI:10.1002/syn.890060301

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

年代:1990

数据来源: WILEY