摘要:

AbstractThe axonal and dendritic domains of neurons with extensive, locally arborizing axons were delineated in the dentate gyrus of the rat hippocampus. In horizontally cut slice preparations neurons were briefly recorded and subsequently filled with biocytin when one or several of the following physiological properties were observed: (i) high‐amplitude short‐latency spike afterhyperpolarization; (ii) lack of spike frequency adaptation; (iii) high firing rate in response to depolarizing current. In a sample of 14 neurons, sufficient dendritic and/or axonal detail was recovered to identify them as non‐principal cells, i.e. non‐granule, non‐mossy cells. Five distinct types of cells were recognized, based on the spatial distribution of dendrites, presumably reflecting the availability of afferents, and on the basis of the highly selective distribution of their axon terminals, indicating synaptic target selectivity. They are: (1) the hilar cell forming a dense axonal plexus in the commissural and association pathway terminal field (HICAP cell; horizontal axon extent 1.6 mm) in the inner one‐third of the molecular layer, and having dendrites extending from the hilus to the top of the molecular layer; (2) the hilar cell with its axon ramifying in the perforant path terminal field (HIPP cell, horizontal axon extent 2.0 mm) in the outer two‐thirds of the molecular layer, whereas its spiny dendrites were restricted to the hilus; (3) the molecular layer cell with its dendritic and axonal domains confined to the perforant path terminal zone (MOPP cell, horizontal extent of axon 2.0 mm); (4) thedentate basketcell (horizontal axon extent 0.9 mm) had most of its axon concentrated in the granule cell layer, the remainder being localized in the inner molecular layer and hilus; (5) the hilarchandeliercell, oraxo‐axoniccell (horizontal axon extent 1.1 mm), densely innervating the granule cell layer with fascicles of radially orientated terminal rows, and also forming an extensive plexus in the hilus. The three cell types having their somata in the hilus projected to granule cells at the same septo‐temporal level where their cell bodies were located. The results demonstrate that there is a spatially selective innervation of the granule cells by at least five distinct types of dentate neurons, which terminate in several instances in mutually exclusive domains. Their dendrites may have access to all (HICAP cell) or only a few (e.g. HIPP and MOPP cell) of the hippocampal afferents. This arrangement provides a framework for independent interaction between the output of local circuit neurons and subsets of excitatory afferents providing input t

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00507.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe sources of GABAergic innervation to granule cells were studied to establish how the basic cortical circuit is implemented in the dentate gyrus. Five types of neuron having extensive local axons were recorded electrophysiologicallyin vitroand filled intracellularly with biocytin (Hanet al., 1993). They were processed for electron microscopy in order to reveal their synaptic organization and postsynaptic targets, and to test whether their terminals contained GABA. (1) The hilar cell, with axon terminals in the commissural and association pathway termination field (HICAP cell), formed Gray's type 2 (symmetrical) synapses with large proximal dendritic shafts (n= 18), two‐thirds of which could be shown to emit spines, and with small dendritic branches (n= 6). Other boutons of the HICAP neuron were found to make either Gray's type 1 (asymmetrical) synapses (n= 4) or type 2 synapses (n= 6) with dendritic spines. Using a highly sensitive silver‐intensified immunogold method for the postembedding visualization of GABA immunoreactivity, both the terminals and the dendrites of the HICAP cell were found to be immunopositive, whereas its postsynaptic targets were GABA‐immunonegative. The dendritic shafts of the HICAP cell received synapses from both GABA‐negative and GABA‐positive boutons; the dendritic spines which densely covered the main apical dendrite in the medial one‐third of the molecular layer received synapses from GABA‐negative boutons. (2) The hilar cell, with axon terminals distributed in conjunction with the perforant path termination field (HIPP cell), established type 2 synapses with distal dendritic shafts (n= 17), most of which could be shown to emit spines, small‐calibre dendritic profiles (n= 2) and dendritic spines (n= 6), all showing characteristics of granule cell dendrites. The sparsely spiny dendrites of the HIPP cell were covered with many synaptic boutons on both their shafts and their spines. (3) The cell with soma in the molecular layer had an axon associated with the perforant path termination field (MOPP cell). This GABA‐immunoreactive cell made type 2 synapses exclusively on dendritic shafts (n= 20), 60% of which could be shown to emit spines. The smooth dendrites of the MOPP cell were also restricted to the outer two‐thirds of the molecular layer, where they received both GABA‐negative and GABA‐positive synaptic inputs. (4) The extensive axonal arborization of thedentate basketcell terminated mainly on somata (n= 26) and proximal dendrites (n= 9) in the granule cell layer, and some boutons made synapses on somatic spines (n= 6); all boutons established type 2 synapses. (5) The dentateaxo‐axoniccell established type 2 synapses (n= 14) exclusively on axon initial segments of granule cells in the granule cell layer, and on initial segments of presumed mossy cells in the hilus. The results demonstrate that granule cells receive inputs from the local circuit axons of at least five distinct types of dentate neuron terminating in mutually exclusive domains of the cell's surface in four out of five cases. Four of the cell types (HICAP cell, MOPP cell, basket cell, axo‐axonic cell) contain GABA, and the HIPP cell may also be inhibitory. The specific local inhibitory neurons terminating in conjunction with particular excitatory amino acid inputs to the granule cells (types 1 – 3) are in a position to interact selectively with the specific inputs on the same dendritic segment. This arrangement provides a possibility for the independent regulation of the gain and long‐term potentiation of separate excitatory inputs, through different sets of GABAergic local circuit neurons. The pairing of excitatory and inhibitory inputs may also provide a mechanism for the downward reseating of excitatory postsynaptic potentials, thereb

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00508.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe interaction of zinc with pre‐ and postsynaptic GABABreceptors was studied in adult rat hippocampal slices using intracellular recording in CA1 and CA3 pyramidal neurons. Zinc (50 – 300 μM) antagonized baclofen responses with a variable potency, whereas CGP‐35348 (100 μM) or barium (300 μM) produced a more substantial and consistent inhibition. Zinc also induced giant GABAA‐mediated depolarizing potentials (GDP) in these neurons. After blocking GABAAand excitatory synaptic transmission, monosynaptic hyperpolarizing inhibitory postsynaptic potentials (IPSP) mediated by GABABreceptors (IPSPB) were inhibited by CGP‐35348 or barium; however, zinc increased the latency and prolonged the duration of the IPSPBand also induced the appearance of spontaneous giant GABAB‐mediated hyperpolarizing potentials (GHP). In some cells, IPSPBs in zinc exhibited a multiphasic appearance. The early component was partially inhibited by 300 μM zinc and was followed by a late GHP. CGP‐35348 at 100 μM inhibited the early monosynaptic IPSPBbut not the GHP; however, at 300 μM both components were blocked. Paired‐pulse inhibition of the IPSPBwas used to assess the effect of zinc on presynaptic GABABreceptors. Neither the zinc‐chelating agent CP94 (400 μM) nor zinc affected this phenomenon. CGP‐35348, barium and polyvalent cations, such as cadmium, copper, cobalt, manganese, iron and aluminium, failed to induce giant potentials in hippocampal neurons. It is concluded that zinc is apparently unique in synchronizing the release of GAB

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00509.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractSpatio‐temporal spreading of activity in the CA1 region of the rat hippocampal slice was studied by two experimental approaches. At identical locations in the tissue we measured both the extracellular field potential distribution with microelectrode recordings and the intracellular potential distribution by optical recording, using voltage‐sensitive fluorescent dyes. Current source density analysis (CSD) was applied to the extracellular field potential distributions (eCSD) to enhance the spatial resolution. In order to obtain an analogous improvement for the optical recordings, we developed a new CSD transformation, which calculates the locations of the transmembrane current generators from the intracellular potential distributions (iCSD). Compared to the underlying fluorescence maps, the new iCSD profiles exhibit a considerable improvement in spatial resolution. Results can be directly interpreted in terms of physiological membrane processes, such as postsynaptic potentials and action potentials. The iCSD profiles show a surprisingly good correspondence with the classical eCSD profiles both qualitatively and quantitatively, the only difference being that cell body activity is reduced in amplitude. Thus, this new optical CSD analysis paves the way for a quantitative interpretation, rather than the hitherto predominantly qualitative interpretation of spatio‐temporal activity profiles from optical recording measure

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00510.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractAxonal transport of the vesicular monoamine transporter was assayed in the rat brain byin vivobinding of the specific ligand [3H] reserpine. Because of the marked localization of reserpine binding sites in dopaminergic cell bodies and nerve terminals, the dopaminergic nigrostriatal pathway was chosen for the study of the axonal transport of the monoamine carrier present in the membrane of synaptic vesicles. When labelled reserpine was injected into the substantia nigra, a delayed accumulation of radioactivity in the ipsilateral striatum was observed ∼4 h after the injection. Similarly, injection into the right striatum was followed by a substantial accumulation of radioactivity in the ipsilateral substantia nigra, which was prevented by peripheral injection of unlabelled reserpine or tetrabenazine. This process was rapid and dependent on microtubules. In senescent rats, the amount of retrogradely transported [3H] reserpine was significantly reduced. These results demonstrate that labelled reserpine may be used to monitorin vivofast axonal transport in central neuron

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00511.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractReactive gliosis, a general response to injury in the central nervous system grey and white matter, represents a serious obstacle to axonal regeneration in mammals. In culture, myelin‐free plasma membranes from normal rat brain tissue promoted neurite outgrowth, whereas myelin‐free membranes purified from injured tissue were inhibitory. The inhibitory activity could be solubilized by detergent, was sensible to glycosaminoglycan lyase digestion and eluted with an apparent molecular weight of 160 – 220 kDa in gel filtration chromatography. When presented as a surface‐bound molecule, the inhibitor prevented neurite initiation; when added in a soluble form to growing neurites, it induced their retraction. These results provide cellular and molecular evidence supporting the classical view that, in the mammalian central nervous system, damage‐evoked gliosis correlates with the expression of molecules capable of preventing neurite

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00512.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractAlthough developing motor neurons express low‐affinity nerve growth factor (NGF) receptors, there is no known biological effect of NGF on developing or adult motor neurons. In this study, we found that, unlike NGF, brain‐derived neurotrophic factor (BDNF), neurotrophin‐3 (NT‐3) and neurotrophin‐4/5 (NT‐4/5) stimulated cholinergic phenotype by increasing choline acetyltransferase (CAT) activity in cultures enriched with embryonic rat motor neurons. Ciliary neurotrophic factor (CNTF) also stimulated CAT activity. The effects of BDNF and NT‐4/5 on CAT activity appeared to be synergistic with that of CNTF. Cotreatment with BDNF and NT‐3 resulted in an additive effect, suggesting that signal transduction was mediated through different high‐affinity receptors tyrosine kinases B and C (Trk B and Trk C). However, cotreatment with BDNF and NT‐4/5 did not result in an increase in CAT activity greater than that of either BDNF or NT‐4/5 alone, suggesting that their effects were mediated via the same receptor Trk B. Supporting our findings that spinal cholinergic neurons are responsive to trophic actions of members of the neurotrophin family, motor neuron‐enriched cultures were found to express mRNA for Trk B and Trk C, which have been identified as high‐affinity receptors for BDNF and NT‐

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00513.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractDuring a critical period of postnatal development the mammalian visual cortex is highly susceptible to experience‐dependent alterations of neuronal response properties. These modifications are facilitated by the neuromodulators noradrenalin and acetylcholine. To identify the cholinergic mechanisms responsible for this facilitation, muscarinic and nicotinic antagonists were infused into the visual cortex of kittens while the animals were subject to monocular deprivation. Subsequently the ocular dominance of cortical cells was assessed by single‐unit recording. Ocular dominance changes were suppressed by scopolamine and pirenzepine but not by gallamine, hexamethonium and mecamylamine. This blocking effect was concentration‐dependent, and control experiments revealed that it was not due to suppression of neuronal responses to light. It is concluded from these results that acetylcholine facilitates neuronal plasticity in the visual cortex through mechanisms activated by muscarinic M1rece

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00514.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractRetinal projections to the pretectal nuclei, accessory optic system and superior colliculus in pigmented and albino ferrets were studied using anterograde tracing techniques. Both Nissl‐ and myelin‐stained material was used to identify the pretectal nuclei, nuclei of the accessory optic system and the layers of the superior colliculus. Following monocular injection of either horseradish peroxidase or rhodamine‐B‐isothiocyanate, four pretectal nuclei, including the nucleus of the optic tract, posterior pretectal nucleus, anterior pretectal nucleus and the olivary pretectal nucleus, could be identified to receive direct retinal input in both pigmented and albino strains. In the accessory optic system, retinal terminals were observed in the dorsal, lateral and medial terminal nuclei as well as in the interstitial nucleus of the superior fasciculus, posterior fibres. The retinal projection to the superior colliculus was found to innervate the three superficial layers. The retinal projections to the pretectal nuclei and nuclei of the accessory optic system in the pigmented animals were bilateral, although the label was most dense contralateral to the injected eye. Ipsilateral retinal projections to the pretectal nuclei and nuclei of the accessory optic system appeared to be absent in albino ferrets, i.e. they were invisible with our methods. In both pigmented and albino ferrets retinal terminals in the contralateral superior colliculus densely innervated the three superficial layers. In both strains the ipsilateral projection appeared as clusters which were absent in rostral and caudal poles. In pigmented animals the ipsilateral projection was much denser and more extensive than in albinos. Following injection of retrograde tracers into the brainstem at the level of the dorsal cap of the inferior olive, retrogradely labelled neurons in the pretectum were found in the ipsilateral nucleus of the optic tract. Their somata overlapped mainly with scattered retinal terminals close to the pretectal surface and rarely or not all with the deeper prominent terminal clusters. In the accessory optic system, inferior olive projecting neurons were observed in all four ipsilateral nuclei and fully coincided with the retino‐recipient zones. In the superior colliculus, retrogradely labelled neurons were found contralateral to the injection site in the de

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00515.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractAs shown previously, neurons in various areas of the cat's visual cortex respond to appropriate visual stimuli with oscillatory activity in the frequency range of 30 – 70 Hz. It has been suggested that synchronization of such responses serves to define assemblies of coherently active cells which represent individual visual objects. In this study, we have investigated this putative binding mechanism in the visual cortex of strabismic cats. We used six adult cats in which divergent squint had been induced surgically at the age of 3 weeks. Multiunit activity was recorded from area 17 with arrays of four or five closely spaced microelectrodes. Subsequently, auto‐ and cross‐correlation functions were computed for all spike trains. To quantify the oscillatory nature of the responses and the strength of synchronization between spatially remote sites, damped sine wave functions were fitted to the correlograms. Analysis of responses obtained from 202 recording sites showed that the vast majority of cells had become monocular. Auto‐correlation analysis revealed that the proportion of oscillatory firing patterns was similar to that observed in normal cats. However, cross‐correlation analysis of 153 response pairs demonstrated that synchronization was reduced significantly between cells dominated by different eyes while it was as frequent and strong as in normal cats between cells dominated by the same eye. These findings indicate that strabismus not only causes a reorganization of afferent inputs but also affects intracortical interactions. Since strabismic cats lack tangential intracortical connections between territories connected to different eyes and are unable to combine signals conveyed by the two eyes these results support the notion that response synchronization is achieved by cortico‐cortical connections and serves as a mechanism for feat

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00516.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY