摘要:

AbstractSpontaneous or evoked brain activity in the hippocampus showed a 20–70 Hz beta rhythm under some conditions, typically during behavioral activation and accompanied by a theta rhythm. Beta rhythms are generated locally, perhaps by a recurrent feedback loop involving pyramidal cells and inhibitory interneurons. Modulation of the local circuit and rhythm by cholinergic inputs has also been demonstrated. Under some behavioral states, neural impulses modulated at the beta frequency may transmit preferentially through the trisynaptic circuit in the hippocampus. It is suggested that the beta rhythm may serve to establish transient physiological connections, reflected in coherence at the beta frequency, among neurons in the hippocampus and related structures. Thus, the beta rhythm may play an essential role in hippocampal functio

ISSN:1050-9631    

DOI:10.1002/hipo.450020202

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

年代:1992

数据来源: WILEY

摘要:

AbstractIn order to demonstrate axonal connections preserved in rat temporal cortex slices the authors used rhodamine‐dextran‐amine as a tracer. The slices contained the neocortical areas Te2 and Te3, the medial and lateral entorhinal cortices (MEC and LEC), the subicular regions, and the dentate gyrus and hippocampus proper. Rhodamine‐dextran‐amine crystals were placed by microinjection into a given area. Following this local lesioning the dye was permitted to diffuse and migrate intraaxonally in antero‐and retrograde directions for about 8 hours. The slices were then formaldehyde‐fixed and analyzed by fluorescence microscopy. Most of the known connections within and between the entorhinal cortex and the hippocampus and denatate gyrus were preserved in the slice preparation, provided that the slices were cut with a near horizontal orientation corresponding to plates 99–108 in Paxinos and Watson (1986). Only the lateral perforant path between the LEC and the hippocampus could not be followed to its full extent. The authors conclude that most aspects of the intrinsic synaptic organization of the temporal lobe can be reliably studied in hippocampal‐entorhinal cortex sli

ISSN:1050-9631    

DOI:10.1002/hipo.450020203

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

年代:1992

数据来源: WILEY

摘要:

AbstractNeuropeptide Y (NPY) has been implicated in the modulation of hippocampal neuronal activity and in the pathophysiology of several neurological disorders involving the hippocampal formation. Thus, this study examines the light and electron microscopic immunoperoxidase labeling of a rabbit polyclonal antibody against porcine NPY in single sections through each lamina of the CA1 and CA3 regions of the hippocampus and the dentate gyrus (DG) of normal adult rats. By light microscopy, the majority of perikarya with intense NPY‐like immunoreactivity (NPYLI) were located in stratum oriens of CA1 and CA3 of the hippocampus and in the hilus of the DG. Fine varicose processes with NPY‐LI were found in all layers of the hippocampal formation, but were densest in the outer third of the molecular layer of the DG. The density of NPY‐labeling was greater in the ventral portion of the hippocampal formation.By electron microscopy, most NPY‐containing perikarya in all three hippocampal regions were: small (8–12 μm) or medium‐sized (12–18 μm) and elongated; or medium‐sized and round. A dense accumulation of NPY‐LI was commonly observed within the individual saccules of Golgi complexes and some rough endoplasmic reticulum in the cytoplasm. Perikarya and dendrites with NPY‐LI usually were directly apposed to other neuronal processes (mostly terminals) and lacked astrocytic appositions. The majority of terminals in contact with NPY immunoreactive neurons were unlabeled and synapsed with the shafts of large and small dendrites. In CA1 and CA3 of the hippocampus, the types of synapses formed by the unlabeled terminals were not significantly different; however, more asymmetric synapses than symmetric synapses were formed by the unlabeled terminals on the shafts of small NPY‐labeled dendrites in the DG.The terminals with NPY‐LI (0.25–1.2 μm) contained many small, clear vesicles and 0–2 large, dense‐core vesicles. The types of synapses (i.e., asymmetric and symmetric) and distribution of NPY‐labeled terminals on the targets were remarkably similar in each lamina of the hippocampal subregions. The NPY‐labeled terminals usually synapsed with one unlabeled perikaryon or dendrite. However, others synapsed either (1) with two unlabeled perikarya or dendrites simultaneously or (2) with one NPY‐containing perikaryon or dendrite. Most of the terminals with NPY‐LI formed symmetric junctions with the shafts of small (distal) dendrites. The remaining NPY‐labeled terminals either (1) formed appositions that lacked a membrane specialization, but were without apparent glial intervention in the plane of section analyzed, with NPY‐labeled and unlabeled perikarya and dendrites; or (2) were closely apposed without glial intervention to unlabeled and NPY‐labeled terminals.The dense input from terminals forming asymmetric (excitatory) junctions and the limited glial coverage may contribute to the vulnerability of NPY‐immunoreactive neurons in disorders such as Alzheimer's disease or epilepsy. Additionally, these results provide cellular substrates in the rat hippocampal formation for (1) the direct synaptic input of NPY‐labeled terminals to non‐NPY‐containing hippocampal neurons; and (2) presynaptic interactions between NPY‐containing terminals a

ISSN:1050-9631    

DOI:10.1002/hipo.450020204

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

年代:1992

数据来源: WILEY

摘要:

AbstractMossy cells in the human dentate gyrus of adults and children of different ages were impregnated using the rapid‐Golgi method. In every case the cause of death was verified by autopsy and the brains were used when neither the history of the patient nor autopsy revealed brainrelated disease.Mossy cells in the human share common light microscopic features with the same cell type in rats and monkeys. Their most characteristic feature is the extremely large and complex excrescences on their proximal dendrites. Distal dendrites display pedunculate spines. Mossy cells have a few somal spines. The axon of mossy cells originates from the cell body and gives rise to several collaterals in the hilar region. The axons could be followed for several hundred microns, but in only one case did an axon collateral enter the granule cell layer of the adult dentate gyrus.In the newborn child, mossy cells display immature somal and dendritic features. The soma frequently bear spines. The dendrites are varicose and terminate in presumed growth cones. Both proximal and distal portions of the dendrites bear a few pedunculate spines and longirregular filopodia. A few small excrescences are present on the proximal dendrites. The first large, complex excrescences on the proximal dendrites of mossy cells appeared in the 7‐month‐old child. Both somata and dendrites dispaly adult‐like characteristics in mossy cells from a 5‐year‐old child. However, not all mossy cells are alike and some dendrites still display long filopodia. The axons of immature mossy cells were similar to adults.The present results indicate that connections between granule cells and hilar mossy cells of the human dentate gyrus develop through an extended postnatal period of time that may last until the

ISSN:1050-9631    

DOI:10.1002/hipo.450020205

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

年代:1992

数据来源: WILEY

摘要:

AbstractRecently, Sloviter et al. reported that adrenalectomy (ADX) of young adult rats after 3 months led to a selective loss of granule neurons in the dentate gyrus (DG) and that this loss could be prevented by low doses of corticosterone. In the present study, the ADX‐induced neuronal degeneration was investigated in Wistar rats, using a silver impregnation method for degenerating neurons. To examine the time course and distribution of the ADX‐induced degeneration, young adult male rats were allowed to survive 2, 3, and 5 days and 1, 2, and 3 weeks after ADX. Argyrophilic neurons were present in the dentate granule cell layer on the second day following ADX. Three days after ADX, the number of argyrophilic granule neurons was much more abundant, and it increased gradually with longer post‐ADX survival times. Argyrophilia was specifically confined to dentate granule cells and was accompanied by the occurrence of pyknotic nuclei as observed in adjacent cresyl violet‐stained section. There were significant differences between individual rats in quantity of argyrophilia. About one fifth of the ADX rats showed sporadic or no argyrophilia, in spite of plasma corticosterone levels below the detection limit (10 ng/mL). Sham‐operated rats and ADX rats receiving corticosterone (10 mg/L) or dexamethasone (15 mg/L) in their drinking water did not display any argyrophilic neurons in the dentate gyrus. The distribution of the argyrophilia within the DG was highly characteristic with the highest number of degenerating cells in the hidden blade of the middle and the temporal thirds of the DG. There was a strong crest‐to‐tip and deep (hilar)‐to‐superficial increase in density of degenerating neurons. Along the entire septotemporal axis of the free blade and at the septal pole of the hidden blade, the number of argyrophilic cells was low. Wistar rats of different sex and aged 1–6 months all showed dentate granule cell degeneration 1 week following ADX. The distribution of the degeneration was identical to that of the young adult male group.In order to examine whether the absence of corticosteroids affects dentate granule cells directly or through other mechanisms induced by ADX, low doses of dexamethasone were infused with a microdialysis probe directly into the hippocampus on one side of ADX rats. As a result, the ADX‐induced neuronal degeneration was selectively prevente

ISSN:1050-9631    

DOI:10.1002/hipo.450020206

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

年代:1992

数据来源: WILEY

摘要:

AbstractShort‐term memory was assessed in two groups of amnesic patients. Six patients had confirmed or suspected damage to the hippocampal formation, and six patients had diencephalic damage as a result of alcoholic Korsakoff's syndrome. Verbal short‐term memory was evaluated with seven separate administrations of the standard digit span test in order to obtain a precise measure of short‐term memory. Nonverbal short‐term memory was evaluated with four tests that assessed apprehension, retention, and the ability to manipulate nonverbal material—all within the span of immediate memory. One of these four tests assessed short‐term memory for spatial location. Patients with damage to the hippocampal formation had a digit span equivalent to that of control subjects and also performed normally on the four tests of nonverbal short‐term memory. The patients with Korsakoff's syndrome had a marginally low digit span and performed poorly on three of the four nonverbal tasks, a finding consistent with the deficits in attention and visuospatial processing previously described for this patient group. These deficits are likely due to the frontal lobe atrophy typically associated with Korsakoff's syndrome, rather than to diencephalic damage. The results support the view that short‐term (immediate) memory, including short‐term spatial memory, is independent o

ISSN:1050-9631    

DOI:10.1002/hipo.450020207

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

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper describes a computational theory of spatial learning and navigation and its possible realization in the hippocampus. In the theory, mammals store memories of their geographical environment as a large number of independentfragments. A typical fragment denotes a few prominent landmarks in some region, their geometric relations, and their nongemetric properties, such as smells and visual cues. Navigation involves piecing together current sense data and relevant fragments to form a local map of the animal's surroundings; this is like solving a jigsaw puzzle. This computational model has been implemented in a computer program, whose performance is broadly consistent with observed levels of animal performance, and laboratory results, in spatial learning.Possible realizations of the model in animal brains are discussed. Unlike some neural net models of spatial learning, the model is strongly geometric, and uses special neural structures to store and manipulate two‐dimensional vectors and bearings. A possible neural architecture is described in which the hippocampus performs the geometric operatios; this has a long‐term memory for fragments (somewhere in the neocortex), which can associatively recall fragments into a number of parallelfragment fitters, in the dentate gyrus and CA3 regions. These vary the positions and orientations of their fragments, to optimize the fit of the fragments to each other and to the animal's recent sense data. A local map of the animal's surroundings is stored in CA1 and subicular regions, where matching of fragment positions and attributes takes place. Mismatches are passed back via the entorhinal cortex to improve the fit during the next hippocampal theta cycle.The model offers the potential for understading current data on spatial learning, on the neuroanatomy of the hippocampus and on place cells in a coherent framework, as well as understanding the role of the hippocampus in nonpositional memory tasks. Comparisons with experimental data are gi

ISSN:1050-9631    

DOI:10.1002/hipo.450020208

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe CA3 network in the hippocampus may operate as an autoassociator, in which declarative memories, known to be dependent on hippocampal processing, could be stored, and subsequently retrieved, using modifiable synaptic efficacies in the CA3 recurrent collateral system. On the basis of this hypothesis, the authors explore the computational relevance of the extrinsic afferents to the CA3 network. A quantitative statistical analysis of the information that may be relayed by such afferent connections reveals the need for two distinct systems of input synapses. The synapses of the first system need to be strong(but not associatively modifiable) in order to force, during learning, the CA3 cells into a pattern of activity relatively independent of any inputs being received from the recurrent collaterals, and which thus reflects sizable amounts of new information. It is proposed that the mossy fiber system performs this function. A second system, with a large number of associatively modifiable synapses on each receiving cell, is needed in order to relay a signal specific enough to initiate the retrieval process. This may be identified, we propose, with the perforant path input to CA3.

ISSN:1050-9631    

DOI:10.1002/hipo.450020209

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

年代:1992

数据来源: WILEY

摘要:

AbstractAcute intoxicating doses of ethanol‐producing blood alcohol levels of 120–200 mg% increase paired‐pulse (PP) inhibition in the dentate gyrus of anesthetized rats suggesting that ethanol increases recurrent inhibitory processes (Wiesner, J. B., and S. J. Henriksen (1987) Ethanol enhances recurrent inhibition in the dentate gyrus of the hippocampus. Neurosci. Lett. 79:169–173). To further understanding of the neuronal mechanisms underlying this phenomenon, the authors studied the effects of the benzodiazepine (BZ), chlordiazepoxide, and acute intoxicating levels of ethanol on extracellular field potential recordings and single‐unit activity in the dentate gyrus and area CA1 of the hippocampus. In the dentate, ethanol had no effect on population excitatory postsynaptic potential (pEPSP) amplitudes or slopes; decreased population spike (PS) amplitudes (25%); increased PP inhibition; decreased dentate granule cell (DGC) spontaneous activity (58%); had no effect on putative interneuron spontaneous activity; and markedly increased post field potential‐evoked interneuron discharges (IDs, 218%). Chlordiazepoxide had no effect on pEPSP amplitudes or slopes or PS amplitudes; increased PP inhibition; decreased DGC (62%) and interneuron (72%) spontaneous activity; and markedly decreased IDs (89%). In CA1, ethanol had no effect on pEPSP amplitudes or slopes; decreased PS amplitudes (26%); had no effect on PP responses; decreased pyramidal cell (PC) spontaneous activity (39%); had no effect on interneuron spontaneous activity; and markedly increased IDs (97%). Chlordiazepoxide had no effect on pEPSP amplitudes or slopes or PS amplitudes; had no effect on PP responses; decreased PC spontaneous activity (41%); and had no effect on interneuron spontaneous activity or IDs. The results suggest that the BZs decrease principal cell excitability by postsynaptic facilitation of inhibitory processes, whereas ethanol decreases principal cell excitability by postsynaptic facilitation of inhibitory processes, whereas ethanol decreases principal cell excitability indirectly by increasing the excitability of inhibitory i

ISSN:1050-9631    

DOI:10.1002/hipo.450020210

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

年代:1992

数据来源: WILEY

ISSN:1050-9631    

DOI:10.1002/hipo.450020201

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

年代:1992

数据来源: WILEY