摘要:

AbstractThere is growing interest in the phenomenon of long‐term depression (LTD) of synaptic efficacy that, together with long‐term potentiation (LTP), is a putative information storage mechanism in mammalian brain. In neural network models, multiple learning rules have been used for LTD induction. Similarly, in neurophysiological studies of hippocampal synaptic plasticity, a variety of activity patterns have been effective at inducing LTD, although experimental paradigms are still being optimized. In this review the authors summarize the major experimental paradigms and compare what is known about the mechanisms of LTD induction. Although all paradigms appear to initiate a cascade of events leading to an elevated level of Ca2+postsynaptically, the extent to which these paradigms involve common expression mechanisms has not yet been tested. The authors discuss several critical experiments that would address this latter issue. Numerous questions about the properties and mechanisms of LTD(s) in the hippocampus remain to be answered, but it is clear that LTD has finally arrived, and will soon be attracting attention equal to its flip side, LTP. © 1994 Wiley‐Lis

ISSN:1050-9631    

DOI:10.1002/hipo.450040203

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe effects of ibotenic acid lesion of the septum were studied in rats implanted with chronically indwelling electrodes and septal cannula. Each rat served as its own control and the properties of the hippocampal theta rhythm were studied before and after ibotenic acid and control saline infusion into the medial septal area. Ibotenic acid preferentially killed neurons in the lateral septum, and significantly attenuated the hippocampal theta rhythm about 50% bilaterally, at both surface and deep electrodes. The coherence and the phase of the theta rhythm at the CA1 apical dendrites, with respect to a superficial electrode, also declined significantly after ibotenic acid lesion. Pilocarpine (25 mg/kg i. p.) induced a theta rhythm of 7–9 Hz during immobility in the lesioned rats that was significantly higher in frequency than that induced in intact rats (4–6 Hz). In lesioned rats, the theta rhythm during tail pinch under urethane anesthesia was largely abolished, and the theta during walking was attenuated by atropine sulfate (50 mg/kg i. p.). Phencyclidine (10 mg/kg i. p.) or parachlorophenylaline (PCPA) alone, which was inferred to abolish an atropine‐resistant theta input, did not affect the power of the walking theta rhythm in either the lesioned or the normal rat. It was concluded that the theta in the behaving rats after ibotenic acid lesion in the septum has a strong astropine‐sensitive component, and that it is not predominantly atropine‐resistant, as suggested previously. The lack of PCPA effect on the theta phase in intact and lesioned rats also suggested a different view of the atropine‐resistant theta in hippocampal region CA1. One possible mechanism of the atropine‐resistant theta at the distal dendrites of pyramidal cells may result from rhythmic inhibition by stratum lacunosum‐moleculare interneurons which may be activated by either serotonergic or cholinergic inputs. © 1994

ISSN:1050-9631    

DOI:10.1002/hipo.450040204

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe present study examines changes in field excitatory postsynaptic potential (EPSP) waveform in association with long‐term potentiation (LTP) in the CA1 region of the hippocampal slice preparation. Experiments were performed in the presence of the GABAA‐antagonist picrotoxin. With test field EPSP about one‐third the size of that evoking spike activity (measured in the cell body layer along the same somatodendritic axis as the dendritic recording) a decreased decay time constant (approximately 8%) was seen in association with LTP. This change in field EPSP waveform was not associated with any apparent spike activity in the cell body recording. Nevertheless, several findings suggest that increased spike activity explains the change in the decay time constant of the field EPSP during LTP. First, when reducing the stimulation strength after the induction of LTP to obtain a field EPSP of the same magnitude as the pretetanus one, the change of the decay time constant was reduced to only 2.8%. Second, when using small test field EPSP (about one‐fourth the size of that evoking spike activity) the decay time constant was not significantly affected in association with LTP. Third, when cutting the slice in such a manner that spike activity originating from somatic regions closer to the stimulating electrode was removed, the EPSPs decay time constant was not significantly affected in association with LTP. It is concluded that LTP is not associated with a change in the shape of the field EPSP. © 1994 Wiley

ISSN:1050-9631    

DOI:10.1002/hipo.450040205

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

年代:1994

数据来源: WILEY

摘要:

AbstractLight and electron microscopic immunocytochemical techniques were used to study the interneuron population staining for somatostain (SRIF) in cultured slices of rat hippocampus. The SRIF immunoreactive somata were most dense in stratum oriens of areas CA1 and CA3, and in the dentate hilus. Somatostain immunoreactive cells in areas CA1 and CA3 were characteristically fusiform in shape, with dendrites that extended both parallel to and into the alveus. The axonal plexus in areas CA1 and CA3 was most dense in stratum lacunosum‐moleculare and in stratum pyramidale. Electron microscopic analysis of this area revealed that the largest number of symmetric synaptic contacts from SRIF immunoreactive axons were onto pyramidal cell somata and onto dendrites in stratum lacunosum‐moleculare. In the dentate gyrus, SRIF somata and dendrites were localized in the hilus. Hilar SRIF immunoreactive neurons were fusiform in shape and similar in size to those seen in CA1 and CA3. Axon collaterals coursed throughout the hilus, projected between the granule cells and into the outer molecular layer. The highest number of SRIF synaptic contacts in the dentate gyrus were seen on granule cell dendrites in the outer molecular layer. Synaptic contacts were also observed on hilar neurons and granule cell somata. SRIF synaptic profiles were seen on somata and dendrites of interneurons in all regions. The morphology and synaptic connectivity of SRIF neurons in hippocampal slice cultures appeared generally similar to intact hippocampus. © 1994 Wiley‐Lis

ISSN:1050-9631    

DOI:10.1002/hipo.450040206

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe hippocampi of species commonly used forin vitrophysiologic studies were examined to determine if there were species‐specific and regional differences in somatostatin immunoreactivity. The distributions of somatostatin‐immunoreactive somata and fiber plexuses were determined, and the concentration of somatostatin along the septotemporal axis of the hippocampus was measured using a radioimmunoassay. There are many similarities in the patterns of somatostatin immunoreactivity in the hippocampi of mice, rats, guinea pigs, and rabbits. All species had a relatively even distribution of somatostatin‐positive perikarya across three fields of the hippocampus (dentate gyrus, CA3, and CA1‐2), a similar distribution of somatostatin‐immunoreactive perikarya across the strata of the CA1‐2 field and the dentate gyrus; and more somatostatin‐positive cells in temporal than in septal hippocampus. However, there are species‐specific differences in the distribution of somatostatin‐immunoreactive perikarya across the strata of CA3. In addition, unlike the other species examined, mice appeared not to have a somatostatin‐immunoreactive fiber plexus in the molecular layer of the dentate gyrus. The functional significance of these differences remains to be determined. ©

ISSN:1050-9631    

DOI:10.1002/hipo.450040207

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

年代:1994

数据来源: WILEY

摘要:

AbstractPrevious experiments have described highly specific effects of noradrenergic agonists on synaptic transmission in the dentate gyrus (DG). For example, perfusion of hippocampal slices with the beta‐noradrenergic agonist isoproterenol induces a long‐lasting potentiation (LLP) of extracellularly recorded responses following stimulation of the medial perforant path (PP), and long‐lasting depression (LLD) of responses evoked by stimulation of the lateral PP (Dahl D, Sarvey JM, 1989, Proc Natl Acad Sci USA 86:4776–4780). To examine the possible interactions of LLP, LLD, and long‐term potentiation induced by tetanic stimulation (LTP), the authors recorded extracellular field potentials evoked in the DG by stimulation of the lateral or medial perforant path following LTP and LLP or LLD, invoked in different orders. After establishment of LLP or LLD by path application of isoproternol, subsequent tetanization of the respective afferents resulted in additional potentiation of the medial PP‐evoked response and return of the lateral PP‐evoked response to baseline levels. In other slices application of isoproterenol after establishment of LTP resulted in further potentiation of medial PP‐evoked responses but no change in the potentiated response evoked by lateral PP stimulation. Thus the pathway specificity was maintained irrespective of the history of previous potentiation or depression. Experiments using the specific beta1antagonist metoprolol further confirmed pathway specificity. Perfusion with 20 μM of metoprolol appeared to reduce LTP evoked by stimulation of the medial but not lateral PP. In a subsequent experiment, metoprolol in the absence of tetanization produced LLD of the medial PP‐evoked response and LLP of the lateral PP‐evoked response, opposite to the effects of ISO. These results confirm the impressive extent of pathway specificity in the DG and reveal the persistent capacity for synaptic modification as exemplified by the processes of LLP, LLD, and LTP. ©

ISSN:1050-9631    

DOI:10.1002/hipo.450040208

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

年代:1994

数据来源: WILEY

摘要:

AbstractAnatomic and physiologic studies in the rat have shown projections from the hippocampal formation (HF) and mediodorsal (MD) thalamic nucleus to the medial prefrontal cortex (mPFC). The authors used multi‐barrel iontophoresis to: confirm the neurotransmitter used in the projection from HF to mPFC; investigate the role of GABAergic inhibition in the regulation of this projection; and examine the functional convergence of projections from HF and MD onto single mPFC neurons. During HF stimulation, nine cells (6%) showed excitation followed by prolonged inhibition, 39 cells (26%) showed prolonged inhibition alone and 100 cells (68%) showed no clear response. In a further 12 cells that showed no predrug excitation to HF stimulation (representing 16% of the cells in this category), iontophoresis of the GABAAantagonist bicuculline methiodide (BMI) revealed excitatory responses. A total of six mPFC cells (38% of the cells showing excitatory responses to HF stimulation) showed convergent excitation to HF and MD thalamic (or adjacent paratenial nucleus) stimulation. Five out of eight (63%) of the predrug or BMI‐revealed excitatory responses of mPFC neurons to HF stimulation were selectively decreased after AMPA antagonist iontophoresis (either CNQX or DNQX). These data confirm that the HF projection to prefrontal cortex is, at least in part, glutamatergic; suggest that the responses of mPFC neurons to activity in this HF pathway are regulated by GABAergic inhibition; and indicate that projections from HF and MD converge onto single mPFC neurons. © 1994 Wiley‐Lis

ISSN:1050-9631    

DOI:10.1002/hipo.450040209

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

年代:1994

数据来源: WILEY

摘要:

AbstractCholinergic denervation of the hippocampus by medial septal (MS) lesions results in the ingrowth of peripheral sympathetic fibers, originating from the superior cervical ganglia, into the hippocampus. To determine the effect of hippocampal sympathetic ingrowth (HSI) [3H]‐QNB (L‐quinuclidinyl [benzilic‐4, 4(n)]benzilate) binding was assessed in the dorsal and ventral hippocampus four weeks after MS lesions. In dorsal hippocampus, HSI was found to signignificantly increase the number (Bmax) of [3H]‐QNB binding sites and to normalize the decrease in affinity found in animals with MS lesions plus ganglionectomy (i. e., no ingrowth). In ventral hippocampus, HSI was found to normalize the increased number of binding sites and decreased affinity found in animals with MS lesions without ingrowth. No effect on either Kdor Bmaxwas found in animals that had undergone ganglionectomy with sham MS lesions. These results suggest that HSI can induce changes in hippocampal muscarinic cholinergic receptors. © 1994 Wiley

ISSN:1050-9631    

DOI:10.1002/hipo.450040210

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe heavy metal bismuth induces a new type of selective neuronal degeneration that shares some common aspects with that seen following hypoxia and ischemia. Continuous application of 3 μm bismuth to organotypic cultures of rat hippocampus resulted after 2–3 weeks in selective degeneration of CA1 pyramidal cells, while CA3 pyramidal cells, dentate granule cells, and subicular neurons were resistant. With 10 μm MK‐801, a noncompetitive NMDA‐antagonist, during the entire culturing period failed to prevent neuronal degeneration induced by 3 μm bismuth. GABA‐immunoreactive interneurons were also affected by bismuth, but were generally less sensitive than CA1 pyramidal cells. Acute application of up to 100 μm bismuth did not change the electrophysiological properties of CA1 pyramidal cells. © 1994 Wil

ISSN:1050-9631    

DOI:10.1002/hipo.450040211

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe neuronal cytoskeleton is disrupted in neurodegenerative disorders such as Alzheimer's disease. Due to the lack of suitable animal models, studies examining the events involved in the neurodegeneration have relied on postmortem human brain tissue obtained from individuals with the disease and from normal controls. However, it is uncertain if the neuronal cytoskeleton is stable during the postmortem interval. Immunohistochemistry and immunoblots were used to examine the microtubule–associated proteins tau, MAP2, and MAP1B in the rat hippocampus at various times after death. Shortly after death, tau immunoreactivity was lost from axons and accumulated in somatodendritic compartments. MAP2 and MAP1B also accumulated in neuronal cell bodies prior to a loss of immunostaining in some regions, notably subiculum. Immunoblots confirmed a loss of MAP2 and MAP1B within a few hours after death. Tau levels remained constant during the 8–hour postmortem interval examined, although the electrophoretic mobility of some tau bands was altered. Human brain tissue obtained at autopsy and at surgery demonstrated similar cytoskeletal alterations in postmortem tissue. These results demonstrate that microtubules and associated proteins are not stable postmortem. © 1994 Wiley‐Lis

ISSN:1050-9631    

DOI:10.1002/hipo.450040212

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

年代:1994

数据来源: WILEY