摘要:

AbstractMuch of the current interest in the hippocampus concerns a rapid and persistent form of synaptic plasticity, called long‐term potentiation (LTP), that is a candidate substrate for some of the mnemonic functions of this structure. There are at least two kinds of LTP in the hippocampus. One form is found at the synapse between the mossy fibers of the granule cells and the pyramidal neurons of the CA3 region. Attempts to examine the mechanism underlying this form of LTP have yielded contradictory conclusions. The authors show how the complex circuitry of the dentate gyrus and adjacent hippocampus may have caused the contradictions. To overcome problems introduced by the circuitry, a specific set of procedures and criteria for evoking and identifying mossy fiber responses is proposed. Use of these or similar procedures and criteria will improve the design and interpretation of experiments on mossy fiber LTP and allow more informative comparisons among species and brain regions and across laboratorie

ISSN:1050-9631    

DOI:10.1002/hipo.450030202

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

年代:1993

数据来源: WILEY

ISSN:1050-9631    

DOI:10.1002/hipo.450030203

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe authors attempted to replicate the study of Castro, Silbert, McNaughton, and Barnes (1989) in which it was concluded that bilateral saturation of hippocampal synaptic enhancement produced a deficit in acquisition of a spatial navigation problem in the Morris swim task. The original protocol was followed as closely as possible, but no effect of long‐term enhancement (LTE) saturation on spatial performance in this task was found. This negative result suggests either that the previous finding using the swim task reflected statistical error or that some as yet undetermined variable is of critical importance in this phenomenon. The present negative finding also raises a question concerning the reproducibility of the earlier results of McNaughton, Barnes, Rao, Baldwin, and Rasmussen (1986) in which LTE saturation apparently led to a prolonged deficit on a different spatial task. Although negative results in such experiments do not constitute grounds for rejecting the underlying hypothesis, the present lack of a positive effect renders uncertain, for the time being, one of the lines of experimental support for the theory that LTE at hippocampal synapses reflects a mechanism for the associative, distributed storage of new spatial informatio

ISSN:1050-9631    

DOI:10.1002/hipo.450030204

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe electrically induced increase in hippocampal synaptic strength known as long‐term potentiation (LTP) is thought to involve some of the same mechanisms as those mediating information storage during spatial learning. Physiological saturation of synaptic weights might therefore be expected to occlude spatial learning. In support of this, Castro et al. (Castro CA, Silbert LH, McNaughton BL, Barnes CA, 1989, Nature 342:545–548) reported that repeated induction of LTP to asymptotic levels, over a 14‐day period, blocked the ability of rats to learn the position of a hidden platform in a water maze shortly afterwards. The authors have attempted to replicate this finding in two experiments. In Experiment I, rats were given either 400 Hz stimulation as 50 trains/day over a 5‐day period, to induce LTP, or were given the same number of stimulus pulses at 1 Hz. Two hours after the last stimulation session they underwent eight spatial learning trials, occurring at 2‐hour intervals. In Experiment 2, the procedure of Castro et al. was followed exactly, with LTP induced by 10 trains of 400 Hz stimulation daily for 14 days. Spatial learning trials began 10 minutes after the last stimulation session and consisted of 12 trials with alternating 30‐second and 2‐minute intervals. In neither experiment was a significant impairment of spatial learning observed. However, there was a strong positive correlation, in both experiments, between the final level of LTP and subsequent performance in t

ISSN:1050-9631    

DOI:10.1002/hipo.450030205

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

年代:1993

数据来源: WILEY

摘要:

AbstractIn two experiments the authors failed to detect an effect of inducing bilateral, long‐lasting synaptic potentiation at perforant path dentate synapses on spatial learning by rats in the Morris place navigation task. Daily sessions of high‐frequency stimulation of perforant path axons produced large increases to an asymptotic level in population spike and field excitatory postsynaptic potential recorded in ipsilateral dentate gyrus. Place learning proceeded normally 24 hours after the last of 14 high‐frequency stimulation sessions in rats that had previously mastered the procedural aspects of place navigation (Experiment 1) and in rats that were naive (Experime

ISSN:1050-9631    

DOI:10.1002/hipo.450030206

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

年代:1993

数据来源: WILEY

摘要:

AbstractThere is some controversy about the role of long‐term potentiation (LTP) in spatial learning. The authors have found that triggering generalized kindled seizures with stimulation of the perforant path disrupts spatial learning in the Morris water maze but that kindling per se does not affect spatial learning. It is suggested that abnormal electrical activity induced by high‐frequency stimulation of the perforant path may have been responsible for the disruption of spatial learning previously attributed to LTP saturat

ISSN:1050-9631    

DOI:10.1002/hipo.450030207

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

年代:1993

数据来源: WILEY

摘要:

AbstractTwo approaches were used to study the relations between the acquisition of place learning in the Morris water maze and long‐term potentiation (LTP), kindling, and afterdischarge (AD). In the first, the possibility of behavioral LTP in the dentate gyrus field potential evoked by stimulation of the perforant path was evaluated in rats that showed robust place learning in the water maze. There was no effect of place learning on the field potential, and field potential measures did not correlate with place learning acquisition measures. In the second approach, the effect of bilateral saturation of LTP on subsequent place learning in the water maze task, begun within 5 minutes of the last LTP session, was evaluated. The effect of kindled seizures evoked bilaterally from the perforant path, or of a single unilateral AD, on acquisition of the water maze task (begun within 10 minutes) were also evaluated. Bilateral LTP saturation did not affect place learning, and the bilateral LTP group learned as readily as controls. In contrast, the kindled and AD groups were severely impaired in their performance of the place learning task. A second day of training in the water maze without any further electrical stimulation indicated that these groups had acquired considerable information on the first day of maze training and were not distinguishable from controls on the second day of training. This indicated that the deficit in these groups on the first day of training was temporary and likely resulted from a temporary perturbation of normal brain function due to the seizures. The results indicate that bilateral saturation of LTP in the dentate gyrus does not affect place learning in the water maze. They also indicate that recent hippocampal seizures, but not kindling, disrupt place learning in this tas

ISSN:1050-9631    

DOI:10.1002/hipo.450030208

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

年代:1993

数据来源: WILEY

摘要:

AbstractSingle neuron activity was recorded in the granular layer of the fascia dentata in freely moving rats, while the animals performed a spatial “working” memory task on an eight‐arm maze. Using recording methods that facilitate detection of units with low discharge rates, it was found that the majority (88%) of cells in this layer have mean rates below 0.5 Hz, with a minimum of 0.01 Hz or less. The remaining recorded cells exhibited characteristics typical of the theta interneurons found throughout the hippocampus. Based on several criteria including relative proportion and the relation of their evoked discharges to the population spike elicited by perforant path stimulation, it was concluded that the low‐rate cells correspond to granule cells. Granule cells exhibited clear spatially and directionally selective discharge that was at least as selective as that of a sample of CA3 pyramidal cells recorded under the same conditions. Granule cells had significantly smaller place fields than pyramidal cells, and tended to have more discontiguous subfields. There was no spatial correlation among simultaneously recorded adjacent granule cells. Granule cells also exhibited burst discharges reminiscent of complex spikes from pyramidal cells while the animals sat quietly; however, the spike duration of granule cells was significantly shorter than CA3 pyramidal cell spike durations. Under conditions of environmental stability, granule cell place fields were stable for at least several days. Following occasional maze rotations relative to the (somewhat impoverished) visual stimuli of the recording room, granule cell place fields were maintained relative to the distal spatial cues; however, frequent rotations of the maze sometimes resulted in a shift in the reference frame to the maze itself. These observations indicate that granule cells of the fascia dentata provide their CA3 targets with a high degree of spatial information, in the form of a sparsely coded, distributed represe

ISSN:1050-9631    

DOI:10.1002/hipo.450030209

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe effects of chronic and acute corticosterone (CORT) administration were investigated on hippocampal long‐term potentiation (LTP) in the dentate gyrus granule cell layer of the rat. Electrophysiological experiments were performedin vivounder urethane anesthesia. Chronic CORT treatment (40 mg/kg/day) over 21 days decreased LTP compared to vehicle controls, even when LTP was measured 48 hours after cessation of CORT treatment, when serum CORT levels had returned to baseline. A single injection of CORT also decreased LTP compared to vehicle controls, but only when CORT levels were high, since at 48 hours after a single acute CORT injection LTP was not depressed. The decrements in LTP were seen both for the slope of the excitatory postsynaptic potential and for the population spike. Yet CORT had no effects on posttetanic potentiation or neuronal excitability. These findings are consistent with previous reports showing a reduction in LTP in the CAI field of animals exposed to stress or acute CORT administratio

ISSN:1050-9631    

DOI:10.1002/hipo.450030210

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

年代:1993

数据来源: WILEY

摘要:

AbstractVasopressin receptors are present in both the developing and mature dentate gyrus of the rat brain and are of the V1vasopressor type. Because vasopressin has been shown to influence memory function when injected into the dentate gyrus, the influence of this peptide on an electrophysiological model of learning and memory using the field excitatory postsynaptic potential (EPSP) of the dentate gyrus was investigated. Results of these studies showed that nanomolar concentrations of [Arg8]‐vasopressin induced a prolonged increase in the amplitude and slope of the evoked population response in the presence of 1.5 mM calcium. Moreover, the expression of the vasopressin‐induced potentiation of the EPSP persisted following removal of vasopressin from the perfusion medium. The vasopressin‐induced sustained increase has been termedlong‐term vasopressin potentiation(LTVP). The closely related neuropeptide oxytocin had no effect upon the EPSP of the dentate gyrus. Preincubation of hippocampal slices in a selective V1antagonist blocked the expression of LTVP. The ability of the V1antagonist to block LTVP demonstrates that the potentiation induced by vasopressin is receptor‐specific. In the presence of 2.5 mM calcium, the effect of vasopressin was opposite to that observed in 1.5 mM calcium. Under the conditions of 2.5 calcium, vasopressin induced a prolonged depression in the amplitude and slope of the EPSP. Expression of both potentiation and depression appeared within 5 minutes of application and persisted for the length of the observation, 60 minutes. These experiments demonstrate that vasopressin can induce long‐lasting changes in the excitability of dentate gyrus neurons that are both calcium‐dependent and rece

ISSN:1050-9631    

DOI:10.1002/hipo.450030211

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

年代:1993

数据来源: WILEY