ISSN:1050-9631    

DOI:10.1002/hipo.450040402

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

年代:1994

数据来源: WILEY

摘要:

AbstractExperiments were carried out to study the spatiotemporal organization of medial entorhinal inputs to the hippocampal system. They were performed in the isolated guinea pig brain in vitro preparation as it provides easy access to the medial entorhinal cortex (mEC) which is difficult to reach in vivo. Multiple simultaneous field potential recordings along the septotemporal extent of the dentate granular layer revealed that the mEC projection to the dentate gyrus (DG) is organized topographically. Thus, stimulation of the caudal regions of the mEC elicited population spikes (PSs) in the septal pole of the DG while successively more rostral stimulation sites activated progressively more temporal sectors of the DG. However, threshold mEC stimuli never elicited PSs over more than one‐third of the DG.In the CAl pyramidal layer, only trisynaptic PSs were evoked by the mEC stimulation (latency>20 ms at 30°C). However, PSs were widely distributed in the transverse and longitudinal axes of the hippocampus and, irrespective of the mEC stimulation site, the latency of CAl PSs gradually increased from the CA3/CAl border toward the subiculum. By contrast, in the longitudinal axis, each segment of the CAl region responded at a shorter latency to stimulation of a given rostrocaudal level of the mEC. Septal CAl levels responded at shorter latencies to caudal mEC stimulation sites while more temporal CAl levels responded at shorter latencies to rostral mEC stimulation sites. When stimulated at threshold stimulation intensity, the initial CAl response propagated to the rest of the CAl field with a conduction velocity of 0.5–0.9 m/s.These results suggest that the associative pathways linking CA3 and CA1 regions can transmit mEC‐elicited DG activities to large segments of the hippocampal formation while preserving the topographical relationship between the mEC and the hippocampus in the time domain. These findings are in contrast to the so‐called lamellar hypothesis. © 1994 Wiley

ISSN:1050-9631    

DOI:10.1002/hipo.450040403

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe effects of darkness on quantitative spatial firing characteristics of 235 hippocampal CA1 “complex spike” (CS) cells were studied in young and old Fischer‐344 rats during food‐motivated performance of a randomized, forced‐choice task on an eight‐arm radial maze. The room lights were turned on or off on alternate blocks of all eight arms.In the dark, a lower proportion of CS cells had “place fields,” and the fields were less specific and less reliable than in the light. A small number of cells had place fields unique to the dark condition. Like CS cells, Theta cells showed a reduction in spatially related firing in the dark. The specificity and reliability of the place fields under both light and dark conditions were similar for both age groups. Increasing the salience of the environment, by increasing the light level and the number of visual cues in the light condition, did not affect the specificity or reliability of the place fields.Even though all rats had substantial prior experience with the environment, and were placed on the maze center under normal illumination before the first dark trial, the correlation between the firing pattern in the light and dark increased after the rat first traversed the maze in the light. Thus, even after considerable experience with the environment over days, experiencing the illuminated environment from different locations on a given day was a significant factor affecting subsequent location and reliability of place fields in darkness.While the task was simple and errors rare, rats that made fewer errors (i.e., re‐entries into the previously visited arm) also had more reliable place cells, but no such correlation was found with place cell specificity. Thus, the reliability of spatial firing in the hippocampus may be more important for spatial navigation than the size of the place fields per se. Alternatively, both spatial memory and place field reliability may be modulated by a common variable, such as attention. © 19

ISSN:1050-9631    

DOI:10.1002/hipo.450040404

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

年代:1994

数据来源: WILEY

摘要:

AbstractAxons from granule cells in the dentate gyrus of the rat hippocampus project to cells in the hilar region, including mossy cells, which project along the longitudinal axis of the hippocampus and synapse in the inner (proximal) one‐third of the molecular layer of the dentate gyrus. To study this feedback system, multiple recording electrodes were located along the longitudinal (septo‐temporal) axis in the dorsal leaf of the dentate gyrus in urethane‐anesthetized rats. Single pulse electrical stimuli delivered to the hilar region evoked negative‐going, monosynaptic field potentials that were largest in the inner one‐third of the molecular layer (commissural zone). These evoked field potentials (EFPs) were recorded simultaneously at three to five locations. The latency to onset and peak amplitude of the EFP varied linearly with distance from point of stimulation, and EFPs were elicited in both directions along the longitudinal axis. The transmission speed was estimated to be 1.4 m/s. Tetanic stimulation of the hilar region potentiated the EFP slopes (mean= 26%). Potentiation lasted at least 2 hours and was specific to responses from the tetanized stimulating electrode; the responses to other stimulating electrodes in the hilus and the angular bundle of the perforant path changed less than 4%. Combined stimulation of the hilus and the medial perforant path increased the magnitude of recorded field potentials and population spikes, demonstrating that both pathways are excitatory. NMDA antagonist NPC‐17742 blocked potentiation of EFP slopes in both the medial perforant path and hilus pathways. The results suggest that the ipsilateral associational system of the dentate gyrus is excitatory and capable of supporting long‐lasting, NMDA‐dependent, synapse‐specific plasticity. © 19

ISSN:1050-9631    

DOI:10.1002/hipo.450040405

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe ability of the perforant path/dentate granule cell synapse of the hippocampal formation to establish and maintain enhanced levels of synaptic transmission in response to tetanization (long‐term potentiation, LTP) was investigated in freely moving rats at 15, 30, and 90 days of age. Measures of (1) the slope of the population excitatory postsynaptic potential (EPSP), and (2) the population spike amplitude (PSA) obtained before, and at several times following tetanization, were used to evaluate the magnitude and duration of LTP as a function of age. Significant enhancement of both EPSP slope and PSA measures was obtained from animals of all three ages in response to perforant path tetanization. The initial degree of enhancement was essentially the same across the age groups, ranging from +27% to +38% of pretetanization levels for EPSP slope measures and +60% to +75% of pretetanization levels for PSA measures, obtained 15 min after tetanization. The duration of this enhancement obtained from animals of the preweaning group was significantly longer than that obtained from either 30‐ or 90‐day‐old animals. Enhanced measures of both EPSP slope and PSA decayed to baseline levels in these older animals 18 to 24 h after tetanization, while animals tetanized at 15 days of age maintained potentiated levels of both measures for a period of 5 days following tetanization. Tetanization of 15‐day‐old animals resulted in a significant reduction in the latency to EPSP onset without affecting the time‐based relationships among the other measured parameters, which included latency of the population spike onset, population spike minimum, and population spike offset. Tetanization had no effect on the latency measure of any of these parameters in either of the two older age groups. The primarily postnatal development of the dentate granule cell population suggests that both functionally immature GABAergic modulation of granule cell activity and the differential development of components of theN‐methyl‐D‐aspartate receptor complex may be involved in the age‐related differences in the induction and expression of the LTP phenomenon. This study represents the first developmental characterization of LTP in the perforant path/dentate granule cell synapse in freely moving rats during early development. The results indicate that LTP can be reliably established and maintained in behaving rats as young as 15 days of age. Whereas the degree of potentiation at this age is equivalent to that obtained from juveniles and young adults, the duration of the effect significantly outlasts that obtained from older animals in which development of the dentate gyrus is more functionally mature.

ISSN:1050-9631    

DOI:10.1002/hipo.450040406

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

年代:1994

数据来源: WILEY

摘要:

AbstractPrevious studies have shown that potassium‐induced long‐term potentiation (LTP) of the Schaffer collateral/commissural synapses in area CA1 of the hippocampus shares common properties with tetanus‐induced LTP. In the present investigation, we performed electrophysiological and binding experiments on CA1 hippocampal slices to evaluate the location and nature of the changes underlying potassium‐induced LTP. Paired‐pulse facilitation, which represents an index of transmitter release, was markedly reduced by potassium‐induced LTP. In addition, KC1‐induced LTP was associated with an increase in3H‐AMPA ([3H]‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionate) binding to CA1 synaptic membranes when measured 40 min after high‐potassium exposure; however, no changes were detected in binding of an antagonist ([3H]‐6‐cyano‐7‐nitroquinoxaline‐2,3‐dione;3H‐CNQX) to AMPA receptors in slices expressing KC1‐induced LTP. Administration of the phospholipase A2(PLA2) inhibitor bromophenacyl bromide (BPB) prior to potassium application prevented LTP formation as well as the changes in paired‐pulse facilitation and3H‐AMPA binding that characterized this type of potentiation. Taken together, these data indicate that potassium‐in‐duced LTP may be related to modifications in both pre‐and postsynaptic properties and confirm the hypothesis that PLA2activation is an important mechanism in long

ISSN:1050-9631    

DOI:10.1002/hipo.450040407

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

年代:1994

数据来源: WILEY

摘要:

AbstractElectrical stimulation and microinfusion techniques were utilized in acute experiments on urethane‐anesthetized rats in order to evaluate the hypothesis that the posterior hypothalamic and supramammillary nuclei comprise a critical part of the ascending brainstem pathway for producing synchronous hippocampal formation (HPC) field activity (theta). Given confirmation of this hypothesis a second objective was to determine the nature of the contribution made by this midline posterior hypothalamic region (PH) to the frequency and amplitude components of HPC theta field activity. The cholinergic nature of the ascending pathway was also examined. Reversible inactivation of the PH was achieved by microinfusion of the local anesthetic procaine hydrochloride. The efficacy of and recovery from procaine inactivation of the PH was quantitatively analyzed either by electrical stimulation of the nucleus pontis oralis (PO) (two experiments) or the PH (four experiments). The results are summarized under the following three headings: (1) The first is the effect of procaine inactivation of the PH on HPC theta elicited caudal to, at the level of, or rostral to the PH. All HPC theta induced caudal to the PH (spontaneous theta, tail pinch‐induced theta, and theta produced by electrical stimulation of the PO) was totally abolished for a minimum 10‐min period. HPC theta induced rostral to the PH by the intrahippocampal infusion of carbachol was unaffected, while HPC theta induced by infusions of carbachol into either the medial septum (MS) or PH was reduced in amplitude with no effect on frequency. (2) Next are comparisons of pre‐ and post‐PH procaine trials of electrical stimulation of the PO and PH. In all experiments, regardless of the anatomical locus or technique used to induce HPC theta, pre‐and post‐PH procaine comparisons of the PO and PH stimulation trials revealed that frequency modulation of HPC theta recovered significantly more slowly than amplitude. (3) Last is the effect of electrical stimulation of the PO and PH on HPC theta induced by carbachol infusions at the level of the HPC, MS, or PH. In all experiments, electrical stimulation of both the PO and PH, at appropriate intensities, resulted in increasing HPC theta frequencies above the frequency induced by the infusion of carbachol into the HPC, MS, and PH. In addition, the post‐carbachol HPC theta frequencies induced by electrical stimulation were significantly higher than those produced in the pre‐carbachol conditions. The data supported the following conclusions: (1) The PH region (posterior hypothalamic and supramammillary nuclei) comprises a critical part of the ascending brainstem pathway for producing HPC theta field activity. Inputs ascending from the brainstem caudal to the PH contribute primarily to the frequency of HPC theta and secondarily to the amplitude of HPC theta; (2) a portion of the neural components of the ascending brainstem pathway, up to and including the HPC, are cholinergic, cholinoceptive, or both. © 19

ISSN:1050-9631    

DOI:10.1002/hipo.450040408

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

年代:1994

数据来源: WILEY

摘要:

AbstractUsing in situ hybridization histochemistry neuropeptide Y (NPY) mRNA expression was investigated after intraperitoneal injection of kainic acid (KA) and after local application of KA or quinolinic acid into the dentate gyrus of the rat. Enhanced concentrations of NPY mRNA were observed in interneurons of the hilus, including presumptive fusiform neurons and pyramidal‐shaped basket cells already 4 hours after initiation of limbic seizures by KA (10 mg/kg, i.p.). IncreaseD NPY expression persisted in neurons resistant to seizure‐induced cell death (6–48 h after i.p. KA). Exceptionally high hybridization signals were found in interneurons of the hilus and the CA1 and CA3 sectors 8 months after KA‐induced limbic seizures. In the granule cell layer only a transient but pronounced increase in NPY mRNA was observed 12–24 h after injection. Only moderate changes were observed in this cell layer at later intervals. Anticonvulsant treatment with thiopental, after a brief period of generalized seizures, prevented the increase in NPY mRNA in granule cells but not in interneurons. No change in NPY message was found also in granule cells of rats which responded with mild “wet dog shake” behvior but not with motor seizures to KA injection.Local injections of low doses of KA (0.05–0.2 nmol) or quinolinic acid (6.5–100 nmol) into the dentate gyrus of the hippocampus under deep thiopental anesthesia, after 24 h, resulted in increased concentrations of NPY message in interneurons of the ipsilateral, but not of the contralateral hilus and not in granule cells. Higher doses of the excitatory amino acid analogs caused partial neurodegeneration at the injection site, but enhanced NPY expression in interneurons of the contralateral dentate. Only the highest dose of quinolinic acid (100 nmol), resulting in general neuronal cell loss at the injection area, induced enhanced NPY mRNA expression also in granule cells of the contralateral dentate gyrus.The experiments suggest different mechanisms for NPY mRNA expression in interneurons and in granule cells of the dentate gyrus. Whereas in the stratum granulosum NPY mRNA expression was only observed after generalized limbic seizures, in hilar interneurons it was augmented by only moderate neuronal stimulation or directly by KA. © 19

ISSN:1050-9631    

DOI:10.1002/hipo.450040409

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

年代:1994

数据来源: WILEY

摘要:

AbstractDuring the past decade, work with monkeys has helped identify the structures in the medial temporal lobe that are important for memory: the hippocampal region (including the hippocampus proper, the dentate gyrus, and the subicular complex) and adjacent cortical areas that are anatomically linked to the hippocampus, i.e., the entorhinal, perirhinal, and parahippocampal cortices. One idea that has emerged from this work is that the severity of memory impairment might increase as more components of the medial temporal lobe are damaged. We have evaluated this idea directly by examining behavioral data from 30 monkeys (ten normal monkeys and 20 monkeys with bilateral lesions involving structures within the medial temporal lobe) that have completed testing on our standard memory battery during the last 10 years. The main finding was that the severity of memory impairment depended on the locus and extent of damage to the medial temporal lobe. Specifically, damage limited to the hippocampal region produced a mild memory impairment. More severe memory impairment was produced when the damage was increased to include the adjacent entorhinal and parahippocampal cortices (the H+lesion). Finally, memory impairment was even more severe when the H+lesion was extended forward to include the anterior entorhinal cortex and the perirhinal cortex (H++lesion). Taken together, these findings suggest that, whereas damage to the hippocampal region produces measurable memory impairment, a substantial part of the severe memory impairment produced by large medial temporal lobe lesions in humans and monkeys can be attributed to damage to entorhinal, perirhinal, and parahippocampal cortices adjacent to the hippocampal region. © 1994 Wiley‐Liss, I

ISSN:1050-9631    

DOI:10.1002/hipo.450040410

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

年代:1994

数据来源: WILEY

ISSN:1050-9631    

DOI:10.1002/hipo.450040401

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

年代:1994

数据来源: WILEY