摘要:

AbstractHippocampal CA1 cells possess several varieties of long‐lasting synaptic plasticity: two different forms of long‐term potentiation (LTP) and at least one form of long‐term depression (LTD). All forms of synaptic plasticity are induced by afferent activation, all involve Ca2+influx, all can be blocked by Ca2+chelators, and all activate Ca2+‐dependent mechanisms. The question arises as how different physiological responses can be initiated by activation of the same second messenger. We consider two hypotheses which could account for these phenomena: voltage‐dependent differences in cytosolic Ca2+concentration acting upon Ca2+substrates of differing Ca2+affinities and compartmentalization of the Ca2+and its substrates. © 1994 Wiley

ISSN:1050-9631    

DOI:10.1002/hipo.450040602

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

年代:1994

数据来源: WILEY

摘要:

AbstractVirtually all of the afferents to the hippocampal formation undergo collateral sprouting after removal of adjacent afferent systems. However, the central noradrenergic (NA) afferents, which demonstrate a remarkable propensity for regeneration and sprouting in other regions of the brain, have not been found to sprout in the denervated hippocampal formation. The present study was designed to determine if the pattern of innervation by NA fibers in the dentate gyrus of adult rats can be altered by interruption of the other major afferents. The innervation pattern of NA fibers was examined in the dentate gyrus 4 weeks after removal of the ipsilateral and/or contralateral entorhinal afferents and/or transection of the fimbria‐fornix and supracallosal stria. The noradrenergic identity of the fibers was indicated by immunoreactivity for dopamine beta hydroxylase (DBH) and peripheral sympathetic fibers were demonstrated by immunoreactivity for nerve growth factor receptor (NGFr), which did not stain cholinergic fibers in this application. In control brains, the noradrenergic innervation of the dentate molecular layer was light and uniform across the width of the layer. Transection of the perforant path (ipsilateral entorhinal afferents) or ventral hippocampal commissure (contralateral entorhinal afferents) resultd in a significant increase in innervation density in the outer half of the molecular layer, and the combination of these two lesions produced the greatest increase. In those brains with transection of the ipsilateral and contralateral entorhinal afferents, the denervated dentate gyrus had a nearly twofold increase in density of DBH‐immunoreactive fibers within the outer half of the molecular layer. These fibers tended to course parallel to the pial surface rather that perpendicular as in control sections. Transection of the fimbria‐fornix alone had no affect on the innervation pattern of DBH‐ir fibers in the molecular layer. When the fimbria‐fornix was transected in combination with both of the other lesions, an overall increase in innervation density occurred, but there was no further increase in the difference between the inner and outer halves of the molecular layer. No NGFr‐immunoreactive fibers were observed in the molecular layer in any of the brains, indicating that the DBH‐immunoreactive fibers in this region were not of peripheral origin. It is concluded that removal of the ipsi‐ and contralateral entorhinal afferents to the dentate gyrus results in the sprouting of central NA fibers in the outer half of the molecular layer. © 1994

ISSN:1050-9631    

DOI:10.1002/hipo.450040603

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

年代:1994

数据来源: WILEY

摘要:

AbstractSingle cells or simultaneously recorded cell pairs in the medial septum (MS) vertical limb of the diagonal band of Broca (vDBB) in the urethane‐anesthetized rat were initially classified as either theta‐on or non‐related according to the system of Colom and Bland (1987, Brain Res 422:277–286). Subgroups of these cells were then studied under various test conditions that included electrical stimulation of the nucleus pontis oralis (PO) or posterior hypothalamus (PH), microinfusion of carbachol into the PO or PH, and the microinfusion of atropine sulfate or procaine hydrochloride into the PH. Electrical stimulation of either the PO or PH induced theta (θ) activity in the hippocampal formation (HPC), and electrical stimulation of the PO resulted in a simultaneous increase in the discharge rate of all MS/vDBB θ‐on cells tested, compared to the rates recorded during HPC large‐amplitude irregular activity (LIA). Five of the MS/vDBB θ‐on cells were tested consecutively with electrical stimulation of the PO and PH, and were shown to be activated in a similar manner in either condition. Microinfusion of carbachol into either the PO or PH resulted in the induction of HPC θ field activity and the simultaneous intense activation of all MS/vDBB θ‐on cells tested. Following the microinfusion of either atropine sulfate or procaine into the PH, electrical stimulation of the PO failed to induce HPC θ field activity or the concomitant rhythmic discharges of all MS/vDBB phasic θ‐on cells tested. Microinfusing procaine into the PH also abolished the coupling between all MS/vDBB cell pairs during HPC θ field activity including that between two cell pairs that were coupled during HPC LIA. The data support the following conclusions: (1) The brainstem HPC synchronizing pathway originating in the pons region ascends to the medial septum via the midline posterior hypothalamic region; (2) the present results taken together with previous work suggest that a major component of the ascending synchronizing pathway, up to and including the hippocampal formation, is cholinergic, cholinoceptive, or both, and the receptors involved are primarily muscarinic; (3) the midline posterior hypothalamic region is an important source of inputs to the medial septum and their major contribution is to provide frequency‐coded inputs to the MS/vDBB for relay into the hippocampal format

ISSN:1050-9631    

DOI:10.1002/hipo.450040604

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe hippocampus and related structures are thought to be capable of (1) representing cortical activity in a way that minimizes overlap of the representations assigned to different cortical patterns (pattern separation); and (2) modifying synaptic connections so that these representations can later be reinstated from partial or noisy versions of the cortical activity pattern that was present at the time of storage (pattern completion). We point out that there is a trade‐off between pattern separation and completion and propose that the unique anatomical and physiological properties of the hippocampus might serve to minimize this trade‐off. We use analytical methods to determine quantitative estimates of both separation and completion for specified parameterized models of the hippocampus. These estimates are then used to evaluate the role of various properties and of the hippocampus, such as the activity levels seen in different hippocampal regions, synaptic potentiation and depression, the multi‐layer connectivity of the system, and the relatively focused and strong mossy fiber projections. This analysis is focused on the feedforward pathways from the entorhinal cortex (EC) to the dentate gyrus (DG) and region CA3. Among our results are the following: (1) Hebbian synaptic modification (LTP) facilitates completion but reduces separation, unless the strengths of synapses from inactive presynaptic units to active postsynaptic units are reduced (LTD). (2) Multiple layers, as in EC to DG to CA3, allow the compounding of pattern separation, but not pattern completion. (3) The variance of the input signal carried by the mossy fibers is important for separation, not the raw strength, which may explain why the mossy fiber inputs are few and relatively strong, rather than many and relatively weak like the other hippocampal pathways. (4) The EC projects to CA3 both directly and indirectly via the DG, which suggests that the two‐stage pathway may dominate during pattern separation and the one‐stage pathway may dominate during completion; methods the hippocampus may use to enhance this effect are discussed. © 1994 Wiley

ISSN:1050-9631    

DOI:10.1002/hipo.450040605

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

年代:1994

数据来源: WILEY

摘要:

AbstractPrevious research has suggested that the entorhinal cortex plays a major role in the production of type 1 rhythmical slow‐wave activity (RSA) recorded in the hippocampus of the freely moving preparation. In the present experiment we investigated the contribution of the entorhinal cortex to the type 2 fields recorded under urethane anesthesia. Rats had stimulating electrodes and cannulae filled with procaine positioned in the perforant pathway of one or both hemispheres. Recording electrodes were positioned in the dorsal hippocampus of each hemisphere to record perforant path and commissural/associational evoked potentials and RSA fields. Following unilateral procaine blockade, a decrease in RSA amplitude was observed in the stratum oriens and fissure regions of both hemispheres. Concomitant with this change in RSA, there was a loss of perforant path evoked responses, although commissural/associational control potentials remained unaltered. A greater reduction in RSA amplitude was observed following bilateral procaine microinfusion. RSA phase reversal also occurred more dorsally in microelectrode depth profiles conducted through the hippocampus during perforant path inactivation. In current source density analyses performed under baseline conditions, large rhythmic sinks were observed in stratum oriens, in stratum radiatum, and in strata adjacent to the hippocampal fissure. A rhythmic source was often observed in stratum pyramidale. Following perforant path inactivation decreases in the magnitude of the phasic sinks located near the fissure and stratum radiatum were observed. In contrast to the reduction in RSA amplitude observed in the stratum oriens region, the sink in this region and the source in stratum pyramidale remained relatively unaltered. These results demonstrate that the entorhinal region contributes to the production of RSA observed under urethane anesthesia. Furthermore, the CSD and amplitude changes following perforant path inactivation suggest that a substantial portion of RSA recorded in stratum oriens may result from ventrally located RSA dipoles. © 1994 Wiley‐Liss,

ISSN:1050-9631    

DOI:10.1002/hipo.450040606

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe objective of this project was to study the behavioral and physiological effects at 6–9 weeks after evoking 15 afterdischarges (ADs) in hippocampal CA1 (partial hippocampal kindling). Rats were trained on the open radial arm maze (RAM) with all eight arms baited, kindled, and then tested again on the RAM, followed by in vitro recordings at 8–9 weeks after kindling. Partial kindling was manifested by an increase in hippocampal AD duration. Enhancement of the commissural basal dendritic excitatory postsynaptic potential (EPSP) was observed for at least 1 day after the ADs kindled rats performed worse than control rats during the 1st but not during the 7th or 8th week after kindling. Rats that were slow in acquiring the RAM showed more RAM errors after kindling than those that showed fast acquisition. At 8–9 weeks after kindling, as shown by field potential recording in the hippocampal slice in vitro, kindled rats showed an increase in paired‐pulse facilitation (PPF) of the EPSP in CA1 but a decreased PPF of the perforant path to dentate gyrus EPSP; no change in the PPF of the population spike was found in CA1 or DG. In a second group of rats that were not run on the RAM, at 6 weeks after kindling, PPF of the population EPSP and population spike were enhanced in the kindled rats compared to the control rats in CA1, but not in DG or CA3 in vitro (at 1.5, 2, or 4 times threshold intensity). In conclusion, partial hippocampal kindling induced persistent physiological effects for up to 8–9 weeks, and it is suggested that the normalization of the paired‐pulse population spike response in CA1 and DG at more than 6 weeks after kindling may be accompanied by a recovery of RAM performance. © 1994 Wil

ISSN:1050-9631    

DOI:10.1002/hipo.450040607

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.450040601

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

年代:1994

数据来源: WILEY