bluuebunny/crossref_metadata_2025_split huggingface dataset:
Equivalent impairment of spatial and nonspatial memory following damage to the human hippocampus
Authors: Cave Carolyn Backer , Squire Larry R. 
Published: May 2005

AbstractThe hippocampus has sometimes been proposed to function as a cognitive map, a memory system that stores information about allocentric space. Work with experimental animals and memory‐impaired patients has raised difficulties with this view by showing that the hippocampus is not performing an exclusively spatial function. However, the possibility has remained that the hippocampus plays a special role in spatial memory or a disproportionately large role in spatial memory compared to other kinds of memory. This study compared spatial and nonspatial memory in amnesic patients with lesions of the hippocampal formation or diencephalon. Subjects studied an array of 16 toy objects and were subsequently tested for object recall, object recognition, and memory for the location of the objects. Control subjects were tested after long retention intervals in order to equate their object memory performance with that of the patients. The main finding was that, when the performance of amnesic patients on the object memory tests was matched to the object memory performance of control subjects, spatial memory performance of the amnesic patients also matched the spatial memory performance of the control subjects. The results were the same for the two groups of patients. These findings suggest that the hippocampus is not especially involved in spatial memory. Spatial memory is simply one instance of a broader category of memory that requires the hippocampus. While cognitive mapping in its most abstract sense may describe hippocampal function, our results support alternative formulations, suggesting that the hippocampus is necessary for the rapid acquisition of relational, configural, or declarative (as opposed to purely spatial) information.
Intragranular mossy fibers in rats and gerbils from synapses with the somata and proximal dendrites of basket cells in the dentate gyrus
Authors: Ribak Charles E. , Peterson Gary M. 
Published: May 2005

AbstractIntragranular and supragranular mossy fibers arise from granule cells and are present in the dentate gyrus of hippocampi from kindled and epileptic animals. The intragranular fibers often appear as fibers perpendicular to the long axis of the granule cell layer at periodic intervals. Rats and gerbils were analyzed to determine whether such mossy fibers are also associated with nongranule cells (including the basket cells), which send their apical dendrites through this layer with a periodicity similar to that of mossy fibers. The results for rats and both epileptic and nonepileptic gerbils show that many intragranular mossy fibers are apposed to the surfaces of the somata and apical dendrites of basket cells where they form asymmetric synapses. This plexus of mossy fiber axons appears to follow the dendrites of these neurons into the inner molecular layer. Based on previous data indicating that basket cells are GABAergic inhibitory neurons, the present findings in normal rats and both types of gerbils suggest that intragranular and supragranular mossy fibers provide additional circuitry for feedback inhibition to granule cells. It is possible that under pathological conditions, such as denervation or kindling, these fibers sprout and form synapses with granule cells.
The effects of reversible inactivations of the hippocampus on exploratory activity and spatial memory
Authors: Thinus‐Blanc C. , Save E. , Poucet B. , Buhot M.‐C. 
Published: May 2005

AbstractThis study was aimed at testing the effects of a reversible inactivation of the ventral hippocampus on behavior in response to a change, following a period of habituation with a hippocampus that functions normally. A new dishabituation paradigm was used, which allowed the testing of visuospatial memory. A salient stimulus was placed under the glass floor of the apparatus during initial exploration and was removed during the test session. The time spent above the zone where the stimulus was initially located indicated the rats' reaction to the change. Unlike the control rats who reacted to the removal of the salient stimulus by reexploring its previous location, lidocaine‐injected subjects did not display any similar searching behavior. Experiment 2 examined the hypothesis that landmarks located under the floor could help hippocampus‐inactivated animals to accurately react to the change. Two objects were located either close to the stimulus or some distance away from it. Even when the objects were closely associated to the stimulus, the same failure to react to the removal of the stimulus was found in lidocaine‐injected rats. However, these animals displayed a higher activity level measured by the time spent on a “neutral” zone. This behaioral pattern suggests a specific localization deficit. The method of reversible inactivation appears to be a promising approach to the study of the time course of memory process with short‐term experimental paradigms such as those used in the present study.
Factors governing the potentiation of NMDA receptor‐mediated responses in Hippocampus
Authors: Muller Dominique , Arai Amy , Lynch Gary 
Published: May 2005

AbstractA modified medium containing an AMPA receptor antagonist and low concentrations of magnesium was used to investigate the factors governing the potentiation of synaptic responses mediated by NMDA receptors. When long‐term potentiation (LTP) was induced in standard medium and NMDA responses were analyzed by changing to the modified medium, no statistically significant differences were observed between potentiated and control pathways. Returning the slices to the standard medium showed that LTP was still present, indicating that the potentiation effect was not reversed by the modified medium. High‐frequency stimulation applied in the modified medium produced an enhancement of synaptic responses, but this was not occluded by prior potentiation in standard medium. The degree of potentiation induced in the modified medium and expressed by NMDA responses was larger in the presence than in the absence of inhibition and, unlike LTP, was proportionately larger when recorded in the stratum pyramidale than in the stratum radiatum. These results indicate that the potentiation of NMDA receptor‐mediated responses triggered by high‐frequency stimulation applied in modified medium differs in several respects from the LTP induced in standard conditions. They confirm that LTP is expressed to a markedly different degree by NMDA and non‐NMDA receptors and suggest that events that do not necessarily accompany LTP affect the potentiation of NMDA receptordependent synaptic responses.
Receptor changes and LTP: An analysis using aniracetam, a drug that reversibly modifies glutamate (AMPA) receptors
Authors: Staubli Ursula , Ambros‐Ingerson José , Lynch Gary 
Published: May 2005

AbstractThe hypothesis that long‐term potentiation (LTP) involves receptor modifications was tested with aniracetam, a nootropic drug that selectively increases currents mediated by the AMPA subclass of glutamate receptors. Aniracetam had different effects on the waveform of synaptic potentials in hippocampus before and after induction of LTP: (1) the drug caused a slight reduction (or delay) of the initial segment of the response after LTP; and (2) the facilitatory effects of aniracetam occurred at a later time point in the response after LTP than before. The interactions between LTP and aniracetam were still present when synaptic responses were greatly reduced by partial blockade of postsynaptic receptors and were not reproduced by increasing release or the number of stimulated synapses. A mathematical treatment of synaptic currents produced the following results: (1) if aniracetam facilitates AMPA receptor currents simply by reducing desensitization, then its complex interaction with LTP emerges when potentiation changes the kinetic and conductance properties of receptor channels; (2) if aniracetam also significantly increases conductance, then the experimental data can be reproduced by modeling LTP as an increase in channel conductance alone.
Spontaneous recovery of deficits in spatial memory and cholinergic potentiation of NMDA in CA1 neurons during chronic lithium treatment
Authors: Richter‐Levin Gal , Markram Henry , Segal Menahem 
Published: May 2005

AbstractThe therapeutic action of lithium in affective disorders is still unclear. One effect lithium is to deplete membrane inositol and consequently to exhaust the phosphoinositide (PI) pathway. Under chronic lithium treatment, rats showed persistent performance deficits in an active avoidance task and in a visually cued maze. The same treatment, however, resulted in only a transient deficit in the performance of rats in a spatial memory task. Lithium treatment caused a similarly transient deficit in the ability of acetylcholine to potentiate responses to N‐methyl‐D‐aspartate (NMDA) in neurons of the hippocampal slice. The authors propose that the development of compensatory mechanisms may account for the lack of severe memory impairments during lithium treatment. It is suggested that the effects of lithium on the PI pathway are not sufficient to explain the behavioral consequences of chronic lithium treatment.
Spatial responsiveness of monkey hippocampal neurons to various visual and auditory stimuli
Authors: Tamura Ryoi , Ono Taketoshi , Fukuda Masaji , Nakamura Kiyomi 
Published: May 2005

AbstractTo investigate involvement of the hippocampal formation in spatial information processing, activity of neurons in the hippocampal formation of the conscious monkey was recorded during presentation of various visual and auditory stimuli from several directions around the monkey. Of 1,047 neurons recorded, 106 (10.1%) responded to some stimuli from one or more directions. Of these 106 neurons with directionally differentiating responsiveness, 49 responded to visual stimulation, 35 to auditory stimulation, and 22 to both. Among 81 neurons, each tested with more than 10 differnt stimuli, one type responded independent of the nature of the stimulus (nonselective, n = 39), and responses of the other type depended on the nature of the stimulus (selective, n = 42). To investigate effects of change in spatial relations between test stimuli and background stimuli fixed on the monkey or fixed in the environment, 59 of 106 neurons were tested while the experimental apparatus holding the stimulus was moved relative to the monkey. Of these 59 neurons, 36 changed their responsiveness; 7 maintained the magnitude of their responses but changed the response direction with the movement of the apparatus, 5 changed direction regardless of the movement, and 24 did not change direction, but decresed or extinguished responses from the preferred direction. Thirty‐two of 106 neurons were also tested by rotating the monkey. The directionally differentiating responsiveness of 11 neurons followed the monkey (egocentric neurons), that of 9 remained in place in the environment (allocentric neurons), and responses of 12 were reversibly extinguished when the monkey was rotated. The results suggest that these hippocampal neurons may be involved in identification of relations among various kinds of stimuli in different spatial frameworks (egocentric or allocentric) and this identification may be developed from multiple sensory modalities.
Neuronal activity in the hippocampus during delayed non‐match to sample performance in rats: Evidence for hippocampal processing in recognition memory
Authors: Otto Tim , Eichenbaum Howard 
Published: May 2005

AbstractNeuronal activity in the CA1 of rats was explored with regard to functional correlates of performance in an odor‐guided continuous delayed non‐match to sample task. Although different CA1 cells fired in association with each identifiable trial event, these analyses focused on cells that fired selectively during the period of odor cue sampling and response generation. The firing patterns of many of these cells reflected the match or non‐match comparison between current and previous odor cues independent of the particular stimuli that composed those comparisons. Such cells were more prevalent in sessions when performance was highly accurate. Hippocampal cells did not demonstrate stimulus‐evoked firing that persisted through the memory delay, nor did they fire differentially to session‐novel vs. repeated odor presentations. These results suggest that the hippocampus contributes to recognition memory by processing comparisons between current information and representations of previous stimuli stored in parahippocampal and neocortical structures.
Mossy cell axonal projections to the dentate gyrus molecular layer in the rat hippocampal slice
Authors: Buckmaster Paul S. , Strowbridge Ben W. , Kunkel Dennis D. , Schmiege Donna L. , Schwartzkroin Philip A. 
Published: May 2005

AbstractThe ipsilateral associational pathway connects different septotemporal levels of the dentate gyrus. Neurons of the dentate hilus project hundreds of micrometers from the cells of origin to the inner molecular layer. The authors hypothesized that mossy cells, the major cell type of the hilus, also project locally to the inner molecular layer. Within a 400 μm slice, mossy cells were (1) recorded intracellularly while the inner molecular layer was stimulated to test for antidromic responses, and (2) labeled with biocytin and examined with light and electron microscopy for axonal projections into the molecular layer. The authors found that mossy cells can be antidromically activated by inner molecular layer stimulation and that axonal projections to the molecular layer can be visualized within a 400 μm hippocampal slice. In 13 of 19 intracellularly labeled and electrophysiologically characterized mossy cells, collaterals could be traced into the molecular layer. These results suggest that mossy cells contribute to the ipsilateral associational pathway and also participate in local recurrent circuitry to influence granule cell activity.
Septotemporal variation of the supragranular projection of the mossy fiber pathway in the dentate gyrus of normal and kindled rats
Authors: Cavazos José E. , Golarai Golijeh , Sutula Thomas P. 
Published: May 2005

AbstractPrevious studies have demonstrated regional variation in the anatomical organization and physiological properties of the hippocampus along its septotemporal (dorsoventral) axis. In this study, regional variation of the supragranular projection of the mossy fiber pathway in the dentate gyrus of normal and kindled rats was characterized with a scoring method for assessment of the distribution of mossy fiber synaptic terminals detected by Timm histochemistry. In normal rats, there was a sparse projection of the mossy fiber pathway into the supragranular region near the tips and crest of the dentate gyrus along the entire septotemporal axis, and a prominent projection into the supragranular region at the temporal pole. Kindling of the perforant path, amygdala, and olfactory bulb induced synaptic reorganization of the mossy fiber pathway into the supragranular region along the entire septotemporal axis of the dentate gyrus. There was regional variation of the seizure‐induced synaptic reorganization along this axis, and distinct septotemporal patterns were observed as a function of the site of kindling stimulation. Kindling of the perforant path induced mossy fiber synaptic reorganization that was relatively more prominent in the septal pole than in the temporal pole of the dentate gyrus. In contrast, rats that received kindling stimulation of the amygdala had a more uniform distribution of synaptic reorganization along the septotemporal axis. As there is regional variation of the anatomical and physiological properties of the human epileptic hippocampus, these observations could be pertinent to human epilepsy.
Quantal and subquantal GABAergic transmissions in cultured rat hippocampal neurons
Authors: Vautrin Jean , Schaffner Anne E. , Barker Jeffery L. 
Published: May 2005

AbstractAt the neuromuscular junction, spontaneous miniature excitatory synaptic currents mediated by acetylcholine are considered elementary, “quantal” transmissions. These miniature conductances can be quantitatively dichotomized into a large‐mode class whose mode is the mean of a normal, bell‐shaped distribution and a small‐mode class whose distribution is skewed to lower values with its mode being a fraction of the large‐mode class. The large‐mode class constitutes the population of synaptic signals originally utilized to formulate tenets of “quantal” transmission, which have been tacitly adopted in more recent studies of fast transmission at central synapses. Large‐ and small‐mode conductance classes of inhibitory synaptic elementary conductances mediated by GABA have now been recorded in cultured hippocampal neurons (Vautrin J, Schaffner AE, Barker JL, 1991, Neurosci Lett 138:67). Pairs of hippocampal neurons were patch recorded at optimal signal‐to‐noise and, using time course analysis, two elementary fluctuations (0.1–0.3 nS and 1–2 nS) were found within synaptic conductances evoked either by presynaptic action potentials or by presynaptic terminal stimulation. These results were interpreted with a simple model that shows how different frequencies of unitary GABA release can generate either small‐mode, skew‐distributed conductance (0.5–3 kHz) or large‐mode, normally‐distributed conductances (≥ 10 kHz). Only the latter satisfies the original tenets of the classic quantal theory.
Epilepsy induced collateral sprouting of hippocampal mossy fibers: Does it induce the development of ectopic synapses with granule cell dendrites?
Authors: Represa Alfonso , Jorquera Isabel , le gal la Salle Gildas , Ben‐Ari Yehezkel 
Published: May 2005

AbstractIn the present study, using Golgi and electron microscopy techniques, experimentally induced epilepsy (kindling and kainate treatment) elicited collateral sprouting of mossy fibers in rat hippocampus. Collateral branches invade the hilus, cross the granule cell layer, and distribute throughout the inner third of the molecular layer. These newly developed collaterals may acquire the typical features of mossy fibers including giant fiber varicosities (mousses), although the mean surface of these mousses was thinner in these collaterals than in terminal branches. Granule cell dendrites may develop giant thorny excrescences, suggesting that the targets of these collaterals are granule cells. Giant synaptic boutons appear in the inner third of molecular layer of epileptic rats. These boutons acquire the morphological features of mossy fiber boutons and made multiple synaptic contacts with dendritic spines. The analysis of the profile types suggests that some of the newly developed collateral mossy fibers made hypotrophic synaptic contacts.
Hyperpolarizing synaptic potentials evoked in CA1 pyramidal cells by glutamate stimulation of interneurons from the oriens/alveus border of rat hippocampal slices. II. sensitivity to GABA antagonists
Authors: Samulack Donald D. , Lacaille Jean‐Claude 
Published: May 2005

AbstractThe receptor type mediating the inhibitory postsynaptic potentials (glut‐IPSPs), recorded in CA1 pyramidal cells, as a result of glutamate stimulation of interneurons in stratum oriens near the alveus (O/A) was assessed and compared to the type mediating recurrent IPSPs evoked by recurrent activation of interneurons through glutamate stimulation of pyramidal cells in stratum pyramidale (PYR). In response to repetitive electrical stimulation, the peak amplitude of both the O/A glut‐IPSP and the PYR glut‐IPSP was attenuated (n = 5) in parallel to the reduction in amplitude of the early and late components of the electrically evoked response (stimulus‐evoked disinhibition). This suggested the involvement of GABAergic receptors and attested that the interneurons activated during glut‐IPSPs were also involved in the circuitry of the electrically evoked IPSPs. The local application of the selective GABAA antagonist bicuculline (100–200 μM) to the slice resulted in a significant reduction in the amplitude of both the O/A (by 76.5%; n = 9) and PYR (by 86.2%; n = 5) glut‐IPSPs, in parallel to a decrease of the electrically evoked early IPSP, but not of the late IPSP. The presence of the GABAB antagonist 2‐hydroxy‐saclofen (1 mM) was able to significantly reduce the amplitude of the O/A glut‐IPSPs (by 27.5%; n = 7) and of the electrically evoked late IPSP, but not the PYR glut‐IPSP (n = 3). Although the application of phaclofen (20 mM) to the slice reduced the amplitude of the O/A glut‐IPSPs (n = 3), the reduction was not statistically significant. These results suggest that recurrent IPSPs elicited from activation of interneurons by stimulation of pyramidal cells are mediated solely via GABAA receptors. Inhibitory postsynaptic potentials elicited from stimulation of interneurons in O/A were also mediated mostly by GABAA receptors, but in addition, displayed a minor component mediated by GABAB receptors. Therefore, since a large proportion of interneurons in O/A are recurrently excited by pyramidal cells (Lacaille J‐C et al., 1987, J Neurosci 7:1979–1993), and since recurrent IPSPs appeared mediated by GABAA receptors, a subpopulation of interneurons activated from O/A might exist that do not receive recurrent excitation but can inhibit pyramidal cells via GABAB receptors.
Maps, routes, and the hippocampus: A neural network approach
Authors: Schmajuk Nestor A. , Thieme Aaron D. , Blair Hugh T. 
Published: May 2005

AbstractThis study describes hippocampal participation in maze navigation in terms of a real‐time, biologically plausible neural network. The system is composed of (1) a goal‐seeking mechanism, (2) a cognitive map system, and (3) a route system. The goal‐seeking mechanism displays exploratory behavior until either the goal is found or a sufficiently strong prediction of the goal is generated. The cognitive map is a topological map that stores associations between places and views of accessible places, and between places and reward. The route system establishes associations between cues and reward. Both systems compete with each other to establish associations with the reward, with the cognitive system generally overshadowing the route system. In agreement with previous models, it is assumed that the hippocampus modulates the storage of cognitive maps in cortical areas and mediates the competition between cognitive maps and route systems. In agreement with previous models, it is assumed that the hippocampus modulates the storage of cognitive maps in cortical areas and mediates the competition between cognitive maps and route systems. After hippocampal lesions, animals navigate through mazes making use of the route system. Computer simulations show that the network effectively describes latent learning, detour behavior, and place learning in normal and hippocampal‐and cortical‐lesioned animals.
Projection of the entorhinal layer II neurons in the rat as revealed by intracellular pressure‐injection of neurobiotin
Authors: Tamamaki Nobuaki , Nojyo Yoshiaki 
Published: May 2005

AbstractA component of the perforant path, projection of the entorhinal layer II neurons, was investigated by recovering intracellularly labeled layer II neurons from the medial or intermediate entorhinal cortex in rats. The labeled layer II spiny stellate neurons had axon collaterals in layers I, II, and III of the entorhinal cortex as well as some axon collaterals in the subiculum. The stem axons gave rise to terminal axon branches that covered the entire extent (suprapyramidal blade, crest, and infrapyramidal blade) of the dentate gyrus and the CA2–3 fields in the transverse plane, forming a sheet‐like formation. The axon arbor in the hippocampal formation spread up to 2 mm wide in a septotemporal direction. The sheet‐like formation of the axon arbors was a narrow layer in the suprapyramidal blade and in the stratum lacunosum‐moleculare of the CA2–3 fields. The layer became wider in the crest and infrapyramidal blade of the dentate gyrus. This study shows that the entorhinohippocampal circuit is not a simple circle from single cells level.