bluuebunny/crossref_metadata_2025 huggingface dataset:
Microelectrode procedures for the determination of silicate and phosphate in waters – fundamental studies
Authors: Carpenter Neil G. , Hodgson Alexia W. E. , Pletcher Derek
Published: May 2005

The voltammetry of the molybdosilicate and molybdophosphate complexes, formed by the addition of hexafluorosilicate and phosphate to anacidic sodium molybdate solution, have been defined at gold microdisk electrodes. It is shown that the reaction conditions influence both the kinetics of formation of the complexes and their voltammetry. It is possible to find conditions where the steady state amperometric response of the Au microdisk electrodes allows a rapid and convenient method for the determination of silicate and phosphate at concentrations in the range 1–1000 μM.
Microdialysis‐bioreactor for on‐line monitoring of glucose in food samples
Authors: Mannino Saverio , Brenna O. , Buratti S. , Cosio M. S.
Published: May 2005

A new microsystem, integrating microdialysis sampling and glucose oxidase immobilized on a tungsten wire inserted into the lumen of the microdialysis probe, has been developed. The microsystem, coupled with amperometric detection, has proved to be viable for glucose determination in food samples. The immobilization procedure, based on the formation of an insoluble net formed by the enzyme with a polyanhydride (in the presence of polyethyleneimine), yielded a very stable enzyme layer that maintained about 75% of its initial activity after one month of daily use. Complex sample matrices (milk, juices) were successfully analyzed with little or no sample pretreatment using the fully automated flow system.
Electrocatalysis of ascorbic acid on the glassy carbon electrode chemically modified with polyaniline films
Authors: Casella Innocenzo G. , Guascito Maria R.
Published: May 2005

Chemically modified electrodes prepared by electropolymerization of aniline on glassy carbon electrodes, exhibited good electrocatalytic properties towards ascorbic acid oxidation. The electrocatalytic response was evaluated by cyclic voltammetry with regard to pH, film thickness, ascorbic acid concentration, scan rate, electrolyte composition, rotation speeds of the electrode, and other variables. The location of the reactions taking place was discussed with experimental evidence that the cross‐exchange reaction is the rate‐determining step. Experiments in flowing streams were performed to characterize the electrode as an amperometric sensor for the determination of ascorbic acid. The electrode stability, precision, limit of detection and linear range were evaluated at a constant potential of 0.350 V (vs. Ag/AgCl). The limit of detection was 1.0 μM (i.e., 1.76 ng injected), and the calibration plot was linear in the range 1.0 μM–0.7 mM (correlation coefficient 0.999). The resulting modified electrode was found to retain 80% of its initial response in flowing streams for 8 h of operating time.
Activated pulsed amperometric detection of cysteine at platinum electrodes in acidic media
Authors: Johll Matthew E. , Williams Douglas G. , Johnson Dennis C.
Published: May 2005

Anodic voltammetric detection of sulfhydryl compounds, represented here by cysteine, at Pt electrodes in acidic media occurs concomitantly with anodic generation of surface oxide. It is speculated that the adsorbed hydroxyl species (PtOH), proposed to be the intermediate product in formation of the inert oxide (PtO), is the source of O‐atoms transferred to the sulfonic acid produced by oxidation of the sulfhydryl moiety. However, as a consequence of this electrocatalytic response mechanism, application of the traditional three‐step waveform for pulsed amperometric detection (PAD) of sulfhydryl compounds is accompanied by a large background signal resulting from PtO formation. To diminish the background signal, the traditional three‐step PAD waveform has been modified by insertion of a brief (100 ms) anodization step prior to the detection step to activate the Ptsurface by the generation of PtOH with minimal conversion to PtO. The subsequent negative step from the activation potential (Eact) to the detection detection potential (Edet < Eact) permits the PtOH to be harvested within the detection mechanism without significant background signal.
Voltammetric determination of hydrazine based on catalytic reaction in the presence of 4‐hydroxy‐2,2,6,6‐tetramethyl‐piperdinyloxy (TEMPOL) radical
Authors: Xia He , Li Hulin , Yang Dequan
Published: May 2005

A rapid, simple and highly sensitive voltammetric method was developed for the determination of hydrazine based on the electrochemical oxidation of hydrazine catalyzed by TEMPOL at a glassy carbon electrode at neutral medium. A linear calibration plot was obtained over the range of 1 × 10−6 M‐5 × 10−4 M. The detection limit was 1 × 10−6 M. The method was applied successfully to the determination of hydrazine in waste and river water.
The electrophysiology of the olfactory–hippocampal circuit in the isolated and perfused adult mammalian brain in vitro
Authors: de Curtis Marco , Paré Denis , Lliás Rodolfo R.
Published: May 2005

The viability and general electrophysiological properties of the limbic system in the adult mammalian brain isolated and maintained in vitro by arterial perfusion are described. The isolated brain preparation combines the advantages of intact synaptic connectivity and accessibility of different areas of the encephalic mass with those of the in vitro approach, i.e., stability and control of the ionic environment. Extracellular field potential as well as intracellular recordings were performed at different levels in the limbic system of isolated adult guinea pig brains. The results demonstrate that in the piriform, entorhinal, and hippocampal cortices, the intrinsic electrical properties of individual cells as well as the spontaneous and evoked electrical activity in the neuronal ensembles they comprise, were virtually identical to those observed in vivo. The properties of the limbic system loop were determined.
Electrophysiological characterization of associational pathway terminating on dentate gyrus granule cells in the rat
Authors: Bekenstein Jonathan W. , Lothman Eric W.
Published: May 2005

The functional topography and parameters of excitation and inhibition were determined in the in situ associational pathway of the rat dentate gyrus. The functional topography was found to be consistent with previous anatomical studies. The greatest amplitude population spikes and the strongest paired‐pulse inhibition were generated with the stimulating electrode placed in the hilus at least 1.5 mm caudal to the ipsilateral dentate gyrus recording electrode. With this standard electrode configuration, neither long‐term potentiation of the population spike nor of the population excitatory postsynaptic potential occurred. Hilar associational pathway activation of dentate gyrus granule cells elicited paired‐pulse responses similar to those produced in granule cells by perforant path stimulation. Thus, the associational pathway provides another way to assess dentate granule cell function electrophysiologically.
Organization of CA1 projections to the subiculum: A PHA‐L analysis in the rat
Authors: Amaral David G. , Dolorfo Cynthia , Alvarez‐Royo Pablo
Published: May 2005

The organization of CA1 projections to the rat subiculum was investigated with the anterograde tracer, Phaseolus vulgaris leucoagglutinin (PHA‐L). Discrete iontophoretic injections of PHA‐L were placed into various transverse positions of the CA1 field at different septotemporal levels of the hippocampus. The distribution of CA1 projections was observed in dissected and extended hippocampal preparations. CA1 cells located proximally in the field, i.e., close to the CA2 field, gave rise to projections that terminated in the distal third of the subiculum, i.e., close to the presubiculum. CA1 cells located distally in the field, i.e., close to the subiculum, gave rise to projections that terminated proximally in the subiculum, i.e., just across the CA1/subiculum border. CA1 cells in the middle of the field projected to a midtransverse portion of the subiculum. The same general pattern of projections was observed at all septotemporal levels of the hippocampus. Varicose fibers from the CA1 neurons terminated among the basal dendrites of the subicular pyramidal cells, within the pyramidal cell layer, and in the deep portion of the molecular layer. In addition to the CA1 to subiculum projections, the discrete PHA‐L injections provided the opportunity of examining the extent of local and associational connections within CA1. In general, associational connections in CA1 are far less extensive than in CA3. CA1 is not entirely without local connections, however. CA1 cells located close to the subicular border, for example, originated axons that first innervated the proximal subiculum and then reentered the CA1 field at the interface between stratum radiatum and stratum lacunosum‐moleculare. In most of the experimental cases, there were collaterals located in stratum oriens of CA1 that branched from the fibers directed toward the subiculum. Thus, the basal dendrites of CA1 cells may receive associational inputs. The organization of the CA1 projections to the subiculum is discussed in relation to the organization of CA3 projections to CA1 and the differential output of transverse regions of the subiculum. The possibility is raised that information may be “channeled” through the hippocampal formation via the transverse organization of these connections and ultimately distributed to different recipients of hippocampal efferent projections.
Connections between the retrosplenial cortex and the hippocampal formation in the rat: A review
Authors: Wyass J. Michael , Van Groen Thomas
Published: May 2005

The retrosplenial cortex is situated at the crossroads between the hippocampal formation and many areas of the neocortex, but few studies have examined the connections between the hippocampal formation and the retrosplenial cortex in detail. Each subdivision of the retrosplenial cortex projects to a discrete terminal field in the hippocampal formation. The retrosplenial dysgranular cortex (Rdg) projects to the postsubiculum, caudal parts of parasubiculum, caudal and lateral parts of the entorhinal cortex, and the perirhinal cortex. The retrosplenial granular b cortex (Rgb) projects only to the postsubiculum, but the retrosplenial granular a cortex (Rga) projects to the postsubiculum, rostral presubiculum, parasubiculum, and caudal medial entorhinal cortex. Reciprocating projections from the hippocampal formation to Rdg originate in septal parts of CA1, postsubiculum, and caudal parts of the entorhinal cortex, but these are only sparse projections. In contrast, Rgb and Rga receive dense projections from the hippocampal formation. The hippocampal projection to Rgb originates in area CA1, dorsal (septal) subiculum, and postsubiculum. Conversely, Rga is innervated by ventral (temporal) subiculum and postsubiculum. Further, the connections between the retrosplenial cortex and the hippocampal formation are topographically organized. Rostral retrosplenial cortex is connected primarily to the septal (rostrodorsal) hippocampal formation, while caudal parts of the retrosplenial cortex are connected with temporal (caudoventral) areas of the hippocampal formation. Together, the elaborate connections between the retrosplenial cortex and the hippocampal formation suggest that this projection provides an important pathway by which the hippocampus affects learning, memory, and emotional behavior.
Evidence for commissurally projecting parvalbumin‐immunoreactive basket cells in the dentate gyrus of the rat
Authors: Goodman Jeffrey H. , Sloviter Robert S.
Published: May 2005

The fluorescent retrograde tracer, fluorogold, was used to identify commissurally projecting neurons in the hippocampus and dentate gyrus. After injection of fluorogold into the hippocampus, the contralateral hippocampus was evaluated for fluorogold‐immunoreactive or fluorescent neurons. In addition to observing labeled hilar neurons and CA3 pyramidal cells that previously have been reported to send commissurally projecting axons to the contralateral hippocampus, the authors unexpectedly found a population of fluorogold‐labeled cells in the granule cell layer with the morphology and location of GABA‐immunoreactive basket cells. Immunocytochemical staining revealed that all fluorogold‐labeled cells of the granule cell layer were immunoreactive for parvalbumin. However, not all parvalbumin cells, shown previously to be a subset of GABA neurons, were fluorogold‐labeled. The association between fluorogold transport and parvalbumin immunoreactivity was unique for these cells of the granule cell layer. In the adjacent hilus, relatively few of the many fluorogold‐labeled cells were parvalbumin‐ or GABA‐immunoreactive. These results (1) identify a population of presumed inhibitory neurons that apparently form commissural projections; (2) document that all of these cells contain the calcium‐binding protein parvalbumin; and (3) indicate that the vast majority of commissurally projecting hilar neurons are neither parvalbumin‐ nor GABA‐immunoreactive.
Evidence for NMDA receptor involvement in environmentally induced dentate gyrus plasticity
Authors: Croll Susan D. , Sharp Patricia E. , Bostock Elizabeth
Published: May 2005

Research has demonstrated environmentally induced plasticity of hippocampal dentate gyrusevoked potentials. Other research has shown a role of the NMDA receptor in dentate gyrus long‐term potentiation (LTP). The authors tested the role of the NMDA receptor in one form of environmentally induced plasticity, in which transferring animals from their home cages to another environment results in significant excitatory postsynaptic potential (EPSP) enhancement and concomitant depression of the population spike. Rats were chronically implanted with stimulating electrodes in the perforant path and recording electrodes in the dentate gyrus bilaterally. Evoked potentials were recorded from freely behaving rats for four 20‐minute sessions (1/wk), which took place immediately following an environmental transfer. Rats received 0.00, 0.05, 0.08, or 0.10 mg/kg MK‐801 s. c. 30 minutes prior to recording sessions in either an ascending‐ or descending‐dose series. Results showed that MK‐801 produced a reduction of the EPSP enhancement, which takes place over the 20‐minute session. The effects of MK‐801 on spike depression varied as a function of dose series and time within a session, suggesting a long‐term effect of MK‐801 on spike depression. There was no detected effect of MK‐801 on behavior. Results suggest a role of the NMDA receptor in this form of environmentally induced plasticity with different effects of NMDA receptor antagonism on EPSP enhancement and spike depression.
Effects of chronic alcohol consumption and withdrawal on the somatostatin‐immunoreactive neurons of the rat hippocampal dentate hilus
Authors: Andrade José P. , Fernando Paulo M. , Madeira Maria D. , Paula‐Barbosa Manuel M. , Cadete‐Leite António , Zimmer Jens
Published: May 2005

Previous studies have demonstrated that the dentate granule and the CA3 pyramidal cells of the rat hippocampal formation are neuronal populations vulnerable to the toxic effects of ethanol. It also has been shown that the resulting alterations do not end after withdrawal from ethanol. As the neurons in the dentate hilus are heavily interconnected with the dentate granule cells, the authors decided to examine the fate of the hilar neurons after chronic alcohol consumption and withdrawal, inasmuch as the hilar somatostatin‐immunoreactive (SS‐I) neurons were found to be sensitive to cerebral ischemia and to seizures.

The following groups of adult rats were studied: (1) alcohol‐fed for 6 and 12 months; (2) alcoholfed for 6 months and then switched to water for a further 6 months; (3) pair‐fed controls; and (4) controls fed ad libitum. The authors determined the numerical density of hilar neurons and the number of its SS‐I subpopulation. These were found to be significantly reduced in both the alcohol‐fed and withdrawal groups when compared with the respective age‐matched controls. The consequent loss of the integrative action of the hilar neurons, including the SS‐Is, could explain some of the alcohol‐related functional deficits as well as their persistence after withdrawal.
Time course and distribution of neuronal degeneration in the dentate gyrus of rat after adrenalectomy: A silver impregnation study
Authors: Jaarsma Dick , Postema Folkert , Korf Jakob
Published: May 2005

Recently, Sloviter et al. reported that adrenalectomy (ADX) of young adult rats after 3 months led to a selective loss of granule neurons in the dentate gyrus (DG) and that this loss could be prevented by low doses of corticosterone. In the present study, the ADX‐induced neuronal degeneration was investigated in Wistar rats, using a silver impregnation method for degenerating neurons. To examine the time course and distribution of the ADX‐induced degeneration, young adult male rats were allowed to survive 2, 3, and 5 days and 1, 2, and 3 weeks after ADX. Argyrophilic neurons were present in the dentate granule cell layer on the second day following ADX. Three days after ADX, the number of argyrophilic granule neurons was much more abundant, and it increased gradually with longer post‐ADX survival times. Argyrophilia was specifically confined to dentate granule cells and was accompanied by the occurrence of pyknotic nuclei as observed in adjacent cresyl violet‐stained section. There were significant differences between individual rats in quantity of argyrophilia. About one fifth of the ADX rats showed sporadic or no argyrophilia, in spite of plasma corticosterone levels below the detection limit (10 ng/mL). Sham‐operated rats and ADX rats receiving corticosterone (10 mg/L) or dexamethasone (15 mg/L) in their drinking water did not display any argyrophilic neurons in the dentate gyrus. The distribution of the argyrophilia within the DG was highly characteristic with the highest number of degenerating cells in the hidden blade of the middle and the temporal thirds of the DG. There was a strong crest‐to‐tip and deep (hilar)‐to‐superficial increase in density of degenerating neurons. Along the entire septotemporal axis of the free blade and at the septal pole of the hidden blade, the number of argyrophilic cells was low. Wistar rats of different sex and aged 1–6 months all showed dentate granule cell degeneration 1 week following ADX. The distribution of the degeneration was identical to that of the young adult male group.

In order to examine whether the absence of corticosteroids affects dentate granule cells directly or through other mechanisms induced by ADX, low doses of dexamethasone were infused with a microdialysis probe directly into the hippocampus on one side of ADX rats. As a result, the ADX‐induced neuronal degeneration was selectively prevented at the treated side.
Navigation by fragment fitting: A theory of hippocampal function
Authors: Worden Robert
Published: May 2005

This paper describes a computational theory of spatial learning and navigation and its possible realization in the hippocampus. In the theory, mammals store memories of their geographical environment as a large number of independentfragments. A typical fragment denotes a few prominent landmarks in some region, their geometric relations, and their nongemetric properties, such as smells and visual cues. Navigation involves piecing together current sense data and relevant fragments to form a local map of the animal's surroundings; this is like solving a jigsaw puzzle. This computational model has been implemented in a computer program, whose performance is broadly consistent with observed levels of animal performance, and laboratory results, in spatial learning.

Possible realizations of the model in animal brains are discussed. Unlike some neural net models of spatial learning, the model is strongly geometric, and uses special neural structures to store and manipulate two‐dimensional vectors and bearings. A possible neural architecture is described in which the hippocampus performs the geometric operatios; this has a long‐term memory for fragments (somewhere in the neocortex), which can associatively recall fragments into a number of parallelfragment fitters, in the dentate gyrus and CA3 regions. These vary the positions and orientations of their fragments, to optimize the fit of the fragments to each other and to the animal's recent sense data. A local map of the animal's surroundings is stored in CA1 and subicular regions, where matching of fragment positions and attributes takes place. Mismatches are passed back via the entorhinal cortex to improve the fit during the next hippocampal theta cycle.

The model offers the potential for understading current data on spatial learning, on the neuroanatomy of the hippocampus and on place cells in a coherent framework, as well as understanding the role of the hippocampus in nonpositional memory tasks. Comparisons with experimental data are given.
Computational constraints suggest the need for two distinct input systems to the hippocampal CA3 network
Authors: Treves Alessandro , Rolls Edmund T.
Published: May 2005

The CA3 network in the hippocampus may operate as an autoassociator, in which declarative memories, known to be dependent on hippocampal processing, could be stored, and subsequently retrieved, using modifiable synaptic efficacies in the CA3 recurrent collateral system. On the basis of this hypothesis, the authors explore the computational relevance of the extrinsic afferents to the CA3 network. A quantitative statistical analysis of the information that may be relayed by such afferent connections reveals the need for two distinct systems of input synapses. The synapses of the first system need to be strong(but not associatively modifiable) in order to force, during learning, the CA3 cells into a pattern of activity relatively independent of any inputs being received from the recurrent collaterals, and which thus reflects sizable amounts of new information. It is proposed that the mossy fiber system performs this function. A second system, with a large number of associatively modifiable synapses on each receiving cell, is needed in order to relay a signal specific enough to initiate the retrieval process. This may be identified, we propose, with the perforant path input to CA3.
Monkey hippocampal neuron responses to complex sensory stimulation during object discrimination
Authors: Tamura Ryoi , Ono Taketoshi , Fukuda Masaji , Nishijo Hisao
Published: May 2005

The purpose of this study was to investigate, during the performance of an object discrimination task, responses of neurons in the monkey hippocampal formation to the sight of several objects that have biological meaning, and compare these responses with those of amygdalar neurons studies previously using the same task. Neuronal activity in the hippocampal formation of conscious monkeys was recorded during performance of a task that led to presentation of familiar rewarding, familiar aversive, or unfamiliar objects. Of 864 neurons recorded in the hippocampal formation and adjacent cortices, 160 (18.5%) responded to the sight of a certain object(s). Responses to the sight of different kinds of objects were analyzed in detail. Nondifferential neurons (n = 73) responded to different objects with no significant difference in response magnitudes, and differential neurons (n = 87) responded to different objects with different response magnitudes. Of the differential neurons, 23 responded more strongly to rewarding objects than to other objects (rewarding‐object‐dominant neurons), but the magnitude of responses to objects did not necessarily correlate with the order of preference to the objects as determined from observation of animal behavior. Aversive‐object‐dominant neurons (n = 13) responded more to aversive objects than to other objects. Unfamiliar‐object‐dominant neuron (n = 7) responded more to unfamiliar objects than to familiar objects. Selective neurons (n = 10) responded selectively to only one object or one category of objects. Fourteen of the rewarding‐ or aversive‐object‐dominant neurons were tested in extinction or reversal trials. In 12 of 14 neurons, responses to a rewarding or aversive object did not change, or slightly weakened, in extinction or reversal trials. The results suggest the following. (1) Responses of rewarding‐or aversive‐object‐dominant neurons may be involved in object‐reward or object‐aversion association. However, responses of many of these neurons might reflect past inputs related to reinforcement rather than extant emotional processing. (2) Responses of unfamiliar‐object‐dominant neurons may be involved in recognition of objects based on their familiar or unfamiliar aspects. These results are further discussed and compared with responsiveness of amygdalar neurons.
Amygdala kindling‐induced seizures selectively impair spatial memory. 1. Behavioral characteristics and effects on hippocampal neuronal protein kinase C isoforms
Authors: Beldhuis Hans J. A. , Everts Henk G. J. , Van der Zee Eddy A. , Luiten Paul G. M. , Bohus Béla
Published: May 2005

Protein kinase C (PKC) comprises a family of kinases consisting of nine subspecies that are differentially distributed in the central nervous system. This implies distinct functions. Its involvement is suggested in cellular and molecular mechanisms by which the hippocampus exerts influence on information processing. In this study, it was questioned whether abnormal activity in the neuronal substrate, particularly the hippocampal formation, induced by amygdala kindling indeed impairs spatial memory performance and correlated α, βI/II, and γ PKC subspecies expression. Rats were trained in a spatial discrimination task (SDT) and simultaneously kindled in the amygdala to induce abnormal, epileptiform activity. Control rats were only trained in the holeboard, a “free choice” maze, in which working (WM) and reference memory (RM) were simultaneously examined. Halfway through and at the end of the experiments the influence of kindling and SDT training on the immunoreactivity for PKC subspecies α, βI/II, and γ was evaluated in the hippocampal formation. Kindling resulted in a gradual increase in afterdischarge duration and motor seizure (MS) severity. Repeated SDT training ultimately resulted in an asymptotic level of WM and RM performance. As soon as generalized MSs developed, kindled rats failed to improve RM, whereas WM was not influenced. Compared to untrained rats, in trained controls PKCγ but not PKCαβI/II immunoreactivity was elevated in CA1 pyramidal and dentate gyrus granular cells. Generalized but not partial MSs abolished these alterations in PKCγ immunoreactivity. The present data indicate that repeated training in a SDT affects the expression of PKC subspecies γ but not of α or β in the rat hippocampus. Generalized epileptiform activity impair both acquisition of new spatial RM information and PKCγ expression. It is argued that PKCγ plays a role in cellular mechanisms through which pathological brain activity impairs certain aspects of spatial memory.
Inverted‐U relationship between the level of peripheral corticosterone and the magnitude of hippocampal primed burst potentiation
Authors: Diamond David M. , Bennett M. Catherine , Fleshner Monika , Rose Gregory M.
Published: May 2005

Studies have shown that peripheral levels of corticosterone correlate with the magnitudes of two well‐described physiological models of memory, long‐term potentiation (LTP) and primed burst (PB) potentiation. In the present experiments, the authors investigated the effects of experimenter‐controlled manipulations of the levels of corticosterone on the magnitude of hippocampal PB potentiation in urethane‐anesthetized rats. Primed burst potentiation is a long‐lasting (at least 30 minutes) increase in the amplitude of the CA1 population spike and EPSP slope in response to physiologically patterned stimulation of the hippocampal commissure. The levels of serum corticosterone were controlled by implanting corticosterone pellets in adrenalectomized rats (ADX/PELLET). In the first experiment, a significant negative linear correlation between elevated (stress) levels of serum corticosterone (greater than 20 μm/dL) and the magnitude of PB potentiation in ADX/PELLET subjects (r = 0.60, P <.05) was found. In the second experiment, the shape of the corticosterone‐PB potentiation function was different at low and intermediate levels of corticosterone than it was at high levels of corticosterone: There was a positive correlation at low levels (0–10 μm/dL), a peak response at intermediate levels (11–20 μm/dL), and a negative correlation at high levels (21–93 μm/dL) of corticosterone. Thus, the overall relationship between corticosterone and PB potentiation is an inverted‐U function. These findings provide strong support for the hypothesis that corticosterone exerts a concentration‐dependent biphasic influence on the expression of hippocampal plasticity.
Phenytoin prevents stress‐ and corticosterone‐induced atrophy of CA3 pyramidal neurons
Authors: Watanabe Yoshifumi , Gould Elizabeth , Cameron Heather A. , Daniels Deborah C. , McEwen Bruce S.
Published: May 2005

Repeated daily restraint stress and daily corticosterone administration to adult male Sprague‐Dawley rats leads to decreases in the number of branch points and length of dendrites of CA3 pyramidal neurons of the hippocampal formation. This decrease is prevented by daily administration of the antiepileptic drug phenytoin (Dilantin), which is known to interfere with excitatory amino acid release and actions. Phenytoin had no obvious effect on behavior during and after stress and failed to prevent stress‐induced reduction of body weight gain and stress‐induced increases of adrenal weight relative to body weight; it also failed to attenuate glucocorticoid‐induced diminution of the size of the thymus gland, indicating that it does not directly antagonize glucocorticoid actions. Stress‐ and corticosterone‐induced effects on dendritic length and branch point number are more pronounced on the apical, as opposed to the basal, CA3 dendrites that receive the largest mossy fiber input from the dentate gyrus. Because phenytoin is also known to prevent ischemic damage, these results are consistent with a model in which stress‐ and corticosterone‐induced CA3 dendritic atrophy is produced by excitatory amino acids released from the mossy fibers.
Age‐related loss of axospinous synapses formed by two afferent systems in the rat dentate gyrus as revealed by the unbiased stereological dissector technique
Authors: Geinisman Yuri , de Toledo‐Morrell Leyla , Morrell Frank , Persina Inna S. , Rossi Marvin
Published: May 2005

Previous attempts to elucidate whether a loss of hippocampal synapses occurs during aging provided conflicting results, possibly due to the unavailability, at the time, of unbiased methods for synapse quantitation. This study was designed to reexamine the issue by means of modern technical procedures that provide unbiased estimates of synaptic numbers. Groups of 14 young adult (5 months old) and 14 aged (28 months old) male Fischer‐344 rats were compared. Synapses were examined in the middle (MML) and inner (IML) molecular layer of the hippocampal dentate gyrus, where synaptic contacts are predominantly formed by different systems of afferents, the entorhinal and commissural‐associational fibers, respectively. The number of synapses per neuron was estimated with the aid of the stereological dissector technique. The results showed that the total number of synaptic contacts per neuron was significantly diminished in the MML (by 23.6%) and IML (by 22.7%) of aged rats relative to young adults. This age‐related synaptic loss involved axospinous, but not axodendritic, junctions of the MML (−24.4%) and IML (−24.0%). Both perforated and nonperforated axospinous synapses (distinguished by a discontinuous or continuous postsynaptic density, respectively) exhibited an age‐dependent decrease in numbers, though this decrease did not reach statistical significance in the case of perforated junctions of the IML. The observed age‐related loss of axospinous synapses may underlie the reduction in the amplitude of excitatory postsynaptic potentials and the decline in functional synaptic plasticity detected in the dentate gyrus of senescent rats.
Spiny neurons of area CA3c in rat hippocampal slices have similar electrophysiological characteristics and synaptic responses despite morphological variation
Authors: Scharfman Helen E.
Published: May 2005

Area CA3c is an area of morphologically diverse neurons. In addition to the presence of interneurons and pyramidal cells that are similar to those found in other subfields of area CA3, many neurons of area CA3c are different. They do not resemble interneurons, since they bear numerous spines, yet they also differ substantially from pyramidal cells in their morphology. To determine if the variants of area CA3c spiny cells are distinct physiologically as well as morphologically, intracellular recordings were made to record the electrophysiological properties of area CA3c cells in rat hippocampal slices, and each cell was identified morphologically following intracellular dye injection. The results show that the spiny cells, regardless of their often extensive morphological variation, have relatively uniform, pyramidal‐like electrophysiological properties. The aspiny cells are quite different from the spiny cells morphologically (i. e., in their paucity or complete lack of spines), and are also extremely different electrophysiologically, exhibiting features of “fast‐spiking” cells. Thus, spiny cells in area CA3c correspond to cells with pyramidal‐like electrophysiology, and the aspiny cells in area CA3c correspond to cells with interneuronal physiological properties. This correlation between structure and function appears to be a rule that pertains to each of the subfields of the hippocampus.
Modification of the responses of hippocampal neurons in the monkey during the learning of a conditional spatial response task
Authors: Cahusac Peter M. B. , Rolls Edmund T. , Miyashita Yasushi , Niki Hiroaki
Published: May 2005

In order to analyze the function of the hippocampus in learning, the activity of single neurons was recorded while monkeys learned a task of the type known to be impaired by damage to the hippocampus. In the conditional response task, the monkey had to learn to make one response when one stimulus was shown, and a different response when a different stimulus was shown. It had previously been shown that there are neurons in the hippocampal formation that respond in this task, to, for example, a combination of a particular visual stimulus that had been associated in previous learning with a particular behavioral response. In the present study, it was found that during such conditional response learning, the activity of 22% of the neurons in the hippocampus and parahippocampal gyrus with activity specifically related to the task altered their responses so that their activity, which was initially equal to the two new stimuli, became progressively differential to the two stimuli when the monkey learned to make different responses to the two stimuli. These changes occurred for different neurons just before, at, or just after the time when the monkey learned the correct response to make to the stimuli. In addition to these neurons, which had differential responses that were sustained for as long as the recordings continued, another population of neurons (45% of those with activity specifically related to the task) developed differential activity to the two new stimuli, yet showed such differential responses transiently for only a small number of trials at about the time when the monkey learned. These findings are consistent with the hypothesis that some synapses on hippocampal neurons modify during this type of learning so that some neurons come to respond to particular stimulus‐response associations that are being learned. Further, the finding that many hippocampal neurons started to reflect the new learning, but then stopped responding differentially (the transient neurons), is consistent with the hypothesis that the hippocampal neurons with large sustained changes in their activity inhibited the transient neurons, which then underwent reverse learning, thus providing a competitive mechanism by which not all neurons are allocated to any one learned association or event.
Changes in protein kinase C isozymes in the rat hippocampal formation following hippocampal lesion
Authors: Shimohama Shun , Saitoh Tsunao , Gage Fred H.
Published: May 2005

The cellular and regional distribution of the four protein kinase C (PKC) isoforms in the rat hippocampal formation and the response of PKC to lesions were determined by employing immunohistochemical and immunochemical techniques with antibodies specific to PKC (α), ‐(β I), ‐(β II), and ‐(γ). PKC (α) intensely stained the periphery of the pyramidal cell in the stratum pyramidale. The granule cells, glial cells, and mossy fibers were anti‐PKC (α) negative. The cytoplasm, axons, and dendrites of basket cells and interneurons in the hilus were labeled with anti‐PKC (α). Anti‐PKC (β I) immunoreactivity was localized on the periphery of pyramidal cells and interneurons of the hilus, as well as the oriens, radiatum, and molecular layers of the CA regions. Anti‐PKC (β II) immunoreactivity was mainly cytoplasmic, extending into the dendrites in the hippocampal pyramidal cells and the dentate granule cells, and also in some glial cells. In the stratum radiatum of the CA1, anti‐PKC (γ) immunoreactivity localized to the pyramidal cell cytoplasm, extending into the dendrites. Following fimbria‐fornix (FF) lesions, the anti‐PKC (α) and ‐(β I) staining of the pyramidal cell periphery was markedly reduced. The anti‐PKC (γ) staining of the pyramidal and granular cells of the dentate gyrus was reduced whereas the interneuron staining in the hilus was increased. In the FF‐lesioned hippocampus, anti‐PKC (α) and antiαPKC (β II) labeled reactive glial cells, whereas anti‐PKC (β I) and ‐(γ) did not. Quantitative Western blot analysis revealed a dramatic increase in the particulate/total PKC for all isozyme forms, although the total levels of PKC, except PKC (γ), did not change following FF lesions. The PKC (γ) concentration doubled after FF lesions. Perforant path lesions resulted in a marked alteration in the neuronal staining in dentate gyrus with anti‐PKC (α) and ‐(β I) and in increased numbers of anti‐PKC (α)‐ and anti‐PKC (β II)‐positive glial cells. Anti‐PKC (γ) staining did not change noticeably. The total PKC concentration did not change for isozymes α, β I, and γ, but PKC (βII) concentration increased by 48% following perforant path lesions as detected by Western blot analysis. The particulate/total PKC decreased for all four isozymes although the reduction in PKC (β I) concentration was not statistically significant. This change in PKC compartmentalization is in marked contrast to an increased level of particulate PKC following FF lesions. Thus, the effects of deefferentation and deafferentation for each PKC isoform were different.
Quantal analysis of modulating action of adenosine on the mossy fiber synapse in hippocampal slices
Authors: Yamamoto Chosaburo , Sawada Satsuki , Ohno‐Shosaku Takako
Published: May 2005

Although adenosine has been considered to depress release of neurotransmitter in central synapses, evidence for this notion is circumstantial. To obtain more direct and quantitative evidence, the suppressing action of adenosine on transmission through the mossy fiber synapse was examined by a quantal analysis in thin transverse sections of the guinea pig hippocampus. Adenosine suppressed excitatory postsynaptic potentials (EPSPs) induced in CA3 neurons by activation of single mossy fibers to 57 ± 19% at 10 μM (6 neurons). The input resistance of the postsynaptic neurons was reduced to 84 ± 5%. The suppression of the unitary EPSPs was accompanied by a reduction of the mean quantal content (m) to 51 = 13% with no significant decrease in mean quantal amplitude (q). These findings indicate that adenosine at 10 μM suppresses transmission through mossy fiber synapses mainly by depressing release of transmitter. This study provides direct evidence for the presynaptic action of adenosine on central synapses for the first time.
Hippocampal circuitry complicates analysis of long‐term potentiation in mossy fiber synapses
Authors: Claiborne Brenda J. , Xiang Zixiu , Brown Thomas H.
Published: May 2005

Much 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 laboratories.
Hippocampal synaptic enhancement and spatial learning in the morris swim task
Authors: Korol Donna L. , Abel Ty W. , Church Lloyd T. , Barnes Carol A. , McNaughton Bruce L.
Published: May 2005

The 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 information.
An examination of the relations between hippocampal long‐term potentiation, kindling, afterdischarge, and place learning in the water maze
Authors: Cain Donald P. , Hargreaves Eric L. , Boon Francis , Dennison Zoe
Published: May 2005

Two 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 task.
Spatial selectivity of unit activity in the hippocampal granular layer
Authors: Jung M. W. , McNaughton B. L.
Published: May 2005

Single 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 representation.