bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lesion‐induced synapse reorganization in the hippocampus of cats: Sprouting of entorhinal, commissural/associational, and mossy fiber projections after unilateral entorhinal cortex lesions, with comments on the normal organization of these pathways
Authors: Steward Oswald 
Published: May 2005

AbstractThis study evaluates whether three forms of sprouting occur in the hippocampus of the cat following unilateral entorhinal cortex (EC) lesions: (1) sprouting of projections from the EC contralateral to the lesion; (2) sprouting of the commissural/associational system; and (3) sprouting of mossy fibers.Tract tracing techniques were used to define the normal organization of the entorhinal cortical projection system, the commissural/associational (C/A) systems, and the mossy fiber projections in normal cats. The same techniques were then used to evaluate whether there were changes in these projections in animals with long‐standing unilateral EC lesions. The projections from the entorhinal cortex were evaluated autoradiographically following injections of 3H proline into the entorhinal area. The projections of the C/A system were traced using the Fink‐Heimer technique after lesions of the hippocampal commissures, and by using autoradiographic techniques after injections of 3H proline into the hippocampus. The distribution of mossy fibers was evaluated using the Timm's stain.The results reveal that unilateral lesions of the EC in cats lead to the same sorts of sprouting that have been described in rats. There is: (1) an increase in the density of the crossed projection from the surviving EC to the contralateral dentate gyrus that had been deprived of its normal EC inputs; (2) an expansion of the terminal field of the C/A projection system into portions of the molecular layer of the dentate gyrus normally occupied by EC projections; and (3) an increase in supragranular mossy fibers in some animals. The mossy fiber sprouting was especially prominent when the lesions encroached upon the hippocampus. The studies also reveal additional details about the normal organization of hippocampal pathways in cats. The most important points are: (1) there is a crossed projection from the entorhinal cortex to the contralateral dentate gyrus; and (2) there is a complex laminar organization of the commissural and associational terminal fields in the molecular layer of the dentate gyrus that appears to be related to the point of origin of the projections along the septotemporal axis of the hippocampus. This heretofore unrecognized aspect of the laminar organization of C/A terminations has important implications for the temporal competition hypothesis, which has been advanced to account for the development of these afferent systems.
Autoradiographic localization of proline uptake in excitatory hippocampal pathways
Authors: Nadler J. Victor , Bray Sherrilynn D. , Evenson Debra A. 
Published: May 2005

AbstractAn autoradiographic method was developed to localize sites of high‐affinity, Na+‐dependent proline uptake in the rat hippocampal formation. Hippocampal slices were incubated with [3H]proline, fixed with a glutaraldehyde/carbodiimide mixture, and cut into frozen sections. The sections were coated with photographic emulsion and autoradiograms were prepared. Autoradiographic grain densities were highest over the inner and outer thirds of the dentate molecular layer, followed by stratum lacunosum‐moleculare of area CA3. Stratum oriens and stratum radiatum of area CA1 and CA3 were fairly intensely labeled. The pyramidal and granule cell body layers, stratum lucidum of area CA3, and middle third of the dentate molecular layer were lightly labeled. Effects of surgical and kainic acid lesions suggested that the lateral perforant path, associational‐commissural fibers in the fascia dentata, and Schaffer collateral‐commissural‐ipsilateral stratum oriens fibers have considerable proline uptake capacity. In contrast, the medial perforant path and the mossy fibers appear to accumulate little or no proline.These results suggest that high‐affinity, Na+‐dependent uptake of proline is expressed by a subset of hippocampal glutamate pathways. The relative capacities of glutamate terminal populations to transport glutamate and proline varies widely. Proline was previously shown to possess neuroexcitatory and excitotoxic properties in the rat hippocampal formation. Taken together, these findings argue that proline plays a role in excitatory transmission. In elucidating this role, comparisons between medial and lateral divisions of the perforant path may prove especially advantageous.
Development of synapsin I and synapsin II in intraocular hippocampal transplants
Authors: Bergman Hanna , Browning Michael , Granholm Ann‐Charlotte 
Published: May 2005

AbstractPrevious studies have indicated that the appearance of synaptic vesicle‐associated proteins known as the synapsins is one indicator of synapse formation. In this study, the levels and morphological distribution of synapsin I and synapsin IIa and IIb were studied in intraocular hippocampal transplants and in situ in the intact hippocampus. No detectable levels of either synapsin I or synapsin II were found in the fetal brain. The in situ levels of the synapsins exhibited parallel increases rapidly after birth, reaching peak levels at 8 weeks, after which a slight decline was noted in synapsin I and synapsin IIb. In hippocampal transplants, a comparable increase in the synapsins was seen during the first 8 weeks in oculo. It is likely that the synapse formation in the hippocampal transplants represents synapses from neurons within the transplant, as well as from various peripheral ganglia that send collaterals into the graft. Peripheral and central synapses express different synapsin I: synapsin IIa and IIb ratios. When the ratios of the synapsin proteins in hippocampal transplants were examined ratios essentially identical to those seen in the normal hippocampus were found, despite the numerous peripheral neurites innervating the grafts. Immunohistochemical studies supported the immunoblot data, showing no detectable immunofluorescence with synapsin antibodies in fetal or newborn hippocampal formation. The density of immunoreactive profiles increased substantially both in transplants and in the hippocampal formation in situ during the first 2 postnatal months.In conclusion, the present data demonstrate that hippocampal transplants in oculo can develop significant levels of the synapsins and that there is no time lag in development in these levels compared to the hippocampal formation in situ.
Amygdala kindling‐induced seizures selectively impair spatial memory. 2. Effects on hippocampal neuronal and glial muscarinic acetylcholine receptor
Authors: Beldhuis Hans J. A. , Everts Henk G. J. , Van der Zee Eddy A. , Luiten Paul G. M. , Bohus Béla 
Published: May 2005

AbstractThe muscarinic acetylcholine receptor is linked via hydrolysis of phosphoinositides to the protein kinase C pathway. In a preceding paper (Beldhuis, H. J. A., H. G. J. Everts, E. A. Vander Zee, P. G. M. Luiten, and B. Bohus (1992) Amygdala kindling‐induced seizures selectively impair spatial memory. 1. Behavioral characteristics and effects on hippocampal neuronal protein kinase C isoforms. Hippocampus 2:397–410), the role of different isoforms of protein kinase C in neurobiological processes associated with plasticity was studied using both a spatial learning paradigm and amygdala kindling in the rat. This study extended the findings on protein kinase C activity to the level of the muscarinic acetylcholine receptor. Rats were trained in a spatial learning paradigm and kindled simultaneously in the amygdala to develop generalized motor convulsions. Control rats were trained only in the spatial learning paradigm to acquire stable working and reference memory performance. Alteration in the expression of the muscarinic acetylcholine receptor was investigated using a monoclonal antibody to muscarinic acetylcholine receptor proteins. Trained control rats that were exposed repeatedly to the spatial learning paradigm showed an increase in immunoreactivity for the muscarinic acetylcholine receptor located in the same hippocampal regions in which the protein kinase C activity was increased. In fully kindled rats, however, this increase located in principal neurons was absent, whereas expression of muscarinic acetylcholine receptor proteins was increased in hippocampal astrocytes. Moreover, fully kindled rats showed an impairment in reference memory performance as compared to trained control rats. It is argued that concomitant alterations at the level of receptor (muscarinic acetylcholine) and second messenger (protein kinase C) reflect an optimal state for neuronal plasticity. Kindling results in a disturbance of this effector system.
Region‐specific age effects on AMPA sensitivity: Electrophysiological evidence for loss of synaptic contacts in hippocampal field CA1
Authors: Barnes C. A. , Rao G. , Foster T. C. , McNaughton B. L. 
Published: May 2005

AbstractThe effects of aging on the responsiveness of hippocampal neurons to iontophoretic application of L‐glutamate and AMPA were studied in vitro. There were no effects of age on neuronal responses to L‐glutamate; however, CA1 pyramidal cells of old rats, but not granule cells in the fascia dentata, showed both a smaller reduction in extracellularly‐recorded synaptic responses following application of AMPA (presumably mediated by depolarization), and smaller extracellular “DC” fields (measured by subtracting the DC potentials at the dendrite and soma following AMPA application in the dendrites). To examine the cellular bases of this age‐related alteration in AMPA sensitivity, two additional electrophysiological approaches were used: (1) measurement of the amplitude ratios of extracellular EPSP and fiber potential components of the Schaffer collateral‐CA1 response; (2) measurement of intracellularly recorded unitary EPSPs and quantal analysis of their fluctuations. The interpretations that would be placed on four hypothetical possible outcomes of such experiments are outlined and assessed in relation to the experimental data. The pattern of results obtained in the present experiments supports the following conclusions: In old rats, individual Schaffer collateral synapses do not appear to have altered AMPA receptor properties, as neither the mean size of the unitary synaptic response nor the apparent quantal size differs between age groups; however, the data do support the conclusion that there are fewer synapses per Schaffer collateral branch in old versus young CA1 pyramidal cells.
Hippocampal plasticity induced by primed burst, but not long‐term potentiation, stimulation is impaired in area CA1 of aged fischer 344 rats
Authors: Moore Christopher I. , Browning Michael D. , Rose Gregory M. 
Published: May 2005

AbstractThe effect of two types of electrical stimulation designed to induce long‐lasting plasticity of the Schaffer/commissural inputs to CA1 pyramidal neurons was investigated using in vitro hippocampal slices made from young (3–6 month) and old (24–27 month) Fischer 344 rats. The first stimulation paradigm, primed burst (PB) stimulation, consisted of a total of five physiologically patterned stimuli: a single priming pulse followed 170 ms later by a burst of four pulses at 200 Hz. The second stimulation paradigm, long‐term potentiation (LTP) stimulation, consisted of a 200 Hz/1 second train (a total of 200 stimuli). Primed burst and LTP stimulation were equally effective at inducing a lasting increase in the population spike recorded from slices made from young rats. However, the enhancement of population spike amplitude produced by PB, but not LTP, stimulation was significantly less in slices made from old rats. These results suggest that the capacity of the hippocampus to demonstrate long‐lasting synaptic plasticity is not altered with age, but that engaging plasticity‐inducing mechanisms becomes more difficult. Furthermore, these data suggest that physiologically patterned paradigms for inducing long‐lasting synaptic plasticity may more accurately assess the functional status of hippocampal memory encoding mechanisms than does conventional LTP stimulation.
On the sites of presynaptic inhibition by neuropeptide y in rat hippocampus in vitro
Authors: Klapstein Gloria J. , Colmers William F. 
Published: May 2005

AbstractNeuropeptide Y (NPY) reduces excitatory synaptic transmission between stratum radiatum and CA1 pyramidal cells in rat hippocampal slice in vitro by a presynaptic action. To understand NPY's role in the control of excitability in hippocampus, its actions on excitatory and inhibitory synaptic transmission were examined, using intracellular, sharp microelectrode, and tight‐seal, whole cell recordings from principal neurons in areas CA1, CA3, and dentate. Bath application of 1 μM NPY reversibly inhibited excitatory postsynaptic potentials (EPSPs) evoked in CA1 pyramidal cells from either stratum radiatum or stratum oriens by about 50%. Neuropeptide Y also inhibited EPSPs at mossy fiber‐CA3, stratum oriens‐CA3, and CA3‐CA3 synapses by between 45% and 55%. As in CA1, the action of NPY was presynaptic. By contrast, NPY did not inhibit EPSPs evoked in dentate granule cells from either perforant path or commissural inputs. Neuropeptide Y did not alter postsynaptic membrane properties in any cell type. Although NPY attenuated the orthodromically evoked (stratum radiatum) inhibitory postsynaptic potentials in CA1 pyramidal cells by about the same amount as it inhibited the EPSPs, it did not affect the IPSPs evoked in the same cells by antidromic stimulation from alveus. Inhibitory postsynaptic potentials evoked in pharmacological isolation in CA1, CA3, or dentate were also not significantly affected by NPY. The evidence supports the hypothesis that NPY acts at feedforward excitatory synapses to presynaptically reduce the amplitude of excitation as it travels through hippocampal circuits. By contrast, synaptically mediated inhibition is not directly affected by NPY. Neuropeptide Y is the only known endogenous substance that selectively reduces feedforward excitatory transmission without causing changes in other properties of the hippocampal circuitry.
Cumulative long‐term potentiation in the rat dentate gyrus correlates with, but does not modify, performance in the water maze
Authors: Jeffery Kathryn J. , Morris Richard G. M. 
Published: May 2005

AbstractThe electrically induced increase in hippocampal synaptic strength known as long‐term potentiation (LTP) is thought to involve some of the same mechanisms as those mediating information storage during spatial learning. Physiological saturation of synaptic weights might therefore be expected to occlude spatial learning. In support of this, Castro et al. (Castro CA, Silbert LH, McNaughton BL, Barnes CA, 1989, Nature 342:545–548) reported that repeated induction of LTP to asymptotic levels, over a 14‐day period, blocked the ability of rats to learn the position of a hidden platform in a water maze shortly afterwards. The authors have attempted to replicate this finding in two experiments. In Experiment I, rats were given either 400 Hz stimulation as 50 trains/day over a 5‐day period, to induce LTP, or were given the same number of stimulus pulses at 1 Hz. Two hours after the last stimulation session they underwent eight spatial learning trials, occurring at 2‐hour intervals. In Experiment 2, the procedure of Castro et al. was followed exactly, with LTP induced by 10 trains of 400 Hz stimulation daily for 14 days. Spatial learning trials began 10 minutes after the last stimulation session and consisted of 12 trials with alternating 30‐second and 2‐minute intervals. In neither experiment was a significant impairment of spatial learning observed. However, there was a strong positive correlation, in both experiments, between the final level of LTP and subsequent performance in the water maze.
Differential effects of kindling and kindled seizures on place learning in the morris water maze
Authors: McNamara Robert K. , Kirkby R. Duncan , dePape Gregory E. , Skelton Ronald W. , Corcoran Michael E. 
Published: May 2005

AbstractThere is some controversy about the role of long‐term potentiation (LTP) in spatial learning. The authors have found that triggering generalized kindled seizures with stimulation of the perforant path disrupts spatial learning in the Morris water maze but that kindling per se does not affect spatial learning. It is suggested that abnormal electrical activity induced by high‐frequency stimulation of the perforant path may have been responsible for the disruption of spatial learning previously attributed to LTP saturation.
Effects of glucocorticoids on hippocampal long‐term potentiation
Authors: Pavlides Constantine , Watanabe Yoshifumi , McEwen Bruce S. 
Published: May 2005

AbstractThe effects of chronic and acute corticosterone (CORT) administration were investigated on hippocampal long‐term potentiation (LTP) in the dentate gyrus granule cell layer of the rat. Electrophysiological experiments were performed in vivo under urethane anesthesia. Chronic CORT treatment (40 mg/kg/day) over 21 days decreased LTP compared to vehicle controls, even when LTP was measured 48 hours after cessation of CORT treatment, when serum CORT levels had returned to baseline. A single injection of CORT also decreased LTP compared to vehicle controls, but only when CORT levels were high, since at 48 hours after a single acute CORT injection LTP was not depressed. The decrements in LTP were seen both for the slope of the excitatory postsynaptic potential and for the population spike. Yet CORT had no effects on posttetanic potentiation or neuronal excitability. These findings are consistent with previous reports showing a reduction in LTP in the CAI field of animals exposed to stress or acute CORT administration.
GABA induces a unique rise of [CA]i in cultured rat hippocampal neurons
Authors: Segal Menahem 
Published: May 2005

AbstractGABA evoked a reversible rise of free intracellular calcium concentration ([Ca]i) in cultured rat hippocampal neurons, detected with Fluo‐3 fluorescence in a confocal laser scanning microscope. The GABA‐evoked change of [Ca]i was mimicked by muscimol and not by baclofen, but was only minimally affected by picrotoxin or bicuculline, indicating that this effect of GABA is not likely to be mediated by activation of GABAB receptor or by a conventional chloride‐linked GABAA receptor. GABA‐evoked rise of [Ca]i expressed a marked desensitization; only 10–20 minutes after a previous exposure to GABA was the response to a subsequent application fully expressed. This desensitization was not seen in electrophysiological responses to GABA or in [Ca]i changes evoked by NMDA in the same neurons. The GABA response appeared to be developmentally regulated and was seen in 1–7‐day‐old more than in 21–28‐day‐old cells. It is suggested that GABA evokes a unique change of [Ca]i in young hippocampal neurons.
Structural synaptic correlate of long‐term potentiation: Formation of axospinous synapses with multiple, completely partitioned transmission zones
Authors: Geinisman Yuri , Detoledo‐Morrell Leyla , Morrell Frank , Heller Richard E. , Rossi Marvin , Parshall Robert F. 
Published: May 2005

AbstractSynapses were analyzed in the middle molecular layer (MML) and inner molecular layer (IML) of the rat dentate gyrus following the induction of long‐term potentiation (LTP) by high‐frequency stimulation of the medial perforant path carried out on each of 4 consecutive days. Potentiated animals were sacrificed 1 hour after the fourth high frequency stimulation. Stimulated but not potentiated and implanted but not stimulated animals served as controls. Using the stereological disector technique, unbiased estimates of the number of synapses per postsynaptic neuron were differentially obtained for various subtypes of axospinous junctions: For atypical (giant) nonperforated synapses with a continuous postsynaptic density (PSD), and for perforated ones distinguished by (1) a fenestrated PSD and focal spine partition, (2) a horseshoe‐shaped PSD and sectional spine partition, (3) a segmented PSD and complete spine partition(s), and (4) a fenestrated, (5) horseshoe‐shaped, or (6) segmented PSD without a spine partition. The major finding of this study is that the induction of LTP in the rat dentate gyrus is followed by a significant and marked increase in the number of only those perforated axospinous synapses that have multiple, completely partitioned transmission zones. No other synaptic subtype exhibits such a change as a result of LTP induction. Moreover, this structural alteration is limited to the terminal synaptic field of activated axons (MML) and does not involve an immediately adjacent one (IML) that was not directly activated by potentiating stimulation. The observed highly selective modification of synaptic connectivity involving only one particular synaptic subtype in the potentiated synaptic field may represent a structural substrate of the long‐lasting enhancement of synaptic responses that characterizes LTP.
Early areal differentiation of the human cerebral cortex: Entorhinal area
Authors: Kostović Ivica , Petanjek Zdravko , Judaš Miloš 
Published: May 2005

AbstractThe early cytoarchitectonic specialization and area‐specific differentiation of the prospective entorhinal cortex were studied in the postmortem human fetal brains (9.5–13.5 postovulatory weeks). At 10 weeks, using the Golgi method, we saw the appearance of area‐specific large neurons (promoter neurons) with widely bifurcating apical dendrites situated at the outer margin of the cortical plate of the prospective entorhinal cortex. The analysis of the serial Nissl‐stained sections revealed the concomitant appearance of a one‐cell‐thick layer (monolayer) at the interface between the cortical plate and the marginal zone and multilaminated spread of the deep part of the cortical plate. This is the earliest sign of area‐specific cytoarchitectonic differentiation of all pallial regions characterized by the presence of the typical cortical plate. The first subareal differentiation within the entorhinal cortex begins at 13 postovulatory weeks with uneven development of fiber‐rich lamina dissecans, which separates two cellular laminae principales (externa and interna), and with the appearance of characteristic cell islands of the prospective layer II. At rostral levels, cell islands begin to develop in the rostromedial entorhinal area at the subpial depths where large promoter neurons reside. At intermediate levels, both lamina dissecans and lamina principalis interna are well delineated. At caudal levels, lamina principalis interna is continuous with the upper subplate zone of the adjacent neocortex. Both area‐specific neurons (promoters) and fiber‐rich (afferent) strata develop synchronously during the earliest areal differentiation of the cerebral cortex. The precocious lamination of the cortical plate is the crucial event in the histogenesis of the entorhinal cortex.