bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatial selectivity of unit activity in the hippocampal granular layer
Authors: Jung M. W. , McNaughton B. L. 
Published: May 2005

AbstractSingle 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.
Vasopressin induction of long‐lasting potentiation of synaptic transmission in the dentate gyrus
Authors: Chen Chong , Brinton Roberta Díaz , Shors Tracey J. , Thompson Richard F. 
Published: May 2005

AbstractVasopressin receptors are present in both the developing and mature dentate gyrus of the rat brain and are of the V1 vasopressor type. Because vasopressin has been shown to influence memory function when injected into the dentate gyrus, the influence of this peptide on an electrophysiological model of learning and memory using the field excitatory postsynaptic potential (EPSP) of the dentate gyrus was investigated. Results of these studies showed that nanomolar concentrations of [Arg8]‐vasopressin induced a prolonged increase in the amplitude and slope of the evoked population response in the presence of 1.5 mM calcium. Moreover, the expression of the vasopressin‐induced potentiation of the EPSP persisted following removal of vasopressin from the perfusion medium. The vasopressin‐induced sustained increase has been termed long‐term vasopressin potentiation (LTVP). The closely related neuropeptide oxytocin had no effect upon the EPSP of the dentate gyrus. Preincubation of hippocampal slices in a selective V1 antagonist blocked the expression of LTVP. The ability of the V1 antagonist to block LTVP demonstrates that the potentiation induced by vasopressin is receptor‐specific. In the presence of 2.5 mM calcium, the effect of vasopressin was opposite to that observed in 1.5 mM calcium. Under the conditions of 2.5 calcium, vasopressin induced a prolonged depression in the amplitude and slope of the EPSP. Expression of both potentiation and depression appeared within 5 minutes of application and persisted for the length of the observation, 60 minutes. These experiments demonstrate that vasopressin can induce long‐lasting changes in the excitability of dentate gyrus neurons that are both calcium‐dependent and receptor‐specific.
Alterations in [3H]‐kainate receptor binding in the hippocampal formation of aged long‐evans rats
Authors: Nagahara Alan H. , Nicolle Michelle M. , Gallagher Michela 
Published: May 2005

AbstractThe present study used in vitro autoradiography to examine the density of [3H]‐kainate (KA) binding in subregions of the hippocampal formation and certain cortical areas in young (7–8 months) and aged (27–29 months) Long‐Evans rats. In addition, the topography of KA binding in the dentate molecular layer was examined for evidence of reactive reorganization in the aged brain. This investigation of age‐related changes in [3H]‐KA binding included correlations with the animals' spatial learning performance in a Morris water maze. The results showed an age‐related decrease in the density of [3H]‐KA binding in several regions of the hippocampal formation (CA3, CA1, hilus) and within related cortical areas (subicular complex, entorhinal cortex, perirhinal cortex). In addition, an expanded zone of KA binding in the molecular layer of the dentate gyrus was observed in the aged group. This expansion of KA binding may reflect sprouting due to a loss of perforant path input to the dentate. The results of additional correlational analyses, however, indicated that these changes in the density and topography of [3H]‐KA binding were not strongly correlated with a decline in place learning ability.
Phase relationship between hippocampal place units and the EEG theta rhythm
Authors: O'Keefe John , Recce Michael L. 
Published: May 2005

AbstractMany complex spike cells in the hippocampus of the freely moving rat have as their primary correlate the animal's location in an environment (place cells). In contrast, the hippocampal electroer cephalograph theta pattern of rhythmical waves (7–12 Hz) is better correlated with a class of movements that change the rat's location in an environment. During movement through the place field, the complex spike cells often fire in a bursting pattern with an interburst frequency in the same range as the concurrent electroencephalograph theta. The present study examined the phase of the theta wave at which the place cells fired. It was found that firing consistently began at a particular phase as the rat entered the field but then shifted in a systematic way during traversal of the field, moving progressively forward on each theta cycle. This precession of the phase ranged from 100° to 355° in different cells. The effect appeared to be due to the fact that individual cells had a higher interburst rate than the theta frequency. The phase was highly correlated with spatial location and less well correlated with temporal aspects of behavior, such as the time after place field entry. These results have implications for several aspects of hippocampal function. First, by using the phase relationship as well as the firing rate, place cells can improve the accuracy of place coding. Second, the characteristics of the phase shift constrain the models that define the construction of place fields. Third, the results restrict the temporal and spatial circumstances under which synapses in the hippocampus could be modified.
Hyperpolarizing synaptic potentials evoked in CA1 pyramidal cells by glutamate stimulation of interneurons from the oriens/alveus border of rat hippocampal slices. I. Electrophysiological response properties
Authors: Samulack Donald D. , Williams Sylvain , Lacaille Jean‐Claude 
Published: May 2005

AbstractTo examine the inhibitory postsynaptic potentials (IPSPs) elicited in pyramidal cells by interneurons situated at the stratum oriens/alveus border (O/A), glutamate was applied by micropressure to this area during intracellular recordings from CA1 pyramidal cells. Glutamate stimulation evoked IPSPs (glut‐IPSPs) of small amplitude (4 mV), delayed peak latency (100–110 ms), and long duration (300–400 ms). Recurrent activation of interneurons via glutamate stimulation of pyramidal cells by local application in stratum pyramidale (PYR) evoked recurrent IPSPs (PYR glut‐IPSPs) with similar amplitude and time course as O/A glut‐IPSPs. The mean equilibrium potential of O/A glut‐IPSPs (−77 mV) was significantly different from that of the PYR glut‐IPSPs (−71 mV), however, neither equilibrium potential was significantly different from that of the electrically evoked early IPSP in the same cells. Glutamate‐evoked IPSPs elicited from O/A displayed some response reversal (27% reversal) like those evoked from PYR (41% reversal). The early IPSP evoked by electrical stimulation displayed significantly more response reversal (67% reversal) than glut‐IPSPs. Both types of glut‐IPSPs (O/A and PYR) were associated with moderate increases in membrane conductance (5.9 and 6.6 nS, respectively), which were significantly less than the conductance change associated with the early IPSP (45.8 nS). In interneurons within PYR, glutamate stimulation in PYR readily elicited a flurry of excitatory postsynaptic potentials, whereas glutamate stimulation in O/A elicited IPSPs. The electrophysiological properties of IPSPs elicited in pyramidal cells by glutamate stimulation of interneurons in O/A were similar to those of recurrent IPSPs evoked from PYR. Given that both of these types of glutamate‐evoked IPSPs were mostly mediated via GABAA receptor channels (Samulack DD, Lacaille J‐C, 1993, Hippocampus 3:345–358), the small differences observed between equilibrium potentials, response reversals, and conductance changes could be due to a more electrotonically distant location from the soma of the synapses involved in O/A glut‐IPSPs as compared to those of recurrent IPSPs elicited from PYR.
Learning and memory after adrenalectomy‐induced hippocampal dentate granule cell degeneration in the rat
Authors: Armstrong John N. , McIntyre Dan C. , Neubort Simon , Sloviter Robert S. 
Published: May 2005

AbstractAdrenalectomy (ADX) of normal adult rats causes selective hippocampal dentate granule cell degeneration that is prevented by corticosterone. The ability to destroy this one hippocampal cell type noninvasively made it possible to address the role of the dentate granule cells in learning and memory. Four months after ADX, 31 of 45 rats failed to show obvious granule cell loss and displayed behavior in the Morris water maze that was similar to 16 sham‐operated control rats and 16 ADX rats maintained on corticosterone throughout the study. Conversely, 14 of the 45 ADX rats experienced a loss of granule cells that varied from minimal to extensive. Although there were no obvious differences between groups in motoric and motivational characteristics or search strategies, ADX rats with moderate to extensive granule cell loss acquired place learning slightly slower than controls or ADX rats with minimal or no obvious cell loss. Furthermore, the ADX rats with moderate to extensive cell loss were temporarily impaired following alteration of either intramaze or extramaze cues compared to controls. In contrast, the rats with granule cell loss remembered an old place and learned a new place as quickly as controls. These results suggest that a normal complement of dentate granule cells may not be necessary for the acquisition or retention of spatial information in the Morris water maze.
Activation, travel distance, and environmental change influence food carrying in rats with hippocampal, medial thalamic and septal lesions: Implications for studies on hoarding and theories of hippocampal function
Authors: Whishaw Ian Q. 
Published: May 2005

AbstractRats transport food from exposed areas to covered areas where they eat it or leave it. Although there is evidence that limbic structures play a role in food transport, their role is controversial. Here it was found that although many rats with large hippocampal, septal/diagonal band of Broca or dorsomedial thalamic lesions did not carry food but ate it where they found it, a few presentations of an auditory stimulus could restore food carrying. Once restored, most features of food carrying in hippocampal rats were normal in relation to food presentation schedules, deprivation levels, ambient illumination, circadian cycles, food size, and eating times. Nevertheless, food carrying impairments reemerged when the testing environment was changed. Hippocampal rats were also excessively responsive to increases in travel distance and stopped carrying food at distances over which control rats would still carry large food pellets. Auditory stimulation did not restore food carrying over long travel distances. The findings that sensory stimulation, environmental change, and travel distance influence food carrying probabilities in rats with limbic system lesions is discussed in relation to research on limbic control of food hoarding and theories of limbic system function.
Perforated axospinous synapses with multiple, completely partitioned transmission zones: Probable structural intermediates in synaptic plasticity
Authors: Geinisman Yuri 
Published: May 2005

AbstractAnalysis of axospinous synapses in the rat dentate gyrus, using three‐dimensional reconstructions from electron micrographs of serial sections, revealed a novel synaptic subtype. Synapses of this subtype exhibit partitions that emanate from the postsynaptic spine head and invaginate the presynaptic axon terminal, dividing its portion contacted by the spine into distinct protrusions. Such complete spine partitions provide barriers between two to four discrete transmission zones, each one being formed by a separate axon terminal protrusion and delineated by a separate segment of the postsynaptic density (PSD). Spine partitions that differ from the complete ones were found in two other synaptic subtypes. One of these is characterized by a sectional partition the base of which is placed between the arms of a horseshoeshaped PSD. Synapses of another subtype exhibit a focal partition the base of which is restricted to a perforation in a fenestrated PSD. Although both sectional and focal partitions invaginate a presynaptic axon terminal, they do not divide into separate protrusions and do not split a single transmission zone into disjointed entities. All three subtypes of partitioned synapses have nonpartitioned counterparts exhibiting segmented, horseshoe‐shaped, or fenestrated PSDs. These observations suggest a model of structural modifications underlying synaptic plasticity. According to this model, synapses with multiple, completely partitioned transmission zones that appear to be designed as elements of an unusually high strength, represent pivotal structural intermediates in synaptic plasticity. The formation of such synapses from those that belong to other subtypes is postulated to result in a sustained increase in the efficacy of synaptic transmission. Conversely, a disassembly of complete partitions with the transformation of multiple transmission zones into a single one is proposed to lead to a persistent depression of synaptic respones.
Parvalbumin‐immunoreactive structures of the adult human entorhinal and transentorhinal region
Authors: Schmidt S. , Braak E. , Braak H. 
Published: May 2005

AbstractParvalbumin‐immunoreactive structures in the entorhinal and transentorhinal region of the adult human brain were studied using the avidin‐biotin‐peroxidase technique. Parvalbumin‐immunoreactive neurons and fibers (axons) were present in all layers (layer nomenclature according to Rose, 1927). The density of fibers was high in the islands of the superficial cell layer pre‐α and in layer pre‐β and still heavier in pre‐γ. In the subjacent lamina dissecans it diminished abruptly and remained low in all layers of the internal principal stratum (layers pri‐α, ‐β, ‐γ). This low density of fibers facilitated recognition of axon cartridges in layers pri‐α and pri‐γ. Axon cartridges were also present within layers pre‐β and pre‐γ but were obscured by the dense fiber network there. Parvalbumin immunoreactivity was observed in the nerve cell soma and throughout the dendritic tree allowing the distinction of numerous nerve cell types. All parvalbumin‐immunoreactive neurons belonged to the class of nonpyramidal neurons. Their lipofuscin pigment patterns differed distinctly from that of the pyramidal and modified pyramidal neurons. Based on their location, soma size, and dendritic arborization, they were grouped as large, mediumsized, and small neurons either of the multipolar or bipolar (vertical or horizontal) type. One type could be identified as an axo‐axonic neuron, more specifically as a chandelier neuron generating axon cartridges. The dense fiber net within layer pre‐γ suggested the existence of another neuronal type, probably a neuron with an extended axonal ramification. The identified neurons were compared to neuronal types described in the literature from Golgi studies.
Transneuronal changes in dendrites of GABAergic parvalbumin‐containing neurons of the rat fascia dentata following entorhinal lesion
Authors: Nitsch Robert , Frotscher Michael 
Published: May 2005

AbstractThe perforant path fibers from the entorhinal cortex form synapses with both granule cells and GABAergic, parvalbumin‐containing (PARV) nongranule cells. The authors recently reported a persistent reduction of PARV‐positive dendrites in the termination zones of entorhinal fibers in the hippocampus proper and fascia dentata after lesion of the entorhinal cortex. In the present study the authors analyzed the effects of de‐entorhination on the ultrastructure of postsynaptic PARV‐positive dendrites in the molecular layer of the fascia dentata. PARV immunocytochemistry was performed 2, 8, 55, and 360 days after an ipsilateral entorhinal lesion and, for comparison, 10 days after an ipsilateral fimbria‐fornix transection that disconnects the hippocampus from its septal and commissural afferents. Two days after entorhinal lesion, the authors observed swelling of the tissue close to the hippocampal fissure. Adjacent distal dendritic tips of PARV‐positive dendrites in the former perforant path termination zone persisted 55 days after entorhinal lesion and could still be observed after postlesional survival times for 1 year. Degenerating axon terminals were still present 55 days following lesion and PARV‐positive dendrites exhibited abnormal invaginations. Fimbria transection did not result in similar dendritic changes in PARV‐positive neurons. The results indicate a long‐lasting process of reorganization in the molecular layer of the fascia dentata followin entorhinal lesion and persisting changes in the morphology of PARV‐immunoreactive dendrites. Entorhinal fibers seem to play a specific role for the maintenance of these dendrites, since similar changes did not occur following removal of septal and commissural fibers.
Mapping the differential effects of procaine on frequency and amplitude of reticularly elicited hippocampal rhythmical slow activity
Authors: Kirk I. J. , McNaughton N. 
Published: May 2005

AbstractHippocampal rhythmical slow activity (RSA, theta) was elicited in urethanized rats by high‐frequency stimulation in the reticular formtion. The effects of procaine infusion (0.5 μL, 20% wt/vol) at various loci in the ascending system from pontine reticular formation to the medial septum/diagonal band area were investigated. It was found that procaine injected at points in the ascending system anterior to the supramamillary nucleus, in the region of the medial forebrain bundle or in the medial septum, reduced the amplitude of reticularly elicited RSA but had no effect on its frequency. Procaine injected at points in the ascending system from just anterior to the reticular formation stimulation site, up to, and including the supramamillary nucleus, reduced both the frequency and amplitude of reticularly elicited RSA. These results indicate that the frequency of reticularly elicited RSA is encoded in the supramamillary area, rather than in the medial septum/diagonal band as have previously been suggested.
Rapid decline of GABAA receptor subunit mrna expression in hippocampus following transient cerebral ischemia in the gerbil
Authors: Li Huiling , Siegel Ruth E. , Schwartz Rochelle D. 
Published: May 2005

AbstractInhibitory neurotransmission may play an important role in neuronal degeneration following transient cerebral ischemia. We studied the effect of transient forebrain ischemia on the GABAA receptor system in the gerbil hippocampus. Gerbils were subjected to 5 minutes of bilateral carotid occlusion and were sacrificed at various times over 4 days following reperfusion. There was a substantial loss of pyramidal cells in the CA1 area of the hippocampus, granule cell layer of the dentate gyrus, and ventroposterior medial and ventroposterior lateral nuclei of the thalamus at any time following ischemia. Examination of brain slices by in situ hybridization histochemistry revealed that a change in expression of the GABAA receptor α1 and β2 subunit mRNAs occurred in two phases following onset of reperfusion. The early phase (rapid) occurred within the first 4 hours following reperfusion. The expression of mRNAs significantly decreased (up to 25%) within 1 hour after occlusion in CA1 and CA3 pyramidal cell layers of the hippocampus and in the granule cell layer of the dentate gyrus. The expression of the mRNAs in these regions continued to decrease for 4 hours (up to 43%). In the second phase, which began between 4 and 12 hours following reperfusion, mRNA expression started to return to control levels in CA3 hippocampus and in the dentate. However, expression of both mRNAs continued to decline slowly in the CA1 pyramidal cell layer (up to 85%) over the next 3 days, concomitantly with degeneration of the CA1 pyramidal cells. Expression of mRNAs in the ventroposterior medial or ventroposterior lateral nuclei of the thalamus was similar to control values. To determine if a change in GABAA receptor distribution paralleled changes in receptor subunit mRNA expression, we also measured the binding of [35S]t‐butylbicylophosphorothionate to GABAA receptor chloride channels. The t‐butylibicyclophosphorothionate [35S] binding decreased between 1 and 4 days after reperfusion in the dendritic fields of CA1 pyramidal cells (strata oriens, radiatum, and lacunosum‐moleculare) but not in the pyramidal cell body layer. These results indicate that expression of GABAA receptor subunit mRNAs decrease well before CA1 pyramidal cell degeneration and loss of GABAA receptors. At present, it is not clear if an early loss of mRNA expression after an ischemic insult leads to a functional defect in GABAA receptors. If so, a loss of GABA neurotransmission may contribute to the development of neuronal degeneration following cerebral ischemia. The maintenance of normal GABA neurotransmission in surviving cells may explain their resistance to ischemia‐induced neuronal death.
Electrophysiological characterization of CA2 pyramidal cells from epileptic humans
Authors: Williamson Anne , Spencer Dennis D. 
Published: May 2005

AbstractThe CA2 region of the hippocampus is more resistant to the principal cell loss seen in CA1 and CA3 in both animal models of temporal lobe epilepsy and in medial temporal lobe sclerosis (MTS), a common neuropathological finding in human temporal lobe epilepsy. There is extensive synaptic reorganization in the MTS hippocampi that is not seen in the hippocampi of patients with tumor–associated temporal lobe epilepsy (TTLE). The authors examined the electrophysiological properties of CA2 pyramidal cells from these two types of human hippocampi. The two main findings are that most MTS cells do not have clear evidence for inhibition yet do not fire synaptically evoked bursts; and that mossy fiber stimulation could evoke excitatory postsynaptic potentials (EPSPs) in the MTS tissue, but not the TTLE cells. These data suggest that in MTS, CA2 cells are resistant to firing epileptiform bursts which may account for their survival. Moreover, the granule cell–CA2 cell connection represents a novel from of synaptic plasticity in this disease. © 1994 Wiley‐Liss, Inc.