摘要:

AbstractThe hippocampal formation presents a special opportunity for realistic neural modeling since its structure, connectivity, and physiology are better understood than that of other cortical components. A review of the quantitative neuroanatomy of the rodent dentate gyrus (DG) is presented in the context of the development of a computational model of its connectivity. The DG is a three‐layered folded sheet of neural tissue. This sheet is represented as a rectangle, having a surface area of 37 mm2and a septotemporal length of 12 mm. Points, representing cell somata, are distributed in the model rectangle in a roughly uniform fashion. Synaptic connectivity is generated by assigning each presynaptic cell a spatial zone representing its axonal arbor. For each postsynaptic cell, a list of potential presynaptic cells is compiled, based on which arbor zones the given postsynaptic cell falls within. An appropriate number of presynaptic inputs are then selected at random. The principal cells of the DG, the granule cells, are represented in the model, as are non‐principal cells, including basket cells, chandelier cells, mossy cells, and GABAergic peptidergic polymorphic (GPP) cells. The neurons of layer II of the entorhinal cortex are included also. The DG receives its main extrinsic input from these cells via the perforant path. The basket cells, chandelier cells, and GPP cells receive perforant path and granule cell input and exert both feedforward and feedback inhibition onto the granule cells. Mossy cells receive converging input from granule cells and send their output back primarily to distant septotemporal levels, where they contact both granule cells and non‐principal cells. To permit numerical simulations, the model must be scaled down while preserving its anatomical structure. A variety of methods for doing this exist. Hippocampal allometry provides valuable clues in this regard. © 1995 Wiley‐L

ISSN:1050-9631    

DOI:10.1002/hipo.450050402

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

年代:1995

数据来源: WILEY

摘要:

AbstractIn the rat dentate gyrus, pyramidal‐shaped cells located on the border of the granule cell layer and the hilus are one of the most common types of γ‐aminobutyric acid (GABA)‐immunoreactive neurons. This study describes their electrophysiological characteristics. Membrane properties, patterns of discharge, and synaptic responses were recorded intracellularly from these cells in hippocampal slices. Each cell was identified as pyramidal‐shaped by injecting the marker Neurobiotin intracellularly (n =17).In several respects the membrane properties of the sampled cells were similar to “fast‐spiking” cells (putative inhibitory interneurons) that have been described in other areas of the hippocampus. For example, input resistance was high (mean 91.3 megohms), the membrane time constant was short (mean 7.7 ms), and there was a large afterhyperpolarization following a single action potential (mean 10.5 mV at resting potential). However, the action potentials of most pyramidal‐shaped cells were not as brief (mean 1.2 ms total duration) as those of most previously described fast‐spiking cells. Many pyramidal‐shaped neurons had strong spike frequency adaptation relative to other fast‐spiking cells. Although these latter two characteristics were apparent in the majority of the sampled cells, there were exceptional pyramidal‐shaped neurons with fast action potentials and weak adaptation, demonstrating the electrophysiological variability of pyramidal‐shaped cells.Responses to outer molecular layer stimulation were composed primarily of excitatory postsynaptic potentials (EPSPs) rather than inhibitory postsynaptic potentials (IPSPs), and were usually small (EPSPs evoked at threshold were often less than 2 mV), and brief (less than 30 ms). There was variability, because in a few cells EPSPs evoked at threshold were much larger. However, regardless of EPSP amplitude, suprathreshold stimulation (up to 4 times the threshold stimulus strength) rarely evoked more than one action potential in any cell. The results suggest that stimulation of perforant path axons produces limited excitatory synaptic responses in pyramidal‐shaped neurons. This may be one of the reasons why they are relatively resistant to prolonged perforant path stimulation.The pyramidal‐shaped neurons located at the base of the granule cell layer have been associated historically with a basket plexus around granule cell somata, and have been called pyramidal “basket” cells. However, basket‐like endings were rare and axon collaterals outside the granule cell layer were common. Many axon collaterals were as far from the granule cell layer as the outer molecular layer and the central hilus, and antidromic action potentials could be recorded in some cells in response to weak stimulation of these areas. Taken together with the electrophysiological variability, the results indicate that these cells are physiologically h

ISSN:1050-9631    

DOI:10.1002/hipo.450050403

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

年代:1995

数据来源: WILEY

摘要:

AbstractSingle‐unit discharge patterns of entorhinal cortex (EC) cells were characterized in relation to simultaneously recorded hippocampal (HPC) field activity according to criteria used previously to classify cells in the hippocampal formation, medial septum, cingulate cortex, and caudal diencephalon. EC cells related to HPC theta field activity were classified as (1) phasic theta‐on, if they discharged rhythmically, and in phase, with ongoing HPC theta, but nonrhythmically during large, irregular hippocampal field activity (LIA); (2) tonic theta‐on, if they discharged nonrhythmically and increased their discharge rates during HPC theta relative to LIA; (3) phasic theta‐off, if they discharged rhythmically, and in phase, with ongoing HPC theta, but increased their discharge rates during LIA; and (4) tonic theta‐off, if they discharged nonrhythmically and decreased their discharge rates during HPC theta relative to LIA. Cells not meeting any of these criteria were classified as nonrelated. A total of 168 EC cells were recorded, and of these 56 (33%) were classified as theta related, with the remaining 112 (67%) classified as nonrelated. Of the 56 theta‐related cells, 41 (73%) had significantly higher discharge rates during HPC theta than during LIA and were classified as theta‐on cells (15 phasic theta‐on cells and 26 tonic theta‐on cells). Nine of the 26 tonic theta‐on cells showed a phase relation of their arrhythmic discharges to simultaneously recorded HPC theta field activity. EC phasic theta‐on cells did not discharge preferentially on any portion of the HPC theta field recorded from the region of the stratum moleculare of the dentate gyrus. In general, cells classified as phasic revealed a wide distribution of phase preferences. The remaining 15 (26.7%) cells were classified as theta‐off cells and discharged at higher rates during HPC LIA than during HPC theta field activity (3 phasic theta‐off cells and 12 tonic theta‐off cells). Systemic administration of physostigmine significantly increased the discharge rate of tonic and phasic theta‐on cells relative to LIA. Electrical stimulation in the posterior hypothalamic region (PH) significantly increased the discharge rate of EC theta‐on cells and significantly decreased the discharge rate of EC theta‐off cells relative to HPC LIA. The discharge rates of nonrelated EC cells were not influenced by electrical stimulation of the PH. Procaine microinfusion into the medial septum (MS) abolished spontaneously occurring HPC theta and theta induced with PH stimulation. In addition, 5 min after MS procaine, the ability of PH stimulation to modulate EC theta‐on cell discharge was abolished. The modulation of cellular discharges produced by PH stimulation recovered by 60 min post‐procaine infusion into the MS. The findings support two main conclusions: (1) theta‐related cells in the EC are comprised of two main populations of cells, theta‐on and theta‐off, similar to other regions of limbic cortex and nuclei of the ascending brainstem synchronizing pathway; (2) the ascending brainstem synchronizing pathway exerts both similar and parallel effects on theta‐related cells in entorhinal c

ISSN:1050-9631    

DOI:10.1002/hipo.450050404

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

年代:1995

数据来源: WILEY

摘要:

AbstractSeveral neurosteroids have proconvulsant and memory‐en‐hancing properties and are potent modulators of the γ‐amino butyric acid (GABA) receptor/chloride‐ionophore complex. The effects of in situ microelectrophoretic application of the natural sulfate ester of the neurosteroid dehydroepiandrosterone (DHEAS) on evoked field responses and single‐unit activity were evaluated in the dentate gyrus and CA1 hippocampal subfield of halothane‐anesthetized rats. The effects of endogenous stimulation of DHEAS by in situ micropressure application of Trilostane ((4α, 5α, 17β)‐4, 5‐epoxy‐3, 17‐dihydroxyandrost‐2‐ene‐2‐carbonitrile (WIN24540)), an inhibitor of 3β‐hydroxysteroid dehydrogenase/isomerase (3β‐HSD), the enzyme that metabolizes DHEAS, on evoked responses and cellular activity in the hippocampus were also investigated. In situ microelectrophoretic application of DHEAS or micropressure application of Trilostane into CA1 markedly increased population excitatory postsynaptic potential (pEPSP) slopes and population spike (PS) amplitudes. Neither DHEAS nor Trilostane altered dentate pEPSP slopes or PS amplitudes, but both increased the amplitude of a late component of the pEPSP. Both DHEAS and Trilostane abolished GABA‐mediated pairedpulse inhibition in both the dentate and CA1. In addition, both DHEAS and Trilostane markedly increased the spontaneous firing rate of dentate hilar interneurons (INTs: 256% and 185%), CA1 pyramidal cells (PCs: 95% and 105%), and CA1 oriens/alveus (O/A) interneurons (179% and 85%) and synchronized their firing to hippocampal theta rhythm induced by tail‐pinch. These findings indicate that exogenous application and endogenous stimulation of DHEAS modulates hippocampal GABA inhibition in a physiologically relevant manner possibly by entraining hippocampal neuron

ISSN:1050-9631    

DOI:10.1002/hipo.450050405

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

年代:1995

数据来源: WILEY

摘要:

AbstractBy means of Timm's procedure and computer‐assisted morphometry, the left and right hippocampi of 69 hybrid guinea pigs from nine age levels (P5, P10, P20, P40, P80, P160, P320, and P610, and P1100) were analyzed for postnatal growth of recurrent hippocampal mossy fiber collaterals (RMFC) terminating below, within, and above the dentate granule cell layer. Postnatal growth of RMFCs showed, in both sexes, a first peak at P40, with stainable mossy fiber boutons covering the cell bodies of large neurones, some of which were reminiscent of basket cells. No significant changes of the density of mossy fiber collaterals were noticed from P40 to P160. At P320 a remarkable expansion of RMFCs was noted in a few animals, and by P610 all animals showed highly proliferated RMFCs which densely covered cell bodies and dendrites of target cells. The oldest group (P1100) showed an equal or slightly lowered density of RMFCs.We conclude that the growth of recurrent mossy fiber collaterals occurs in two spurts. The first completes just before sexual maturity. The second spurt occurs in the mid‐life period, between P160 and P610. © 1995 Wiley‐Lis

ISSN:1050-9631    

DOI:10.1002/hipo.450050406

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

年代:1995

数据来源: WILEY

摘要:

AbstractFollowing transient global ischemia most of the neurons containing somatostatin in the fascia dentata of the dorsal hippocampal formation die, while somatostatinergic neurons in the CA1 region survive. These neurons react to ischemia with a transiently reduced expression of somatostatin mRNA and peptide. We have tested the hypothesis that this selective vulnerability is solely related to those somatostatinergic neurons which do not express the calcium‐binding protein parvalbumin. Postischemic changes were studied in rat dorsal hippocampus at 2 and 16 days after 10 min of global cerebral ischemia using a four‐vessel occlusion model. We performed a double‐staining visualizing the mRNA coding for somatostatin by non‐radioactive in situ hybridization and parvalbumin protein by immunocytochemistry. Only 5% of the somatostatinergic cells in the fascia dentata contained parvalbumin. The number of somatostatinergic cells was permanently reduced following ischemia. Among surviving neurons we found cells with and without parvalbumin expression. Thus, expression of parvalbumin is not predictive for survival of somatostatinergic cells in the fascia dentata. In contrast, in CA1, 37% of the somatostatinergic cells contained parvalbumin. These cells were unaffected by the transient ischemic period. The somatostatinergic cells lacking parvalbumin showed transiently reduced mRNA levels at day 2, but recovered to control values at the 16th postischemic day. Thus, expression of the calcium‐buffering protein parvalbumin coincides with resistance of somatostatinergic neurons in CA1 to transient effects of ischemia.We conclude that the calcium‐buffering capacity of parvalbumin may partially contribute to the protection of somatostatinergic neurons from ischemia in the dorsal hippocampus. However, the survival of somatostatinergic cells without parvalbumin indicates the importance of other factors as well. © 1995 Wil

ISSN:1050-9631    

DOI:10.1002/hipo.450050407

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

年代:1995

数据来源: WILEY

摘要:

AbstractThis study describes changes in the immunoreactivity for muscarinic acetylcholine receptors (mAChRs) in the hippocampus of mice in relation to spatial discrimination behavior, employing the monoclonal antibody M35 raised against purified bovine mAChR protein. Performance in a hole board in which the animals learned the pattern of 4 baited holes out of 16 holes served as the measure of spatial discrimination learning and memory. Twenty‐six adult male house mice were used, divided into four groups. Three groups served as various controls: group N (naive; blank controls); group H (habituated; animals were introduced to the hole board with all holes baited for 5 consecutive days), and group P (pseudotrained; the animals were admitted to the hole board for 13 consecutive days with all holes baited). The T group (trained) was subjected to the hole board for 5 consecutive habituation days with all holes baited (similar to the H and P groups), followed by 8 successive training days with only four holes baited in a fixed pattern. During the 8 training days, the T group gradually acquired a pattern to visit the baited holes, whereas the P group continued visiting holes in a random fashion. The mice were killed 24 h after the last behavioral session.All principal cells in the cornu ammonis (CA) and dentate gyrus (DG) of the habituated animals revealed increased levels of mAChR immunoreactivity (mAChR‐ir) over the naive mice. A minor increase in mAChR‐ir was found in the apical dendrites of the CA1 pyramidal cells. Pseudotraining resulted in a CA1‐CA2 region with a low level of mAChR‐ir, resembling naive animals, whereas the trained mice showed a further increase in mAChR‐ir in the CA1‐CA2 pyramidal cell bodies and apical dendrites. Optical density measures of the mAChR‐ir in the CA1 region revealed a significant (P<0.05) increase in the pyramidal cell bodies of the H and T group over the N and P group, and a significant (P<0.05) increase in the apical dendrites of the T group over all other groups. In contrast to the CA1‐CA2 region, both pseudotrained and trained mice revealed high mAChR staining in the CA3‐CA4 region and the DG. These results indicate that prolonged exposure to the hole board is sufficient for an enhanced mAChR‐ir in the CA3‐CA4 and DG, whereas the increase in CA1‐CA2 pyramidal cells is a training‐specific feature related to spatial orientation. Nonpyramidal neurons within the CA1‐CA2 region with enhanced mAChR‐ir in the pyramidal cells, however, revealed a decreased level of mAChR‐ir. The opposing effect of pyramidal and nonpyramidal cells suggests a shift in the excitability of the hippocampal microcircuitry.Previously we demonstrated an increase and redistribution of hippocampal protein kinase C γ‐immunoreactivity (PKC γ‐ir) induced by hole board learning in mice (Van der Zee et al., 1992, J Neurosci 12:4808–4815). Immunofluorescence double‐labeling experiments conducted in the present study in naive and trained animals revealed that the principal cells and DG interneurons co‐express mAChRs and PKCγ, and that the immunoreactivity for both markers increased in relation to spatial orientation within these neurons. The mAChR‐positive nonpyramidal cells of the CA1‐CA2 region were devoid of PKCγand revealed an opposite training‐induced effect. These results suggest that the postsynaptic changes in mAChR‐ and PKCγ‐ir reflect functional alterations of the hippocampal for

ISSN:1050-9631    

DOI:10.1002/hipo.450050408

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

年代:1995

数据来源: WILEY

摘要:

AbstractThirteen dogs were trained to perform spatial delayed responses to auditory cues in a three‐choice Nencki testing apparatus with a delay of 0 s and then 10 s with a criterion of 90% correct responses in 90 consecutive trials. Then six dogs received bilateral surgical removal of the hippocampus via the cortex of the suprasylvian gyrus (without additional injury to the entorhinal and parahippocampal cortex). Three dogs received control surgical ablation of the suprasylvian gyrus, which was damaged in ablation of the hippocampus, and four dogs served as intact controls. After the surgery or rest period, the dogs were tested for their retention (10‐s delay), and then they were given additional tests with extended delays (30, 60, and 120 s) and with distractions during the 60‐s delay period. In comparison with both control groups, dogs with hippocampal ablations had moderately impaired postoperative retention, as evidenced by the elevated numbers of errors on criterion. In subsequent stages of testing with extended delays, the impairment was greater and was significantly correlated with the extent of injury to the hippocampus. These data, together with an analysis of the animals' responses to the three‐choice situation, indicate that in dogs lesions of the hippocampus impair spatial memory. © 1995 Wiley

ISSN:1050-9631    

DOI:10.1002/hipo.450050409

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

年代:1995

数据来源: WILEY

ISSN:1050-9631    

DOI:10.1002/hipo.450050401

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

年代:1995

数据来源: WILEY