摘要:

AbstractResponses to theta pattern stimulation, and the long‐term potentiation (LTP) they induce, were compared in the basal versus apical dendrites of neurons in field CA1 of hippocampus. A series of 10 theta bursts produced more than twice as much LTP in basal synapses as in their apical counterparts as measured with field EPSPs. This confirms earlier field potential studies showing that the maximum degree of potentiation (the LTP ceiling) is considerably greater in stratum oriens than stratum radiatum. Experiments with whole‐cell clamp recording obtained similar results, indicating that synapses at different loci on the same neuron reach different LTP ceilings following prolonged theta burst stimulation. The basal synapses also required fewer theta bursts to reach their LTP ceiling than did the apical synapses. Tests with paired‐pulse facilitation and an antagonist of the NMDA receptor gave no indication that the greater LTP in basal synapses was qualitatively different from the lesser effect obtained in apical contacts. Intracellular recording revealed significant differences between basal versus apical responses to single theta bursts and trains of bursts: the within‐burst depolarization was greater and the between‐burst hyperpolarization was smaller for the basal dendritic responses. These two variables have previously been proposed to influence the magnitude of LTP and the observed differences between basal versus apical synapses are in accord with this hypothesis. Together with recently described immunocytochemical results, the findings reported here suggest that variations in LTP across dendritic subfields of hippocampus reflect a differential distribution of a subclass of GABAergic int

ISSN:1050-9631    

DOI:10.1002/hipo.450040103

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

年代:1994

数据来源: WILEY

摘要:

AbstractIntracellular recordings were made from rabbit hippocampal CA1 neuronsin vitrousing slices from aging and young adult rabbits. Calcium action potentials were studied in the presence of 4 μm tetrodotoxin using electrodes filled with 2M CsCl. Increasing concentrations of the dihydropyridine L‐type calcium channel antagonist nimodipine were tested on the amplitude and time course of calcium action potentials. The calcium action potential (AP) consisted of two components: an initial fast phase followed by a slower plateau phase. No difference in the peak amplitude of the initial fast phase was observed between age groups. The amplitude and duration of the slower plateau phase of the calcium AP was significantly larger in aging neurons. Switching to a zero Ca2+medium in the presence of 200 μm CdCl2completely blocked the calcium AP. Nimodipine decreased the plateau phase of the calcium AP at concentrations as low as 100 nm in aging neurons and 10 μm in young neurons. Switching to higher concentrations of nimodipine did not reveal any substantially increased block of the calcium AP plateau phase. These data suggest that enhanced calcium influx through L‐type calcium channels is largely responsible for the enhanced calcium action potentials observed in aging CA1 neurons. The action of nimodipine in reducing the plateau phase of the calcium action potential may underlie the drug's notable ability to improve learning in hippocampally dependent tasks in aging a

ISSN:1050-9631    

DOI:10.1002/hipo.450040104

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

年代:1994

数据来源: WILEY

摘要:

AbstractIn this study, the patch‐clamp technique was applied to brain slices to test for the presence of GABAAand glutamate receptors in glial cells of an intact tissue preparation, the hippocampus from 9–12 day old mice. Two types of glial cells were studied in the CA1 stratum pyramidale, termedpassiveandcomplexcells, which were distinct by their characteristic pattern of voltage‐dependent currents. Both cell types were previously identified as glial by combining electrophysiology with ultrastructural inspection (Steinhäuser et al., 1992, Eur J Neurosci 4:472–484). A subpopulation of passive cells was positive, all complex cells were negative for immunocytochemical staining against glial fibrillary acidic protein, a marker of mature astrocytes. In both cell types, GABA activated currents compatible with GABAA‐receptor mediated responses. The glutamate response in complex and in most of the passive cells was mediated by a ligand‐gated ion channel and closely matched the pharmacology of the kainate receptor. Activation of glutamate receptors led to a transient decrease of the resting K+conductance in complex cells and to an irreversible decrease in the passive cells. In three passive cells, glutamate‐activated currents were most likely dominated by an electrogenic uptake. In a small group of passive cells NMDA‐activated currents were observed. This study provides evidence that glial cells from an intact tissue express receptors for the most abundant transmitters in the central nervous system, glu

ISSN:1050-9631    

DOI:10.1002/hipo.450040105

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

年代:1994

数据来源: WILEY

摘要:

AbstractField recordings of the entorhinal cortex (EC) were studied and compared to those recorded concomitantly in the dentate region of the hippocampal formation (HPC) in the urethane anesthetized rat. The EC, like the HPC, showed two main variations of spontaneous field activity: a desynchronized, large amplitude irregular activity and a synchronized, rhythmic, slow frequency field activity (RSA or theta). Corroborating previous research, a phase reversal was seen across layer II of the EC and when recorded superficial to this layer, EC theta was phase‐locked to that recorded from the HPC (dentate). Entorhinal cortex (and HPC) theta could be evoked by the application of moderate tail pinches (sensory stimulation), by pharmacological treatments enhancing cholinergic transmission, and by electrical stimulation of the posterior hypothalamus. Spectral analysis revealed that in all cases, theta was produced coherently across the two limbic structures. Entorhinal cortex (and HPC) production of theta could be abolished by pharmacological treatments disrupting cholinergic transmission, and by reversible procaine inactivation of the medial septal region. Therefore, it was concluded that limbic theta is modulated spontaneously, and with sensory and hypothalamic stimulation through the activity of cells in the medial septal region via muscarinic neurotransmission. It was also hypothesized that the activation of cells in the posterior hypothalamus linearly codes the frequency, and to a lesser extent the power, of EC and HPC theta. Given these findings and the coincidence and coherence of the occurrence of theta across the EC and HPC, it was postulated that it occurs via a parallel mechanism in the two area

ISSN:1050-9631    

DOI:10.1002/hipo.450040106

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

年代:1994

数据来源: WILEY

摘要:

AbstractIndividual differences in the extent of the infrapyramidal mossy fiber porjection (IIP‐MF) correlate with performance in tasks sensitive to hippocampal lesions, notably two‐way avoidance, radial maze learning, and swimming navigation. Previous studies of swimming navigation suggested that the capacity of reversal learning and measures of directionality might also be related to asymmetries in the distribution of the IIP‐MF. In order to verify these findings, the authors crossed the Collins High‐ and Low‐lateralized mice (known to differ in mossy fiber morphology and brain asymmetries) and obtained a F2‐generation characterized by strong individual differences in these traits. Twenty‐three (13 females, 10 males) mice were tested during 3 days for acquisition of swimming navigation (16 trials) toward a central platform, and during two days (12 trials) for their capacity of reversal learning toward a shifted platform. Morphometry of Timm‐stained hippocampi revealed several, partially independent correlations: Larger IIP‐MF projections were associated with prolonged crossing over the former platform position during the entire reversal learning; larger IIP‐MF projections on the left were correlated with more precise crossing of the former platform position during the first 45 seconds of reversal learning; both extent and asymmetry of IIP‐MF correlated positively with overnight improvement of reversal learning; the size of the entire mossy fiber projection (CA4, suprapyramidal and IIP‐MF) correlated positively with the time spent in the platform quadrant and measures of initial orientation during acquisition of the task; and the mice showed an ipsilateral turning bias (spin) toward the side with the larger mossy fiber projection. The authors conclude that an intact hippocampus mediates differential processes underlying swimming navigation, and that left and right subfields may have

ISSN:1050-9631    

DOI:10.1002/hipo.450040107

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe mossy cells represent a prominent cell type of the hilar region. Whereas the morphology of these neurons, their synaptic connections, and physiological characteristics have been described in some detail, information about their neurotransmitter is still lacking. Using immunocytochemistry in combination with Golgi impregnation, the authors demonstrate that identified mossy cells are GABA‐immunonegative but stain for glutamate. These results do not prove that these cells use glutamate as a transmitter, since glutamate is a ubiquitous metabolite. However, together with the lack of GABA staining and a recent report on asymmetric spine synapses formed by identified mossy cell axons, the present results support an excitatory nature of these neuron

ISSN:1050-9631    

DOI:10.1002/hipo.450040108

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

年代:1994

数据来源: WILEY

摘要:

AbstractProtein kinase C (PKC) is highly concentrated in the hippocampus and is thus a possible neural substrate of learning and memory. This study was designed to determine whether partial acquisition (i.e., the minimal amount of training leading to above‐chance performance) of a spatial discrimination in an eight‐arm radial maze alters hippocampal PKC activity. Mice were sacrificed at different times (5 minutes, 1 hour, 24 hours) after the second learning session, and PKC activity was measured in both cytosolic and membrane fractions of the hippocampus. In order to determine which component of the task was involved in the alterations in enzymatic activity, hippocampal PKC activity was also measured in a group of mice that was allowed to explore the maze freely. Significantly less PKC activity was found in the cytosolic fraction from the trained animals than from the quiet or active control groups. No differences were observed between the quiet and active controls. In contrast, there were no significant between‐groups differences in membrane‐bound PKC activity, although a negative correlation between the membrane‐bound PKC activity and learning scores (accuracy) was noted. These results suggest that hippocampal PKC activity is involved essentially in the associative component of the task. The lack of learning‐induced alterations in membrane‐bound PKC activity and the negative correlation between this enzymatic activity and learning accuracy

ISSN:1050-9631    

DOI:10.1002/hipo.450040109

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

年代:1994

数据来源: WILEY

摘要:

AbstractChanges in hippocampal calbindin immunoreactivity were investigated after repeated electroconvulsive shocks. Adult rats were subjected to 10, 20, or 36 electroconvulsive shocks (50 mA, 0.5 seconds), given as on shock per day, 5 days a week. The rats were sacrificed and processed for calbindin immunohistochemistry 1, 2, and 30 days after the last electroconvulsive shock. In the rats receiving 10 or 20 electroconvulsive shocks, a selective reduction of the calbindin immunoreactivity of the dentate granule cell bodies, dendrites, and mossy fibers was noted 1 and 2 days after the last electroconvulsive shock. After 36 electroconvulsive shocks there was an almost complete loss of calbindin immunoreactivity from the granule cell bodies and dendrites, and the calbindin immunoreactivity of the mossy fibers was markedly reduced. Thirty days after the last of 36 electroconvulsive shocks, the calbindin immunoreactivity was back to normal. Besides demonstrating pronounced changes associated with repeated electroconvulsive shocks, the results confirm the transient nature of these changes.

ISSN:1050-9631    

DOI:10.1002/hipo.450040110

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

年代:1994

数据来源: WILEY

摘要:

AbstractMaterial for the study came from one 126 day‐old rhesus monkey fetus and two 3 day‐old neonates. The immunocytochemical detection of somatostatin, neurotensin (NT), parvalbumin, calbindin D‐28K, DARPP‐32 as well as tyrosine hydroxylase (TH), dopamine‐β‐hydroxylase and serotonin (5‐HT), was carried out on serial cryostat sections of the entorhinal cortex. The authors reported in a previous paper the precocious differentiation of the entorhinal cortex in rhesus monkey fetuses and featured the conspicuous expression of calbindin D‐28K, somatostatin, neurotensin, and the monoaminergic innervation during the first half of gestation. The present study shows distinct temporal profiles of neurochemical development during the second half of gestation: the dense neuropeptidergic innervation remained a constant feature; the three aminergic systems gradually increased in density; parvalbumin, unlike calbindin D‐28K, was primarily expressed during the last quarter of gestation. Three othe prominent features of the last quarter of gestation are illustrated: the refinement of the modular neurochemical organization of the lamina principalis externa, the delayed chemoanatomical development of the rhinal sulcus area, and the establishment of a distinct rostrocaudal pattern of neurochemical distribution. In correspondence with the cluster‐like organization of the lamina principalis externa, the authors observed in the olfactory, rostral, and intermediate fields of the neonate monkey entorhinal cortex, a particular subset of pyramidal‐shaped neurons: located in layer III, they were characterized by fasciculated apical dendrites ascending between the cellular islands of the discontinuous layer II and the coexpression of calbindin D‐28K and DARPP‐32. Besides, most of the other chemical systems displayed a distinct, area‐specific, patcy distribution, except for the homogeneously distributed noradrenergic innervation. In the olfactory and rostral fields, TH positive dopaminergic fibers accumulated on the neuronal islands of layers II‐III, and parvalbumin labeled fibers on those of layer III, whereas patches of 5‐HT and NT‐like reactive terminals were segregated between the cellular islands, overlapping the DARPP‐32/calbindin D‐28 K labeled dendritic bundles. At the opposite, in the intermediate field, 5‐HT positive terminals overlapped the cellular islands of layer II and thin fascicles of dopaminergic fibers ran in the inter island spaces. The somatostatin‐LIR innervation was apparently too dense to reveal a patchy distribution that existed at earlier developmental stages. In the cadual field, the patchy pattern was replaced by a predominant bilaminar type of distribution of NT, 5‐HT, and TH‐like positive afferents. Numerous parvalbumin positive multipolar neurons and basket cells participated to a dense parvalbumin labeled network, extending through layers II‐V, whose partial extrinsic origin is open to discussion. The rhinal sulcus, still reduced to a small dimple at E126, appeared fully developed at birth. The fundus of the sulcus was marked by a sharp decrease of the neurotensin and parvalbumin‐LIR innervations whereas the density of somatostatin and aminergic terminals increased markedly in the perirhinal cortex. Although a transitory overexpression of some of the neurochemical systems under study might occur during development, their modular organization in the lamina principalis externa of the neonate represents a basic feature of the entorhinal cortex and adds further support to the evidence that neurons of layers II‐III that project to different parts of the hippocampal formation, belong to distinct heterogeneous systems. This extensive prenatal development is in line with recent data emphasizing the critical role of limbic structures in early recognition memory in infant monkeys. The question arises, however, in view of the delayed development of the rhinal sulcus area, as to whether the preferential connections of the lateral entohinal and perirhinal cortex with regions of polymodal sensory convergence such as the prefrontal cortex and superior temporal gyrus might be established later than

ISSN:1050-9631    

DOI:10.1002/hipo.450040111

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

年代:1994

数据来源: WILEY

摘要:

AbstractWith the aim of establishing a quantitative structural basis for comparative and experimental studies, the volumes of the hippocampal subdivisions and the total number of neurons in each subdivision were estimated in domestic pig brains using modern stereological techniques. In addition to a detailed description of the stereological methods used in the analysis, comprehensive descriptions of the architectonic boundaries of the subdivisions are included. The absolute and relative volumes of the subdivisions were compared to those of a number of other species and the relationship between the number of neurons and the volume of the subdivisions was compared to that in homologous subdivisions of laboratory rats and humans. The methodology used to estimate the volumes and the total number of neurons in the individual subdivisions were evaluated with regard to the sensitivity that they can provide in experimental studies.

ISSN:1050-9631    

DOI:10.1002/hipo.450040112

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

年代:1994

数据来源: WILEY