Neuronal transmission in the dentate gyrus: role of inhibitory mechanisms

Assaf, S.Y.; Miller, J. F. A. P.

doi:10.1016/0006-8993(78)91091-0

Cited by 65 publications

(14 citation statements)

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“…Apparently contrary to either such simple interpretation, however, is the fact that the decline in latency of the population spike is consistent with the first dass of mechanism, but not with the second, whereas the dedine in spike amplitude is consistent with the second dass ofmechanism, but not with the first. As a general explanation for this overall pattern of results, it should be noted that numerous factors, such as momentary behavioral state, and activity levels in subcortical areas projecting to the hippocampus have been shown to affect the population spike for these responses, and often do so in the absence of any effects on EPSP values (Abraham & Goddard, 1982;Alvarez-Leefmans & Gardner-Medwin, 1975;Assaf, Mason, & Miller, 1979;Assaf & Miller, 1978;Dahl & Winson, 1986;Fantie & Goddard, 1982;Green, Barnes, & McNaughton, 1986;Robinson & Racine, 1986;Winson, 1980;Winson & Abzug, 1977Winson & Dahl, 1985). Changes in many ofthese factors almost certainly occur as a result of the behavioral manipulations used here.…”

Section: Discussionmentioning

confidence: 89%

Exploration-dependent modulation of evoked responses in fascia dentata: Fundamental observations and time course

1989

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The hippocampal formation is thought to be involved in spatiallearning. A role as a more general, intermediate-term memory store has also been suggested. In this report, we address a moderately persistent change in propagation of excitation through hippocampal circuitry which resulted from exposure of animals to environments in which they were free to move and explore. Rats were prepared for chronic recording of perforant path-evoked dentate granule-cell population responses. A large increase in the synaptic component of this response developed over the first several minutes after the animals were transferred to a different but not necessarily novel environment, and decayed with a time constant of about 5 min. This apparent growth in synaptic strength was remarkably weIl correlated with the animal's recent history of exploratory behavior, and was not due simply to handling or to the electrical stimulation. The amplitude of the population-spike component also varied over time, but was not obviously correlated with changes in the synaptic component. These response changes were different in both apparent mechanism and time course from previously reported, longer lasting, environmentally induced changes in the population-spike component. They also differed from the behavioral state-dependent gating effect reported by Winson and Abzug (1977) to the extent that the present effects long outlasted the behaviors that produced them. Although further analysis is required, it is possible that this phenomenon may reflect one mode of information storage in the hippocampal formation.

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Section: Discussionmentioning

confidence: 89%

Exploration-dependent modulation of evoked responses in fascia dentata: Fundamental observations and time course

1989

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“…The relevant SUM afferents travel through the ipsilateral column of fornix and dorsal fornix, whereas MS afferents project through the dorsal fornix/fimbria. 4. Single units recorded in stratum granulosum (SG) were assessed with respect to several parameters.…”

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confidence: 99%

“…8), median and dorsal raphe (e.g., Ref. 4), substantia nigra (32), the parafascicular region (9), and the brain stem reticular formation (38). Another major source of afferents originates in the supramammillary nucleus (SUM) of the hypothalamus (e.g., Refs.…”

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confidence: 99%

A comparison of supramammillary and medial septal influences on hippocampal field potentials and single-unit activity

Mizumori

McNaughton

Barnes

1989

Journal of Neurophysiology

132

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SUMMARYAND CONCLUSIONS 1. A comparison was made between the influences of supramammillary (SUM) and medial septal (MS) nuclei on hippocampal physiology in Nembutal-anesthetized rats. Specifically, the effects of prestimulation of the SUM or MS on the perforant path-dentate field potential, on spontaneous activity of single units, and on perforant path-induced unit activation were assessed. Another series of experiments addressed the issue of whether the SUM and MS effects on the perforant path-dentate field response are independent.2. Prestimulation of the SUM or MS significantly facilitated the perforant path-dentate population spike with no clear effect on the field excitatory postsynaptic potential (EPSP) recorded in the subgranular zone of the dentate hilus. Prestimulation of either nucleus also reduced the threshold for spike onset. The major differences between the two spike facilitation effects were the magnitude of the change and possibly the optimal interstimulus intervals required to obtain the effects.3. Acute transection of the ipsilateral column of fornix or dorsal fornix eliminated the SUM population spike facilitation effect. MS lesion or dorsal fornix/fimbria transection eliminated the MS spike facilitation effect. The MS lesion did not alter the effects of SUM prestimulation. Cingulum or medial forebrain bundle transection affected neither SUM-nor MS-mediated spike facilitation. Thus the SUM and MS influences on the dentate field response appear to be independent of one another. The relevant SUM afferents travel through the ipsilateral column of fornix and dorsal fornix, whereas MS afferents project through the dorsal fornix/fimbria.4. Single units recorded in stratum granulosum (SG) were assessed with respect to several parameters. These included the mean firing rate, whether or not excitation occurred prior to the field population spike and at lower threshold, and whether or not a driven unit responded to a second perforant path stimulus delivered at short latency following the first (during the period of population spike depression). The latter parameter in particular appeared to separate SG cells into two classes. The cells that were not activated during the second field potential were classified as granule cells, whereas those that were activated were classified as basket cells. Based on this distinction, significant differences were also found between the two cell classes on the other parameters. In particular, cells classified as granule cells often had very low firing rates. We conclude that many previous studies have mistakenly identified as granule cells inhibitory interneurons, which are much more commonly encountered (at least partly due to their higher discharge rates). This misidentification has led to several hypotheses concerning the mechanism of heterosynaptically induced population spike facilitation that we now conclude are untenable.5. Stimulation of the SUM or MS alone resulted in a reduction in the spontaneous firing rate of more than one-half of the cells recorded in the S...

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“…Despite the inhibitory effects on spontaneous activity of neurons in the hippocampus [1][2][3][4], activation of the forebrain serotonergic innervation in vivo, results in an increased responsiveness of dentate granule cells (DG) to afferent stimulation [4][5][6]. Although manipulations of intrahippocampal reactivity of neurons may underlie the serotonergic modulation of granule cells reactivity [4,6,[7][8][9][10][11], it is possible that these effects are mediated, in part by serotonergic effects on other forebrain areas, interacting with the hippocampus.…”

Section: Introductionmentioning

confidence: 99%

Raphe Grafts in the Hippocampus, But Not in the Entorhinal Cortex, Reverse Hippocampal Hyperexcitability of Serotonin-Depleted Rats and Restore Their Responsiveness to Fenfluramine

Richter‐Levin

Segal²

1992

Dev Neurosci

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We compared the effects of embryonic raphe grafted into either the hippocampus or the entorhinal cortex, on the responsiveness of dentate granule cells to stimulation of the perforant path. Raphe grafts in the hippocampus reversed the hyperexcitability of granule cells, resulting from depletion of the serotonergic innervation. Such grafts also restored the responsiveness of the granule cells to application of a serotonin releasing drug, fenfluramine (FFA). In contrast, hyperexcitability was not reversed when the graft was placed in the entorhinal cortex. Furthermore, although some increase in population spike size was observed in these rats after application of FFA, this increase had a response profile which was different from that of control and of lesioned rats that were grafted in the hippocampus. These results suggest that the serotonergic innervation, within the hippocampus and not in the entorhinal cortex, modulates granule cells excitability.

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Neuronal transmission in the dentate gyrus: role of inhibitory mechanisms

Cited by 65 publications

References 14 publications

Exploration-dependent modulation of evoked responses in fascia dentata: Fundamental observations and time course

Exploration-dependent modulation of evoked responses in fascia dentata: Fundamental observations and time course

A comparison of supramammillary and medial septal influences on hippocampal field potentials and single-unit activity

Raphe Grafts in the Hippocampus, But Not in the Entorhinal Cortex, Reverse Hippocampal Hyperexcitability of Serotonin-Depleted Rats and Restore Their Responsiveness to Fenfluramine

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