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Pharmacological and electrophysiological evidence for a role of the median raphe nucleus in the control of hippocampal theta rhythm

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Date Issued:
1994
Summary:
Available evidence suggests that the median raphe nucleus (MRN), when activated, produces a desynchronized hippocampal electroencephalog ram (EEG), and that this effect is sensitive to serotonergic (5-HT) manipulations. Experiment 1 examined the effect of injections into the MRN of agents that non-specifically (procaine) or selectively (8-OH-DPAT and buspirone) inhibit serotonin-containing MRN neurons. These substances produced hippocampal theta rhythm at short latencies and for long durations, suggesting that MRN 5-HT neurons are specifically responsible for controlling the hippocampal EEG. MRN 5-HT neurons are modulated by a facilitatory excitatory amino acid (EAA) input and an inhibitory influence from GABAergic interneurons within the MRN. Experiments 2 and 3 examined the effect of manipulations of these systems on the hippocampal EEG. Experiment 2 demonstrated that injections of the specific (AP-7) and non-specific (MK-801) NMDA antagonists, as well as the kainate/quisqualate antagonist (GAMS) into the MRN produce theta at short latencies and for long durations. Experiment 3 demonstrated that injections of the GABA$\sb{\rm A}$ agonist, muscimol, into the MRN produced hippocampal theta rhythm at short latencies and for long durations. In light of recent evidence suggesting a theta-pacemaker role for numerous brain nuclei, experiment 4 sought to re-examine the role of the medial septum/diagonal band complex (MS/DB) in hippocampal theta rhythm produced by injections of 8-OH-DPAT into the MRN. Four categories of MS/DB neurons were described: (1) cells which burst rhythmically with theta (rhythmical); (2) cells displaying a tonic increase in discharge with theta (theta-on); (3) cells displaying a dramatic decrease or cessation of discharge with theta (theta-off); and (4) cells which showed no changes in discharge in relation to theta (no-change). It was shown that injections of 8-OH-DPAT into the MRN caused a change in discharge of rhythmic MS/DB cells from an irregular non-bursting pattern during baseline conditions to a rhythmical, bursting pattern which was highly coherent with the hippocampal EEG.
Title: Pharmacological and electrophysiological evidence for a role of the median raphe nucleus in the control of hippocampal theta rhythm.
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Name(s): Kinney, Gene G.
Florida Atlantic University, Degree Grantor
Charles E. Schmidt College of Science
Department of Psychology
Type of Resource: text
Genre: Electronic Thesis Or Dissertation
Issuance: monographic
Date Issued: 1994
Publisher: Florida Atlantic University
Place of Publication: Boca Raton, Fla.
Physical Form: application/pdf
Extent: 152 p.
Language(s): English
Summary: Available evidence suggests that the median raphe nucleus (MRN), when activated, produces a desynchronized hippocampal electroencephalog ram (EEG), and that this effect is sensitive to serotonergic (5-HT) manipulations. Experiment 1 examined the effect of injections into the MRN of agents that non-specifically (procaine) or selectively (8-OH-DPAT and buspirone) inhibit serotonin-containing MRN neurons. These substances produced hippocampal theta rhythm at short latencies and for long durations, suggesting that MRN 5-HT neurons are specifically responsible for controlling the hippocampal EEG. MRN 5-HT neurons are modulated by a facilitatory excitatory amino acid (EAA) input and an inhibitory influence from GABAergic interneurons within the MRN. Experiments 2 and 3 examined the effect of manipulations of these systems on the hippocampal EEG. Experiment 2 demonstrated that injections of the specific (AP-7) and non-specific (MK-801) NMDA antagonists, as well as the kainate/quisqualate antagonist (GAMS) into the MRN produce theta at short latencies and for long durations. Experiment 3 demonstrated that injections of the GABA$\sb{\rm A}$ agonist, muscimol, into the MRN produced hippocampal theta rhythm at short latencies and for long durations. In light of recent evidence suggesting a theta-pacemaker role for numerous brain nuclei, experiment 4 sought to re-examine the role of the medial septum/diagonal band complex (MS/DB) in hippocampal theta rhythm produced by injections of 8-OH-DPAT into the MRN. Four categories of MS/DB neurons were described: (1) cells which burst rhythmically with theta (rhythmical); (2) cells displaying a tonic increase in discharge with theta (theta-on); (3) cells displaying a dramatic decrease or cessation of discharge with theta (theta-off); and (4) cells which showed no changes in discharge in relation to theta (no-change). It was shown that injections of 8-OH-DPAT into the MRN caused a change in discharge of rhythmic MS/DB cells from an irregular non-bursting pattern during baseline conditions to a rhythmical, bursting pattern which was highly coherent with the hippocampal EEG.
Identifier: 12364 (digitool), FADT12364 (IID), fau:9265 (fedora)
Collection: FAU Electronic Theses and Dissertations Collection
Note(s): Adviser: Robert P. Vertes.
Thesis (Ph.D.)--Florida Atlantic University, 1994.
Subject(s): Biology, Neuroscience
Health Sciences, Pharmacology
Biology, Animal Physiology
Held by: Florida Atlantic University Libraries
Persistent Link to This Record: http://purl.flvc.org/fcla/dt/12364
Sublocation: Digital Library
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Host Institution: FAU
Is Part of Series: Florida Atlantic University Digital Library Collections.