Author Type

Graduate Student

Date of Award

1994

Document Type

Thesis

Publication Status

Version of Record

Submission Date

October 2026

Abstract

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.

Extent

152 p.

Comments

FAU Electronic Theses and Dissertations Collection|Adviser: Robert P. Vertes.|Thesis (Ph.D.)--Florida Atlantic University, 1994.|FAU Electronic Theses and Dissertations Collection

Identifier

FADT12364

Format

pdf

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