Differential modulation of hippocampal signal transfer by tuberomammillary nucleus stimulation in freely moving rats dependent on behavioral state

Tuberomammillary histamine neurons (TM) in the posterior hypothalamus project to extensive parts of the brain, including the hippocampal formation. The purpose of the present experiments was to investigate whether activation of the TM modulates signal transfer from the perforant pathway (PP) or vent...

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Bibliographic Details
Published in:Synapse (New York, N.Y.) N.Y.), 1998-04, Vol.28 (4), p.294-301
Main Authors: Weiler, H.-T., Hasenöhrl, R.U., van Landeghem, A.A.L., van Landeghem, M., Brankack, J., Huston, J.P., Haas, H.L.
Format: Article
Language:English
Subjects:
Animals
Behavior, Animal - physiology
behavioral modulation
dentate gyrus
Dentate Gyrus - physiology
Electric Stimulation - methods
Exploratory Behavior - physiology
hippocampus
Hippocampus - physiology
histamine
Male
Mammillary Bodies - physiology
perforant path
Perforant Pathway - physiology
rat
Rats
Rats, Wistar
Signal Transduction - physiology
synaptic plasticity
theta rhythm
ventral hippocampal commissure
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Summary:Tuberomammillary histamine neurons (TM) in the posterior hypothalamus project to extensive parts of the brain, including the hippocampal formation. The purpose of the present experiments was to investigate whether activation of the TM modulates signal transfer from the perforant pathway (PP) or ventral hippocampal commissure (VHC) to the dentate gyrus (DG) in freely moving rats. Paired pulses of electrical stimulation were delivered to PP or VHC, and evoked field potentials (fEPSPs and pop spikes) were recorded in the DG. Before activating PP or VHC, the TM was triggered by electrical stimulation. Experimentation was performed during four behavioral conditions: exploration, grooming, awake immobility, and slow‐wave sleep. Electrical activation of the TM was found to modify dentate fEPSPs evoked by PP or VHC stimulation without generating a field potential by itself. Train stimulation of the TM (100 Hz, 500 ms) preceding paired pulses on the hippocampus by 50 ms decreased dentate fEPSPs in dependence of the ongoing behavior and the pathway stimulated. During exploration but not consummatory behavior, the PP signal was reduced when preceded by TM stimulation; during consummatory behavior but not exploration, the VHC signal was reduced. In contrast to other hippocampal afferents which increase pop spikes but leave fEPSPs unchanged, TM stimulation decreased dentate fEPSPs without affecting pop‐spike activity. Thus, the TM‐histaminergic system seems to modulate signal processing in the dentate gyrus in a specific way, exerting an inhibitory action on the entorhinal input only during learning‐related exploratory behavior. Synapse 28:294–301, 1998. © 1998 Wiley‐Liss, Inc.
ISSN:0887-4476
1098-2396
DOI:10.1002/(SICI)1098-2396(199804)28:4<294::AID-SYN5>3.0.CO;2-4