title: Alpha 2-noradrenergic modulation of hippocampal theta activity.
abstract: The purpose of the present study was to determine the role of norepinephrine in the generation of hippocampal theta activity. Experiments were performed on urethane-anesthetized rats, implanted with recording electrodes in the dentate gyrus and stimulating electrodes in the dorso-medial posterior hypothalamus. The effects of norepinephrine on hippocampal theta activity was studied by directly infusing norepinephrine and other noradrenergic agents into the hippocampus. Norepinephrine microinfusion produced a decrease in the amplitude of theta activity as observed in the polygraph chart record. Subsequent spectral analyses demonstrated a decrease in power at peak theta frequencies, as well as a decrease in power at frequencies between 20-25 Hz (noise). The inhibitory effect of norepinephrine on hippocampal type 2 theta activity was found to be mediated by alpha 2-adrenergic receptors. Microinfusions of an alpha 2 agonist (detomidine) mimicked the effects produced by norepinephrine, whereas alpha 1 and beta agonists were ineffective. The inhibitory effect of detomidine was blocked by microinfusions of an alpha 2 antagonist (tolazoline), which indicates that the site of action was specific to the noradrenergic alpha 2 receptor.
authors.affiliation: Department of Psychology, University of Calgary, Alberta, Canada.
authors.forename: A J
authors.initials: AJ
authors.lastname: Heynen
authors.forename: R S
authors.initials: RS
authors.lastname: Sainsbury
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000818:Animals; D001831:Body Temperature / Q000502:physiology; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D006339:Heart Rate / Q000502:physiology; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D007093:Imidazoles / Q000037:antagonists & inhibitors / Q000494:pharmacology; D007263:Infusions, Parenteral; D008297:Male; D009638:Norepinephrine / Q000502:physiology*; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D013826:Theta Rhythm / Q000187:drug effects; D014043:Tolazoline / Q000494:pharmacology; D014520:Urethane
chemical_list: D000316:Adrenergic alpha-Agonists; D007093:Imidazoles; D011942:Receptors, Adrenergic, alpha; D014520:Urethane; C041255:detomidine; D014043:Tolazoline; D009638:Norepinephrine