Volume 16, Number 21,
Issue of November 1, 1996
pp. 6999-7009
Copyright ©1996 Society for Neuroscience
Enhancement of Behavioral and Electroencephalographic Indices of
Waking following Stimulation of Noradrenergic
-Receptors within the
Medial Septal Region of the Basal Forebrain
Received May 7, 1996; revised July 18, 1996; accepted Aug. 6, 1996.
Craig W. Berridge1 and
Stephen L. Foote2
1 Psychology Department, University of Wisconsin,
Madison, Wisconsin 53706-1611, and 2 Psychiatry Department,
University of California, San Diego, La Jolla, California 92093
Previous studies in halothane-anesthetized rat documented potent
electroencephalographic (EEG) modulatory actions of the locus coeruleus
(LC) noradrenergic system, with LC neuronal activity causally related
to the maintenance of EEG activity patterns associated with enhanced
arousal/alertness. Recent studies, also in halothane-anesthetized rat,
demonstrated that the region of the basal forebrain encompassing the
medial septum/vertical limb of the diagonal band of Broca (MS) is a
site at which noradrenergic efferents act to influence EEG state via
actions at
-receptors.
These and other observations are consistent with the hypothesis that
the LC noradrenergic system participates in the modulation of
behavioral state. However, the degree to which this system modulates
EEG state in the absence of anesthesia and to what extent such actions
are accompanied by behavioral modulatory actions remain to be
determined. The current studies examined whether small infusions of
isoproterenol (ISO), a
-adrenergic agonist, into MS alter
behavioral, EEG, and electromyographic (EMG) measures of sleep and
waking in the resting, undisturbed rat.
These infusions resulted in a significant increase in time spent awake,
defined by both behavioral and EEG/EMG measures, and in the nearly
complete suppression of REM sleep. EEG/EMG responses either coincided
with or preceded behavioral responses by 10-320 sec. The pattern of
behavioral responses observed following MS-ISO infusions was
qualitatively similar to that associated with normal waking. Infusions
of vehicle into MS or ISO into sites adjacent to MS did not elicit
consistent alterations in behavioral state. These results suggest that
the LC noradrenergic system exerts potent behavioral and EEG-activating
effects via actions of norepinephrine at
-receptors located within
MS.
Key words:
norepinephrine;
medial septum;
arousal;
EEG;
-receptors;
sleep;
locus coeruleus