ABSTRACT
Orexin A and orexin B are neuropeptides produced by a group of neurons located in the lateral hypothalamus which send widespread projections virtually to the whole neuraxis. Several studies indicated that orexins play a crucial role in the sleep-wake regulation and in the pathomechanism of the sleep disorder narcolepsy. As no data are available related to the EEG effects of orexin A in healthy, freely moving rats, the aim of the present experiments was to analyze EEG power changes in the generally used frequency bands after intracerebroventricular orexin A administration.Orexin A administration (0.84 and 2.8 nM/rat) differently affected fronto-occipital EEG waves in the different frequency bands recorded for 24 hours. Delta (1-4 Hz) and alpha (10-16 Hz) power decreased, while theta (4-10 Hz) and beta (16-48 Hz) power increased. Decrease of the delta power was followed by a rebound in case of the higher orexin A dose. This complex picture might be explained by the activation of several systems by the orexin A administration. Among these systems, cortical and thalamic circuits as well as the role of the neurons containing corticotrophin-releasing factor might be of significant importance.
Subject(s)
Circadian Rhythm/drug effects , Electroencephalography/drug effects , Intracellular Signaling Peptides and Proteins/pharmacology , Intracellular Signaling Peptides and Proteins/physiology , Neuropeptides/pharmacology , Neuropeptides/physiology , Neurotransmitter Agents/pharmacology , Alpha Rhythm/drug effects , Animals , Beta Rhythm/drug effects , Cerebral Cortex/drug effects , Cerebral Cortex/physiology , Delta Rhythm/drug effects , Hypothalamus/drug effects , Hypothalamus/physiology , Injections, Intraventricular , Male , Motor Activity/drug effects , Neurotransmitter Agents/physiology , Orexins , Rats , Rats, Sprague-Dawley , Sleep/drug effects , Thalamus/drug effects , Thalamus/physiology , Theta Rhythm/drug effectsABSTRACT
The basal forebrain (BF) is a heterogeneous structure located in the ventral aspect of the cerebral hemispheres. It contains cholinergic as well as different types of noncholinergic corticopetal neurons and interneurons, including GABAergic and peptidergic cells. The BF constitutes an extrathalamic route to the cortex, and its activity is associated with an increase in cortical release of the neurotransmitter acetylcholine, concomitant with electroencephalographic (EEG) low-voltage fast activity (LVFA). However, the specific role of the different BF cell types has largely remained unknown due to the lack of chemical identification of the recorded neurons. Here we show that the firing rate of immunocytochemically identified cholinergic and parvalbumin-containing neurons increase during cortical LVFA. In contrast, increased neuropeptide Y neuron firing is accompanied by cortical slow waves. Our results, furthermore, indicate that BF neurons posses a distinct temporal relationship to different EEG patterns and suggest a more dynamic interplay within BF as well as between BF and cortical circuitries than previously proposed.
