RHYTHMIC DELTA-FREQUENCY ACTIVITIES IN THE NUCLEUS-ACCUMBENS OF ANESTHETIZED AND FREELY MOVING RATS

In urethane-anesthetized rats, a membrane potential osciilation (MPO) of up to 30 mV and 0.5-2 Hz (delta frequency range) was found in neuro ns of the nucleus accumbens, The membrane potential oscillations were of similar frequency and reversed in phase to the extracellular EEG of about 0.5 mV. In freely moving rats, a rhythmic delta EEG of 0.5-3 Hz was found in the nucleus accumbens, and it was of highest amplitude a nd regularity during awake immobility: and face washing, less regular during slow wave sleep, and of the lowest amplitude during body and he ad movements and rapid eye movement sleep. The behavioural relation of the accumbens EEG was not critically affected after amphetamine, halo peridol, and parachlorophenylalanine, which depleted serotonin, althou gh the accumbens EEG during awake immobility was less regular after bl ocking muscarinic cholinergic receptors by atropine sulfate. However, stimulation of the ventral tegmental area suppressed the accumbens del ta membrane potential oscillations and EEG, and this effect was antago nized by haloperidol, suggesting that endogenous dopamine release may suppress the accumbens delta rhythm. It was concluded that the delta r hythm in the nucleus accumbens may represent a state of bilateral sync hrony among accumbens neurons that is perhaps characteristic of an idl ing system, while desynchronization of the delta rhythm may occur clos ely with motor action.