Nuclear size variations in cells of the locus ceruleus during sleep, arousal and stress.

The nuclear size of the neurons in the locus ceruleus is highly sensitive to varitions in wakefulness expressed by the amount of delta activity in the EEG of sleeping, sleep-resistant, and aroused rabbits. Karyometric studies show that the nuclear diameter is particularly small during sleep (with high delta activity) induced by stimulation of the hypnogenic thalamic region, and in the control animals. It increases in sleep-resistant animals (with low delta activity) under the influence of stress. The stress-induced enlargement of the nucleus depends on the duration of the stress situation. It starts 15 min after the onset of experimental stress and reaches a steady maximum 30 min later. The highest karyometric values were found in rabbits aroused by stimulating the midbrain reticular formation and presenting a minimum of delta activity.