The ultradian EEG rhythm coincides temporally with the ultradian rhythm of histamine release in the posterior hypothalamus.

In the posterior hypothalamus of the rat, EEG power and release rates of several neurotransmitters oscillate according to ultradian rhythms. To investigate whether a causal relationship exists between EEG power and histamine release, the posterior hypothalamic area of the anaesthetized rat was superfused through a push-pull cannula combined with a tungsten electrode. Simultaneous EEG recording and determination of histamine release revealed that ultradian rhythms in the delta and theta frequency bands are negatively correlated to the release rate of histamine; periods of high neuronal activity, which might reflect synchronization of firing, coincide temporally with low release rate of histamine, while periods of low neuronal activity coincide with high histamine release rate. The alpha and beta frequency bands did not correlate with histamine release. The ultradian rhythm of EEG power and histamine release might be of importance for regulatory mechanisms, such as the secretion of hormones.