TTX-resistant ca²⁺ oscillation in cultured hypothalamus: Similarity to the mammalian circadian pacemaker

Dissociated cultures of rat hypothalamic cells showed spontaneous oscillations in intracellular Ca²⁺ with periods of 5-8 s (ultradian rhythm). Replacement of H₂O by deuterium oxide in the culture medium lengthened the period of this oscillation, while tetrodotoxin did not inhibit the deuterium oxide sensitive Ca²⁺ oscillation. Since these characteristics resemble those of the mammalian circadian pacemaker, the ultradian Ca²⁺ rhythms may be involved in the circadian rhythm or have a similar rhythm generation mechanism. The gap junction inhibitor, halothane, stopped this oscillation. Gap junctions may be necessary in order to generate rhythmic oscillations.