Synchronization of circadian firing rhythms in cultured rat suprachiasmatic neurons
Tetsuo Shirakawa, Sato Honma, Yumiko Katsuno, Haruhisa Oguchi and Ken-ichi Honma
European J of Neuroscience (2000), 12, 2833-2838
The circadian clock in mammals is located in the suprachiasmatic nucleus (SCN) which consists of multiple oscillating neurons. Integration of the cellular oscillations is essential for the generation of a single circadian period in the SCN. By using a multielectrode dish (MED), we measured circadian firing rhythms in individual SCN neurons for more than 2 weeks continuously, and examined the involvement of synaptic communication in the synchronization of circadian rhythms. Cross-correlation analysis of spontaneous action potentials revealed that a neuron pair was functionally connected by synapses when their circadian rhythms were synchronized. Calcium (Ca2+)-dependent synaptic transmission in the cellular communication was indicated by dose-dependent lengthening of an intercellular spike interval and loss of spike correlation with a Ca2+ channel blocker. Approximately 60% of the SCN neurons in culture were immunoreactive to antibodies against g-aminobutyric acid (GABA) or glutamic acid decarboxylase (GAD) Spontaneous firing of all the neurons tested was either increased or decreased by bicuculine, the GABAA receptor antagonist. These findings indicate that synaptic communication plays a critical role in the synchronization of circadian rhythms in individual SCN neurons and that GABAergic transmission is involved in the synchronization mechanism.
Download PDF
