[Application of electrophysiological methods in vivo to study circadian clock mechanisms in mammals]

The suprachiasmatic nuclei (SCN) of the hypothalamus and the intergeniculate leaflet (IGL) of the thalamic lateral geniculate complex are two main oscillators for circadian timing system. A lot of anatomical evidences indicated a strong neuronal connections between SCN and IGL. Relatively less, however, is know about the electrophysiology and functional interactions between SCN and IGL. The spontaneous firing rate of SCN neurons exhibits a remarkable circadian rhythm with a higher activity in the day and a lower at the night both in vivo and in vitro preparations. However, these rhythms my represent only clock output rather then the intrinsic clock mechanism. Last data described for the first time ultradian rhythmic neuronal oscillation recorded in vivo in the rat SCN and IGL. These isoperiodic phasic discharge probably constitute a basis necessary to generate circadian rhythms in mammals.