抄録
The response of the neuronal firing activity in and around the suprachiasmatic nucleus (SCN) to the retinal illumination was investigated with extracellular single unit recording in anaesthetized mice during daytime and nighttime. Retinal illumination during nighttime increased firing frequency of most SCN neurons with spontaneous firing. When animal was exposed to light during daytime, spontaneous firing rate in the SCN increased in 33% of total recording neurons and not changed in 67% of total neurons. Spontaneous firing decreased in a part of SCN neurons (11%) after retinal illumination. Outside the SCN, the light-suppressed neurons were observed more frequently than light-activated neurons and there was no difference in the proportion of the types of light response between daytime and nighttime. In light-activated cells in the SCN at Zeitgeber time 16, light intensity threshold for activation was <1011 photons cm−2 s−1 and the maximum response was evoked at 1014 photons cm−2 s−1, which was comparable to those in photic resetting of behavioral rhythms. These results suggest that the photic entrainment of locomotor activity rhythms are closely associated with the light-induced changes in firing frequency in the SCN cells in mice. [Jpn J Physiol 54 Suppl:S208 (2004)]
