title: Light response of the neuronal firing activity in the suprachiasmatic nucleus of mice.
abstract: To investigate the neural mechanisms underlying the mammalian photic entrainment of circadian rhythms, the response of neuronal extracellular firing activity to retinal light stimulation was investigated in the suprachiasmatic nucleus (SCN) of anesthetized mice during nighttime and daytime. In nighttime, most recorded SCN cells (83%) increased their firing frequency in response to retinal illumination. Some SCN cells (11%) responded by decreasing their firing rate. In daytime, the retinal illumination increased the firing rate in only 26% of the SCN cells, and no response was observed in the remaining cells. The light intensity threshold for the activation of SCN cells at zeitgeber time (ZT) 16 was approximately 3 x 10(11) photons cm(-2)s(-1) and the maximum response was observed at approximately 1 x 10(14) photons cm(-2)s(-1). Therefore, photic response in the firing of mouse SCN cells may be phase-dependent and have a higher threshold, which corresponds to properties of the photic entrainment in locomotor activity of mice.
authors.affiliation: Division of Neurobiology and Behavior, Department of Translational Medical Sciences, Graduate School of Biomedical Sciences, Nagasaki University, 1-12-4 Sakamoto, Nagasaki 852-8523, Japan.
authors.forename: Takahiro J
authors.initials: TJ
authors.lastname: Nakamura
authors.forename: Koichi
authors.initials: K
authors.lastname: Fujimura
authors.forename: Shizufumi
authors.initials: S
authors.lastname: Ebihara
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Shinohara
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009474:Neurons / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods*; D013493:Suprachiasmatic Nucleus / Q000502:physiology*