Reduced light response of neuronal firing activity in the suprachiasmatic nucleus and optic nerve of cryptochrome-deficient mice.
To examine roles of the Cryptochromes (Cry1 and Cry2) in mammalian circadian photoreception, we recorded single-unit neuronal firing activity in the suprachiasmatic nucleus (SCN), a primary circadian oscillator, and optic nerve fibers in vivo after retinal illumination in anesthetized Cry1 and Cry2 double-knockout (Cry-deficient) mice. In wild-type mice, most SCN neurons increased their firing frequency in response to retinal illumination at night, whereas only 17% of SCN neurons responded during the daytime. However, 40% of SCN neurons responded to light during the daytime, and 31% of SCN neurons responded at night in Cry-deficient mice. The magnitude of the photic response in SCN neurons at night was significantly lower (1.3-fold of spontaneous firing) in Cry-deficient mice than in wild-type mice (4.0-fold of spontaneous firing). In the optic nerve near the SCN, no difference in the proportion of light-responsive fibers was observed between daytime and nighttime in both genotypes. However, the response magnitude in the light-activated fibers (ON fibers) was high during the nighttime and low during the daytime in wild-type mice, whereas this day-night difference was not observed in Cry-deficient mice. In addition, we observed day-night differences in the spontaneous firing rates in the SCN in both genotypes and in the fibers of wild-type, but not Cry-deficient mice. We conclude that the low photo response in the SCN of Cry-deficient mice is caused by a circadian gating defect in the retina, suggesting that Cryptochromes are required for appropriate temporal photoreception in mammals.
Division of Neurobiology and Behavior, Department of Translational Medical Sciences, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan. t.nakamura@thu.ac.jp
Takahiro J
TJ
Nakamura
Shizufumi
S
Ebihara
Kazuyuki
K
Shinohara
D000818:Animals; D056931:Cryptochromes / Q000235:genetics / Q000502:physiology*; D008027:Light; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008839:Microelectrodes; D009474:Neurons / Q000502:physiology*; D009900:Optic Nerve / Q000166:cytology / Q000502:physiology*; D013493:Suprachiasmatic Nucleus / Q000166:cytology / Q000502:physiology*
D056931:Cryptochromes