期刊
EUROPEAN JOURNAL OF NEUROSCIENCE
卷 17, 期 9, 页码 1727-1735出版社
WILEY
DOI: 10.1046/j.1460-9568.2003.02594.x
关键词
circadian rhythms; light response; patch-clamp electrophysiology; photoentrainment; retinal ganglion cells; trp channels
资金
- NIMH NIH HHS [MH 63364, R01 MH067094, R21 MH063364-01, R21 MH063364-02, R01 MH067094-01A1] Funding Source: Medline
- NINDS NIH HHS [NS07466, T32 NS007466] Funding Source: Medline
In mammals, light entrainment of the circadian clock, located in the suprachiasmatic nuclei (SCN), requires retinal input. Traditional rod and cone photoreceptors, however, are not required. Instead, the SCN-projecting retinal ganglion cells (RGCs) function as autonomous photoreceptors and exhibit light responses independent of rod- and cone-driven input. Using whole-cell patch-clamp recording techniques, we have investigated the morphological and electrophysiological properties of this unique class of RGCs. Although SCN-projecting RGCs resemble Type III cells in form, they display strikingly different physiological properties from these neurons. First, in response to the injection of a sustained depolarizing current, SCN-projecting cells fired in a transient fashion, in contrast to most RGCs which fired robust trains of action potentials. Second, in response to light, SCN-projecting RGCs exhibited an intensity-dependent transient depolarization in the absence of rod and cone input. This depolarization reached a peak within 5 s and generated increased spiking activity before decaying to a plateau. Voltage-clamp recordings were used to characterize the light-activated conductance which generated this depolarization. In response to varying light intensities, SCN-projecting RGCs exhibited a graded transient inward current which peaked within 5 s and decayed to a plateau. The voltage dependence of the light-activated current was obtained by subtracting currents elicited by a voltage ramp before and during illumination. The light-activated current displayed both inward and outward rectification and was largely unaffected by substitution of extracellular Na+ with choline. In both respects, the intrinsic light-activated current observed in SCN-projecting RGCs resembles currents carried by ion channels of the transient receptor potential (trp ) family, which are known to mediate the light response of invertebrate photoreceptors.
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