Photoreceptor adaptation in intrinsically photosensitive retinal ganglion cells.
A rare type of mammalian retinal ganglion cell (RGC) expresses the photopigment melanopsin and is a photoreceptor. These intrinsically photosensitive RGCs (ipRGCs) drive circadian-clock resetting, pupillary constriction, and other non-image-forming photic responses. Both the light responses of ipRGCs and the behaviors they drive are remarkably sustained, raising the possibility that, unlike rods and cones, ipRGCs do not adjust their sensitivity according to lighting conditions ("adaptation"). We found, to the contrary, that ipRGC sensitivity is plastic, strongly influenced by lighting history. When exposed to a constant, bright background, the background-evoked response decayed, and responses to superimposed flashes grew in amplitude, indicating light adaptation. After extinction of a light-adapting background, sensitivity recovered progressively in darkness, indicating dark adaptation. Because these adjustments in sensitivity persisted when synapses were blocked, they constitute "photoreceptor adaptation" rather than "network adaptation." Implications for the mechanisms generating various non-image-forming visual responses are discussed.
Wong
Kwoon Y
KY
Department of Neuroscience, Brown University, Providence, Rhode Island 02912, USA. kwoon_wong@brown.edu
Dunn
Felice A
FA
Berson
David M
DM
D000200:Action Potentials / Q000502:physiology / Q000528:radiation effects; D000221:Adaptation, Ocular / Q000502:physiology* / Q000528:radiation effects; D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology / Q000528:radiation effects; D003623:Dark Adaptation / Q000502:physiology / Q000528:radiation effects; D008027:Light; D055537:Light Signal Transduction / Q000502:physiology* / Q000528:radiation effects; D008297:Male; D009415:Nerve Net / Q000502:physiology* / Q000528:radiation effects; D009473:Neuronal Plasticity / Q000502:physiology / Q000528:radiation effects; D010775:Photic Stimulation; D010786:Photoreceptor Cells / Q000502:physiology* / Q000528:radiation effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D012165:Retinal Ganglion Cells / Q000502:physiology* / Q000528:radiation effects