Retinal ganglion cells in birds: day-timers and non-visual photoreceptors

GUIDO ME; VALDEZ DJ; NIETO PS; VERRA DM; DÍAZ NM; CONTÍN MA; GARBARINO PICO E

Congreso; International Congress of Eye Research (ICER) 2014; 2014

International Society for Eye Research

Chicken retinal ganglion cells (RGCs) contain autonomous oscillators that generate daily rhythms in the synthesis of melatonin and in the activity of its regulatory enzyme arylalkylamine N-acetyltransferase (AA-NAT). An intrinsically photosensitive RGC subpopulation (ipRGCs) expresses the photopigment melanopsin (Opn4) and project to brain areas controlling light-regulated activities (entrainment of rhythms, pupillary light reflexes (PLR), etc.). Blind chickens (GUCY1*) lacking functional photoreceptor cells do express Opn4, exhibit PLR and synchronize their feeding rhythms to light after brain occlusion. Here, we investigated light and circadian-regulation of RGC activities and their potential roles in the non-visual circuit function. Chicken retinas from animals maintained in constant dark (DD), light (LL), or a 12:12 h LD cycle for 48 h, were lyophilized and processed. PLR in dark-adapted GUCY1* chickens (consensual reflex) to white or blue bright lights at different circadian times (CT) in DD, and feeding rhythms after synchronization to diverse LD cycles were assessed. AA-NAT activity in RGCs displays a circadian rhythmicity with highest levels during day in DD, LL or the light phase of a LD cycle; however, a brief light pulse or dopamine administration (50 nmol/eye) had no effect on AA-NAT activity. The ipRGC regulated-photic entrainment of feeding rhythms was evaluated in GUCY1* birds after head occlusion to avoid extraocular photoreception; birds synchronized their feeding rhythms to LD cycles with L>12 lux. When released to LL, blind chickens became arrhythmic; however, after head occlusion, they free-ran with a 24.5 h period. To further characterize the ipRGC circuitry, we found that PLRs in GUCY1* birds were subject to a daily variation after white or blue light exposure with maximum constriction at CT6. Chicken RGC oscillators and ipRGCs are part of a non-visual circuit controlling melatonin synthesis locally and non-visual activities displaying maximal responses at midday. Supported by ANPCyT-FONCyT PICT 2010-647, CONICET, SeCyT-UNC.