Resumen:
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.