Aims: 

Vertebrate pineal gland and retina synthesize melatonin in light-dependent rhythmic fashion controlled by endogenous circadian clock. This work was aimed at studying effects of prolonged exposure of turkeys to constant darkness (DD) and continuous light (LL) on serotonin N-acetyltransferase (AANAT; a key regulatory enzyme in melatonin biosynthesis) activity in the pineal gland and retina.

Methods: 

Newly hatched turkeys after adaptation to 12 h light: 12 h dark (LD) cycle were kept under DD for 14 days or LL for 7 days. The animals were killed at 4-h intervals, isolated pineal glands and retinas were used for measurements of AANAT activity.

Results: 

AANAT activity in the turkey pineal gland oscillated in circadian rhythm for 7 days of DD (tau = 23.8 ± 0.02 h) or LL (tau = 24.3 ± 0.05 h). Under DD AANAT activity in the retina also exhibited circadian rhythm (tau = 23.7 ± 0.05 h), but its amplitude progressively dampened, and no rhythmicity was observed after five days of DD. Low amplitude rhythmic changes in retinal AANAT activity disappeared on the third day of LL.

Conclusions: 

AANAT activity in the turkey pineal gland and retina is regulated by endogenous circadian pacemaker and light. The melatonin-generating system in the turkey retina is more sensitive to changes in the environmental light than is the system of pineal. In contrast to mammals, in pineal gland of galliforms the circadian melatonin rhythm persists under conditions of LL.

Supported by the grant 2 P06D 025 29 MNiSW, Warsaw, Poland.