Pineal rhythms are synchronized to light-dark cycles in congenitally anophthalmic mutant rats

Genetically mutant anophthalmic rats lacking a complete visual system due t o the absence of eyeballs and optic nerves up to the optic chiasma were use d as a model to study photo-regulated physiological activities. The photore ception in these mutant rats was determined by measuring the neuroendocrine response of the pineal,aland-melatonin levels in the serum, and synaptic r ibbon complexes (SRCs) in the pinealocytes. These parameters were studied i n both normal and anophthalmic rats maintained under light-dark (LD 12:12), continuous dark (DD) and Light (LL) conditions. Both normal and mutant ano phthalmic animals showed nocturnal increases in serum melatonin levels and in the number and diameter of SRC and their vesicles in the pinealocytes in LD. The daily rhythms persisted even upon transfer to DD both in normal an d mutant rats, whereas in LL, the nocturnal elevation of both the parameter s disappeared. These observations suggested that congenitally blind rats ca n perceive light. The studies of these parameters in both normal and mutant rats in reversed-LD conditions confirmed that pineal rhythms can be entrai ned by light-dark cycles in congenitally anophthalmic mutant rats through a nonvisual system for light perception. (C) 1999 Elsevier Science B.V. All rights reserved.