A quantitative study of synaptic ribbons in pinealocytes of adult Chinese hamsters (Cricetulus griseus) under different photoperiodic conditions.

Synaptic ribbons (SR) in pinealocytes of adult (120-130 day-old) male Chinese hamsters (Cricetulus griseus) were classified into types 1, 2 and 3; these have a central dense structure showing rod-like, various and ring-like profiles, respectively. The central structure of the type-2 SR usually appeared as round, oval or comma-like bodies, and occasionally as plates showing various profiles or club-shaped bodies. The quantity of each type of SR, expressed as the SR index, was determined over a 24-h period under a light/dark regime (LD) 12:12 or LD 14:10. On comparing the results obtained from adults with previously published data from young (60-70-days-old) animals under LD 12:12, it was found that, in both young and adult animals, the type-1 and type-3 SR indices exhibited different 24-h variations, whereas the type-2 SR index remained constant over a 24-h period. In addition, the indices of the type-2 SR, but not those of the other SR types, were found to be significantly larger in adult than in young animals. In adult animals, the effects of the photoperiod were different between the three types of SR. A nocturnal increase in the type-1 SR index was observed under both LD 12:12 and LD 14:10, its time course being different for each of these photoperiods. Under LD 14:10, the type-2 SR index showed a significant 24-h rhythm with larger values during the dark period; this was not observed under LD 12:12. The type-3 SR index was almost the same under LD 12:12 and LD 14:10.(ABSTRACT TRUNCATED AT 250 WORDS)