No differences in pineal synaptic ribbon and spherule numbers in different stocks and strains of laboratory rats

Previous studies have shown that the pineal glands of different stocks and strains of laboratory rats have different melatonin-forming capacities. In the present investigation a widely studied morphological parameter of the pineal, i.e. synaptic ribbon (SR) and synaptic spherule (SS) numbers, was explored in 6 different stocks and strains of laboratory rats, viz.:Han:WIST (albino), LEW/Han (albino), DA/Han (agouti), BN/Han (dark brown), LE/Han (black hooded) and (LEW x BN)/F1 (black with white belly). The rats were maintained under the usual laboratory conditions (lights on from 06.00-18.00 h) for 3 weeks and killed between 10.00-12.00 h, when they were 6 weeks old. The pineals were rapidly excised and processed for transmission electron microscopy. The morphology, distribution (in singles or groups, distant from, or near cell membrane etc.) and number of SR and SS per 20,000 microns2 area of pineal tissue were similar in all groups of rats studied. It is concluded that, in contrast to pineal gland size and melatonin synthesis, SR number is a fairly constant pineal parameter in different stocks and strains of laboratory rats and independent of pigmentation.