THE SHAPE OF SYNAPTIC RIBBONS IN THE RAT PINEAL-GLAND

Under the transmission electron microscope, synaptic ribbons (SRs) of the mammalian pineal gland appear as rod-like organelles. Their three- dimensional structure is not precisely known. In the present study, pi neal SRs were investigated using serial sections obtained from rats ki lled at noon and midnight. The shape of the SRs was reconstructed base d on SR profile length and the number of sections in which the profile s were contained. The results obtained show that SRs are basically fla t plate-like structures with polymorphic lateral edges. Reconstruction s of SRs revealed that they had average dimensions of 300x150x35 nm an d were 19.3% larger at night than at day; the difference in SR size po ints to perhaps major differences in synaptic function between day and night.