Synaptic bodies (SBs) are small, rare organelles involved in signal transduction in the retina, inner ear and pineal gland. In vivo they undergo changes in number and size. In this study the disector, a counting method independent of size and shape of investigated particles, was used to verify numerical changes in vivo and to clarify whether they occur also in vitro. Disector and single section profile counts of SBs were performed on electron microscopic sections of chicken pineal glands removed at day or night and cultured in an incubator for 12 hours.
In vivo significant increases of SB number, SB profile number and SB profile length were seen from noon to midnight. Pineal glands removed at noon and incubated for 12 hrs showed significant (p < 0.05) increases of SB number, SB profile number and length. The increase in length was less pronounced than in vivo at 24.00, whereas the SB and SB profile increase was more evident.
In pineal glands removed at 24.00 and incubated for 12 hrs significant decreases of SB profile number and length and an insignificant decrease of SB number were encountered. In vitro significantly more SBs and SB profiles were present, the latter were insignificantly shorter (p = 0.3) than in vivo.
Our data suggest that SB number and length in the chicken pineal gland are subject to endogenous control, retaining their day/night rhythm in organ culture. As the changes in number were less pronounced in vitro than in vivo, it is assumed that in vivo the day/night rhythm is accentuated either by the innervation of the gland or by light or by both.
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