MORPHOMETRY OF PINEAL SYNAPTIC RIBBON PROFILE NUMBERS AFTER CYTOCHALASIN-D TREATMENT

Synaptic ribbons (SRs) are electron-dense, plate-shaped synaptic organ elles, to which electron-lucent synaptic vesicles (SVs) are attached b y tiny stalks, In the mammalian pineal gland SRs are dynamic organelle s, waxing and warning in number under different physiological and expe rimental conditions, The way in which SRs are formed, or catabolized, is not known, Since it has been suggested that actin may be part of SR s, in the present study the effect of the actin-disrupting drug cytoch alasin D (CD, 1 mu g/ml, for 3 h) was examined in cultured guinea pig and rat pineal glands. The glands were preincubated for 38 h so that i ntrapineal sympathetic nerve fibres degenerate and no longer release n oradrenaline which may distort the results, CD had no effect on SR pro file numbers in guinea pigs, but decreased them in rats (p > 0.05), Th e nonsignificant depressive effect of CD in rats was verified in a sec ond experiment. To clarify the issue, acutely cultured rat pineal glan ds were treated with CD for 4 h, without effect. The results taken tog ether suggest to us that CD has no major effect on pineal SR profile n umbers, but that in rats preincubation for 38 h makes them vulnerable to catabolic processes. In all the experiments, the electron-dense pla te of the SRs was qualitatively unaffected. However, the SVs were ofte n larger and more irregular in shape and the stalks linking the SVs wi th the SRs were less frequently seen in CD-treated glands, In guinea p ig pineals, in which SRs frequently lie in groups and parallel to each other, neither the distance between neighboring SRs nor the thickness of individual SRs were affected by CD. It is concluded that actin is not a major component of the SRs and the connecting stalks.