Synaptic ribbons of the rat pineal gland: responses to in-vivo and in-vitro treatment with inhibitors of protein synthesis.

To elucidate the role of protein synthesis in the nocturnal increase of synaptic ribbons in the rat pineal gland, actinomycin-D, which inhibits transcription, and cycloheximide, an inhibitor of translation, were used. To assure that the drugs were effective and to relate morphological changes to pineal biosynthetic phenomena, the activity of N-acetyltransferase and levels of pineal indoleamine were measured. Results of in-vivo, short-term and long-term treatment with either drug suggest that transcription of proteins related to synaptic ribbon formation occurs during the first half of the light phase, whereas translation takes place during the first few hours of the dark phase. In contrast, proteins involved in enhanced melatonin synthesis are transcribed and translated during the first few hours of the dark phase. In vitro, preincubation with inhibitors of protein synthesis abolished the increase in the numbers of synaptic ribbons after stimulation with dibutyryl-adenosine-cyclic-monophosphate, indicating that the results of the in-vivo experiments are due to an interaction of the drugs with the pineal gland itself. The present study shows that, although in the rat pineal enhanced melatonin synthesis and increased numbers of synaptic ribbons occur at the same time, transcription of proteins involved in both rhythms is temporally separated.