Circadian and photoperiodic correlation between the number of pineal gland synaptic ribbons and serum melatonin levels in the rat.

A study is made of the number of pineal gland synaptic ribbons in 35 male Wistar rats over a 24-hour period during the months of September and February, in correlation to the serum melatonin levels during the same periods and photophases. The results of the study confirm those reported by others authors and suggest that the synaptic ribbons may be the stimuli-transmitting organs facilitating pineal secretory function.