Light and drug induced changes of epiphysial synaptic ribbons

Summary In the present investigation experiments were carried out to determine whether the functionally obscure synaptic ribbons of mammalian pinealocytes can be affected by acute changes in environmental lighting and which chemical processes may be involved in their regulation. Experiments carried out in male guinea-pigs have shown that the amounts of synaptic ribbons are immediately affected by changes in the lighting pattern. Extension of the light period reduced the normally occurring increase, whereas extension of the dark period inhibited the normally occurring decrease in the amount of synaptic ribbons. Results following injections of a number of drugs known to influence pineal function (noradrenaline, L-DOPA, propranolol, reserpine and p-chlorophenylalanine, respectively) suggest that synaptic ribbons may be directly or indirectly regulated by -adrenergic mechanisms.Dedicated to Professor Wolfgang Bargmann on the occasion of his 70th birthday.