LACK OF EFFECT OF OXYTOCIN ON THE NUMBERS OF SYNAPTIC RIBBONS, CYCLICGUANOSINE-MONOPHOSPHATE AND SEROTONIN N-ACETYLTRANSFERASE ACTIVITY INORGAN-CULTURED PINEALS OF 3 STRAINS OF RATS

In addition to the stimulating influence of the sympathetic system on the function of the mammalian pineal gland, neuropeptides such as neur opeptide Y, vasoactive intestinal polypeptide and arginine-vasopressin (AVP) are thought to function as modulators. Since AVP has been shown to influence pineal melatonin synthesis, the aim of the present study was to investigate the possible effects of the second hypothalamic no napeptide oxytocin (OT), which likewise has been detected in the pinea l gland. We therefore studied ''synaptic'' ribbon (SR) numbers, N-acet yltransferase (NAT) activity and the intracellular concentration of cy clic guanosine monophosphate (cGMP) following in vitro incubation of r at pineals in media containing OT (10(-5) M), noradrenaline (NA, 10(-5 ) M) or both NA and OT. Pineal glands were derived from rats of three different strains (Sprague-Dawley, Long-Evans and the AVP-deficient st rain Brattleboro). Neither morphological nor biochemical analyses show ed a difference between control and OT-incubated organs in any of the strains tested. In Brattleboro rats, but not in the other strains, nor adrenaline slightly increased the number of SR which was not observed when NA and OT were combined. The addition of NA resulted in distinct augmentation of NAT activity and cGMP content, which were not affected by additional OT application. These results suggest that oxytocin is not crucially involved in the regulation of pineal gland function.