REGULATION OF SYNAPTIC RIBBONS IN RAT PINEAL-GLAND EXPLANTS BY NOREPINEPHRINE AND SYMPATHETIC NEURONS IN A COCULTURE MODEL

The hypothesis that synaptic ribbons in the mammalian pinealocyte are influenced by adrenergic mechanisms was tested in the present study us ing a coculture model of pineal glands and superior cervical ganglia f rom neonatal rats. Pineal gland explants survived and showed a high de gree of differentiation when cultured for up to 30 days regardless of the presence or absence of superior cervical ganglia. Pineal glands al so had neurotrophic properties promoting the survival and neurite exte nsion from superior cervical ganglia. Synaptic ribbons were a common u ltrastructural feature in all pineal cultures. There was a significant decline in synaptic ribbon numbers when co-cultured with superior cer vical ganglia for both 7 and 30 days. A similar significant decrease i n synaptic ribbon frequency was observed after treatment of pineal exp lants with norepinephrine (10(-5) M) for both 7 and 30 days. These fin dings are consistent with the hypothesis that neural mechanisms play a n important role in regulating synaptic ribbon numbers, at least durin g early development. The study also illustrates the utility of pineal gland-superior cervical ganglia co-cultures as a model for future inve stigations of neuron-target interactions in the pineal.