Norepinephrine suppresses both photoreceptor and neuron-like properties expressed by cultured rat pineal glands

Our previous study showed that pineal glands of the newborn rat express properties of both photoreceptors and endocrine cells, when transferred to cell culture conditions, whereas opsin was not detected in cells of the intact pineal glands of the postnatally developing or mature rats (Araki et al., 1988). In the present study we asked a question why photoreceptor-like cells do not differentiate in vivo, although the pineal cells have the potency as revealed in cell culture conditions. Our hypothesis was that norepinephrine (NE) may suppress the differentiation of cells with photoreceptor properties. This was proved by adding NE into the culture medium, and only few opsin-like immunoreactive cells, if any, were differentiated in the presence of 10(-6) M NE. NE also suppresses the extension of neurite-like processes by serotonin-like immunoreactive (endocrine) cells, another property expressed in cultures. Other aminergic neurotransmitters, such as dopamine and serotonin, did not have such effects. These results imply that the massive innervations of the pineal gland by the sympathetic ganglion may suppress both photoreceptor and neuron-like properties of the mammalian pineal gland in vivo.