SIGNAL TRANSMISSION IN THE PHOTOSENSITIVE PINEAL ORGAN OF THE RAINBOW-TROUT - MODULATION OF GANGLION-CELL ACTIVITY BY INTRINSIC DOPAMINE

The photosensitive pineal organ of the rainbow trout (Oncorhynchus myk iss) transduces photic information into nycthemeral neuronal signals. To investigate origin, cellular localization, and functional significa nce of pineal catecholamines, we performed HPLC-analysis of catecholam ines and tyrosine hydroxylase (TH) activity, as well as immunocytochem ical and electrophysiological studies. In biochemical and immunocytoch emical investigations, pineal cells were found to contain endogenous T H. Using HPLC-analysis, the presence of a catecholamine precursor (L-d opa), catecholamines (dopamine, norepinephrine, epinephrine), and a me tabolite (DOPAC) was demonstrated. The release of L-dopa, dopamine and DOPAC from isolated pineal organs was shown by superfusion experiment s. Extracellular recordings were used to monitor the action of dopamin ergic drugs on electrical activity of ganglion cells. Dopamine increas ed the discharge activity of action potentials, whereas dopamine recep tor antagonists resulted in a reduction of ganglion cell activity. Our data provide evidence for establishing dopamine as an intrinsic neuro transmitter or neuromodulator in the photosensitive pineal organ of th e rainbow trout.