EFFECTS OF DOPAMINERGIC AND NORADRENERGIC MECHANISMS ON THE NEURONAL-ACTIVITY OF THE ISOLATED PINEAL ORGAN OF THE TROUT, ONCORHYNCHUS-MYKISS

The effects of exogenous applied catecholamines on the neuronal activity of ganglion cells of the luminance type (achromatic cells) were investigated in the photosensitive pineal organ of the trout, Oncorhynchus mykiss. Extracellular recordings were performed on neurons of the superfused isolated pineal organ. Addition of dopamine to the superfusion medium increased the spontaneous activity of more than 60% of the achromatic neurons (n = 25). The D1-dopamine antagonist SCH-23390 and D2-dopamine antagonist spiperone reversed the dopamine-induced stimulation of ganglion cells and inhibited their maintained activity, which suggests that dopamine acts via both D1- and D2-receptors. Norepinephrine, the beta-adrenergic agonist isoproterenol, and DOPA enhanced the spontaneous activity of most of the ganglion cells, whereas the beta-antagonist propranolol depressed the discharge rate and reversed the action of isoproterenol. This suggests that catecholamines might play a modulatory role in the regulation of the neural activity of pineal luminance neurons.