DISTRIBUTION OF CHOLINERGIC AND DOPAMINERGIC RECEPTORS IN RAINBOW-TROUT PINEAL-GLAND

The involvement of multiple receptors in modulating the function of the pineal gland was investigated by searching for dopaminergic and cholinergic receptors in trout pineal gland. Dopamine D-1 and D-2 receptors were measured using [H-3]SCH23390 and [H-3]spiperone, respectively. Muscarinic and nicotinic chorinergic receptors were measured using quinuclidinyl benzilate ([H-3]QNB) and [H-3]methylcarbamyl choline, respectively. High-affinity choline uptake sites were measured using [H-3]hemicholinium-3. The distribution of dopaminergic receptors varied throughout the pineal gland in that the density of D-2 receptors, which was higher than that of D-1 receptors, was most abundant in the distal region, exhibiting a value of 112 +/- 17 fmol/mg tissue. The distribution of both muscarinic and nicotinic receptors was uniform throughout the pineal gland. However, the highest value for the high-affinity choline transporter (106 +/- 17 fmol/mg tissue) occurred in the proximal portion of the trout pineal gland. The results of these studies indicate that the pineal gland should not be viewed as a homogenous tissue possessing identical density of various receptors. Furthermore, these results, along with previous data, are interpreted to suggest that different regions of pineal gland may indeed possess unique functions.