MELATONIN ADMINISTRATION INCREASES THE AFFINITY OF D2 DOPAMINE-RECEPTORS IN THE RAT STRIATUM

Rats receive melatonin (MEL) (476 +/- 6.5 mu g/kg/day) via their drink ing water for 2 weeks. At the end of this period, the density of D2 do pamine (DA) receptors and their affinity for [H-3]-YM-09151-2 are meas ured in the striatum. MEL treatment increases the apparent affinity (d ecreases the Kd) of D2 DA receptors for [H-3]YM-09151-2 by 48%, while it does not significantly alter the density (Bmax). These findings ind icate that the affinity of D2 DA receptors in the striatum is influenc ed by exposure to MEL. The possible implications of these results are discussed.