The effect of various concentrations of morphine on the transport of dopamine (DA) into slices from the mouse brain cortex and diencephalon was investigated. It was observed that sub-analgetic levels of morphine, 3.5 × 10-8M, produced mixed inhibition in the cortex and uncompetitive inhibition in the diencephalon. When the concentration of morphine was increased to within the therapeutic range (3.5 × 10-6), a greater effect on DA affinity rather than reaction velocity was observed in the cortex although the inhibition remained mixed. Only the increase in inhibition of DA transport observed by increasing the morphine concentration from 3.5 × 10-8 to 3.5 × 10-6 M was blocked by the morphine antagonist naloxone. Increasing the morphine concentration in the diecephalon changed the type of inhibition from uncompetitive to mixed kinetics.
Bibliographical noteFunding Information:
The authors wish to thank Mrs. Barbara Hitzemann for technical assistance and Mrs. Kaye Welch and Miss Jean Cart for help in preparation of the manuscript. This study was supported in part by USPHS Grants MH-24036 and DA-00564 and project grant 7-T, Bureau of Research, Department of Mental Hygiene, State of California.
- Catecholamine transport