Investigation of possible interactions between substance P and transmitter mechanisms in the substantia nigra and corpus striatum of the rat.

The effect of substnace P (SP) on the uptake and release of radiolabelled dopamine (3H-DA), 5-hydroxytryptamine (3H-5-HT) and y-aminobutyric acid (3H-GABA) was studied in slices of rat substantia nigra and corpus triatum. SP, 10(-9) to 10(-5) m, failed to modify the uptakes of these compounds during incubations (10-90 min) with slices of either brain region. SP, 10(-6)M, had no apparent effect on the spontaneous output of any of these compounds in either substantia nigra or corpus striatum. In the corpus striatum, SP seemed to potentiate the potassium-stimulated outflow of 3H-DA and 3H-5-HT, but not 3H-GABA, while the realeases from substantia nigra were unaffected. Morphine (10(-3)M), but not met-enkephalin (5 X 10(-6)M), weakly antagonized K+- EVOKED RELEASE OF 3/-DA in the corpus striatum. These results are discussed with reference to the possible interaction of SP with transmitter mechanisms at presynaptic sites in the central nervous system.