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

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Abstract
The effect of substance P (SP) on the uptake and release of radiolabelled dopamine (3H-DA), 5-hydroxytryptamine (3H-5-HT) and γ-aminobutyric acid (3H-GABA) was studied in slices of rat substantia nigra and corpus striatum. SP, 10−9 to 10−5m, failed to modify the uptakes of these compounds during incubations (10–90 min) with slices of either brain region. SP, 10−6m, 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 releases from substantia nigra were unaffected. Morphine (10−3m), but not met-enkephalin (5 × 10−6m), weakly antagonized K+-evoked release of 3H-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.