Effects of intranigral application of dopamine and substance P on the in vivo release of newly synthesized [(3)H]-dopamine in the ipsilateral caudate nucleus of the cat.

The effects of intranigral applications of dopamine (DA) and substance P on the release of DA in the ipsilateral caudate nucleus were examined in vivo in the 'encéphale isolé' cat preparation. A push-pull cannula was inserted into the caudate nucleus to measure the release of [(3)H]DA continuously synthesized from l-[3,5-(3)H]tyrosine. DA (10(-7) M) and substance P (10(-8) M) were introduced for a period of one hour into the substantia nigra using a second push-pull cannula. The superfusion of substantia nigra with DA was associated with a decrease in [(3)H]DA release in the caudate nucleus. Substance P induced an opposite effect.