EFFECTS OF A NIGRAL APPLICATION OF SUBSTANCE P AND OF AN ANTI-SUBSTANCE P SERUM ON DOPAMINE RELEASE FROM DENDRITES AND NERVE TERMINALS OF THE NIGROSTRIATAL DOPAMINERGIC NEURONS IN THE CAT

Using push-pull cannulae, the release of newly synthesized 3H-DA was estimated in one substantia nigra (SN) and in the ipsilateral caudate nucleus (CN) of halothane anaesthetized cats. Applied into the SN, substance P (10−8M) reduced the dendritic release of 3H-DA but stimulated the release of the 3H-transmitter from nerve terminals in the CN. In contrast, a purified gamma-globulin fraction of a rabbit antiserum against substance P introduced into the SN reduced the release of 3H-DA from dendrites and induced an opposite effect in the CN. These results indicate that the striato-nigral substance P neurons exert an excitatory tonic influence on the nigrostriatal dopaminergic neurons. They are in agreement with the hypothesis of a critical role of the dendritic release of DA in the control of the activity of the dopaminergic neurons.