Optimum parameters for substantia nigra self-stimulation as reflected by peripheral autonomic responses.

Lever-pressing rate, arterial blood pressure, heart rate and respiration were continuously recorded during substantia nigra self-stimulation with systematically varied stimulus parameters in cats. During self-stimulation with fixed pulse train duration, the shorter the pulse train duration the higher was the lever-pressing rate. The rate of responding was a curvilinear function of pulse voltage and frequency during self-stimulation, both at fixed pulse train duration and with self-regulation of pulse train duration. Substantia nigra self-stimulation was always associated with peripheral autonomic changes, which were found within a certain range during self-stimulation with the stimulus parameters producing the highest lever-pressing rate. The preferred level of the peripheral functions under study was characterized by an increase up to 150/130--190/160 mm Hg in blood pressure, an increase up to 190--290/min in heart rate, and an increase up to 60--120/min in respiration. It is concluded that the optimum parameters for substantia nigra self-stimulation may be reflected by the preferred level of peripheral autonomic functions. The results support our earlier suggestion that a peripheral feedback mechanism plays an important role in the timing of lever-pressing behaviour.