the effect of stimulation of the substantia nigra on low and highthreshold startle reflexes in the cat effects of the substantia nigra pars compacta stimulation on two functional types of startle reflexes were studied in chloraloseanesthetized cats the reflexes were the lowthreshold ones evoked by tactile stimuli treflex and highthreshold ones evoked by intense peripheral nerve stimulation spinobulbospinal sbs reflex it was found that substantia nigra stimulation exerted mainly inhibitory influences on both types of reflexes however the depression of the sbsreflex was always more profound and long lasting up to 8 min than that of treflex the latter reflex was sometimes facilitated