Influences of pyramidal tract on the subthalamic nucleus in the cat

In adult cats, with mesencephalic decerebration sparing the cerebral peduncles and ablation of the sensorimotor cortex, changes in firing of single cells of subthalamic nucleus (STN) were analyzed upon stimulation of ipsilateral medullary pyramidal tract (PT). Twenty-two out of 44 of the STN cells exhibited, following PT stimulation, discharge changes that in the greatest part of cases (91%) were excitatory in nature. Excitations, always followed by inhibitory rebound, appeared with latency values compatible with a monosynaptic linkage.