The globus pallidus occupies a critical position in the indirect pathway of the basal ganglia.By innervating all the other basal ganglia nuclei,the globus pallidus plays an important role in normal movement regulation and in the pathophysiology of basal ganglia disorders.Substance P is a member of neurokinin family.Previous studies have reported the existence of substance P and its high affinity receptor,neurokinin-1 receptor,in globus pallidus.However,the function of substance P in globus pallidus is not well known.In the present study,we employed both in vivo extracellular recordings and behavioral test to study the effects of substance P in globus pallidus of rats.Micro-pressure ejection of selective neurokinin-1 receptor agonist,[Sai9,Met(O2)11] substance P (SMSP),increased the spontaneous firing rate of pallidal neurons in a concentration-dependent pattern,with the increase at 27.3% (0.01 mmol/L),33.4% (0.03 mmol/L),45.5 % (0.1 mmol/L),38.4% (0.3 mmol/L) and 36.4% (1.0 mmol/L),respectively.The selective neurokinin-1 receptor antagonist,SR140333B,prevented the excitatory effects induced by SMSP.