Objective: The aim of this study is to research effects of parafascicular nucleus(Pf) stimulation on visceral pain induced discharges of neurons in the posterior thalamic nuclei(PO). Methods: Experiments were performed on 1% chloralose anesthetized cats. Glass micropipettes were used for recording neuronal discharges in the right PO (AP: 4.0～5.5 mm

RL: 3.5～5.0 mm

H:1.0～3.5 mm). The stimulating electrode was inserted into the left Pf region (AP: 7.0 mm

RL: 1.3 mm

H:1.3 mm) for stimulating Pf with parameters of clusters of unidirectional rectangular waves (5 pulses/train)

0.5 mA and 0.5 ms wave duration. As an index of visceral pain

the greater splanchnic nerve (GSN) was stimulated electrically (25～30 V

0.5 ms wideth single pulses). The effects of Pf stimulation on the unit discharges were also studied with test conditioning stimulation techniques. Results: A total of 59 PO neurons responding to electrical stimulation of GSN were observed. Following Pf stimulation (conditioning stimulation)

discharges of majority of PO neurons (45/59

76.27%) were inhibited

presenting prompt suppression (23/45)

delayed suppression (7/45) and continuous suppression (15/45); 4 neurons (6.78%) were excited

4 (6.78%) presented inhibition excitation or excitation inhibition responses and the rest 6 (10.17%) had no apparent changes. Conclusion: Pf may be involved in the regulation of visceral pain

mainly showing an inhibitory effect on visceral pain.