65 nociceptive neurones in the PAG of 55 male SD rats were recorded by glass microprobe tech- nique. The effects of angiotensin Ⅱ (AII) on the electrical activity of nociceptive neurones in PAG and on the antinociceptive effect of morphine were observed. The results are as follows: (1)The injection of AII (50ng/5μl.1μg/5μ1. 2 μg /5μl

i. c. v. ) produced striking excitatory effect both on nociceptive dis- charges and spontaneous discharges of PEN in PAG; (2) In 9 pain inhibitory neurones(PIN)

the elec- trical activity of & units was inhibited after the i. c. v. injection of All

and the electrical activity of 1 unit kept unchanged; (3) I. C. V. injection of AII(50ng

2μg/5μl)partly reversed the inhibitory effect of morphine (i. p.

2. 5mg/kg weight) on the PEN in. PAG. The above results suggest that modula- tion of AII on the transmission of nociceptive messages and antagonism on the antinociceptive function of morphine may be completed by facilitating PEN and inhibiting PIN in PAG.