Experiments were performed on 60 Sprague-Dawley rats. Using the extracellular recording method

We recorded the frequencies of spontaneous and evoked discharge of pain excitation neurons in the periaqueductal gray (PAG) to investigate the effects of TRH

ACh microinjected into nucleus cuneiformis(NCF) on the frequencies of evoked discharge of pain(PEN) and the relation of TRH to cholinergic nerve. The results as follows: (1) Injection of TRH(0. 5μg/0. 5μl

n = 12)

ACh(2. 5μg/o. 5μl

n=11)into NCF could all suppress the frequencies of evoked discharge of PEN in PAG(P<0.001

0.01

0. 05)

the maximal inhibitory rate was 77. 3±7. 5 % and 78. 4 ±7.0 % respectively. (2)Inhibitory effects of ACh (n = 5) could be antagonised by preinjection of atropine(2. 5μg/0. 5μl) into NCF(P < 0.05)

but TRH(n = 6) not. (3) Atropine(2. 5μg/0.5μl

n = 8 ) injected into NCF could not significantly influence the evoked discharge of PEN in PAG. These findings suggest that some neurons in NCF might participate in the process to modulate noxious information transmission in CNS. TRH and ACh might be a neuromodulator or transmitter in the antinociception of NCF. The inhibitions of ACh may be mediated by cholinergic M-receptor. but TRH could not be mediated by cholinetgic Mreceptor.