The Effect Of Crotoxin On Pain-evoked Discharge Of Neurons In Thalamic Parafascicular Nucleus And The Preliminary Investigation On Its Mechanism

To investigate the effect of Crotoxin on pain-evoked discharge of neurons in thalamic parafascicular nucleus (Pf) and its mechanism, the pain-evoked discharge was recorded extracellularly with glass microelectrode from Pf. Different doses of Crotoxin were injected intracerebroventricularly(i.c.v.). Normal saline and morphine were used as negative and positive control, respectively. To analyze the mechanism of effects of Crotoxin on pain-evoked discharge of neurons in Pf, i.c.v. injection of atropine and naloxone, intraperitoneal injection (ip) para-chlorophenylalanine (pCPA), and lesion of nucleus raphe dorsalis (DR) were used.The experimental results indicated that :(1)The spontaneous unit discharges had two types: rhythmic and cluster discharge. (2)There were three types of responses after noxious stimulation: excitatory type, inhibitory type and no response type. (3)The frequency, the latency and the duration of pain-evoked discharge of thalamic parafascicular neurons were inhibited after i.c.v. injection of large, medium and small doses of Crotoxin. The effect was dose-dependent. (4)There was no influence on the inhibitory effect of Crotoxin on pain-evoked discharge of neurons in Pf after i.c.v. injection of atropine or naloxone. (5)The inhibitory effect of Crotoxin on pain-evoked discharge of neurons in Pf was partially reversed after pCPA pre-treatment, as well as after DR lesion.The results suggested that: (1)Crotoxin has an analgesic effect which is dose-dependent. (2)Central cholinergic and opioidergic system may not participate in the...