Cobratoxin inhibits pain-evoked discharge of neurons in thalamic parafascicular nucleus in rats: involvement of cholinergic and serotonergic systems.
The present study investigated the inhibitory effect of cobratoxin (CTX) on pain-evoked discharge of neurons in thalamic parafascicular nucleus (Pf) of rats and analyzed some of the mechanisms involved in this effect. Intracerebroventricular injection (icv) of CTX at 0.56, 1.12 and 4.50 microg/kg resulted in a dose-dependent inhibitory effect on the pain-evoked discharges of Pf neurons. The inhibition of pain-evoked discharges of Pf neurons by CTX at high dose (4.50 microg/kg) persisted at least for 2h, while the inhibitory effect of morphine (40 microg) persisted no longer than 30 min. The inhibitory effect of CTX was reversed by pretreatment with atropine (icv, 5 microg). In contrast, icv injection of naloxone (4 microg) had no effect on CTX-induced inhibition. Furthermore, pretreatment with parachlorophenylalanine, a specific inhibitor of tryptophan hydroxylase, also significantly attenuated the inhibitory effect of CTX. The results suggested that: (a) CTX has a dose-dependent inhibitory effect on pain-evoked discharges of Pf neurons, confirming electrophysiologically the antinociceptive action of CTX; (b) the inhibitory effect of CTX has a longer duration compared to that of morphine; (c) central cholinergic and serotonergic systems, but not opioidergic system, are involved in the inhibitory effect of CTX.
Cheng
Bo-Chao
BC
Department of Neurobiology and Medical Psychology, Medical College, Soochow University, Suzhou 215123, PR China.
Zhou
Xi-Ping
XP
Zhu
Qi
Q
Gong
Shan
S
Qin
Zheng-Hong
ZH
Reid
Paul F
PF
Raymond
Laurence N
LN
Yin
Qi-Zhang
QZ
Jiang
Xing-Hong
XH
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D003039:Cobra Neurotoxin Proteins / Q000494:pharmacology*; D005071:Evoked Potentials / Q000187:drug effects*; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects*; D010146:Pain / Q000473:pathology*; D051381:Rats; D017208:Rats, Wistar; D011950:Receptors, Cholinergic / Q000502:physiology*; D011985:Receptors, Serotonin / Q000502:physiology*; D013787:Thalamic Nuclei / Q000187:drug effects* / Q000473:pathology
D003039:Cobra Neurotoxin Proteins; D011950:Receptors, Cholinergic; D011985:Receptors, Serotonin; D009270:Naloxone; D001285:Atropine