The elucidation of the onset organization of the trigeminal neuralgia using a trigeminal nerve damage animal.

口面部有皮肤和粘液区，福尔马林注射到这两个不同的区域会导致不同的明示行为。皮下注射稀释福尔马林到大鼠的上嘴唇，比注射到舌头引起更多的明示行为。当将福尔马林注射到嘴唇而不是舌头时，预先给予GABA_A受体拮抗剂荷包牡丹碱对行为的抑制作用更大。其致病行为和药理上的差异可能是由于C-纤维种群数量和质量分布的差异所致。舌部C-纤维的初级传入神经元(三叉神经)比唇部皮肤少，在三叉神经尾侧亚核(VC)的I层和III层分布有相当数量的P物质(SP)、神经激肽-1(NK-1)受体神经元。我们通过向大鼠枕大池预先注射SP和核糖体失活毒素皂苷(SP-SAP)来消除这些带有NK-1的神经元。在这些SP-SAP预处理的大鼠中，福尔马林诱导的致病行为减少，荷包牡丹碱预给药增强致病行为，而荷包牡丹碱则使幼年大鼠的致病行为减弱。这些结果表明，NK-1神经元通过上行和下行的伤害性易化环参与伤害性感受器的传递，其中GABA作为伤害性感受的促进环。

The orofacial region has skin and mucous region and the formalin injection into the two different region induces different nocifensive behavior. The subcutaneous injection of diluted formalin into the rat upper lip induced more nocifensive behaviour than into the tongue. The behavior was inhibited more by the preadministration of an antagonist of GABA_A receptor, bicuculline, when formalin was injected into the lip than into the tongue. The resultant differences of nocifensive behaviour and pharmacology could be caused by the differences in the quantitative and qualitative distribution of C-fiber population. The tongue has fewer primary afferent neurons (trigeminal nerve) in the range of C-fiber than the lip skin.Considerable number of neurons-bearing receptors of substance P (SP), neurokinin-1 (NK-1) are distributed in lamina I and less in lamina III of trigeminal subnucleus caudalis (Vc). We have eliminated these NK-1-bearing neurons by preadministration of SP conjugated with a ribosome-inactivating toxin, saporin (SP-Sap) into the rat cisterna magna. In these SP-Sap-pretreated rats, the formalin-induced nocifensive behaviour was reduced and the preadministration of bicuculline enhanced the nocifensive behaviour, when bicuculline reduced it in the naive rats. These results show that NK-1-bearing neurons are involved in pro-nociceptive transducer through ascending and descending nociceptive facilitating loop, where GABA acts as prpnociceptive.