[Effects of strong and weak electroacupuncture on endotoxin-induced changes of electrical activities of heat-sensitive neurons in preoptic area and anterior hypothalamus in rabbits].

Objective To observe the effects of weak and strong electroacupuncture(EA) on endotoxin(ET) thermolysis-induced changes of discharges of neurons in the preoptic region and anterior hypothalamus(PO-AH) so as to explore its underlying mechanism in antipyretic and thermolytic actions and its relation to the receptive system of acupoints.Methods Eighteen New Zealand rabbits were randomly divided into ET group,ET+weak-EA group and ET+strong-EA group.Extracellular discharges of the PO-AH neurons were recorded by using tungsten microelectrodes.A "U"-shape stainless steel tube was implanted in the region(P0.4-A4.4,L0.5-1.7) crossing the hypothalamus for changing local temperature by perfusion of cool(25 ℃) or warm(41 ℃) solution in order to distinguish the heat sensitive neurons(HSN),cold sensitive neurons(CSN) and insensitve neurons to temperature changes.Intravenous injection of endotoxin(25 EU/rabbit) was given to rabbits to induce increase of tempe rature.EA(8 Hz,wave width 0.1 ms,weak stimulation: 4.5 V,strong stimulation: 25 V) was applied to bilateral "Yongquan"(KI 1) for observing changes of firing rates of HSN in PO-AH.Results Compared with the basal values of firing rates of PO-AH neurons in each group,the average changing ratios of both ET and ET+weak-EA groups decreased significantly from 55-60 min on in ET group and from 40-45 min on in ET+weak-EA group after intravenous injection of ET(P0.05),suggesting no marked effect of weak EA for preventing discharges of PO-AH neurons from decrease.While in ET+strong-EA group,the firing rates of HSN of PO-AH kept stable after injection of ET during EA and after cease of EA(P0.05 vs basal value),suggesting that strong EA could antagonize ET thermolysis-induced decrease of firing rates of PO-AH neurons.Conclusion Stronger EA stimulation of KI1 can antagonize ET thermolysis-induced effect on electrical activities of PO-AH HSN,which may be initiated by the activation of the high-threshold thin nerve fibers in the acupoint region.