Objective: To investigate the effect of ovariectomy and electroacupuncture(EA) on LH release and its possible neuroendocrinological mechanism.Methods: Twentyfour female SD rats were randomly and evenly divided into sham-operation(control) group

sham operation +EA group

ovariectomized(OVX

model) group and OVX +EA group.EA(2-3 Hz

1-2 mA

continuous waves) was applied to "Guanyuan"(CV 4)

"Zhongji"(CV 3)

bilateral "Zigong"(TE 6) and unilateral "Sanyinjiao"(SP 6) for 30 min

once per day

3 days altogether.The techniques of radioimmunoassay(RIA)

immunohistochemistry

Western blot and reversed transcription-polymerase chain reaction(RT-PCR) were used for assay of serum luteinizing hormone(LH) level

expression of hypothalamic orphanin(O)FQ mRNA

ORL_1 receptor(ORL_1) mRNA and protein.Results: Compared with control group

serum LH level increased abnormally in OVX group(P<0.05);and comparison between OVX and OVX+EA groups showed that serum LH of the later group was significantly lower than that of the former group(P<0.05).No significant difference was found between EA and OVX+EA groups in serum LH levels(P>0.05).Immunohistochemical results indicated that the number of OFQ immunoreaction(IR)-positive cells of hypothalamic ventromedial nucleus(VMN) and medial preoptic area(MPOA) and the relative optical density(OD) value of OFQ IR-positive fibers of the median eminence in OVX group decreased considerably(P<0.05);the number of OFQ IR-positive cells and OD value of IR-positive fibers of OVX+EA group were significantly higher than those of OVX group(P<0.05).Results of RT-PCR and Western blot examination showed that OD values of OFQ and ORL_1 mRNA and ORL_1 receptor protein of hypothalamic basal part in OVX group were significantly lower than those in control group(P<0.05);while OD value of OFQ mRNA in OVX+EA group was significantly higher than that of OVX group(P<0.05).No significant differences were found between control and EA groups in OD values of OFQ mRNA and ORL_1 mRNA and ORL_1 receptor protein

and between OVX and OVX+EA groups in OD values of ORL_1 mRNA and ORL_1 receptor protein. Conclusion:Hypothalamic OFQ and ORL_1 receptor may play a role in the regulation of LH release

and OFQ is involved in the normalization effect of EA on subnormal function of hypothalamus-pituitary-ovary axis in ovariectomized rats.