Objective:To observe the effect of electroacupunc ture (EA) at different tim e and frequencies on somatostatin (SOM)mRNA expression positive neurons in the l ateral septal nucleus (LSN) in rats. Methods: A total of 60 SD rats were randomi zed into control

2 Hz-EA and 128 Hz-EA groups which were further divided int o 5-o ’clock

11-o’clock

17-o’clock and 23-o’clock subgroups. Unilateral “Hu anti ao”(GB 30) was punctured and stimulated electrically by setting the parameters being strength of 3 V

wave-width of 1 ms

frequencies of 2 Hz and 128 Hz

and stimu lating duration of 30 min. After acupuncture treatment

the rats were killed for taking out the brain samples. Following freezing

the brain tissue was cut into sections (40 μm) and the in situ hybridization histochemical method was used for displaying SOM mRNA expression. The number of SOM mRNA expression positive neuro ns of LSN (4 sections/rat) was calculated under light microscope. Re sults: After EA of “Huantiao”(GB 30)

compared with control group

SOM mRNA positive neurons in LSN of 2 Hz-EA group at 11- and 17-o’clock and 128 Hz-EA group at 5-

1 7- and 23-o’clock increased significantly in the number (P<0.05～0.01). Com parison between 2 Hz- and 128 Hz-EA groups showed that SOM mRNA positive neur ons in LSN of the later group at 5-

17- and 23-o’clock were markedly more tha n those of the former group at the same time courses

suggesting that the effect of 128 Hz EA on SOM mRNA expression was apparently stronger than that of 2 Hz E A. In 128 Hz-EA group

comparison among different time courses

SOM mRNA positive neu rons at 17-o’clock were markedly more than those of 5-

11- and 23-o ’clock

indicating that the effect of EA at 17-o’clock on SOM mRNA expressi o n was stronger than those of EA in the other time courses.Conclusion: EA stimulation in duced increase of the number of SOM mRNA expression positive neurons in the LSN h as a close association with the time and frequencies of EA in rats.