AIM: To study the effect of intrahippocampal infusion of interleukin-6
(IL-6) on active avoidance in rats and the possible involvement of ni
tric oxide (NO). METHODS: Using a shuttle-box model, the effects of bi
laterally intrahippocampal infusion of IL-6 3.2, 16, and 80 ng as well
as sodium nitroprusside (SNP) 400 ng on active avoidance were studied
on d 8 after administration. The levels of nitrite as an index of NO
in the hippocampus were detected using a fluorometric assay 24 h after
infusion of IL-6 3.2 or 80 ng. RESULTS: IL-6 16 and 80 ng impaired th
e acquisition performance of active avoidance by prolonging the latenc
y of avoidance in training, but not the retention performance in testi
ng. IG-6 80 ng and SNP 400 ng also resulted in a marked impairment in
acquisition performances by decreasing the rate bf avoidance, but not
in retention performances. IL-6 80 ng markedly elevated the nitrite le
vels from 10.6 +/- 0.7 in control rats to 13,6 +/- 2.0 (nmol/g wet wt)
(P < 0.01). IL-6 3.2 ng had no effect on active avoidance nor on nitr
ite levels. CONCLUSION: Intrahippocampal infusion of IL-6 impaired lea
rning acquisition of active avoidance in rats.