Effect of morphine and naloxone on release of the excitatory amino acids of spinal astrocytes induced by TNF-α

The effect of morphine and naloxone on release of the excitatory amino acids (EAAs) of spinal astrocytes induced by TNF-a was studied. Astrocytes were purified from 2- to 3-day old SD rats and divided into 8 groups: group 1 (without any stimulatants); group 2 (10 ng/ml TNF-alpha); group3 (10 ng/ml TNF-alpha + 0.5 micromol/L morphine); group 4 (10 ng/ml TNF-alpha + 1.0 micromol/L morphine); group 5 (10 ng/ml TNF-alpha + 2. 0 micromol/L morphine); group 6 (10 ng/ml TNF-alpha + 0.5 micromol/L naloxone); group 7 (10 ng/ml TNF-alpha + 1.0 0Lmol/L naloxone); group 8 (10 ng/ml TNF-alpha + 2. 0 micromol/L naloxone). In group 2, 3, 4 and 5, 0, 0.5, 1.0 or 2.0 micromol/L morphine was added to the cells cultured with serum-free Neurobasal/B27 medium containing 10 ng/ml TNF-alpha respectively, while in group 6, 7 and 8, 0.5, 1.0 or 2.0 micromol/L naloxone was added respectively to the cells cultured with serum-free Neurobasal/B27 medium containing 10 ng/ml TNF-alpha. After 30 min incubation, high-pressure liquid chromatography (HPLC) was used to measure the levels of EAAs in all cultured cells. The results showed the level of EAAs in group 2 was significant higher than in group 1 (P < 0.01). As compared with group 2, the levels of EAAs in group 3, 4 and 5 were decreased with the difference being significant between group 5 and group 2 (P < 0.01) or between group 4 and group 2 (P < 0.05). The levels of EAAs in group 6, 7 and group 8 was significantly lower than in group 2 (P < 0.05 or P < 0.01). It was concluded that TNF-alpha could promote the release of glutamate and aspartate from astrocytes, and morphine and naloxone might reduce the release of EAAs in cultured spinal astrocytes induced by TNF-alpha.