OBJECTIVETo investigate the effects of intrathecal injection of ginsenoside Rg1 at different doses on the changes of the behavior and the expressions of excitatory amino-acid transporter 1 (EAAT1), i. e., glutamate-aspartate transporter (GLAST) in the spinal dorsal horn of the arthritis rats with chronic morphine tolerance, and further to explore its mechanisms for morphine tolerance.

METHODSAfter successful intrathecal injection, an adjuvant arthritis model was established in 36 healthy male SD rats. They were randomly divided into 6 groups, 6 in each group. They were intrathecally injected with 10 microL normal saline (Group NS), 10 microg morphine (Group M), 10 microg morphine + 50 microg ginsenoside Rg1 (Group MG50), 10 microg morphine +100 microg ginsenoside Rg1 (Group MG100), 10 microg morphine + 200 microg ginsenoside Rg1 (Group MG200), and 100 microg ginsenoside Rg1 (Group G100), respectively. The normal saline and morphine were intrathecally injected twice daily, while ginsenoside Rg1 at different doses was intrathecally injected once daily, for 7 successive days. Fifty percent mechanical paw withdrawal threshold (PWT) was dynamically detected to evaluate their behaviors. The rats were sacrificed on day 7 after medication. The L3-L5 segment of the spinal cord was isolated for determining the expression of GLAST in the spinal dorsal horn using immunofluorescence staining.

RESULTSThe PWT of Group M was significantly higher than that of Group NS on the 1st and 3rd day after medication (P < 0.05). But it was gradually shortened along with the increasing days of medication. There was no statistical difference between Group M and Group NS on the 7th day (P > 0.05), indicating the formation of morphine tolerance. The PWT of Group MG100 also showed a decreasing tendency, but obviously slower than that of Group M (P < 0.05). The PWT of Group G100 was higher than that of Group NS (P < 0.05). Compared with Group NS, the expression of GLAST in the spinal dorsal horn of rats in Group M was down-regulated (P < 0.01). Compared with Group M, the expression of GLAST in the spinal dorsal horn of rats in Group MG100 and Group G100 was up-regulated (P < 0.05).

CONCLUSIONSSingle application of ginsenoside Rg1 showed mild antinociceptive effect in adjuvant-induced arthritis rats. Intrathecal injection of 100 microg ginsenoside Rg1 could attenuate the formation of morphine tolerance. Its mechanisms might be correlated with up-regulating of the expression of GLAST.