آيا اثر 17 -بتا استراديول در هسته لوكوس سرولئوس در تعديل درد موشهاي صحرايي نر به وسيله گيرنده هاي GABAA وساطت ميشود؟

Is the pain modulatory action of 17p-estradiol in locus coeruleus of male rats mediated by GABAa receptors

Introduction: Estradiol is a neuroactive steroid, which is found in several brain areas such as locus coeruleus (LC). Estradiol modulates nociception by binding to its receptors and also by allosteric interaction with other membrane- bound receptors like glutamate and GABAa receptors. LC is involved in noradrenergic descending pain modulation. Methods: In order to study the effect of 17p-estradiol on both acute and persistent pain modulation and its mechanisms, formalin was injected into the hind paw of male rats. 17p-estradiol was unilaterally injected into the right LC by Hamilton syringe. Formalin-induced responses including licking and flexing duration and paw jerking frequency were recorded for 60 min after injection of 50 pi of 2% formalin. Also, the expression of a2 and yi subunits of GABAa receptor genes were examined by RT-PCR technique. Results: The results of the current study showed that intra-locus coeruleus injection of 17p-estradiol attenuated the second phase, but not the acute phase of formalin induced pain (P< 0.05). GABAa receptor antagonist (bicuculline) reversed the antinociceptive effect of 17P-estradiol, but the expression level of a2 and yj subunits of GABAa receptor genes were not significantly changed. Conclusion: It may be concluded that the analgesic effect of 17p-estradiol in formalin induced inflammatory pain is possibly mediated through the interaction with membrane-bound GABAa receptors, however this effect is not exerted at the gene expression level. YAY Key words: locus coeruleus nucleus, 17-p-estradiol, bicuculline, pain modulation, rat