Intrathecal injection of MK-801 inhibited the NOS activity and NO content of hippocampus in rat during the process of formalin-induced inflammatory pain / 中国应用生理学杂志

ABSTRACT

<p><b>AIM</b>To study the effect of intrathecal injection of MK-801, a NMDA receptor antagonist, on the NOS activity and NO content of hippocampus in rat during the process of formalin-induced inflammatory pain as well as the pain behavior of rat.</p><p><b>METHODS</b>The degree of pain was determined by observing the time of licking and biting the injected paw. NOS expression in the hippocampus was determined by using NADPH-d histochemical staining. NO content of hippocampus was determined by assaying NO3; and NO2.</p><p><b>RESULTS</b>Subcutaneous injection of formalin elicited a characteristic pain behavioural response consisting of licking and biting the injected paw, etc. Intrathecal injection of MK-801 could shorten obviously the time of licking and biting representing pain behavioural response in phase 2. It is suggested that intrathecal injection of MK-801 could block the pain behavioural response induced by formalin (P < 0.05). The number and staining degree of NADPH-d positive neurons in formalin group significantly increased at 12 h after the formalin injection in CA1, CA2-3 and DG of hippocampus compared with control group as well as NO content, however, the number and staining degree of NADPH-d positive neurons in formalin + MK-801 group significantly decreased in contrast to those of formalin 12 h group as well as the NO content (P < 0.01).</p><p><b>CONCLUSION</b>Intrathecal injection of NMDA receptor antagonist MK-801 could inhibit the NOS activity and NO production in hippocampus of rat, which showed the increase of hippocampal NO production was mainly induced by the peripheral nociceptive information input.</p>