Expression of nitric oxide synthase isoforms in the dorsal horn of monoarthritic rats: effects of competitive and uncompetitive N-methyl-D-aspartate antagonists

Abstract

Chronic pain is associated with N-methyl-D-aspartate (NMDA) receptor activation and downstream production of nitric oxide, which has a pivotal role in multisynaptic local circuit nociceptive processing in the spinal cord. The formation of nitric oxide is catalyzed by three major nitric oxide synthase (NOS) isoforms (neuronal, nNOS; inducible, iNOS; endothelial, eNOS), which are increased in the spinal cord of rodents subjected to some tonic and chronic forms of experimental pain. Despite the important role of NOS in spinal cord nociceptive transmission, there have been no studies exploring the effect of NMDA receptor blockade on NOS expression in the dorsal horn during chronic pain. Furthermore, NOS isoforms have not been fully characterized in the dorsal horn of animals subjected to arthritic pain. The aim of this work was therefore to study the expression of nNOS, iNOS and eNOS in the dorsal horns of monoarthritic rats, and the modifications in NOS expression induced by pharmacological blockade of spinal cord NMDA receptors. Monoarthritis was produced by intra-articular injection of complete Freund's adjuvant into the right tibio-tarsal joint. At week 4, monoarthritic rats were given either the competitive NMDA antagonist (±)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) or the uncompetitive NMDA antagonist ketamine. After 6 and 24 hours, animals were killed and posterior quadrants of the lumbar spinal cord were dissected. Sample tissues were homogenized and subjected to immunoblotting with anti-nNOS, anti-iNOS or anti-eNOS monoclonal antibodies. The nNOS isoform, but not the iNOS and eNOS isoforms, were detected in the dorsal horns of control rats. Monoarthritis increased the expression of nNOS, iNOS and eNOS in the dorsal horns ipsilateral and contralateral to the inflamed hindpaw. Intrathecal administration of CPP and ketamine reduced nNOS expression in monoarthritic rats but increased the expression of iNOS and eNOS. Results suggest that blockade of spinal cord NMDA receptors produces complex regulatory changes in the expression of NOS isoforms in monoarthritic rats that may be relevant for nitridergic neuronal/ glial mechanisms involved in the pathophysiology of monoarthritis and in the pharmacological response to drugs interacting with NMDA receptors.

Neuron–astrocyte signaling network in spinal cord dorsal horn mediates painful neuropathy of type 2 diabetes

“…For example, Kitto and colleagues observed inhibition of NMDA-induced hyperalgesia as a result of intrathecal L-NAME treatment (Kitto et al 1992). Increased NOS expression was also reported in an inflammatory pain model (Infante et al 2007). In addition, L-NAME inhibits neuropathy-induced thermal hyperalgesia (Inoue et al 1998; Thomas et al 1996).…”

Interaction between NMDA glutamatergic and nitrergic enteric pathways during in vitro ischemia and reperfusion

“…In cerebellar granule cells, suppression of both NMDA and AMPA receptor-mediated spontaneous synaptic signalling resulted in the up-regulation of nNOS expression (Baader and Schilling, 1996). In rat spinal cord of rats subjected to arthritic pain the NMDA antagonists, CPP and ketamine, drastically reduced nNOS expression (Infante et al, 2007). Analogously, the increased expression of nNOS in the spinal cord of morphine-tolerant rats was reduced by the NMDA antagonist, MK801 (Wong et al, 2000).…”

Minocycline prevents impaired glial glutamate uptake in the spinal sensory synapses of neuropathic rats

“…For example, proinflammatory cytokines (IL-1β and TNFα) reduce glial glutamate uptake through pathways related to the release of nitric oxide (Hu et al, 2000; Ye and Sontheimer, 1996) and activation of NF-κB (Han et al, 2001; Ye and Sontheimer, 1996; Zou and Crews, 2005). Peripheral nerve injury or tissue inflammation results in the activation of glial cells, increases levels of proinflammatory cytokines (Watkins et al, 2001), and activates NF-κB (Tegeder et al, 2004) and nitric oxide synthase (Infante et al, 2007; O'Rielly and Loomis, 2006) in the spinal dorsal horn (Milligan and Watkins, 2009). Therefore, we suggest that the inhibition of glial cell activation by minocycline and the subsequent suppression on both the production of proinflammatory cytokines and the activation of NF-κB and nitric oxide synthase result in the preservation of glial GT expression and function in the spinal dorsal horn.…”