Intraspinal Injection of Adenosine Agonists Protect Againstl-NAME Induced Neuronal Loss in the Rat

Abstract

Intraspinal injection of the nonspecific inhibitor of nitric oxide synthase N-nitro-L-arginine methyl ester (L-NAME) results in a dose-dependent loss of neurons in the rat spinal cord. This effect is thought to result from a reduction in basal levels of nitric oxide (NO), thereby producing an ischemic reaction secondary to vasoconstriction and reduced spinal cord blood flow (SCBF). An important component of this ischemic reaction is the release of excitatory amino acids and the initiation of an excitotoxic cascade. In the present study, microinjections of adenosine A1 and A2 receptor agonists were made in the spinal cord to evaluate the neuroprotective effects of these drugs against neuronal loss produced by L-NAME. Animals were divided into six groups based on the composition of injected solutions: (a) L-NAME; (b) L-NAME + N6-cyclopentyladenosine (CPA, A1 agonist); (c) L-NAME + 5'-(N-cyclopropyl)-carboxamidoadenosine (CPCA, A2 agonist); (d) L-NAME + CPA + CPCA; (e) N-methyl D-aspartate (NMDA); and (f) NMDA + CPA. Injections of L-NAME or NMDA produced a unilateral loss of spinal neurons, a local inflammatory response, and darkly stained pyknotic nuclei surrounding the area of neuronal loss. CPA and CPCA significantly reduced the area of L-NAME-induced neuronal loss, and a synergistic effect was observed when ineffective doses of these agonists were co-injected with L-NAME. The excitotoxic effects of NMDA were not affected by CPA. The results have shown that A1 and A2 receptor agonists provide significant neuroprotection against L-NAME induced neuronal loss, presumably by inhibiting ischemia induced release of excitatory amino acids (A1 agonist), or by restoring SCBF secondary to vasodilation (A2 agonist). It is suggested by these results that the intraspinal injection of L-NAME is an effective model to study the pathological consequences of vasoconstriction, reduced SCBF, and ischemia secondary to decreased NO production in the rat spinal cord. Finally, the results provide support for the continued investigation of specific adenosine agonists as therapeutic agents directed against the ischemic and excitotoxic components of spinal injury.

Effect of oxidative stress induced by intracranial iron overload on central pain after spinal cord injury

“…We also showed that the thermal pain threshold in the lower extremities was significantly decreased in the SCI/CP groups, thus triggering hyperalgesia. These results indicated that both spontaneous and induced pain were induced in this rat model, in line with previous studies [ 30 – 32 ]. Treatment with DFO or arginine significantly increased the thermal pain threshold and reduced excessive grooming behavior, suggesting that these drugs relieved the induced and spontaneous SCI-associated CP.…”

The Role of Reactive Nitrogen Species in Secondary Spinal Cord Injury

“…Pretreatment with L‐NAME causes deterioration of hind‐limb motor dysfunction, whereas posttreatment with it reduces motor disturbance, suggesting that • NO formation by constitutive NOS protects against ischemia/reperfusion damage and that • NO produced by inducible NOS may be toxic. Intraspinal injection of L‐NAME induced a dose‐dependent loss of neurons in the rat spinal cord, further supporting the protective effect of constitutive • NO (Dora et al, 1998).…”

Evidence that quinolinic acid severely impairs energy metabolism through activation of NMDA receptors in striatum from developing rats

“…2005) and in other pathological conditions (Sharma et al . 2005) have been already described in animal studies, although acute and chronic neurotoxic effects of this nitric oxide synthase inhibitor have also been reported (Dora et al . 1998; Ciani et al .…”

“…Pyruvate treatment decreased iNOS expression in astrocytes by about 50% (Ryu et al 2004), which may explain the partial prevention of creatine kinase activity inhibition and reinforces our present data indicating that this inhibition is at least in part mediated by formation of nitric oxide or its derivative peroxynitrite. In this regard, other neuroprotective actions of L-NAME in situations with energy deprivation, such as in cerebral ischemia (Margaill et al 1997) and hyperargininemia (Delwing et al 2003), as well as in a model of Parkinson's disease (Barthwal et al 2001;Kurosaki et al 2002;Singh et al 2005) and in other pathological conditions (Sharma et al 2005) have been already described in animal studies, although acute and chronic neurotoxic effects of this nitric oxide synthase inhibitor have also been reported (Dora et al 1998;Ciani et al 2001).…”