dynorphins and 7-nitroindazole

The pharmacological effects of nitric oxide synthase (NOS) inhibitors, NO donor, and NOS substrate on dynorphin(Dyn) A(1-17) spinal neurotoxicity were studied. Intrathecal (i.t.) pretreatment with both 7-nitroindazole 1 micromol, a selective neuronal constitutive NOS (ncNOS) inhibitor, and aminoguanidine 1 micromol, a selective inducible NOS (iNOS) inhibitor, 10 min prior to i.t. Dyn A(1-17) 20 nmol significantly ameliorated Dyn-induced neurological outcome. Both 7-nitroindazole and aminoguanidine significantly antagonized the increases of cNOS and iNOS activities measured by conversion of 3H-L-arginine to 3H-L-citrulline in the ventral spinal cord, and blocked the Dyn-induced increases of ncNOS-immunoreactivity in the ventral horn cells 4 h after i.t. Dyn A(1-17) 20 nmol. Pretreatment with Nomega-nitro-L-arginine methyl ester (L-NAME) 1 micromol, a cNOS inhibitor nonselective to both ncNOS and endothelial NOS (ecNOS), did not antagonize Dyn A(1-17) 20 nmol-induced permanent paraplegia but aggravated Dyn A(1-17) 10 nmol-induced transient paralysis and caused permanent paraplegia. Pretreatment with L-NAME 1 micromol 10 min before i.t. Dyn A(1-17) 1.25 and 2.5 nmol, which produced no significant motor dysfunction alone, induced transient paralysis in seven out of 12 and five out of seven rats, respectively. L-NAME 1 micromol plus Dyn A(1-17) 10 nmol induced ncNOS-immunoreactivity expression in ventral horn cells. Both low and high doses of aminoguanidine (0.2-30 micromol) did not affect spinal motor function, but high doses of L-NAME (5-20 micromol) induced dose-dependent hindlimb and tail paralysis associated with spinal cord injury in normal rats. Pretreatment with low-dose Spermine NONOate, a controlled NO releaser, 0.1 and 0.5 micromol 10 min before i.t. Dyn A(1-17) 20 nmol, significantly prevented Dyn spinal neurotoxicity, and high-dose Spermine NONOate 2 micromol i.t. per se induced transient and incomplete paraplegia. But pretreatment with L-Arg 10 micromol 10 min before Dyn A(1-17) 20 nmol produced only partial blockade of Dyn-induced paraplegia. These results demonstrated that relatively specific inhibition of ncNOS and iNOS block Dyn-induced increases in cNOS and iNOS activities and ncNOS-immunoreactivity in ventral spinal cord, but nonspecific inhibition of ncNOS and ecNOS aggravated Dyn spinal neurotoxicity. It suggested that both ncNOS and iNOS play an important role, but ecNOS might be beneficial in Dyn spinal neurotoxicity. Moderate productio

Topics: Animals; Arginine; Dose-Response Relationship, Drug; Dynorphins; Enzyme Inhibitors; Guanidines; Immunohistochemistry; Indazoles; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type I; Nitric Oxide Synthase Type II; Nitrogen Oxides; Rats; Rats, Wistar; Spermine; Spinal Cord; Time Factors

To investigate the different role of neuronal constitutive nitric oxide synthase (nc-NOS) in dynorphin (Dyn) A(1-17) spinal neurotoxicity and analgesia.. The cNOS activity in ventral and dorsal spinal cord in rats was measured with H-L-arginine conversion, and ncNOS immunoreactivity(IR) was observed with strepavidin-peroxidase immunohisto-chemistry.. Intrathecal administration of Dyn A(1-17) produced dose-dependent paralysis of hindlimbs and tail as well as inhibition of tail flick (TF) and foot flinch (FF) reflexes. Dyn A(1-17) 10 nmol induced only transient paralysis and apparently reduced the ncNOS-IR in the superficial dorsal horn but did not induce any change of ncNOS-IR in the ventral horn cells as compared with saline control. Dyn A(1-17) 20 nmol produced permanent paraplegia with irreversible spinal cord damage, characterized by central and progressive necrosis. Dyn A(1-17) 20 nmol remarkedly induced the expression of ncNOS-IR in the ventral horn cells whereas inhibited ncNOS-IR in the superficial dorsal horn. Dyn A(1-17) 20 nmol also significantly increased the activities of cNOS in the ventral spinal cord but did not affect cNOS activities in the dorsal spinal cord. Intrathecal pretreatment with 7-nitroindazole (7-NI) 1 mumol, a selective ncNOS inhibitor 10 min prior to i.t. Dyn A(1-17) 20 nmol significantly ameliorated Dyn-induced neurological outcome, but TF and FF remained inhibited. 7-nitroindazole also significantly antagonized the increases of cNOS activities and ncNOS-IR in the ventral spinal cord at 4 h after i.t. Dyn A(1-17) 20 nmol, but did not affect or even potentiated Dyn-induced inhibition of cNOS activity and ncNOS-IR in the dorsal spinal cord.. Over-expression or over-activation of ncNOS in the ventral spinal cord may be involved in Dyn spinal neurotoxicity, whereas as the reduction of ncNOS activities in the dorsal spinal cord might reflect Dyn spinal analgeisia or pain modulation.

Topics: Analgesics; Animals; Dynorphins; Female; Indazoles; Male; Nerve Tissue Proteins; Nitric Oxide Synthase; Nitric Oxide Synthase Type I; Pain Threshold; Paraplegia; Rats; Rats, Wistar; Spinal Cord