OUABAIN RELEASES STRIATAL POLYAMINES INVIVO INDEPENDENTLY OF N-METHYL-D-ASPARTATE RECEPTOR ACTIVATION

Intrastriatally infused ouabain (200 or 1,000 muM) markedly increased the extracellular levels of striatal spermidine and spermine in dialysis experiments in halothane-anesthetized rats. The effects of ouabain (1 mM) on spermidine release were rapid and unaffected by local infusion of the competitive N-methyl-D-aspartate (NMDA) antagonist 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP; 100 muM) or by systemically administered MK-801 (0.3 mg/kg i.p.), both of which treatments markedly inhibit the effects of intrastriatally administered NMDA. The peak effects of ouabain (1 mM) on spermine release were delayed with respect to those on spermidine release, or to the effects of NMDA, and were also insensitive to locally administered CPP (100 muM). However, systemically administered MK-801 (0.3 mg/kg i.p., 30 min before the striatal infusion of drugs), which totally inhibits the effects of NMDA, or CPP (10 mg/kg i.p.; 30 min before the striatal infusion of drugs) partially inhibited the effects of ouabain on spermine release, suggesting partial mediation of the delayed effects of ouabain on spermine release by indirect NMDA-receptor activation. Despite partial sensitivity of ouabain-induced spermine release to systemically administered NMDA antagonists, both spermidine and spermine can be released in vivo by sodium-pump inhibition, independently of NMDA-receptor activation.