Prophylactic effect of methylene blue against neurotoxicity of sodium nitroprusside

To examine the effect of methylene blue (MB) on cytotoxicities of sodium nitroprusside (SNP) and cyclic guanosine monophosphate (cGMP) in cultivated cerebellar neurons.

The cytotoxicities of xenobiotic SNP and cGMP on cultivated murine cerebellar neurons were examined according to Dessi's method. Toxicity of SNP i.c.v. to mice and the prophylactic effect of i.c.v. MB were investigated with respect to the incidence of seizure and the mortality of mice within 24 h.

Ten min treatment of SNP 1 mmol.L-1 decreased the survival rate of murine cerebellar nerve cells from 92% of normal control to 35%. Incubation with cGMP 0.1 mmol.L-1 for 1 h declined the survival rate from 94% of normal to 40%. Injection i.c.v. SNP 20 nmol killed one tenth of the mice in 24 h, and SNP 30 nmol killed 11/13 of the mice. MB (100 nmol) i.c.v. injection protected 11/13 of the mice against seizure and death caused by SNP (30 nmol, i.c.v.), and completely eliminated the toxicity of SNP 20 nmol.

SNP and cGMP inhibit the vitality of murine neurons in vitro. MB injection i.c.v. markedly antagonizes the dose-dependent neuron-toxic effect of SNP in respect of convulsion and mortality of mice.