Spinal reflexes in normal and sulfite oxidase deficient rats: effect of sulfite exposure

Sulfites, which are commonly used as food preservatives, are continuously formed in the body during metabolism of sulfur-containing amino acids. Sulfite is oxidized to sulfate ion by sulfite oxidase (SOX, EC. 1.8.3.1). Although sulfite treatment has been reported to increase the excitability of some neurons in vitro, the possible effects of sulfite on neuronal excitability in vivo remain unclear. The aim of this study was to investigate the possible effects of sulfite treatment on spinal reflexes in anesthetized SOX competent and deficient rats. For this purpose, male albino rats used in this study were divided into four groups such as control group (C), sulfite group (CS), SOX deficient group (D), and SOX deficient + sulfite group (DS). Rats in SOX deficient groups were made deficient in SOX by the administration of low molybdenum (Mo) diet (AIN 76, Research Dyets Inc., USA) with concurrent addition of 200-ppm tungsten (W) to their drinking water in the form of sodium tungstate (NaWO4). Sulfite in the form of sodium metabisulfite (Na2O5S2, 70 mg/kg) was given orally by adding to drinking water to the S and DS groups. Monosynaptic reflex potentials were recorded from the ipsilateral L5 ventral root. SOX deficient rats had an approximately 15-fold decrease in hepatic SOX activity compared with normal rats. This makes SOX activity of SOXD rats in the range of human SOX activity. The results of this study show that sulfite treatment significantly increases the amplitude of the monosynaptic reflex response in both S and DS groups with respect to their respective control groups (C and D). SOX deficient rats also had enhanced spinal reflexes when compared with control rats. In conclusion, sulfite has increasing effects on the excitability of spinal reflexes and we speculate that this compound may exhibit its effects on nervous system by affecting sodium channels.