The effect of raphé nuclei lesions on striatal tyramine concentration and dopamine turnover in the rat

This is an investigation of the effects of electrolytic lesions (1 mA, 10s, anodal) on the median and dorsal raphé nuclei of Wistar rats on the striatal concentrations of p-tyrosine, p-tyramine, m-tyramine, DA, DOPAC, and HVA. The extent of the lesions was estimated in terms of the depletion of 5-hydroxytryptamine and 5-hydroxyindole acetic acid as well as histological examination of the lesioned area. The results show that the raphé nuclei lesions increased rat striatal levels of DOPAC and HVA while levels of DA were unaffected, an effect that was observed within the first day after the lesions were made. The increases in DOPAC and HVA were accompanied by a reduction in striatal p-tyramine and an increase in m-tyramine. The results further support the existence of a reciprocal relationship between p- and m-tyramine concentrations and dopamine metabolism. Previous experiments have demonstrated depletion of p-TA following nigral lesions. The present results are, therefore, important in relation to tyramine distribution in brain. The p- and m-tyramine concentrations were not reduced at 7 days after the raphé nuclei lesions indicating that if the striatal tyramine-containing neurons exist, they do not originate in or pass through the dorsal or median raphé nuclei.