DECREASED RAPHE SEROTONIN IN RABBITS WITH EXPERIMENTAL HERPES-SIMPLEXENCEPHALITIS

Increased monoamine metabolism in experimental herpes simplex virus (H SV) encephalitis is well established. Both serotonin (5-HT) and dopami ne (DA) systems are affected. HSV invades the raphe nuclei after its e ntry into the brain stem. However, no studies have been published conc erning influences of HSV on the neurotransmitters in the raphe. In the present study, concentrations of 5-HT and DA and their metabolites in the raphe nuclei and related brain regions in rabbits with fulminant HSV encephalitis have been analyzed using high-pressure liquid chromat ography. Encephalitis was induced by corneal inoculation with HSV. Hom ovanillic acid (HVA) and dihydroxyphenyl acetic acid (DOPAC) concentra tions and HVA/DA ratios were increased in the raphe nuclei suggesting increased DA turnover. The most substantial changes were bilaterally d ecreased 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) concentrations i n the raphe nuclei. The decrease in the raphe 5-HT was reflected also to the projection areas in the hemispheres, where 5-HT concentrations were lower in HSV-inoculated rabbits than in controls. The changes str ongly suggest a direct influence of HSV on serotoninergic neurons. Sin ce the ventral parts of the limbic system have rich serotoninergic aff erents from the raphe, this also suggests that HSV may reach hemispher es in HSV encephalitis from the brain stem via the ascending serotonin ergic system.