Decreased startle reactivity in the end-to-side portacaval shunted rat

A rat with an end-to-side portacaval anastomosis (PCA) is an extensively used experimental animal for characterization of biochemical alterations following diversion of portal blood flow from the liver; but few behavioral abnormalities have been detected. Biochemical changes observed in rats after PCA include increased plasma and brain levels of the serotonin precursor tryptophan, with increased brain serotonin and its metabolite 5-hydroxyindoleacetic acid. Accumulating evidence indicates that serotonin may be involved in the modulation of the startle response in the rat. In this study, the magnitude of startle responses to both tactile and auditory stimuli were shown to be abnormally decreased in chronic PCA rats. The simplicity of this animal model and the reproducibility of the effect suggest that evaluation of startle responses in rats with PCA may enable assessments of the efficacy of putative therapeutic strategies for the treatment of some of the dysfunctions associated with hepatic encephalopathy.