Effects of chronic experimental liver dysfunction and L-tryptophan on behaviour in the rat.

Rats with chronic experimental portocaval anastomosis were hypoactive as indicated by diminished activity in the home cage, during habituation in red light to an observation box and during exposure in white light to an open-field. Food intake and responsiveness to electric shock were also decreased. However, there was an abnormally high frequency of social activity when anastomosed rats were paired together after having been caged singly for 3 weeks. Also, sham-operated rats interacted more with anastomosed rats than they did with other sham-operated animals. Anastomosis also raised brain concentrations of tryptophan, 5-hydroxytryptamine and 5-hydroxyindoleacetic acid. Administration of tryptophan to sham-operated rats increased shock threshold and decreased ambulation in an open-field. Thus, while anastomosed rats are not comatose they do have considerable behavioural abnormalities for which brain tryptophan changes may be in part responsible.