title: Differential effect of 5-hydroxytryptophan on approach and avoidance behavior in rats.
abstract: The current hypersensitive postsynaptic serotonin receptor theory of depression developed and expanded by Aprison and Hingtgen was based on an animal model of behavior in which food-reinforced approach behavior was suppressed following 5-hydroxytryptophan (5-HTP) administration. In this paper, data are presented to show that when the same animal is taught to emit, alternatingly, approach and avoidance behavior, and the serotonin precursor, 5-HTP, is administered, only the approach behavior is affected. Adult, male Wistar rats were trained on Sidman avoidance (RS20:SS10) and food-reinforced approach (VI 1) schedules. During the first part of this study, rats received separately 50-min sessions for approach and avoidance responding. For the second part, both schedules were given in the same experimental chamber. In the third part, 10-min alternating approach and avoidance components were combined in the same 50-min sessions. Significant behavioral suppression of approach responding was observed following administration of L-5-HTP (50 mg/kg IP), as well as after D,L-5-HTP (25 and 50 mg/kg IP) in a dose-dependent relationship, whereas no significant effect was seen for Sidman avoidance responding during this type of session. These results support the role of serotonin in food-reinforced approach behavior and suggest that suppression of Sidman avoidance behavior may be mediated by other neurotransmitter systems.
authors.affiliation: Department of Psychiatry, Indiana University School of Medicine, Indianapolis 46202-4887.
authors.forename: W K
authors.initials: WK
authors.lastname: Park
authors.forename: J N
authors.initials: JN
authors.lastname: Hingtgen
authors.forename: M H
authors.initials: MH
authors.lastname: Aprison
mesh_terms: D006916:5-Hydroxytryptophan / Q000494:pharmacology*; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011985:Receptors, Serotonin / Q000187:drug effects; D013237:Stereoisomerism
chemical_list: D011985:Receptors, Serotonin; D006916:5-Hydroxytryptophan