title: Effects of multiple exposures to D-cycloserine on extinction of conditioned fear in rats.
abstract: Previous research has shown that an acute, post-training injection of D-cycloserine (DCS) facilitates extinction of conditioned fear in rats; however, the effects of multiple exposures to DCS in this situation are not known. In Experiment 1, rats were conditioned (light-shock pairings) and 24 h later given six extinction (light-alone) trials followed by an injection of DCS (15 mg/kg) or saline. The next day, all rats were tested for light-elicited freezing. In Experiment 2, the effect of DCS on extinction was tested in the same manner, except that rats were pre-exposed to DCS (0, 1, or 5 injections) just prior to conditioning. In Experiment 3, rats received five pre-exposures of DCS but conditioning occurred either 2 or 28 days after the last pre-exposure. The results showed that DCS facilitated extinction of conditioned freezing to the light CS when no drug pre-exposure had occurred, but pre-exposure to DCS just prior to conditioning disrupted the facilitation of extinction effect. When 28 days were interposed between pre-exposure and conditioning, the facilitatory effects of DCS on extinction were restored. These findings suggest that DCS has significant clinical value but that behavioral desensitization may occur with multiple exposures; however, desensitization is not permanent and is reduced by the passage of time.
authors.affiliation: School of Psychology, University of New South Wales, Sydney 2052, Australia.
authors.forename: A Sophie
authors.initials: AS
authors.lastname: Parnas
authors.forename: Marianne
authors.initials: M
authors.lastname: Weber
authors.forename: Rick
authors.initials: R
authors.lastname: Richardson
mesh_terms: D000818:Animals; D000963:Antimetabolites / Q000008:administration & dosage*; D001245:Association Learning / Q000187:drug effects; D003214:Conditioning, Classical / Q000187:drug effects*; D003523:Cycloserine / Q000008:administration & dosage*; D004334:Drug Administration Schedule; D005108:Extinction, Psychological / Q000187:drug effects*; D005239:Fear / Q000187:drug effects*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000963:Antimetabolites; D003523:Cycloserine