title: Forced-choice discrimination of equimolar NaCl and LiCl solutions in rats: effects of ablating the chemosensitive area postrema on acquisition and retention.
abstract: The area postrema (AP), a chemosensitive organ located in the fourth ventricle, has been shown to mediate the formation of a lithium-induced conditioned taste avoidance (CTA) in rats. The present experiments examined the role of the AP in the discrimination between two equimolar solutions of sodium chloride (NaCl) and lithium chloride (LiCl). In the first experiment adult male rats were trained to discriminate between equimolar (0.12 M) solutions of NaCl and LiCl in a forced-choice procedure over a 10-day acquisition phase. Subsequently half of the rats (n = 7) received AP lesions (APX) and the other half (n = 7) were given sham lesions (SHAM). In the retention phase all animals were again exposed to the same salt solutions over a 10-day period. Good discrimination (P < 0.001) between the two salt solutions was demonstrated by the end of the acquisition phase and both the APX and SHAM groups exhibited robust retention (P < 0.01) of this discrimination in the second phase. However, when only a LiCl solution was available the APX group ingested significantly more (P < 0.01) than the SHAM rats. No significant group difference emerged when only NaCl was available. In the second experiment rats received ablations of AP or sham lesions and were then trained to discriminate between 0.12 M NaCl and LiCl solutions in a forced-choice procedure over a 10-day period. Both groups exhibited a clear discrimination (P < 0.01) between the two solutions by the end of the acquisition phase. APX rats ingested significantly more LiCl (P < 0.01) than did the SHAM group when this was the only type of fluid available. Again, no such difference was evident when only NaCl was available. These experiments demonstrate that the AP is not necessary for either the acquisition or retention of a discrimination between equimolar solutions of NaCl and LiCl in a forced-choice procedure and that this discrimination is not mediated by a conditioned taste aversion to the LiCl solution.
authors.affiliation: Neuroscience Program, University of Western Ontario, London, Canada. ossenkopp@sscl.uwo.ca
authors.forename: K P
authors.initials: KP
authors.lastname: Ossenkopp
authors.forename: R L
authors.initials: RL
authors.lastname: Ladowsky
authors.forename: L A
authors.initials: LA
authors.lastname: Eckel
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D002552:Cerebral Ventricles / Q000033:anatomy & histology / Q000502:physiology*; D004193:Discrimination Learning / Q000187:drug effects / Q000502:physiology; D004192:Discrimination, Psychological / Q000187:drug effects*; D004326:Drinking / Q000187:drug effects / Q000502:physiology; D018021:Lithium Chloride / Q000494:pharmacology*; D008297:Male; D008568:Memory / Q000187:drug effects / Q000502:physiology; D051381:Rats; D012965:Sodium Chloride / Q000494:pharmacology*; D013649:Taste / Q000187:drug effects*
chemical_list: D012965:Sodium Chloride; D018021:Lithium Chloride