Conditioned taste aversions induced by 1-5-hydroxytryptophan are mediated by the area postrema

Previous studies have shown that injections of 5-HTP can induce conditioned taste aversions when paired with a novel taste. Adult male albino rats received either lesions of the area postrema or were subjected to a sham lesion procedure. All rats were adjusted to a 23 1/2 hr/day water deprivation schedule and on the conditioning day were given a 0.15% saccharin solution for 1/2 hr. After drinking the saccharin fluid 9 area postrema lesioned and 10 sham lesioned rats were injected i.p. with 25 mg/kg 1-5-hydroxytryptophan. Similarly 10 area postrema lesioned and 6 sham lesioned rats were injected with the vehicle solution. A two-bottle choice test between the saccharin solution and water was given to all animals on the third and fourth days after the conditioning day. The sham lesioned rats injected with the 1-5-hydroxytryptophan exhibited a strong aversion to the saccharin taste whereas the vehicle injected sham lesioned rats showed an equal preference for the two fluids. The difference in group mean saccharin preference ratio was significant (p less than .01). Both area postrema lesioned groups exhibited saccharin preference ratios that were comparable to and not significantly different from the sham lesioned animals injected with the vehicle solution. These results show that an intact area postrema is necessary for induction of conditioned taste aversions with 1-5-hydroxytryptophan.