Taste aversions conditioned with intravenous copper sulfate: Attenuation by ablation of the area postrema

Abstract

Borison and Wang identified the area postrema as the locus of chemoreceptors that mediate emetic reflexes elicited by blood-borne toxins. In the present experiments we have extended a systematic investigation of the afferent pathways mediating taste aversions by examining the effects of area postrema lesions on the aversions that follow either intravenous or intragastric administration of copper sulfate. Intrajugular cannulas were implanted in rats after ablation of the area postrema (Group AP-L) and in operated controls (Group AP-C). Every third day rats were offered a saccharin solution and immediately afterward were injected intravenously with 0.05 ml isotonic CuSO 4. A group of pseudo-conditioned rats (Group SAC-C) was injected with CuSO 4 approximately 24 h after ingestion of saccharin. Compared to control animals, rats with area postrema damage acquired significantly weaker aversions to saccharin when it was paired repeatedly with intravenous CuSO 4. After three conditioning trials, the rats in Group AP-L that were most resistant to acquisition of a taste aversion (Group AP-L *) were again offered saccharin, but ingestion in this case was followed immediately by intragastric injection of CuSO 4. After a single conditioning trial rats in Group AP-L * demonstrated a robust aversion. The results are discussed in terms of the parallels in afferent systems between emetic physiology and some instances of taste aversion conditioning.