Area postrema lesions in rats enhance the magnitude of body rotation-induced conditioned taste aversions.

The role of the area postrema, a circumventricular organ located on the dorsal medulla in the fourth ventricle, in body rotation-induced conditioned taste aversions was examined in male hooded rats. One group of rats received lesions of the area postrema, another group was given sham lesions, and two other groups received no surgery. Three groups of rats, those with area postrema lesions, those with sham lesions, and one unoperated group, were given pairings of 1-hr access to a 0.1% sodium saccharin solution with 30 min of body rotation at 70 rpm (on a schedule of 15-sec on--5-sec off). A fourth group of unoperated rats was given pairings of access to the saccharin solution with 30 min of sham rotation. The three rotated groups all developed a taste aversion to the saccharin solution whereas the sham-rotated group did not. The group with lesions of the area postrema exhibited a greater aversion to the saccharin taste than the other two rotated groups. In a second phase of the experiment all rats were given pairing of 1-hr access to chocolate milk with injections of scopolamine methyl nitrate (1 mg/kg). The area postrema-lesioned group failed to exhibit a taste aversion to the chocolate milk whereas the other groups all showed very strong aversions. It was concluded that area postrema lesions abolish taste aversions induced by blood-borne toxins such as scopolamine methyl nitrate, but enhance taste aversions induced by motion sickness. Some speculations concerning the enhanced taste aversions induced by motion sickness in area postrema lesioned rats, are provided.