Brain Research, 346 (1985) 1-7 1 Elsevier BRE 11082 Research Reports Taste Aversions Conditioned with Multiple Exposures to Gamma Radiation: Abolition by Area Postrema Lesions in Rats KLAUS-PETER OSSENKOPP and LUIGI GIUGNO Department of Psychology, Universityof Western Ontario, London, Ont. N6A 5C2 (Canada) (Accepted January 15th, 1985) Key words: area postrema - - gamma radiation - - conditioned taste aversion - - low-level radiation - - nucleus of the solitary tract - - rat Lesions which destroy the area postrema (AP) and damage the adjacent nucleus of the solitary tract (NTS) attenuate conditioned taste aversions (CTA) induced by a variety of pharmacological agents as well as exposure to radiation. In this experiment the possibili- ty that AP lesions might not attenuate a radiation-induced CTA, when multiple pairings of the novel taste stimulus and exposure to gamma radiation occurred, was examined. Three groups of male rats received lesions of AP and another 3 groups received sham le- sions. Following a recovery period all rats were adapted to a 23.5 h/day water deprivation schedule. A sodium saccharin solution (0.1% ) was offered to all rats during the regular drinking period (0.5 h) on two days per week, with water available on the other days. Access to saccharin was followed by exposure to 0, 20 or 40 rad of gamma radiation with one lesioned and one sham-lesioned group as- signed to each dose level. After 4 pairings of saccharin with radiation the sham-lesioned groups exposed to 20 and 40 rad of radiation exhibited a dose-dependent aversion to the saccharin solution (P < 0.0001), whereas the AP-lesioned groups did not differ significant- ly from the 0 rad sham-lesioned group. Subsequent two-bottle choice tests, which are a more sensitive measure of CTA, confirmed that the AP-lesioned rats exposed to 20 and 40 rad radiation did not develop a significant CTA relative to the two 0 rad radiation groups. Thus, AP lesions abolished the CTA normally induced by multiple pairings of saccharin with exposure to 20 or 40 tad gamma radiation. INTRODUCTION Mammals have evolved several mechanisms to deal with potential ingestion of toxins. In those ani- mals having an emetic reflex, chemoreceptors in the upper gastrointestinal tract or located centrally, can be stimulated by some toxins and produce vomiting 7. Animals without an emetic reflex, such as rats, show neophobia to novel foods and ingest only small amounts. If no adverse gastrointestinal conse- quences are experienced, the animals learn that this novel food is safe to consume 14. If the novel food con- tains a toxin capable of stimulating the chemorecep- tors located in the upper gastrointestinal tract or the central nervous system, ingestion of this food is strongly avoided in the future1,9,14A5. Such condi- tioned aversions can be produced experimentally by pairing a novel flavored substance with injection of an appropriate toxic substance. Using classical condi- tioning notation the conditioned stimulus (CS) is the novel taste and the unconditioned stimulus (US) is the toxin, and the subsequent avoidance of the novel taste is termed a conditioned taste aversion (CTA)2, 24. A profound CTA can also be produced by pairing a novel taste with a single whole body expo- sure to ionizing radiation 30. Not only does such an aversion develop rapidly32,33, it also lasts for a long time period 15. There is some evidence to indicate that a humoral factor, resulting from the radiation treat- ment, may be the US effective in conditioning the taste aversion observed~S-2]. In rodents the area postrema (AP) is a midline cir- Correspondence: K.-P. Ossenkopp, Department of Psychology, University of Western Ontario, London, Ont. N6A 5C2, Canada. 0006-8993/85/$03.30 © 1985 Elsevier Science Publishers B.V. (Biomedical Division)