Attenuation of conditioned taste aversions by external stressors

Conditioned taste aversions (CTAs) were produced by low doses of toxins injected 30 or 60 min after rats finished drinking saccharin solution. Attempts were made to attenuate these CTAs by subjecting the rats to stress or to injections of glucocorticoids (primarily dexamethasone) during the interval between saccharin consumption and injection of the toxin. The stressors used were statistically indistinguishable in their effects: swimming, constant footshock (for 2 min), or intermittent footshock (for 10 min). The extent to which different agents attenuated CTAs depended on which toxin was used to produce the CTA as follows. The stressors produced marked CTA attenuation when lithium was the toxin, but none when cisplatin was the toxin. The glucocorticoids exhibited an opposite pattern of marginal CTA attenuation with lithium and marked CTA attenuation with cisplatin. CTAs produced by morphine were more like those produced by cisplatin than like those produced by lithium. Our belief that the CTA attenuation demonstrated here indicates alleviation of the distress produced by the toxin was supported by the results of the final two experiments as follows: 1) The stress does not raise saccharin preference independently of interference with the aversiveness of the toxin since, in similar experiments in which toxins were not administered, footshock administered in conjunction with exposure to saccharin solution reduced later saccharin preference. 2) Probably CTA attenuation does not occur because stress interferes with the taste-toxin association since footshock administered before the saccharin drinking session (instead of after it) also produced CTA attenuation.