Saccharin aversions induced by lithium chloride toxicosis in a backward conditioning paradigm

Abstract

Seven experimental groups of seven rats each were allowed to consume saccharin solution at different times relative to intubation of lithium chloride solution. Six backward conditioning (BWDj groups were intubed 0.5, 1,2,3,4, and 8 h before saccharin consumption, and a forward conditioning (FWD) group was intubed 0.5 h after saccharin consumption. A no-lithium control group of 14 rats received no intubation. Only the 0.5-h FWD and the 0.5-h BWD groups showed an aversion to saccharin relative to the no-lithium controls. The aversion to saccharin in the 0.5-h FWD group was more pronounced than that in the 0.5-h BWD group. This shows that the aversive effects of lithium toxicosis dissipate far sooner than the aversive effects of X-irradiation. If ingestion of a flavored substance, such as saccharin solution, is followed by toxicosis induced by some independent means, such as X-irradiation, rats will avoid the flavored substance on subsequent occasions (Revusky & Garcia, 1970). With saccharin. this is true even if the interval between ingestion and exposure is extended up to 12 h (Smith & Roll, 1967). Furthermore, it has been shown that rats will form an aversion to saccharin solution when the solution is consumed up to 12 h after exposure to radiation ceases (Scarborough, Whaley, & Rogers, 1964). It was initially suspected that the reduced preference was due to unlearned factors (Mel.aurin, 1964), or to backward conditioning, which is generally considered impossible (Kimble, 1961). A better explanation is that the aversive physiological aftereffects of the radiation continue long after exposure ceases (Scarborough et aI, 1964; Smith, Taylor, Morris, & Hendricks, 1965; Revusky & Garcia. 1970). Thus, although the operational paradigm may involve backward conditioning, consumption of the saccharin solution may well precede the peak of the sickness. Lithium chloride is the most effective known chemical toxicosis for producing flavor aversions in animals (Nachman & Ashe, in press). Nachman (1970) has shown that forward conditioning can take place when the interval between saccharin consumption and lithium toxicosis is up to at least 4 h. However. the backward conditioning curve for lithium has not been investigated. The best guess is that the backward curve for lithium would be much shorter than that for X-irradiation. In radiation sickness with humans, the prodromal symptoms of nausea and vomiting do not become pronounced until approximately 7 h after radiation (Gerstner, 1960). According to reports of investigators who themselves consumed lithium, lithium