Tyler J. Gerritsen, Gregory N. Ervin, Psychology

Taste aversion conditioning is a uniquely learned behavior. In most laboratory cases, the subjects receive a dose of the drug in question and a bottle of saccharin (sacc). Ordinarily, rats will strongly prefer drinking sacc to water (Fig. 1). Whereas with taste aversion, rats develop an aversion to the sacc and choose to mainly drink water instead. If the rat avoids the water as well as the sacc, the dosage is probably so strong that the rat loses motivation to drink anything. The actual reason for taste aversion is not known. Garcia and Koelling (1966) have suggested that aversion is caused by “agents which produce nausea and gastric upset”.1 Others point out that psychoactive drugs are capable of producing conditioning responses in the absence of any signs of toxicity.2 There are many other hypotheses for why taste aversion happens.

Many drugs, peptides, etc. have been tested for their taste aversive effects. Pre-exposure of a substance which normally has aversive effects can influence the aversion process. For example, chlordiazepoxide effects were observed in pre-exposure studies by Elkan Gamzu.3 Dr. Ervin has previously done aversion testing 4 with cholecystokinin (26-33) (CCK-8) and lithium chloride (LiCI); therefore, we decided to study the effects of preexposure of these substances on laboratory rats. CCK-8 is a neurotransmitter peptide found in the brain. Lithium chloride is a compound commonly used for therapeutic purposes.

Sixty rats were tested in our study. The rats were assigned to one of five groups: a control group (NaCl was administered for both conditioning (Pre-Rx) and aversion testing (Rx) (Fig. 1)); a group which received Pre-Rx NaCl and CCK-8 Rx (Fig. 2); a group which received CCK-8 for both Pre-Rx and Rx (to test for preexposure (Fig 3.); and two groups similar to the CCK-8 groups, but using LiCl (Fig 4,5).

Previous studies have concluded that LiCl produces a stronger aversion than does CCK4. By comparing figures 2,3 and 4,5, we can see that LiCl does produce a stronger aversion. We also found that pre-exposure to CCK-8 induced an aversion which lasted longer and seemed to have a greater effect on the rats. Aversions of both the control LiCl group and the Pre-Rx LiCl (Fig. 4 and 5) were equally pronounced on test day 1. But the aversive effects on the Pre-Rx LiCl group did not continue as prominently as the control group.

References

1. Garcia, J., & Koelling, R.A. A comparison of aversion induced by X-rays, toxins, and drugs in the rat. Radiation Research, 1967, 7 (Suppl.) 439-450.
2. Cappell, H., & LeBlanc, A.E. Gustatory avoidance conditioning by drugs of abuse: Relationships to general issue in research on drug dependence. In N.W. Milgram, L. Krames, & T.M. Alloway, (Eds.), Food aversion learning. Plenum Press, 1976.
3. Gamzu, E. Preexposure to unconditioned stimulus alone may eliminate taste aversions. Paper presented at the 15th Annual Meeting of the Psychonomic Society, Boston, 1974.
4. Mosher, J.T., Johnson, M.F., Birkemo, L.S., & Ervin, G.N. Several roles of CCK(A) and CCK(B) receptor subtypes in CCK-8 induced and LiCl-induced taste aversion conditioning.