Evaluation of intrathecal contrast media by aversion conditioning in rats

A method for quantification of aversion conditioning in rats was adapted to assess intrathecal neurotoxicity of contrast media (CM). Metrizamide, iopamidol, nonionic dimers DL-2-87 and DL-3-117, experimental iodophenyl glucose ethers DL-2-98 and DS-1-132, and Ringer's solution were injected into non-anesthetized rats drank water mixed with their preferred flavors, and subsequently were injected with 22.5 and/or 45 mgI/kg (200 and/or 400 mgI/ml concentration). From the intake of the preferred flavored water, expressed as percentage of total fluid intake consumed during a preference test and during a subsequent free choice test, a percentage avoidance/preference score was calculated as a measure of conditioning. At 12.5 mgI/Kg level, DL-2-87, which unexpectedly precipitated from solution in vivo, caused the most aversion, followed by metrizamide. The remaining compounds induced no significant aversion and were statistically indistinguishable from one another. At 45 mgI/kg dose level, all monomeric CM induced aversion of a statistically equal degree, while DL-3-117 proved nonaversive, equal to Ringer's solution.