J - Learning and Memory: Conditioned Avoidance

Objectives:

To condition a rat to avoid a sweet flavor using a powerful one-trial conditioned taste avoidance procedure.

Introduction:

Taste is an important sense for rats exploring their world (Spector, 2005). Rats are unable to vomit, and therefore show neophobia for new flavors, consuming only a little to determine if it is safe. If they become ill, they learn to avoid those foods. Conditioned taste avoidance is a powerful learning phenomenon, requiring only one exposure in many cases (Parker, 2003). Anyone who has suffered food poisoning will understand how pervasive this effect can be, as they will often avoid those foods and flavors associated with the illness for a number of years, even if they were previously highly enjoyable foods. The avoidance can be very specific. Because this avoidance behavior is acquired so rapidly and persists for so long, this behavior is a good model for understanding the neural basis of conditioned learning. A popular paradigm has been to pair a novel flavor with an injection of lithium chloride, which induces nausea (Welzl et al., 2001). Conditioned avoidance has direct implications for not only for people experiencing food poisoning, but also for cancer patients undergoing chemotherapy, as they often develop conditioned taste avoidances for foods eaten around the same time that they receive their chemotherapy agents (Jacobsen et al., 1993).

Procedure:

Preparation: Prepare lithium chloride solution (Sigma-Aldrich product code L9650; concentration 100mg/ml of sterile saline, dose 120mg/kg). Prepare a saccharine solution (Sigma-Aldrich product code 109185; 0.15% solution or 1.5g per L of solution. The rats should be habituated to the test chamber for a number of days before hand (5minutes / day for 5 days). The test chamber should be equipped with 2 water bottles.

Test: Day 1: 4-6 hours before the lab, remove the waterbottle from the rat’s homecage. This procedure is adapted from (Swank et al., 1995). Place the rat in the testing chamber. Put the 0.15% saccharin solution in one of the water bottles, and remove the other waterbottle temporarily. Allow the rat to explore and drink for 30 minutes. Once the rat starts drinking the saccharin solution, put a bottle of plain water at the other location (this procedure ensures that your thirsty rat actually discovers the saccharin solution). Observe its facial features when it drinks the saccharin solution. Measure how much time the rat spends drinking from each water bottle. At the end of the exploration period, remove the rat and give it an i.p. injection of either LiCl (120mg/kg) or saline. Return the rat to its home cage.

Day 2 Place the saccharin bottle and plain water bottle in the same locations as yesterday. Place the rat into the testing chamber for 30 minutes. Note which bottle the rat approaches first. Observe its facial features when it drinks the saccharin solution. Measure how much time the rat spends drinking from each water bottle. Report your treatment condition (Saline or LiCl) and your drinking times per bottle to your TA, who will collate the results from all the students