I - Fear and Anxiety

Objectives:

To gain experience with a variety of tests designed to probe fear and anxiety.

Introduction:

Models of fear and anxiety are important for understanding the neurobiology of various psychological illnesses and the development of new pharmacotherapies. For instance, diazepam (Valium) was the highest selling pharmaceutical in the US during the 1970’s. A variety of tests have been developed for the rat that tap into fear and anxiety. Many of these involve delivery of an electric shock, and we will not be using these tests in this laboratory exercise. While the shocks are very mild and brief (more mild than touching a 9V battery to your tongue to determine if it still carries a charge), there are ways to study anxiety in animals without electricity that are appropriate for an undergraduate lab in behavioral neuroscience. These include the elevated plus maze (Metz et al., 2005), open field (Crawley, 1985) and a startle version of the defensive burying task.

Procedure:

Preparation:

Two of these tests will use the Any-Maze software. You can download this software for free from the supplier to become familiar with its operation (http://www.anymaze.com). Your TA should have the any-maze protocols set up for these tests ahead of time.

Tests:

Elevated Plus Maze For the Elevated Plus Maze test, start the capture program, and make sure the plus maze template has been properly set up. Start the capture program and then place the animal in the maze. Flip a coin to determine if the rat will face an open or a closed maze (head = open, tails = closed). Allow the rat to explore the maze for 5 minutes, counting arm entries (open or closed) and amount of time spent in the arms (open or closed). Any-maze should score this automatically.

Open Field For the open field test, start the capture program, and make sure the plus maze template has been properly set up. The area should be brightly lit. Start the capture program and then place the animal in the middle of the open field. Allow the animal to explore the open field for 5 minutes. Score how long it spends in against the wall and in the open area. Any-maze should score this automatically. The number of fecal pellets and urination occurrences can be counted.

Defensive Burying Task The defensive burying task usually involves delivery of a mild electric shock produced by a novel object (Treit and Pinel, 2005). Anything that startles the rat should also elicit defensive burying. Place the rat’s homecage on a low table and remove the cage lid. Push the bedding to one half of the cage, exposing the bare cage floor on the other half. Hold a marble in your hand about 1 meter above bare part of the cage. When the rat is in the side with the bedding, drop the marble. The goal is to have the marble make a loud noise when it hits the floor. Make every effort to avoid hitting the rat! Ideally the rat should be startled by the marble hitting the floor of its cage and then engage in burying behavior. Time how long the rat bury the object, how many burying bouts there are in 10 minutes, how long it takes until the burying begins, how many times it approaches the marble, if it freezes following the marble falling, and if so, how long the freezing lasts. Videotaping the session will help you score this wide variety of behaviors.

Variations:

If the marble task does not elicit defensive burying, a different marble task can be used. Place a number of marbles (~15) into a cage, evenly spaced, resting on the bedding. Place the rat in the cage. After 30 minutes, remove the rat and count how many marbles are buried. Anxiolytic drugs suppress this burying behavior (De Boer and Koolhaas, 2003)