Radial Maze Test

Another task in which short-term memory can be differentiated from long-term memory is the radial maze (Olton 1986). This apparatus consists of a central platform with arms radiating from it like the spokes of a wheel. A hungry rat or a mouse is placed in the centre of the maze and can find food at the end of each arm. An ideal performance during a trial would be for the animal to visit each arm once to collect food. This task requires therefore that, during a trial, the animal 

Long-term or reference memory can also be assessed by having a restricted number of arms baited, but always the same. The animal must visit only the baited arms during a test session. 

The protocol described below assesses only working memory in that all the arms are baited. 

The radial maze we use consists of a central platform (30 cm in diameter) with 8 arms (68 x 10 cm) surrounded by walls (Height = 10 cm). A food receptacle is located at the end of each arm. The receptacle is in the form of a small hole in the floor rendering the food invisible from the entrance to the arm. The apparatus is constructed of black Plexiglas and is elevated 80 cm above the floor. 

During the week preceding the beginning of the experiment the animals are placed on a restricted food regime (15 g standard diet per day) with free access to water. 

---

FIGURE 10 Effect of bethanechol on memory in lesioned rats. Be-thanechol was released from PCPP-SA 50 50 implanted intracerebrally in rats. The effect of the bethanechol released on the performance of lesioned rats in a radial maze test was performed as described in the text. 

In a radial maze a number of arms of equal length radiate from a central point, where the animal is placed. Initially food is placed at the end of each arm and the rat is expected to learn that fact by exploring and entering each arm. The test of memory is to see whether on re-exposure to the maze the rat remembers only to enter an arm not previously visited and so still containing food. 

Fig. 11. The effects of dizocilpine (MK-801) on the 3 parameters measured (errors, running times, response strategy) during the radial maze task in the rat (mean of 3 sessions). Note the dose-dependent increase in the number of errors without any effect on running times. A decrease in response strategy occurs only at the highest dose tested.

Another approach to reference memory is to use the radial maze task as a repeated acquisition task with different arms being baited during each test session (Levin et al. 1998). In this way the task can be modified to evaluate exclusively reference memory. As with repeated passive avoidance sessions, this use of the radial maze is very time-consuming, and we do not recommend it for safety pharmacology purposes. 

After initial training with six of the arms on a 12-arm radial maze baited in a random pattern, half the rats were tested with the pattern rotated 180°, and the other half were tested with a new random pattern. 

Following single 60 min VX vapor exposures in the range of 0.016 to 0.45 mg VX/m, Genovese et al. (2007) examined blood AChE activity, dose estimation by regeneration assay, transient miosis, and behavior parameters in adult male SD rats. Behavioral evaluation included a radial maze task and a variable-interval schedule-of-reinforcement task. At all concentrations tested, transient miosis and AChE activity inhibition were observed and some subjects exhibited transient ataxia and slight tremor. Following 3-month post-exposure evaluations of behavior, the authors concluded that performance deficits were minor and transient at these concentrations. Further, no delayed effects were observed. 

Shukitt-Hale, B., McEwen, J.J., Szprengiel, A, Joseph, J.A. (2004). Effect of age on the radial arm water maze - test of spatial learning and memory. Neurobiol. Aging 25 223-9. 

However, the discipline of behavioural toxicology, for all its recent methodological and interpretative improvements, is still a science in its infancy, and a healthy if somewhat unjustified prejudice exists against some of the conclusions made from behavioural studies. This is probably due to the fact that behaviour is a very sensitive to extrinsic (or indeed, intrinsic) influences, and often it may be difficult to separate the two. Another reason is the use of a lexicon that is often difficult to comprehend. Examples from this lexicon include terms such as paradigm, acquisition or performance. Paradigm, when used in this context, is a behavioural test type. Often there may be differences between behavioural apparatus in different locations, but the measured behaviour is the same. An example of this is spontaneous alternation, which can be measured in a T-maze, but also E- or Y-mazes. Acquisition is a curious term which is used extensively in experimental psychology. It is defined as the state when a experimental animal has established some form of response in which it can solve a given experimental situation. This could be called learned or conditioned behaviour. However, it is not possible to conclude that an animal has learned a maze merely because it can solve it. An example of this can be shown in radial mazes, where an animal merely turns left (or, for example, third left) when it leaves a visited arm. To all intents and purposes it may be concluded that the... 

---