Shallow Water (Paddling) Variants of Water Maze Tests in Mice

Abstract

When Richard Morris devised his water maze in 1981 7 , most behavioral work was done in rats. However, the greater understanding of mouse genetics led to the mouse becoming increasingly important. But researchers found that some strains of mutant mice were prone to problems like passively floating or diving when they were tested in the Morris water maze 11. This was unsurprising considering their natural habitat; rats swim naturally (classically, the "sewer rat"), whereas mice evolved in the dry areas of central Asia.To overcome these problems, it was considered whether shallow water would be a sufficient stimulus to provide escape motivation for mice. This would also avoid the problems of drying the small creatures with a towel and then putting them in a heated recovery chamber to avoid hypothermia, which is a much more serious problem than with rats; the large ratio of surface area to volume of a mouse makes it particularly vulnerable to rapid heat loss.Another consideration was whether a more natural escape strategy could be used, to facilitate learning. Since animals that fall into water and swim away from the safety of the shore are unlikely to pass on their genes, animals have evolved a natural tendency to swim to the edge of a body of water. The Morris water maze, however, requires them to swim to a hidden platform towards the center of the maze -exactly opposite to their evolved behavior. Therefore the paddling maze should incorporate escape to the edge of the apparatus. This feature, coupled with the use of relatively non-aversive shallow water, embodies the "Refinement" aspect of the "3 Rs" of Russell and Burch 8 .Various types of maze design were tried; the common feature was that the water was always shallow (2 cm deep) and escape was via a tube piercing the transparent wall of the apparatus. Other tubes ("false exits") were also placed around the walls but these were blocked off. From the inside of the maze all false exits and the single true exit looked the same. Currently a dodecagonal (12-sided) maze is in use in Oxford, with 12 true/false exits set in the corners. In a recent development a transparent paddling Y-maze has been tested successfully.

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“…The testing method and design of paddling pool (MK2/octagonal) was adopted as previously reported from the laboratory of Deacon (2013) . The apparatus walls contained eight true/false exits among which one was true, whereas, seven were false exits occluded by plastic plugs.…”

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“…Hypothermia in turn can affect behavior and impair performance during tasks involving swimming (Iivonen et al, 2003;Taltavull, Chefer, Shippenberg, & Kiyatkin, 2003). Therefore, it is advised to use higher temperatures, but not too high because this would decrease the motivation of animals (Deacon, 2013). During the initial training to use the platform, you can use water at room temperature (21°C-22°C) because the task is very simple and is not associated with prolonged swimming.…”

From Systemic Inflammation to Neuroinflammation: The Case of Neurolupus

“… Tests used for behavioral evaluation of mice. ( A ) Forced-swim test (or Porsolt test) used to assess depressive-like behavior; ( B ) elevated plus-maze and ( C ) dark/light preference test to measure anxiety-like behavior; ( D ) Morris water maze (or paddling test) [ 53 ]; ( E ) T-maze that is considered very sensitive to alteration in hippocampal pathways. …”