Constructing and Implementing a Low-Cost On-Demand Morris Water Maze Platform

Background

The Morris water maze (MWM) is widely considered a gold standard in behavioral neuroscience for assessing spatial learning and memory in rodents [1]. The basic protocol involves a circular pool filled with opaque water, where a submerged platform is hidden just below the surface. Rats or mice are placed in the water, where they must learn to locate the platform using spatial cues in the environment around the pool. With each learning (acquisition) trial, animals learn the location of the platform and will swim directly to it, demonstrating their spatial learning and memory abilities. The task is used extensively to assess the effects of various genetic, pharmacological, and environmental manipulations on cognitive function.

“Probe tests” provide converging evidence to that acquired by other behavioral measures. In the water maze, probe tests are classically implemented by removing the submerged platform from the tank; the experimenter measures the time the animal spends swimming in the area of the tank where the platform was previously located. Animals that recall the location of the platform spend more of their time near where the platform was previously located. A variant of the original MWM protocol assesses spatial memory over multiple probe trials, not just one. However, removing the platform during these probe trials results in these being extinction trials, since escape is not available. To address this, the probe trial can be modified so that the platform becomes available after a period of time. This procedure maintains response reinforcement in the probe trials as it is for the acquisition trials: go directly to the platform location and remain there. This modification to the protocol limits strategies like circling the wall of the tank until the platform is located, and instead promotes a spatial learning, hippocampus-dependent strategy [2]. Operationally, this requires the height of the platform to be adjustable (“on-demand”) such that it is just under the water surface during acquisition trials, or deep in the tank out of reach from the animal during probe trials [3].

The mechanisms controlling the height of on-demand platforms vary considerably, from cables and/or levers that are not visible to the rat to more technologically advanced methods that include remote-controlled devices. Notable advantages to the latter approach include greater consistency of raising/lowering timing, predictable speed, and minimizing disruption of behavior (e.g., experimenter visibility). However, the cost of such equipment is prohibitively expensive for modestly funded research programs [4]. Here, we developed a do-it-yourself remote-controlled on-demand platform, plus the tank, that costs less than a commercially available counterpart of the platform alone. The primary objective of this report is to disseminate a protocol for constructing a low-cost on-demand platform. However, in addition, we offer an abbreviated account of how we prepared the tank, set up the testing environment, ran a MWM protocol, tracked behavior, and analyzed data. As our aim was not to present a comprehensive MWM how-to, we direct the readers to other resources that, for example, provide more detailed protocols [5–8], detail the many variations of MWM protocols [6], describe its wide ranging applications [9], or offer parallel efforts to lower fiscal barriers to establishing MWM testing [4]. To validate functionality, we implemented our protocol to test whether our setup was sensitive to detect spatial learning and memory deficits among aged F344 rats.