The height test closely resembles the Visual Cliff test. It is used to observe rodent’s behavior when subjected to aversive, anxiogenic and novel situations. The apparatus can be used in combination with other stress based tests like Elevated plus maze to analyze the behavioral and hormonal changes showed by rodents in an anxiogenic situation. The height test examines the subject’s anxious behavior using height as a determinant. Presence of high platforms in the apparatus induce fear and stress in the subject resulting in endocrinological, physiological and behavioral changes.

When rodents are exposed to novel and stressful situations a sudden rush of corticosterone and Adrenocorticotropic hormone (ACTH) is observed in their plasma. The increased level of these hormones indicates the development of biological stress and anxiety in rodents (Frederic et al. 1997). Different genotypes of rodents also respond differently to anxious situations. The height test provides an environment for evaluating the role of cerebral structures, hypothalmo-pituitary-adrenal system and hormonal changes in a subject on encountering a novel and stress-inducing situation.

The height test apparatus is a rectangular acrylic box containing a startle platform placed on a mast. Two other platforms are arranged at a specific height from each other creating a stress-inducing environment for the subject. The apparatus evaluates the escaping response of the subject from a specific height. Other apparatus that can be used to analyze the responses of rodents in stressed and anxious situations include the Stress Alternatives Model Maze, the Elevated T Maze, and the Automated Elevated Plus Maze.

The height test apparatus consists of an acrylic box having following dimensions height 100 cm, length 80 cm and, width 40 cm. A startle stable platform is fixed on a 50 cm high mast located in the center of the apparatus. The measurements of the platform are 5 x 5 cm. Two square platforms are arranged in the height maze such that the top platform is 2 cm under the startle platform and the bottom platform is 50 cm distant from the startle platform. Each platform is 40 x 40 cm in dimension and is painted with black and white squares (each square 2 x 2 cm). Both platforms are covered with 0.5 cm thick glass.

Clean the apparatus with 35% alcohol to reduce the chances of interference caused by odor cues during the trial. An external tracking and recording systems such as Noldus Ethovision XT can be used with the height test apparatus for recording the mice behavior.

The test approach used in a height test is based on novelty and does not require pretraining before the trial.

Height Test

Place each subject on the startle platform directing its head towards the floor platform. Allow the subject to escape from the startle platform through either of the two lower platforms (high and floor platform) placed under it.

Behavioral Analysis of Lurcher mice in a Stress Inducing Test

Hilber, Lorivel, Delarue, and Caston (2004) analyzed the behavioral changes and corticosteroid level of Lurcher mice by using the elevated plus maze and the height test. Two groups of subjects were selected,  +/Lc and +/+ naive mice. Both groups were evaluated in a height test for awareness and response towards aversive stimuli that is the height between the startle platform and the other two platforms. Subjects of both groups escaped from the startle platform through the high platform. Hence, it was concluded that the mutant Lurcher mice were aware of the nature of the stressful situation and thus chose a less fearful height platform for escaping from the startle platform.

The following parameters can be observed using the height test:

• Time spent on the startle platform
• Time spent on the high platform
• Time spent on the floor platform
• Percentage escaping from the high platform
• Percentage escaping from the floor platform

Strengths

The height test is an easy test and can produce results in less time. The apparatus is based on novelty. Therefore training of subjects is not required. The simple and practical design of the apparatus allows easy cleaning and maintenance of the apparatus. The behavioral responses exhibited by rodents in a height test can be further analyzed for their pharmacological, endocrinological and physiological basis in rodents and human.

Limitations

The performance of subjects in a height test is highly dependent upon their strain and genotype. Different mutants of same species may exhibit different responses in the height test. Important factors to obtain unbiased results in a height test include subject health, age, and gender equality.  Proper cleaning and drying of the apparatus are essential to prevent lingering odor cues from affecting the subject behavior.

• The height test analyzes the stress and anxiety in rodents that are the indicators of cerebral functioning and hormonal activity in their body.
• The presence of two platforms at different heights tests the subject’s awareness of aversive stimuli.
• The apparatus is based on novelty and therefore, does not require subject training for operation.
• Factors that are important to consider for obtaining unbiased results in a height test are subject health, age, and gender equality.
• The behavioral responses exhibited by rodents in a height test can be further analyzed for their pharmacological, endocrinological and physiological basis in rodents and human.

1. Frederic, F., Chautard, T., Brochard, R., Chianale, C., Wollman, E., …, Delhaye-Bouchaud, N. M. (1997). Enhanced endocrine response to novel environment stress and endotoxin in Lurcher mutant mice. Neuroendocrinology, 66(5), 341-347.
2. Hilber, P., Lorivel, T., Delarue, C., & Caston, J. (2004). Stress and anxious-related behaviors in Lurcher mutant mice. Brain Research, 1003(1), 108-112. doi:10.1016/j.brainres.2004.01.008