Sensory Functions

Assessment of sensory functions (pain sensitivity, hearing, vision, olfactory ability) will allow you to avoid misinterpretation of the obtained behavioural data. For instance, impaired pain sensitivity in your mice will affect the expression of fear conditioning and, hence, learning & memory results.

Many strains of congenic, inbred, and mutant mice suffer from sensory deficits that alter their behaviour. For instance, genetic strains of mice (e.g. C3H, CBA, Swiss) may suffer from retinal degeneration and perform poorly in tests requiring visual acuity (e.g. object recognition, elevated plus-maze, Morris water maze). Some strains of mice such as DBA/2 and C57BL/6J (B6) become deaf by age and therefore perform poorly in tests requiring auditory discrimination (e.g. PPI, Acoustic Startle Response). Other genetic mutants may have disrupted olfactory sensitivity, somatosensory deficits, or abnormal pain sensitivity. In each of these cases, poor performance in behavioural tests may be interpreted due to their sensory rather than cognitive deficits.

Acoustic Startle Reflex

Procedure

Acoustic Startle Reflex is indirect measurement of hearing function.

To measure acoustic startle reactivity, each mouse is placed into the startle chamber and allowed to acclimatize for 10 minutes. After acclimitization 110 startle stimuli of varying intensities are presented, with a duration of 50 ms and variable interstimulus interval of 20–30 seconds. The following stimulus intensities are applied: 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, and 120 dB. Ten trials were presented in three blocks of eleven stimuli and in pseudorandom order within a block.

Tail Flick Test

Procedure

Carefully holding the animal, the tail is immersed (1-2 cm) gently in the hot water bath (50 ± 1C). The latent period of the tail-flick response is taken as the index of antinociception. The reaction time is taken as a mean of three trials. 

Cliff Test

Procedure

Animals are handled daily for several days before beginning the visual cliff test which is conducted in an arena under ordinary laboratory fluorescent light (about 100 µW/cm²).

Each mouse is lifted by its tail and lowered until all 4 limbs are firmly on the middle part of the beam when it is released. At this moment, the trial is initiated and continued until 5 minutes had elapsed or the mouse stepped off the center beam with all 4 paws placed one side of the beam. The mouse is then placed back into its cage.

Olfactory Test

Procedure

Rodent food pellets are removed from the home cage and should remain food deprived for 24 hours.

A piece of pellet is placed in a randomly chosen area on the cage floor and then the entire cage floor is covered with corncob bedding to a depth of 2.5 cm.

The subject is then placed into the cage and latency to find the food is recorded up to a maximum time limit of 15 minutes.