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Center for Functional Genomics at Northwestern University

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Protocols ›› Preliminary Assessments

The following Preliminary Assessments are being done to:

  1. provide supplemental information that may aid in the interpretation of data in our primary screens
  2. identify individuals which may have impairments affecting their performance in a primary screen so that data is interpreted appropriately or the animal is excluded from testing
  3. identify individuals which may respond or behave differently in a primary screen and whose data should be viewed differently

Body weight

Body weight will be determined for each individual at least twice during the course of the screen. Body weight data is most directly relevant to the neuroendocrine screen. Altered feeding behavior, activity levels, and weight gain are all associated with altered HPA axis or HPT axis activity (see Neuroendocrine screen). Together with anxiety measures such as the elevated plus maze and open field behavior, animals with aberrant weight gain may be targeted for follow-up assessment of HPA function. Additionally, animals with either seriously impaired growth or obesity may be ill -suited for the 4-week running wheel activity recording for the circadian screen, and such vulnerable individuals would be precluded from this test. The measure is rapid, quantitative, easily accomplished in numerous individuals and will not interfere with other measures being taken.

Elevated plus maze

The elevated plus maze is frequently employed as a complementary measure to open field behavior. The maze is constructed with two enclosed arms and two open arms; the time spent in the enclosed rather than the open arms is used as a measure of anxiety as the open arms are anxiety-provoking. Elevated plus maze behavior is sensitive to experiential modification and social isolation effects. It has been used as a measure for anxiolytic effects of drugs; significant strain differences have been reported with good agreement with other anxiety measures and targeted mutants which would be predicted to have increased anxiety responses (corticotropin-releasing hormone binding protein deficient) spend significantly less time in the open arms. The measure is rapid (5 min duration) and amenable to automation, and although stressful, should not produce lasting alterations in behavior that would compromise subsequent tests.

Open field behavior

Open field behavior is actually not a single behavior or measure but a set of measures which are made in an animal's response to a simple, novel, and potentially anxiogenic environment. Among the factors which may be reflected in these measures are exploration, activity, anxiety, fear, and emotionality/reactivity. In mice, strain differences, some major gene influences, and QTLs have been identified. Targeted mutants (knockouts) of the 5-HT5A receptor show increased open field activity. Like elevated plus maze, it is a rapid (typically 3 or 5 min duration) single trial test, amenable to automation, and should not be expected to have lasting effects on subsequent measures.
Open field activity (OFA) is a measure of exploration and activity level. However, animals which are very low in OFA may be inhibited due to innate fearfulness of an open, brightly lit environment. Animals which are very inactive may also indicate some other defect which would have direct relevance to primary screen phenotypes involving activity or activity related measures, such as wheel-running, freezing, and response to psychostimulants.

The proportion of time spent in the periphery as opposed to venturing into the center of the open field is used as a measure of the animal's desire to explore as opposed to its aversion to open, brightly lit environment. As such, this is used as a measure of fear or anxiety (as opposed to novelty-seeking). Fear or anxiety measures are important for the neuroendocrine screen as well as for fear conditioning. Novelty-induced activity also provides an important baseline for comparison of activity induced by psychostimulants.

Open field defecation (OFD) is used as a measure of what is termed "emotionality" or "reactivity". It provides an index based upon an autonomic response and does not depend on motor activity. Emotional reactivity will have significance for the neuroendocrine screen as well as for measures which rely on emotional responses such as fear conditioning.

Preyer reflex

The Preyer reflex is a distinctive movement of the pinna in response to a sudden sound. It can be rapidly measured with the use of a "clickbox" which emits a 90dB 20kHz sound burst. While not a quantitative sensitivity measure, it can reliably identify profound impairments and can discriminate mice with mutations producing deafness. Since auditory cues are a component of the fear conditioning tests, animals with such severe impairments need to be identified. It is very rapid and hence amenable to high throughput, and it should not compromise subsequent tests. Visual cues are also obviously a component of the fear conditioning tests, but as visual function is assessed in a separate primary screen, no vision test is included here.