Academic journal article Genetics

Exploratory Activity in Drosophila Requires the Kurtz Nonvisual Arrestin

Academic journal article Genetics

Exploratory Activity in Drosophila Requires the Kurtz Nonvisual Arrestin

Article excerpt

ABSTRACT

When Drosophila adults are placed into an open field arena, they initially exhibit an elevated level of activity followed by a reduced stable level of spontaneous activity. We have found that the initial elevated component arises from the fly's interaction with the novel arena since: (1) the increased activity is independent of handling prior to placement within the arena, (2) the fly's elevated activity is proportional to the size of the arena, and (3) the decay in activity to spontaneous levels requires both visual and olfactory input. These data indicate that active exploration is the major component of elevated initial activity. There is a specific requirement for the kurtz nonvisual arrestin in the nervous system for both the exploration stimulated by the novel arena and the mechanically stimulated activity. kurtz is not required for spontaneous activity; kurtz mutants display normal levels of spontaneous activity and average the same velocities as wild-type controls. Inhibition of dopamine signaling has no effect on the elevated initial activity phase in either wild-type or krz^sup 1^ mutants. Therefore, the exploratory phase of open field activity requires kurtz in the nervous system, but is independent of dopamine's stimulation of activity.

LOCOMOTION is a fundamental and vital behavior. Through movement, animals can exert control over their surroundings to locate essential resources and avoid hazards. Without efficient and productive movement, animals can be easily preyed upon. Experimentally, we rely on an animal's movement to instruct us on the acuity of sensory systems, the vigor of courtship, and even the strength of learned associations. Locomotion, however, is a complex biological response encompassing sensory processing, integration of stimuli, executive functions, and motor response pathways. By understanding the genetic determinants underlying an animal's decision to move, we may gain significant insights into the molecular mechanisms involved in all of these levels of processing.

Activity in an open field arena is one of the oldest and most widespread experimental behavioral tasks (HALL 1936; WALSH and CUMMINS 1976). This task is typically used as a simple measure of general activity. Many species, however, display nonlinear activity profiles when first placed into an open field, indicating a complexity in this behavior. Drosophila melanogaster, several species of rodents, chickens, domestic cats, and dogs all demonstrate an elevated level of initial activity, followed by a rapid decline to a lower steady-state level of ambulation when assayed in an open field arena (GLICKMAN and HARTZ 1964; CONNOLLY 1967; CANDLAND and Nagy 1969; LÁT and GOLLOVÁ-HEMON 1969). Some insight into the initial elevated activity component came when EWING (1963) and CONNOLLY (1967) selectively bred Drosophila for differences in locomotor activity. The selected genotypes were actually found to have differences in how they react to stimulation, including the presence of other flies. The highly reactive flies had more activity because they were more vigorously running away from the other flies present in the apparatus (EWING 1963). These flies also displayed differences in initial activity when individually placed into an open field arena, but not in the steady-state level of spontaneous activity (EWING 1963; CONNOLLY 1967). This early, elevated component of activity has been consequently termed reactivity or stimulated activity (MEEHAN and WILSON 1987). Surprisingly, very little is known about why animals increase their activity when placed into the open field, what the proximal causes for this stimulated activity are, or what the genetic determinants are that govern this response.

Herein we demonstrate that the kurtz (krz) gene of D. melanogaster is required within the nervous system for the elevated initial activity phase in an open field arena, but is not required for spontaneous activity. …

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