Circadian modulation of dopamine receptor responsiveness in Drosophila melanogaster

Abstract

We investigated the circadian function of Drosophila dopamine receptors by using a behaviorally active decapitated preparation that allows for direct application of drugs to the nerve cord. Quinpirole, a D2-like dopamine receptor agonist, induces reflexive locomotion in decapitated flies. We show that the amount of locomotion induced changes as a function of the time of day, with the highest responsiveness to quinpirole during the subjective night. Furthermore, dopamine receptor responsiveness is under circadian control and depends on the normal function of the period gene. The head pacemaker is at least partly dispensable for the circadian modulation of quinpirole-induced locomotion, because changes in agonist responsiveness persist in decapitated flies that are aged for 12 h. This finding suggests a role for the period-dependent molecular oscillators in the body in the modulation of amine receptor responsiveness.

Figure 1

Quinpirole-sensitive receptors are under circadian control. w1118 flies were decapitated at different time points during the 24-h period. Locomotion is expressed in mm per 2-min observation period starting immediately after 5 mM quinpirole application. Data are presented as mean locomotion of 30–50 flies tested at each time point (± SEM). (A) LD-entrained flies assayed 30 min after decapitation. One-way ANOVA shows a significant effect of the time of day on the amount of quinpirole-induced locomotion, (P < 0.001). (B) LD-entrained flies released into LL and tested after 25, 31, 37, 43, 49, and 55 h of constant light. One-way ANOVA shows the significant effect of the subjective time of day on the amount of induced locomotion (P < 0.001).

Figure 2

Circadian changes in quinpirole-induced locomotion are per dependent. LD-entrained per^o flies were decapitated and then placed into (A) LD or (B) LL light conditions, and tested by application of 5 mM quinpirole at the indicated times. Data are presented as mean locomotion of 30–50 flies tested at each time point (± SEM). In LD, one-way ANOVA shows a significant effect of the time of day on locomotion (P < 0.002), but in LL, the modulation of quinpirole-induced locomotion disappears (P = 0.96).

Figure 3

Circadian modulation of nerve cord dopamine receptor responsiveness continues after decapitation. Wild-type w1118 (A or B) or per^o (C or D) flies were LD entrained. Flies were decapitated at ZT 7 or ZT 19, and then assayed with 5 mM quinpirole either 30 min (no delay) or 12-h (12-h delay) later. A Student's t test for samples, assuming equal variance, was performed comparing the no delay and 12-h delay means to the means for flies decapitated and tested 12 h earlier. (*, P < 0.05; **, P < 0.01.) (A) Wild-type flies decapitated and tested in LD. (B) Wild-type flies decapitated and tested in LL. (C) per^o flies decapitated and tested in LD. (D) per^o flies decapitated and tested in LL.