Chronic cocaine exposure in Drosophila: life, cell death and oogenesis

Developmental signaling cascades that can be perturbed by cocaine and other drugs of abuse have been difficult to study in humans and vertebrate models. Although numerous direct neural targets of cocaine have been elucidated at the molecular level, little is known about the specific cellular events that are impacted indirectly as a result of the drug's perturbation of neural circuits. We have developed oogenesis in Drosophila melanogaster as a model in which to identify downstream biochemical and/or cellular processes that are disrupted by chronic cocaine exposure. In this model, cocaine feeding resulted not only in expected reductions in viability, but also in unanticipated developmental defects during oogenesis, including aberrant follicle morphogenesis and vitellogenic follicle degeneration. To identify mechanisms through which cocaine exerted its deleterious effects on oogenesis, we examined candidate components of neural and hormonal signaling pathways. Cocaine-induced disruptions in follicle formation were enhanced by juvenile hormone exposure and phenocopied by serotonin feeding, while cocaine-activated follicle apoptosis was enhanced by concomitant dopamine feeding. HPLC analysis of dopamine and serotonin in the ovary suggests that these neurotransmitters could variably mediate cocaine's effects on oogenesis indirectly in the brain and/or directly in the ovary itself. We confirmed the involvement of hormone signaling by measuring ecdysteroids, which increase following cocaine exposure, and by demonstrating suppression of cocaine-induced follicle loss by hormone receptor mutants. Cocaine-induced ovarian follicle apoptosis and adult lethality appear to be caused by modulation of dopamine levels, while morphological defects during follicle formation likely result from perturbing serotonin signaling during cocaine exposure. Our work suggests not only a new role for juvenile hormone and/or serotonin in Drosophila ovarian follicle formation, but also a cocaine-sensitive role for dopamine in modulating hormone levels in the female fly.