Environmental effects on Drosophila brain development and learning

Abstract

Brain development and behavior are sensitive to a variety of environmental influences including social interactions and physicochemical stressors. Sensory input is a mosaic of both enrichment and stress, yet little is known about how multiple environmental factors interact to affect brain anatomical structures, circuits and cognitive function. In this study, we addressed these issues by testing the individual and combined effects of sub-adult thermal stress, larval density and early-adult living spatial enrichment on brain anatomy and olfactory associative learning in adult In response to heat stress, the mushroom bodies (MBs) were the most volumetrically impaired among all of the brain structures, an effect highly correlated with reduced odor learning performance. However, MBs were not sensitive to either larval culture density or early-adult living conditions. Extreme larval crowding reduced the volume of the antennal lobes, optic lobes and central complex. Neither larval crowding nor early-adult spatial enrichment affected olfactory learning. These results illustrate that various brain structures react differently to environmental inputs, and that MB development and learning are highly sensitive to certain stressors (pre-adult hyperthermia) and resistant to others (larval crowding).

Social behavior and aging: A fly model

“…Therefore, it is often useful for D. melanogaster behaviors to be characterized by determining either which structure (s) or type (s) of neuron is involved. 67 After pupal eclosion into an adult, fiber number increases by 15%, reaches a maximum by the end of the first week, then decreases after 3-4 weeks of age. The mushroom bodies (MB) neural region is primarily involved in associative learning and memory, 65 but is also important for some aspects of locomotor activity 66 and sensory integration.…”

“…65 The number of fibers in the MB depends on sex, experience, and age. 67 After pupal eclosion into an adult, fiber number increases by 15%, reaches a maximum by the end of the first week, then decreases after 3-4 weeks of age. 68 Although the behavior of old flies does not seem to correlate to that of MB-less flies, particularly at the level of conditioned learning, 66,69,70 the plateau in behavioral performance (see below-stage 2 in Figure 1) of the fly's life corresponds to a similar plateau in the number of MB fibers.…”

“…[71][72][73] The CC is thus considered to be a center for "decision-making" in the fly. Studies reporting the effects of experience 67 and aging on central nervous system structure 67,75,76 indicate that most neuropil regions of the D. melanogaster brain, including the MB and the CC, are continuously reorganized throughout life in response to specific social living conditions, such as the sex of a partner and crowding during larval and adult stages. Studies reporting the effects of experience 67 and aging on central nervous system structure 67,75,76 indicate that most neuropil regions of the D. melanogaster brain, including the MB and the CC, are continuously reorganized throughout life in response to specific social living conditions, such as the sex of a partner and crowding during larval and adult stages.…”

“…The behaviors of CC mutants mimic some of the deficits that are observed in aging flies, 74 displaying an altered locomotion. 67,76 However, it remains unclear how senescence may otherwise affect the CC and whether such changes might affect the fly's motivation. 67,76 However, it remains unclear how senescence may otherwise affect the CC and whether such changes might affect the fly's motivation.…”

“…The behaviors of CC mutants mimic some of the deficits that are observed in aging flies, 74 displaying an altered locomotion. Studies reporting the effects of experience 67 and aging on central nervous system structure 67,75,76 indicate that most neuropil regions of the D. melanogaster brain, including the MB and the CC, are continuously reorganized throughout life in response to specific social living conditions, such as the sex of a partner and crowding during larval and adult stages. 67,76 However, it remains unclear how senescence may otherwise affect the CC and whether such changes might affect the fly's motivation.…”