Summary: A study of fruit flies reveals how the insects retain neural circuits for certain motor functions while their edge on other functions declines as a result of aging.
Source: University of Iowa
Biologists at the University of Iowa have pinpointed how fruit flies—no matter their age—maintained neural circuits for certain motor functions, while losing their edge in other performance measures.
The biologists looked at how well individual neurons and neural circuits function as flies age and when they are subjected to stressors such as changes in temperature and an erosion in protective anti-oxidants in their bodies. They identified biomarkers of aging in the electrical performance of specific motor circuits, separating circuits that weakened as flies aged to those that remained the same no matter the fly’s age.
One of the “aging-resilient circuits,” the biologists found, was in the fly’s ability to escape danger (such as a fly swatter).
On the other hand, flies’ muscle activity during flight and the neural circuits recruited during seizures weakened as they got older.
“Our identification of aging ‘landmarks’ in motor circuit function will help future studies in uncovering genetic pathways or environmental factors contributing to healthy aging in the brain as well as age-related neurodegeneration,” says Atulya Iyengar, post-doctoral researcher in the Department of Biology and a researcher with the Iowa Neuroscience Institute.
Distinct aging-vulnerable and -resilient trajectories of specific motor circuit functions in oxidation- and temperature-stressed Drosophila
In Drosophila, molecular pathways affecting longevity have been extensively studied. However, corresponding neurophysiological changes underlying aging-related functional and behavioral deteriorations remain to be fully explored.
We examined different motor circuits in Drosophila across the lifespan and uncovered distinctive age-resilient and age-vulnerable trajectories in their established functional properties. In the giant-fiber (GF) and downstream circuit elements responsible for the jump-and-flight escape reflex, we observed relatively mild deterioration toward the end of lifespan.
In contrast, more substantial age-dependent modifications were seen in the plasticity of GF afferent processing, specifically in use-dependence and habituation properties. In addition, there were profound changes in different afferent circuits that drive flight motoneuron activities, including flight pattern generation and seizure spike discharges evoked by electroconvulsive stimulation. Importantly, in high temperature (HT)-reared flies (29 °C), the general trends in these age-dependent trajectories were largely maintained, albeit over a compressed time scale, lending support for the common practice of HT rearing for expediting Drosophila aging studies.
We discovered that shortened lifespans in Cu/Zn superoxide dismutase (Sod) mutant flies were accompanied by altered aging trajectories in motor circuit properties distinct from those in HT-reared flies, highlighting differential effects of oxidative vs temperature stressors.
This work helps to identify several age-vulnerable neurophysiological parameters that may serve as quantitative indicators for assessing genetic and environmental influences on aging progression in Drosophila.
Comparisons of the aging trajectories of performance changes of several motor circuits in Drosophila revealed remarkably heterogeneous age-progressions.
We identified “aging-resilient” and “aging-vulnerable” circuits in both normal control and flies with shortened lifespans due to either elevated rearing temperature or oxidative stress.
Motor circuit components including flight motor neuron and the giant-fiber pathway responsible for the escape reflex showed only mild functional decline, whereas distinct trajectories throughout lifespan were seen in the flight pattern generator, interneuron inputs to the giant-fiber system, and circuits generating seizure discharge patterns. Notably, high-temperature rearing generally compressed aging trajectories while Sod mutation-induced oxidative stress led to distinct patterns of motor defects.
Together, these results elucidate potentially salient neurophysiological markers for aging in flies.