Krill, Jennifer L.

The human brain functions within a narrow range of temperatures and
variations outside of this range incur cellular damage and death and, ultimately,
death of the organism. Other organisms, like the poikilotherm Drosophila
melanogaster, have adapted mechanisms to maintain brain function over wide
ranges in temperature and, if exposed to high temperatures where brain function
is no longer supported, these animals enter a protective coma to promote survival
of the organism once the acute temperature stress is alleviated.
This research characterized the role of different neuronal cell types,
including glia, in the protection of brain function during acute hyperthermia,
specifically looking at two protective pathways: the heat shock protein (HSP)
pathway and the cGMP-dependent protein kinase G (PKG) pathway. Whole
animal behavioral assays were used in combination with tissue-specific genetic
manipulation of protective pathways to determine the specific cell types sufficient to confer protection of neuronal function during acute hyperthermia. Using the
neuromuscular junction (NMJ) preparation, calcium imaging techniques were
combined with pharmacological and genetic manipulations to test the hypothesis
that alterations in ion channel conductance via endogenous mechanisms
regulating the cellular response to high temperature stress alter neuronal function.
Expression of foraging RNAi to inhibit PKG expression in neurons or glia
demonstrated protection of function during acute hyperthermia measured
behaviorally through the extension of locomotor function. This extension of
function with the tissue-specific inhibition of PKG was also confirmed at the cellular
level using the genetically encoded calcium indicator (GECI), GCaMP3, to image
calcium dynamics at the NMJ, where preparations expressing foraging RNAi could
continue to elicit changes in calcium dynamics in response to stimulation. Over
the course of this study, the mechanism underlying a novel glial calcium wave in
the peripheral nervous system was characterized in order to elucidate glia’s role in
the protection of neuronal function during acute hyperthermia.

Previous work demonstrates that PKG pathway modulation in Drosophila controls
tolerance to stress in adults and larvae. Through the use of genetics and pharmacology, PKG
inhibition leads to significant protection of function while activation causes increased sensitivity
and early coma onset. In this study we investigate the effect of PKG modulation on neurons and
glia during acute hyperthermia, and begin to determine the underlying physiological
contributions of both tissues.
Glia have been found to influence single neuron activity and global brain function. Neurons, the
most energy-demanding cells in our bodies, are most sensitive to stress. As humans, our neurons
function under stress until permanent failure, resulting in brain damage and even death. Insects
are much more tolerant to environmental stressors. Although stress-activated protective
pathways are highly conserved in both insects and humans, their outcome on neuronal function
and survival are very different.