Rapamycin and other mTOR inhibitors are being heralded as possible treatments for many human ailments. It is currently being utilized clinically as an immunomodulator after transplantation procedures and as a treatment for certain forms of cancer, but it has numerous potential clinical indications. Some studies have shown profound effects on life cycle and muscle physiology, but these issues have not been addressed in an organism undergoing developmental processes. This paper fills this void by examining the effect of mTOR inhibition by rapamycin on several different qualities of larval Drosophila. Various dosages of the compound were fed to second instar larvae. These larvae were monitored for pupae formation to elucidate possible life cycle effects, and a delay to pupation was quantified. Behavioral deficits were documented in rapamycin-treated larvae. Electrophysiological measurements were taken to discern changes in muscle physiology and synaptic signaling (i.e. resting membrane potential, amplitude of excitatory post-synaptic potentials, synaptic facilitation). Pupation delay and effects on behavior that are likely due to synaptic alterations within the central nervous system were discovered in rapamycin-fed larvae. These results allow for several conclusions as to how mTOR inhibition by rapamycin affects a developing organism. This could eventually allow for a more informed decision when using rapamycin and other mTOR inhibitors to treat human diseases, especially in children and adolescents, to account for known side effects.

Proprioceptive neurons monitor the movements of limbs and joints to transduce the movements into electrical signals. These neurons function similarly in species from arthropods to humans. These neurons can be compromised in disease states and in adverse environmental conditions such as with changes in external and internal pH. We used two model preparations (the crayfish muscle receptor organ and a chordotonal organ in the limb of a crab) to characterize the responses of these proprioceptors to external and internal pH changes as well as raised CO2. The results demonstrate the proprioceptive organs are not highly sensitive to changes in extracellular pH, when reduced to 5.0 from 7.4. However, if intracellular pH is decreased by exposure to propionic acid or saline containing CO2, there is a rapid decrease in firing rate in response to joint movements. The responses recover quickly upon reintroduction of normal pH (7.4) or saline not tainted with CO2. These basic understandings may help to address the mechanistic properties of mechanosensitive receptors in other organisms, such as muscle spindles in skeletal muscles of mammals and tactile as well as pressure (i.e., blood pressure) sensory receptors. KEYWORDS: Proprioception; Sensory; Invertebrate; Carbon Dioxide; Protons; Mechanosensory; Intracellular pH; Extracellular pH

Proprioception of limbs and joints is a basic sensory function throughout most of the animal kingdom. It is important to understand how proprioceptive organs and the associated sensory neurons function with altered environments such as increased potassium ion concentrations ([K]) from diseased states, ionic imbalances, and damaged tissues. These factors can drastically alter neuronal activity. To assess this matter, we used the chordotonal organ in a walking leg of a blue crab (Callinectes sapidus) and the muscle receptor organ of the crayfish (Procambarus clarkii). These organs serve as tractable models for the analysis of proprioception. The preparations can help serve as translational models for these effects, which may be observed in other invertebrate species as well as mammalian species (including humans). When extracellular potassium concentration ([K]) is increased to 20 mM in both preparations, mixed results are observed with activity increasing in some preparations and decreasing in others after mechanical displacement. However, when [K] is increased to 40 mM, activity drastically decreases in all preparations. Additionally, proprioceptor sensory activity declines upon exposure to a diluted muscle homogenate, which contains a host of intracellular constituents. The robust effects of altered [K] on proprioception in these models illuminate the potential detriments on neuronal function in cases of severe tissue damage as well as altered [K].

The endotoxin lipopolysaccharide (LPS) from Gram-negative bacteria exerts a direct and rapid effect on tissues. While most attention is given to the downstream actions of the immune system in response to LPS, this study focuses on the direct actions of LPS on skeletal muscle in Drosophila melanogaster. It was noted in earlier studies that the membrane potential rapidly hyperpolarizes in a dose-dependent manner with exposure to LPS from Pseudomonas aeruginosa and Serratia marcescens. The response is transitory while exposed to LPS, and the effect does not appear to be due to calcium-activated potassium channels, activated nitric oxide synthase (NOS), or the opening of Cl− channels. The purpose of this study was to further investigate the mechanism of the hyperpolarization of the larval Drosophila muscle due to exposure of LPS using several different experimental paradigms. It appears this response is unlikely related to activation of the Na-K pump or Ca2+ influx. The unknown activation of a K+ efflux could be responsible. This will be an important factor to consider in treatments of bacterial septicemia and cellular energy demands.

With the looming global population crisis, it is more important now than ever that students understand what factors influence population dynamics. We present three learning modules with authentic, student-centered investigations that explore rates of population growth and the importance of resources. These interdisciplinary modules integrate biology, mathematics, and computer-literacy concepts aligned with the Next Generation Science Standards. The activities are appropriate for middle and high school science classes and for introductory college-level biology courses. The modules incorporate experimentation, data collection and analysis, drawing conclusions, and application of studied principles to explore factors affecting population dynamics in fruit flies. The variables explored include initial population structure, food availability, and space of the enclosed population. In addition, we present a computational simulation in which students can alter the same variables explored in the live experimental modules to test predictions on the consequences of altering the variables. Free web-based graphing (Joinpoint) and simulation software (NetLogo) allows students to work at home or at school.