Olfactory and Neuromodulatory Signals Reverse Visual Object Avoidance to Approach in Drosophila
Sensory plasticity in insects is mediated by behaviour-regulating biogenic amines. Some of these regulated behaviours include olfactory learning, aggression, and feeding. In Drosophila melanogaster, octopamine influences flight patterns and the response of motion-detecting neurons. This study analyzed both odor- and optogenetic-induced flight patterns using a flight simulator and odour delivery system. In addition to this, Aurora’s 200B miniPID sensor was used to at the beginning of each experiment to confirm air/odour at the location of the fly. In odourless air, it was found that the flies steered toward a vertical bar, which may mimic a plant stalk, but avoided a small box. It is thought that the small box may appear to be threatening but could also appear to be food. As such, they tested the animals’ response to each object in the presence of odours considered attractive to D. melanogaster. When Apple Cider Vinegar or ethanol odourant was added to the air, flies approached the small box that was previously avoided, and more strongly approached the vertical bar. However, in the presence of the odourant benzaldehyde, an odour that flies avoid, the flies displayed avoidance of the small object but continued to approach the vertical bar. These results suggest that visual valence reversal is produced by attractive odourants, but not aversive odourants. To elucidate how olfactory signals are coupled with behaviours, the authors tested whether aminergic neuromodulation was involved in odour-induced visual valence reversal. Transgenic flies expressing Chrimson, a red shifted excitatory channelrhodopsin, in aminergic neurons were subjected to stimulation by Chrimson-exciting illumination. Optogenetic depolarization of octopaminergic (OA) or tyraminergic (TA) neurons by the Tdc2-Gal4 driver changed the flight response to the small box from aversion to approach. Similar avoidance reversal was seen in 15/16 flies upon Tdc2 > Chrimson activation and in flies expressing Chrimson in T4 and T5 neurons. Taken together, this study provides insight into a model for multisensory processing in which attractive odors stimulate Tdc2 release, thus increasing response gain of the motion vision pathway.
Effects of Prolonged Dietary Curcumin Exposure on Skeletal Muscle Biochemical and Functional Responses of Aged Male Rats
Sarcopenia, an age-related condition involving the decline of muscle mass and function, affects 11-50% of those 80 years and older. The causes of sarcopenia are complex as the process of aging is characterized by several biological events. Skeletal muscle oxidative stress is one example and can result in disrupted cellular redox regulation and altered transcription factor activity. In this paper, the authors focus on characterizing the effects of curcumin, a compound shown to combat oxidative damage-inducing agents in aging skeletal muscle. As such, this study analyzed muscle mass and function in aged F344xBN rats exposed to long-term dietary curcumin. Rats were divided into three groups, one of which was provided a curcumin supplemented diet (CUR), the second consisting of rats given a modified amount of food to match the food consumption of CUR rats (PAIR), and a control group consuming a standard diet (CON). After four months of dietary supplementation, functional assessment of the rat plantaris muscle was assessed in situ. Contractile characteristics were measured isometrically at optimal length to determine maximum twitch and tetanic tension using the 1305A 3-in-1 Whole Animal System. The authors found that plantaris muscle mass and peak tetanic tension was significantly greater in CUR mice when compared to PAIR mice. Furthermore, both CON and CUR mice had significantly greater plantaris peak twitch tension than PAIR mice. In addition to this, molecular analysis showed that CUR mice exhibited greater levels of nuclear nrf2 and lower levels of oxidative damage markers when compared to PAIR mice. These differences in expression may mediate the increased peak twitch tension and peak tetanic tension seen in CUR mice, as oxidative stress can cause muscle contractile dysfunction and thus decreased force. In a complimentary study, CUR mice exhibited a greater peak twitch and specific tetanic tension response of the plantaris when administered curcumin via osmotic pumps. Taken together, these findings may help in elucidating the effectiveness of long-term curcumin supplementation in treating sarcopenia.
Gut bacteria are critical for optimal muscle function: a potential link with glucose homeostasis
Gut microbiota influence the development of several chronic diseases including obesity, diabetes, and allergies. Recent studies suggest that an imbalance of gut microbiota may also influence muscle metabolism and contribute to muscle atrophy. This study focused on characterizing the impact of gut microbiota depletion on skeletal muscle by analyzing mice treated with gut-microbiota depleting antibiotics (ABT), mice treated with antibiotics followed by natural reseeding of microbiota (NAT), and control mice (CTL). Each group underwent running tests, where no differences were found in maximal aerobic velocity between each group. For the “Limit time to exhaustion during submaximal running test”, Tlim was significantly lower at day 9 than day 0 in both ATB and NAT mice. However, Tlim at day 19 was lower than day 0 in only the ATB group. Ex vivo contractile tests were then conducted using Aurora’s 305C Dual-Mode Muscle Lever and 701C High-Power Stimulator. EDL maximal strength was unaffected by the running tests; however, EDL muscle fatigue index was significantly reduced in ATB mice when compared with CTL and NAT mice. To investigate the role of gut microbiota on muscular glucose homeostasis, the authors analyzed markers linked to glucose metabolism in the gut-skeletal muscle. Levels of fasting-induced adipocyte factor (Fiaf) were significantly higher in the ATB group. In addition to this, free fatty acid receptor 3 (Gpr41) expression decreased. Following natural reseeding of the NAT group, increased levels of Gpr41 mRNA were observed when compared with the ABT group. Ileum muscle glycogen was also found to be significantly lower in ATB mice. These results highlight the interplay between gut microbiota and skeletal muscle. This study also provides insight into microbiome-based strategies for muscle therapy.