![]() Given that some mobility is still retained at Tpref, and that acclimation is in itself costly, the energetic benefits of selecting cooler temperatures between feedings may outweigh the costs associated with reduced locomotor performance. The energetic savings associated with a lower Tpref in unfed leeches effectively doubled the estimated time until depletion of energy reserves. 6 weeks at Ta resulted in no detectable acclimation in locomotor performance or aerobic metabolism. The Q10 values of 1.7 to 2.9 for energetic and swimming parameters indicate a substantial temperature effect, although part of the decline in swimming performance can be attributed to temperature-related changes in water viscosity. Aerobic metabolic rate was also reduced from 0.20 ± 0.03 W kg⁻¹ at Ta to 0.10 ± 0.03 W kg⁻¹ at Tpref. The transition from Ta to the unfed Tpref significantly reduced speed and propulsive cycle frequency during swimming, and extension and retraction rates during crawling. These costs could be limited if mobility is unimpaired at low temperatures, or if acclimation can restore locomotor performance to the levels at Ta. Energetic benefits may have an associated cost if low temperatures reduce mobility and the ability to locate further hosts. This may reduce energy expenditure and defer starvation if feeding opportunities are limited. 2011), while unfed leeches have a lower preferred temperature (Tpref, 12.5 ☌). Immediate postprandial preferences are for warmer than their initial acclimation temperature (Ta, 21 ☌, Petersen et al. Medicinal leeches (Hirudo verbana) thermoregulate with respect to their sanguivorous feeding behavior. Manipulating the serotonin pathway, through oral supplementation of 5-HTP, influences signaling pathways and cellular processes in adipose and muscle related to endocrine and metabolic functions which might translate into improvements in calf growth and development. Adipocyte surface area was smaller and muscle fiber area was not different in the 5-HTP group. Supplementation of 5-HTP increased cell proliferation and total cell number in adipose and muscle. In muscle, enriched pathways were related to histone acetyltransferase binding, Jak-STAT signaling, PI3K-Akt signaling and cell proliferation. Enriched pathways in adipose tissue revealed serotonin’s participation in lipid metabolism and PPAR signaling. Notably, Interferon gamma inducible protein-47 was highly expressed and upregulated in muscle and adipose (avg. Twenty-two genes were differentially expressed in adipose, and 33 in muscle. Calves were euthanized on d10 to harvest adipose and muscle for RNA-Sequencing and histological analyses. Holstein bull calves (21 ± 2 days old) were fed milk replacer supplemented with saline (CON, 8 mL/day n = 4) or 5-hydroxytryptophan (5-HTP, 90 mg/day, n = 4) for 10 consecutive days. Herein, we characterized the transcriptomic profile and microstructure of adipose and muscle in pre-weaned calves with increased circulating serotonin. In mammals, peripheral serotonin is involved in regulating energy balance.
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