Caffeine, dopamine and thermoregulation

Use of fecal microbiome to understand the impact of housing conditions on metabolic stress responses in farmed saltwater crocodiles (Crocodylus porosus)

Introduction

Understanding the impact of housing conditions on the stress responses in farmed saltwater crocodiles (Crocodylus porosus) is crucial for optimizing welfare and management practices.

Methods

This study employed a multi-omics methodology, combining targeted and untargeted LC-MS for metabolite, lipid, and hormone profiling with 16S rRNA gene sequencing for microbiome analysis, to compare stress responses and changes in fecal samples of crocodiles housed in single versus group pens. Metabolic responses to a startle test were evaluated through multivariate analysis, and changes post-stress were examined.

Results

A total of 564 metabolic features were identified. Of these, 15 metabolites were linked to the cortisol biosynthesis pathway. Metabolite origin analysis showed that 128 metabolites originated from the host, 151 from the microbiota, and 400 remained unmatched. No significant differences in fecal corticosterone levels were observed between single and group pens. However, metabolic profiling revealed distinct differences in stress responses: single pen crocodiles exhibited downregulation of certain compounds and upregulation of others, affecting pyrimidine and purine metabolism pathways when compared to grouped pen crocodiles, linked to altering energy associated induced stress. Additionally, fecal microbiome analysis indicated increased Firmicutes:Bacteroides (F:B) ratio in group-housed animals, suggesting greater stress.

Discussion

The study highlights that while traditional stress indicators like corticosterone levels may not differ significantly between housing conditions, metabolic and microbiome analyses provide deeper insights into stress responses. Single pens are associated with less metabolic disruption and potentially better health outcomes compared to group pens. These findings underscore the value of fecal microbiome and metabolomics in assessing animal welfare in farmed crocodiles.

Increased Rate of Heat Storage, and No Performance Benefits, With Caffeine Ingestion Before a 10-km Run in Hot, Humid Conditions

PURPOSE

Although the effect of caffeine in thermoneutral or cool environmental conditions has generally shown performance benefits, its efficacy in hot, humid conditions is not as well known. The purpose of this study was to further examine the effect of caffeine ingestion on endurance running performance in the heat.

METHODS

Ten trained endurance runners (6 males; mean [SD] age = 26 [9] y, height = 176.7 [5.1] cm, and mass = 72.1 [8.7] kg) came to the lab for 4 visits. The first was a VO₂max test to determine cardiorespiratory fitness; the final 3 visits were 10-km runs in an environmental chamber at 30.6°C and 50% relative humidity under different conditions: 3 mg·kg^-1 body mass (low caffeine dosage), 6 mg·kg^-1 (moderate caffeine dosage), and a placebo. Repeated-measures analyses of variance were used to determine the effect of condition on the 10-km time, heart rate, core temperature, rating of perceived exertion, and thermal sensation.

RESULTS

There was no difference in the 10-km time between the placebo (53.2 [8.0] min), 3-mg·kg^-1 (53.4 [8.4]), and 6-mg·kg^-1 (52.7 [8.2]) conditions (P = .575, ηp2=.060 ). There was not a main effect of average heart rate (P = .406, ηp2=.107 ), rating of perceived exertion (P = .151, ηp2=.189 ), or thermal sensation (P = .286, ηp2=.130 ). There was a significant interaction for core temperature (P = .025, ηp2=.170 ); the moderate-dosage caffeine condition showed a higher rate of rise in core temperature (0.26 [0.08] °C·km^-1 vs 0.20 [0.06] and 0.19 [0.10] °C·km^-1 in the low-caffeine and placebo conditions, respectively).

CONCLUSION

The results support previous research showing a thermogenic effect of caffeine, as the moderate-dosage condition led to a greater rate of heat storage and no performance benefits.

National Athletic Trainers' Association Position Statement: Exertional Heat Illnesses

OBJECTIVE

To present best-practice recommendations for the prevention, recognition, and treatment of exertional heat illnesses (EHIs) and to describe the relevant physiology of thermoregulation.

BACKGROUND

Certified athletic trainers recognize and treat athletes with EHIs, often in high-risk environments. Although the proper recognition and successful treatment strategies are well documented, EHIs continue to plague athletes, and exertional heat stroke remains one of the leading causes of sudden death during sport. The recommendations presented in this document provide athletic trainers and allied health providers with an integrated scientific and clinically applicable approach to the prevention, recognition, treatment of, and return-to-activity guidelines for EHIs. These recommendations are given so that proper recognition and treatment can be accomplished in order to maximize the safety and performance of athletes.

RECOMMENDATIONS

Athletic trainers and other allied health care professionals should use these recommendations to establish onsite emergency action plans for their venues and athletes. The primary goal of athlete safety is addressed through the appropriate prevention strategies, proper recognition tactics, and effective treatment plans for EHIs. Athletic trainers and other allied health care professionals must be properly educated and prepared to respond in an expedient manner to alleviate symptoms and minimize the morbidity and mortality associated with these illnesses.

National Athletic Trainers' Association Position Statement: Exertional Heat Illnesses

OBJECTIVE

To present best-practice recommendations for the prevention, recognition, and treatment of exertional heat illnesses (EHIs) and to describe the relevant physiology of thermoregulation.

BACKGROUND

Certified athletic trainers recognize and treat athletes with EHIs, often in high-risk environments. Although the proper recognition and successful treatment strategies are well documented, EHIs continue to plague athletes, and exertional heat stroke remains one of the leading causes of sudden death during sport. The recommendations presented in this document provide athletic trainers and allied health providers with an integrated scientific and clinically applicable approach to the prevention, recognition, treatment of, and return-to-activity guidelines for EHIs. These recommendations are given so that proper recognition and treatment can be accomplished in order to maximize the safety and performance of athletes.

RECOMMENDATIONS

Athletic trainers and other allied health care professionals should use these recommendations to establish onsite emergency action plans for their venues and athletes. The primary goal of athlete safety is addressed through the appropriate prevention strategies, proper recognition tactics, and effective treatment plans for EHIs. Athletic trainers and other allied health care professionals must be properly educated and prepared to respond in an expedient manner to alleviate symptoms and minimize the morbidity and mortality associated with these illnesses.

Performance in the heat-physiological factors of importance for hyperthermia-induced fatigue

This article presents a historical overview and an up-to-date review of hyperthermia-induced fatigue during exercise in the heat. Exercise in the heat is associated with a thermoregulatory burden which mediates cardiovascular challenges and influence the cerebral function, increase the pulmonary ventilation, and alter muscle metabolism; which all potentially may contribute to fatigue and impair the ability to sustain power output during aerobic exercise. For maximal intensity exercise, the performance impairment is clearly influenced by cardiovascular limitations to simultaneously support thermoregulation and oxygen delivery to the active skeletal muscle. In contrast, during submaximal intensity exercise at a fixed intensity, muscle blood flow and oxygen consumption remain unchanged and the potential influence from cardiovascular stressing and/or high skin temperature is not related to decreased oxygen delivery to the skeletal muscles. Regardless, performance is markedly deteriorated and exercise-induced hyperthermia is associated with central fatigue as indicated by impaired ability to sustain maximal muscle activation during sustained contractions. The central fatigue appears to be influenced by neurotransmitter activity of the dopaminergic system, but inhibitory signals from thermoreceptors arising secondary to the elevated core, muscle and skin temperatures and augmented afferent feedback from the increased ventilation and the cardiovascular stressing (perhaps baroreceptor sensing of blood pressure stability) and metabolic alterations within the skeletal muscles are likely all factors of importance for afferent feedback to mediate hyperthermia-induced fatigue during submaximal intensity exercise. Taking all the potential factors into account, we propose an integrative model that may help understanding the interplay among factors, but also acknowledging that the influence from a given factor depends on the exercise hyperthermia situation.