The blood-brain barrier (BBB) maintains a stable environment for the central nervous system (CNS) by regulating the influx and efflux of molecules. Metabolic changes during prolonged exercise may lead to increased BBB permeability (Chaouloff, 1997; Sharma et al. 1991). This may affect normal brain function and contribute to the development of central fatigue during exercise by altering the transport kinetics of neurotransmitter precursors or allowing the accumulation of unwanted substances in the CNS. The aim of this preliminary study was to examine changes in serum S100b, a proposed peripheral marker of BBB permeability (Kapural et al. 2002), following prolonged exercise in temperate and warm conditions.

With ethics committee approval, seven active males (mean ± S.D.; age 26 ± 5 years, Î{special}J{special}_,peak 4.07 ± 0.22 l min^-1) completed experimental trials in temperate (Tmp) and hyperthermic (Hyp) conditions separated by at least 7 days. Subjects entered the laboratory in the morning following an overnight fast, and were seated in a comfortable environment (22-24 °C) for 15 min before sitting immersed to the neck in water at 35.0 ± 0.1 °C (Tmp) or 39.0 ± 0.1 °C (Hyp) for 30 min. Subjects then entered a room maintained at either 18.3 ± 1.8 °C (Tmp) or 35.0 ± 0.3 °C (Hyp) and cycled for 60 min at 60 % Î{special}J{special}_,peak. Serial venous blood samples were collected and analysed for serum S100b by microplate ELISA. Differences (P < 0.05) between trials were evaluated using ANOVA with repeated measures and Tukey’s post-hoc and paired t tests as appropriate.

Serum S100b was elevated after exercise in the Hyp trial (+0.12 ± 0.10 µg l^-1; P = 0.02), but not after the Tmp trial (P = 0.238). Water immersion and exercise elevated core temperature by 2.1 ± 0.5 °C to 39.5 ± 0.3 °C at the end of exercise in the Hyp trial compared to a 0.9 ± 0.2 °C increase during the Tmp trial (P < 0.001). Heart rate (P < 0.001), as well as blood glucose (P < 0.001) and lactate (P < 0.001), was significantly higher during exercise in the warm environment. Ratings of perceived exertion (P < 0.001) and thermal comfort (P < 0.001) were markedly higher throughout the Hyp trial than the Tmp trial.

This study has demonstrated that serum S100b is elevated following prolonged exercise in a warm environment, suggesting that BBB permeability may be altered. Previous animal studies have observed a marked increase in BBB permeability following forced swimming exercise (Sharma et al. 1991). The development of hyperthermia, an upregulation in central serotonin synthesis and an increased production of cytokines have all been suggested as possible factors contributing to this response.