Physical Exercise Affects Serotoninergic System in Horse Leukocytes.

Area of Science:

• Veterinary Medicine
• Neuroendocrinology
• Exercise Physiology

Background:

• Serotonin (5-hydroxytryptamine, 5-HT) influences metabolic processes in various cells, including leukocytes.
• In horses, 5-HT plays a role in physiological and behavioral functions, with physical exercise known to affect its levels.
• The precise signaling mechanisms of 5-HT in response to exercise in horses remain unclear.

Purpose of the Study:

• To investigate the impact of intensive racehorse training on plasma 5-HT levels.
• To analyze the expression of serotonin transporter (SERT) and specific 5-HT receptors (5HT1A, 5-HT2A, 5-HT1B, 5-HT7) in peripheral blood mononuclear cells (PBMCs).
• To evaluate the changes in pro-inflammatory cytokine expression (interleukin-1 beta and tumor necrosis factor-alpha) in response to training.

Main Methods:

• Plasma 5-HT levels were measured using ELISA in 12 trained horses at pre-training (T0), 30 minutes post-training (T1), and 2 hours post-training (T2).
• PBMCs were isolated for real-time PCR to quantify mRNA levels of SERT, 5-HT receptors, and cytokines.
• In vitro experiments were conducted to corroborate the in vivo findings.

Main Results:

• Significantly elevated plasma 5-HT, 5HT1A, and 5-HT2A levels were observed at T1 compared to T0 and T2.
• A significant decrease in SERT, 5-HT1B, 5-HT7, and both cytokine mRNAs was noted in PBMCs at T1.
• These exercise-induced changes suggest a potential reduction in 5-HT storage, leading to higher plasma concentrations.

Conclusions:

• Intensive training induces transient changes in the serotonergic system and cytokine expression in racehorses.
• Leukocyte 5-HT receptor mRNA levels are notably influenced by physical exertion.
• Understanding these neuroendocrine responses to exercise can inform the development of optimized training strategies for racing horses.