Serotonin and serum Heat Shock Protein (HSP70) changes in horses during different stress condition: acute exercise, slaughter and Toxoplasmosis disease

Heat shock proteins (Hsps) are a group of highly preserved proteins present in the cells of several mammalian species. They are highly inducible by a variety of pathological, physiological, and environmental stress. A serotonin synthesis inhibitor reduces Hsps production in the rat following trauma (Sharma et al., 1995). An increase in serum 5-HT concentrations is often related both to acute exercise and common horse’s pathologies as laminitis. Unlike other animal species, the Horse is resistant to Toxoplasma gondii infection. Toxoplasma gondii is a tryptophan autotrophic consumer. We hypothesized that stressors such as acute exercise, time attending slaughter and Toxoplasmosis disease in horse would result in the increase in plasma 5-HT concentrations and in the release of Hsp70 from stressed cells into the blood. Also, Hsp70 gene (mRNA) expression and serotonin precursor enzyme Tph1 (tryptophan hydroxylase) in horse intestine and leukocytes, as well as the Tph2 in brain and leukocytes, has been observed. The study was carried out on 95 clinically healthy horses. All samples were assayed for the T. gondii research by Real Time PCR with Taq man probes targeting B1 gene (locus AF146527) and serologically using the "Equine IgG kit" (Fuller Laboratories). Leukocytes pellet were obtained from whole blood by insulation with Lympho-Paque (Genaxxon Bioscence) and total RNA was extracted using "Quiazol" from leukocytes pellet and from organs (brain, intestine) in the slaughter. mRNA was reverse-transcribed into cDNA using the "Quantitect Reverse Transcription kit"(Qiagen) and the target genes were amplified by PCR real time with "Quantinova Sybr Green PCR kit". Data obtained by horses who underwent acute exercise (gallop) showed that exercise induces a significant post-exercise increase of plasma 5-HT and serum Hsp70. Moreover, a significant increase of gene (mRNA) Hsp70 expression and serotonin precursor enzyme Tph1 expression, and a relative decrease of Tph2 in leukocytes, was observed. In the T. gondii positive horses the Tph1 expression was more elevated than in the T. gondii negative horses. Slaughter horses were assessed for leukocytes and intestines Hsp70 gene expression, showing an increased expression in the first. Furthermore, Tph2 showed greater expression values than Tph1 in intestine and brain. In conclusion, both physical exercise and metabolic stress activate Hsp and serotonin pathway in the horse.