Comparison of the data of the current study with the data obtained from the synovial tissues of horses with metacarpophalangeal joint disease could be of interest to verify whether mRNA of Cnr1, Cnr2, TRPV1, GPR55, and PPARA, and the immunoreactivity for the same receptors are up- or down-regulated during joint disease. This evidence concerns the gene GPR55 and arthropathy.