Changes in purines concentration in the cerebrospinal fluid of patients experiencing pain: A case-control study - Schmidt, André P.; Böhmer, Ana Elisa; Soares, Félix A.; Posso, Irimar P.; Machado, Sheila B.; Mendes, Florentino Fernandes; Portela, Luiz Valmor C.; Souza, Diogo O. (Neuroscience Letters, 2010)