Functional activation of the periaqueductal gray matter during conditioned and unconditioned fear in guinea pigs confronted with the Boa constrictor constrictor snake - Paula, B. B. de; Vieira-Rasteli, E. B; Calvo, F.; Coimbra, Norberto Cysne; Leite-Panissi, Christie Ramos Andrade (Brazilian Journal of Medical and Biological Research, 2022)