We greatly acknowledge Mr. Daniel Gómez for the technical assistance with the animals. The skillful work Mr. Fructuoso Cuentas on the maintenance of the P50 equipment donated by the International Foundation for Science (IFS) is also gratefully acknowledged. This work was supported in part by the “Consejo Nacional de Ciencia y Tecnolog??a” (CONCYTEC) Lima—Perú, the Institut Francais d'Etudes Andines (IFEA) and the IFS.