FIGURE 1.

Examples of estrous cycles in C57BL/6J and Swiss Webster Mice. A, C, and E show regular 4–5 day estrous cycles in C57BL/6J mice. B and F show examples of regular cycling Swiss Webster mice. D shows the estrous cycle in a Swiss Webster mouse that has undergone a prolonged period in diestrus (8 days, pseudopregnancy) then undergone two regular estrous cycles. Red arrows and dots represent days during the cycle in which blood samples for measurements of prolactin and LH were taken. A–D, and F show tail tip blood sampling occurring on either diestrus or proestrus across subsequent cycles and E shows when tail tip blood samples were taken continuously through diestrus and proestrus