Abstract
It has been shown that major histocompatibility complex (MHC) types affect the mating choices of mice and that mice can be trained to distinguish arms of a Y maze scented by odors from MHC-congeneic mice. It is now shown that sensory discrimination of MHC types by trained mice in the Y maze is equally effective with urine as the source of odors. Trained mice, male and female, successfully distinguished between urines of MHC-dissimilar F2 segregants of an MHC-congeneic cross but not between urines of MHC-identical F2 segregants. In a control study with a transfer of training procedure, in which reward was withheld to eliminate any basis for new learning, the trained mice successfully distinguished between urines from panels of MHC-congeneic inbred and F2 segregant congeneic mice that had not previously been used as urine donors. Thus urine, which is a source of chemosensory signals in many species, is also a potent source of the MHC-determined odors that distinguish individual mice.