The Maudsley reactive and nonreactive strains: a North American perspective.

The Maudsley experiment involving bidirectional selection for differences in open-field defecation (OFD) is briefly reviewed. Attention is focused on the North American stocks of these strains since problems have been encountered with regard to the open-field behavior and continued viability of the British stocks. The open-field behavior of the colonies of the Maudsley strains at the National Institutes of Health and at the University of Northern Iowa closely resembles that originally exhibited by the British strains, provided they are compared under standard conditions. On more complex behaviors, such as escape-avoidance conditioning, serious discrepancies have emerged between the British and North American findings. These may be resolved when attempts are made to replicate more closely the procedures used in the British studies. Particular emphasis has been placed on the potential of a second nonreactive strain, the MNRA/HAR strain, to serve as a replicate of selection for decreased emotionality. The value of the RXNRA group of recombinant-inbred strains, developed and maintained by the author, for examining the reliability of associations between traits is also stressed. A correlation between OFD and biochemical aspects of sympathetic function has been found in the Maudsley strains. This finding lends credibility to Hall's claim that the expression of emotionality is linked to autonomic arousal.