Sex and strain related effects of melatonin and 5-methoxytryptophol on open field behaviour in paired mice

Abstract

The effects of two methoxyindoles, melatonin (MEL) and 5-methoxytryptophol (5-MTL), on partner investigation and other aspects of pair behaviour in the open field, were observed on male and female mice of the albino TO, and the pigmented C57BL/6 strains. Both indole derivatives are major secretory products of rodent (and human) pineal glands. They were administered by i.p. injection (100 μg/kg) to both members of the pair 1 h before each 10 min open field exposure. The testing took place on 3 consecutive days. There were no significant differences in behaviour over days, and group means were used in subsequent data analysis (MANOVA and Dunnet's test). Males, more socially active than the females in both strains, responded to MEL by a reduction in contact time; 5-MTL had the same effect on C57 males (TO males showed no change). Females, on the other hand, did not respond to MEL, and increased their social contact seeking after 5-MTL. There was no consistent effect of either indole on locomotion, and erratic (TO strain only) effects on defaecation. The data are discussed in terms of possible actions of pineal indoles on determinants of social behaviour.