A comparison of hypothalamic cell numbers in dwarf and normal weight rats exposed prenatally to methylazoxymethanol (MAM)

Decreased dominance in a limited access test but normal maternal behavior in micrencephalic rats

Micrencephalic offspring produced by gestational treatment with the antimitotic compound/methylazoxymethanol acetate (MAM) are remarkable for substantial preservation of function concurrent with severe neural stunting. Altered behaviors in these micrencephalics, including light shyness and response perseveration, are similar to those produced by frontal cortex lesions. Consistent with this, the frontal cortex is one of several regions severely stunted by gestational MAM treatment. Because the frontal cortex has been implicated in rodent social behavior, maternal behavior in females and dominance in both sexes were assessed. Dominance was measured via water competition in 24-h water-deprived dyads (1 control and 1 MAM) matched for sex and body weight. Micrencephalic rats exhibited shorter drinking time than controls (males: 101 vs. 219 s, p < 0.001; females: 114 vs. 176 s, p < 0.03), indicating that micrencephalics were more submissive. For maternal behavior tests, micrencephalic and control females were bred to control males and pup retrieval was measured on postnatal days 3-13. Micrencephalic dams were unimpaired in any aspect of pup retrieval. Of 8 standard behavior measures used here and previously, access time in water competition tests produced the clearest differentiation between control and micrencephalic rats. These studies indicate that at least one aspect of social dominance in both sexes is severely reduced by MAM treatment while maternal behavior remains intact.