Genetic variation in hypothalamic methyltrienolone (R1881) binding in male mice

Methyltrienolone (R1881) binding to androgen receptors (AR) from combined hypothalamic-preoptic-septal cytosol was examined in CF-1, CFW, and CD-1 male mice, strains that differ in their sensitivity to the aggression-promoting property of this hormone. Both the affinity of R1881-AR binding and the number of binding sites (Bmax) significantly differed among the genotypes. The dissociation constant (Kd) was lower in CF-1 males (6.7 nM), a behaviorally responsive strain, in comparison to the insensitive CFW and CD-1 males (3.0 nM and 2.0 nM, respectively). The number of binding sites was higher in CF-1 and CFW males (9.07 and 8.81 fmol/mg protein, respectively) than in CD-1 males (5.11 fmol). The results were basically consistent with studies of neural dihydrotestosterone (DHT) binding in these genotypes, and the implications and limits of these data for understanding the androgenic regulation of intermale aggression are discussed.