A simple measure of relative dominance status (cardinal rank) is described which we have termed the dominance index. Like more familiar techniques for assessing rank order, it is based on the direction of aggressive and submissive b,ehaviors between all possible paired combinations of animals in a social group. Using data from five groups of female rhesus monkeys, it reliably produced the same ordinal ranks as fight interaction matrices. There was also good agreement with the cardinal ranks produced by two additional measures of dominance and with those produced by observer ratings. The dominance index can be calculated when fights have not actually occurred and is largely independent of the frequency of agonistic interactions. It has, therefore, wide application and can estimate dominance during brief sampling periods (one hour) and also in stable groups when agonistic interactions are low. Its application is described in experiments in which the male in a group of females was changed and the hormonal status of the females was altered. Estrogen increased female dominance status relative to other females.
Conversion of testosterone into estradiol is important for male rat sexual behavior, and both steroids probably contribute to mating. The distributions of neurons containing androgen receptors (AR) and estrogen receptors (ER) overlap, and many AR-immunoreactive (AR-ir) neurons express Fos immunoreactivity (Fos-ir) induced by mating. Because mating-induced Fos-ir in the male rat occurs mainly in AR-ir neurons, and because both steroids are important for mating, we hypothesized that (i) AR-ir and ER-ir are colocalized and that (ii) some of these neurons are activated during mating. We examined, in adjacent sections from the medial preoptic area (MPN) through the central tegmental field (CTF), the expression of ER-ir in: (i) AR-ir-containing neurons, and (ii) Fos-ir-expressive neurons. PG21 anti-AR, OA-11-824 anti-c-fos, H222 or 1D5 anti-ER primary antibodies were visualized, respectively, with cyanine-conjugated, fluorescein- or cyanine-conjugated, and fluorescein-conjugated secondary antibodies in male rats which were killed 1 h after ejaculating with a receptive female. In MPN, bed nucleus of the stria terminalis (BNST), and medial amygdala (MEA), 80–90% of ER-ir labeling occurred in AR-ir-positive neurons but only about 30% of AR-ir neurons were ER-ir-positive. No ER-ir was found in the CTF. This suggests the presence of three types of brain neurons sensitive to gonadal steroid hormones: neurons sensitive to androgens only, neurons sensitive to both androgens and estrogens, and neurons sensitive to estrogens only. About 50% of ER-ir labeling occurred in cells expressing mating-induced Fos-ir but only about 30% of Fos-ir neurons were ER-ir-positive. These findings suggest that, in the MPN, at least two different neuronal populations are activated during mating: the first contains AR-ir only and the second contains AR-ir and ER-ir. In the BNST and MEA, at least three hormonally sensitive populations are activated during mating: the two described above plus a third population which expresses ER-ir only.
Copulatory behavior was studied in five groups of sexually experienced, gonadally intact male rats in which: (i) the nonsteroidal aromatase inhibitor Fadrozole (CIBA-Geigy CGS 16949A) was delivered bilaterally (0.756 µg in 6.0 µl saline in 24 h to each side) into the medial preoptic area (POM) together with normal saline given s.c. via osmostic minipumps (n = 10); (ii) normal saline was delivered bilaterally into POM together with the same dose of Fadrozole s.c. (n = 9); (iii) Fadrozole was delivered bilaterally into the lateral preoptic area together with normal saline given s.c. (n = 6); (iv) Fadrozole was delivered bilaterally into the cerebral cortex together with normal saline given s.c. (n = 6), and (v) unoperated controls (n = 14). Mounting and ejaculation were significantly decreased in rats receiving Fadrozole in POM compared with the behavior of rats in the other 4 groups. Few differences occurred between rats in the latter 4 groups, all of which continued to mate. The H222 and ER-715 anti-estrogen receptor (ER) antibodies were used to examine the distribution of ER immunoreactive (ERir) neurons in hypothalamic and limbic sites in gonadectomized controls and in some of the rats in groups i, ii and v. Since labeling of ERir neurons in rat brain with the H222 anti-ER antibody is reported to be inhibited by estrogen, it was used here to identify regions (with staining) where the aromatization of testosterone (T) into estradiol (E2) had been suppressed. Intense H222 ERir nuclear neuronal labeling was confined to the POM of males receiving Fadrozole in POM, and significantly more labeled neurons were found in the POM of these rats than in the POM of rats treated with saline in POM. In contrast, the ER-715 antibody, which is reported to stain neurons independently of hormonal status, labeled neuronal nuclei in hypothalamic and limbic regions of all groups, demonstrating the presence of ER. These findings show that conversion of T into E2 in the POM of the male rat is important for male rat copulatory behavior and that H222 ERir nuclear neuronal labeling can be used to identify the neurons in POM that were affected by Fadrozole.
Fractionation of vaginal secretions from rhesus monkeys by partitioning and chromatographic procedures, combined with behavioral studies, demonstrates that short-chain aliphatic acids are responsible for stimulating the sexual behavior of males. Injection of estradiol into ovariectomized females increases the concentration of volatile acids in secretions which will then sexually stimulate these male primates.
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