An autoradiographic study of projections ascending from the midbrain central gray, and from the region lateral to it, in the rat.

Ascending projections from the midbrain central gray (CG) and from the region lateral to it were traced in the rat using tritiated amino acid autoradiography. Leucine or a cocktail of amino acids (leucine, proline, lysine, histidine, and tyrosine) were used as tracers. In addition to projections within the midbrain, ascending fibers follow three trajectories. The ventral projection passes through the ventral tegmental region of Tsai and the medial forebrain bundle to reach the hypothalamus, preoptic area, caudoputamen, substantia innominata, stria terminalis, and amygdala. There are labeled fibers in the diagonal bands of Broca and medial septum, and terminal labeling in the lateral septum, nucleus accumbens, olfactory tubercle, and frontal cortex. The dorsal periventricular projection terminates in the midline and intralaminar thalamic nuclei. The ventral periventricular projection follows the ventral component of the third ventricle into the hypothalamus, passing primarily through the dorsal hypothalamic area and labeling the rostral hypothalamus and preoptic area. Projections from the region lateral to the CG are similar, but exhibit stronger proximal, and weaker distal, projections. Rostral levels of the CG send heavier projections to the fields of Forel and the zona incerta, but fewer fibers through the supraoptic decussation, than do caudal levels. Ascending projections from the CG are both strong and widespread. Strong projections to the limbic system and the intralaminar thalamic nuclei provide an anatomical substrate for CG involvement in nociception and affective responses.

Subordination in male talapoin monkeys lowers sexual behaviour in the absence of dominants.

Three experiments assessed the consequences of social status for the socio-sexual behaviour and endocrine state of adult male talapoin monkeys (Miopithecus talapoin). In the first study, each of five males was individually placed into a group of adult females. Neither behavioural responses, nor plasma levels of testosterone, cortisol, or prolactin, predicted males' rank or hormone levels when all males were subsequently placed with these females. In the second study, each of four mixed-sex social groups lived continuously in a large cage for periods ranging from 9-15 months. There were marked differences between the behaviour and hormone levels of highest- and lowest-ranking males. In the third study, each highest- and lowest-ranking male from these groups was individually placed with females. Males that had experienced social subordination for long periods (9-15 months) showed infrequent sexual behaviour and had elevated levels of cortisol and prolactin. These results indicate that the experience of chronic social subordination is a strong predictor of how males will subsequently behave, since both the endocrine and behavioural effects of subordination persist even after the dominant males are removed.

Social influences on circulating levels of cortisol and prolactin in male talapoin monkeys.

Three captive groups of adult talapoin monkeys (Miopithecus talapoin), each with four males and four or five ovariectomized, estrogen-treated females, were observed. Behavioral interactions were recorded and levels of cortisol and prolactin were measured. In each group, males formed a linear dominance order, determined by the direction of spontaneous aggression; highest male rank was associated with frequent socio-sexual interactions and lowest rank with infrequent socio-sexual behavior. The first study compared males' cortisol and prolactin titers when all males were either housed with estrogen-treated females, or singly caged. The two lowest-ranking males of each group had elevated cortisol levels when group-housed; prolactin levels did not reflect these changes. In the second study, males of one group interacted with females when only the lowest-ranking, or the highest-ranking, female was made attractive (i.e., received estradiol), while the other females were present, but not estradiol-treated. Across these conditions (1) frequencies of some socio-sexual and aggressive behaviors changed, (2) cortisol levels increased in all males, and (3) prolactin levels decreased in three of four males. Dissociation of changes in cortisol and prolactin titers suggests that these hormones may be differentially responsive to social modifications, not simply reflecting a single intervening variable, such as "stress."

Effects of rank and novel females on behaviour and hormones in male talapoin monkeys.

Two social groups of captive talapoin monkeys (Miopithecus talapoin), each with three intact adult males and three or four ovariectomized, estrogen-treated adult females, were observed. Socio-sexual and aggressive interactions were recorded, and levels of testosterone, cortisol, and prolactin were measured in male serum. Cortisol and prolactin titers did not reflect male rank, nor did changes in one of these hormones parallel changes in the other. In both groups males formed a linear dominance hierarchy, defined in terms of the direction of aggression among animals. Highest male rank was associated with frequent socio-sexual interaction and elevated testosterone levels, even in the absence of ejaculations. Males in one group copulated with females, but no male in the other group copulated. All males of each group were then housed with all females of the other group which resulted in marked changes in males' behaviour; socio-sexual interactions increased in C group males and decreased in B group males. This illustrates the influence that females may have on male behaviour in general, and in particular outlines the potential for female dominance and the consequences this may have especially on reproductive behaviour.