Narcotic tolerance and dependence and serotonin turnover.

stimuli. Access to and copulation with the females was accompanied by becoming the alpha, or dominant, male in a new group. It is possible that the latter experience isa provocative stimulus to increased testosterone secretion, along with frequent sexual activity. Studies are needed to clarify this issue. With more indirect techniques of assessing testosterone secretion, such as measurement of urinary metabolites, it has been reported that testosterone secretion appeared to fall following exposure to stressful situations (6). In the rat, plasma testosterone has been observed to fall following ether anesthesia or foot shock (7). In humans, plasma testosterone has been reported to fall following surgery (8), and recently testosterone levels were observed to be suppressed in young men during the early stressful phase of officer candidate training in the army (9). The fall in testosterone levels in the four males following defeat could be secondary to the wounding they received, as well as related to the psychological effects of such an experience. While all four males showed marked decreases in plasma testosterone, only two animals were seriously wounded. However, it is still possible that physical injury could account for the fall in testosterone levels. Preliminary results of studies in progress indicate that testosterone also falls after males are subjected to defeat and fall in dominance rank without the occurrence of physical injury. The males in the present study were placed back in individual cages after their defeat. When defeated animals remain in the group, they assume a very depressed dominance rank and restrict their social interaction with other animals for a prolonged period of time. These observations suggest that defeat and loss of dominance is a very significant and meaningful experience for the male rhesus, and may thus present the most relevant explanation for the fall in plasma testosterone observed. These data support the interpretation that testosterone secretion can be influenced by social and environmental variables and is not fixed. It is also possible, however, that although the pituitary-gonadal system is subject to influence by environmental events, the subsequent alterations in plasma testosterone may significantly affect behavior. It could be argued that the fall in testosterone following defeat and loss of dominance rank functions as an