Final answer:
Testosterone can act as a facilitator or inhibitor of sexual behavior expression. It, alongside estrogens and progesterone, influences sexual characteristics and behaviors through gene expression regulation and endocrine system interactions.
Step-by-step explanation:
The steroid hormone that can be either a facilitator or an inhibitor of the expression of sexual behavior is testosterone. Testosterone and androstenedione, as primary male sex hormones or androgens, are crucial for controlling the development of male sexual characteristics. However, estrogens and progesterone, which are vital in regulating female sexual and reproductive characteristics, also play a significant role. While it’s common to associate androgens with male characteristics and estrogens with female traits, both sexes produce these hormones in varying levels.
Steroid hormones function by binding with receptor proteins within the cell, forming a complex that moves to the nucleus and influences gene expression. They also interact with the hypothalamus and pituitary gland to mediate sexual development and reproductive functions. In the endocrine system's web of influences, steroid hormones like testosterone can facilitate the inhibition or expression of sexual behaviors, depending on the context and levels present within the body.