Prep for Exam 2 Flashcards
Organizational v Activational Effects
Organizational: active during development to modify structure or physiological function
- relatively permanent changes
Activational: active later in life to trigger or modulate behavior or seasonal expression of a trait
Testosterone
- androgen (group of steroid hormones)
- male sex hormone synthesized in testes
- responsible for secondary male sex characteristics
- produced from progesterone
Estrogen
- estrogen
- principle female sex hormone
- produced in ovaries
- responsible for secondary female sex characteristics
Example of organizational effects
Rooster experiment
- examines the effects of castration and testicular replacement on appearance and behavior in the rooster
conclusion: testicles critical to sexual differentiation
Sex Hormones and Behavioral Development
- males castrated as adults will respond to testosterone to facilitate male sexual behavior
- males will not respond to estradiol and progesterone facilitation of female behavior
- female pups injected with testosterone early in development will later respond to testosterone to facilitate male sexual behavior (masculinization)
Summary
- early development determines masculinization or feminization of behavior (org. effects of testosterone)
- puberty is associated to activation of behavior (activational effects of testosterone)
Chart
Ovary -> no testosterone -> feminization -> female behavior
Testicles -> testosterone peak -> masculinization -> male behavior
What determines gonadal development?
(gonads are ovary/testis)
- Genes on Y chromosome
- SRY gene located on Y chromosome
- SRY gene product (testis determination factor) determines the differentiation of gonads
- Early testosterone critical to development of Wolfian ducts in males
- Mullerian Inhibitory Hormone (by testis) inhibits development of Mullerian ducts in males
Mullerian v Wolfian ducts
In males:
- testosterone promotes wolfian ducts
- mullerian inhibitory hormone: inhibits mullerian ducts
Summary / Chart
XX -> ovary -> no testosterone -> feminization -> female behavior
XY (SRY gene on Y chromosome) -> testis -> testosterone peak -> masculinization -> male behavior
Development of gender specific phenotypes (genitalia)
- perinatal testosterone determines male genitalia (scrotum, penis) and phenotype
- “default system” - no testosterone leads to the development of female genitalia (vaginal opening, clitoris) and phenotype
- expression of SRY gene determines testicular development and male phenotype
- Absence of testosterone means no wolfian duct system development = female phenotype
- testicles also responsible for the production of anti-mullerian hormone inhibiting the mullerian duct system
sexual phenotype development - males
T ——> DHT
- DHT activates androgen receptors
- masculinization of genitalia
- genitalia is androgen dependent - behavior is not
XY (SRY gene) -> testicle -> testosterone peak -> masculinization of behavior and masculinization of genitalia
How does organizational effects determine behavior?
- neural development
- some brain areas are bigger in males while others are bigger in females
- some neurotransmitters are more expressed in males, while others are more expressed in females (ex: kisspeptin) \
- In males early peak of testosterone may affect trophic factors such as cell division, apoptosis (cell death), resulting in bigger structures
Testosterone metabolism & DHT & 5-alpha
- testosterone cane be transformed into 5 alpha reductase
- DHT: male sex hormone that comes from testosterone in the body’s peripheral tissues
- in men, DHT binding to androgen receptors is responsible for facial hair
- The conversion of testosterone to DHT is primarily facilitated by the enzyme 5-alpha reductase.
- if enzyme is missing it can lead to sexual confusion, for example missing 5alpha in genitals will affect phenotype
Testosterone metabolism & DHT & 5-alpha continued
- Testosterone can be transformed into DHT by 5-alpha reductase and then binds to androgen receptors in the brain and genitalia
- or testosterone can be transformed by aromatase to estradiol and bind to estradiol receptors in the brain
- in males, metabolism of testosterone into estradiol and 5-alpha plays a critical role in masculinization and defeminization
Sexual differences and sex dimorphism
- sexual differences: giving men and women different hormones and looking at them
example: increased androgen in women = increase facial hair and muscles
example: castration of males and give them estrogen = change of appearance as well as more hips and increase of breasts - sex differences are normally reversible
Sex dimorphism: irreversible for the most part
- castrate men rats at birth for example or give women rats androgen at birth
- can only be reversed by perinatal treatment
Developmental mishaps and sex confusion
- in mammals, specific genes on the Y chromosome determine sexual differentiation of the gonads
- early androgen release perinatally determines sexual differentiation of external genitalia
genital development thru SRY lens
Male Genitalia: In the presence of the SRY gene and testosterone, the indifferent gonads develop into testes, leading to the formation of male external genitalia (penis and scrotum) and internal reproductive structures (epididymis, vas deferens).
Female Genitalia: In the absence of the SRY gene and low levels of testosterone, the indifferent gonads develop into ovaries, resulting in female external genitalia (vagina, labia) and internal structures (uterus, fallopian tubes).
