puberty and adolescence

puberty 

physical changes by which the body matures into an adult body capable of sexual reproduction 

adolescence

maturation of cognitive, emotional, and social behaviors necessary for independence and successful navigation of the adult world

puberty timing in females

around 8-10 years of age; terminates at around 12-14 years of age

puberty timing in males

around 11-12 years of age; terminates at around age 17

timing of adolescence

extends from puberty to adulthood (independence)

rats pubertal milestones

females: vaginal opening followed by first estrus

males: preputial separation - separation of foreskin from the glans of the penis

human pubertal milestones

females: first menses, breast development, growth spurt, public and underarm hair

males; testicular enlargement, penis growth, growth spurt, deepening of the voice, facial hair growth 

james tanner

pediatric endocrinologist that developed a scale which measures the stages of puberty based on external characteristics

GnRH

portal blood system

anterior pituitary

LH

FSH

testes

ovaries

gonadal steriods

hypothalamic - pituitary - gonadal axis

neurosecretory cells secrete BLANK in pulses from terminal in median eminence. GnRH enters the BLANK BLANK BLANK, and travels to the BLANK BLANK to signal synthesis and secretion of BLANK and BLANK from gonadotropes. Bloodborned LH and FSH act on target cells in BLANK and BLANK to direct secretion of BLANK BLANK

gamete development

reproductive brain behavior

promote secondary sex characteristics and physical growth

increase in gonadal steriods at puberty play a role in:

growth hormone

increases during puberty; stimulate the growth of bones and muscles 

GHRH

hypothalamus

anterior pituitary

GH

somatotropic cells

BLANK is released from neurosecretory cells in the BLANK in the portal blood system down the BLANK BLANK, which releases BLANK in pulsatile manner from BLANK BLANK

increased pulse frequency

pulsatile pattern of GnRH secretion changes at puberty → required to product pattern of gonadotropin and steriod secretion that supports gonadal function and reproductive behaviors

environmental

social

metabolic

signals that time puberty onset

leptin

protein hormone derived from fat tissue that enters the blood stream; the metabolic signal for puberty 

• receptors found on GnRH neurons in hypothalamus, regulate or may initiate the onset of GnRH secretion and thus puberty 

GPR54

gene required for mammalian puberty

kisspeptin

hypothalamic neuropeptide involved in activating GnRH neurons in mammalian puberty through its actions at its G-protein coupled receptor

gain of function mutation

kisspeptin receptor signaling is enchanced, which lead to increased activation of HPG axis → puberty starts before the normal age

precocious puberty

puberty starts before normal age

loss of function mutation

leads to idiopathuc hypogonadotropic hypogonadism

IHH

failure to undergo puberty; infertile due to failure to produce LH and FSH → problem is with the normal release of GnRH

early puberty effects

1. short stature

2. increase risk for metabolic disorders

3. increased risk for breast cancer 

lupron

GnRH agonist; suppresses GnRH and halts precoious puberty via negative feedback

delayed puberty

child does not show physical changes of puberty by age 14 (girls) and age 15 (boys)

• treated with hormone therapy

delay puberty effects

1. short stature

2. low bone density - osteroporosis

3. fertility issues

4. protective against reproductive cancers

steriod hormones

required for the expression of reproductive behavior

organizational effects

irreversible changes in CNS structure and programming of adult behavioral responses to hormones caused by exposure to steriods during sensitive period in early development

activational effects

faciltation of behavior by steriods in adulthood - which is reversible if hormone is removed

2-stage model

gonadal hormones permanently organize the brain and behavior during two critical periods

perinatal period

puberty

2 sensitive periods of the 2-stage model

perinatal period

initial steriod dependent sexual differenitation occurs

puberty period

second wave of steriod neural organization during this time point which builds on and refines neural circuits that were sexually differentiated during early development 

syrian hamster

used to understand the effects of pubertal hormones on social behavior

experimental paradigm

remove testes of syrian hamsters after sexual differenitation and before puberty; administer testosterone in adulthood

experimental results

when testicular hormone was absent during adolecent brain development, syrian hamster had disrupted social and sexual behaviors — this was irreversible

• consistent with hypothesis that adolescence may be a sensitive period for further steriod-dependent organization of neural circuits mediating reproductively relevant behavior

normal behavior

male rats do not interact with one another in a novel behavior

castrate rats before puberty

male rats interact with one another in a novel environment - do not develop anxiety

reinstate testosterone during puberty

reinstates anxiety/normal behavior in male rats

reinstate testosterone during adulthood

does not reinstate anxiety/normal behavior in male rats 

spatial tasks

males tend to do better on these tasks compared to females

spatial task experimental paradigm

• Men with IHH that started before puberty - no/low testosterone during puberty 

• Men who acquired IHH that started in adulthood - had normal levels of testosterone during puberty 

  • Controls - healthy men and women

spatial task experiemental results and conclusion 

• men that developed IHH before puberty performed worse on spatial tasks than healthy men and men that developed IHH during adulthood 

  • Performed similar to females 

Conclusion: spatial cognition may be programmed by testosterone during pubertal development

Morris Water Maze Task

spatial task that males tend to do better on compared to females

Morris Water Maze experiment and results

• females with non-classic CAH (mild form; diagnosed in childhood) - they have higher levels of testosterone due to its overproduction from adrenal glands throughout puberty - These females performed better on the Morris Water Maze Task compared to females, and did similar to males

• CONCLUSION - cognitive function in humans can be programmed by steroid hormones during puberty 

Revised two-stage model

this model includes two periods of elevated hormone secretion within a large post-natal window of decreasing sensitivity to organizing actions of testosterone 

• The adolescent brain is sensitive to neural organization by hormones; even if there isn’t a distinct critical period of development 

Are there actually two stages:

Test by examining whether hormonal exposure is critically necessary only during adolescence or if testosterone has a similar organizing effect if it occurs outside the age-range during which adolescence normally occurs 

Hypothesis - if adolescence marks the opening of a unique sensitive period for testosterone dependent behavioral organization, then only those males receiving testosterone during normal time of puberty should display typical male behaviors 

Experimental paradigm - castrate syrian hamsters, and then reinstate testosterone during these three time points: 

1. Before puberty (early)

2. During puberty (on time)

3. After puberty (late) 

Results: both early and on-time puberty groups displayed appropriate male sexual behavior in adulthood; early treatments most effect in organizing mating behavior

Adolescence is not a sensitive period for testosterone-dependent behavioral organization distinct from the neonatal period rather, adolescence if part of a protracted sensitive period that likely begins perinatally and ends in late adolescence 

Sensitivity to the organizing actions of testosterone decreases across the post-natal development

Implication: organizing effects of testosterone at puberty may differ if puberty occurs early vs. late - this could lead to individual differences in sex-typical behaviors

pre-frontal cortex 

a brain region critical for impulse control, emotional regulation, and executive function - not fully developed in teens 

are hormones involved

unknown how much of a causal role pubertal hormones play in the development of the adolescent brain