Reproduction Topic #4 Puberty

Puberty

_____ is defined as the aquisition of reproductive competenece that occurs over time.

NOT A BIG EVENT

Puberty is ______

Hypothalamus

Puberty is defendent on the ________ production of GnRH at appropriate frequency and  quantities to stimulate production of FSH and LH

Gamete Production

Puberty 

• Required for _________

Estrogen

Puberty

2. Differs between male and female - responses to _______

Nutrition, Season, Social Cues, Genetics

Puberty

3. Presynaptic neurons to transmit information to GnRH neurons.

   1. These neurons are influenced by:

      1. __________ (influence hypothalamus)

Female

The hypothalamus is inherently _______

Testosterone

During male embryonic development __________ defeminizes the hypothalamus and eliminates the GnRH surge center → Males don’t need surges of testosterone

Estradiol

Testosterone defeminizes the hypothalamus, but it must first be converted to _________.

Estrogen

The female fetal brain is protected from _______

Blood-Brain Barrier

FEMALE

• Fetal estrogen does not cross____________

  • Estrogen travels to the brain binded to alpha-feto proteins that prevents the estrogen from entering the brain.

GnRH

FEMALE

• The lack of estrogen in the brain is permissive to ____ and surge center development 

Defeminizes 

MALE

• Fetal testosterone _______ the hypothalamus

Estradiol

MALE

• Testosterone crosses the blood brain barrier and is converted to ______

  • Lead to NO DEVELOPMENT of GnRH surge center (defeminization) 

Female Hypothalamus

The surge center is specific to the ________

Males don’t have surges, stable production

If males do not have a surge center, how do you think GnRH and LH secretions differ in males and females?

Spikes

Surge center: responsible for GnRH ______ (+ve, -ve feedback)

Basal 

Tonic center: responsible for ____GnRH secretion. 

Surge Center

The tonic center regulates the _____

Surge

After puberty, LH does not ____ in the male

• Males have low amplitude and predictable LH surges 

High amplitude or basal

LH can be _________ in the female

Pre-Ovulatory

Females have high amplitude ______ LH surges

Ovulation

Females also have basal pulsatile epides between ______

Pregnancy 

Definitions of Puberty

FEMALE

1. Age at which a female can support _____

Ovulation 

Definitions of Puberty

FEMALE

2. Age at first _______ - How do we know if ovulation has occured → ultrasound 

Estrus

Definitions of Puberty

FEMALE

3. Age at first _____ (heat) - usually 1st behavioral estrus 

   1. Female becomes sexually receptive

   2. Sexually receptivity DOES NOT always indicate ovualtion 

The one being mounted

In this photo the animal that in heat is

Mounting and Erection

Definitions of Puberty

MALE

1. Age when behavioral traits first expressed

   1. ________- behaviors that precede sexual maturity

Ejaculation

Definitions of Puberty

MALE

2. Age at first _____

   1. Coordination of nerves, muscles, seminal fluids

   2. Substantially preceds ability to produce enough sperm for fertilization 

Spermatozoa 

Definitions of Puberty

MALE

3. Age when ejaculation contains threshold _______ for fertilization 

   1. Species differenes

   2. Bull: > 50 × 10^6 sperm/mL w/10% motility 

Body Size (threshold) and Enviornment and/or social cues?

What two factors impact hypothalamic GnRH neurons?

1. ________

2. ________

Body Size (threshold)

Factors Impacting Hypothalamic GnRH Neurons

1. _____

• Fat Deposition (Increased fat will each puberty faster)

Enviornment and/or social cues 

Factors Impacting Hypothalamic GnRH Neurons

2. ________

• Season of partutition 

• Photoperiod onset of puberty (sunlight exposure)

• Presenece of opposite sex

• Denisty of animals of the same sex

• Genetics- breed specific 

Genetics 

Onset of Puberty

________________

• Early maturing breeds have earlier onset of puberty than late maturing breeds 

  • Cattle: Angua < Charolais, Braham 

Maternal Breeds 

Onset of Puberty

• _______ reach puberty earlier than meat type breeeds 

  • Cattle: Holstein < Charolais 

  • Swine: White Landrace < Yorkshire 

GnRH

The major limiting factor for onset of puberty is _____ secretion

LH Spike

The hypothalamus must secrete enough GnRH to induce an ______ → Ovulation

gradually with age

GnRh release increase __________ (male and female)

Exogenous GnRH

GnRH

Female: Prepubertal pituitary and ovaries respond to ____________ - mechanics (neurons) are already in place!

Can regulate the surge center 

Female: Remember the tonic center regulates the pulse frequency in GnRH and this the surge center … so the tonic center must also reach a functional state so that it ________

Low amplitude and low frequency

GnRH neurons release __________________ of GnRH

Minimial Follicular Growth

GnRH Neurons (Female)

Low Estrogen means there is a lack of surge center stimulation (GnRH secretion) → the tonic center has a high sensitivity to negative feedback of E2 before puberty and this the surge center cannot respond.  

• LH Pulse Frequency is Low 

  • Low estrogen is due to ________________

Puberty

GnRH secretion changes after _____

Surge Center 

GnRH secretion and puberty (Female)

• With age estrogen increases to reach the minimum threshold to activate the __________. (Tonic center activates to secrete GnRH from surge center)

  • Thus: LH/FSH increases

  • Follicle Development increases 

  • Positive Feedback on estrogen to INCREASE GnRH surge center 

• LH SURGE causes ovualtion 

Surge

Onset of Puberty in the Female

The female surge center can respond to estrogen even at birth. So the sensitivity of the _______ to Estrogen never really changes. However, the sensitivity to negative feedback in the tonic center decreases with age and TRIGGERS PUBERTY

Estrogen

Onset of Puberty Female

• The surge center responds to positive feedback of ______

Cannot Respond

Onset of Puberty Female

• The tonic center has a high sensitivity to negative feedback of Estrogen before puberty, and thus the surge center ________

• Tonic center has to be active before surge center → regulates 

yes

LH frequency increases with GnRH secretions, look at Graph

• as ovarian follciles get bigger → producing more Estrogen 

Endocrine and Ovarain Changes with Puberty (look at notes)

Hypothalamus Defeminization

Males do not have a surge center due to _________ before or after birth.

Negative Feedback 

MALE

How does the male hypothalamus respond to GnRH sensitivity?

Densensitized 

MALE

Estrogen and Testosterone from prepubertal males causes negative feedback on GnRH secretion 

• • As puberty increases the GnRH become ________ to the Testosterone and Estrogen resulting in Increased GnRH → LH & FSH secretion (gradual process) 

    • Testes develop and produce more sperm and testosterone 

Slighty Faster 

Overfed animals may reach puberty ______

Correlated 

Metabolic Factors that regulate the onset of puberty

• Free fatty acids and glucose are ______ (proportional) to GnRH concentrations 

  • Thus, Overfed animals may reach puberty slightly faster 

Leptin

Metabolic Factors that Regulate the Onset of Puberty

• __________: hormone secreted by adipocytes (fat) with receptors on the pituitary 

  • Increase in fat → Increase in Leptin → Increase on pituitary → Increase in Gonadotropins

Glucose

Moment to Moment regulation of GnRH only occurs when ____ is availiable

GnRH neurons to produce GnRH

Metabolic Factors and Onset of Puberty 

Glucose → Fuels Glucose Sensing Neurons → Innervates Kisseptin Neurons → Innervate ____________

GnRH neurons to produce GnRH

Metabolic Factors and Onset of Puberty

Aipocytes (Fat) → Forms Blood Leptin → Innervates Neuropeptide Y Neurons → Innervates Kisspeptin Neurons → Innervate _______

GnRH neurons to produce GnRH

Metabolic Factors and Onset of Puberty

Adipose Fatty Acids → Innervate Fatty Acid Sensing Neurons → Innervate Kisspeptin Neurons → Innervate ______GnRH neurons to produce GnRH

Regulate

KIsspeptin Neurons ______ GnRH Secretion

Regulate Puberty 

Enviornmental and Social Conditions that _______

• Season of Birth 

• Social Cues from Males

• Size of Social Group 

Hasten

Social cues ____ the onset of puberty in some livestock

Olfactory Recognition of Pheromones in Urine 

Social Cues that Hasten the Onset of Puberty

• ___________________ (Rat, Ewe, Sow, and Possibly Cow)

• Pheremones: volatile chemical compounds secreted by the body that are detected by olfactory system in some species - CAN STIMULATE GnRH

External Factor 

Social Cues Hastening Onset of Puberty

_______

• Opitic and Olfactory Neurons 

  • Act on hypothalamus to increase GnRH

Season of Birth 

Social Cues Hastening Onset of Puberty

• __________ particularly in seasonal breeders like sheep and horse 

  • Present in rams but not bulls

  • Bitch: minimal seasonal effects on puberty 

  • Queen: increased photoperiod (more light) hastens onset of puberty 

Fall

Season of Birth

Short-Day Breeders = ______

Spring 

Season of Birth

Long-Day Breeders = ____

All external stimuli

Despite social cues, puberty onset cannot be achieved without a threshold metabolic status to initiate hypothalamic (T and E2) responsiveneess to ______

Puberty

The month of birth influences the age of _____ in sheep

Faster 

Sheep born in the spring reach puberty ______ than those born in the Fall

Puberty

Social Cues in Swine

• _________ dictated by number of gilts in a pen and exposure to intact males

(not even physical contact → fence line exposure similar to physical contact)

Delayed Puberty

Social Cues in Swine

• Gilts housed in small groups experienced _________

FASTER

Social Cues in Swine

• Gilts exposed to males will enter puberty ____ THAN LARGE OR SMALL GROUPS OF GILTS WITH NO EXPOSURE 

Accelerate

Bulls ____ the onset of puberty in heifers