Puberty and seasonality Flashcards
Development of what is important for puberty to happen?
Hypothalamus
What are the differences between the male and female hypothalamus?
The female hypothalamus has a surge centre and a tonic centre. Post puberty there is a LH surge.
The male has no surge centre and LH is secreted in a relatively consistent pattern. (LH binds to leydig cells to make testosterone)
How is the female brain feminised and the male brain masculinised?
Binding of E2 to aFP prevents e2 passing through blood brain barrier in female so surge centre can develop in the female.
E2 can cross BBB in male and prevents development of surge centre.
At puberty what happens to the neurons?
Presynaptic neurons synapse onto Gnrh neruons at puberty there is a change in activity of the presynaptic neurons.
In men what happens to the frequency of GnRH after puberty?
There are no surges in the male but there is an increase in basal frequency.
In women what happens to the frequency of GnRH after puberty?
The surge centre develops and controls the pre-ovulatory surge of GnRH that causes the pre-ovulatory surge of LH.
How does nutritional status effect puberty in the female?
GnRH neurones are sensitive to metabolic status
The three main types are pre-synaptic neurones
— Glucose sensitive neurones
— Fatty acid sensitive neurones
— Leptin sensitive neurones
Leptin (produced by adipose tissue), fatty acids &
glucose thought to promote activity in “kisspeptin
neu rones” these neurons synapse on GnRH
neurons.
Therefore good nutrition means earlier puberty.
What are some seasonal polyestrus long day breeders?
The mare
What are some seasonal polyestrus short day breeders?
Ewe, doe, elk, nanny
What are some examples of mono-oestrus breeders?
Dog, wolf, fox, bear
What are some examples of polyoestrus breeders?
Cow, pig, rodent.
With regards to seasonal breeders what triggers return to cyclicity?
Long day breeders — lengthening daylight hours — increasing plane of nutrition Short day breeders — shortening daylight hours Melatonin which is synthesised by the pineal gland
What does melatonin do to long day breeders?
Represses reproduction in the short months. The delcining melatonin (darkness) in long days triggers GnRH release.
What does melatonin do to short day breeders?
Stimulates reproduction. The increase in melatonin (darkness) in the short days triggers GnRH release.
What are the controlling factors of cyclicity?
Photoperiod, melatonin, temperature, nutrition, lactation, pregnancy.
What does LH do and where is it produced?
LH: The surge induces ovulation, is a hormone produced by gonadotropic cells in the anterior pituitary gland. In females, an acute rise of LH triggers ovulation and development of the corpus luteum. In males, where LH had also been called
interstitial cell—stimulating hormone (ICSH), it stimulates Leydig cell production of testosterone. It acts synergistic-ally with FSH.
What does FSH do and where is it produced?
• FSH: stimulates follicular growth, particularly small antral follicles, it also stimulates the recruitment wave of follicles thereby increases estradiol E2.
FSH: anterior pituitary
What are the characteristics of short day breeders?
Short day breeders (e.g. sheep, goat)
— Increasing melatonin (shortening daylight hours)
— Increased synthesis
— Increased FSH, then LH
What are the characteristics of long day breeders?
Long day breeders (e.g. horse, fox, queen)
— Decreasing melatonin (lengthening daylight hours)
— In conjunction with increasing plane of nutrition
— Increased GnRH synthesis
Do uterine involution and resumption of ovarian activity happen at same time?
No. It varies. Some are influence by weaning even if uterus has involuted.
In the mare the uterus involutes in 14 days and returns to ovarian cyclicity in 5-12 days however in te Ewe and bitch there are atleast 30-40 days between involution and return to cyclicity.
What can cause extended anoestrus post partum?
Lactation/suckling
Prolactin (particularly in sows, women)
— Prevents pregnancy before weaning
. Mammary stimulation/suckling suppresses GnRH
. Offspring influences e.g. visual, olfactory, auditory
- eg beef vs dairy cows
. Weaning promotes ß/LH secretion
What can hasten cycle resumption?
Early weaning.
What are common influences on delayed return to cyclicity?
Suckling
• prolactin/ presence of offspring
• ATCH/Corticosteroids
Peri-parturient abnormalities
• Retained fetal membranes
• Endometritis
Milk yield/Nutrition
• Body condition score
• Negative energy balance t
Parity
. Especially in primiparous (bearing
of first child)
