Lecture 12 (Luckman) Flashcards
adolescence v puberty
“Adolescence is the phase of gradual transition between childhood and adulthood”
involves brain development and physical changes.
risky behaviour
puberty - physical sexual changes to become fertile.
Secondary sex characteristics appear, physical growth, reproductive competence is achieved.
brain development during adolescence
subcortical regions - amygdala + NAc develop much faster than frontal areas (PFC)
imbalance can lead to risky or emotional behaviour
role of the amygdala?
emotional processing
adolescent responses to external stimuli
wrt. facial expressions and money
facial expressions show increased amygdala response in adolescence > and increased NAc response for monetary reward
HPG axis? (general)
GnRH (x2)
FSH, LH (+Oe)
Inhibin (+follistatin)
Neurosteroid axis
Hypothalamic-Pituitary-Gonadal (HPG) Axis
GnRH causes LH/FSH release.
LH/FSH activated production of sex steroids, feedback onto hypothalamus/anterior pituitary gland loop.
GnRH(Hyp) –(hypophyseal portal)–> binds GnHRs on secretory cells of adenohypophysis–>LH, FSH (blood stream)
FSH,LH (F)- activate ovaries to produce oestrogen and inhibin, oestrogen forms -ve fb loop (inhibiting GnRH production in Hyp)
Inhibin (+follistatin) inhibits activin (peripherally produced GnRH stimulator)
Recent research has shown that a neurosteroid axis exists, which helps the cortex to regulate the hypothalamus’s production of GnRH
when does onset of puberty occur in females?
when sufficient nutrients attained.
obesity advances onset.
undernutrition delays onset.
physical excercise delays. onset.
Menstruation
Oestrogen, FSH, LH, Progesterone
FSH stimulates egg maturation and oestrogen release
oestrogen peaks day 14 just before ovulation, stops FSH production as only 1 egg needed and stimulates LH release.
Day 14 peak LH ovulation day, LH causes mature egg release to uterus which can now be fertilised.
Uterus lining thickens, maintained by Progesterone.
progesterone decreases when no pregnancy occurs, lining sheds and menstruation day 28.
HPG axis in pregnant/non pregnant
oestrogen feeds back onto hypothalamus/anterior pit and progesterone inhibits hypo/anterior pit.
+ve fb loop between oestrogen and LH prepares follicle (in ovaries) and uterus for ovulation and implantation
empty follicle sac releases progesterone following egg release to inhibit Hyp and aPit (stops fb loop)
if conception occurs, placenta secretes progesterone and mother cannot ovulate again, if not, decreasing progesterone will allow Hyp to restart GnRH secretion
as males age
T
less testosterone.
decrease muscle mass increase fat lose libido impotence decreased attention
kisspeptin
Kiss1 gene.
binds GPCR54
GPCR54 (renamed Kiss1R)
essential for pubertal development and reproductive function
GPCR54 mutations
GPR54 mutations/deletions lead to sexual immaturity, failure of gonadal function and hypogonadotropism
infertile and less sexual hormones
kisspeptin structure
In primates, the Kiss1 gene encodes a 54 amino acid peptide (kp-54)
In rodents, the mature kisspeptin product is 52 amino acids.
precursor prepro kisspeptin 125 AA long.
numerous kisspeptins of various length.
where is kisspeptin found?
Brain: - AVPV/PeN (anteroventral periventricular nucleus-periventricular nucleus continuum)
- ARC (arcuate nucleus)
Peripheral tissues: placenta, ovary, testis, pituitary, pancreas and adipose tissue
where is the Kiss1R gene found?
Brain: hypothalamus, preoptic area, hippocampus, habenula, amygdala
Peripheral tissues: placenta, testis, pituitary, pancreas and kidney
kisspeptin distribution in the brain across species?
varies- table
GnRH and kisspeptin?
GnRH-Ns don’t have oestogen receptors, so how does HPG work?
kisspeptin have oestrogen receptors and androgen receptors.
GnRH have kisspeptin receptors.
AVPN and ARC GnRH neurons differences in rat?
AVPV - positive feedback in adult females
ARC - negative feedback in adults of both sexes.
AVPV project to cell bodies of GnRH neurons.
ARC project to axon terminals of GnRH neurons.
sexual dimorphism in Kiss1cells in AVPV.
25x more kisspeptin expression in females than males.
need to detect the big changes in oestrogen just before ovulation to produce LH surge on day of ovulation.
AVPV - also prod galanine and tyrosine hydroxylase.
ARC - also produce neurokinin B, dynorphin (Kndy neurons)
HPG axis in males
GnRH, LH, T, FSH and inhibin
In males, GnRH, LH, FSH production similar but effect different
LH stimulates the interstitial cells (testes) to produce testosterone (normal spermatogenesis, inhibits HYP)
FSH plays a role in spermatogenesis. Only small amounts of estrogen are secreted in males. FSH stimulates sustentacular cells to release ABP (promotes T binding).
Inhibin is produced by the spermatogenic cells, which, also through inhibiting activin, inhibits the hypothalamus. After puberty these hormones levels remain relatively constant.
Leptin, insulin and ghrelin on the HPG axis (+Kisspeptin)
Leptin and insulin have stimulatory effects and ghrelin has inhibitory effects on gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus. Kisspeptin also influences GnRH secretion.
HPG axis and puberty
The activation of the HPG axis in both males and females during puberty also causes individuals to acquire secondary sex characteristics.
