Presented by Zeleke Mekuriaw at the EIAR-DBARC-ICARDA-ILRI (LIVES)-FAO Training Workshop on Reproduction in Sheep and Goat, Debre Berhan, Ethiopia, 13-15 October 2014

1. Neuro-endocrine control of reproduction in sheep
Zeleke Mekuriaw
EIAR-DBARC-ICARDA-ILRI (LIVES)-FAO Training on Reproduction
in Sheep and Goat, Debre Berhan, Ethiopia, 13-15 October 2014

2. Outline
• Introduction
• Hypothalamic-pituitary-Gonadal axis (HPG)
• Hypothalamus
– Production and release of GnRH
– Function of GnRH
• The Pituitary gland
– Functions & regulations of gonadotrophin hormones
• Gonadal (steroid) Hormones
• Hormone from Pineal gland
• Summary of integration of organs & hormones to regulate reproduction 2

3. Introduction
• The nervous system &
endocrine systems work
jointly
• One affects the other (NS -by
producing neurotransmitters;
ES-feedback mechanisms)
• Maintain homeostasis
(internal stability)

4. Hypothalamic-pituitary-Gonadal axis (HPG)
• The reproductive process governed by
HPG axis
• A complex neuro-endocrine system
• Composed of 3 anatomically &
functionally distinct structures
• Regulate reproduction with
coordination

5. Hypothalamus
• Part of brain
• Has close apposition with
pituitary gland
• Produces GnRH(a master
molecule- neurotransmitter)
• Controls the function of
pituitary gland

6. Production and release of GnRH
• The hypothalamic area that
controls reproduction is
represented by scattered
neurons producing GnRH.
• The dispersed GnRH
neurons, collectively called
‘GnRH pulse generator’.
• GnRH pulse generator
receives and integrates
endogenous cues and
external stimuli.

7. Function of GnRH
• Controls gonadal activity by
regulating synthesis & release of
pituitary gonadotropins (LH & FSH).
• Pulsatile GnRH secretion induces an
identical pattern of LH secretion &
increases FSH synthesis.
• Leads to gametogenesis &
steroidogenesis

8. Pituitary gland
• A ‘master’ gland
• Located at the base of brain
• Anterior & posterior lobes
• Anterior- major source of reproductive hormones
• Produces FSH & LH (tropic hormones-affect other glands)
• Function both in male & female
• Role in gametogenesis & steroidogenesis

9. Functions and regulations of gonadotropin hormones
• LH:
– For the synthesis of
testosterone
– For final maturation of ovum
– For ovulation of matured egg
– For the formation and
maintenance of CL
– Pulsatile (tonic) and surge
(burst)
• FSH:
– spermatogenesis in male
– Follicular growth in female

10. Gonadal Hormones -steroid hormones
 In Female
– Ovarian Hormones
– Oestradiol
• From matured follicle
• Secondary sexual characteristics
• sexual desire in female
– Progesterone
• From CL
• Maintenance of pregnancy

11. Gonadal Hormones -steroid hormones…
• Inhibin
– From dominant follicle
– Inhibits secretion of FSH
• Uterine Hormone
– Prostaglandin
– Luteolysis (disintegration of CL)

12. Integration among structural and hormonal changes during
the oestrous cycle
Estrus
Estrus
CL
0 2 4 6 8 10 12 14 16 17
Day of the Estrous Cycle
LH surge
PGF2ɚ
LH surge
Follicles
ovulation
ovulation
LH pulses LH pulses

13. Gonadal Hormones -steroid hormones…
 In Male
– Testosterone
• Produced from ledying cells of testis
• Action of LH required
• Role:
– Libido
– Secondary sexual characteristics
– Musculature
– Androgen binding proteins
• Produced by sertoli cells
• Development of accessary organs
– Inhibin
• Produced by sertoli cells
• Inhibits production of FSH

14. Hormone from Pineal gland
 Pineal gland-‘Third eye’
– Located in the brain
– Transducer of photo stimuli
to hormone
 Melatonin
– Produced during dark hours
– Seasonality of reproduction
– Both on male & female
– More potent in female
– Long duration secretion =
stimulatory
– Short duration = inhibitory

15. Summary of integration of organs & hormones to regulate
reproduction
15

16. www.lives-ethiopia.org
The presentation has a Creative Commons licence. You are free to re-use or distribute this work, provided credit is
given to ILRI.