Tonic and Preovulatory Surge of GnRH! Animal Science 434! Lecture 11: The Follicular Phase of the Estrous Cycle!! (-)! Hypothalamus! GnRH! Estradiol! (-)! Tonic and Preovulatory Surge of GnRH! Anterior! Pituitary! LH, FSH! Inhibin (-)! LH, FSH! CL! Ovary! Estradiol! Follicular Phase! (-)! Hypothalamus! GnRH! Estradiol! (-)! Anterior! Pituitary! LH, FSH! Inhibin (-)! LH, FSH! CL! Ovary! Estradiol!
Hypothalamus! GnRH! Estradiol! (+)! Follicular Phase Anterior! Pituitary! LH, FSH! Ovary! Inhibin (-)! LH, FSH! Estradiol! Follicular Progression! Growth and Atresia of Follicles! Primordial Primary Secondary Tertiary Atresia Fate of follicles and oocytes! Total # of follicles At birth 100,000 12 months 75,000 4-6 years 21,000 Aged cow 2,500 Follicles undergo atresia at all stages of development. Maximum number of oocytes ovulated for a cow 17 cycles/year x 8 year = 136 oocytes ovulated / lifespan Fate of follicles and oocytes! Total # of follicles At birth 100,000 100 Days of Gestation 12 months 75,000 2.9 million 4-6 years 21,000 Aged cow 2,500 Follicles undergo atresia at all stages of development. Maximum number of oocytes ovulated for a cow 17 cycles/year x 8 year = 136 oocytes ovulated / lifespan Superovulation; rescue follicles from undergoing atresia with FSH treatment.
Initial Follicular Growth! Gonadotropin! Independent! Small Antral 50-60 days FSH! Atresia Recruitment Dominance Selection FSH Sensitive Pool Recruitment! Day After Atresia Recruitment Dominance Selection Atresia estradiol inhibin Selection FSH estradiol (-) inhibin (-) FSH Dominance FSH estradiol (-) inhibin (-) FSH Sensitive Pool Recruitment FSH estradiol (-) Day After Day After Dominance Selection Atresia Recruitment Day After Day After
Dominance Selection Recruitment Day After Day After Two Follicular Waves! Follicular Wave Emergence! Recruitment = Emergence! FSH always controls emergence! Increase in FSH precedes emergence! 10! 21! Day After Species Variation in Follicular Waves! Cattle - 2 or 3 / cycle! Sheep - 4 or 5 / cycle! Pigs - 1 / cycle! Horses - 1 / cycle! Human - 1 / cycle! Cl-progesterone Cl-progesterone, inhibin Gonadotropin Action Within the
Granulosa Antral Theca Internal Receptor! Cholesterol! Testosterone! Granulosa! Theca Interna! FSH! Receptor! Testosterone! Estradiol! Blood! Receptor! Cholesterol! Testosterone! Granulosa! Theca Interna! Selection! FSH! Receptor! Testosterone! Estradiol! Dominant Express LH Receptor! Receptor! Blood! Germinal Epithelium! Tunica! Albuginea! Theca Externa! Theca Interna! Basement Membrane! Blocking of these events in the! follicle prevents ovulation.! protein synthesis! steroid synthesis! prostaglandin synthesis! plasminogen activator synthesis! Granulosa!
Preovulatory LH Surge! Cumulus Expansion! Cumulus! Expansion! Hyaluronic Acid and Protein Production! Oocyte! Separates! From! Follicular! Wall! Unexpanded! Expanded! Preovulatory LH Surge! Cumulus and Oocyte! Separation! Cumulus! Expansion! Protein synthesis changes! in and around! Activator! Prostaglandin Synthesis! PGE and PGF! Oocyte! Separates! From! Follicular! Wall! Preovulatory LH Surge! Histamine! PGE2! Cumulus! Increased Blood! Expansion! Protein synthesis changes! Flow to Ovary and! in and around! Activator! Prostaglandin Synthesis! PGE and PGF! Preovulatory LH Surge! Cumulus! Increased Blood! Expansion! Protein synthesis changes! Flow to Ovary and! in and around Vascular Permeability!! Activator! Collagenase (inactive)! Oocyte! Separates! From! Follicular! Wall! Edema! Histamine! PGE2! Prostaglandin Synthesis! PGE and PGF! Plasmin! Oocyte! Collagenase (active)! Separates! Follicular Wall! From! Weakens! Follicular! Vascular Permeability! Edema! Wall! Follicular pressure! Follicular pressure!
Preovulatory LH Surge! Histamine! PGE 2! Cumulus! Expansion! Protein synthesis changes! in and around Increased Blood! Flow to Ovary and!! Activator! Collagenase (inactive)! Plasmin! Oocyte! Collagenase (active)! Separates! From! Follicular Wall! Follicular! Weakens! Wall! Prostaglandin Synthesis! PGE and PGF! Contraction! of Smooth! Muscle! Vascular Permeability! Edema! Follicular pressure! Types of Ovulators! Spontaneous Ovulators! Induced Ovulators! Induced Ovulators! Blood! Hypothalamus! Nerve endings sensing copulation! Sensory Neurons! Stimulation! Time (hr)! GnRH! Anterior Pit.! Posterior Pit.! Copulation! Penis! Spinal Chord!
Cats! Nerve endings sensing copulation! Induced Ovulators! Single copulation! Only works 50% of the time! Multiple copulations! Higher LH surge! Sensory Neurons! Copulation! Penis! Spontaneous Ovulators! Retain some neural control of ovulation! heifers can alter the timing of the LH surge by clitoral stimulation! human rape cases result in higher than expected pregnancy rates! Oogenesis! Migration to germinal ridge! Mitotic divisions! Oogonia! Initiation of Meiosis! Interphase! DNA synthesis! Meiotic prophase begins! Gonadotropin! Independent! Gonadotropin! Dependent! Oogonia in Egg Nest! Fetal Pig Ovary Primordial Germ Cells! Primary! Oocyte! Growth! Follicle Cells! Prophase of Meiosis! leptotene! zygotene! pachytene! diplotene! dictyotene! Meiotic Arrest! zona pellucida formation! mrna production! protein synthesis! cortical granule formation! nuclear maturation! cytoplasmic maturation! Oogonia and Primary Oocytes!
Primary Oocytes in Primordial Follicles! Primary Oocyte in Primary Fetal Oocyte Development! Ovulation of Tertiary Mitosis! Fertilization! Meiosis! Birth! Cow! 280 d! Sow! 114 d! Mouse! 19 d! Formation of the Zona Pellucida! Corona Radiata Zona Pellucida Oocyte Corona Radiata Oocyte Zona Pellucida Gap Junctions
During Oocyte Growth and Before the LH Surge! The LH Surge! OMI! GV! OMI - Oocyte Maturation Inhibitor MPF - Maturation promoting factor pre-mpf! MPF! GV - germinal vesicle (nucleus)! Gap Junctions Allow Cell to Cell Communication!! Gap Junctions are Destroyed!! The LH Surge! LH Surge! Resumption of! Meiosis! First polar body! emitted, arrest at! metaphase II of meiosis! GVBD! pre-mpf! MPF! GV! Resumption! of Meiosis! 4N! 4N! 2N! Primary Oocyte! Secondary! Oocyte! (most species)! Zygote (pronucleate egg)! N! N! 2N! Sperm! Penetration! Gap Junctions are Destroyed!! LH Surge! Resumption of! Meiosis! First polar body! emitted, arrest at! metaphase II of meiosis! 4N! 4N! 2N! Primary Oocyte! Dog! Fox! Sperm! Secondary! Penetration! Oocyte! Dog! Fox! Zygote (pronucleate egg)! (most species)! N! N! 2N! Sperm! Penetration!