Animal Science 434 Lecture 10: The Follicular Phase of the Estrous Cycle

Tonic and Preovulatory Surge of GnRH

Hypothalamus GnRH Anterior Pituitary Anterior Pituitary CLFollicle Ovary LH, FSH LH LH, FSH Inhibin (-) Estradiol Progesterone Estradiol (-)

Tonic and Preovulatory Surge of GnRH

Follicular Phase

Hypothalamus GnRH Anterior Pituitary Anterior Pituitary Follicle Ovary LH, FSH Inhibin (-) Estradiol (-) LH Progesterone (-) CL Estradiol (+)

Follicular Phase

Follicular Progression Primordial Primary Secondary Tertiary

Growth and Atresia of Follicles Atresia

Fate of follicles and oocytes. Total # of follicles At birth 100, months 75, years 21,000 Aged cow 2,500 Follicles grow to tertiary characteristic and degenerate. Maximum number of oocytes ovulated for a cow 17 cycles/year x 8 year = 136 oocytes ovulated/lifespan 100 Days of Gestation 2.9 million 100 Days of Gestation 2.9 million Can increase with superovulation with FSH to stimulate the rescue of follicles which would have undergone atresia Can increase with superovulation with FSH to stimulate the rescue of follicles which would have undergone atresia

Gonadotropin Independent FSH Recruitment Initial Follicular Growth Small Antral Follicle days

Follicular Waves in Cattle Ovulation Follicular Size Day After Ovulation FSH Sensitive Pool Recruitment Selection Dominance Atresia Progesterone

Follicular Waves in Cattle Ovulation Follicular Size Day After Ovulation Recruitment FSH estradiol (-) Selection FSH estradiol (-) inhibin (-) Dominance FSH estradiol (-) inhibin (-) Atresia estradiol inhibin Progesterone

Follicular Waves in Cattle Ovulation Follicular Size Day After Ovulation Recruitment Selection Dominance Atresia Progesterone

Follicular Waves in Cattle Ovulation Follicular Size Day After Ovulation Progesterone Dominance Recruitment Selection Ovulation FSH, E 2 FSH, E 2 inhibin, LH

Two Follicular Waves 10Ovulation21 Follicular Size Recruitment Selection Dominance Atresia Ovulation Day After Ovulation

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 Follicle

Antral Follicle Granulosa Theca Internal

Theca Interna Granulosa Blood Receptor LH cAMP Cholesterol Testosterone PKA Receptor FSH Testosterone cAMP Receptor LH Selection Dominant Follicle Express LH Receptor cAMP Estradiol PKA

Ovulation

Tunica Albuginea Germinal Epithelium Theca Externa Theca Interna Granulosa Basement Membrane

protein synthesis steroid synthesis prostaglandin synthesis plasminogen activator synthesis Blocking of these events in the follicle prevents ovulation.

Preovulatory LH Surge Ovulation Cumulus Expansion Oocyte Separates From Follicular Wall

Cumulus Expansion Unexpanded Expanded Hyaluronic Acid and Protein Production

Cumulus and Oocyte Separation

Preovulatory LH Surge Ovulation Increased Blood Flow to Ovary and Follicle Increased Blood Flow to Ovary and Follicle Vascular Permeability Plasminogen Cumulus Expansion Cumulus Expansion Oocyte Separates From Follicular Wall Oocyte Separates From Follicular Wall Contraction of Smooth Muscle Contraction of Smooth Muscle Collagenase (inactive) Follicular Wall Weakens Follicular Wall Weakens Plasmin Collagenase (active) Protein Synthesis in and around Follicle Protein Synthesis in and around Follicle Plasminogen Activator Plasminogen Activator Progesterone Prostaglandin Synthesis PGE and PGF Prostaglandin Synthesis PGE and PGF

Types of Ovulators

Spontaneous Ovulators

Induced Ovulators

Sensory Neurons Nerve endings sensing copulation Penis Copulation Induced Ovulators

GnRH Blood LH Time (hr) LH Spinal Chord Anterior Pit. Posterior Pit. Hypothalamus Stimulation

Sensory Neurons Nerve endings sensing copulation Penis Copulation LH

Cats Induced Ovulators Single copulation –Only works 50% of the time Multiple copulations –Higher LH surge

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

Manipulating Ovulation Hormonal induction of ovulation –PGF 2  –GnRH –Progestins Superovulation –FSH –eCG

Principle of PGF 2  Use Regress active corpus luteum –Only effective on day corpus luteum –Not effective on days: (CL not responsive) (CL already regressed)

Induction of Ovulation with PGF 2  Ovulation Follicular Size Day After Ovulation Dominance Recruitment Selection Ovulation Progesterone PGF 2 

7 Days hours GnRH PGF 2  hours Timed AI GnRH Eliminate current follicular wave Ovsynch LuteolysisOvulates dominant follicle

Induction of Ovulation with PGF 2  Ovulation Follicular Size Day After Ovulation Dominance Recruitment Selection Ovulation Progesterone GnRH PGF 2  GnRH AI

7 Days hours GnRH PGF 2  hours Timed AI GnRH Eliminate current follicular wave Ovsynch LuteolysisOvulates dominant follicle

Principle: Maintain the cow under the influence of progesterone until corpus luteum regresses, remove progesterone - animal respond to progesterone with estrus and ovulation 2-5 days later. Administration: Injection Feed Implant Pessary or Control Internal Drug Release (CIDR) Use of Progestogens This does not regress the CL!!!!

Progestens Effect on Ovulation Ovulation Estrus Progesterone From C.L. Progesterone From C.L. Estrus Ovulation Follicular Wave Estrus Follicular Wave Follicular Wave Follicular Wave Follicular Wave Follicular Wave Follicular Wave P 4 from CL P 4 from CIDR Remove CIDR Ov.

Stimulating Follicular Development Ovulation Estrus Progesterone From C.L. Progesterone From C.L. eCG or FSH Estrus Multiple Ovulations Multiple Ovulations 17 Estrus eCG or FSH First Follicular Wave First Follicular Wave PGF 2 

Oogenesis Primordial Germ Cells Oogonia Primary Oocyte Growth Initiation of Meiosis Interphase DNA synthesis Meiotic prophase begins zona pellucida formation mRNA production protein synthesis cortical granule formation nuclear maturation cytoplasmic maturation Migration to germinal ridge Mitotic divisions Prophase of Meiosis leptotene zygotene pachytene diplotene Meiotic Arrest dictyotene Gonadotropin Independent Gonadotropin Dependent Follicle Cells

Fetal Oocyte Development Fertilization Birth MitosisMeiosis Mouse 19 d Sow 114 d Cow 280 d

Ovulation of Tertiary Follicle

Formation of the Zona Pellucida Corona Radiata Zona Pellucida Oocyte

Corona Radiata Zona Pellucida Oocyte Gap Junctions

OMI - Oocyte Maturation Inhibitor MPF - Maturation promoting factor GV - germinal vesicle (nucleus) pre-MPF MPF GV During Oocyte Growth and Before the LH Surge OMI cAMP Gap Junctions Allow Cell to Cell Communication! cAMP PKA

GV GVBD The LH Surge Resumption of Meiosis Gap Junctions are Destroyed! pre-MPF MPF cAMP PKA

LH Surge Resumption of Meiosis First polar body emitted, arrest at metaphase II of meiosis Ovulation Primary Oocyte Secondary Oocyte Sperm Penetration Zygote (pronucleate egg) 4N 2N N N Ovulation Dog Fox Ovulation Dog Fox Sperm Penetration Dog Fox Sperm Penetration Dog Fox (most species)

Hormonal Production by Follicles Recruitment Selection Dominant Estradiol Estradiol, Inhibin Atretic Androgen or No steroid and No Inhibin