10_Male sex behavior II

Overview

• Review Quiz 4 and answers chosen in Lockdown Browser

Male Sexual Behavior II: Hormonal and Neural Regulation

Overview

• Focuses on the hormonal and neural aspects of male sexual behavior

• Authored by Alexandra Martin

Hypothalamo-Pituitary-Gonadal (HPG) Axis

• Daily processes:

  • Pulsatile release of GnRH: Gonadotropin-releasing hormone releases in pulses.

  • GnRH stimulates gonadotropins: Hormones released include LH (Luteinizing Hormone) and FSH (Follicle-Stimulating Hormone).

    • LH: Stimulates testosterone production.

    • FSH: Stimulates sperm production.

• This axis regulates reproductive function.

Hormonal Profiles

LH Profiles of Female and Male Rats

• Graph Summary:

  • Shows blood concentrations of LH in ng/ml over various hours in both sexes.

  • Female and male LH levels compared.

Hormonal Effects

Key Hormones

• Testosterone: Major androgen affecting sexual behavior.

• Estradiol: Form of estrogen critical for male sexual performance.

• Dihydrotestosterone (DHT): Another androgen with specific roles.

• **Key Enzymes:

  • Aromatase:** Converts androgens to estrogens.

  • 5α reductase: Converts testosterone to DHT.

• Receptors:

  • Androgen Receptors (AR)

  • Estrogen Receptors (ERα and ERβ)

Behavioral Implications

• DHT is insufficient to restore sexual behaviors like mounting and intromission.

• Estradiol is crucial for these behaviors.

• Combination of DHT and estradiol fully restores male sexual behavior.

• Effects on erection: DHT helps maintain penile tactile sensitivity

Human Sexual Behavior

• Anastrazole: Aromatase inhibitor affecting hormonal profiles in men.

• Case Study: Men pretreated with a GnRH agonist show altered testosterone and estradiol levels.

Sexual Response Cycle in Humans

Four Phases

1. Excitement

2. Plateau

3. Orgasm

4. Resolution

• Refractory period: Decreased sexual arousal post-orgasm.

The Coolidge Effect

• Observed in studies with sheep: a new female can decrease the refractory period in males.

• Case Study: Anecdotal story of President and Mrs. Coolidge illustrating this phenomenon.

Hormones and Male Sexual Motivation

• Hypogonadal men: Low testosterone levels show altered sexual responses.

• Graphs depict mean weekly erectile responses and coital attempts before and after testosterone treatments.

Brain Regions in Male Copulation

• MPOA (Medial Preoptic Area): Lesions here abolish copulation but not motivation.

• Importance of receptors: Both sex steroid and dopamine receptors are crucial for sexual behavior.

Neural Circuits for Reproduction in Rodents

• Hormonal Action: Androgens converted to estrogen influence several brain sites affecting behavior.

• Key structures involved: MPOA, Basal ganglia, Ventral midbrain, and spinal cord for erection and ejaculation.

Distribution of Sex Steroid Receptors

• Location of receptors across different brain areas including cortex, amygdala, and hypothalamus.

Individual Differences in Sexual Motivation

• Example from guinea pigs based on pre-screening changes in sexual behavior with varying hormonal levels.

Testosterone and Aging

• Overview: Natural decline in testosterone with age, particularly noted during the 90s.

Unique Sexual Behavior in All-Female Species

• Example: Whiptail lizards reproduce through parthenogenesis, showing male-like behavior mediated by progesterone.

Class Discussions and Homework Assignments

• Group discussions: Specific questions regarding research on testosterone effects in guinea pigs.

• Assignments: Read literature on male sexual behavior and prepare for discussions and quizzes.