NEUR101 Hormones, Sexual and Reproductive Behavior

NEUR 101: Hormones, Sexual and Reproductive Behavior

Differences between Neural and Hormonal Communication

  • Neurocrine Communication

    • Messages travel along fixed channels to precise locations (analogous to a telephone system).

    • Rapid response (milliseconds).

    • Typically have "all-or-none" responses.

    • Some voluntary control over this communication.

  • Endocrine Communication

    • Messages are dispersed throughout the body, interfacing with scattered cells that possess appropriate receptors (similar to a television broadcasting system).

    • Slower response (seconds or minutes).

    • Graded in strength.

    • No voluntary control over this communication.

Regulation of Hormone Secretion – Negative Feedback

  • Hormone secretion levels are maintained to meet the body's ongoing needs (homeostasis).

  • Negative Feedback Loop:

    • Secreted hormones inhibit further production by feeding back on the endocrine cells (analogous to a thermostat).

Oxytocin and the Milk Letdown Reflex

  • Oxytocin Release Mechanism:

    • Initiated by nerve impulses to the hypothalamus.

    • Synthesized in the paraventricular and supraoptic nuclei, then released by the posterior pituitary.

Hormonal Pathways in Male and Female Reproductive Functions

(A) Male Pathway

  • Steroid Hormones:

    • GnRH (Gonadotropin-Releasing Hormone) → LH (Luteinizing Hormone) or FSH (Follicle-Stimulating Hormone) → Release of gonadal hormones (e.g., testosterone).

(B) Female Pathway

  • Regulatory Mechanism:

    • GnRH and GNIH (Gonadotropin-Inhibiting Hormone) stimulate and inhibit respectively.

    • FSH and LH regulate follicular development, ovulation, and hormonal secretion (estrogens and progesterone).

Gonadal Hormones Overview

  • Color Coding of Hormones:

    • Androgens (e.g., testosterone)

    • Estrogens (e.g., estradiol)

    • Progestins (e.g., progesterone)

  • Conversion of Hormones:

    • Enzymes can convert progestins to androgens and androgens to estrogens.

    • No steroid hormone is sex-specific; proportions differ by sex.

Vasopressin and Oxytocin in Behavior

  • Oxytocin:

    • Released during orgasm, promoting feelings of pleasure and intimacy.

    • Knockout studies show social amnesia in oxytocin absence.

  • Pair Bonding in Voles:

    • Prairie voles form monogamous bonds based on oxytocin and vasopressin.

Hormone-Behavior Interactions

  • Changes in hormone release can lead to changes in experiences and behaviors.

Stages of Reproductive Behavior

Key Stages:

  1. Sexual Attraction:

    • Initial pull between male and female.

    • Often synchronized with peak fertility.

  2. Appetitive Behavior:

    • Proceptive behaviors that stimulate sexual interaction.

  3. Copulation:

    • Actual mating, often influenced by physiological conditions.

  4. Postcopulatory Phase:

    • Period after copulation, involving refractory periods.

Sexual Attraction and Learning

  • Attraction can be influenced by hormonal signals and learned experiences such as preferences shaped through exposure.

Sexual Selection and Dimorphism

  • Darwin's Principle of Sexual Selection:

    • The differential pressures exerted by each sex leading to favored reproductive features.

    • Examples include peacock tails signaling genetic fitness.

Appetitive Behaviors

  • Typical behaviors from females to entice males.

  • For instance, females may use ear wiggling or agile movements to prompt male interest.

Copulatory Behavior Specificities

  • Females often dictate the copulation decision based on reproductive timing; the lordosis response is a significant factor.

Postcopulatory Dynamics

  • Refractory Period:

    • Time post-copulation where males are unable to mate again.

  • Coolidge Effect:

    • Shorter refractory periods observed when presented with new female partners.

Gonadal Hormonal Influences

  • Androgens in Males:

    • Facilitates not just reproductive behaviors but also broader physiological functions.

  • Estrogens and Progesterone in Females:

    • Promotes reproductive organ functions and prepares the body for possible implantation.

Disorders of Sexual Differentiation

  • Turner's Syndrome: Characterized by one missing X chromosome affecting secondary sexual characteristics.

  • Congenital Adrenal Hyperplasia: Causes overexposure to androgens in XX individuals, leading to intersex characteristics.

  • Androgen Insensitivity Syndrome: XY individuals with defective receptors, leading to female physical traits despite the presence of male XY chromosomes.

Hormonal Organizational Effects

  • Early exposure to androgens can have lasting effects on behavior and physiological development in offspring.

Conclusion

  • Understanding hormonal influences on behavior reveals the complex interactions between physical, psychological, and social factors influencing sexual development and reproductive behaviors.