EXAM2 Behavioral Endo

Organizational Effects vs. Activational Effects

Organizational: early life critical components where hormones have permanent effect on the brain

Activational: hormones that affect behavior in puberty and adulthood → can be turned on and off

Experiment: Study effects of prenatal/early postnatal androgen
treatment on female reproductive behavior

• Females typically arch their backs for mating, if exposed to androgens later in life (no mounting)

  • Female exposed to androgens during critical prenatal state will display mounting behavior if re-exposed → proof of organization

Steroid Hormones

Derived from cholesterol, similar at core structural level

• Testosterone (primary male sex hormone)

  • can be converted to DHT, but cannot be reversed

  • can be converted to estrogen

• Estrogen (primary female sex hormone)

  • cannot be converted to testosterone

α-fetoprotein

Protects developing male rat fetuses from maternal estrogen

• binds to maternal estrogen and prevents it from disrupting fetal development (brain masculinization)

Rat vs. Primate brain masculinization:

Estrogen plays a major role in masculinization in rats, while androgens play a larger role in primates.

• Rats: Testosterone is converted into estradiol (estrogen) in the brain, which masculinizes brain development.

• Primates: Testosterone acts more directly through androgen receptors to masculinize the brain.

Male Sexual Behavior

All the male behaviors that evolved to mate and produce offspring

• frequency can vary among individuals and species

3 Phases of Mating Behavior (Rodents)

1) Mounting – assuming mating (copulatory) posture
2) Intromission – insertion of penis
3) Ejaculation – expulsion of semen

Postejaculatory interval (PEI) – time between ejaculation and the next mating series

• Absolute refractory phase: Male is completely non-responsive to sexual and other stimuli

• Relative refractory phase: Only a new or very potent sexual stimulus elicits responsiveness.

Two components:

• Sexual Motivation: initial drive/ desire to mate

• Sexual Performance: execution of the physical act once engaged

Coolidge Effect

A male’s sexual interest returns when he is introduced to a new female, even after becoming sexually satiated with the previous female

New partner → renewed sexual interest

Measuring Sexual Motivation in Male Rodents

• Mount latency: time between meeting female and mounting displayed

• Measure how long it takes for male to overcome physical obstacle tomate with female

Mammalian Mating Patterns

• Mating position

• Sexual motivation and frequency

• Mating strategies

• Hormonal dependence: extent where sex steroids influence mating behavior

• Social influence

• Refractory period (time after ejaculation where male becomes ready)

Male Sexual Behavior: Dopamine and Serotonin

Dopamine stimulates sexual responses, while serotonin suppresses them

• Dopamine: Promotes male sexual behavior and increases sexual responses.

• Serotonin: Inhibits male sexual behavior by suppressing dopamine activity.

Pattern after Castration in Rodents

Castration reduces sexual responsiveness in male rats, treatment with testosterone restores it

Testosterone and estrogen maintain mating behavior in castrated males. DHT does nothing to maintain behavior (needed for penile sensitivity)

1. Males take longer to initiate mounting and insertion

2. Less insertion occurs prior to ejaculation

3. After 1-2 weeks cannot mate to ejaculation

4. Decline in # of mounting and insertion

5. Loss of mounting behavior

Estrogen and Aromatase: Male Sexual Behaviors in Rodents

Main takeaway: Testosterone can support male mating behavior partly because it is converted into estrogen by aromatase.

• Estrogens: Help maintain male mating behavior; blocking estrogen receptors reduces testosterone's ability to restore behavior.

• Aromatase: Converts testosterone into estrogen in the brain, helping support male sexual behavior.

Social Influence on Male Mating Behavior: Rodents and Humans

Social context can influence both hormonal responses and sexual behavior.

• In humans, social situations can affect testosterone levels,

• In rodents, a novel female and early social experience can influence mating behavior

  • (Coolidge Effect) Males are often observed to mate after being sated (no mating >90 mins) if they are introduced to a novel female

  • POA lesion interferes with coordinating normal male sexual →

    • rats raised in iso will not copulate

    • rats raised in mixed group learn to copulate normally

Male Sexual Behaviors among Mammals

Among mammals, male sexual behavior is unusual

• There is no universal or stereotyped mating position.

• Male copulatory behavior cannot easily be divided into mounting, intromission, and ejaculation.

• There is substantial individual variation in sex drive and frequency of sexual behavior.

• The role of testosterone in regulating sexual behavior is less clear.

Human male sexual behavior is more variable and less stereotyped than that of many other mammals.

Challenge Hypothesis

The challenge hypothesis explains how testosterone levels change depending on social competition and mating opportunities.

• Low testosterone: When males are not competing for mates or defending territory.

• Increasing testosterone: When males face social challenges, such as competition with other males.

• High testosterone: During periods of intense competition for mates or territory.

MPOA, amygdala, and olfactory bulbs: Male sexual behavior rodents

Olfactory bulbs → Amygdala → MPOA → Sexual behavior

• Olfactory bulbs: Detect chemical signals and help males identify females.

• Amygdala: Integrates sensory information and sends it to the MPOA.

• MPOA: Integrates information and coordinates male sexual performance.

Populations used to examine the role of hormones in male
sexual behavior in humans

Researchers study hypogonadal men, men with aromatase deficiency, castrated men, and men receiving hormone-suppressing treatments.

• Limitations include rare studies, individual variation, and inconsistent results.

NO in male sexual performance in humans, how it relates to
DHT and how Viagra works

Important points about Viagra:

• It does not appear to increase sexual motivation.

• It does not cause an erection without sexual stimulation

NO (Nitric Oxide) relaxes smooth muscle and increases blood flow to produce an erection. DHT helps support NO production. Viagra inhibits PDE5, allowing NO's effects to last longer and helping produce an erection during sexual stimulation.

Sexual dimorphism and Male Polymorphisms

• Sexual dimorphism = differences between the sexes.

• Male polymorphism = different types of males within one species.

Orangutans: Flanged males use a “sit, call and wait” strategy, while unflanged males use a “go, search and find” strategy.

Midshipman fish: Type I and Type II males have different hormone levels and reproductive behaviors

Male polymorphisms in relation to organizational/ activational effects

• Organizational = hormones help organize what type of male develops.

• Activational = hormones activate behaviors that the male displays.

Male morphs differ in Midshipman fish compared to Orangutans

• Orangutans: Unflanged males can eventually develop into flanged males. This transition is irreversible.

  • Reversible “badge of status” in red skin color

• Midshipman fish: Type I and Type II males are distinct male types and do not transition from one type to the other.

Estrus and Anestrus

Estrus: The period when a female mammal is sexually receptive and allows mating (copulation)

• Females actively seek males.

• They are more likely to initiate copulation.

• They tend to stay close to males.

Anestrus: The period when a female is not sexually receptive

• Not ovulating so less likely of pregnancy

• Do not actively seek out males or initiate copulation.

• May behave aggressively toward males that approach them.

Research on Female Sexual Behavior compared to Male Sexual Behavior

There is less research on Female Sexual Behavior bc

1. Female sexual behavior is more complex than male sexual behavior

2. Removing the ovaries is harder than removing testes

• Removal of testes established relation between hormones and sexual behavior

3. Female reproduction is a cycle= hormones and sexual behavior fluctuate throughout

4. Research bias: females were viewed as passive participates so more focus on male sexual behavior

Vaginal Cytological Assay

Allows researchers to track changes in female reproductive cycle without surgically removing and examining the ovaries (before)

• Collect cells from a vaginal swab and determine stage of reproductive cycle → changes in cell types that correspond to ovarian function

Lordosis

An important posture that allows for successful mating (copulation) in female rodents

• Lordosis: female arches her back, moves tail to the side, and remains relatively still → allows male to successfully mount and intromission (penis insertion)

  • Triggered by physical contact: male mounting and touching her sides (flanks)

• Intromission impossible without Lordosis

Human Sexual Behavior compared to other Mammals

1. Most female mammals:

• Have a specific period called estrus (heat).

• Are sexually receptive primarily during this period.

• Show noticeable fluctuations in sexual activity throughout their reproductive cycle.

2. Humans:

• Do not have a traditional estrus cycle.

• Can engage in sexual behavior throughout the menstrual cycle, rather than only around ovulation.

• Sexual behavior is more variable and is not as tightly restricted to hormonal changes.

3 Aspects of Female Sexual Behavior

1. Attractivity

• How attractive a female is to males.

• Can be influenced by physical and hormonal signals.

2. Proceptivity (motivation)

• The female's motivation to seek out a male.

• ex: approaching males, initiating interactions, or soliciting mating.

3. Receptivity

• The female's willingness to accept mating when a male approaches.

• ex: female rodents displaying the lordosis posture.

Testosterone: Female Sexual Behavior

• Testosterone is produced by both the ovaries and adrenal glands.

• Testosterone levels fluctuate during the menstrual cycle, but less than estrogen and progesterone levels.

• Higher testosterone concentrations are positively associated with:

  • Sexual desire and anticipation of sexual activity.

• Birth control w/ high estrogen can lower free circulating testosterone and lead to lower libido

**Association between testosterone and female libido does not mean it is directly causing the change

“Vaginal Code” of Rats

Optimal pattern of vaginal stimulation that promotes successful reproduction

• Females control the pacing of intromission (penis insertion)

• Multiple intromissions stimulate prolactin release, which supports the corpora lutea and progesterone production needed to sustain pregnancy.

Induced and Spontaneous Ovulation

Ovulation means releasing egg and makes female fertile

Spontaneous ovulation: The female releases an egg as part of her regular reproductive cycle, without needing to mate

Induced ovulation: Ovulation is triggered by stimulation associated with mating or the presence of a male.

• Female prairie voles do not have regular estrus cycles. The presence of a fertile male, or his urine, can trigger hormonal changes that lead to ovulation

Induced and Spontaneous Pseudopregnancy

Pseudopregnancy is a state in which a female shows some of the hormonal and reproductive changes associated with pregnancy, even though she is not actually pregnant.

• Spontaneous pseudopregnancy: The pseudopregnant state occurs without mating stimulation

• Induced pseudopregnancy: The pseudopregnant state is triggered by mating-related stimulation, even when fertilization does not occur

Social/ Ecological Factors on Reproductive Cycles

Social interactions and environmental conditions can influence when or whether females enter reproductive cycles

• Close habitation with other females may lead to cycle syncing on their period (chemosensory?)

• Female prairie vole have induced ovulation from fertile male urine (unless it is a related male)

• Lack of proper nutrient can disrupt ovarian cycle

• Stress can disrupt ovarian cycle

Menstruation in Humans vs. Bleeding in Dogs

• Human menstruation occurs when estrogen and progesterone levels fall

• Bleeding in dogs occurs during proestrus (before estrus), which does not coincide with mating ← estrus cycle

Ovarian Cycle

1. Follicular phase:

• A follicle develops in the ovary and produces estrogen.

• Estrogen helps prepare the uterine lining.

• Menstruation occurs at the beginning of this phase if pregnancy did not occur in the previous cycle.

2. Ovulation:

• An egg is released from the mature follicle.

• A surge in LH triggers ovulation.

3. Luteal phase:

• The remaining follicle becomes the corpus luteum.

• The corpus luteum mostly produces progesterone, which helps maintain the uterine lining in case pregnancy occurs.

If pregnancy doesn't occur:

• The corpus luteum breaks down.

• Progesterone and estrogen levels fall.

• Without these hormones maintaining it, the uterine lining sheds (menstruation), beginning the next follicular phase.

Bruce and Vandenbergh effect

• Bruce effect: An unfamiliar male's scent can cause a pregnant female mouse to stop supporting the pregnancy.

• Vandenbergh effect: An adult male's scent can cause a young female mouse to reach puberty earlier.

Difference between Combination and Mini Pill: Birth Control

Combination pill:

• Contains estrogen + progestin.

• Suppresses ovulation by preventing follicle maturation.

Mini-pill:

• Contains progestin only.

• Primarily thickens cervical mucus and thins the uterine lining.

• May also suppress ovulation, but less consistently.

Negative and Positive Feedback Loops in the HPG
axis in Women

• Negative feedback: low/moderate estrogen suppresses GnRH, FSH, and LH.

• Positive feedback: sustained high estrogen stimulates an LH surge, triggering ovulation. (neg to pos during Follicular phase)

• After ovulation: progesterone and estrogen restore negative feedback.

Grandma/ Evolution of Menopause

Menopause as an evolutionary adaptation that may have helped older females increase the survival of their grandchildren

• They may help provide food, care for grandchildren, and support their families → likelihood that their grandchildren survive and reproduce.

• Family stays close

• ex: humans and killer whales (orcas)

*Hypothesis

Why include females in medical and animal research?

Sex differences affect disease symptoms, drug metabolism, and treatment responses.

What is a volumetric brain difference?

A difference in the size of a brain region or group of neurons.

What is a connective brain difference?

A difference in synapses or neural connections.

Why are dog urinary postures useful for studying sex differences?

They are sexually dimorphic behaviors that can be changed by early hormone exposure.

• Dog sexual differentiation: Late gestation through about 10–15 days after birth

Why are birds useful for studying neural sexual differentiation?

Their mating behavior avoids the issue of external genital differences influencing behavior.

Male and Female Play in Primates and Humans

Males engage in rough and tumble play