BI230 Exam 1 study guide

Dr. Pain (this set's still a WIP)

What’s an endocrine manipulation that pre-exists the field of behavioral endocrinology?

castration

Explain Berthold’s capons (castrated cock chickens) experiment in 1848. What does it demonstrate?

Explanation: Removed the testes of immature chickens (1 group left intact; 2nd group testes fully removed; 3rd group testes removed and one replaced in abdominal cavity) → Both intact and reimplanted groups developed and behaved like typical male roosters

• when he dissected a rooster w/ the reimplanted testis, he found it had attached itself to the intestines, developed a vasculature supply, and doubled in size

Demonstrates: Substance, which affects behavior and is produced by testes, travels through bloodstream

Define hormone

Organic chemical messengers produced and released by endocrine glands

How do hormones affect cells?

• released into bloodstream

• act on target organs/tissues

  • hormones can only directly influence TARGET cells that have specific receptors for that particular hormone

  • interaction between hormone and its receptor starts series of cellular events that leads to either activation of enzymatic pathways or to effects on gene expression and protein synthesis

• coordinate physiology and behavior by regulating, integrating and controlling bodily functions

  • alter gene expression

  • change rate of cellular function

  • increase/decrease probability that a behavior will occur in the presence of a specific stimulus

• compared to neurotransmitters, hormones operate over much greater distances and time frames

• compared to neural communication, hormonal communication is generally less under voluntary control, but the line between them is becoming blurrier

What must be demonstrated to show a direct link between hormones and behavior?

1. a hormonally dependent behavior should disappear when hormone source is removed or the hormone actions are blocked

2. restoration of missing hormonal source or its hormone should reinstate the absent behavior

3. hormone concentrations and the behavior should be covariant (efficacy of a variable depends on the values of other variables)

(note: hormones DON’T CAUSE behavioral changes, instead they influence the 3 systems (input aka sensory, integrator aka CNS, output aka effectors like muscles))

• cause specific stimuli to be more likely to elicit certain responses in specific behavioral or social contexts)

Explain the differences between chemical communication forms

• intracrine mediation - intracrine substances regulate intracellular events

• autocrine mediation - auatocrine substances feed back to influence the cells that secreted them

• paracrine mediation - paracrine cells secrete chemicals that affect adjacent cells like neurons

• endocrine mediation - endocrine cells secrete chemicals into bloodstream

• ectocrine mediation - ectocrine substances like pheromones are released into the environment by individuals to communicate with others

Difference between pheromones and allomones

• pheromones = chemical substance that is usually produced by an animal and serves especially as a stimulus to other individuals of the SAME species for one or more behavioral responses

• allomones = chemical messengers released by members of one species to influence behavior of members of ANOTHER species

  • Greek allo means “other”

  • can be used to mimic pheromones produced by recipient species

  • example: flowers emit chemical attractants to guide pollinators to them, and repellants produced for defense like skunk sprays

Explain major characteristics of endocrine system

• endocrine glands are DUCTLESS and have a RICH BLOOD SUPPLY

• hormones are secreted into bloodstream and can travel in the blood to virtually every cell in the body + interact with cells that have appropriate receptors

• hormone receptors are specific binding sites that interact with particular hormone or class of hormones

Differences between endocrine and exocrine glands

• ENDOcrine glands secrete products directly into the bloodstream

  • most only produce only a ONE (1) class of hormone

• EXOcrine glands have tubes or ducts into which their products are released, either into the internal or external environment

  • examples: salivary, sweat and mammary glands

What are the 4 major classes of hormones (secreted by endocrine glands)?

• protein/peptide hormones

• steroid hormones

• monoamines

• lipid-based hormones

Explain differences between protein/peptide hormones and steroid hormones

• protein/peptide hormones

  • most vertebrate hormones fall into this class

  • consist of amino acid building blocks

    • hormones made of SHORT amino acid chains = peptide hormones

    • LONG amino acid chains = protein hormones

  • water-soluable

    • stored in secretory granules or vesicles which fuse with cell membrane to release their content into extracellular space

    • DON’T require carrier proteins

  • many have autocrine and paracrine functions

  • vary in structure (think amino acid sequence) betwee vertebrates

  • small differences in amino acid sequence of protein/peptide hormones can exist even between diff species of mammal

    • These variations generally don’t prevent a hormone from one mammalian species from having biological activity when injected into another mammalian species

    • Prolonged exposure to a protein/peptide hormone from another mammalian species may cause the recipient to mount an immune response ← Main reason why protein hormones extracted from other species are not used to treat humans

  • examples: insulin, LH, FSH, growth hormone, prolactin, oxytocin, vasopressin

• steroid hormones

  • cholesterol = precursor to all vertebrate steroid hormones

  • fat-soluable

    • leave endocrine cells easily; not stored, so they’re produced and released almost immediately

    • generally must bind to water-soluble carrier proteins, which protect the steroid hormones from degrading prematurely

  • steroid hormone structures are virtually identical among vertebrates

  • examples: glucocorticoids, androgens, estrogens

Know commonly used terms like neuropeptide, neurhormone, etc

• chemical messenger: any substance produced by a cell that affects another cell’s function

  • cytokine - chemical messenger that provokes proliferation of other cells, especially in the immune system

  • hormone - chemical messenger that is released into the bloodstream/tissue fluid system that affects the function of target cells some distance away from the source

    • neurohormone - hormone produced by a neuron

    • neuromodulator - hormone that changes the response of a neuron to some other factors

    • neuropeptide - peptide hormone produced by a neuron

    • neurosteroid - steroid hormone produced by a neuron

  • neurotransmitter - chemical messenger that acts across neural synapse

Explain difference between positive and negative feedback

In behavioral endocrinology:

• Positive Feedback: This occurs when a hormone's action enhances or amplifies its own production. For example, during childbirth, oxytocin release increases contractions, which in turn stimulates more oxytocin release.

• Negative Feedback: This involves a hormone's action inhibiting its own production. For instance, when cortisol levels rise, they signal the hypothalamus and pituitary to reduce the release of corticotropin-releasing hormone (CRH) and adrenocorticotropic hormone (ACTH), thus lowering cortisol production.

List the major endocrine glands

• hypothalamus = control of hormone secretions

• pineal gland = reproductive maturation; body rhythms

• pineal gland

  • anterior pituitary = hormone secretion by thyroid, adrenal cortex, and gonads; growth

  • posterior pituitary = water balance; salt balance

• thyroid = growth and development; metabolic rate

• adrenal glands

  • adrenal cortex (outer bark) = salt and carbohydrate metabolism; inflammatory reactions

  • adrenal medulla (inner core) = emotional arousal; stress response

• pancreas = sugar metabolism

• gut = digestion and appetite control

• gonads (testes/ovaries) = body development; maintenance of reproductive organs in adults

List the names and functions of common hormones

• protein/peptide hormones

  GnRH = gonadotropin-releasing hormone

  • insulin = only known hormone that can lower blood sugar

  • LH (luteinizing hormone) = “plays an important role in sexual development in children and fertility in adults: In women who menstruate (have periods), LH helps control the menstrual cycle. It also triggers the release of an egg from the ovary, which is called ovulation“

  • FSH (follicle-stimulating hormone) = “plays an important role in sexual development in children and fertility in adults. In women who menstruate (have periods), FSH helps control the menstrual cycle. It triggers the growth of eggs in the ovaries and gets the eggs ready for ovulation“

  • oxytocin = important in birth in mammals (causes uterine contractions) and milk letdown; ½ neurohormones (other is Vasopressin) reserved in posterior pituitary, but produced by hypothalamus

• steroid hormones

  • glucocorticoids = “anti-inflammatory in all tissues, and control metabolism in muscle, fat, liver and bone. Glucocorticoids also affect vascular tone, and in the brain influence mood, behaviour and sleep‒wakefulness cycles“

  • androgens = “crucial for male sexual and reproductive function. They are also responsible for the development of secondary sexual characteristics in men, including facial and body hair growth and voice change. Androgens also affect bone and muscle development and metabolism“

  • estrogens = “development of female secondary sexual characteristics. These includes breasts, endometrium, regulation of the menstrual cycle etc. In males estrogen helps in maturation of the sperm and maintenance of a healthy libido“

  • progesterone = steroid hormone that’s key in the female reproductive system; “helps prepare the body for pregnancy by stimulating glandular development and the development of new blood vessels. This provides a good environment for implantation by a fertilized egg. If the egg isn't fertilized, the corpus luteum breaks down, leading to a drop in progesterone levels“

• monoamine hormones

  • norepinephrine = helps with focus and alertness plus maintain sleep-wake cycle; “plays an essential role in the regulation of arousal, attention, cognitive function, and stress reactions“

  • epinephrine (aka adrenaline) = administered during severe allergic reactions; causes blood vessels to constrict, which helps increase blood pressure and reduce swelling; relaxes muscles around airways; increases heart rate (helps maintain blood flow)

  • melatonin = “[monoamine] hormone that your brain produces in response to darkness. It helps with the timing of your circadian rhythms (24-hour internal clock) and with sleep. Being exposed to light at night can block melatonin production“

• hCG (human chorionic gonadotropin) = hormone produced by the placenta during pregnancy; helps thicken a person's uterine lining to support a growing embryo and tells the body to stop menstruation; stimulates the corpus luteum to produce progesterone

What are hormonal axes? Provide examples of those discussed

• hormonal axes - complex network of interactions between glands, hormones, and the feedback mechanisms that together regulate physiological processes

  • glands and hormones involved are interconnected, with each component influencing the next

  • implies directional flow of information/regulation

• examples:

  • HPA (hypothalamus-pituitary-adrenal) axis

  • HPG (hypothalamus-pituitary-gonadal) axis

  • HPT (hypothalamus-pituitary-thyroid) axis

Oldest method to study hormones (or establish hormone-behavior relationship) in behavioral endocrinology?

ablation/replacement = removal/expiration of the hormonal source

• when ablation occurs in the brain, the result often refers to a lesion

• 4 steps of ablation:

  • 1. surgical removal of suspect gland

  • 2. observation of effects of removal

  • 3. hormone replacement either by reimplanting the gland or injecting a homogenate/extract from the gland (or a purified hormone)

  • 4. observation of effects of replacement (asking whether behavioral alteration is reversed)

• a less invasive approach = studying individuals with diseased or congenitally dysfunctional endocrine glands

• modern version:

  • administration of DRUGS that block hormone synthesis or hormone receptor activity

  • manipulation of genes to block hormone production or hormone receptor function

• recent studies emphasize the importance of REPLACING hormones in patterns and doses similar to those found in nature

  • example: implantable timed-release hormone capsules

What are the principles of a bioassay?

• bioassay = test of the effects of the hormone on a living animal or living tissue

  • not necessarily conducted on same species from which the hormone was obtained

  • can be used to measure unknown levels of hormone in animal of interest

  • steps are:

    • 1. generate dose-response curve (DRC) by injecting known quantities of purified hormone into animal and measuring change

    • 2. inject sample obtained from animal of interest into assay animal and compare change to DRC

  • Limitations:

    • contaminants in samples might interfere with results because generally, circulating concentrations of hormones in blood are very small

    • depends on purified “standard“ hormone used to calibrate DRC

What’s the updated version of a bioassay?

• immunoassay = measure hormone concentrations via binding of antibody to its antigen

  • Steps are:

    • 1. inject hormone of interest into animal to produce antibody

    • 2. collect antibody from blood and purify it

    • 3. develop standard curve using competitive binding of hormone and labeled hormone

    • 4. measure sample concentrations using amount of label

• 2 major types:

  • radioimmunoassay - uses radioactive label

  • enzymeimmunoassay - uses enzyme label (changes color of substrate molecule)

What’s the Friedman test (rabbit test)? What’s it used for?

• most commonly used pregnancy test in North America until 1950s

• Friedman test = bioassay pregnancy test; test for presence of human chorionic gonadotropin (hCG) in urine by injecting the urine into rabbit

  • if hCG was present, the rabbit’s ovaries would form corpora lutea (ovarian endocrine structures formed after ovulation) within 48 hours

*How are standard curves developed/used in a bio-/immunoassay?

• BIOassay → by injecting known quantities of purified hormone into animal and measuring change

• IMMUNOassay → by using competitive binding of hormone and labeled hormone

Why should immunoassays need to be validated if used with non-invasive samples (urine, feces, hair)?

• “Validation studies are conducted to document that an analytical method, in this case an immunoassay, performs as specified for the purpose intended“ + we’re not measuring the hormone itself, but the species-specific metabolites

• Validation process

  • analytical validation

    • parallelism

    • accuracy

  • biological validation

Difference between analytical and biological validation?

• Validation process

  • analytical validation (does the assay perform well?)

    • parallelism

    • accuracy

  • biological validation (are we measuring something meaningful?)

*What methods can be used with living subjects?

• SOME brain imaging

  • fMRI

  • PET

(NOT ablation/replacement, blot test)

Define sex in biology

• Defined on the basis of differential gamete production (anisogamy)

  • female = sex producing larger gamete/ova

  • male = sex producing smaller gamete/sperm

Difference between genetic and environmental sex determination? What general taxonomic groups are found in each form (e.g., mammals, birds, etc.)?

2 major patterns of sex determination in vertebrates

• genetic sex determination

  • found in mammals, birds, and some snake species, turtles, amphibians, and fish

• external sex determination (usually via temperature)

  • found in crocodiles and some snake species, turtles amphibians, and fish

Explain the difference between homogametic and heterogametic sex. Which is which in birds and mammals?

genetic sex determination

• homogametic sex = 2 similarly shaped sex chromosomes

  • homogametic sex in mammals is female (XX)

  • homogametic sex in birds is male (ZZ)

• heterogametic sex = 2 differently shaped sex chromosomes

  • heterogametic sex in mammals is male (XY)

  • heterogametic sex in birds is female (ZW)

• the reverse pattern of human’s genetic sex determination applies for birds

Define gonochorism

• gonochorism = sexual system where there are 2 sexes and individuals are usually either male or female (this is fixed)

  • characterizes 95% of animals and 99% of vertebrates

Define parthenogenesis

• parthenogenesis = asexual reproduction in vertebrate animals

  • only one sex (ex: all female species like whiptail lizards)

  • adults produce genetically identical eggs that develop into female offspring

• Greek parthenos = virgin, genesis = creation

Define synchronous hermaphroditism

• individuals have sex organs of both sexes and can produce both gamete types

  • self fertilization is possible for some species and not others

Define sequential hermaphroditism

• individuals can change sex over the course of their lifetime

  • switch between sexes is usually cued by social environment or achievement of certain size/age

Explain the Red Queen Hypothesis for the evolution of sexual reproduction

• answers the question “why sex?“

• proposed in 1973; species must constantly adapt and evolve to survive when pitted against ever-evolving opposiing species

  • serves as potential explanation for why sexual reproduction is beneficial

Explain the stages of sexual differentiation in mammals. How does variation in these stages lead to DSD/intersexuality (Differences in Sex Development or Disorders of Sex Development)?

• mammalian sex differentiation

  • embryonic mammals (whether XX or XY) have a thickened ridge of tissue on the ventromedial surface of each mesonephros (protokidney) called the germinal ridge

  • germinal ridge will develop into either testis or ovary but is bipotential in current stage of development

  • in most mammals studied so far, germinal ridge’s fast is governed by presence or absence of TDF, which is encoded by SRY gene

  • following the gonads’s formation, hormonal secretions from testes or ovaries will determine whether the individual develops in a male or female manner

• DSD = congenital conditions affecting reproductive system, in which chromosomal, gonadal or anatomical sex doesn’t develop along strictly male or female pathway

  • sex differentiation is a complex process, so there’s ample room for variation to occur

What’s role of SRY in development?

• SRY = sex determining region on the Y chromosome; aka testis determination factor (TDF)

  • TDF binds to a specific hormone response element in the promoter region of other genes (these genes are regulated by SRY)

  • together these genes produce other proteins which cause the middle of the germinal ridge to develop into testis

• if SRY isn’t expressed… outer part of germinal ridge develops into an ovary

Explain why female development is considered the “default“ in mammals

• because neither ovaries or hormones are necessary for female typical development before puberty

What are the roles of androgens and MIH in male development?

• androgens are responsible for the development of male external genitalia

  • genital tubercle → penis

  • genital folds → scrotum

• MIH (Müllerian inhibitory hormone) and testosterone from the embryonic testes required for the process of the Wolffian duct system (develops into male accessory sex organs) while the Müllerian duct system regresses

What’s the role of 5-alpha reductase and DHT (5-alpha dihydrotestosterone) in the development of external genitalia?

• DHT is important for the process of genital fusion in males

• testosterone→ DHT conversion mediated by enzyme 5-alpha reductase

• in other words, “5-Alpha reductase is the enzyme responsible for the conversion of testosterone into 5-alpha dihydrotestosterone (DHT), a potent androgen involved in male sexual differentiation“

Explain the organizational-activation hypothesis

• states that steroid hormones permanently organize the nervous system during development, which is reflected in adult male and female typical behavior

• in adulthood, the same steroid hormones activate, modulate and inhibit these behaviors

What experiments were done to demonstrate organizational compared to activation effects

• Young’s experiment

  • Administered testosterone propionate in varying doses to pregnant guinea pigs during their gestation period (69 days)

    • Some female offspring had external genitalia that were masculinized (indistinguishable from male-typical genitalia)

    • Other female offspring (whose mothers were given lower androgen doses) had female-typical external genitalia

  • Once the guinea pigs reached sexual maturity (both experimental groups of females as well as control males and females), they were gonadectomized

    • Experimental phase 1:

    • Injected with estrogens and progestins to try to induce female-typical behaviors

    • Paired with an intact male guinea pig

    • Experimental phase 2:

    • Injected with androgens to try to induce male-typical behaviors

    • Paired with an intact female guinea pig

  • Results of prenatal androgens given to experimental females

    • Decreased tendency in both experimental groups to display lordosis in adulthood

    • Increased tendency in both experimental groups to display mounting behavior in adulthood in response to androgen treatment

    • Control males showed no deleterious effects on male-typical behaviors

  • conclusions:

    • A clear distinction can be made between the prenatal actions of hormones in causing differentiation of neural substrates for behavior (organizing effects) and the actions of hormones in adulthood (activational effects)

    • Critical periods of perinatal development exist during which an animal is maximally susceptible to the organizing effects of hormones

    • The nervous system of males are normally masculinized and defeminized during development and vice versa for females

  • follow-up experiments

    • Young and colleagues experiment demonstrated that the potential for female- typical and male-typical behaviors is organized by early exposure to hormones

    • Additional work on rodents has confirmed this

Explain differences between organizational and activation effects

• organization effects are permanent and take place during a critical period

• activational effects are reversible and short-lived

How are testosterone, estradiol, and DHT related? Which can/can’t be converted into which?

• testosterone is a prohormone (physiologically inactive precursor of a hormone) for an estrogen (estradiol) and an androgen (DHT)

Explain the role of alpha-fetoprotein in protecting developing rat fetuses from maternal estrogens

• necessary to protect developing fetuses from maternal estrogens during development

• perinatal rats produce large quantities of the protein alpha-fetaprotein, which binds to circulating estrogens but not to androgens

• “Alpha-fetoprotein (AFP) is a glycoprotein produced by the fetal liver that plays a crucial role in protecting developing rat fetuses from maternal estrogens. AFP binds to estrogens in the maternal circulation, preventing them from crossing the placenta and affecting the fetus. This binding reduces the potential for estrogen-related developmental issues, ensuring proper growth and differentiation of fetal tissues. Additionally, AFP helps maintain a stable hormonal environment necessary for fetal development.”

Explain differences between sexual dimorphism and male polymorphisms

• sexual dimorphism = differences between the sexes of the same species in physical appearance, size and behavior, beyond the differences in their reproductive organs

  • typically thought to arise through sexual selection/natural selection

  • common aspects: size, coloration, ornamentation

• male polymorphism = members of the same sex (often males) display variable morphology

  • often called “morphs” or “types”

    • look distinct from one another

  • typically, these physical differences are accompanied by differences in behavior + mating tactics (alternative reproductive tactics)

  • often one male morph is territorial and defends access to females, while another morph resembles the female of the species and attempts to mate stealthily [sneaky fuckers]

Explain male polymorphisms in relation to organizational/activational effects

“Male polymorphisms refer to the variations in male phenotypes that can arise due to genetic differences. In the context of organizational and activational effects:

• Organizational Effects: These are permanent changes in the brain and body structure due to exposure to hormones during critical developmental periods (e.g., prenatal exposure to androgens). This can lead to different male morphologies or behaviors.

  • Examples:

    • Exposure to androgens (like testosterone) during development can lead to the differentiation of male-typical traits. This might result in the formation of distinct male morphs that express different traits (e.g., size or coloration) based on their early hormonal environment

    • Some species, organizational effects can lead to a divergence in reproductive strategies—some males may develop as more aggressive and dominant, while others may become smaller and more sneaky, reflecting different strategies for attracting mates or competing for resources

• Activational Effects: These are temporary changes that occur in response to hormone levels in adulthood, influencing behaviors such as aggression or mating strategies. Variations in these responses can lead to different male phenotypes based on environmental or social contexts.

  • Example: in polymorphic males, the activation of specific traits (like aggression or courtship displays) might depend on the current hormonal status or the social context (e.g., presence of rivals or potential mates).

  • Meaning, even if two males have the same underlying organizational structure, their behaviors and interactions can differ significantly depending on their hormonal state at a given time.”

• interplay between organization and activation effects

  • Developmental Pathways: The initial organizational effects set the stage for later activational responses. For instance, a male that developed with high levels of androgens might be predisposed to express aggressive behavior later in life, while another male with lower androgen exposure might be more inclined to display courtship behaviors.

  • Environmental Influences: External factors, such as competition for mates or resource availability, can trigger activational effects that influence which male morphs are favored in a given context. This can lead to fluctuating population dynamics where different morphs become more or less prevalent depending on ecological circumstances.

  • Fitness Strategies: The presence of polymorphisms allows for diverse reproductive strategies within the same population, increasing the overall fitness of the species. This can facilitate adaptability in changing environments, as different male types can exploit different niches.

Difference between sexual motivation (aka sex drive) and sexual performance

• 2 components of male sexual behavior

  • sexual motivation (sex drive)

    • “Refers to the desire or drive to engage in sexual activity, influenced by biological, psychological, and social factors“

    • sexual arousal is a related concept, and some researchers think motivation = arousal

    • male sex drive is expressed overtly after puberty when the testes become active

      • testes influence sexual motivation—involved in regulating sexual behavior

    • sexual behavior “controlled“ by androgens but not in a simplistic way

      • androgens affect the likelihood that mating behaviors occur

  • sexual performance

    • “Refers to the actual execution of sexual activities, including physical ability and responsiveness during sexual encounters”

What are some characteristics that vary between mammalian mating patterns?

• frequency of sexual behaviors

• extent to which sexual behaviors are mediated by hormones

• Yes or No to… (16 total patterns)

  • copulatory lock

  • thrusting

  • multiple intromissions

  • multiple ejaculations

Explain why severing the connection between the brain and spinal cord was used to study sexual motivation in rats

• if animals fail to mate after castration, it can be difficult to ascertain whether sexual performance, sexual motivation or both have been affected

  • so, presuming the brain drives sexual motivation, the brain is isolated from the spinal cord

  • then, erectile repertoire is programmed in the spinal cord

  • this way, appropriate stimulation causes rat w/ spinal cord severed from brain to show erections and penile reflexes underlying intromission, thrusting, and ejaculation

What’s the role of the brain in inhibiting the spinal mechanisms of erections in rodents?

• term “sex drive“ implies that the brain drives sexual behavior through some excitatory messages to the periphery via spinal cord

  • yes, BUT it PRIMARILY INHIBITS the spinal mechanisms of erection

Explain the roles of dopamine and serotonin in male sexual behavior

• dopamine (DA) releases into the Medial Preoptic Area (MPOA) when a male mammal (or bird) encounters a receptive female

  • DA secretion increases during copulation

  • stimulation of DA receptors in MPOA contributes to both genital reflexes and sexual motivation

    • testosterone (or more commonly, its metabolite—17-beta estradiol) partially promotes copulation by provoking DA release in the MPOA

    • locally produced 17-beta estradiol in the brain promotes sexual motivation, but NOT sexual performance

    • after ejaculation, DA is inhibited in part by release of serotonin

  • serotonin (5-HT)

    • in contrast to DA, 5-HT inhibits male sexual behavior

    • during ejaculation, increased serotonin secretion in the MPOA inhibits DA which reduces male sexual responses

    • sexual dysfunction = one side effect of antidepressant drugs that work by elevating synaptic serotonin levels (SSRIs)

What’s the importance of the MPOA, amygdala and olfactory bulbs in male sexual behavior in rodents?

• MPOA

  • critical for integrating environmental, physiological and psychological information prior to/during copulation

  • lesions here in adult males eliminate sexual performance, but NOT sexual motivation

  • is part of brain circuity mediating the reward properties of sexual behavior

    • micro (μ) opioid receptors activate and internalize in the MPOA after ejaculation → male sexual behavior evokes secretion of endogenous opioids

  • electrical stimulation of MPOA accelerates ejaculation in male rats

    • in castrated males, chemosensory stimuli from females still results in olfactory bulb electrical activity, but no longer results in electrical activity in MPOA

  • located anterior to the hypothalamus

• amygdala

  • projections from the accessory and main olfactory bulbs travel to the amygdala

  • critical for integration of sensory information

  • information from the amygdala is relayed to MPOA

  • 2 regions of amygdala have been studied in rodents

    • basolateral nuclei - its removal reduces sexual motivation, NOT reproductive behavior

    • corticomedial nuclei - its removal has variable impacts on sexual performance

• olfactory bulbs

  • critical for successful expression of male reproductive behavior in many rodent species (also carnivores and ungulates aka hoofed animals)

    • inputs from both main olfactory neurons and Vomeronasal Organ (VNO) necessary for rodent mating behavior

    • in mice and rats, 2 families of chemosensory receptors have been characterized in the VNO

      • a functional VNO required for males to distinguish between male and females during mating

      • VNO neurons express specific receptors and appear to respond to either male or female urine

What are the ways in which researchers can measure male sexual motivation in rodents?

1. mount latency = time between introduction of male and female and when mounting occurs

   • similarly, researchers can place an obstacle (often physical barrier or electrified floor) between them and measure how long it takes the male to get around it

2. “Intromission and Ejaculation: Recording the number of intromissions and the latency to ejaculation.

3. Conditioned Place Preference: Assessing preference for areas associated with mating.

4. Hormonal Manipulation: Evaluating changes in motivation with hormone treatments.

5. Sexual Incentive Motivation Tests: Measuring responses to sexual stimuli or cues.”

6. postejaculatory interval (PEI) = time between ejaculation and the onset of the next copulatory series

   • absolute refractory phase = males are completely non-responsive to sexual, mildly painful, and other stimuli

   • relative refractory phase = only a new or very potent sexual stimulus elicits responsiveness

   • PEI is very variable between species

     • <30 sec in Syrian hamsters / about 5-15 min in rats / several hours or even days in other species

What’s the typical pattern of loss of sexual behaviors following castration in rats?

• castration reduces sexual responsiveness in male rats while treatment with testosterone restores it

  • males start taking longer to initiate mounting and intromission

  • fewer intromissions occur prior to ejaculation

  • after 1-2 weeks, males cannot mate to ejaculation

  • decline in number of mounts with intromissions

  • loss of mounting behavior

• post-castration testosterone treatment restores sexual behavior in a way that mirrors its loss over the course of several days

Explain the importance of estrogens and aromatase to male sexual behavior in rats

• estrogens (like estradiol)

  • effective at maintaining mating behavior post-castration

  • “influences sexual motivation, copulatory behavior, and the development of male reproductive structures“

• aromatase (an enzyme that converts an androgen like testosterone into estrogens like estradiol)

  • “essential for the brain's estrogen levels, affecting neural circuits involved in sexual behavior“

  • inhibiting the conversion of androgens to estrogens reduces sexual behaviors (searching for females, mounting, intromissions, ejaculating)

  • 2 androgens maintain mating behavior in castrated rodents

    • testosterone

    • androstenedione (weakly androgenic precursor of testosterone

    • MEANWHILE, dihydrotestosterone (DHT) doesn’t prevent post-castration loss of mating behavior, but still important for maintaining penile tactile sensitivity

Why is male sexual behavior unusual among mammals?

• lacks universal/stereotyped sexual position

• male copulatory behavior can’t easily be partitioned into mounting, intromission, ejaculation

  • ^^both suggest that hormonal regulation of the muscle pattern underlying human sexual behavior is unlikely

    • meaning, hormonal regulation of human copulatory behavior must differ fundamentally from that of rodents

What are the populations we can examine the role of hormones in male sexual behavior in humans? What are these studies’ limitations?

“Populations to Examine Hormones in Male Sexual Behavior:

1. Clinical Populations: Men with hormonal disorders (e.g., hypogonadism).

   • Results of double-blind study on hypogonadal men → unclear if testosterone affects sexual behavior directly or if it serves as a prohormone (like in rodents):

     • testosterone and DHT both effective in improving sexual activity in hypogonadal men

     • neither blocking estrogen receptors nor treatment with aromatase inhibitors influences sexual behavior in “normal“ men

2. Healthy Adult Males: Studies on testosterone levels and sexual behavior.

3. Aging Populations: Research on hormonal changes and sexual function in older men.

4. Transgender Men: Effects of hormone therapy on sexual behavior.

Limitations of Studies:

• Sample Size: Often small, limiting generalizability.

• Confounding Variables: Psychological, social, and environmental factors can influence results.

• Ethical Constraints: Difficulties in manipulating hormone levels for experimental purposes.

• Self-Reporting Bias: Reliance on subjective measures of sexual behavior.”

What’s the role of NO in male sexual performance in humans? How does it relate to DHT and how Viagra works?

• neurotransmitter Nitric Oxide (NO) = key mediator in penile erections in humans

  • used to treat erectile dysfunction

  • NO releases in the penis from both neuronal and endothelial sources

    • NO causes smooth muscle relaxation which allows increased blood flow

• DHT is important for NO production, and DHT production decreases in 40+ year old men

• Viagra (sildenafil citrate - released in 1998 by Pfizer)

  • works by enhancing the effects of NO on the mechanism of penile erection → this inhibits an enzyme (PDE5) which breaks down nucleotide which NO helps produce

  • doesn’t seem to have an effect on sexual motivation

  • also doesn’t affect penile erection in the absence of sexual stimulation

How can social context influence male hormonal responses/sexual behavior in humans and rodents?

• humans = lab studies on steroid hormone-sexual behavior interactions have been mixed

  • many studies have found no hormonal changes following masturbation or sex to ejaculation

  • another study found no change in testosterone following sexual thoughts

  • one study found that men visiting a sex club had 10% rise in testosterone if they watched people engage in sexual activities, but 70% rise if they participated

• rodents

  • defined as “sexually sated“ when no more mating is observed for 90 minutes or longer

    • “Coolidge effect“ phenomenon = males mating after being sated if they’re introduced to a novel female

  • natural sexual behavior might be constrained by testing environments in the lab (both physical and social)

    • rats in nature tend to mate in a group rather than in pairs

    • space is much more constrained in labs (gives males more control over mating than observed in nature)

• both humans and rodents

  • “Social context can influence male hormonal responses and sexual behavior by altering stress levels, social hierarchies, and mating opportunities

  • factors like competition, presence of potential mates, and social interactions can lead to changes in testosterone levels, which in turn affect sexual motivation and behavior“

Aside from sexual behavior, what else are androgens necessary for? Why might this explain why androgen concentrations appear to be higher than needed to maintain sexual behaviors?

• androgens are also necessary for:

  • development of male reproductive tissues

• explains why androgen concentrations appear higher than necessary because:

  • local testis androgen levels must be high to support spermatogenesis

  • high androgen concentrations are also important in aggression

  • high androgen levels support secondary sexual characteristics

What’s the role of testosterone, estrogen, and DHT in the sexual behavior of male birds?

• reproductive behavior in male birds—both sex drive and performance—highly depend on androgens

  • castration eliminates ritualized courtship behaviors (dancing, singing)

  • treatment of castrated birds with either testosterone or DHT restores most aspects of mating behavior to pre-castration levels

    • but, DHT doesn’t restore copulation, rather it restores display (like strutting, crowing)

  • testosterone must be converted into estrogen by androgen enzyme to produce an effect on copulatory behavior (ex: Japanese quail)

Define estrus

• estrus = period in which female mammals will permit copulation

  • Latin oestrus = “in a frenzy“ aka “heat“

• females in estrus will seek out males, initiate copulations, and prefer to maintain close proximity to males

• estrus females are also more attractive to males compared to anestrus females

Define anestrus

• anestrus = term for female mammals when they’re not in estrus aka “heat“

• females in anestrus will NOT seek out males, initiate copulations, or stay in close proximity with males

  • in many species, anestrus females behave aggressively towards males

Why has less research been done on female sexual behavior than male sexual behavior (until the 20th century)?

• female sexual behavior is more complex

  • ovariectomy is a much more difficult procedure than removal of testes

  • cyclical nature of female reproduction poses a challenge to research

• bias among (mainly male) research community, which view females as passive participants in copulation

Why was the vaginal cytological assay an important advance in methods?

• allowed researchers to know what stage of the ovarian cycle a subject was in without having to remove and examine the ovaries. This meant that multiple points of behavioral data could be collected on the same individual

• no longer required surgical examination of the ovaries

  • before, at the start of the 20th century, cyclic ovarian changes could only be examined surgically, so ovaries were removed and histologically fixed for examination under the microscope

• technique began with guinea pigs and then expanded to other rodents (mice and rats), later to many more species

  • changes in vaginal cell types were closely correlated with changes in ovarian function in guinea pigs

Why is lordosis important in rodent copulatory behavior?

• intromission is impossible without the lordosis posture

  • lordosis posture is assumed when females are touched on the flanks

  • back arched, tail to one side, immobile posture

Explain why human sexual behavior varies from that of most other mammals

• some primate species have estrus cycles (like marmosets) whose female sexual behavior is highly stereotyped while others (like humans) have more variable female sexual behavior

  • so, the latter doesn’t limit mating behavior to a specific portion of an estrus cycle that they don’t have

Difference between attractivity, proceptivity, and receptivity

• Beach’s 3 components of female sexual behavior

  • attractivity = stimulus value of a female for a given male

    • this concept infers from observing a conspecific’s (member of the same species) behavior

    • always measured in relationship terms

    • non-behavioral components (can include morphological changes that coincide with ovulation)

      • changes in odor (like urine or vaginal secretions)

      • perigenital swellings in some primate species

    • behavioral components (includes behaviors that solicit males)

      • assuming a mating posture or standing in front of male to exhibit genitalia

      • can involve vocalization or other species-specific behaviors

  • proceptivity = extent to which a female initiates copulation (= sex drive/motivation in males)

    • dependent on attractiveness of available male partners

    • behavioral measures to access proceptivity

      • measures of affiliation = behaviors used to establish and maintain proximity to males

      • number of socilications made

      • alternating approach and retreat behaviors

      • investigating male’s anogenital region

      • in some species, mounting behavior shown by highly proceptive females (either to males or females)

  • receptivity = a female’s state of responsiveness to sexual initiation of another individual (= consummatory phase of mating behavior in which the female reacts necessarily and sufficiently for fertile copulation)

    • for all non-primate mammals, involves a species-specific mating posture

    • nearly all non-mammalian species have a characteristic mating posture too

    • most behavioral measures of reciprocity are expressed in ratios that compare a male’s mating attempts with a female : number of successful copulations

• sex steroid hormones, especially estrogens, affect all 3 components of female sexual behavior

How do testosterone concentrations impact female sexual behavior?

• reduced testosterone → women in monogamous relationships instead of women with multiple partners or single women

  • decrease seems to be linked cues from partners

• testosterone concentrations increase in women in new relationships, but decrease after a brief time

• testosterone produced by both ovaries and adrenal glands

  • T concentrations fluctuate across the menstrual cycle, but to a lesser extent than estrogens/progestins

  • plasma levels of testosterone found to be positively related to sexual desire, sexual thoughts, anticipation of sexual activity

• circulating free T levels decrease after taking birth control pills with relatively high estradiol levels → linked to low levels of sexual desire (aka low sexual motivation)

• remains unclear if testosterone alone enhances libido in women

Explain the “vaginal code“ of rats

• vaginal code = pattern of stimulation which is optimal for producing offspring

  • may also be involved with partner preferences

How does the pacing of mating impact the likelihood of a successful pregnancy?

• temporal patterning of matings is important to induce the functioning of the corpus luteum in rats

  • if no or insufficient mating stimulation occurs than the corpora lutea regresses soon after being formed, meaning there’s not sufficient progesterone secreted to sustain a pregnancy

• “Studies indicate that optimal mating frequency enhances sperm competition and increases the chances of fertilization. Mating too infrequently may lead to lower sperm viability, while excessive mating can cause stress and reduce reproductive success“