Introduction to Behavioral Neuroscience PDF - PSYC 211 Lecture 14 - Sex

Introduction to Behavioral Neuroscience PSYC 211 Lecture 14 of 24 – Sex Chapter 10 in the textbook Professor Jonathan Britt Questions? Concerns? Please write to [email protected]  SEXUAL DIMORPHISM Sexual dim...

Introduction to Behavioral Neuroscience PSYC 211 Lecture 14 of 24 – Sex Chapter 10 in the textbook Professor Jonathan Britt Questions? Concerns? Please write to [email protected]  SEXUAL DIMORPHISM Sexual dimorphism is the condition where the two sexes of the same species exhibit different characteristics beyond the differences in their sexual organs. female These differences may be subtle or exaggerated and can include differences in male size, weight, color, behavior and cognition. They include secondary sex characteristics (i.e., features that occur during puberty). female female male male  TRIPLEWART SEADEVIL female Male (Just a tiny, rudimentary creature that lives on his lady friend parasitically - basically just a sperm-producing appendage.) Sexual dimorphism is associated with genetic and hormonal differences, both before and after birth.  SEXUAL DIMORPHIC BEHAVIOR Sexual dimorphic behaviors are behaviors that take different forms, or occur with different probabilities, or under different circumstances across males and females of the same species. In mammals, the most striking category of sexual dimorphic behaviors are reproductive behaviors, including courting, mating, parenting, and most forms of aggression. In terms of human behaviour, there are differences between the sexes, on average, in their mixture of talents, temperaments, and interests. The brain gives rise to sexual dimorphic behaviors because it is a sexually dimorphic organ. The average size and interconnectivity of different brain regions vary according to sex. Sex differences in the brain can be the result of biology, socialization, and the interaction of the two.  SEX / GENDER TERMINOLOGY Sex is often defined at birth by the presence of particular sex chromosomes, sex hormones, and sex organs. Gender refers to the range of characteristics that pertain to, and differentiate between, masculinity and femininity, which are the characteristics associated with men and women, respectively. These characteristics reflect biology and culture. Gender expression is the expression of masculinity and femininity. Gender role refers to the behaviors and attitudes that are deemed typical, appropriate, or desirable for people of a given sex. Sexual behavior refers to the actual sex acts performed by the individual. Sexual orientation refers to one’s enduring romantic or sexual attractions. Sexual identity refers to an individual’s conception of themselves in terms of whether they identify (or not) with a sexual orientation. Gender identity is one’s personal sense of their gender. It is usually but not always consistent with masculine and feminine body development.  GENDER IS A SOCIAL CONSTRUCT The consensual rules for determining gender (and race) designations differ across time and across cultures in a manner that is independent of changes in biology. This is evidence that our understanding and categorization of masculinity and femininity are socially constructed from our shared experiences. Biology influences these social constructions, but its contributions are not decisive. How large or small the biological contributions are depends on contemporaneous cultural influences. Our brains and our behaviours (as well as our conceptions of them) are complex outcomes of both biological and cultural influences.  DIFFERENCES BETWEEN THE SEXES There are ______ differences between the brains of males and females. big small  It is hard to interpret this statement without essential trivial more information (in relation to what?) fundamental inconsequential A larger issue is that we don’t really know key trifling how most of the brain processes information. basic nuanced significant unimportant major minor There are ______ differences in the behaviour of men and women. This kind of statement is typically an opinion about the relative influence of innate biology versus culture on gender expression (masculinity & femininity). The problem is that the strength of the culture determines the strength of the biological influences. Confusingly, biological differences are most influential in cultures where everyone is treated the same and gender isn’t taught. In contrast, cultures with strong and specific ideas about gender tend to mask the complexity and variability of the biology. Thus, arguments about the size and importance of innate sex differences are generally opinions about the how strong the cultural influences should be and not about the extent that biological differences should be respected.  SOCIALIZATION When socializing children, we sometimes support whatever behaviours spontaneously emerge. More commonly, we pre-emptively encourage/discourage certain behaviours to ensure their expression is congruent with our values and the dominant culture. These days there are strong disagreements about whether (and how much) certain expressions of gender are toxic, good, or innocuous. How does the study of biology help resolve these arguments? Things that are innate, natural, or biological are not inherently good or bad. The value of these things is determined by people based on their culture. Note: General intelligence (or even aptitude to perform any particular job) is not located in a single neuroanatomical structure. Traits like general intelligence are hard to define, let alone measure, and we know that very different brains can produce similar levels of intellectual performance.  SEX AND REPRODUCTIVE BEHAVIOUR The developmental program of many species produces male and female specializations. In these species, reproduction involves sex and the fusion of specialized cells known as gametes (one from each parent). Gametes are mature reproductive cells made by gonads (ovaries or testes). They are either ova (egg cells) or sperm. Unlike all other cells in your body, which typically have 23 pairs of chromosomes (23 from your biological mother and 23 regular cell from your biological father), gametes only have one copy of each chromosome (a gamete mix from your mother and father). One pair of chromosomes are called the regular cell sex chromosomes, as they usually determine the organism’s sex. They come in X and Y varieties.  SEX DETERMINATION Five factors present at birth are typically used to determine an animal’s biological sex: Sex chromosomes: XX or XY Gonads: testes or ovaries Sex hormones: androgen signaling Internal reproductive anatomy The three categories External anatomy of sex organs Generally, the five factors are either all male or all female. Atypical combinations give rise to intersex conditions, in which the person cannot be distinctly identified as male or female.  EMBRYONIC SEX ORGANS To appreciate the biological differences between males and females, it is helpful to understand the differential development of the sexes. All embryos contain precursors for both female and male sex organs. Undifferentiated Embryonic precursor of ovaries/testes gonads Müllerian system Embryonic precursors of female internal sex organs Wolffian system Embryonic precursors of male internal sex organs During the second month of gestation, the undifferentiated gonads typically develop into ovaries or testes. During third month of gestation, typically either the Müllerian or Wolffian system develops while the other withers away.  MALE SEX ORGAN DEVELOPMENT The SRY gene that is normally located on the Y chromosome encodes a protein that causes undifferentiated fetal gonads to develop into testes. (This gene overpowers XX-ovary instructions, so XXY individuals develop testes.) embryonic testicular Stops development of release of: Mullerian system (internal Development 1) anti-Müllerian hormone. SRY gene   female sex organs) of testes 2) androgens (testosterone)  Triggers development of male sex organs (both internal and external)  MALE SEX ORGAN DEVELOPMENT Defeminizing Effect of anti-Müllerian hormone early in development, which effect prevents development of the female-typical internal anatomy Masculinizing Effect of androgen hormones early in development, which effect triggers development of male-typical anatomy Androgens Male sex hormones Testosterone is the principal mammalian androgen. It is released by the testes, and it triggers development of the Wolffian system (internal male sex anatomy). Some testosterone is converted into dihydrotestosterone, which is what triggers development of external male sex anatomy.  FEMALE SEX ORGAN DEVELOPMENT Development Which are If you do not have two XX chromosome   largely silent X chromosomes, you of ovaries until puberty will not have ovaries. Puberty is triggered by hormones released from gonads (ovaries or testes). The ovaries do not release any critical signalling molecules before puberty. So, what triggers development of female reproductive anatomy? In the absence of anti-Mullerian signaling, the Mullerian system develops into internal female reproductive anatomy, which includes the inner vagina, uterus, and fallopian tubes. In the absence of testosterone signaling, external female sex organs (vulva) develop while the Wolffian (male internal) system withers away.  GENETIC ABNORMALITIES The impact of variations in sex organ signaling cascades underscore the complexity and delicateness of signaling cascades in general. The development of the gonads into testes or ovaries requires the SRY gene or two X chromosomes, respectively. But what happens if you have neither? Turner Syndrome is when you only have one sex chromosome (X-). Swyer Syndrome is when you are XY but have a bad SRY gene. - female-typical remain undifferentiated development  GENETIC ABNORMALITIES The impact of variations in sex organ signaling cascades underscore the complexity and delicateness of signaling cascades in general. The development of the gonads into testes or ovaries requires the SRY gene or two X chromosomes, respectively. But what happens if you have neither? Turner Syndrome is when you only have one sex chromosome (X0). Swyer Syndrome is when you are XY but have a bad SRY gene. In both cases, gonads do not develop (nether testes nor ovaries), but female-typical sex organs develop normally. People without gonads are infertile. They also do not naturally experience puberty, but that is easy to artificially induce with hormone injections. – Turner Syndrome is associated with other developmental abnormalities on account of missing a full chromosome. – It is possible to have two (or more) X chromosomes as well as the SRY gene (e.g., XXY or XXXY). This usually results in typical male development patterns (but also infertility).  GENETIC ABNORMALITIES Now let’s assume a person has healthy XY chromosomes (male) and their SRY gene successfully triggers teste development. The testes normally release 2 hormones: anti-Müllerian and androgen. What if the production of anti-Müllerian hormone is insufficient or the receptors for it are lacking in either number or function? female-typical development male-typical development Insufficient anti-Müllerian hormone signaling will cause insufficient anatomical defeminization: both male and female internal sex organs will develop and get tangled together. There is often functional external male genitalia.  GENETIC ABNORMALITIES What if there is insufficient androgen signaling? male-typical development female-typical development Androgen insensitivity syndrome results in anatomical defeminization with partial or no masculinization. In severe cases, no internal sex organs develop. In these cases, people typically develop normal external female genitalia and identify as heterosexual women, but they will be infertile and have a short vagina. In mild cases, the external genitalia is fully masculinized. Intermediate cases are associated with ambiguous external genitalia.  SEX HORMONES Organizational Sex hormones influence the development of the body Effects and brain. These effects are permanent and put you on a particular trajectory going forward. Behavioral Refers to organizational effect of androgens on defeminization the brain that prevent animals from displaying female-typical behaviors in adulthood Behavioral Refers to organizational effect of androgens on masculinization the brain that enables animals to engage in male-typical behaviors in adulthood  SEX HORMONES Organizational Sex hormones influence the development of the body Effects and brain. These effects are permanent and put you on a particular trajectory going forward. Behavioral Refers to organizational effect of androgens on defeminization the brain that prevent animals from displaying female-typical behaviors in adulthood Behavioral Refers to organizational effect of androgens on masculinization the brain that enables animals to engage in male-typical behaviors in adulthood Activational Puberty causes sex hormones to be released by the Effects gonads, which influence both body and mind. The production of sperm, ovulation, and general horniness are all examples of activational effects. How the mind and body respond to activational hormone signaling in adulthood depends on how the body and brain were organized by hormone signaling in utero.  HORMONAL CONTROL PUBERTY kisspeptin kisspeptin hypothalamus pituitary follicle-stimulating hormone (FSH) luteinizing hormone (LH)  HORMONAL CONTROL PUBERTY Kisspeptin Neuropeptide produced by neurons in the hypothalamus that initiates puberty and maintains reproductive ability by triggering release of gonadotropin-releasing hormone Gonadotropin- Hypothalamic hormone that stimulates anterior pituitary releasing hormone gland to secrete gonadotropic hormones Gonadotropic Hormones of pituitary gland (follicle-stimulating hormones hormone, FSH, and luteinizing hormone, LH) that have stimulating effect on cells of gonads.  MALE SEXUAL BEHAVIOUR Human males are like other male mammals in their behavioral responsiveness to testosterone. With normal levels of testosterone, males can be fertile; without testosterone, sperm production ceases, and sooner or later, so does the ability to have sex. A castrated male rat will cease sexual activity, but it can be reinstated with an injection of testosterone. Men taking a gonadotropin-releasing hormone antagonist will not show testicular release of androgens and have a decrease in sexual interest and intercourse  FEMALE SEXUAL MATURATION Estrogen Class of sex hormones released by the ovaries that cause maturation of the physical features and characteristic of females, such as growth of breast tissue and female genitalia Estradiol Principal estrogen of many mammals, including humans  HORMONAL CONTROL OF FEMALE REPRODUCTIVE CYCLES Both menstrual and estrous cycles are controlled by the two ovarian hormones estradiol and progesterone Menstrual cycle Estrous cycle Female reproductive cycle of Female reproductive cycle of most most primates, including mammals (other than most primates) humans Females that have estrous cycles do Characterized by menstruation not menstruate; they reabsorb their (if pregnancy does not occur), endometrium. They also display concealed ovulation, and the clear outward signs of ovulation and absence of a mating season. fertility. Sexual arousal is somewhat They are typically only sexually influenced by ovarian active during the estrous phase of hormones, but ability to mate is their cycle, which is referred to as not. Animals with a menstrual being “in heat”. This change in cycle exhibit sexual activity physiology and behavior alters the throughout the cycle. behavior of nearby males.  HUMAN FEMALE SEXUAL BEHAVIOR Relative to the estrous cycle, menstrual cycles are associated with only very small fluctuations in sexual behaviour and sexual desire. Mean scores of care-giving, care-receiving, in-pair sexual desire, and extra-pair sexual desire as a function of menstrual cycle phase in adult women. HORMONAL CONTROL OF SEXUAL BEHAVIOR The organizational effects of hormones on the body (i.e. sex organs) is largely over by birth. However, the organizational effects of hormones on the brain continues for a few weeks after birth, at least in rodents. One consequence of this is that we can masculinize or feminize the brain of rodents by altering hormone signaling immediately after birth, after the anatomical development of their sex organs is complete. For example, when male rodents are castrated at birth (which stops further androgen signaling), they develop some female-typical behaviours. If they are injected with female sex hormones in adulthood (estradiol and progesterone), they will try to get other males to have sex with them (i.e., they will assume lordosis in the presence of other males). Injections of female sex hormones in non-castrated male rats (or males castrated in adulthood) have relatively small behavioural consequences, at least following single injections. RODENT FEMALE SEXUAL BEHAVIOR This chart shows how female rats respond in adulthood when given injections of male or female sex hormones, depending on whether or not they were given testosterone injections immediately after birth. HORMONAL CONTROL OF SEXUAL BEHAVIOR Similar phenomena are seen in humans. Human adrenal glands, which are present in men and women, typically secrete a small amount of androgens. However, some people’s adrenal glands secrete abnormally large amounts of androgens, which can start either before or after birth. In males, excess androgen signaling from adrenal glands has minimal effect, since their testes already secrete tons of androgens. However, in females, excess androgen signaling can cause some degree of masculinization of either the body or brain or both. If the condition is present at birth, it is congenital adrenal hyperplasia (CAH). Depending on the amount of androgen signaling during development, sex organs can become slightly masculinized (e.g., enlarged clitoris, partially fused labia). Brain anatomy and function can also be masculinized. Females with CAH have a higher likelihood of identifying as a man and being sexual attracted to women in comparison to other females. The implications of this research are that sexual orientation and gender identity might be determined by the timing and effectiveness of androgen signaling in the brain during early development. FEMALE SEXUAL BEHAVIOR NEURAL CIRCUITRY By injecting transneuronal retrograde tracer in muscles responsible for lordosis response in female rats, researchers identified the important neural pathways: VMH PAG nPGi motor neurons in spinal cord  FEMALE SEXUAL BEHAVIOR NEURAL CIRCUITRY Ventromedial nucleus of hypothalamus (VMH) Large nucleus in the hypothalamus that plays essential role in female sexual behavior. In rodents… Electrical stimulation of VMH facilitates female sexual behavior. Injections of estradiol and progesterone directly into VMH also stimulates sexual behavior, even in females whose ovaries have been removed. Female with bilateral lesions of VMH will not display lordosis, even if she is treated with estradiol and progesterone MALE SEXUAL BEHAVIOR NEURAL CIRCUITRY The important neural pathways for male sexual behavior include: mPOA PAG nPGi motor neurons in spinal cord MALE SEXUAL BEHAVIOR NEURAL CIRCUITRY Medial Preoptic Area (mPOA) Nucleus in the anterior hypothalamus that plays essential role in male sexual behavior. Electrical stimulation of mPOA in rodents elicits male copulatory behavior. Within the mPOA, there is an area called the sexually dimorphic nucleus (SDN) of preoptic area. This nucleus is much larger in males than in females. Lesioning the mPOA of female rats does not affect their sexual behavior, but it does cause them to ignore their offspring. This figure shows the preoptic area of a rat brain in (a) a typical male, (b) a typical female, and (c) an androgenized female that was given testosterone immediately after birth. SDN = sexually dimorphic nucleus of the preoptic area; OC = optic chiasm; V = third ventricle; SCN = suprachiasmatic nucleus; AC = anterior commissure.  PAIR BOND FORMATION Formation of long lasting, monogamous-ish pair bonds In approximately 5 percent of mammalian species, sexually mature couples tend to form long-lasting, fairly monogamous pair bonds. Some species of prairie voles form long-term pair bonds. Some don’t. The formation of pair bonds seems to relate to two peptides in brain: vasopressin and oxytocin. (These compounds are released as neuropeptides in the brain and as hormones in the blood.) Levels of them are elevated during sex, childbirth, and breastfeeding. The prairie vole species that form long term pair bonds have more vasopressin and oxytocin receptors in their ventral forebrain than other species do. Pharmacologically blocking or activating these receptors influences who they pair up with and when. Artificially increasing the expression of these receptors in non- monogamous vole brains causes them to form life-long, monogamous-ish pair bonds.  REGULATION OF OUR PRIORITIES Falling in love (or becoming a drug addict) To ensure that we attain critical biological goals (e.g., survival, reproduction), specific brain circuits determine how valuable things are to us. Unlike memorizing your numbers and letters, deep emotional learning completely alters what matters to you. Love and addiction do not affect overall intelligence; they skew priorities and choice behaviour. “I felt as though I couldn’t survive without it.” If you believe that something silly is essential to your survival, your priorities won’t make sense to others. People with an addiction can push through negative experiences because they feel as though they can’t survive without that thing, substance, or person. Getting over a devastating breakup is somewhat like recovering from addiction. Healing a broken heart is difficult and often involves relapses into obsessive behavior. The brain areas that mediate these decisions and set priorities regulate our motivational processes and feelings of pleasure and happiness.