PSY304: Biopsychology - Hormones & Sex
Hormones & Sex
What's a Hormone?
Hormones are secreted by cells, then enter the bloodstream and affect target cells. They bind to receptors on or in the target cells to alter their function.
Glands That Release Hormones
Glands releasing hormones include the pineal gland, hypothalamus, pituitary gland, thyroid, parathyroids, thymus, adrenals, pancreas, ovaries (in females), and testes (in males).
Types of Hormones
Protein hormones (peptide hormones): Composed of different amino acids, e.g., Adrenocorticotropic hormone (ACTH).
Amine hormones: Smaller. Example is Thyroxine (tetraiodothyronine).
Steroid hormones: Modified lipids. Example is Estradiol.
Types of Hormone Receptors
Protein hormone receptors: Located in the cell membrane and function like metabotropic receptors. When a protein hormone binds to the receptor, it activates a second-messenger system, leading to multiple biological effects.
Steroid hormone receptors: Located inside the cell and are floating around. Steroid hormones diffuse into the cell and bind to receptor molecules. The steroid-receptor complex then binds to DNA, altering gene expression (genomic effect) and leading to new protein production and multiple biological effects.
The Pituitary Gland
The pituitary gland is connected to the hypothalamus. It has two lobes:
Anterior lobe (gland tissue)
Posterior lobe (nerve tissue)
Posterior Pituitary Gland
Neuroendocrine cell bodies in the hypothalamus extend axons into the posterior pituitary and release hormones (oxytocin and vasopressin) into the bloodstream.
Oxytocin
Discovered in 1906 by Henry Dale.
Stimulates uterine contractions during childbirth.
Stimulates the milk-letdown reflex.
Vasopressin
Discovered in 1922.
Also known as anti-diuretic hormone.
Constricts arterioles, raising blood pressure.
Bonding Behaviors in Voles
Meadow Voles: Promiscuous; males leave their partner and offspring after mating.
Prairie Voles: Monogamous, bonding for life; males help raise offspring.
Oxytocin and Vasopressin Receptors in the Brain
Explain pair-bonding/promiscuity:
Prairie vole (monogamous): higher expression of oxytocin receptors (OTR) in the nucleus accumbens (NAcc) and vasopressin receptors (V1aR) in the ventral pallidum (VP).
Meadow/montane vole (promiscuous): lower expression of these receptors.
Genetic manipulations:
Subtracting vasopressin receptors in the ventral pallidum in Prairie Voles makes them promiscuous.
Adding vasopressin receptors in the ventral pallidum in Meadow Voles makes them monogamous.
One genetic difference between Prairie and Meadow Voles lies in the gene encoding the Vasopressin receptor.
Details on Oxytocin and Vasopressin Receptor Expression
Oxytocin receptors (OTRs) in female voles:
Higher expression in NAcc of monogamous female voles than promiscuous ones.
Inhibiting OTRs makes a monogamous female more promiscuous.
Boosting OTR expression in NAcc makes a promiscuous female more monogamous.
Vasopressin receptors (V1aR) in male voles:
Higher expression in VP of monogamous male voles than promiscuous.
Inhibiting V1aRs makes a monogamous male more promiscuous.
Boosting V1aR expression in VP makes a promiscuous male more monogamous.
Addiction and Dopamine
Addictive drugs affect the activity of dopamine neurons. Oxytocin affects the output of dopamine neurons in the nucleus accumbens.
Pair Bonding in Humans and Dopamine
Pictures of loved ones activate the dopamine system in humans.
Vasopressin Receptor Gene in Humans
Differences in the vasopressin receptor gene in humans are correlated with pair-bonding behaviors (Walum et al., 2008).
Conclusion on Pair Bonding
Correlation (expression) and intervention (inhibiting/boosting) experiments strongly implicate posterior pituitary hormones in pair bonding.
Anterior Pituitary Gland
Tropic hormones (act on specific glands with receptors for that hormone) are controlled by releasing hormones secreted by the hypothalamus into the hypothalamic-pituitary portal system (a network of blood vessels connecting the two regions).
Releasing and Tropic Hormones
Releasing hormones:
CRH (corticotropin-releasing hormone)
TRH (thyrotropin-releasing hormone)
GnRH (gonadotropin-releasing hormone)
GnIH (gonadotropin-inhibiting hormone)
Prolactin-releasing peptide
Prolactin-inhibiting factor (may be dopamine)
Somatocrinin (stimulates)
Somatostatin (inhibits)
Tropic hormones:
ACTH (adrenocorticotropic hormone) acts on the adrenal cortex, which releases corticosteroids.
TSH (thyroid-stimulating hormone) acts on the thyroid, which releases thyroid hormones.
LH (luteinizing hormone) acts on the testes (releasing testosterone/androgens) and ovaries (releasing estrogens/progestins).
FSH (follicle-stimulating hormone) acts on the testes and ovaries.
Prolactin acts on mammary glands (milk production).
GH (growth hormone) acts on bones (bone growth).
How Releasing and Tropic Hormones Work
Releasing hormones:
Produced by neurosecretory cells in the hypothalamus.
Travel to the anterior pituitary via the hypothalamic-pituitary portal system.
Control hormone release from the anterior pituitary.
Tropic hormones:
Produced by secretory cells in the anterior pituitary.
Travel to target glands via the bloodstream.
Control hormone release from other glands.
Sex Determination
Sex and gender are expressed in many different ways by humans and it's complicated biologically, conceptually and linguistically.
“Male/female” – “biological” traits typical for individuals with a certain combination of sex chromosomes.
“Male/female/non-binary” – gender identities that shape human interactions.
Sex determination happens in many different ways across species.
Sex Chromosomes
Humans have two “sex chromosomes”, X and Y.
XX -> female sex
XY -> male sex
Genes on Sex Chromosomes
X Chromosome: Contains 900-1600 genes, including those related to Duchenne muscular dystrophy (DMD), colorblindness, etc.
Y Chromosome: Contains 70-200 genes, the most important one being the testis-determining factor.
Gonadal Determination
testis-determining factor (TDF) is expressed from the SRY gene (Sex-determining Region of the Y chromosome) at 6 weeks, causing gonads to develop into testes.
Organizational Effects of Sex Hormones
Anti-Müllerian hormone, released by testes, prevents the development of female sex organs (defeminizing effects).
Androgens (e.g., testosterone), released by testes, promote the development of male sex organs (masculinizing effects).
Development of Sex Organs
In the indifferent stage, both Mullerian and Wolffian ducts are present. In males, the Wolffian duct develops into the epididymis and vas deferens. In females, the Mullerian duct develops into the oviduct, uterus, and vagina.
Genetic vs. Phenotypic Sex
Genetic sex: Determined by sex chromosomes (XY or XX).
Gonadal sex: Determined by the presence of testes or ovaries.
Hormones: Testes release testosterone; ovaries release no testosterone.
Phenotypic sex: Development of penis/scrotum (male) or clitoris/labia/vagina (female).
Nature's "Default" is Female
In the absence of androgens, a human will show feminine characteristics whether having an XX or an XY genetic makeup.
Androgen Insensitivity Syndrome
Caused by a mutation in the gene for the Androgen Receptor. People with XY chromosomes develop feminine characteristics because they lack androgen receptors throughout their body and brain.
Persistent Müllerian Duct Syndrome
Caused by a mutation in the gene for anti-Müllerian hormone (or receptors). Individuals with XY chromosomes develop masculine external sex organs but have both masculine and feminine internal sex organs.
Turner's Syndrome
Individuals only have one sex chromosome (X0). They develop a feminine body, gonads, and genitalia. Feminine sex organs need two XX chromosomes to develop. Ovaries are underdeveloped, leading to infertility.
Congenital Adrenal Hyperplasia
A masculinization of the brain (and often the genitals) of an XX person due to an overproduction of androgens by the adrenal glands.
Activational Effects of Sex Hormones
During puberty:
Estradiol (estrogen) triggers female secondary sex characteristics: breasts develop, hips widen, uterus develops.
Testosterone triggers male secondary sex characteristics: facial, body, and pubic hair grow, voice lowers, muscles develop.
Sex Differences (Dimorphisms) in the Brain?
The sexually dimorphic nucleus of the preoptic area (SDN-POA) is much larger in male rats than in females. Perinatal testosterone leads to larger SDN-POAs in XX mice. Pubertal or adult testosterone does not affect its size.
Quantitative vs. Qualitative Sex Dimorphisms
Sex dimorphisms are mostly quantitative and not qualitative.
“Quantitative” – average differs but distributions are overlapping.
“Qualitative” – all or nothing differences (e.g., having a Y chromosome).
Human Sexual Dimorphisms
Human sexual dimorphisms form overlapping distributions for traits such as height and brain volume. Cognitive dimorphisms also form very overlapping distributions.
Sex Dimorphisms in Human Brains (MRI)
Overall, sex differences tend to be evident in regions that are known to possess receptors for sex steroids. Some structures are larger in the healthy female brain relative to cerebrum size, and others are larger in the healthy male brain.
MRI in Transgender People
Mega-analysis of 803 subjects identified significant differences in various brain areas between trans men (TM), trans women (TW), cis men (CM), and cis women (CW).
The Bed Nucleus of the Stria Terminalis (BNST)
Part of the limbic system. May be a hub for connecting cognition and emotion areas to hormonal and motor response areas. Also implicated in stress and addiction. Size is correlated with gender identity (not sex assigned at birth or sexual orientation).
Hypothesis on Sex Differences in Humans
Sex differences are proportional to testosterone level during development and puberty. More testosterone -> “manlier brain”. Brain areas should co-vary together with testosterone effect.
Most brains are a mix of