Sex and Stress

C81BIO – Semester 2, Lecture 5

Dr. Mark Haselgrove

Overview of the lecture

(2) Development of the Sex organsGonadsInternal sex organs (and what happens when things go wrong)External Sex organs (and what happens when things go really wrong)

(3) Sexual MaturationHormones

(1)StressFight or flightControl of glucocorticoidsHealth effects of stress

(4) Hormonal control of sexual behaviourAnimal studiesHuman sexual behaviour

Stress

- Stress (n, vb): Walter Cannon“Physiological reaction to the perception of aversive/threatening events”

- Stressor: “Stressful stimuli”

- Stress response: “individual’s reaction to a stressor”

Some definitions…

StressFight or flight? – Walter Cannon

- Preparation for a threatening situation:

Body’s energy reserves are mobilised by the adrenal gland:

- Epinephrine → affects glucose metabolism, muscle stored nutrients become available

- Epinephrine & nor-epinepherine → ↑ heart rate (and blood pressure)

Adrenal cortex secretes Cortisol (a glucocorticoid)

- Glucocorticoids → Convert protien to glucose Make fats available for energy

Increase blood flow Increase behavioural responsiveness

Adrenal medulla secretes epinephrine & nor-epinephrine

StressControl of Glucocorticoids

(1) PVN of the Hypothalamus secretes a peptide: CRH

(2) CRH stimulates the anterior pituitary gland to release ACTH

(3) ACTH enters the general circulation and stimulates the adrenal cortex to release glucocorticoids

StressHealth effects of Long term stress

Cohen (1953) survivors of concentration camps have poorer health later in life than controls

Theorell et al. (1992) Subway train drivers that injure or kill people more likely to be ill, months later

Selye (1976) All down to glucocorticoids:

↑ blood pressure, damage muscle tissue,↑ infertility, suppress immune system, ↑ steroid diabetes, Inhibit growth

StressEffects of Long term stress on

learning

Development of the Sex organs

- Gonads (Testes/Overies).

- First sex organ to develop

- Have two roles:(1) Produce sperm or ova.(2) Secrete hormones - Organisation effects (determines sex organs &

brain)- Activation effects (effects occur later, produce

sperm, induce ovulation, erection etc.)

Three classes of Sex organs: (i) gonads, (ii) internal genitalia (iii) external genitalia

- Foetuses are undifferentiated till 6th week of pregnancy

- Sry, (Sex-determining Region Y) gene on the Y chromosome – causes the gonads to become testes

Development of the Sex organs

- Internal Genitalia

- Until 3rd month of gestation, embryo possesses the precursors to both ♂ and ♀ sex organs

- Mullerian System (♀)- Wolffian system (♂)

- At this point one precursor withers

- “Nature’s impulse is to create a girl”

- Testes secrete:(1) Anti-Mullerian hormone: de-feminising effect(2) Androgens (e.g. testosterone): masculinising effect

Development of the Sex organs

- Internal Genitalia

- Can sometimes go wrong…

Androgen insensitivity syndrome (Money & Ehrhardt, 1972)

Genetically male (XY)Mutation prevents the formation of androgen receptors

Primitive gonads → Testes

Secrete: Anti-mullarian hormone(Prevents internal genitalia development)

Androgens – no effect(thus no masculinisation)

Development of the Sex organs

- Internal Genitalia

- Can sometimes go wrong…

Persistent Mullerian duct syndrome (Warne & Zajac, 1998)

Caused by either:(i) Absence of the anti-Mullerian hormone, or(ii) Absence of receptors for this hormone

If it occurs in Genetic males: Androgens → Masculinising effect but no defeminisation occurs

Thus individual develops both sets of internal sex organs

Development of the Sex organs

- Internal Genitalia

- Can sometimes go wrong…

Turner’s Syndrome “Natures impulse is to create a girl”

Caused by the development of an X0 foetus

- No Y chromosome (testes do not develop)- XX needed to produce ovaries (thus these are not present)

- Still develop normal female internal and external genitalia however

- Absence of ovaries means turner’s syndrome women cannot bear children

Development of the Sex organs

- Internal Genitalia

- Can sometimes go wrong…

Adrenogenital syndrome

- A decrease in the levels of cortisol released from Adrenal cortex results in abnormally high levels of adrenal androgens.

Little effect on Males (but can accelerate onset of puberty)

Major effects on Females:

Enlarged clitoris, fused labia (ambiguous external sex organs)

Development of the Sex organs

- External Genitalia

No female hormones needed for the developmentof external sex organs.

Development of male sex organs dependent on anandrogen

(Explains characteristics of Turner’s syndrome)

Sexual Maturation

- Onset of puberty occurs when:

(1) Hypothalamus secretes: Gonadotrophin-releasing hormones (GnRH)

(2) Stimulates anterior pituitary gland to release gonadatrophic hormones

(3) Stimulates the gonads to produce their hormones…

(i) Follicle-stimulating hormone (FSH)(ii) Luteinizing hormone

In Women: Produce follicles, and enables luteinisation (→ menstruation). Ovaries secrete estrogens

In Men: Stimulate testes to produce sperm & secrete testosterone

Hormonal control of Sexual Behaviour

(1) Animal studies - Males

Rats Studied more than any other laboratory animal:

Upon encountering a receptive female: NuzzlingGenital sniffing, lickingMounting (and intromission)

After about 10 intromissions (each lasting 0.25 s) ejaculation occurs.

Refractory period – interval between successive ejaculations increases

Once a male is “exhausted” – introducing a new female rejuvenates him:

Coolidge effect (Beamer et al., 1969) in rams – depends upon identification by odour

Hormonal control of Sexual Behaviour

(1) Animal studies - Females

More passive role in many mammals

- Lordosis: Move tails away (if she has one)Stand rigidly

Raise hind quarters

Many female rodents have an active role in initiating sex:

McClintock & Adler (1978) Quick, short hopping movements & ear wiggling

Completely irresistible to male rat

Male rats attempting to copulate with a non-oestrus female → female: flees or fights

Hormonal control of Sexual Behaviour

(2) Human sexual behaviour - Women

0

5

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Folicular Ovulatory Midluteal Premenstrual

Phase of womans Menstrual Cycle

% o

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Female initiated

Male inititated

Van Goozen et al (1997)

Women initiate sex more during ovulation when estradiol levels are high

Hormonal control of Sexual Behaviour

(2) Human sexual behaviour - Men

Testosterone:

Bagatell et al (1994): Men given a GnHR antgonist, or a placebo

GnHR group reported decreases in: Sexual interest Fantasys

Intercourse

- Effect removed by replacement doses of testosterone

Works both ways: Thinking about sex ↑ testosterone:

Hellhammer et al (1985): Watching an erotic film increases men’s testosterone

Reading

Pinel, J. P.J. (2008) Biopsychology, Pearson. Ch’s 13 & 17

Carlson, N. R. (2007) Physiology of Behavior, Allyn & Bacon. Ch’s 10 & 17

Kalat, J. W. (2007) Biological Psychology, Thompson. Ch’s 11 & 12

Next Week: Animal Learning with Dr. Cassaday

Email: Mark.Haselgrove@nottingham.ac.uk