Behavioural neuroscience- hormones

What is the endocrine system

The endocrine system is a network of glands that produce and release hormones directly into the bloodstream to regulate various bodily functions, including metabolism, growth, and mood.

What is the main control of hormones in the brain?

Hypothalamus

How does the brain release hormones?

The brain releases hormones through the hypothalamus, which signals the pituitary gland to produce and release hormones into the bloodstream.

What do these hormones do?

These hormones stimulate release of other hormones by glands throughout the body, e.g. stimulation of ovaries to release estradial

How does an ovary or a testis develop?

gonadal differentiation

Wolfian (male) system

is the embryonic structure that develops into the male reproductive organs such as the epididymis, vas deferens, and seminal vesicles under the influence of testosterone.

Mullerian (female) systems

is the embryonic structure that develops into the female reproductive organs including the fallopian tubes, uterus, and upper two-thirds of the vagina in the absence of testosterone.

External differences between male and female reproductive systems

The conversion of testosterone to dihydrotestosterone (DHT) leads to the differentiation of external genitalia

Gender differences in the brain

Men’s brain 15% larger than women’s brains.

Women’s hemisphere’s share more functions that men

Different size in Medial preoptic area of hypothalamus

Causes of differences between Male and females brains

Masculinzing of brain is cause by Estradiol

Aromatization of testosterone produces Estradiol

Blocking aromatisation blocks masculisation

Human females protected from mothers estradiol by placenta

Hormonal disorders- Androgen insensitivity syndrome

A condition where a person's body is unable to respond to androgens, leading to the development of female physical traits despite a male XY chromosome composition. This results in female external genitalia and the lack of male reproductive structures.

Hormonal disorders- congetial adrenal hyperplasia

A group of inherited disorders affecting the adrenal glands, leading to the production of excess androgens. This can result in ambiguous genitalia in females and early onset of puberty in males.

Hormonal disorders- Turner’s syndrome

Results from abnormal sex chromosomes X O chromosome- neither ovaries or testes develop. Individuals develop normal female internal sex organs and external genitalia

Hormonal disorders- Persistent Mullerian duct syndrome

Has 2 causes: either a failure to produce anti-Mullerian hormone or the absence of receptors for this hormone. Both sets of internal sex organs, male and female, develop. The presence of the additional female sex organs usually interferes with normal functioning of the male sex organ.

Behavioural differences due to hormones

Maternal stress causes the release of cortisol

Medial preoptic area (MPA) of the brain, normally larger in males than females, is reduced in male rats born to stressed mothers

These male rats are less likely to display male sexual behaviour

Behavioural differences- study in human population

Ice storm

Children exposed in utero to high levels of objective stress had lower full scale IQs, verbal IQs and language abilities compared to children exposed to low or moderate levels of objective prenatal maternal stress

Behavioural differences- pre-natal hormonal control of aggression in females

Being next to a male fetus increases female blood levels of testosterone

2 million females are more likely to engage in inter-female aggressiveness

Hormonal control of sexual behaviour- males

Reduction in testosterone levels leads to reduction in sexual behaviour

Thinking about sex increases levels of testosterone

Makes you grow a beard faster

Castration might cause only slow decline in sexual activity, maybe related to previous levels of activity

Androgens produced by adrenal gland, prostate gland and fat tissue

Oxytocin responsible for refractory period

oxytocin increases memory for faces but not nonsocial stimuli in both men and women

Hormonal control of sexual behaviour- females

fluctuations in ovarian hormones showed little correlation with sexual activity

study of lesbian couples found significant increase in activity during synchronised ovulation

testosterone released from adrenal gland highest just prior to ovulation

studies on hormone replacement in women following hysterectomy found injection of testosterone increased sexual motivation

Other hormonal control of sexual behaviour

Pheromones

Women attending all female college had synchronised cycles

Exposure to sweat increases social interactions

Women exposed to androstadienone (AND) found in men’s sweat raised attention and mood while for men it increased drowsiness and decreased positive mood

AND activated the preoptic area in women but not in men, an estrogenic chemical had similar results for men

Hormonal control of sexual orientation

No difference in levels of testosterone in homosexual and heterosexual males

30% of female homosexuals have elevated levels of testosterone

Hormonal control of sexual orientation- prenatal effects

Study on 30 women with CAH reported incidence of homosexuality four times higher than in wider population

cases of androgen insensitivity show no indication of sexual interest in women

maternal stress in rats leads to reduced exposure to androgens, reduced sexual behaviour in males and a reduced preoptic area the hypothalamus

preoptic area is smaller in human females than ,ales, one study has shown it to be smaller in homosexual men

control of parental behaviour

3 hormones involved with control of maternal behaviour: prolactin, progesterone and eostrodial

there is no evidence of an organisational effect like testerosterone with sexual behaviour

prolactin stimulates nest building in females

pregnant rats will not care for foster pups until their own are born

Neural control of maternal behaviour

oxytocin plays a role in parent infant bond formation. increased levels facilitated maternal behaviour

reduced maternal behaviour in animals treated with oxytocin antagonist

an fMRI study found that when mothers looked at pictures of their infants, brain regions involved in reinforcement and those that contain receptors for oxytocin showed increased activity

regions involved with negative emotions such as the amygdala, showed decreased activity

Control of paternal behaviour- animals

prairie voles are monogamous, meadow moles are promiscuous

no sexual dimorphism in MPA of prairie voles

activation of neurons in MPA when male prairie voles are exposed to pups

monogamous voles have a higher level of V1 a vasopressin receptors in the ventral forebrain than do polygamous voles

control of paternal behaviour- humans

fathers with higher blood levels of prolactin reported stronger feelings of sympathy and activation when they heard the cries of infants

higher levels of prolactin were associated with more exploratory toy-manipulating play behaviour with their infants, and that higher levels of oxytocin were associated with synchronous, coordinated emotional behaviour between father and infant