13.3 - Hormones and Sexual Development of Brain and Behaviour

Question 1

Are there differences between the male and female brain?

Answer 1

yes

Question 2

what are the x differences referenced between the male and female brain (5)

Answer 2

1. male brains are 15% larger
2. difference inn average volume across areas, nuclei, fibre tracts
3. number and types of neural and glial cells that compose certain structures
4. plasticity of certain structures
5. number and types of synapses that connect the cells in various structures

Question 3

Explain the Pfiffer study on castrated neonatal rats and their gonadotropin release

Answer 3

neonatal rats were castrated, others were not, some received transplants, others did not

• the castrated rats of either sex developed into adults w the female cyclic pattern of gonadotropin release
• transplantation of testes into any female neonatal (castrated or not) caused them to develop steady gonadotropin release
• transplantation of ovaries had no effect on patters

Question 4

what did Pfeiffer conclude from his studies on castrated neonatal rats

Answer 4

female cyclic pattern of gonadotropin release develops unless it is overidden by testosterone

Question 5

Why was Pfeiffer incorrect?

Answer 5

concluded that testosterone influenced pituitary development, but we now know that the release of gonadotropins from the ant pit are controlled by the hypo thal

Question 6

What did the knowledge that gonadotropin release from the ant pit is determined by the hyp. thal contribute to Pfeiffer’s findings on castrated neonatal rats

Answer 6

the first evidence for the role of perinatal androgens in overriding programmed female cyclic gonadotropin release

Question 7

what is aromatization

Answer 7

Gonadal and adrenal sex hormones are steroid hormones
- since all steroid hormones are derived from cholesterol, they have very similar structures and can be converted into one another
changing the testosterone molecule by an enzyme (aromatase) converts it to estradiol - called aromatization

Question 8

what is the aromatization hypothesis

Answer 8

perinatal testosterone doesn’t masculinize the brain, it is masculine by estradiol that has been aromatized form perinatal testosterone

Question 9

what are the two strongest pieces of evidence for the aromatization hypothesis
(2 on 2)

Answer 9

1. findings that show masculinizing effects on the brain of early injections of estradiol
2. a) masculinization of the Brian does not occur in response to testosterone when it is administered alongside agents that block aromatization
   b) masculinization also doesn’t occur in the presence of other androgens that cannot be aromatized (dihydrotestosterone)

Question 10

How do females prevent being masculinized by estradiol which their mothers circulate through fetal blood supply?

Answer 10

Alpha fetoprotein, which is present in the blood during the perinatal period - deactivates circulating estradiol by binding to it
- solid finding in rodents, not so sure in humans

Question 11

How does estradiol masculinize the brain of male rodent fetus even in the presence of deactivating alpha fetoprotein?

Answer 11

testosterone is immune to it, can travel unaffected from testes to brain, where it can be aromatized to estradiol
- estradiol can function in the brain because alpha fetoprotein can’t really cross the BBB

Question 12

what was the original assumption about the aromatization hypothesis?
is this correct?

Answer 12

that it was the sole mechanism that produced sex differences in the Brain
no

Question 13

Are there ay brain differences with clear behavioural significance?
is it likely that there are not such differences?

Answer 13

No

no

Question 14

what is the primary principle when considering sex differences in the brain

Answer 14

they are never masculinized or feminized wholesale, they develop independently in different parts of the brain at different points in time and by different mechanisms

Question 15

what is an example of brain-area dependent sex differences

Answer 15

aromatase is found in only a few areas of the rat brain (hypthal) and only in these areas is armozatization critical for testosterones mascluinizing effects

Question 16

are all brain differences developed perinatally?

Answer 16

no, some do not arise until puberty, so probs not due to aromatization or whatever

Question 17

what are the two factors that play little or no tole in the sexual differentiation of repro organs that do influence sex diff in the brain?

Answer 17

1. sex chromosomes - influence brain dev independent of their effects on hormones
2. although female program of repro organs proceeds in the absence of gonadal steroids, evidence suggests that estradiol plays and active role
   - knockout mice without the gene that forms estradiol receptors do not develop typical brains

Question 18

what is an example of the fact that sex chromosomes influence brain dev independent of their effects on hormones

Answer 18

different patterns of gene expression exist in the brains of male and female mice even before gonads become functional

Question 19

what complicates the study of brain differences in sexes?

Answer 19

the mechanisms that cause it are different in different mammals - aromatization is less important in primates than in rats and mice

Question 20

Explain the Pheonix et al (1959) study on the effects of perinatal testosterone

Answer 20

• injected pregnant guinea pigs w T
• when born, ovariwctomized the females
• when the ovariectomized females matured, they injected them w T to test their copulatory behaviour
• females exposed to perinatal T displayed more male mounting behaviours in response to T injections in adulthood
• when injected with progesterone and estradiol and mounted by males, they displayed less lordosis

Question 21

Describe the Grady, Pheonix and Young study on the effects of perinatal testosterone

Answer 21

• lack of early experience to T both feminizes ad demasculiizes their repro behaviour as adults
• when castrated right after birth, males dont display mounting, intromission (dick insert) and ejaculationeven if given T as adults and a prime lady to make love to
• when injected w estrogen and progesterone as adults, they exhibited more lordosis than uncastrated conntrols

Question 22

What process is important for the defeminizing and masculinizing of copulatory behaviour
In what species?
Is this universal?

Answer 22

aromatization of perinatal T to estradiol
rodents
monkeys

Question 23

Is there a critical period for the effects of perinatal testosterone? if yes, when?

Answer 23

yes, the ability of single injections of T to masculinize and defeminizie rat repro behaviour is restricted to the first 11 days of life

Question 24

what is a preceptive behaviour

Answer 24

a solicitation behaviour for sex

Question 25

What do we know about the influence of perinatal T in preceptive behaviours

Answer 25

• little,

- but, disrupts the preceptive hopping, darting, and ear wiggling of receptive females

Question 26

why do we need both the terms masculinizing and defeminizing

Answer 26

they are not the same thing, we can have male and female behaviours in the same individual, and dont necessarily change in opposite directions ion they receive physiological treatments such as hormones or brain lesions

Question 27

Explain the findings of Dulac and Kimchi on male and female sexual behaviours

Answer 27

male behaviours (like mounting) have been observed in females in many mammals, ad female behaviours such as lordosis have been observed males

Question 28

What area can we lesion to abolish male reproductive behaviours? does this effect only occur in males? Does it effect female behaviours?

Answer 28

the medial preoptic area
no, also females
It does not affect feminine behaviours in either sex

Question 29

what is a sexual dimorphism

Answer 29

instances where a behaviour or structure comes in two distinct types along gender lines, into which we can unambiguously assign individuals

Question 30

Are there sexual dimorphism in humans? In what sense

Answer 30

yes, but only reproduction related behaviours

Question 31

what is the main contributor to the development of sexually dimorphic traits in human reproductive behaviours

Answer 31

prenatal T

Question 32

what are some of the more statistical and overlapping ways that men and women differ

• what do we know about the causes of these differences?

Answer 32

play behaviour
social interaction 
reaction to pain
language 
cognition 
emotionality 
drug sensitivity 
responses to stress
- prenatal T def contributes, but we dont really know how exactly

Question 33

What are some examples of behavioural disorder susceptibility differences between males and females
(M>F examples)

Answer 33

1. dyslexia
2. early onset Schiz
3. stuttering,
4. ASD
   - all around 3x

Question 34

What are some examples of behavioural disorder susceptibility differences between males and females
(F>M examples)

Answer 34

Twice as likely for 
1. depression
2. anxiety disorders
3. alzheimers 
ten times as likely for eating disorders

Question 35

do we know why there are such differences between male and female susceptibility in certain behavioural disorders?

Answer 35

nope!