06. Social & Reproductive Behaviour - Part 1 (Reproductive)

Question 1

The experimental wedding

Answer 1

• ↑oxytocin for both (love hormone)
• ↑cortisol for wife (before and after), ↓cortisol for man (after wedding)
• ↓vasopressin (possession hormone) for husband
• ↑testosterone (x2) for husband

Couple got married and measured their hormones

Question 2

Castration and hormone replacement in chickens (Arnold Berthold, 1803-1861)

Answer 2

• Castration (in chicks) causes caponisation (abnormal male development) when fully grown
• Castration and reimplantation of testis -> normal male development
• Even works when transplanting testis from a different chick
• Effect mediated by hormones

Question 3

What is a hormone?

Answer 3

A signalling molecule that carries messages to distant targets through the bloodstream

Question 4

What are the hormone classes?

Answer 4

• Steroids -> derived from cholesterol (can pass through cell membrane)
• Amine hormones -> derived from amino acid tyrosine (cannot pass through cell membrane)
• Peptide & protein hormones -> amino acid chains (cannot pass through cell membrane)

Question 5

Examples of steroids:

Answer 5

• Cortisol
• Progesterone

Question 6

Example of an amine hormone:

Answer 6

• Thyroid hormone (TH)

Question 7

Examples of peptide & protein hormones:

Answer 7

Peptide
- Oxytocin
- Vasopressin

Protein
- Prolactin
- Insulin

(all end with -in)

Question 8

Where are sex hormones produced?

Answer 8

• Ovaries: oestrogen and progesterone
• Testes: testosterone

Question 9

Where are non-sex hormones produced?

Answer 9

• Pituitary gland: Growth Hormone (GH)
• Thyroid gland: thyroxine (TH)
• Pancreas: insulin
• Adrenal gland: adrenaline (ADH)

Question 10

Which female hormones control sexual behaviour?

Answer 10

Follicle-stimulating hormone (FSH)

• causes release of oestradiol

Luteinising hormone (LH)

• causes ovulation -> sexual behaviour

corpus luteum causes increase in oestradiol + progesterone

Question 10

What are the phases of menses?

Answer 10

• Follicular phase (follicle matures, then releases egg - ovulation)
• Luteal phase (thickening of uterine lining, controlled by corpus luteum)

Question 11

What hormone controls sexual behaviour in male rodents?
What are the sexual behaviours?

Answer 11

(Sonoeren et al., 2014; Whalen et al., 1971)
- Behaviour: mounts, intromission, ejaculation
- Depends on testosterone levels
- Castrated male rats injected with testosterone reinstate sexual behaviour

Question 12

Hormones and sexual behaviour in female rodents

Answer 12

• Behaviour: lordosis (coupling position)
• Female initiates copulation & approaches male
• Depends on oestradiol and progesterone
• Ovariectomised rats show no sexual behaviour

Question 13

Neural control of sexual behaviour: experimental tools

Answer 13

• Identifying neurons with sex hormone receptors
• Injection of pseudorabies virus (retro-tracing) in sexual organs (to find the circuit that controls sexual organs) (Marson & Murphy, 2006)
• Activation of Fos (marker of neuronal activity) in key brain regions

Question 14

Neural control of sexual behaviour: Male humans

Answer 14

• Men with spinal cord injuries (complete transection) above the 10th thoracic segment can ejaculate (Brackett et al., 1998)
• Neurons in the lumbar region control ejaculation (Allard et al., 2005)
• These neurons are lumbar spinothalamic cells (LSt)
• In rats: destroying LSt cells stops ejaculation (Allard et al., 2005)

Question 15

What brain area controls sexual behaviour in male rats?
(Carlson et al., 2002)

Answer 15

• Sexually dimorphic nucleus (SDN) is 3-7x larger in males than females (rats)
• Also larger in male humans
• Involved in gender identity
• Lesions to SDN decrease masculine sexual behaviour

Question 16

Neural control of sexual behaviour: Female rats (Carlson et al., 2002)

Answer 16

• Females do not have a spinal circuit controlling sexual behaviour.