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

Question 1

The experimental wedding

Answer 1

• Couple got married and measured their hormones
• Both: ↑oxytocin (love hormone)
• Wife: ↑cortisol (both before and after)
• Husband: ↓vasopressin (possession hormone), ↓cortisol (after wedding), ↑testosterone (x2)

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

Examples of amine hormones:

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

How do female hormones control sexual behaviour?

Answer 10

Follicle-stimulating hormone (FSH) -> 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

Hormones and sexual behaviour in male rodents (Sonoeren et al., 2014 Whalen et al., 1971)

Answer 11

• 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
• Retro-tracing to define the circuit that controls sexual organs (Marson & Murphy, 2006)
• Injection of pseudorabies virus (retro-tracing) in sexual organs
• 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

Neural control of sexual behaviour: 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.