Social and Reproductive Behaviour

Question 1

The experimental wedding:

Answer 1

· Linda and Nic, both science writers
· Studied their ‘love hormones’ during their wedding in Devon.
· Measured oxytocin, vasopressin, cortisol, and testosterone, before and after the ceremony

Question 2

Data from the experimental wedding:

Answer 2

· Oxytocin (the ‘love hormone’) levels were up
· Vassopressin ( the “possession hormone”) went down in Nic.
· Cortisol (the “stress hormone”) was up in Linda before and after (even higher), whereas in Nic they went down after the ceremony.
· Testosterone levels doubled in Nic.

Question 3

Castration and hormone replacement:

Answer 3

· Testis transplantation restores normal development in roosters.
· Transplanted testis were not connected to blood supply or neuronal networks.
· Their effect was mediate by chemicals released to the blood stream:
- Hormones

Question 4

Testis transplant from farm animals was also tested in humans with mixed results:

Answer 4

· Brinkley’s surgeries were a success for some time, but ethical, methodological, and safety aspects made this enterprise unsustainable.
· Note: Viagra, introduced in 1998, produced $1B sales that year, highlighting the market for sexual enhancers.

Question 5

What are hormones?:

Answer 5

· Hormone - signalling molecular that can carry messages to distant targets through the blood stream.
· Neurohormone - an hormone released by neurons. Targets neighbouring or distant cells.
· Target - organs/cells that can detect hormone/s and it is affected by it/them.

Question 6

Hormone classes:

Answer 6

· Steroid hormones - derived from cholesterol, they can easily travel across cell membranes. e.g., cortisol and progesterone.
· Amine hormones - derived from the amino acid tyrosine. Cannot easily cross the cell membrane. e.g., thyroid hormone (TH).
· Peptide and protein hormones - amino acid chains. Cannot travel through cell membrane = activate membrane receptors. E.g., oxytocin, vasopressin (peptides), prolactin, insulin (protein).

Question 7

Where are hormones produced?:

Answer 7

· Ovaries - estrogen and progesterone
· Testes - testosterone
· Pituitary gland - growth hormone
· Thyroid gland - thyroxine
· Adrenal gland - adrenaline
- Pancreas - insulin

Question 8

Genetic sex:

Answer 8

· Offspring genetic sex depends on the sex chromosome carried by the sperm and ovum that generates them.
· Genetic sex depends on the father sperm cells, which carry X or Y sex chromosomes

Question 9

Development of sex organs:

Answer 9

· All the information to develop bodies of either sex is present in the 22 nonsex and the X chromosomes.
· Exposure to sex hormones, both before and after birth, is responsible for sexual dimorphism.
· The Y chromosome controls the development of the glands that produce the male sex hormones.
· Sex organs: gonads (ovaries and testes), internal sex organs, and external genitalia.

Question 10

Gonads:

Answer 10

· Gonads (testes or ovaries) are the first to develop: produce ova or sperm, and hormones.
· Sex-determining region Y (SRY) gene (from Y chromosome) express SRY protein that differentiates gonads into testes.
· Lack of SRY results in ovaries development.

Question 11

Internal sex organs:

Answer 11

· During the first two months of gestation, fetus can develop into either male or female.
· At month three, if testes are present and producing hormones (anti-Müllerian hormone and androgens), the internal sex organs develop into male ones.
- Female internal organs do not need the presence of any other hormone to develop.

Question 12

External genitalia:

Answer 12

· As with internal sex organs, external genitalia do not need hormonal influence to develop into female organs.
· Dihydrotestosterone (androgen produce by testes) develops external genitalia into male version

Question 13

Sexual maturation:

Answer 13

· So far we revised the primary sex characteristics, present at birth.
· Secondary sex characteristics develop during puberty and are influenced by hormones.
· The hypothalamus release gonadotropin-releasing hormone (GnRH), which ultimately stimulates hormone release by testes or ovaries.
· Testes release testosterone.
· Ovaries release estradiol.
· Gonadotrophins (testosterone and estradiol) are responsible for development of secondary sexual characteristics in males and females, respectively.

Question 14

Hormonal control of sexual behaviour:

Answer 14

· Hormones not only control sexual development, but also interact directly with the nervous system to affect sexual behaviour.
· E.g., hormones control the female reproductive cycle: the menstrual cycle. (estrous cycle in non-primate mammals).
· In non-primate females, sexual behaviour is linked to ovulation. Primate females mate at any time during their menstrual cycle.

Question 15

Hormones and sexual behaviour in male rodents:

Answer 15

· Male rodents sexual behaviour: mounts, intromission, and ejaculation.
· Depends on testosterone levels: castrated male rats injected with testosterone reinstate sexual behaviour.

Question 16

Hormones and sexual behaviour in female rodents:

Answer 16

· Sexual behaviour in female rodents: lordosis.
· The female initiates copulation. When receptive, it will approach the male.
· Sexual behaviour depends on estradiol and progesterone. Ovariectomised rats (ovaries removed) display no sexual behaviour.
· ER: estradiol receptor. ER -/-: ER knockout rats
· Similar effects with progesterone receptor KO females (Lydon et al, 1995)

Question 17

Neural control of sexual behaviour - tools:

Answer 17

· Retro-tracing to define the circuit that control sexual organs (e.g., Marson & Murphy, 2006). Injection of pseudorabies virus (retrograde tracing) in sexual organs (penis, vagina, clitoris).
· Activation of Fos, a marker of neuronal activity, in key brain regions.
· Identify of neurons containing sex hormone receptors: estrogen and progesterone or testosterone.

Question 18

Neural control of sexual behaviour - males:

Answer 18

· Spinal mechanisms.
- Men with complete spinal cord transection above the 10th thoracic segment can ejaculate.
· A group of neurons in the lumbar region (spinal ejaculation generator) lumbar spinothalamic (LSt) cells control ejaculation.
· Destruction of LSt cells in rats abolishes ejaculation, without affecting mounts or intromissions.
· Brain mechanisms - excite or inhibit spinal circuits
· Fos - neuronal activation marker

Question 19

Neuronal controls of sexual behaviour - females:

Answer 19

· Contrary to males, females do not have a spinal circuit controlling sexual behaviour.
· Brain mechanisms:
- Neurons contain estrogen and progesterone receptors - VMH and medial amygdala
· Fos: neuronal activation marker

Question 20

Parental behaviour:

Answer 20

· Most mammalian species show parental behaviour.
· Hormonal and neuronal control, mostly based on rodents.
· Most research on maternal behaviour.
· Mice/rats pups at birth:
- Blind.
- Do not regulate their own temperature.
- Cannot release urine and faeces.
· Nest building is one of the first maternal behaviours during gestation.

Question 21

Maternal behaviour:

Answer 21

· Birth assistance by pulling the pups gently.
· Nursing.
· Periodical licks pups’ anogenital region to stimulate urination and defecation (a way of recycling water – very useful under low water availability).
· Pups retrieval if they leave or are removed from the nest.
- Maternal behaviour is influenced by prenatal hormones, but passage of pups through the birth canal also helps (Yeo & Keverne, 1986)

Question 22

Maternal behaviour 2:

Answer 22

· Hormones can influence maternal behaviour, but do not control it.
- I.e., progesterone, the main pregnancy hormone, can facilitate nest building. But, nest building continues after birth, when progesterone is significantly lower.
· Medial preoptic area (MPA; involved in male sexual behaviour) is crucial for maternal behaviour.
· The VTA-NAC pathway, involved in the reward system, is also necessary for maternal behaviour. It is activated when mothers encounter pups.
· Encountering pups is more rewarding than cocaine in lactating females (Ferris et al., 2005).
· Human mothers show activation of the reward system when presented with pictures of their babies (Bartels & Zeki, 2004)

Question 23

Paternal behaviour 2:

Answer 23

· A few mammalian species show paternal care for the offspring.
· Monogamous prairie voles share offspring care, whereas polygamous male meadow voles leave the female after mating.
· Size of MPA is less sexually dimorphic in prairie voles than in meadow voles.
· MPA lesions disrupts paternal behaviour in rats and prairie voles.

Question 24

Affiliative behaviours:

Answer 24

· Positive social behaviours within the same or different species.
· Can involve individuals of the same or different sex.
- Formation of pair bonds in voles.
- Prosocial behaviours in humans.
- The neuropeptides oxytocin (OXT) and vasopressin (VP) are key for complex social behaviours.

Question 25

Oxytocin and vasopressin:

Answer 25

· The neuropeptides oxytocin (OXT) and vasopressin (VP) are produced in the hypothalamus.
· They can be released from the posterior pituitary gland as hormones.
· Or from axons projecting to specific brain regions, as a neuromodulator or neurotransmitter.

Question 26

Pair bonding:

Answer 26

· Only 3-5% of mammals are monogamous. Explain in humans and other species.
· Biparental species: males and females raise the young.
· Voles are a prime example:
- Prairie voles: monogamous – bond for life.
- Meadow voles: polygamous or promiscuous – male leaves the female after mating.
· These rodents have been extensively studied to identify the neurobiological bases of affiliative social responses.

Question 27

Hormones influencing pair bonding:

Answer 27

· Exposure to a partner while injected with VP or OXT increased the preference for that partner.
1. Male and female paired for 1h. One of them receives intraventricular administration of OXT or VP.
2. Then animals are submitted to a partner preference test (180 min) where they can choose to spend time alone, with a stranger, or with the partner they were exposed during drug administration.

Question 28

Neurobiology of pair bonds:

Answer 28

• Pair bonding is associated with the density of VP receptors in the rewards areas of the brain

Question 29

What about oxytocin receptors?:

Answer 29

• OXT receptors are highly expressed in PFC and Nacc in prairie voles

Question 30

Promiscuous to monogamous?:

Answer 30

• Overexpression of vasopressin receptor in the ventral pallidum (V1aR-vp) enhanced mate preference in meadow voles

Question 31

Formation of pair bonds in humans:

Answer 31

· Oxytocin and vasopressin seem to influence pair bonding in humans too, but manipulating these carry ethical concerns, so we do not know for sure.
· OXT intra-nasal caused relaxation and anxiety reduction in humans (Heinrichs et al., 2003).
· Maternal and romantic love activated regions of the brain rich in vasopressin and oxytocin receptors.

Question 32

Prosocial behaviour:

Answer 32

· The term “prosocial” is associated with a wide range of positive social behaviors, including trust, cooperation, care, empathy, and altruism—all of which are key for forming and maintaining adaptive human social relationships.

Question 33

Role of oxytocin in prosocial behaviour:

Answer 33

· Administration of oxytocin has subtle effects in social behaviours in humans:
- Trust
- Empathy
- Social approach
- Altruism
· Oxytocin has effects on brain regions related to reward and fear related processing.
· Growing interest in translating oxytocin administration for the treatment of psychiatric conditions ranging from anxiety disorders to autism spectrum disorder.
· Oxytocin effects on behaviour are highly influenced by individual and contextual conditions.

Question 34

Oxytocin and trust:

Answer 34

· Subjects given oxytocin show significantly higher MU transfer levels.

Question 35

Oxytocin and altruism:

Answer 35

· Altruism: non-reciprocal prosocial acts which are aimed at improving the welfare of another individual at a personal cost to the altruist.
· Experiment 1:
1. Saliva samples to measure internal OXT.
2. Participants received 10 €1 coins.
3. Social or environmental donation task.
- Positive correlation between OXT levels and social donation.
- No effect in the ecological frame.
· Experiment 2:
4. Saliva samples to measure internal OXT.
5. Participants received 10 €1 coins.
6. Social or environmental donation task.
- OXT administration increased donations in the social frame, but decreased those in the ecological frame.

Question 36

Oxytocin and empathy:

Answer 36

· Empathy: cognitive (recognizing emotional states in others) or emotional (sharing experiences of emotional states perceived in others).
· Experiment:
1. OXT or placebo, intranasal.
2. 45’ later, “Multifaceted Empathy Test” (MET).
- OXT administration increased empathy ratings in all dimensions

Question 37

Oxytocin and social approach:

Answer 37

· Approach behaviour to others was measured after intranasal OXT in women.
· Experiment:
1. OXT or placebo, intranasal.
2. 45’ later, Stop Distance Paradigm with female or male experimenters.
· OXT administration decreased the social distance that female participants kept between themselves and an unfamiliar friendly male experimenter.

Question 38

Role of oxytocin in prosocial behaviour:

Answer 38

· The involvement of oxytocin in prosocial behaviour seems to be more complex than simply increasing one dimension specifically.
· Expression of OXT and OXT receptor maps into areas involved in anticipatory, appetitive, and aversive cognitive states.