PSYC 304 - 2.24

Hormones

Hypothalamic-Pituitary-Gonadal (HPG) Axis

Hypothalamic peptide that plays key role in puberty onset 

• Hypothalamus produces: 

  • Gonadotropin-inhibiting hormone (GnRH)

  • Inhibits secretion by producing gonadotropin-inhibiting hormone (GnIH)

• Pituitary produces:  

  • Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH) 

• Targets: 

  • Gonads (ovaries/testes) 

Kisspeptin

Stimulated GnRH neurons in hypothalamus

Gonads

Two main structures:

• Hormone-producing compartment

  • Produces sex steroids 

• Gamete-producing compartment 

  • Produces eggs or sperm 

Include ovaries/testes

Ovaries

• Luteinizing hormone (LH): Estrogens/progesterone

• Follicle-stimulating Hormone (FSH): Promotes follicle development + estrogen synthesis 

• Produces gametes (ovum/egg) 

• Produces hormones in cycles (4 weeks in humans)

2 Main classes of Ovaries

• Estrogens: 

  • Have organizational roles in shaping reproductive tissues 

  • At puberty, trigger breast development + maturation of reproductive organs

• Progesterone: 

  • Works alongside estrogen to regulate reproductive cycles 

  • Prepares uterus for pregnancy

Testes

• LH: testosterone 

• FSH: promotes spermatogenesis 

• Sertoli cells: Produce sperm (regulated by FSH)

• Leydig cells: produce + secrete androgens (ex. testosterone)

  • stimulated by LH

Testosterone

• Shapes male reproductive organs + brain development before birth 

• Later drives puberty (ex. Deeper voice, genital growth, body hair)

Steroid Conversion

• Progestins can be converted into androgens

• Androgens can be converted into estrogens

• None of these hormones are exclusive to male/female

Sexes differ in proportion of these steroids

Give an example of an enzyme modifying existing steroids

Testosterone can be converted into estradiol (via enzyme aromatase) → major precursor for estrogen production 

• creates new signalling molecules

Sex Differences for Steroid Conversion

• Ovaries: high aromatase levels rapidly convert most testosterone + androgens into estrogens

• Testes: lower aromatase levels produce only small amounts of estrogens

Posterior Pituitary

• Releases hormones directly into the bloodstream 

• Stores + releases (not produced) oxytocin + vasopressin 

• Magnocellular neurosecretory cells 

  • Large neurons located in supraoptic (SON) and paraventricular (PVN) nuclei of hypothalamus 

• Axons extend down pituitary stalk into posterior lobe → synthesized hormones transported + released into bloodstream 

• Axons project within the brain (allows oxytocin + vasopressin to act as neuromodulators) 

Oxytocin

• Also works as a neuropeptide in the brain! 

• Involved in reproductive and parenting behaviour 

• Stimulates uterine contraction during childbirth 

• Promotes lactation 

• Also involved in:

  • Social bonding, trust, maternal behaviour

  • Stress, anxiety, social recognition

Milk Letdown Reflex

• Stimulation of nipple by baby activates neurons in hypothalamus to release oxytocin 

• Mammary cells contract to produce milk 

• Baby rewarded for actions with milk → will continue suckling 

Vasopressin

• Ex. antidiuretic hormone (ADH)

• Works closely with kidneys → regulated blood volume + salt concentration 

• Increases blood pressure + inhibits urine formation when dehydrated

• Also involved in: 

  • Social behaviours (ex. Pair bonding and aggression)

  • Stress, anxiety, memory

Hormones + Social Behaviour

• Hormone effects are highly context dependant + influenced by several factors 

• Same hormone can promote bonding, aggression, trust, or competition depending on the situation

Testosterone and Aggression

• Males have more circulating testosterone than females

• Male aggression peaks during life stages when testosterone is highest 

• Original hypothesis: Testosterone causes aggression. However, testosterone does not directly cause aggression → context-dependent 

• Amplifies pre-existing social tendencies 

• Promotes behaviours that maintain/enhance social status, may manifest as aggression in competitive situations (not in cooperative ones) 

  • Ex. talapoin monkeys → mid-ranking males given testosterone became more aggressive, but only towards lower-ranking individuals (didnt fight with higher-ups) 

    • Testosterone exaggerated existing social patterns, but didnt create new ones

Testosterone + Aggression Studies

• Subtraction studies: castration of males reduces aggression 

• Replacement studies: giving testosterone back to castrated males restores aggression to pre-castration levels 

Testosterone levels + individual/team sports

Rise!

• Increases before event (anticipation) and after (esp amongst winners)

• Even watching a favorite team can raise testosterone 

  • Highlights connection with dominance, self-esteem, and identification rather than physical exertion 

• Social Economic Games: 

  • Participants who thought they received testosterone (regardless of actual hormone) made less generous offers

    • Ex. if gambling made more confident bets 

  • Behaviour can be influences by expectations of testosterone, not just hormone levels 

Context + Experience Modulate Effects of Testosterone

1. Past experiences

• Males with more prior aggressive experience show continued aggression even after castration 

• Suggests aggression becomes partly independent of testosterone through social learning 

2. Basal testosterone levels are poor predictors

• Individual differences in baseline testosterone generally do not predict who will be aggressive across birds, fish, mammals, primates 

3. Challenge hypothesis 

• Rising testosterone levels increase aggression only at time of social challenge 

• When testosterone rises after a challenge, does not prompt aggression → prompts whatever behaviour is needed to maintain status

Oxytocin Pro-Social Effects

• Facilitates recognition of members of your own species (conspecifics)

• In some species, promotes ingroup preference + social cohesion 

• In monogamous species, promotes pair bonding 

• Improved emotional recognition 

• Can increase trust, empathy, cooperation 

• Makes individuals more responsive to social reinforcement

Oxytocin not pro-social effects

• Increased maternal aggression 

• Linked to aggression and biases towards outgroup members

• Trolley problem: 1 person vs 5 ppl to die

  • Ex. germans were given names of members; if 1 person had german name, more inclined to save that people 

• When playing against strangers, decreases cooperation + enhances envy when losing + gloating when winning 

• Enhanced charitability but only those who were already charitable 

Vasopressin + Pair Bonding

Vole: Cute bubby rodent

• Prairie voles form monogamous mating pairs for life → vasopressin facilitates formation of pair-bonds in male prairie voles

  • Dense concentration of vasopressin receptors!

  • Meadow voles who don't form pair bonds have far fewer vasopressin receptors 

Neuro-endocrine coordination

• Hormonal + neural systems interact to produce response 

• Our actions modify sensory input

• Hormones adjust body’s responses to match demands of stimulus 

• Reciprocal influences of each other → experience affects hormone secretions, hormones effect behaviour, behaviour effects future experiences 

Types of Neuro-Endocrine Communication

1. Neural-to-neural

• Synaptic signalling → one neuron sends message to another using NT 

• Ex. sensory input activating motor circuits 

2. Neural-to-endocrine

• Neurons stimulate hormone release from endocrine cells

• Ex. hypothalamic neurons trigger pituitary hormone secretion 

3. Endocrine-to-endocrine

• Hormones from one endocrine gland influence other endocrine glands 

• Ex. ACTH from pituitary stimulates cortisol release from adrenal gland cortex 

4. Endocrine-to-neural 

• Hormones act on brain + alter neural activity 

• Ex. oxytocin modulating social behaviour

Endocrine Pathology

• deficient/excessive hormone secretion associated with a variety of disorders

• Many hormonal disorders mimic/contribute to psychiatric symptoms