Lecture 16: Hormones and Behaviour Flashcards
What contexts do hormones affect behaviour across?
- biological rhythms
- eating and drinking
- social behaviour
- reproductive behaviour
- stress
What are circadian rhythms?
regular activity patterns (eg humans active during the day and sleepy at night = diurnal, rodents active at night and sleepy in the day = nocturnal)
How is melatonin used in a circadian rhythm?
- released almost exclusively at night (inhibited by light)
- provides a signal to track daylength and season
- controls the timing of onset of sleep (in humans)
- controls breeding condition in seasonally breeding animals
What is the function of the pineal gland in circadian rhythms?
- in birds and reptiles, can sense light directly through the skull
- in mammals, light sensory input via retinohypothalamic pathway
- phasic (cf. tonic) secretion of melatonin in cyclic patternshourly, diurnal, monthly, seasonally…
- important in regulating cyclical functions
Explain the stages of circadian rhythms?
- Inhibited by light detected via the retina in the eyes
- Signal sent to suprachiasmatic nucleus in the hypothalamus, then from here to the spinal chord, then to the cervical ganglia, which inhibit the pineal gland.
- Suprachiasmatic nucleus is the centre of regulation for biological rhythms in mammals
- Influences sleep onset
- Used to treat jet lag
How do hormones impact our eating and drinking?
- peptide secreted by cells in the stomach
- Peptide (short chain of aminoacid – acts on surface cell receptors)
- Involved in eating behaviour and obesity.
- Other hormones and signals involved in eating behaviour – their messages are integrated in the hypothalamus
- Peptide (short chain of aminoacid – acts on surface cell receptors)
- stimulates feeding
- stimulates release of growth hormone (GH) from pituitary
- Also secreted in the brain to control of feeding
Other hormones and signals involved in eating behaviour – their messages are integrated in the hypothalamus
What is the function of the hormone ghrelin?
Ghrelin is a powerful appetite stimulant
Circulating levels
- rise prior to mealtimes and at night
- drop following a meal
Treatment with exogenous ghrelin provokes increased appetite
What are the hormone levels of obese people?
- have lower ghrelin before eating
- but following a meal their levels do not drop
→ a ghrelin system unresponsive to feeding and therefore always hungry?
What is the function of oxytocin?
- a mammalian peptide hormone that acts on the central nervous system
- generally associated with uterine muscle contraction at birth and milk letdown
- also governs a suite of prosocial behaviours
- as do analogues (e.g. isotocin) in other taxonomic groups
Explain how oxytocin impacts parental care
- female rats bred for high levels of maternal behaviours have more oxytocin receptors in the central nucleus of their amygdala
- Amygdala, small structure involved in emotions
- female prairie voles that show more maternal behaviour have higher oxytocin receptor density in their nucleus accumbens
- Nucleus accumbens, part of the reward system in the brain (involved in motivation and pleasure)
- Oxytocin = peptide hormone, requires membrane receptor
- blocking these receptors inhibits maternal behaviour
Explain Madden & Clutton-Brock (2010)’s study
- N = 36 meerkats (28 males, 8 females) injected with oxytocin vs saline control
- treatments reversed 3–5 days later
- recorded suite of prosocial behaviours
What did Madden & Clutton-Brock (2010) find?
Those in oxytocin group showed higher signs of:
- Guarding
- Pup feeding
- Closeness to pups
- Communal digging
However, those in saline group showed higher signs of
- Aggression
Explain Zak et al (2007) study
- N = 68 men
- ‘one-shot’ economic game involving a voluntary donation
- given oxytocin vs control (placebo saline) via nasal spray
- donations were ~80% higher in oxytocin group
What are the similarities between the endocrine and nervous system?
Both are communication and control systems
Both take inputs and effect outputs
Both can be influenced by prior exposure (habituation/immunity)
What does the endocrine system have that the nervous system doesn’t?
- chemical substance
- conveyed in blood
- diffuse effect across body
- analogue (graded) signal
- ‘slow’ response (secs or mins)
- response persists over time
- no voluntary control
What does the nervous system have that the endocrine doesn’t?
- action potential
- transmitted along nerve fibre
- targeted effect in specific cell or organ
- digital (all-or-nothing) signal
- fast response (ms)
- responses generally short-lived
- some voluntary control
What is the neuroendocrine system?
- Fast initial response
- Prolonged action if required
- Enables regulation and control of homeostasis
- Ensures that the appropriate response is given to a stimulus
