Lecture 4 hormones and behaviour


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Lecture 4 hormones and behaviour

  1. 1. Hormones and Behaviour• Endocrine glands secrete hormones into circulatory systems in response to internal and external stimuli• Hormones are also secreted by neurons – neurosecretory cells• Hormones are slower than nerve impulses and are thus suited for physiological and behavioral that are sustained over minutes, days or even months• Rapid response of nervous system and sustained hormonal influences complement each other
  2. 2. • How do Hormones affect Behaviour? – Effects on the NS – Effects on Sensory Perception – Effects of Effector Systems – Effects on development• Techniques for studying includes surgery, hormone replacement, manipulation of hormone concentration and correlational studies (See Fig 3.28)
  3. 3. Effects on Nervous System• Affects many aspects of ns – anatomy, biochemistry, impulse transmissions, basic structural and functional changes within CNS – Reflex actions are accelerated by high levels of thyroxin – Sex differences in behaviour in rats (sexual dimorphism) are associated with anatomy of cells in neurophile of hypothalamus – mediated by neonatal levels of androgen – A given hormone can have different effects on behaviour depending on the region of the CNS
  4. 4. – Studies by Nyby et al. (1992) – studied effects of intracranial implants of testosterone (androgen) in male mouse on • Social and sexual behaviour – ultrasonic vocalisation, urine marking, mounting and aggression • Implanted hormones in brain – septum, medial prepoptic area, and anterior hypothalamus
  5. 5. • Controls given subcutaneous implants of testosterone or empty implants in brain – Controls performed all behaviours at normal level for sexually responsive males while empty implants showed no response
  6. 6. • At site specific implants (experimental): – increased ultrasonic vocalisation – median preoptic area – Median preoptic area and hypothalamic region showed urine markings but less than testosterone controls – Mounting – testosterone controls and median preoptic area – Aggression rare in all males given implants
  7. 7. • Data suggests complex functional interactions between different areas of the brain containing testosterone receptors• Hormones may act as “primers” facilitating other hormones influencing behaviour through their effects on the nervous system – In female hamsters primed with oestrogen the behaiour typical of oestrus can be induced if progesterone is injected into ventricles of the brain – If subcutaneouly or in absence of oestrogen progesterone doses fail to induce response
  8. 8. Effects on Sensory Perception• Hormones affect an animals sensory capability by altering the animals perception of the environment and the way it responds to particular stimuli – Seasonal migration of the stickle back (Gasterosteus aculeatus) – spring migration from sea to freshwater (breeding grounds) – they move in waters that changes in salinity – to facilitate transition, hormones secreted by pituitary and thyroid mainly thyroxin alter fishes’ salinity preferences from salt to freshwater – Female rats are more responsive to tactile stimulus and orientates the body to facilitate penetration (lordosis) (See Fig 3.29)
  9. 9. Effect on Effector Systems• Animals use a range of appendages and external structures in performing different behaviours – hormones affect development of the structures – In male frogs – muscle development – hypertrophied brancial muscles used in coupling – Serotonin and octopamine prime receptor in muscles of lobsters – serotonin primes for flexion when another lobster comes into view and octapamine inhibits flexion – In human female the strength of certain muscles is affected by levels of oestrogen and progesterone – fluctuation in physical performance at different stages of the cycle – In newts, prolactin important for the development of enlarged tail fin in males – use to fan a water stream at the female during courtship – In many birds the development and maintenance of secondary sexual characteristics depend on sex steroids (presence of androgen or absence of oestrogen) (See Fig 3.30)
  10. 10. Effect on Development• Hormones effect development of young and impart characteristic features to their behaviour as adults• Hormonal effects on sexual responses occur during critical periods in an animals development – prenatal or post natal – Female rates given testosterone at 4 days of age – oestrous cycle and sexual behaviour as adults is suppressed – Male rats given oestrogen at 4 days of age – loss of sexual responsiveness through partial functional castration and impaired development of the penis – Thyroxin deficiency in human mothers results in deficient motor and cognitive functions in offsprings
  11. 11. • Factors influencing relationships between Hormones and Behaviour – Hormones can affect behaviour directly or indirectly • Individual genotype • Seasonal variation • Effects on experience • Ecological influences
  12. 12. • Individual Genotype – Differences in genotype are sources of variations – Male domestic fowls showed different responses to castration and androgen treatment – hormone treatment caused birds to resume precastration mating behaviour – Androgen administration to females that came from aggressive males showed increase in aggression but had little effect from those of non aggression male strains – between strains – Even strains individuals show consistent differences in hormone-related behaviour (See Fig.3.31 for guinea pigs)
  13. 13. • Seasonal variation – Important in determining behavioral responses • Red deer (Cervus elephus) – administration of testosterone to stags in winter brings about full rutting behaviour but in late spring no effect • Female receptivity to males of the desert lizard (Anolis carolensis) • Size of song control centre nuclei formation (HVC) (seasonal) in the forebrain of canaries is controlled by testosterone (formation of new nerve cells) – Seasonal changes in hormonal levels and associated behaviour are widespread and can persist even when seasonal cues (external) are removed under controlled laboratory conditions
  14. 14. • Effects of Experience – Past experience has influence on the behavioral effects of hormones – Copulatory behavior in males cats following castration is protracted (lengthened) if males had previously experienced mating (as compared to those without experience) – Experience leads to changes in hormonal state – bidirectional relationship between hormonal change and behaviour • In squirell monkeys (Siamiri sciureus) testosterone levels prior to grouping did not predict social rank (See Fig. 3.32) • After rank establishment – showed relationship between rank and testosterone concentration – alpha male having highest testosterone levels and gamma lowest (Mendoza et al. 1979) • If females were present, the disparity was even more pronounced • Social relationships between males and the nature of the social environment appear to determine the hormonal levels
  15. 15. • Ecological Influences – Hormonal secretion affecting behaviour vary with ecological conditions and impacts of hormonal effects on individual reproductive success • In blackbirds (Agelaius phoeniceus) testosterone levels peak during when males defend breeding territories and guarding mates from rivals – Testosterone levels higher in males defending territories high in pop density (higher competition) – Testosterone levels higher in territorial males as compared to non territorial males – Elevated testosterone reflects the need for aggressive defence of breeding resources • Challenge hypothesis (Wingfield et al., 1990) – increased reproductive aggression due to elevated testosterone is evident during periods of social instability and declines when social relationships are stable – social instability hypothesis of testosterone driven aggression
  16. 16. • Reproductive aggression is a devise for increasing reproductive success but there is conflict with other components of reproductive success, caring for the young – In male birds that care for young testosterone levels drops from initial peak during competitive phase of breeding – When caring males were given testosterone they reduced their commitment to caring young – testosterone secretion and its behavioral consequences appear to be constrained by the bird’s liife histroty strategy– The control of behaviour is influenced by several different hormones acting simultaneously or in sequence (See Fig. 3.33 for the canary)
  17. 17. Neural and Hormonal Mechanisms and long term control of Behaviour – Biological rhythms• Ns and hormones allow for a combination of immediate, short term control of behaviour and long term patterns such as seasonal cycles• Cyclical influences of environment – Light dark – Tides and moon• Animals have acquired endogeneous physiological and behavioral rhythms that matches to the relevant rhythm(s) in the environment• The rhythms persist even if environmental cycles are removed – reflects and endogeneous time base or “clock”
  18. 18. Rhythmic Behaviour• Basic features of rhythmic behaviour (See Fig. 3.34) – Cycles – repeating units – Period – duration – Amplitude – degree of change between peak and trough – Phase – any part of the cycle• Biiological rhythms and behaviour can be entrained to cues in the external environment but not dependent on latter for subsequent expression – pacemaker of the clock can be adjusted
  19. 19. Basic characteristics of rhythmicbehaviour
  20. 20. • Aschoff’s Rule – the rate and direction of drift away from 24 h depends on light intensity and whether the animal is nocturnal or diurnal in its pattern of activity – Nocturnal flying squirrel (in constant darkness) – the free running period starts earlier each night (Fig. 3.34b) – Male crickets kept in light, (normally nocturnal) singing behaviour starts later
  21. 21. • Animals kept in lab without environmental cues have their clocks continue running but may be slightly out of phase to the cues to which they were originally entrained (See Fig. 3.34b, c) – Flying squirrel and stonechat under lab conditions (constant temp and light) show systematic drift in their normal circadian activity and circannaul testicular and moult cycles respectively