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. • 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)

4. 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

5. – 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

6. • 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

7. • 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

8. • 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

9. 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)

11. 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)

13. 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

14. • Factors influencing relationships
between Hormones and Behaviour
– Hormones can affect behaviour directly or
indirectly
• Individual genotype
• Seasonal variation
• Effects on experience
• Ecological influences

15. • 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)

17. • 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

18. • 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

20. • 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

21. • 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)

23. 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”

24. 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

25. Basic characteristics of rhythmic
behaviour

26. • 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

28. • 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