Lesson 7: Hormones and Behavior

Question 1

what is a hormone

Answer 1

*A hormone is a chemical substance released by a gland cell into the bloodstream

*Because it is carried by the blood, a hormone can potentially act anywhere within the body;

*Cells that respond to hormones have specific receptor molecules for that hormone (so cells without receptors are unaffected)

Question 2

How to study homones: Anolis Carolinensis

Answer 2

Background: Knowing the animal, Anolis
carolinensis (aka green anole, Carolina
anole)
*Reptile in which gonads shrink outside
of the breeding season
*Testes regrow in response to warm
temperatures in the spring
*Growth of testes causes increase of
testosterone

Question: what causes
dewlap displays to occur
at the right season?

Question 3

First step: what events correlate with the
behavior?

*Question: Does the testosterone trigger
dewlap displays or is it something else that
correlates in time?

Question 4

Mating behavior in absence of testosterone in red-sided
garter snakes

Answer 4

Background: knowing your animal. Red-sided
garter snakes (Thamnophis sirtalisparietalis)

• Reptile in which testes shrink at end of
  breeding season and grow back after
  hibernation ends
• Hibernation needed because this subspecies
  found in cold areas of Upper Midwest, US and
  central Canada
• When male emerges from hibernation, it
  carries out courtship and mating even though
  testes have not grown back yet and
  testosterone is zero

Question 5

How can male be
ready to mate in
spring BEFORE
testes have
regrown?

Answer 5

Experiment: captured
animals at end of summer
when testoseterone levels
were still high.

Then:
* half were left intact as
controls and
* half were castrated so
that there was no source
of testosterone
* Followed for 4 years

RESULTS:
* During the next three
years the % of intact
males who courted
females stayed high
* but the % of
castrated males who
courted decreased
with each year

Question 6

Conclusion from first
three years of results:

Answer 6

In years 2 & 3, intact
males had testosterone in
the previous summer
while castrated ones did
not. It looks like
testosterone affects
behavior months later…

Question 7

To test that idea
directly see Year 4:

Answer 7

added back
testosterone in
summer and see
behavior is restored
the next spring.

Question 8

Background: An increase in
prolactin is associated with egg
incubation behavior in female
penguins.

Answer 8

This study looks at how hormones
can interact with environmental
signals (Massaro, Setiawan, &
Davis 2007)

Specifically, they asked
whether prolactin levels were
affected by
1) the sightof an egg (visual
stimulus) or
2)the feelof an egg (tactile
stimulus)

Question 9

Methods: Two kinds of Stimuli

Answer 9

1. Provided visual stimulus by
   placing an artificial egg near
   the nest.
2. Provided a tactile (& visual)
   stimulus by placing an
   artificial egg in the nest

Question 10

other info

Answer 10

*Methods: Sampling times of prolactin
levels
*Prior: before an artificial egg was
added
*After Stimulus: 3 to 4 days after
artificial egg added
*Control: Sampled at 3 to 4 days - the
same time as Group 2, but no egg was
added

Question 11

Prolactin and incubation in penguins

Answer 11

*Results:
*Birds that could only see eggs
did NOT have elevated prolactin
levels (the first two bars are not
statistically different from each
other)

*Birds that had eggs added to the
nest did have higher prolactin
levels than controls (both the
prior and the penguins sampled
at the same time)

Question 12

Conclusion:

Answer 12

Prolactin and incubation in penguins
Conclusion:

*Presence of an egg in nest
results in increased prolactin
production in these birds

*Hormones are altered by
experience

*This means that the bird will
have the right behavior when it
needs it

Question 13

ways that hormones alter behavior: activational effects

Answer 13

triggering a beavior

Question 14

ways that hormones alter behavior: organizational effects

Answer 14

reorganizing the brain to make permanent changes

Question 15

Sexual Behavior in Rats

Answer 15

Male behavior includes ‘mounting’ and
female behavior includes ‘lordosis’

• Testosterone during days 1-5 has an organizational effect
• Days 1-5 represent a CRITICAL PERIOD for that organizational effect given
  that castration has no effect during days 6-10
• Testosterone has an activational effect in adulthood

Female Testosterone
implant
none Testosterone
pulse
Mounting

The female brain does not respond to testosterone in
adulthood – so there is no activational effect. Also true
for the male in Regime #1 because it has a female type
of brain

Question 16

Monogamy and Polygyny in Voles

Answer 16

Getting to know your animal: the
prairie vole (Microtus
ochrogaster) and the meadow
vole (Microtus pennsylvanicus)
are small rodents that live in
grasslands.

A key difference between them is
that meadow voles are
polygynous while prairie voles
are monogamous.

Question 17

Prairie voles

Answer 17

emales spend more time
in direct physical contact with offspring
– nursing and huddling.

*Males are monogamous & nest with
female & often groom & huddle with
young

Question 18

Meadow voles

Answer 18

females spend less time;
males do not nest with female so spend
no time with young - polygynous
Monogamous prairie vole
parents with young

Question 19

Cross-Fostering Experiment:

Answer 19

baby
meadow voles were put into nests
of prairie voles. The prairie vole
adults accepted them as their own
and gave them typical parental care

*Control: baby meadow voles put
into nest of other meadow voles
(different parents but same
species)

Results:
*Cross-fostered female meadow voles
spent more time than controls
huddling and nursing young
*4 of 8 cross-fostered male meadow
voles nested with their mates and
spent time with young (a prairie vole
behavior) – were monogamous

Conclusion:
*Parental behavior is highly influenced
by environment BUT note that 4 of 8
cross-fostered males were still
polygynous (a meadow vole
behavior) so still see some effect of
genes

Question 20

Clue that the hormone vasopressin might
be important:

Answer 20

When prairie voles copulate multiple times
with the same female, there is a surge of
vasopressin released from the pituitary
gland into the bloodstream of the male.
The vasopressin stimulates a brain region
(the ventral pallidum) involved in feelings
of reward (the so-called “pleasure center”)

Question 21

Monogamy vs Polygyny: Genes, Hormones, and the Brain

Answer 21

f being with one female
causes a feeling of
reward for the male,
that might lead to
monogamous behavior.
So it might be really
important that the gene
for the vasopressin
receptor, avpr1a, is
expressed in the ventral
pallidum of the brain

Question 22

To test this idea, researchers created three transgenic
lines of prairie voles:

Answer 22

1) Avpr1a-VP: had an extra copy of avpr1a expressed

in the ventral pallidum (reward center)
2) Avpr1a-CP: an extra copy was expressed in a
different brain area, the caudate putamen

(Unrelated to the reward center)
3) lacZ-VP/CP: the bacterial lacZ gene was expressed
in the VP and CP as a control for gene manipulation

Question 23

Behavioral test:

Answer 23

Male caged with a non-estrous female for 36 hours. Then given chance to spend time with
the same, familiar female or with a stranger female

Question 24

behavioral test

Answer 24

Results
show that males with
extra vasopressin
receptors in the ventral
pallidum spent more time
with the familiar female,
but this was not seen
with the other transgenic
lines

Next: created transgenic male
meadow voles (the polygynous
species) with avpr1ain ventral
pallidum.
These males with extra vasopressin
receptors in the ventral pallidum
spent dramatically more time
huddling females – a monogamous
behavior that they don’t normally
have

Question 25

summary

Answer 25

Release of vasopressin
mediates feelings of reward when the
prairie vole male engages in social bonding
with a female

*This reward leads to monogamous
behavior.

*Similar behavior can be elicited in meadow
voles simply by increasing expression of
the vasopressin receptor in the ventral
pallidum

Question 26

To spell it out:

Answer 26

When voles mate, it appears
that vasopressin is released. If a prairie vole,
the vasopressin will bind to the reward center
(ventral pallidum) and the male will have a
feeling of reward that can lead to formation
of a pair-bond and monogamous behavior.
Meadow voles do not normally have
vasopressin receptors in the ventral pallidum
so do not normally feel rewarded when
hanging with the same female