Chp 8: Hormone-Behavior Relations in the Regulation of Parental Behavior Overview: Parental behavior evolved to supplement physiological mechanisms of

Chp 8: Hormone-Behavior Relations in the Regulation of Parental BehaviorOverview:

• Parental behavior evolved to supplement physiological mechanisms of

reproduction--increasing the likelihood that the offspring will survive.

• Different patterns of parental behavior

• In females, hormones of pregnancy synchronize several events:

– reproductive tract: stimulate uterine contractions (parturition or childbirth)

– mammary gland: stimulate production and secretion of milk (lactation)

– central nervous system: stimulate parental behavior

• In males, hormonal changes are not strongly linked to parental responses

• Consider two main examples in detail:

– hormones, pregnancy and parental behavior in the female rat

– hormones and parental behavior in male and female ring doves

• Link: oxytocin--maternal behavior--social bonds

Hormonal Regulation of Parental Behavior

Parental behavior varies in different species:

Species exhibiting oviparity (egg laying):

• Ex: birds, reptiles, fish

• parental behavior involves:

– laying eggs (and building nests)

– incubating eggs until they hatch

– brooding--care of hatchlings by providing warmth, feeding and protection

Species exhibiting viviparity (birth of live young):

• Ex: rats, mice, horses, primates (humans)

• parental behavior involves:

– care of the young at the time of birth--warmth, feeding (nursing), protection


Three main patterns of parental behavior based on developmental status of young:

Nesting Pattern:

• species with altricial newborn: young that are very immature at birth--cannot

see, hear or move well, nor regulate their body temperature or feed themselves

• require extended parental care (prolonged care in nests)

• Avian species: robins, pigeons, doves

– parental care involves building nests, feeding, warmth, protection (aggression toward

intruders)

– 80% of all bird species are altricial

• Mammalian species: rats, rabbits, cats

– parental care involves building nests, feeding (nursing), licking to stimulate waste

elimination, pup retrieval, and protection



Leading-Following Pattern:

• species with precocial newborn: young that are quite mature at birth--young

have vision, hearing, locomotive ability, and the ability to achieve

thermoregulation

• parental care is limited--young depend on mother for food (may include nursing)

and protection, but soon after birth young can feed themselves

• in many instances, the mother leads the young who follow her

• Avian species: chickens and ducks (10% avian species)

• Mammalian species: ungulates (sheep, cows), guinea pigs, whales



Clinging-Carrying Pattern:

• species with semialtricial/semiprecocial newborn: young are considered

“intermediate” in development compared to altricial and precocial species;

typically, young can hear and see, but require assistance in locomotion

• parental care involves transportation (young will cling to mother or be carried

by her), feeding (nursing), thermoregulation and protection

• Avian species: gulls and terns (10% avian species)

– nestbuilding is minimal, young are fairly mobile and parents feed young special food

which is often regurgitated

• Mammalian species: most primate species (including humans)


What role do hormones play in parental behavior?

• female rat as a model

Broad overview:

• events that occur with mating, fertilization and the start of pregnancy

• events that occur during pregnancy (22 gestation period in the rat)

• events that occur at the end of pregnancy:

– parturition

– lactation

– maternal behavior

– aggressive behavior

– postpartum estrus

Female Rat is a Spontaneous Ovulator:

Ovulation:

• as follicles develop in ovary

– increasing levels of estrogen

are released

– in female rats, increases in

estrogen lead to a GnRH

surge (positive feedback)

– GnRH surge leads to LH

surge

– LH surge leads to ovulation

GnRH Neuron

HYPO

ANTPIT

OVARY

FSHLH

GnRH+

GnRH: gonadotropin-releasing hormoneFSH: follicle stimulating hormoneLH: luteinizing hormone

follicle

“ovulation”

estrogenLH surge

GnRHsurge

Formation of the Corpus LuteumNot Spontaneously Functional:

• corpus luteum will not form unless

female engages in copulation

– Ex: rats

• critical stimulus--vaginocervical

stimulation (e.g., intromissions)

• insertion of penis into vagina by

male during mating will stimulate a

neuroendocrine reflex in the

female leading to release of PRL

which then acts to form the corpus

luteum

• corpus luteum will secrete

progesterone

PRF Neuron

HYPO

ANTPIT

OVARY

PRL

progesterone

PRF+

PRF: prolactin releasing factorPRL: prolactin

follicleegg

“corpus luteum”forms

vaginocervicalstimulation

spinal cord

PRL Neuroendocrine Reflex

Female Rat as a Model

Events that occur with mating, fertilization and the start of pregnancy:

• a female rat has gone through a spontaneous estrous cycle

– increased estrogen lead to a GnRH surge, LH surge and ovulation

– increased estrogen followed by a preovulatory rise in progesterone stimulated proceptive

and receptive behaviors--female mated with a male rat (multiple eggs are released and

fertilized by sperm leading to development of several embryos)

• intromissions associated with mating activated a neuroendocrine reflex leading to

formation of the corpus luteum

– prolactin maintains the corpus luteum

– LH stimulates production of progesterone from corpus luteum (smaller amounts of

estrogen)

– estrogen: important for preparing uterus for implantation

– progesterone: important for implantation of embryo into uterine wall and maintenance

of pregnancy


Events that occur with mating, fertilization and the start of pregnancy:

• a placenta will be formed between each developing embryo and will become

embedded into wall of uterus

• placenta is a high vascularized

organ that allows nutritive

substances and gases in

mother’s blood to diffuse to

embryo and a mechanism for

metabolic wastes to leave

developing embryo

• placenta can also produce

hormones

MOM embryo

nutrients

gases

metabolicwaste

products

placenta


Events that occur during pregnancy:

• pregnancy lasts approximately 22 days in the rat (gestational period)

• progesterone: levels rise shortly after mating and are elevated throughout

pregnancy until near parturition (end of pregnancy)

• estrogen: levels are relatively low during first half of pregnancy, but rise

significantly during the second half of pregnancy

• midway through pregnancy (days 12-13), regulation of ovarian hormone secretion

switches from Mom’s anterior pituitary to the placenta

– LH (released from Mom’s pituitary) is replaced by chorionic gonadotropin

– PRL (released from Mom’s pituitary) is replaced by placental lactogen

– species differences in terms of when, and if, this switch takes place (summarized in

Table 8.1)


1 12 221st Half 2nd Half

OVARY

progesterone(estrogen)

follicle

egg

“corpus luteum”

Placenta

Mom’sAnteriorpituitary

chorionicgonadotropin

placentallactogen

gonadalsteroids

LH

PRL



• mammary glands must develop to provide milk for nursing (lactation)

• full development of the mammary glands requires hormones and stimulation of the

nipples and genital region

• hormonal control:

– progesterone stimulates proliferation of secretory cells located in the alveoli of mammary

gland

– estrogen stimulates duct development (carry milk from secretory cells to nipple)

– prolactin (placental lactogen) stimulates synthesis of milk by secretory cells

– at parturition, with nursing of young, oxytocin (from Mom’s posterior pituitary) will

stimulate release of milk (milk-letdown)

– at parturition, with nursing of young, prolactin (from Mom’s anterior pituitary) will rise

and stimulate milk synthesis



• somatosensory control:

– during pregnancy, the female rat will lick her ventral body region (nipples and genital

region)

– this sensory input is critical for normal development of mammary glands

– Exp. #1: if you block the ability of a female to lick her ventral region by fitting her with a

collar so that she can’t lick her body, mammary development will be significantly

impaired (50% of normal development on day 21)

– Exp. #2: if you take another group of collared females (that cannot lick themselves), and

stimulate them with a brush along the nipples and genital region, you can stimulate full

mammary development


Events that occur at the end of pregnancy:

• levels of progesterone drop

• levels of estrogen remain elevated

• levels of prolactin rise

• These hormonal events (and others) signal the end of pregnancy, initiate labor

(parturition), and initiate maternal behavior and maternal aggression.

• In addition, the process of giving birth--uterine-cervical-vaginal stimulation--

stimulates postpartum estrus:

• 8-11 hours after parturition, females will be sexually receptive and will mate

• 18 hours after parturition, ovulation occurs and the female can become pregnant

(although implantation is delayed while female engages in nursing)


Maternal Behavior:

• 4 components of maternal behavior in the female rat:

– nestbuilding

– pup licking

– nursing

– pup retrieval

• maternal behavior increases gradually during 2nd half of pregnancy--all components

of behavior can be seen 24-48 hours prior to parturition

• maternal behavior lasts for 3-4 weeks


Maternal Aggression:

• aggression displayed toward other adults viewed as “ intruders”

– When an intruder comes near the nest, the mother will approach and sniff the intruder and

then launch an attack that is aimed at the intruder’s neck and head region. The female

bites at the neck of the intruder, climbs its back and pins it in place. The intruder usually

will flee, but if escape is not possible, the intruder will become immobile and may turn

over on its back--freezing and submissive behavior usually terminates the female’s

aggression, although repeated attacks can occur.

• aggressive behavior protects newborn from attacks and cannibalism

• increases gradually during 2nd half of pregnancy--high levels of aggression seen 24-

48 hours prior to parturition

• maternal aggression also lasts for 3-4 weeks


Hormones have two main effects on processes associated with pregnancy:

• hormonal “priming”--action of one or several hormones that prepare the way for

subsequent hormones to produce their effects

– elevations in estrogen and progesterone during pregnancy set the stage for elevated levels

of estrogen to stimulate several events at parturition

• hormonal “triggering”--action of estrogen in triggering or stimulating several

events at the time of parturition

– estrogen levels are elevated while progesterone levels drop

– estrogen acts to stimulate: maternal behavior, aggressive behavior, sex behavior, uterine

contractions and lactation

– estrogen’s actions involve several processes: 1) increased expression of the estrogen

receptor, 2) increased expression of receptors for other hormones, 3) increased synthesis

and release of other hormones


hormonal “priming”

• elevations in estrogen and progesterone during pregnancy stimulate the expression

of estrogen receptors within MPOA (but not within hypothalamus!)

– estrogen receptors within the MPOA reach “peak” levels by day 13 of pregnancy and

remain elevated through day 22 (parturition)

– replicate finding--pretreatment of nonpregnancy females with estrogen and progesterone

for 16 days can elevate estrogens receptors within MPOA

• the “priming” effect of estrogen and progesterone on estrogen receptors within

MPOA is thought to be important for the rapid onset of maternal behavior

– MPOA is important for maternal behavior--lesioning MPOA will block maternal

responses

– estrogen implants in MPOA (in addition to elevated levels of progesterone) can stimulate

maternal behavior in nonpregnance female rats


hormonal “triggering”

• estrogen levels are elevated while progesterone levels drop

• drop in progesterone allows estrogen to stimulate several processes:

– maternal behavior

– sex behavior

– uterine contractions

– lactation

• estrogen’s actions involve several processes:

– increased expression of the estrogen receptor (ER)

– estrogen--ERs-->increased expression of receptors for other hormones: oxytocin

receptors, prostaglandin receptors, prolactin receptors

– estrogen--ERs-->increased synthesis and release of other hormones: oxytocin, prolactin



myometriumof uterus

progesteroneinhibitsuterine

contractility

drop inprogesterone

stimulatesuterine contractility

pregnancy parturition

deliveryof

fetus



myometriumof uterus

drop inprogesterone

estrogen increases ERs in uterus;estrogen-ERs leads to:

increase in oxytocin receptors in uterus

oxytocin stimulatesuterine contractility(posterior pituitary)

increase in prostaglandin receptors in uterus

prostaglandins stimulatesuterine contractility

(uterus)



lactationprogesterone

inhibitsrelease of

prolactin &oxytocin

intobloodstream

increasedrelease of

prolactin &oxytocin


nursing

PRF Neuron

HYPOTHALAMUS

Anterior

MAMMARYGLAND

PRL

PRFPITUITARY

Posterior

Oxytocin Neuron

oxytocin


drop in progesterone

estrogen increases in ERs inneurons in hypothalamus;

estrogen-ERs leads to:

stimulates release ofprolactin from anteriorpituitary and oxytocin

from posterior pituitary

prolactin acts to stimulatemilk synthesis while

oxytocin acts to stimulatemilk letdown (release)



female sexbehavior progesterone

inhibitsdisplay offemale sexbehavior

(inhibitory partof the biphasic

action of progesterone--due

to prolongedexposure)

display ofpostpartum

estrus


continuationof

reproductiveactivities



female sexbehavior

drop inprogesterone

increase in ERs in VMHestrogen-ERs leads to:

display ofproceptive

andreceptivebehaviorsif a maleis present



maternalbehavior maternal behavior

develops graduallyduring gestation,

and is present24-48 hrs

prior to parturition;high levels of

progesterone inhibitrapid display of

maternal behavior

just prior to, andimmediately after,

parturitionfemale shows

maternal behavior(rapid onset)


survivalof

offspring

PRF NeuronHYPO

Anterior

MAMMARYGLAND

PRL

PRFPITUITARY

Posterior

Oxytocin Neuron

oxytocin

hormonal “triggering”drop in progesterone

estrogen increases ERs in neurons in MPOA &

hypothalamus;estrogen-ERs leads to:

increased release of PRL into blood and brain, increased expression of PRL-Rs in MPOA, and maternal behavior

MPOA

prolactin acts at PRL-Rsin MPOA to stimulate

maternal behavior

MaternalBehavior

?

E

E E

+

synergism between estrogen &PRL--1) PRL can stimulate

ERs in MPOA, and 2) estrogen can increase PRL-Rs

and PRL release in MPOA


2 phases to maternal behavior:

• hormonal phase:

– decrease in progesterone, increase in prolactin with elevated levels of estrogen

– hormonal changes are important for the initiation of maternal behavior

– however, once maternal behavior has been initiated, removal of the ovaries, adrenal gland,

pituitary and placenta will not affect behavior (i.e., removal of gonadal steroids and

peptide/protein hormones present within bloodstream)

• nonhormonal phase:

– a transition occurs in which maintenance of maternal behavior depends on stimuli received

from young (pups): suckling by pups at nipple, visual stimuli, auditory stimuli (crying)

– neurocircuits within the brain that process somatosensory, visual, auditory information can

feed into, and stimulate, neurons within MPOA to stimulate maternal behavior

• transition period last approximately one week following parturition

PRF NeuronHYPO

Anterior

MAMMARYGLAND

PRL

PRFPITUITARY

Posterior

Oxytocin Neuron

oxytocin

OLD SLIDE: hormonal “triggering”drop in progesterone



increased release of PRL into blood and brain, increased expression of PRL-Rs in MPOA, and maternal behavior

MPOA


maternal behavior

MaternalBehavior

?

E

E E

+

synergism between estrogen &PRL--1) PRL can stimulate

ERs in MPOA, and 2) estrogen can increase PRL-Rs

and PRL release in MPOA

PRF NeuronHYPO

Anterior

MAMMARYGLAND

PRL

PRFPITUITARY

Posterior

Oxytocin Neuron

oxytocin

NEW SLIDE: hormonal “triggering”drop in progesterone



increased synthesis and release of PRL into blood and brain, and stimulation of maternal behavior

MPOA


maternal behavior(rapid onset)

MaternalBehavior?

E

E E

+

synergism between estrogen & PRL1) PRL may enhance interaction of estrogen to its receptor,2) estrogen can increase PRL synthesis and release

PRL Neuron

E

Interaction Between Estrogen and Prolactin

Estrogen and prolactin both act to facilitate maternal behavior at the level of the MPOA.

How does this occur?

• Prolactin can enhance interaction of estrogen with its receptor

– Ex. Mammary gland

– prolactin changes the form of the estrogen receptor within cytoplasm

– 4S receptor is found in the unstimulated tissue, while 8S receptor is observed following

administration of hormone; 8S form shows increased binding of estrogen

– prolactin changes the form of the estrogen receptor: 4S-->8S (in cytoplasm); thus, prolactin

increases “sensitivity of ERs to estrogen” by changing the form of the receptor (can be thought

of as increasing the number of “functional” ERs)

– estrogen then binds to ER and stimulates its translocation from the cytoplasm to the nucleus;

estrogen bound to ER in the nucleus can then mediate gene transcription

• It is possible that prolactin is stimulating a similar process in MPOA to enhance display

of maternal behavior--however, we don’t have direct proof!


Prolactin can act at the MPOA to stimulate rapid onset of maternal behavior.

– In steroid primed females, administration of prolactin into the MPOA can stimulate rapid

onset of maternal behavior.

– Prolactin neurons exist within the brain and project into the MPOA (as well as within

other brain regions).

– A subset of prolactin neurons within the brain also accumulate estrogen receptors;

estrogen can positively regulate levels of prolactin within the brain..

– There is also evidence that prolactin can be transported from blood into the brain via

specific transporters.

– If you block the rise in prolactin with an inhibitor bromocriptine, you can delay but not

prevent the onset of maternal behavior.

– Prolactin is believed to act by stimulating rapid onset of maternal behavior--critical

because in real life, if mom (or dad) does not care for the pups they will die.


Estrogen and prolactin both act to facilitate maternal behavior at the level of the MPOA.

How do these mechanisms interact? Don’t fully understand...

• Prolactin increases can increase sensitivity of neurons to the effects of estrogen.

• Estrogen is important for the initiation of maternal behavior.

• However, once maternal behavior is initiated, estrogen levels are relatively low, and are

not believed to be important for maintenance of maternal behavior.

• Suckling by pups is one stimulus that has been shown to be important for maintenance of

maternal behavior.

• Suckling increases levels of prolactin within the blood and brain.

• Prolactin is believed to be important for the rapid onset of maternal behavior (which is

critical).

• Blocking prolactin levels delays the onset of maternal behavior but it does not prevent it…

possibility that other mechanisms may also exist to facilitate response.


2 phases to maternal behavior:

• hormonal phase:

– decrease in progesterone, increase in prolactin with elevated levels of estrogen

– hormonal changes are important for the initiation of maternal behavior

– however, once maternal behavior has been initiated, removal of the ovaries, adrenal gland,

pituitary and placenta will not affect behavior (i.e., removal of gonadal steroids and

peptide/protein hormones present within bloodstream)

• nonhormonal phase:

– a transition occurs in which maintenance of maternal behavior depends on stimuli received

from young (pups): suckling by pups at nipple, visual stimuli, auditory stimuli (crying)

– neurocircuits within the brain that process somatosensory, visual, auditory information can

feed into, and stimulate, neurons within MPOA to stimulate maternal behavior

• transition period last approximately one week following parturition


Key differences between hormonal and nonhormonal phases on maternal behavior:

• at parturition, the drop in progesterone allows the rise in estrogen to stimulate

numerous processes including maternal behavior (stimulating the synthesis and

release of hormones and the expression of their receptors)

• once young are born, gonadal steroid levels are relatively low during nursing (even

though female engages in maternal behavior)

• stimuli from pups can maintain maternal behavior in the absence of high levels of

estrogen

– Ex. somatosensory stimuli associated with suckling at the nipple activates a

neuroendocrine reflex leading to increased release of PRL and oxytocin within the

bloodstream, and increased release of PRL within the MPOA

PRF Neuron

HYPO

Anterior

MAMMARY GLAND

PRL

PRFPITUITARY

Posterior

Oxytocin Neuron

oxytocin

MPOA

MaternalBehavior?

PRL Neuron

sucklingat nipple

sucklingat nipple

otherstimuli

otherstimuli

Ring Dove as a ModelBoth male and female ring doves engage in parental behavior.

• Parental behavior:

– nest building, laying of eggs (by female), incubation of eggs, and brooding (care of

hatchlings--warmth, protection, feeding)

– feeding involves producing and regurgitating “crop milk”

• Hormones play a major role in parental behavior in both sexes:

– during courtship and nest building, the levels of estrogen and progesterone are high in

female ring doves, and the level of testosterone is high in male ring doves

– as levels of gonadal steroids drop following courtship and nest building, the female will

lay eggs, and both the male and female ring doves initiate incubation behavior

– rise in prolactin during incubation behavior is important for maintenance of incubation

behavior and for initiation of brooding

– somatosensory cues associated with incubating eggs stimulate prolactin synthesis and

release within bloodstream and brain-->development of the crop gland, production of crop

milk, and display of behaviros to care for young once hatched

Ring Dove as a ModelDuring courtship and nest building:

• gonadal steroids are high

• gonadal steroids stimulate formation of a brood patch:

– brood patch is a defeathered, highly vascularized and edemic (fluid-filled) area

– this region will contact eggs during incubation, providing warmth to egg (important for

development of embryo)

– this region will also provide the parent with somatosensory stimulation important for

maintaining release of PRL

– a brood patch will be seen in male and female ring doves, as they both engage in

incubation behavior

• there are bird species in which neither the mother nor the father incubate eggs

– Ex. brown-headed cowbird

– considered parasitic as female lays her eggs in the nests of other birds

– no brood patch is formed in either the mother or father brown-headed cowbird

Ring Dove as a ModelBoth male and female ring doves incubate eggs--incubation behavior.

• incubation behavior is initiated as gonadal steroids decline and after eggs are layed

• prolactin levels rise midway during incubation:

– maintain incubation behavior

– prepare Mom and Pop for the next stage--brooding: 1) development of crop gland, and 2)

production of “crop milk”

Both male and female ring doves show brooding behavior.

• prolactin levels are high at initiation of brooding behavior

– prolactin maintains crop gland and production of “crop milk”

– prolactin stimulates feeding the young --regurgitation of ”crop milk”

– prolactin stimulates “sitting” on hatchlings to provide warmth

Ring Dove as a Model

Initiation and maintenance of incubation behavior:

drop in gonadalsteroids, and

laying of eggs

remove eggsfrom nest

(initiation)

incubationbehavior

(sitting on eggs)

decrease inprolactin levels

prolactinsynthesis

and release

(maintenance)

“somatosensorystimulation”

decrease inincubationbehavior

administerprolactin

Comparison--Female Rat and Ring Dove

Interesting parallels between female rat and male and female ring doves:

Female Rat Male & Female Ring Dove

estrogen and progesterone prime the brain to respond

to estrogen and PRL to initiate maternal behavior

at parturition

rise in gonadal steroidsprime the brain to

initially show incubation behavior

after laying eggs

shift in control of maternal behavior (nursing, pup

retrieveal, licking) from gonadal steroids to stimuli associated with pups (e.g.,

suckling at nipple)

tactile stimulation fromeggs is important for

maintaining incubationbehavior and for

stimulating brooding responses

PRL plays critical role PRL plays critical role

Documents

Chp 8: Hormone-Behavior Relations in the Regulation of Parental Behavior Overview: Parental behavior evolved to supplement physiological mechanisms of