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Overview: 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:

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chp 8 hormone behavior relations in the regulation of parental behavior
Overview:

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

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

Hormonal Regulation of Parental Behavior
hormonal regulation of parental behavior3
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

Hormonal Regulation of Parental Behavior
hormonal regulation of parental behavior4
Three main patterns of parental behavior based on developmental status of young:

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

Hormonal Regulation of Parental Behavior
hormonal regulation of parental behavior5
Three main patterns of parental behavior based on developmental status of young:

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)

Hormonal Regulation of Parental Behavior
hormonal regulation of parental behavior6
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

Hormonal Regulation of Parental Behavior
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

Female Rat is a Spontaneous Ovulator:

GnRH Neuron

HYPO

+

GnRH

GnRH

surge

ANT

PIT

FSH

LH

follicle

LH surge

estrogen

OVARY

“ovulation”

GnRH: gonadotropin-releasing hormone

FSH: follicle stimulating hormone

LH: luteinizing hormone

formation of the corpus luteum
Not 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

Formation of the Corpus Luteum

PRL Neuroendocrine Reflex

PRF Neuron

HYPO

+

PRF

ANT

PIT

PRL

spinal cord

follicle

egg

OVARY

vaginocervical

stimulation

progesterone

“corpus luteum”

forms

PRF: prolactin releasing factor

PRL: prolactin

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

Female Rat as a Model
female rat as a model11
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

Female Rat as a Model
  • 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

metabolic

waste

products

placenta

female rat as a model12
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)

Female Rat as a Model
female rat as a model13
Female Rat as a Model

1

12

22

1st Half

2nd Half

Placenta

OVARY

chorionic

gonadotropin

follicle

LH

egg

Mom’s

Anterior

pituitary

placental

lactogen

PRL

“corpus luteum”

gonadal

steroids

progesterone

(estrogen)

female rat as a model14
Events that occur during pregnancy:

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

Female Rat as a Model
female rat as a model15
Events that occur during pregnancy:

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

Female Rat as a Model
female rat as a model16
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)

Female Rat as a Model
female rat as a model17
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

Female Rat as a Model
female rat as a model18
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

Female Rat as a Model
female rat as a model19
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

Female Rat as a Model
female rat as a model20
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

Female Rat as a Model
female rat as a model21
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

Female Rat as a Model
female rat as a model22
hormonal “triggering”Female Rat as a Model

pregnancy

parturition

progesterone

inhibits

uterine

contractility

drop in

progesterone

stimulates

uterine contractility

myometrium

of uterus

delivery

of

fetus

female rat as a model23
hormonal “triggering”Female Rat as a Model

myometrium

of uterus

drop in

progesterone

estrogen increases ERs in uterus;

estrogen-ERs leads to:

oxytocin stimulates

uterine contractility

(posterior pituitary)

increase in oxytocin

receptors in uterus

prostaglandins stimulates

uterine contractility

(uterus)

increase in prostaglandin

receptors in uterus

female rat as a model24
hormonal “triggering”Female Rat as a Model

pregnancy

parturition

lactation

progesterone

inhibits

release of

prolactin &

oxytocin

into

bloodstream

increased

release of

prolactin &

oxytocin

nursing

slide25
hormonal “triggering”

drop in progesterone

HYPOTHALAMUS

estrogen increases in ERs in

neurons in hypothalamus;

estrogen-ERs leads to:

PRF Neuron

Oxytocin Neuron

PRF

PITUITARY

stimulates release of

prolactin from anterior

pituitary and oxytocin

from posterior pituitary

Posterior

Anterior

oxytocin

PRL

prolactin acts to stimulate

milk synthesis while

oxytocin acts to stimulate

milk letdown (release)

MAMMARY

GLAND

female rat as a model26
hormonal “triggering”Female Rat as a Model

pregnancy

parturition

female sex

behavior

progesterone

inhibits

display of

female sex

behavior

(inhibitory part

of the biphasic

action of

progesterone--due

to prolonged

exposure)

display of

postpartum

estrus

continuation

of

reproductive

activities

female rat as a model27
hormonal “triggering”Female Rat as a Model

female sex

behavior

drop in

progesterone

increase in ERs in VMH

estrogen-ERs leads to:

display of

proceptive

and

receptive

behaviors

if a male

is present

female rat as a model28
hormonal “triggering”Female Rat as a Model

pregnancy

parturition

maternal

behavior

maternal behavior

develops gradually

during gestation,

and is present

24-48 hrs

prior to parturition;

high levels of

progesterone inhibit

rapid display of

maternal behavior

just prior to, and

immediately after,

parturition

female shows

maternal behavior

(rapid onset)

survival

of

offspring

slide29
hormonal “triggering”

E

E

E

drop in progesterone

estrogen increases ERs in

neurons in MPOA &

hypothalamus;

estrogen-ERs leads to:

MPOA

Maternal

Behavior

?

+

HYPO

PRF Neuron

Oxytocin Neuron

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

PRF

PITUITARY

Posterior

Anterior

prolactin acts at PRL-Rs

in MPOA to stimulate

maternal behavior

oxytocin

PRL

synergism between estrogen &

PRL--1) PRL can stimulate

ERs in MPOA, and

2) estrogen can increase PRL-Rs

and PRL release in MPOA

MAMMARY

GLAND

female rat as a model30
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

Female Rat as a Model
slide32
OLD SLIDE: hormonal “triggering”

E

E

E

drop in progesterone

estrogen increases ERs in

neurons in MPOA &

hypothalamus;

estrogen-ERs leads to:

MPOA

Maternal

Behavior

?

+

HYPO

PRF Neuron

Oxytocin Neuron

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

PRF

PITUITARY

Posterior

Anterior

prolactin acts at PRL-Rs

in MPOA to stimulate

maternal behavior

oxytocin

PRL

synergism between estrogen &

PRL--1) PRL can stimulate

ERs in MPOA, and

2) estrogen can increase PRL-Rs

and PRL release in MPOA

MAMMARY

GLAND

slide33
NEW SLIDE: hormonal “triggering”

E

E

E

E

drop in progesterone

estrogen increases ERs in

neurons in MPOA &

hypothalamus;

estrogen-ERs leads to:

MPOA

Maternal

Behavior

+

?

PRL Neuron

HYPO

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

PRF Neuron

Oxytocin Neuron

PRF

prolactin acts at PRL-Rs

in MPOA to stimulate

maternal behavior

(rapid onset)

PITUITARY

Posterior

Anterior

oxytocin

PRL

synergism between estrogen & PRL

1) PRL may enhance interaction

of estrogen to its receptor,

2) estrogen can increase PRL

synthesis and release

MAMMARY

GLAND

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!

Interaction Between Estrogen and Prolactin
interaction between estrogen and prolactin35
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.

Interaction Between Estrogen and Prolactin
interaction between estrogen and prolactin36
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.

Interaction Between Estrogen and Prolactin
female rat as a model37
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

Female Rat as a Model
female rat as a model38
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

Female Rat as a Model
slide39

MPOA

other

stimuli

Maternal

Behavior

other

stimuli

?

HYPO

PRL Neuron

PRF Neuron

Oxytocin Neuron

PRF

PITUITARY

Posterior

Anterior

oxytocin

PRL

suckling

at nipple

suckling

at nipple

MAMMARY GLAND

ring dove as a model
Both 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 Model
ring dove as a model41
During 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 Model
ring dove as a model42
Both 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
ring dove as a model43
Initiation and maintenance of incubation behavior:Ring Dove as a Model

remove eggs

from nest

drop in gonadal

steroids, and

laying of eggs

decrease in

prolactin levels

(initiation)

incubation

behavior

(sitting on eggs)

decrease in

incubation

behavior

(maintenance)

“somatosensory

stimulation”

prolactin

synthesis

and release

administer

prolactin

comparison female rat and ring dove
Interesting parallels between female rat and male and female ring doves:Comparison--Female Rat and Ring Dove

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 steroids

prime 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 from

eggs is important for

maintaining incubation

behavior and for

stimulating brooding responses

PRL plays critical role

PRL plays critical role