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||Sensory factors in maternal behaviour|
After studying the material on this page you should be able to:
Human maternal behaviour
It is perhaps not surprising that women become increasingly focussed on the process of motherhood (maternal engrossment) as pregnancy advances, and after the baby is born. However, towards the end of pregnancy there may be a slight dip in the woman's self-image (Fleming et al, 1990).
"Over the centuries, the attachment between a mother and her newborn infant has been considered a natural process and it is expected of the mother to care for and nurture her infant. However, the process by which a mother and her baby develop a close relationship is not clearly understood. It is known that maternal behavior is influenced by multiple factors that include the mother's own upbringing, socioeconomic conditions, her cultural beliefs and background, her relationship with her father, as well as her experiences with present and past pregnancies. ... eye-to-eye contact may be an important factor in enhancing maternal behavior " (Sosa, 1980).
Eye to eye contact may qualify as a universal or fixed action pattern.
"..given the frequent news reports of women failing to care for their newborn infants, i.e. a lack of the onset of maternal behavior, this is not a health problem of trivial significance. Certainly there are cultural and social influences involved in these tragic instances of infanticide, but there are also likely to be biological ones as well." McCarthy (1997).
One of the most striking aspects of maternal behaviour is how much we take it for granted. We assume that mothers will look after their children and society expresses outrage when things go wrong. A breakdown of normal maternal behaviour is so unusual that it makes headline news as in these two cases.
In August 1999 a young mother threw her three-year-old son into the back of a dustcart because she thought he was "rubbish". The woman was suffering from paranoid schizophrenia and thought all her problems would go away if her child died. Fortunately the lorry's machinery was switched off and dustmen rescued the boy before he could come to any harm. Obviously this tragic case can be expained on the basis of the mother's incapacitating illness, but sometimes maternal care crumbles in the face of apparently normal circumstances.
Samantha Watts came from a respectable family and had a full-time job, but she concealed her pregnancy from family and friends. She allowed her 11-month-old baby to starve to death while her cupboards were full of food. Watts was jailed for life in September 2000.
These cases illustrate that we tend to take 'mother love' for granted. But a moment's reflection shows that if we do not understand why maternal behaviour sometimes breaks down, then we do not understand how it works in normal circumstances. I call this an example of 'the riddle of the ordinary'.
of maternal behaviour at
|For obvious reasons,
most of our knowledge about the biological bases of maternal behaviour
has come from studies of animals. For example, it would be unethical to
artificially manipulate hormone levels in women in order to investigate
the role of hormones in their behaviour. Nevertheless it is possible
that the principles governing such an important behaviour that emerge
from studies of animals may be echoed in the behaviour of our own
This section of the lecture will outline some of the hormonal factors that regulate maternal behavior in the rat.
Studies of maternal behaviour in rats have been concerned with
Maternal behavior is thought to be influenced by hormonal conditions that exist during pregnancy but sensory stimuli provided by the offspring are also important in initiation and maintenance. The idea that maternal behavior is "switched on" and maintained by hormones and sensory factors and maintained by sensory stimulation is central to this lecture.
behaviour is an attractive behaviour to study because it consists of a
number of clear-cut behaviours
Maternal behavior in rats and mice consists of the following elements:
In this photograph the dam is shown on her back suckling pups. Normally mothers crouch over pups in the 'nursing posture'. This picture shows an anaesthetized mother, and was taken during a research programme into the role of sensory cues in suckling behaviour .
Onset of maternal behaviour
|Here is an animated version of this diagram|
Hormone levels during pregnancy
observation that blood transfusions from maternal rats induced maternal
behaviour in nonpregnant females, suggested that hormones may play an
important role in switching on (initiating) maternal
behavior. The diagram illustrates the dramatic changes in hormone
levels around parturition in rats. Similar changes occur during human
Is this cluster of hormonal changes responsible for switching on maternal behavior ? It is difficult to study the role of hormones in natural pregnancy because if you inject or remove hormones during pregnancy there are multiple effects on lactation and behavior that are difficult to disentangle.
|Here is an animated version of this diagram|
Hormones and maternal behaviour
Jay Rosenblatt examined the hypothesis that the decline in progesterone level seen towards the end of pregnancy triggers the onset of maternal behaviour. In order to produce a decline in progesterone level, pregnant rats were hysterectomised.
Hysterectomy and ovariectomy in the rat: what is involved?
Before we can explore the effects of this operation on maternal behaviour here are some diagrams that help to explain what is removed in the hysterectomy and ovariectomy operations that were used by Rosenblatt in these studies.
|This diagram shows the
relative position in the rat of the:
In mammals the fertilied egg passes through several stages before birth:
Rats normally give birth to large families of pups! A pregnant uterus can contain 16 or more unborn pups.
Examine the effects of hysterectomy and ovariectomy
Maternal behaviour after hysterectomy
Hysterectomy involves removing the uterus which contains the pups and causes progesterone level to fall.
Rosenblatt reasoned that if a decline in progesterone is responsible for the initiation of maternal behaviours at the end of a normal pregnancy, then we would expect to see the onset of these behaviours in hysterectomised rats as progesterone declines after the operation .
The diagrams show the effect of hysterectomy on
levels during pregnancy & after hysterectomy
This diagram shows falling progesterone level in intact pregnant rats, and rats that were hysterectomised (H) on day 10, 13, 16 or 19 of their pregnancy
behaviour after hysterectomy
diagram shows the cumulative percentage of females showing maternal
behaviour following hysterectomy (H) on day 10, 13, 16 or 19 of
pregnancy . The first test (0) of maternal behaviour was given 48 hours
after surgery, and testing continued for a further 5 days.
|Here is an animated version of this diagram||Here is an animated version of this diagram|
At first the mother rat pays no attention to the pups, but with time
she begins to show maternal behavior . Hysterectomy during pregnancy
produces a decline in progesterone and stimulates the onset of maternal
behavior .The later in pregnancy the rat is hysterectomised, the
greater this effect is.
Notice how hysterectomy and parturition are both associated with a decline in progesterone and an increase in maternal behavior .
The next question is: 'Are these changes causally linked?' Does the decline in progesterone trigger the onset of maternal behavior, or does the effect depend on some other effect of the operation?
Maternal behaviour after hysterectomy + ovariectomy
|In further experiments, Rosenblatt investigated the possibility that changes in estrogen level were responsible for the emergence of maternal behaviour after hysterectomy. In his first series of studies he removed the ovaries (ovariectomy) from hysterectomised pregnant rats at various stages of pregnancy. You can see the results in the slide below.|
Effect of estrogen on maternal behaviour after hysterectomy + ovariectomy
|In this experiment the
behaviour of three groups of prgnant rats was comapred. These rats were
diagram shows the cumulative percentage of 10 day pregnant rats
exhibiting maternal behaviour after hysterectomy or
hysterectome-ovariectomy plus estradiol benzoate treatment (100 or 200
microgram/kg). Maternal behaviour tests began 48 hours after surgery
and hormone injection.
This result suggests that estrogen stimulates maternal behavior when progesterone levels are low. Recall that estrogen rises and progesterone declines at the end of a normal pregnancy.
However estrogen stimulates prolactin release so these effects may involve prolactin which increases dramatically around birth. This explanation is thought unlikely because blocking the release of prolactin with ergocornine or apomorphine does not interfere with the ability of estrogen to stimulate maternal behaviour. Consequently, the initiation of maternal behavior is probably caused by estrogen.
Summary table:Effect of hormones on maternal behaviour
|Treatment||Effect on hormones||Effect on maternal behaviours|
|Remove uterus (hysterectomy)||Progesterone
|Remove uterus & ovaries (hysterectomy+ovariectomy)||Progesterone
|Administer estradiol & ergocornine (blocks prolactin)||Estradiol
Although these experiments show that it is possible to facilitate the onset of maternal behaviour by manipulating progesterone and estrogen levels it is clear that none of these manipulations on their own are able to reproduce the rapid onset of maternal behaviour seen under normal conditions.
Oxytocin elicits rapid onset of maternal behaviour
In labour, minor contractions of the uterus may begin spontaneously because of the reversal of progesterone dominance. These contractions may serve as the stimulus for oxytocin secretion, which then augments and intensifies uterine contractions and leads to delivery.
Oxytocin is normally seen as primarily involved in the milk letdown reflex and in the stimulation of uterine smooth muscles during parturition. Pedersen et al,(1982) claimed that injection of oxytocin into the brain can lead to a rapid onset of maternal behaviour.
This diagram is a dose response plot of the percentage of virgin female rats displaying full maternal behaviour within 1 hour after receiving an intracerebroventricular (injection into the ventricles of the brain) injection of oxytocin given 48 hours after ovariectomy and priming with estrogen.
These results are potentially very important because they are the first indication that a chemical factor could be responsible for the rapid initiation of maternal behaviours seen shortly after parturition.
However the interpretation of Pedersen's data has been challenged by Wambolt & Insel (1987).
McCarthy (1997) reviews a series of experiments by Fahrbach et al (1984) that resolved this controversy.
factors in maternal behaviour
Maternal behaviour declines after pup removal
In the rat, maternal behaviour continues for about 28 days until the pups are weaned onto solid food, but it declines rapidly if pups are removed at parturition. This prompts several questions:
There is not much evidence that hormones are involved in the maintenance of maternal behaviours:
Therefore the consensus of opinion holds that pup stimulation may maintain maternal behavior postpartum .
contact establishes maternal behaviour
There appears to be a transitional period just after birth during which a bond is formed between rat pups and their mother. This occurs in the first few hours or minutes postpartum.This effect is reminiscent of human mothers who learn to distinguish the odour of their child after just a few hours exposure.
The diagram shows the results of several experiments in which the amount of contact between the mother rat and her pups was varied.
If the mother's pups are delivered by Caesarean section so that she has no opportunity to interact with them then her maternal behaviour takes a long time to develop when she is given foster pups to look after 25 days after her pups were delivered artificially.
Similarily if the mother is allowed to deliver her litter of pups normally, but the pups are immediately removed so that she has no contact with them she will take a long time to exhibit maternal behaviour to foster pups when these are given to her 25 days after the birth of her own litter.
But if dams are allowed contact with pups during parturition,then the pups are removed and test pups are given to her 25 days later she will behave maternally towards these foster pups within two days.
The figure also shows another surprising result. Virgin females will exhibit maternal behaviour towards pups, but only after they have been exposed to them for several days.
This effect has been known since the 1930s - it is called sensitization This process is thought to involve virgins coming to terms with the odour of pups which they initially find repulsive, and maternal behaviour can be elicited from male rats as well.
Davis (2002) WebMD Feature Stress and the sexes
Shelley E. Taylor, PhD, a psychology professor at UCLA and author of The Tending Instinct suggests that new research -- drawing on psychology, genetics, evolutionary biology, and neuroscience -- shows that there are distinct differences in how men and women react to stressors or aggressors. While men will fight -- or simply hide -- women have a stronger instinct to "tend and befriend".
A woman is biologically hard-wired to nurture, provide comfort, and seek social support in times of stress, Taylor writes. Our hormones, brain chemistry, and response to the world around us all reflect this natural instinct. Men have this instinct too, but to a lesser degree because of hormone differences and personal choices, she says. more ...
Dissanayake (2002) "The Poetics of Baby Talk" Presented at Darwinian Feminism. Special Session, South Central Modern Language Association Meeting, Austin, Texas., October 31-November 2, 2002
Dissanayake suggests that suggests that humans are born with natural (innate, universal) predispositions to interact as ,and with, babies.
Gammie, January 4, 2001 Maternal Aggression in Mice. Requires RealAudio and RealVideo
Scientists studying the origins of aggression have highlighted areas in the brains of mouse mothers that may generate fierce attacks on males who pose a potential threat to their pups. Postdoctoral researcher Stephen Gammie recently explained the research and findings in a brief video. View the video. Requires RealAudio and RealVideo
Varendi (2001) Human newborn behavior during exposure to maternal and other odors. Published by The Karolinska Institutet Dissertation Database.
From the abstract: "Olfaction appears to play a pivotal role in immediate postnatal interactions between mammalian mothers and their offspring. The present study examined:
...the newborn and its mother communicate by means of olfaction. Several common hospital care routines such as washing the baby immediately after birth and the mother's breasts before feeding interfere with this communication and should be avoided until we know more about its clinical significance. "
Mayo Clinic in Rochester( 2001). Changes in Hormone Levels in Men Who Become Fathers
A published study of hormonal changes in a group of Canadian men becoming fathers for the first time showed a decrease in testosterone and cortisol levels and a higher level of estradiol concentrations, a hormone known to influence maternal behavior. more ...
Most literature on postpartum psychiatric disorders accepts the premise that there are three general categories of postpartum disturbance, along a spectrum of increasing severity: "blues," depression, and psychosis.1-3 The most benign and most common condition is postpartum blues, experienced by approximately 50% of women who give birth. The blues are usually characterized as a mild, self-limited form of depression. There is a growing body of evidence to suggest that the term postpartum blues is a misnomer. This article reviews data supporting the idea that the blues are experientially and biologically distinct from depression . Rather, they are a normal state of psychophysiologic reactivity that facilitates attachment and maternal behavior. Reconceptualizing the blues this way should change the focus of research from variables relevant to depression to variables relevant to attachment. It may also foster a greater clinical understanding of attachment and disorders of attachment.
are called "a biological underclass" and "a lost generation." Those are
just two of the milder name tags attached to the children we have come
to believe were permanently damaged by their mothers' use of cocaine.
The poster in maternity clinics conjure up the same image of the
prenatally doomed: "Some people who smoke crack never get over it." The
schools too have been put on emergency alert: "The crack babies are
coming, the crack babies are coming." Indeed, the phrases "crack
babies" and "crack kids" are shorthand for monster-children who are
born addicted. These are the kids destined to grow up without the
ability to pay attention or to learn or to love. But just when the name
has stuck, it turns out that "crack baby" may be a creature of the
imagination as much as medicine, a syndrome seen in the media more
often than medicine.
study of rat brains may offer hope to women who reject their babies.
Published in New Scientist 13/12/97
The Daily Mail (30th April, 1998) announced it as a "PMT Breakthrough" and explained that "Pre-menstrual syndrome and postnatal depression are closely related to the 'cold turkey' experienced by addicts trying to give up drugs ..". Here is the description of the research given in Nature.
GABA receptor a4 subunit suppression prevents withdrawal properties of an endogenous steroid. Nature 392, 926 (1998)
"The hormone progesterone is readily converted to 3a-OH-5a-pregnan-20-one (3a,5a-THP) in the brains of males and females. In the brain, 3a,5a-THP acts like a sedative, decreasing anxiety and reducing seizure activity, by enhancing the function of GABA (g-aminobutyric acid), the brains major inhibitory neurotransmitter. Symptoms of premenstrual syndrome (PMS), such as anxiety and seizure, susceptibility, are associated with sharp declines in circulating levels of progesterone and, consequently, of levels of 3a,5a-THP in the brain. Abrupt discontinuation of use of sedatives such as benzodiazepines and ethanol can also produce PMS-like withdrawal symptoms. Here the authors report a progesterone-withdrawal paradigm, designed to mimic PMS and post-partum syndrome in a rat model. In this model, withdrawal of progesterone leads to increased seizure susceptibility and insensitivity to benzodiazepine sedatives through an effect on gene transcription. Specifically, this effect was due to reduced levels of 3a,5a-THP which enhance transcription of the gene encoding the a4 subunit of the GABAA receptor. The authors also find that increased susceptibility to seizure after progesterone withdrawal is due to a sixfold decrease in the decay time for GABA currents and consequent decreased inhibitory function. Blockade of the 4 gene transcript prevents these withdrawal properties. PMS symptoms may therefore be attributable, in part, to alterations in expression of GABAA receptor subunits as a result of progesterone withdrawal. "
Reference: S S Smith, Q H Gong, F-C Hsu, R S Markowitz, J M H ffrench-Mullen & X Li, GABAA receptor a4 subunit suppression prevents withdrawal properties of an endogenous steroid. (Letter to Nature) Nature 392, 926 (1998)
Thanks to Bernadette Millmore (Yr2) for bringing my attention to this research.