Lecture 9 The chemistry of social bonding – hormones of love and attraction in man and animals II Flashcards
maternal care innate?
Onset of maternal care involves a switch in the valence of pup stimuli, resulting from inhibition of avoidance and activation of approach neural systems in response to infant stimuli.
non selective recognition?
A non-selective recognition typically occurs in mothers that give birth to altricial young, lots of young
maternal care is directed toward generic infant stimuli rather than to particular infants, and mothers will care for any conspecific infant throughout the postpartum period.
General infant stimuli are recognized as positive, rather than negative, social stimuli.
selective recognition?
A selective recognition operates in mothers that give birth to precocial young (e.g. sheep), or semi-mobile young (e.g. primates)
selective maternal care is ultimately directed toward the particular offspring that the mother gives birth to, while other (alien) young are rejected.
Key role for early olfactory cues in selective offspring recognition
what happens if virgin rats are continuously exposed to healthy pups?
maternal behaviour
eventually occurs.
around 7 days (sensitization latency).
will even show nursing behaviour despite not being able to lactate and feed.
mothers can’t show such delay, pups would die of neglect, therefore hormal events occuring at the end of pregnancy must allow for immediate materal responsiveness at parturition.
oxytocin in mother infanct bonding?
oxytocin injections induce maternal behaviour in mice/rats/sheep (dolly aw).
can cause non pregnant females to accept alien lambs.
intracerebroventricular injection to virgin female rats display full maternal behaviour within 1 hour.
sex drive?
Testosterone = strongest sexual motivation in males and females
Estrogens also increase female sex drive
progesterone alone can inhibit sex drive, but in combination with oestrogen increases female sexual motivation.
timing to increase just before ovulation, maximise changes of pregnart. high estrogen low progest in humans.
pheromone sensing behaviour throughout mice estrus cycle?
5 day cycle.
test response to males.
durign oestrust increases attraction, due to VNO response.
Fluctuations in progesterone during oestrous cycle can alter attraction related pheromone sensing in VNO (in mice) decrease sexual motivation.
effects of progesterone and oestrogen during pregnancy?
progesterone helps to suppress immune responses of the mother to fetal antigens, which prevents rejection of the fetus
progesterone inhibits uterine contractions
Oestrogens and progesterone stimulate lobular alveolar growth (facilitating milk production). Also drives prolactin production
increasing ratio of estrogen to progesterone makes uterine smooth muscle more sensitive to stimuli that promote contractions (e.g. OT)
how do hormones change during pregnartcy?
huge surge in oestrogens in the lead up to birth, both humans and rats, almost all animals.
humans - Rise in circulating estrogen and progesterone secreted by the ovaries during pregnancy, followed by the precipitous drop in progesterone at the end of pregnancy, signals that parturition is eminent
oxytocin in labour?
stimulates contractions, positive feedback which also releases oxytocin in the brain/PVN
how to induce maternal behaviour?
sheep?
Vagino-cervical stimulation (VCS) can mimic effects of birth and stimulate maternal behaviour and selective bonding
Diminished with oxytocin antagonist
just as good as oxytocin injections.
how is maternal behaviour primed immediately?
Maternal behaviour is primed at end of pregnancy and by parturition
High oestrogen/progesterone ratio
OT release into the brain from VCS
OT release stimulated by suckling (again via brainstem relay to PVN)
These actions on the brain stimulate the immediate onset
of maternal behavior at parturition.
BUT once maternal behavior becomes established during the early postpartum hours, enduring attraction between a mother and her infant(s) persists after the hormonal events that activated the behavior have waned
(i.e. independent of hormone signals)
bit of a summary
During late pregnancy, receptors for OT are up-regulated in both the brain and the uterus in response to elevated oestrogen levels.
OT synthesized in the hypothalamic neurons, is released into the brain at birth, facilitating olfactory recognition of offspring, aiding parturition and stimulating the onset of maternal care.
The maintenance of maternal behaviour during lactation also involves OT (but also prolactin and dopamine (DA) systems).
MPOA
medial preoptic area (MPOA) and the adjoining bed nucleus of the stria terminalis (BST) are essential components of the neural circuitry regulating maternal behavior
MPOA neurons are robustly activated by pup stimuli
OT administration into the MPOA increase maternal behavior in rats
MPOA activity is necessary for maternal behaviour in sensitized virgin rats
MPOA is essential for maternal motivation in ewes as depression of MPOA activity blocks the onset and maintenance of maternal behavior
MPOA destruction?
Destruction of the MPOA/BST abolishes maternal care (rats/sheep)
inputs to MPOA?
PVN produce oxytocin and send there. PVN primarily responsive to suckling/VCS
stimuli go through amygdala to MPOA.
estradiol stimulates the expression of OT receptors in MPOA.
OT at the MPOA (from PVN activation by VCS and suckling) is essential for the onset of maternal behaviour at parturition in rats
MPOA outputs?
DOP OUTPUTS
MPOA –> VTA –> NAc
NMPOA –> PVN —> VTA
testing sensitization latency and NAc
rats allowed 1h of postpartum maternal experience and then the pups removed. Immediately after this 1h experience, DA receptor antagonists, an OTR antagonist (OTA), or control solutions were injected into NAs.
Ten days later, females were re-exposed to young foster pups on a daily basis and sensitization latencies for the re-initiation of maternal behavior were recorded.
D1 or D2 blockade increases sensitization latency slightly.
Blockade of both D1 and D2 receptors in NAs effectively disrupted maternal memory, back to virgin state - 7 days.
blockade of OT receptors in NAs also disrupted maternal memory formation.
limbic motor integration?
“limbic-motor integration”
VP is a major motor output relay for reward systems
VP GABA inputs from NAc, sits behind NAc.
when dopamine high, inhibits NAc, which lessens inhibition of VP
big ol summary of pathways on podcast.
ye watch that again m8.
VTA signal in humans when responding to own children
fMRI big ol signalling, same pathways as ratbois.
avoidance areas activate when not own child
testosterone humen
In many species, testosterone supports mating effort at the
expense of parenting effort.
selectivity of mother infant bond
Selective maternal recognition involves neural plasticity within both the olfactory bulbs and the amygdala.
VCS activates norepinephrine (NE) and OT release into the olfactory bulbs, which may influence the particular types of lamb stimuli that are relayed to the amygdala
NE release into the olfactory bulbs is necessary for the development of maternal selectivity
Inhibition of neural communication in the amygdala can disrupt the development of maternal selectivity without interfering with ongoing maternal motivation (Ewes showed maternal behavior toward their own and alien lambs, while control females only cared for their own lamb).
testis size
Testes size is also correlated with increased investment in mating, both across and within nonhuman species
In human fathers, testes size has a significant negative correlation with instrumental caregiving. Testes size also has a robust inverse correlation with the VTA activation in response to viewing pictures of one’s own child
summary of oxytocin brain regions
Activation of the PVN causes the release of OT
into several different brain regions
OT release into MPOA, VTA, and NAc boosts maternal motivation and attraction to young at parturition.
OT and DA release into NAc promotes the synaptic plasticity within the NAc–VP circuit so that maternal attraction to young persists throughout the postpartum period in the absence of continued pregnancy hormone stimulation.
In species that form selective attachments to particular young, OT action on the olfactory bulbs and amygdala (MeA/CoA) influences the development of selective recognition.
