Developmental Neurobiology 2 - postnatal Flashcards
At what stage of development do we see a much larger proportion of neurons in the brain?
Around 9 months to 2 years, then these decrease as synapses go through pruning process in adulthood
List the five main neural processes involved in postnatal development from newborn to adult
Newborn: proliferation; 1 month: migration; 9 months: synaptogenesis; 2 years: exuberance; to adulthood: pruning
What is Apoptosis?
When cells that haven’t developed or connected properly die
At what stage of gestation do the migration of immune stem cells and expansion of progenitor cells occur?
Around 10-16 weeks
What do short-term and long-term effects of maternal immune activation depend on?
Genetic predisposition, time window of fetal or postnatal brain development, and strength of insult
What does synaptic pruning refer to?
The process of extra neurons or synaptic connections being retracted (or eliminated) to increase the efficiency of neural transmissions
Describe the process of proliferation
Cells divide in the ventricular zone (of neural tube) and form new neurons; some will migrate along radial processes to brain and nervous system, others will undergo cell death (apoptosis)
What occurs during migration and process formation?
Axons (in nucleus, ganglian or cortical layer) elongate towards their different targets
Are all initial synaptic circuits established through to adulthood?
No, some connect to transient targets and will disappear (e.g. cells at top of neocortex will die at postnatal stage)
What do synaptogenesis and process elimination refer to?
Once neurons innervate towards target structures and form synapses with dendrites, the connections are refined and excess neurons are eliminated
How does early and transient spinal (locomotor) activity develop in frogs, and what may this activity direct throughout all vertebrate species?
At embryonic stage (tadpole) electrical activity innervates left & right halves of the tail so they move in an alternated fashion (enables them to swim away from predators); as limbs start to form there’s innervation of the muscles in hind limbs and left & right flexors & extensors are activated at the same time; may direct cerebro-spinal and local spinal circuit formation
Compare the activity of motor neuron clusters and flexor and extensor muscles at embryonic day in rodents to just before birth?
Flexors allow extension of limbs and extensors make complimentary movements; they’re initially synchronous (not coordinated), then before birth, innervation of motor neurons lead to alternate activity patterns (one muscle relaxes as the other contracts to allow for movement)
Describe the stage of selective stabilisation
An additional growth of dendritic branches takes place; dendrites with less trophic support start to regress
What was discovered about ocular dominance columns in the visual cortex of cats?
Some neurons respond exclusively to contralateral input, and others to ipsilateral input (graded responses from 1-7)
What evidence has been found in the visual cortex of both humans and cats to suggest there are critical periods of development?
When eyelids were sutured closed in kittens from birth and re-opened after 2 months, cells only responded to ipsilateral input in the open eye (monocular deprivation); when deprived later in development (12-38 months), there was a reduced number of cells responding but a normal distribution (between both eyes)
What does ocular dominance deprivation in the visual cortex at different developmental stages in humans tell us about critical periods?
There’s less impact on the formation of the columns if deprived later in development (6wks) than straight after birth
How are motor circuits refined throughout the nervous system?
Motor neurons innervate many muscle fibres and more specific projections occur later in development
At birth, many clusters of ganglian cells project to muscle fibres. How does this change during maturity?
There’s more one to one refinement of these projections (development of fine motor skills)
Describe the concept behind Hebbian Plasticity
Cells that wire together fire together; synaptic connections are stronger when their action potentials fire in synchrony (frequency and timing correlate with the output pattern), otherwise they retract
Compare the effects of blocking binocular and monocular spontaneous activity in the lateral geniculate nuclei (in thalamus) of rodents
Blocking one eye (monocular) disrupts the whole system in that hemisphere; but if both eyes are blocked (binocular) you can rescue a pattern of projection from one or both eyes (though not completely)
During development, there’s waves of activity in the retina traveling from one side to the other (retinal waves), what happens to this activity in a mutant mouse and what does this suggest?
There’s a disruption in the waves so their distribution is much broader; suggests that refinement of projections from retina to superior collicus depend on the travelling waves that happen during development
During the critical period of thalamacortical plasticity in mice, there’s an increase in Early Gamma Oscillations (EGOs), then what happens just before 10 days old?
EGOs decline and then Adult Gamma Oscillations start to increase after 2 weeks as the organism starts to explore and gain independence
What’s required to ensure correct targeting of the corpus callosum?
Balanced interhemispheric cortical activity (spatial arrangement is also important)
Neural activity across the developing neocortex starts to become more symmetrical by P13 in which three domains?
Duration, diameter (size) and frequency
Subtle differences in the structured dynamics across the developing neocortex can lead to what kinds of deficits?
Autism and schizophrenia
What has been found after differential stimulation of particular finger digits in owl monkeys, and after digit 3 amputations?
They show a larger representation in the topographic map in neocortex (more neurons respond); after amputations adjacent regions take over and enlarge (rearrangement of cortical maps)
As a person develops into adulthood, synaptogenesis is taken over by what process?
Synaptic reduction; synapses are refined and pruning occurs
What has been found in the motor cortices of professional footballers (e.g. Neymar)?
Smaller amounts of neuron activation than nonprofessionals as they perform more precise movements
What factors contribute to quality of care received by the infant?
Maternal stress, nutrition, sensitivity and deprivation; social behaviour; response to reward; cognitive ability; stress responsivity
A low amount of licking and grooming from the mother of a mouse can lead to what?
Lower levels of GR expression (hormone receptors), leading to high corticosterone and anxiety levels (opposite for high licking and grooming)
What effects has cross-fostering been found to have on anxiety levels of adult mice?
Low-licking behaviour from mother prenatally with high-licking postnatally from surrogate mother leads to low anxiety; high-licking from mum with low-licking from surrogate also leads to low anxiety (combination of genetics and environment)
How has maternal presence been found to influence learning fear and attraction in infancy?
Pairing odor with shock in infant pups; during sensitive period (8 days) pups preferred odor with shock with/without maternal presence; postsensitive period (12-15 d) they learned aversion to odor/shock without maternal presence only; weaning period (21-23 d) they learned odor avoidance with or without maternal presence (making own decisions)
It’s been proposed that problems with MIA (maternal immune activation) and other stressors can lead to what neuronal dysfunctions?
Severe brain malformation (premature death/natural abortion); cerebral palsy; autism; mental illness (depression, schizophrenia); alzheimer’s; parkinson’s disease
How do microglia mediate synaptic pruning?
They’re related to immune response; when cells are dying, inflamed or inactive they’ll eat synaptic parts of neural tissue (e.g. dendrites)
Explain how synaptic pruning by microglia is activity dependent
Surveillance is enhanced when there’s a higher amount of electrical/neuronal activity
An increase in the expression of which complex variation of genes has been found in schizophrenic patients?
Complement Component 4 (C4); relates to immune system; suggests there’s problem in fine synaptic refinement (pruning process)
What are Oligodendrocytes?
They’re glial cells that form myelin sheaths, which provide electrical insulation and enhance the speed of action potentials
The formation of myelinated axons are almost complete by what age?
Between 1 and 3 years old
Explain how the myelination process is selective
Formation of the myelin sheaths depends on electrical activity; Highly active axons are more likely to be myelinated than inhibited axons, whereby the release of vesicles is blocked, leading to retraction and failure to properly form myelin
There is a positive correlation between the length of breastfeeding and what?
The degree of myelination in axonal tracts of infants; and development of sensory-motor functions and language
Which diurnal and social rodent has been used as a model for developmental studies, and uses complex vocalisations and biparental care of the young?
Octogon degus
When newborn octogon degus pups were isolated for an hour daily over a week, what was found?
Anterior cingulate (involved in emotional responses) showed an increased number of dendritic spines; somatosensory cortex remained intact; less spines in the dendate gyrus of the hippocampus
How were the effects of sexual dimorphism suggested in the study with octogon degus pups?
Mothers’ vocalisations rescued separation-induced receptor effects in the prefrontal cortex of female pups only; hearing her voice restored dopamine and seretonine receptors and effects of isolation
Both male and female hormones originate from cholesterol before transformation into other molecules occurs. How is the probability of feminine behaviour in neonates influenced by the mother’s hormones?
It depends on small changes in enzymes and amounts of testosterone in the uterus; these changes are relevant for the formation and maturation of the brain
How do hormones affect the way synapses communicate on the maturing sexual brain?
By differences in gene expression; can promote or inhibit transcription (long and slow or fast and direct responses)
Where are most estradiol-sensitive neurons located in the brain?
Pre-optic area, hypothalamus and amygdala (cells in hypothalamic region are very responsive to sexual molecules)
What region and activity do the reward system (governing sex, drugs, addiction and risky behaviour) recruit?
Basal forebrain (e.g. nucleus accumbens and globus pallidus) and dopaminergic input
What do studies about the monogamy of prairie voles suggest about pair bonding?
Mating with a partner will trigger reward regions of the brain and cause them to keep choosing that same partner
How have dopamine receptors been found to mediate affiliative and aggressive behaviour in pair-bonded males
They display affiliative behaviour more strongly to a partner they’ve been pair bonded with, and are more likely to attack strangers; but if dopamine receptors are blocked this will be eliminated
How are hypothalamic connections involved in sexual functions organised?
Neural connections between anterior (and other regions of) hypothalamus with amygdala, thalamus, neocortex, hippocampus, motor output (via brain stem and spinal cord) and pituitary; hormonal connections to pituitary and endocrine organs (which feedback to the brain regions)
Expression of which two hormones was higher in prairie voles compared to non-monogamous montane voles?
Vasopressin and oxytocin
How was intranasal oxytocin found to modulate social distance to an attractive female in monogamous males?
OT participants in relationships were much less comfortable with a close distance to the female than singles (and placebos), whether there was eye contact or not
Which network of regions are impacted by OT?
Insula, cingulate cortex, MPFC, inferior medial frontal gyrus, amygdala, brain stem and pituitary gland
Pheromone odor from which phase of the menstrual cycle has been found to accelerate ovulation in other females, and odors from which phase delays this process?
Accelerates: follicular phase; Delays: ovulatory phase
Which neural system has been suggested to be involved with processing pheromones?
Accessory olfactory system
Researchers have synthesised two different molecules - AND (female) and EST (male). What have they found when exposing these to males and females
Different brain responses between males and females despite reporting they can’t tell the difference
Similarities in brain responses have been found to putative pheromones in men, between who?
Homosexual males and heterosexual females
