ANAT 322 Lecture Notes - Lecture 9: Solitary Tract, C-Fos, Receptor Antagonist
7 Jun 2018
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ANAT 322 Winter 2017
Lectures
Lecture 9:
→ Parturition and Lactation
1. Oxytocin is what people call the love hormone but it does a lot more things.
2. Vasopressin and oxytocin are similar peptides that are very short, only 9 amino acids, and these are
found in magnocellular neurons of the paraventricular nucleus (PVN) but also in the supraoptic nucleus
(SON).
3. Oxytocin has many different functions but one of the important roles is during parturition or birth and
lactation or suckling so it is important to produce uterine contractions for delivery and it is also
important for the milk ejection reflex.
It has neuroendocrine, cognitive, social, osmoregulation (together with vasopressin), emotional and
autoregulatory effects so it is a multifaceted hormone.
4. It plays an important role in the contraction of smooth muscle cells in the uterus so oxytocin
receptors are upregulated in the uterus. In lactation, oxytocin stimulates smooth muscle contraction and
it will increase intermammillary pressure which will lead to milk delivery.
Other hormones are implicated in lactation such as progesterone, glucocorticoids, estrogens and
prolactin.
Oxytocin is released in bursts so there is bursts of secretion (opposite to tonic secretion). Its release
can be triggered by the cry of a baby even if the mother is not nursing anymore. Oxytocin is released
under certain stress conditions as well so maybe there is an association between these two.
5. Studies showing the release of oxytocin in the SON during different events. Parturition leads to higher
increases in oxytocin followed by suckling. This is not the case for vasopressin which is not as responsive
for those conditions.
6. Oxytocin is released in the posterior pituitary, like vasopressin, where long axons project and it is this
oxytocin that will have the systemic effects in both the uterus and in the mammillary glands.
It is the central mechanisms that regulate the oxytocin secretion and people have found recently that
kisspeptin fiber density around oxytocin neurons (magnocellular) in the supraoptic nucleus increases in
late-pregnant rats. These fibers originate form the kisspeptin neurons in the periventricular nucleus and
these fibers go around towards the supraoptic nucleus (not within it). It is though that this stimulates
the release of oxytocin at the level of the supraoptic nucleus.
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ANAT 322 Winter 2017
Lectures
7. Illustration of kisspeptin fiber density in a non-pregnant animal and at different gestation times. There
is increase of fiber density around the supraoptic nucleus or the perinuclear zone.
8. If we look at the kisspeptin neurons in the periventricular zone, of a non-pregnant animal and a day
before parturition, we can see a large increase in kisspeptin expression in those neurons in the small
layers of the periventricular zone.
So what triggers the oxytocin neurons closer to parturition is probably through kisspeptin activation
of oxytocin.
9. Other changes occur in the supraoptic nucleus neurons in late pregnancy and lactation and this has to
do with the morphological coupling of these neurons. Those neurons start to be more coupled together
so glial cells retract which allows the neurons to interact more closely and there is a lot of appositions
among adjacent cell bodies. This allows for coordinated metabolism among those neurons and
coordinated electrical activity which is promoted because we have increase somatic appositions and
contact among dendrites.
The contact among dendrites in supraoptic neurons leads to a process called dendritic priming. This is
helping enhanced the release of oxytocin both in terms of the release into the general circulation
through the posterior pituitary and the local release of supraoptic oxytocin. Oxytocin released in the
brain can act in many different areas and affect behaviors and social bonding.
10. Study that shows the increase somatic apposition in oxytocin neurons in the SON. There is a large
increase in the soma contacts between oxytocin neurons with advanced gestation. During lactation the
morphological changes remain but then they will disappear.
If we have a second lactation, the same process occurs but it maybe last longer (diparous, black bars)
compared to primiparous in which there is only one pup. This system has evolved to increase the
coordination of activity between oxytocin neurons so we can produce a milk-injection reflex.
11. Normally, we have an oxytocin neuron that is responsive to electrical stimulation and the response
of that neuron is to secrete oxytocin through the posterior pituitary into the general circulation. Some
signals around can mobilize intracellular Ca2+ stores so oxytocin itself can do that or other peptides such
as α-MSH that can prime the oxytocin neurons.
We have some oxytocin floating around in the neuron and it will increase intracellular Ca2+ stores
and produce the dendritic release. There is no release into the posterior pituitary but this is strictly
dendritic release which primes the large dense core vesicles containing oxytocin in the dendrite to move
from a storage pool to a readily releasable pool. Next time there is a stimulation of the oxytocin neuron,
we get both the release into the posterior pituitary and dendritic release. So if oxytocin is released
there, it will act on nearby neurons and that will prime the next neurons which is why we can have a
find more resources at oneclass.com
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Document Summary
In lactation, oxytocin stimulates smooth muscle contraction and it will increase intermammillary pressure which will lead to milk delivery. Other hormones are implicated in lactation such as progesterone, glucocorticoids, estrogens and prolactin. Oxytocin is released in bursts so there is bursts of secretion (opposite to tonic secretion). Its release can be triggered by the cry of a baby even if the mother is not nursing anymore. Oxytocin is released under certain stress conditions as well so maybe there is an association between these two: studies showing the release of oxytocin in the son during different events. Parturition leads to higher increases in oxytocin followed by suckling. It is the central mechanisms that regulate the oxytocin secretion and people have found recently that kisspeptin fiber density around oxytocin neurons (magnocellular) in the supraoptic nucleus increases in late-pregnant rats. These fibers originate form the kisspeptin neurons in the periventricular nucleus and these fibers go around towards the supraoptic nucleus (not within it).
