Welcome to The Visible Embryo
The Visible Embryo Birth Spiral Navigation
Fetal Timeline--- -Maternal Timeline-----News-----Prescription Drugs in Pregnancy---- Pregnancy Calculator----Female Reproductive System

WHO International Clinical Trials Registry Platform

The World Health Organization (WHO) has a Web site to help researchers, doctors and patients obtain information on clinical trials.

Now you can search all such registers to identify clinical trial research around the world!




Pregnancy Timeline

Prescription Drug Effects on Pregnancy

Pregnancy Calculator

Female Reproductive System


Disclaimer: The Visible Embryo web site is provided for your general information only. The information contained on this site should not be treated as a substitute for medical, legal or other professional advice. Neither is The Visible Embryo responsible or liable for the contents of any websites of third parties which are listed on this site.

Content protected under a Creative Commons License.
No dirivative works may be made or used for commercial purposes.


Pregnancy Timeline by SemestersDevelopmental TimelineFertilizationFirst TrimesterSecond TrimesterThird TrimesterFirst Thin Layer of Skin AppearsEnd of Embryonic PeriodEnd of Embryonic PeriodFemale Reproductive SystemBeginning Cerebral HemispheresA Four Chambered HeartFirst Detectable Brain WavesThe Appearance of SomitesBasic Brain Structure in PlaceHeartbeat can be detectedHeartbeat can be detectedFinger and toe prints appearFinger and toe prints appearFetal sexual organs visibleBrown fat surrounds lymphatic systemBone marrow starts making blood cellsBone marrow starts making blood cellsInner Ear Bones HardenSensory brain waves begin to activateSensory brain waves begin to activateFetal liver is producing blood cellsBrain convolutions beginBrain convolutions beginImmune system beginningWhite fat begins to be madeHead may position into pelvisWhite fat begins to be madePeriod of rapid brain growthFull TermHead may position into pelvisImmune system beginningLungs begin to produce surfactant
CLICK ON weeks 0 - 40 and follow along every 2 weeks of fetal development

Developmental Biology - Brain Nerve Cells

Glutamate Stimulates Nerve Growth

Glutamate receptors affect development of brain cells...

Whenever we learn or save information, so-called ionotropic glutamate receptors play a crucial role in the process. These receptors are proteins located in the membrane of nerve cells that bind to the neurotransmitter glutamate. Glutamate causes excitation of the nerve cell, which transmits that excited state as a signal to its neighbors.

A subgroup of glutamate receptors, kainate receptors, are known to help regulate neuronal networks. Now, researchers at Ruhr-Universität Bochum (RUB) in Germany have discovered that these kainate receptors also affect the way nerve cells develop immediately following birth.

The research was headed by Alexander Jack PhD and Professor Petra Wahle from the Developmental Neurobiology research group, publishing their findings in the journal Molecular Neurobiology.

Cell activity affects dendrite growth

For their experiments, researchers used cells from the visual cortex of rats, adding small doses of kainic acid to cultures grown in their lab. "We observed that at a very early stage it caused cells to become much more active," explained Jack.
This increase in kainic acid activity affected the growth of a particular group of neurons called pyramidal cells. Pyramidal cells began growing more extensions that specialised in receiving signals and spread from the cell body towards the cerebral cortex.

human cerebral cortex

"We wondered which variant of the receptor is responsible for this phenomenon," says Jack. Subsequent experiments focused on the GluK2 subunit as the main suspect. GluK2 has long been known to affect the excitation of individual neurons and, as a result, to regulate the overall activity of entire networks.

Novel Research Approach

In the adult brain, these functions are crucial to higher cognitive function. "Not much research had been conducted to determine the role GluK2 plays in early maturation of nerve cells," explains Jack. Researchers then caused the nerve cells to produce greater amounts of the kainate receptor subunit GluK2, and observed how these manipulated cells became considerably more active earlier than typically expected. They also increased their dendrite growth.

Overall, researchers successfully tested a naturally occurring protein involved in the regulation of GluK2: tau tubulin kinase 2 (TTBK2). TTBK2 causes kainate receptors with a GluK2 subunit to be transported from the nerve cell membrane to within the cell where they cannot function. This is how the body can prevent excessive excitation of too many nerve cells.
Humans with a mutated TTBK2 protein suffer a motor disorder spinocerebellar ataxia type 11. It occurs from over-excitation in the spinocerebellum, within the cerebellum, causing neurons to die.
human brain cerebellum

In experiments conducted by Ruhr Universität Bochum biologists, overproduction of TTBK2 reduced neuronal excitation and branching of nerves - the exact opposite of effects triggered following enrichment of the GluK2 receptor.

During neuronal development, AMPA receptors (AMPARs) and NMDA receptors (NMDARs) are important for neuronal differentiation. Kainate receptors (KARs) are closely related to AMPARs and involved in the regulation of cortical network activity. However, their role for neurite growth and differentiation of cortical neurons is unclear. Here, we used KAR agonists and overexpression of selected KAR subunits and their auxiliary neuropilin and tolloid-like proteins, NETOs, to investigate their influence on dendritic growth and network activity in organotypic cultures of rat visual cortex. Kainate at 500 nM enhanced network activity and promoted development of dendrites in layer II/III pyramidal cells, but not interneurons. GluK2 overexpression promoted dendritic growth in pyramidal cells and interneurons. GluK2 transfectants were highly active and acted as drivers for network activity. GluK1 and NETO1 specifically promoted dendritic growth of interneurons. Our study provides new insights for the roles of KARs and NETOs in the morphological and physiological development of the visual cortex.

Alexander Jack, Mohammad I. K. Hamad, Steffen Gonda, Sebastian Gralla, Steffen Pahl, Michael Hollmann and Petra Wahle.

The project was funded by the German Research Foundation (no. WA 541/9-1 no. 541/9-2) and by the foundation Wilhelm und Günter Esser-Stiftung.

Return to top of page

Dec 11, 2018   Fetal Timeline   Maternal Timeline   News   News Archive

Rat pyramidal cell. Image: Research Gate.

Phospholid by Wikipedia