Introduction
This page is the second part of a study of the article
Adult neurogenesis: integrating theories and separating functions by James B. Aimone, Wei Deng, and Fred H. Gage
The maturation process of new neurons
Adult neurogenesis produces new neurons into the dentate gyrus. However, these neurons cannot function like an older neuron and also doesn’t have any connections with other neurons.
They have to develop into the neural circuit of the dentate gyrus from scratch, “do novo”.
There survival isn’t an assured fact either. There are chances that they don’t survive until maturation.
However, it was found that activities that stimulate the hippocampus such as exercise, new environments and learning can increase the chance of survival.
Stage 1 : up to 2 weeks
From their creation to 2 weeks after, the GABA neurotransmitter is extremely important for their survival and growth. The new cells receive mainly GABA inputs that help survival, migration and neurite outgrowth.
Neurite outgrowth
A neurite is any kind of projection from a young neuron. They will then develop to become axons and dendrites.
Neurite outgrowth is the process in which new extensions of the neuron are created.
As a result, mossy fiber axons start to extend.
One thing to note is that in the young cell, the GABA input is actually depolarising because of the high intracellular concentration of chloride ions.
Stage 2 : 2 to 3 week old
The NMDA receptor also becomes important in survival.
During this stage, several growth processes occur such as the formation of dendritic spines and rapid spine growth.
This means that dendrites start to appear and excitatory synapses from the mossy fiber axons to downstream CA3 neurons are created.
Downstream
A signalling pathway in which a response is caused after the activation of the pathway.
These links to other neurons mean the neuron starts to hold a function in the network.
Stage 3 : 19 days to 4 weeks old
The ionic concentration inside the cell changes cause the transition of GABA inputs from being excitatory to inhibitory. Although it is still more excitable and less inhibited than fully mature cells.
At 4 weeks, the density and composition of inward spines starts to develop and finally at 8 weeks, they are approximately mature.
Spine
The part of the axon that is involved in the synaptic transmission. The name comes from the shape of this part.
The number of their synapses becomes stable. But, they still have one difference in that they have a high plasticity.
Emotional states on neurogenesis
Emotional states are found in our everyday lives and have a big influence on memories, behaviours and our brains.
It is logical to think, considering the closeness of the amygdala to the hippocampus, they would have an impact on the growth of these new neurons.
For example, certain anti-depressants can increase the survival of new neurons.
They increase monoamine levels whose signalling regulates the effects on neurogenesis.
Monoamine
The group of neurotransmitters that holds one amino group.
Serotonin, dopamine and noradrenaline are a part of this group.
A pathway called the BDNF-TrkB signalling pathway is involved in the regulation of mood but not only.
BDNF TrkB signaling pathway
The response system of BDNF and its receptor TrkB.
It is involved in activity dependent neuroplasticity and also protects neurons from reactive oxygen species.
It was also found to be involved in survival, dendritic morphogenesis and LTP induction of new neurons.
Morphogenesis
The development of the shape of an organ, tissue, cell.
Accessible Science 
2 Comments