This week we learned how to identify neurotransmitters. We learned that there are three criteria that must be met for a molecule to be considered a neurotransmitter:
- The molecule must be synthesized and stored in the presynaptic neuron.
- The molecule must be released by the k
- presynaptic axon terminal upon stimulation.
- The molecule, when experimentally applied, must produce a response in the postsynaptic cell that mimics the response produced by the release of neurotransmitter from the presynaptic neuron.
All the methods to determine whether these conditions are fulfilled were not already familiar to us. Two quite similar methods to determine whether a transmitter candidate is localized in, and synthesized by, a particular neuron was introduced; Immunocytochemistry and in Situ Hybridization. Both of them rely on a marker that is attached to a molecule that reveals whether the transmitter candidate is synthesized by, and localized in a particular neuron. With Immunocytochemistry a colorful marker is placed to an antibody that color those cells that contain the transmitter candidate. In Situ Hybridization the marker is placed to the complementary strand of mRNA that sticks, when released to the tissue, to the mRNA molecule in the cell, where there are instructions to code the transmitter candidate.
Additionally, this week gave us some perspective that how difficult it can be to find some new information from biological systems. The process to identify whether a molecule is a neurotransmitter is a complicated task and the determination whether the candidate fulfills the first criteria is easy compared to the second and third criteria.
One thing that remained unclear was the function of single cascades. In this week’s quiz it was asked what are the benefits of single cascades over simple transmitter-gated channels. We had understood that single cascades are these kind of following events and do only occur in g-coupled-protein transmitters. In transmitter-gated channels the neurotransmitter binds to the receptor and has an immediate effect and there are no chain of events such as in g-coupled-protein receptors. Therefore, the quiz question made the concept of single cascades to remain unclear.
As another achievement of this week, we can mention the relation of neurotransmitter systems with normal central nervous system development. Neurons should have an efficient communication with each other in order the nervous system to have a normal function. Release of neurotransmitters and specialized receptors on target cells are the main parts involved in neuronal communication mechanism. Here we try to focus on three classes of chemical neurotransmitters only: (1) amino acids (2) biogenic amines and (3) other (e.g., adenosine, adenosine triphosphate, and acetylcholine)
Neurotransmitter release can be regulated by neurotransmitter receptors. Also the chemical neurotransmitter and its synaptic level can be decreased by enzymatic breakdown or reuptake into the axonal terminal. The recruitment of progenitor cells into the neural plate shows the beginning of development of the nervous system. By folding the neural plate the neural tube is formed, this is where the progenitor cells are transformed into neuronal and glial cells. Axons, dendrites, and synapses are gradually acquired once immature neurons travel to their ultimate location. The fact that whether synapses should be maintained or removed is determined by exchange of information between axons and dendrites, and in each of these neuronal developmental stages the chemical neurotransmitters own the key roles. Progenitor cell proliferation, migration, and differentiations are regulated by GABA and glutamate even before synapses are formed (1.Manent and Represa 2007). Growing axons can be where these neurotransmitters are released through reverse action of neurotransmitter transporters. Also, in immature neurons, the contribution of GABA and glutamate to the maturation of dendrites and axons and their participation in the generation and refinement of synaptic contacts should be taken into consideration (2.Cline and Haas 2008). Within development and maturity, neurotransmitter systems have different properties. For example, one of the key elements in the construction of neuronal networks is oscillatory electrical activity that is generated by neurons throughout the developing central nervous system. Neuronal circuits can be formed and matured through these particular properties, also susceptibility of immature neuronal networks to genetic or environmental insults can be made through these unique properties (3.Ben-Ari 2008).
Ruhoollah, Väinö and Maria
- Manent JB, Represa A. Neurotransmitters and brain maturation: Early paracrine actions of GABA and glutamate modulate neuronal migration. Neuroscientist. 2007;13:268–279.
- Cline H, Haas K. The regulation of dendritic arbor development and plasticity by glutamatergic synaptic input: A review of the synaptotrophic hypothesis. Journal of Physiology. 2008;586:1509–1517.
- Ben-Ari Y. Neuro-archaeology: Pre-symptomatic architecture and signature of neurological disorders. Trends in Neurosciences. 2008;31:626–636.