Synapses: NCBS: Zebrafish study reveals how the brain makes its connections

What is the News?

Researchers at the National Centre of Biological Sciences, Bengaluru, have studied Zebrafish to understand how Synapses are formed.

What are Synapses?

Neurons, or nerve cells in the brain, connect by means of junctions known as synapses through which they also transmit signals.

Types of Synapses

Chemical Synapses: In this, there is a space of about 20 nanometres between two neurons and the way they communicate is this: One neuron converts the electrical signal into chemical signals and this chemical is released into the synaptic space and the receiving neuron converts the chemical signal back into an electrical signal. 

Electrical Synapse: In this, the two neurons have a physical connection and the conversion of electrical to chemical need not occur, and they communicate directly. Electrical synapses are like a physical wire, communication is faster, but they are also fewer in number.

What was the study conducted by Researchers? 

It is known that electrical synapses are formed before chemical synapses. Electrical synapses are like a blueprint in which neurons make a handshake. This results in the making of chemical synapses. 

Research on organisms such as leeches showed that if one can remove electrical synapses, the chemical synapses do not form. However, the mechanism of how it happens in higher organisms such as vertebrates was not known.

Researchers have chosen Zebrafish as a model organism to study this process.(Zebrafish are transparent, and neuron development in larval zebrafish can be observed from day to day by injecting a dye or by engineering the fish to express fluorescent proteins).

What did the researchers find out?

The researchers found that knocking out a particular protein known as the gap junction delta 2b (gjd2b) in the cerebellum of zebrafish affected levels of the enzyme CaMKII. Levels of CaMKII were seen to increase in the Purkinje neurons in the cerebellum.

While zebrafish have about 300-400 Purkinje neurons, humans have thousands of these. In humans, for example, excess abuse of alcohol leads to damage of Purkinje neurons, which results in a lack of coordination in movement.

Moreover, the researchers found that in the absence of gap junction protein, CaMKII levels prematurely increase. Due to this, chemical synapses do not form.

Source: This post is based on the article “NCBS: Zebrafish study reveals how the brain makes its connections” published in The Hindu on 10th January 2022