Recent work by researchers at the National Centre of Biological Sciences, Bengaluru, has thrown light on what stimulates the synapses (connection of nerve cells) to form.

What are Synapses?

• Neurons, or nerve cells, in the brain connect by means of junctions known as synapses through which they transmit signals.
• There are two types of synapses – chemical and electrical:

(1) Chemical Synapse

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

(2) Electrical synapse

• In these synapses, 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.

Observing these synapses

• Researchers from TIFR-National Centre of Biological Sciences, Bengaluru, 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.
• It was observed that electrical synapses are formed before chemical synapses, they 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 you 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.

What induces these synapses?

• The group observed 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.
• These neurons and the cerebellum itself control coordination of movements in the organism.

Why study this?

• In humans for example, excess abuse of alcohol leads to damage of these cells, which results in lack of coordination in movement.
• The cerebellum shows an evolutionary continuity in all vertebrates, so, too, the Purkinje neurons.
• Even though fish and humans diverged from a common ancestor about 500 million years ago, the cerebellum has been evolutionarily conserved.
• While zebrafish have about 300-400 Purkinje neurons, humans have thousands of these.

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