Zebrafish Study reveals how the brain makes connections.

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News: How the nerve-end connections known as synapses form is highlighted in this study of Purkinje neurons in the cerebellum of knockout zebrafish. Read the news here.

Let’s Understand In Simple Language:

Nerve impulses are the basic currency of the brain. They allow neurons to communicate with each other. When a neuron spikes it releases a neurotransmitter, a chemical that travels a tiny distance across a synapse before reaching other neurons. This we know as the basic functioning of nerve impulses and how the information is processed. But recently, researchers at the National Centre on Biological Sciences, Bengaluru have found out what stimulates these synapses to form.

According to the research, there are two types of synapses:

  1. Chemical Synapse: Here one neuron converts electrical signal into chemical signal and this chemical is then released in to the synaptic space which is about 20 nanometers. Once this chemical signal is received, the neuron then converts the chemical back to an electrical signal. Thus following a communication process.
  2. Electrical Synapse: Here unlike the chemical synapse, the process followed is not that of conversion of chemical to electric or vice versa. Instead there is a physical connection between the two neuronsthrough which the communication takes place directly. They are like the physical wire through which the communication becomes faster, however they are fewer in number.
Image Credit: https://www.cell.com/current-biology/comments/S0960-9822(14)01490-0

Why Zebrafish was chosen?:

The zebrafish is a freshwater fish that is native to South Asia, especially in the Indo Gangetic plains. Because of its regenerative capabilities, it is a key vertebrate model organism used by researchers for drug development, especially for pre-clinical development. It is a tiny fish barely 2 to 3 cms long. This fish is transparent during the embryonic stages, allowing the observation of all organs, including heartbeats and blood circulation.

Zebrafish are transparent and the neuron development in the larval stage can be observed daily by injecting a certain dye or by injecting the fish to express fluorescent proteins. Zebrafish’s ability of transparency is the reason why the researchers at the National Centre of Biological Sciences, Bengaluru was chosen for study. In fact, the mechanism of a neuron handshake could be clearly studied in a zebrafish.

A neuron handshake is like a blueprint in which the neurons make a handshake or at least it appears as such. It was studied that the electrical synapses form before the chemical synapse, which appears to be making a handshake which results in the making of chemical synapses. Moreover, researchers have also found that if you remove the electrical synapses the chemical ones do not form at all.

Purkinje neurons:

A common query here is how do these synapses get induced in the first place?

The researchers 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 (or camk2). These levels of CaMKII then led to the increase of Purkinje neurons in the cerebellum. These neurons and the cerebellum controls the coordination of movements in the organisms.

Human cerebellum and Purkinje neurons, illustration. The human brain with highlighted cerebellum and close-up view of Purkinje neurons, one of the commonest types of cells in the cerebellar cortex.

Purkinje neurons are the neurons in vertebrate animals located in the cerebellar cortex of the brain. Purkinje cell bodies are shaped like a flask and have many threadlike extensions called dendrites, which receive impulses from other neurons called granule cells.

How is the Study of a fish valid for human brain funtioning?

Even though fish and humans diverged from common ancestors about 500 million years ago, the cerebellum has found a way to conserve. Thus the cerebellum shows an evolutionary continuity in all vertebrates including Purkinje neurons. Humans have thousands of such neurons whereas there are only 300 to 400 in a zebrafish.

Questions related to the topic:

Q. The term  CAMK is associated with which of the following:

A) These are the enzymes that get activated by increases in the concentration of intracellular calcium ions (Ca2+) and calmodulin.

B) They are nonmetallic substances used in furnaces.

C) They are like stents used in heart-related ailments.

D) It’s a chemical used for preserving grains.

Answer: A) CAMKCa2+/calmodulin-dependent protein kinase class of enzymes.

Q. Which of the following is true regarding Zebrafish:

  1. They are native to South Asian Plains.
  2. They are transparent which makes them lucrative for the study of heart and blood flow.
  3. They are 2 to 3 metres long which make them hard to study.
  4. These fishes are thick and cloudy at the embryonic stages and become transparent as they mature.


A) 1 and 2 only.

B) 1,2, and 4

C) 2,3 and 4

D) all of the above.

Answer: A)

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