A small group of nerve cells in the fish brain control swim posture

With the help of optogenetics, scientists are able to activate small sets of neurons (purple) within the nMLF-region of the zebrafish larva’s midbrain (red box). Credit: MPI of Neurobiology/ Thiele

For a fish to swim forward, the nerve cells, or neurons, in its brain and spine have to control the swishing movements of its tail with very close coordination. However, the posture of the tail, which determines swimming direction somewhat like a rudder, also needs to be fine-tuned by the brain's activity. Using the innovative method of optogenetics, scientists from the Max Planck Institute of Neurobiology in Martinsried have now identified a group of only about 15 nerve cells which steer the movements of the tail fin. Movements of the human body are also controlled via nerve pathways in the same region of the brain, which may therefore use processing mechanisms similar to those in fish.

For a long time, neurobiologists have been trying to find out how neuronal networks control both animal and human behaviour. In this context, there is controversy as to whether the brain's organisation is decentralised as opposed to modular. In decentralised organisation, the interaction of a large number of produces a specific behaviour pattern. If this is the case, cannot be assigned an exact function. On the other hand, if the brain has a modular structure, individual regions might possess certain competencies, each making a specific contribution to behaviour. These types of neuronal circuit modules could be combined in many ways and influence a broad range of different behavioural responses.

Switches in the fish brain?

Researchers in Herwig Baier's Group at the Max Planck Institute of Neurobiology want to get to the bottom of the brain's organisational structure with the aid of zebrafish larvae. A network known as the descending reticular formation is located in the brainstem of these animals. The neurons of that region are optimally suited for studying the organisation of the brain: the cells are in direct contact with in the spinal cord of the fish and can thus directly influence tail movements. "The reticular formation is a like a 'cockpit' for the fish, and we asked ourselves whether there are individual 'switches' or 'joysticks', which are used to control the movements of the tail", is how Herwig Baier summarises this challenge.

Functional significance of neuronal activity: During the experiment neurons in the nMLF-region are activated by blue light, which deflects the larva’s tail. Credit: MPI of Neurobiology/ Thiele

In their search for these switches, the researchers concentrated on a small brain nucleus (nMLF) within the reticular formation. But how can the influence of individual nMLF neurons on tail movements be studied? It is only recently that such investigations even became a possibility. Using the new method of optogenetics, the activity of can be influenced with light. Since a zebrafish larva – including its brain – is transparent, scientists can very accurately "switch on" small sets of genetically modified cells by exposing the larva to blue light. Consequently, tail movements that are induced in this way can be attributed to identified neurons.

Neurons and tillers

The first series of tests showed that the cells of the nMLF region seem to be involved in a variety of movements – from forward propulsion to rotational motion. A second experimental series using optogenetic stimulation, however, suggested that the cells control the deflection of the tail in particular. Are the nMLF cells thus part of a multifunctional centre or are they truly specialised to perform certain functions? To resolve this question, the neurobiologists performed another set of trials in which they very specifically removed small sets of nMLF cells from the circuit. "This experiment gave us our breakthrough", recalls Tod Thiele, lead author of the now published study.

The results show that, while nMLF cells are active in many aspects of swimming, a subset of these neurons contribute to only one part of the movement: they determine swimming direction through the posture of the tail. Thus, this population of neurons in the nMLF region are more akin to a specialised module within a decentralised control system of the swimming apparatus. Herwig Baier explains it like this: "We can compare the whole setup with the propulsion of a motorboat". The boat's engine, which drives the propeller, determines the thrust, whereas the tiller steers the boat. It seems that the tasks in the brain are divided up in a very similar way.

Some time ago, Herwig Baier's team discovered a small region in the hindbrain, which acts like an engine and propels the fish forwards. "With the nMLF cells, we have now also found the tiller in the fish brain", says Herwig Baier. In the human brain, movements are also controlled by a multitude of nuclei in the reticular formation. The study therefore suggests that the allocation of tasks in our could be similar to that of the zebrafish.

More information: Tod R. Thiele, Joseph C. Donovan, Herwig Baier, "Descending Control of Swim Posture by a Midbrain Nucleus in Zebrafish," Neuron, Available online 24 July 2014, ISSN 0896-6273, DOI: 10.1016/j.neuron.2014.04.018.

add to favorites email to friend print save as pdf

Related Stories

A brain area responsible for grasping

Apr 04, 2014

(Medical Xpress)—The research group led by Silvia Arber at the Friedrich Miescher Institute for Biomedical Research and the Biozentrum of the University of Basel has shown that limb motor control is regulated ...

Learning brakes in the brain

May 13, 2014

A brain capable of learning is important for survival: only those who learn can endure in the natural world. When it learns, the brain stores new information by changing the strength of the junctions that ...

Recommended for you

New ALS associated gene identified using innovative strategy

5 hours ago

Using an innovative exome sequencing strategy, a team of international scientists led by John Landers, PhD, at the University of Massachusetts Medical School has shown that TUBA4A, the gene encoding the Tubulin Alpha 4A protein, ...

Can bariatric surgery lead to severe headache?

5 hours ago

Bariatric surgery may be a risk factor for a condition that causes severe headaches, according to a study published in the October 22, 2014, online issue of Neurology, the medical journal of the American Academy of Neurol ...

Bipolar disorder discovery at the nano level

6 hours ago

A nano-sized discovery by Northwestern Medicine scientists helps explain how bipolar disorder affects the brain and could one day lead to new drug therapies to treat the mental illness.

Brain simulation raises questions

9 hours ago

What does it mean to simulate the human brain? Why is it important to do so? And is it even possible to simulate the brain separately from the body it exists in? These questions are discussed in a new paper ...

Human skin cells reprogrammed directly into brain cells

9 hours ago

Scientists have described a way to convert human skin cells directly into a specific type of brain cell affected by Huntington's disease, an ultimately fatal neurodegenerative disorder. Unlike other techniques ...

User comments