For the first time in history biologists have made a real time observation of how fish’s brain operates during hunting. The experiment was made possible thanks to the jellyfish genes that produce fluorescent proteins.Biologists from the National Institute of Genetics, Japan, contrived to record in real time the way nerve impulses are transmitted in the subcortical centres of fish’s brain responsible for analyzing visual signals during hunting. The new technology that allows visualizing signal interaction of neurons at the cellular level is likely to be employed as an effective way of studying core brain processes, on which perception, memory, analysis and decision-making are based.
The article featuring the description of the technology and experiments which helped the biologists to understand how a fish thinks was published on Thursday night in the Current Biology journal.
The problem of how exactly the brain perceives and processes information and forms motor commands while the operation surroundings around it are constantly changing, remains one of the fundamental questions of neuroscience. The opportunity to see how nerve impulses circulate in the brain of a living creature in real time without using crude invasive methods, such as measuring the electrical activity in nerve cells with the help of microelectrodes inserted into the brain tissue, appeared only after the method of fluorescentanalysis has been invented, in which fluorescent proteins, which are implanted into the body of an animal as a marker of cellular activity.
The scientists chose danio-rerio (or zebrafish) as model animal most convenient for direct visual monitoring of the brain’s work.
Not only are zebrafish a popular pet, but they also are a well-studied model organism which has first been implanted with fluorescentjellyfish genes as early as in 2003. The working of this fish’s brain lends itself to observation. First of all, zebrafish embryo and larva tissues are almost transparent, which allows direct observation of the modified cells’ green luminescence that makes the body of the fish glow blue. Secondly, in the course of 10 years genetic engineers have gained a lot of experience in breeding zebrafish modified in a way, that makes fluorescent protein be produced in particular cells, for example in neurons.
The larvae of zebrafish develop quite quickly and start to hunt their first prey – various species of micro plankton –by the fourth day after the fertilization. In order to make neurons in the brain of the fish glow at the moment of neuronal activity, the gene responsible for the fluorescent proteins has to be modified so that the intensity of the glow increases in proportion to the rise of calcium ion concentration at the moment of the impulse transmission between two neurones.
Thus, having implanted the neurons of the midbrain subcortical centres that function as visual processors with the fluorescent genes, biologists inserted a genetically modified sensor of calcium activity, which becomes active the moment the nerve cell is stimulated, into these neurons.
Immobilizing the larva in a specially designed reservoir, biologists stimulated the activity of its brain’s neurons first with the help of a moving blinking dot, projected on the LCD screen, and then, by live food, single-cell paramecia, swimming right in front of the larva. In each case the calcium sensors, implanted into the neurons of the subcortical ‘bumps’ became active the moment the impulse was transmitted. The stimulated neuron began glowing, allowing the chain of brain signals to be recorded, and synchronised accurately with the movement of the object in front of the larva. The experiment was monitored in real time with the help of a confocal microscope with a very high resolution.
The experiment allowed the scientists to see for the first time how a fish thinks when it feels there is something tasty within its reach.
For sure, 'thinking' in this case means a chain of signals appearing in the section of fish’s brain responsible for analysing visual information. However, the authors of the study claim that the technology may be used in order to create a more complex picture of the operation of the vertebrates’ spinal cord, which eventually will help to understand the neuron operation principles on which more complex processes are based, such as memorizing, learning, decision-making, emotions and motorcommands.
Source: The Voice of Russia
Image courtesy of ciamabue via Flickr (CC BY 2.0)
