Researchers explain evolution of nervous system

A latest study has given an insight into how animal nervous systems evolved from simple structures to become the complex network transmitting signals between different parts of the body.

As part of the study, researchers used simple multicellular organisms called Placozoa to reveal the beginnings of the nervous systems found in more complex animals. The international research team found that Placozoa can coordinate their movement and body shape, in the absence of a nervous system, by signaling with small peptides between cells.

Professor Jekely, the lead researcher of the study, believes that a peptidergic signaling system allows a very high complexity of the behavioural organisation. The study is published in the journal of Current Biology.

Jekely said, "Each peptide can be used individually as a different signal, but the peptides could also be used sequentially or together in different combinations which allow for very high numbers of unique signals between cells. This explains how Placozoans can coordinate sophisticated behavioural sequences such as feeding."

Placozoans, the simplest of all animals, resembles a small, hairy disc about 1mm in size, with just three cell layers. Although they have no true nerve or muscle cells, they glide across surfaces in the ocean with apparent ease.

The new study explored how this multicellular animal with no nervous system can coordinate all the cells in its body to perform the complex behaviour.

They found that Placozoan cells contain a variety of small peptides, made up of 4-20 amino acids that are secreted from one cell and detected by neighboring cells as a means of communication.

Crucially, this echoes how more complex organisms use similar peptides, known as neuropeptides, for signaling within the nervous system.

Dirk Fasshauer, co-author of the study said, "These new findings show that outer appearances can be deceiving because cells that look the same are actually signaling with different molecules and are very likely to have different functions."

Using synthetically constructed versions of the Placozoan signaling peptides, the researchers could tap into this hidden signaling system to understand the role of each peptide in coordinating movement and body shape.

The experiments revealed that the peptides changed Placozoan behaviour within seconds. Each peptide had a unique effect, which in some cases was very dramatic.

The main behavioural changes caused by the peptides included crinkling, turning, flattening, and internal churning, a behaviour associated with feeding.

Dr. Frederique Varoqueaux, also from the University of Lausanne, added: "It might seem strange to use an animal with no neurons or synapses to study nervous system evolution, but although Placozoans are nerveless, you can still find within their cells the basic molecules needed for communication in complex nervous systems.

"So studying Placozoans can tell us more about the origins of neurons and how they became the body's control system.