Hydra has a simple nervous system, which consists of a diffuse neuronal network (labeled here in purple), mostly abundant in the head and tentacles of the animal. In contrast to other animals where the loss of the nervous system is usually fatal, Hydra can survive and adapt to the absence of nerve cells and maintain some excitability and spontaneous pacemaker activity. After the nervous system is experimentally removed, epithelial cells reprogram themselves by expressing a series of genes and decapitated animals can regrow a new head in just eight days.
The animals were fixed and the nervous system was stained, and colored in purple, while the nuclei are labeled in green. The images were recorded with a confocal microscope.
Wanda Buzgariu, PhD and Brigitte Galliot, MD, PhD, Department of Genetics and Evolution, University of Geneva, Switzerland