Connectivity of a Praying Mantis Movement Detecting Neuron

Insects are not only important in research for pest control but also give us the opportunity to investigate the underlying neuronal principles of biological systems. They are rewarding to study as their neurons are often easy identifiable and accessible, in contrast to neurons of more complex organisms. The project Connectivity of a movement detecting neuron in the praying mantis aims to investigate the visual system of the praying mantis as the visual system is a good model for questions about the contribution of neurons in a neuronal circuit to the computation of information. The praying mantis uses stereopsis to estimate the distance to potential prey which distinguishes it from most of the other insects. With its unique stereo vison the praying mantis is a promising animal for neuronal studies of its visual system. Our main objective is to investigate neurons which contribute to the detection of potential predators. For an animal it is vital to recognise them early enough to start defence actions or to flee. Such a special neuron was described in locusts in the third optical ganglion, the lobula complex. Physiological experiments suggest that a similar neuron is present in the praying mantis. To verify this, we will use a new electron microscopic technique which is called ATUMtome SEM and allows us to produce several thousand of ultra-thin sections (with a thickness below 70 nm) through the lobula complex and collect them on a special tape for further investigations. In a scanning electron microscope the sections are scanned and neurons of interest can be tracked over consecutive sections. By that single neurons of whole neuron populations in the recorded volume can be traced and reconstructed. This allows us not only to reveal the morphology and ultra-structure but also the interactions between the neurons. The synapses, the structure were information is passed on from one neuron to another, can be easily identified in the electron micrographs. The knowledge about the wiring between the neurons is vital for our understanding of how the sensory stimuli are processed in the neuronal system. The collected image data in this project will be public accessible in an online database. Through this database other research groups all around the world can browse the data and use them for their research questions. This is necessary due to the amount of image data that will be produced during this project.

In the project " Connectivity of a Praying Mantis Movement Detecting Neuron" the brains of praying mantises were examined using high-resolution electron microscopy. The focus was on the brain region responsible for processing visual information. To obtain a detailed representation of the ultrastructure of individual nerve cells (neurons), in particular the chemical contact points, the so-called synapses, the sample preparation protocol was optimized, and the samples were subsequently prepared for scanning electron microscopy using a special sectioning technique. Animals from the Chinese mantis (Tenodera sinensis) were bred by the project partner at Kyushu University (Japan), and the dissected, fixed brains were sent to Graz for electron microscopic analysis. Samples from various developmental stages were collected to document the precise development of the connections (neuronal-connectivity) of the visual nerve cells. Investigating neuronal connectivity in biological systems, which have a comparatively simple neuronal structure, helps us draw conclusions about how information processing functions in significantly more complex brains, such as those of humans. During the course of the project, several series of sections were prepared. The largest, with over 3,300 individual sections, covers a length of approximately 200 m. From this series, a volume measuring 100 x 100 x 200 m was imaged using a scanning electron microscope at a resolution of 10 x 10 x 60 nm. Three-dimensional models of the nerve cells and their finest branches can be created within this volume. The morphology of the different nerve cells, in addition to their physiological properties, is an important characteristic feature for classification of those cells. Neurons over a length of more than 13 mm were documented within this volume. Along this length, over 350 synapses were identified. The sheer volume of data from this project will enable further research for many years to come. Ultimately, the collected data has added another piece to the puzzle of better understanding information processing in neural systems.