Nitric oxide neuritogenesis and synaptogenesis

The formation of functional connections, called synapses, between individual nerve cells enables them to communicate with each other and is therefore critical for nervous system function. This process is closely linked to the growth of nerve cells as only nerve cells that come into physical contact with each other can directly communicate. However, not all nerve cells that contact each other will also communicate. The formation of connections is a highly complex and specific process that organises nerve cells into functional networks for the processing of sensory information and the control of behaviour. This project will look at the relationship between the effects of the gas nitric oxide on the growth of nerve cells and the formation of functional connections between nerve cells. Functional connections between nerve cells are first formed during the development of the nervous system, but this process continues in the adult nervous system, where learning can induce the formation of new connections. Similarly, injury can trigger the re-organisation of connections in the adult nervous system. Interestingly, nitric oxide is known to play a role in all of these events. Nitric oxide synthase, the enzyme that produces nitric oxide, can be found in specific neuronal and non-neuronal cells from an early developmental state, where it has been shown to affect the growth of nerve cells. Blocking nitric oxide signalling also interferes with many forms of learning and the formation of long-term memories that are linked to the formation of new connections. Finally, nitric oxide appears to play a role in the re-organisation of nerve cell connections after injury. However, so far it is not clear whether nitric oxide directly affects the formation of connections, or whether nitric oxide has only indirect effects on this process by altering the pattern of nerve cell growth. Here, we will study directly the relationship between the effects of nitric oxide on the growth of nerve cells and the formation of nerve cell connections. We will use the nervous system of the common pond snail as a model system. The organisation of the snail's nervous system is less complex than the nervous system of higher animals such as mice. Furthermore, individual nerve cells are relatively large and easily identifiable. They are also accessible for experimental manipulations. Snail neurons can be isolated from the nervous system and maintained in cell culture, where they grow and form functional connections. Importantly, the basic processes and factors that control the growth of nerve cells and the formation of functional connections are highly conserved in all animals. Thus, the nervous system of the snail is an ideal model system for this study. The specific aim of the project is the study of the precise relationship between the effects of nitric oxide on nerve cell growth and the formation of functional connections in a selection of identified nerve cells. The results will show, what effects nitric oxide has on nerve cell growth and on the formation of functional connections. They will also show whether the effects of nitric oxide on nerve cell growth and the formation of connections are independent of each other, or whether nitric oxide's effects on the formation of connections depend on nerve cell growth. In a broader context, the results will contribute to a better understanding of the factors that control nerve cell growth and the formation of functional connections. This is relevant to the understanding of the development of the nervous system. It is also significant for the understanding of the processes that control nerve cell regeneration following injury. Finally, the results might provide some new insights why nitric oxide plays such an important role in many forms of learning and the formation of long-term memories that are linked to the formation of new connections between nerve cells.

The project will study the relationship between the effects of nitric oxide (NO) on neuritogenesis and synaptogenesis. These processes are intricately linked in the developing nervous system. However, whilst developmental studies have provided strong evidence that NO can affect neuritogenesis, the pattern of neuronal projections and nervous system organisation, it is less clear if it also has a direct effect on synaptogenesis. Here I will investigate how NO effects synaptogenesis between neurons that form physical contacts, and how this is related to changes in neuritogenesis. I will study the effects of NO on isolated neurons and neuron pairs in cell culture, and on neurons in the whole nervous system in tissue culture. Imaging techniques will be used to study the effects of NO on neuritogenesis, whilst electrophysiological and immunohistochemical methods will be used to study NO effects on the formation of functional synapses and the morphological organisation of synaptic structures. Pharmacological tools (NO donors, NO synthase inhibitors) will be used to either administer NO or to block endogenous NO production. The project is divided into three major objectives: - Effects of endogenously generated NO on neuritogenesis and synaptogenesis - Analysis of NO effects on neuritogenesis - Analysis of NO effects on synaptogenesis The results will be relevant to the understanding of the role of NO in neuritogenesis and synaptogenesis during the development of the nervous system. These processes also play a role during learning and long-term memory formation, and during the re-organisation of neuronal interactions following injury in the adult nervous system. Thus, the results can also contribute to a better understanding of a wide range of learning paradigms that are known to be affected by NO, and of the role of injury-induced up-regulation of NO synthase activity.