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Nitric oxide modulation of locomotor control networks in the spinal cord and brainstem of a model vertebrate

Reference	BB/F015488/1
Principal Investigator / Supervisor	Professor Keith Sillar
Co-Investigators / Co-Supervisors
Institution	University of St Andrews
Department	Biology
Funding type	Research
Value (£)	359,868
Status	Completed
Type	Research Grant
Start date	10/10/2008
End date	09/10/2011
Duration	36 months

Abstract

The aim is to understand, on multiple levels, the modulation by nitric oxide (NO) of spinal cord and brainstem locomotor networks, from cells and synapses to network interactions and behaviour. We will utilize Xenopus frog tadpoles as a simple and accessible system where the swimming network, sources of NO and some NO mechanisms have already been characterized. We will describe how NO modulates the electrical properties of spinal neurons and synaptic interactions between them. Experiments will seek to understand the ion channels and conductances which enable NO to depolarize spinal motorneurons and increase their input resistance. At the level of synaptic connections in the locomotor network we will follow up on preliminary data indicating presynaptic inhibition of excitatory transmission by NO. Using anatomical techniques we will identify NO targets in the spinal cord and image how these appear during development. We aim to identify the co-transmitters of brainstem nitrergic neuron clusters and attempt to link NOS activity to locomotor activity using the DAF-2DA fluorescence method as a monitor of NO generation in brainstem neurons. This method, for which we have obtained 'proof of concept' for NO production in Xenopus skin cells, could also be invaluable in studies of brainstem NOS positive neurons, by facilitating visually-guided patch recordings. Patch clamp recordings from brainstem nitrergic neurons will be performed to characterize their activity patterns and describe how they respond to NO. To bring together these various strands of the project we will develop ideas relating to NO's role as a 'metamodulator' by testing the hypothesis that serotonergic and noradrenergic systems of the brainstem are mutually inhibitory and that NO alters the balance between them to influence subordinate spinal locomotor circuitry.

Summary

Only 20 years ago it was discovered that free radical gas nitric oxide is an important biological signalling molecule which controls the diameter of blood vessels. Since then nitric oxide has been found to play a wide variety of important roles in other types of tissue including the brain where it regulates nerve cell development, as well as numerous brain functions like learning and memory. How nitric oxide is able to participate in regulating electrical activity in virtually every region of the brain is still a bit of a mystery. However, we know that certain nerve cells can make and release nitric oxide which then controls the ability of other nerve cells to communicate with each other. One of the reasons why it has been difficult to make progress in because the brain of adult animals, especially mammals is extremely complex and nitric oxide can be produced simultaneously, not just by many different nerve cells but also by the myriad of blood vessels that ramify throughout the brain. The aspect of brain function that we have selected to study in order to gain insights into the basics of nitric oxide biology is the control of movement, particularly the neural networks of the spinal cord that control locomotion and how these networks are controlled by the brainstem. We study the far simpler networks located in the central nervous system of young frog tadpoles which are assembled to regulate swimming movements. Our previous work in this area characterized nerve cells that can manufacture nitric oxide and these are located exclusively in the brainstem. In this project we wish to understand more about these nerve cells and characterize what other neurotransmitters they are able to make and release. The nitric oxide nerve cells belong to specific clusters which project to the spinal cord so it will be important to understand their activity during swimming and how they interact with each other in the presence or absence of nitric oxide. The nitric oxide produced in the brainstem acts on nerve cells of the spinal cord that generate movement, called motorneurons. Nitric oxide changes the electrical activity of motorneurons and hence how they respond to signals that tell the tadpole to swim, but how does nitric oxide achieve this 'modulation' of motorneurons and rhythmic movements for swimming? The advantages of studying nitric oxide signalling in the brain and spinal cord of this simple model system are numerous. Importantly the neural circuits that regulate locomotion bear many similarities to those of adult vertebrates, including mammals because they all derive from a common ancestry and are therefore built on a similar plan. In addition, the relative simplicity of the networks at early stages of development mean that nitric oxide effects can be studied at the level of single cells and understood in relation to the behaviour being regulated. From an ethical perspective it is advantageous to be able to study mechanisms of nitric oxide function that are highly conserved in an organism that does not possess the brain power to detect pain in the way that adult mammals like mice and cats do, if at all. Finally, the nitric oxide system is one of tremendous therapeutic importance and therefore our work may yield important clues as to how the system can be manipulated to the benefit of mankind in the future.

Committee	Closed Committee - Animal Sciences (AS)
Research Topics	Neuroscience and Behaviour
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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