Identification of enteric nerve circuits controlling gut motility

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Project Summary The enteric nervous system (ENS) is a semi-autonomous division of the autonomic nervous system. The ENS controls gastrointestinal motor function, absorption and secretion of nutrients and water and gut sensation. The nerve circuits controlling these important functions are incompletely mapped. In specific aim 1, we will use an antibody against the vesicular nucleotide transporter (VNUT), a protein marker for purinergic nerves to identify these pathways. Purinergic neurotransmission is important in the ENS but there are no data describing the purinergic neurons or pathways in the ENS. These will be important new data that will broaden our knowledge of enteric synaptic connectivity. In specific aim 2 we will use cre-lox technology and adeno-associated virus (AAV9) transduction of myenteric neurons to express the light-activated ion channel, channel rhodopsin-2 (ChR2) in specific neuronal subtypes. This will allow selective activation of specific functional classes of neurons (interneurons, motorneurons, sensory neurons) to determine their specific synaptic connections and the neurotransmitters that these neurons release. These studies will be done in mice and guinea pigs. We will use cre driver mice where cre is driven by neuron-subtype specific promoter (choline acetyltransferase, purines, nitric oxide synthase, 5-HT, for example) crossed with mice containing the floxed gene encoding ChR2. We will measure excitatory and inhibitory junction potentials (EJPs, IJPs) using microelectrode electrophysiology techniques to determine the neurochemical phenotype of neurons synapsing with excitatory and inhibitory motorneurons supplying the longitudinal and circular muscle layers. In specific aim 3, we will also use the cre- lox approach to study synaptic connections in myenteric ganglia. We will also use electrochemical methods to measure local release of ATP and nitric oxide (NO) from myenteric neurons. We will optically stimulate individual ganglia and make intracellular recordings from myenteric neurons on the oral and anal sides of the site of stimulation. We will use microelectrodes filled with neurobiotin so the recorded neurons can be identified in subsequent immunohistochemical studies to identify the neurochemical phenotype of neurons receiving synaptic input from the optically stimulated neurons. These studies will identify synaptic connections responsible for periodic propulsive colonic contractions. Successful completion of these studies will identify synaptic connections between neurochemically identified subsets of myenteric neurons. These connections control coordinated contractions and relaxation of gut smooth muscle leading to propulsion of gut content. A more complete understanding of these pathways will aid in identifying deficits in neural control of gut motility and identification of new drug or genetic treatments of gut motility disorders.