Neurobiology of Intrinsic Primary Afferent Neurons

Project Summary / Abstract The gastrointestinal (GI) tract is the only organ system that is capable of intrinsic neural reflexes. These are initiated by a unique neuron type called intrinsic primary afferent neurons (IPANs). IPANs are key to orchestrating neural reflexes that allow efficient processing of meals for nutrient uptake by rapidly adapting to changing luminal content to alter vascular, secretory and motor function. In the guinea pig, IPANs use multiple mechanisms of neuroplasticity to adapt to inflammatory, hormonal and neural stimuli. From these studies it is clear that IPAN neuroplasticity mediates digestive disease. Even though the mouse has become the vertebrate animal model of choice for digestive disease, murine IPANs have lacked consensus markers making precise studies of mouse IPANs inconceivable. These issues are now resolved by our recent transcriptome and morphological analysis of the ENS, which challenges the dogma that IPANs are a single class of neuron, and suggest that rather there are four classes of IPANs. In combination with recent advances in morphological (i.e. tissue clearing) and physiological approaches (i.e. genetically-encoded markers and activity indicators) we are now able to study mouse IPANs in a relatively high throughput manner. The objective of this proposal is to test the overall hypothesis that different classes of IPANs possess morphologies and physiology that uniquely contribute to intestinal function. This hypothesis will be tested in a series of experiments designed to address three specific aims: Specific Aim 1: determine the structure of receptive fields and connectivity of murine IPANs; Specific Aim 2: determine responses of murine IPANs to mechanical and chemical stimuli; Specific Aim 3: determine the role of IPANs in gastrointestinal physiology. Collectively, these studies address a critical gap in our knowledge on the basic neural control of gut functions. Deciphering sensory capabilities and functional responses of molecularly defined IPANs are likely to pave the way for future improvements in diagnostic and therapeutic strategies of digestive disease.