The impact of the neuronal Kv7.2 current on cholinergic control of pancreas secretion

PROJECT SUMMARY The parasympathetic nervous system uses the vagus nerve to modulate the secretion of both insulin and digestive enzymes from the pancreas. Because of its diffuse innervation pattern targeting multiple visceral organs as well as the indirect approaches used to assess the role of the vagus nerve in the pancreas, interpretation of the existing evidence is difficult. Furthermore, intrapancreatic neurons, which are the exclusive targets and mandatory relays of the efferent vagus nerve in the pancreas, have not been sufficiently studied. It is widely believed that they act as mere conduits of vagal input and do not substantively contribute to autonomic control of pancreas function. In preliminary studies, I found that intrapancreatic neurons respond to cholinergic input through stimulation of both nicotinic (nAChRs) and muscarinic acetylcholine receptors (mAChRs). Neuronal responses elicited by mAChR activation, which do not occur in canonical parasympathetic ganglia, resulted in long lasting, rhythmic bursts of activity. Additionally, I found that intrapancreatic neurons possess the molecular and functional signatures of the neuronal M-current, a voltage gated K+ conductance mediated by Kv7.2/7.3 ion channels indirectly inhibited my mAChR activation. These results indicate that intrapancreatic neurons indeed possess functional characteristics supporting the notion that they are centers integrating and processing cholinergic input from the vagus nerve. I therefore hypothesize that intrapancreatic neurons transform cholinergic input through an mAChR associated mechanism and rely on the function of Kv7.2/7.3 ion channels to achieve efficient control of pancreatic targets. In Aim1, I propose to use living pancreas slices generated from a transgenic mouse model that expresses the genetically encoded Ca2+ indicator GCaMP3 in intrapancreatic neurons to understand the contribution of mAChR activation and associated M-Current inhibition on intrapancreatic neuron activity. I will also use electrophysiologic techniques to interrogate the M-Current. In Aim2, I will explore how Kv7.2/7.3 channels influence the transmission of neuronal input from intrapancreatic neurons to exocrine and endocrine targets within the pancreas following targeted neuronal chemogenetic stimulation. The rationale for the proposed research is that, if we want to develop therapies leveraging electrical stimulation of the vagus nerve to treat or prevent diseases like diabetes and pancreatitis, it is imperative to elucidate the mechanisms by which intrapancreatic neurons, not only relay, but integrate and transform vagal cholinergic input to the pancreas. Additionally, Kv7.2/7.3 channelopathies due to mutations in KCNQ2 and KCNQ3 can result in severe epilepsy and developmental delay as well as gastrointestinal symptoms and autonomic dysfunction. The proposed research is significant because it will produce mechanistic insight into how local intrapancreatic neurons functionally impact endocrine and exocrine compartments of the pancreas and will lay the groundwork for studying the impact of Kv7.2/7.3 channelopathies on pancreas function.