Cholera Toxin Induces Sustained Hyperexcitability in Submucosal Secretomotor Neurons in Guinea Pig Jejunum

Background & Aims: Neural mechanisms underlying cholera toxin (CT)-induced intestinal hypersecretion remain unclear. We investigated long-term excitability changes in vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) secretomotor neurons after prolonged luminal exposure to CT. Methods: isolated segments of guinea pig jejunum were incubated with saline or CT +/- neurotransmitter antagonist in the lumen; the submucosal plexus was then dissected clear, circumferentially adjacent to intact mucosa. Synaptic inputs and firing properties of S neurons in ganglia next to the mucosa in control saline were studied using intracellular recording. Neurons were processed for VIP and NPY immunoreactivity. Results: Thirty S neurons (20 VIP+, 7 NPY+, 3 VIP-/NPY-) from CT-treated preparations and 27 control S neurons (19 VIP+, 4 NPY+, 4 VIP-/NPY-) in ganglia adjacent to intact mucosa were analyzed. VIP+ and NPY+ neurons in CT-treated preparations fired significantly more action potentials and for longer periods during injected depolarizing current pulses (50-350 pA) than control neurons. Addition of tetrodotoxin, hexamethonium, granisetron, or the neurokinin-1 (NK1) antagonist SR140333 during the CT incubation blocked CT-induced effects in both neuron types. The NK3 antagonist SR142801 blocked CT-induced effects in NPY+ neurons and reduced the number of action potentials in VIP+ neurons. Synaptic activity was unaffected by CT. Conclusions: CT induces specific and sustained hyperexcitability of secretomotor neurons in enteric pathways. CT acts in the mucosa. Its effect is neurally mediated and depends on 5-hydroxytryptamine-3, nicotinic, and NK1 receptors. This system represents a unique model to understand the neural mechanisms of action of CT and to identify therapeutic targets.