Myenteric neurons of the mouse small intestine undergo significant electrophysiological and morphological changes during postnatal development

Organized motility patterns in the gut depend on circuitry within the enteric nervous system (ENS), but little is known about the development of electrophysiological properties and synapses within the ENS. We examined the electrophysiology and morphology of myenteric neurons in the mouse duodenum at three developmental stages: postnatal day (P) 0, P10-11, and adult. Like adults, two main classes of neurons could be identified at P0 and P10-11 based on morphology: neurons with multiple long processes that projected circumferentially (Dogiel type II morphology) and neurons with a single long process. However, postnatal Dogiel type II neurons differed in several electrophysiological properties from adult Dogiel type II neurons. P0 and P10-11 Dogiel type II neurons exhibited very prominent Ca2+-mediated afterdepolarizing potentials (ADPs) following action potentials compared to adult neurons. Adult Dogiel type II neurons are characterized by the presence of a prolonged afterhyperpolarizing potential (AHP), but AHPs were very rarely observed at P0. The projection lengths of the long processes of Dogiel type II neurons were mature by P10-11. Uniaxonal neurons in adults typically have fast excitatory postsynaptic potentials (fEPSPs, ` S-type' electrophysiology) mainly mediated by nicotinic receptors. Nicotinic-fEPSPswere also recorded fromneuronswith a single long process at P0 and P10-11. However, these neurons underwent major developmental changes in morphology, from predominantly filamentous neurites at birth to lamellar dendrites in mature mice. Unlike Dogiel type II neurons, the projection lengths of neurons with a single long process matured