Early Emergence of Neural Activity in the Developing Mouse Enteric Nervous System

Neurons of the enteric nervous system (ENS) arise from neural crest cells that migrate into and along the developing gastrointestinal tract. A subpopulation of these neural-crest derived cells express pan-neuronal markers early in development, shortly after they first enter the gut. However, it is unknown whether these early enteric neurons are electrically active. In this study we used live Ca2+ imaging to examine the activity of enteric neurons from mice at embryonic day 11.5 (E11.5), E12.5, E15.5, and E18.5 that were dissociated and cultured overnight. PGP9.5-immunoreactive neurons from E11.5 gut cultures responded to electrical field stimulation with fast [Ca2+](i) transients that were sensitive to TTX and omega-conotoxin GVIA, suggesting roles for voltage-gated Na+ channels and N-type voltage-gated Ca2+ channels. E11.5 neurons were also responsive to the nicotinic cholinergic agonist, dimethylphenylpiperazinium, and to ATP. In addition, spontaneous [Ca2+](i) transients were present. Similar responses were observed in neurons from older embryonic gut. Whole-cell patch-clamp recordings performed on E12.5 enteric neurons after 2-10 h in culture revealed that these neurons fired both spontaneous and evoked action potentials. Together, our results show that enteric neurons exhibit mature forms of activity at early stages of ENS development. This is the first investigation to directly examine the presence of neural activity during enteric neuron development. Along with the spinal cord and hindbrain, the ENS appears to be one of the earliest parts of the nervous system to exhibit electrical activity.