Electrophysiological and morphological features of myenteric neurons of human colon revealed by intracellular recording and dye fills.

Background: Ex vivo intracellular recordings and dye fills, combined with immunohistochemistry, are a powerful way to analyze the enteric nervous system of laboratory animals.

Methods: Myenteric neurons were recorded in isolated specimens of human colon. A key determinant of successful recording was near-complete removal of circular muscle from the surface of ganglia.

Key Results: Treatment with a collagenase/neutral protease mix before dissection significantly improved recording success and reduced damage to the plexus. Carboxyfluorescein in microelectrodes allowed recorded neurons to be routinely labeled, analyzed, and subjected to multi-layer immunohistochemistry. Carboxyfluorescein revealed morphological details that were not detected by immunohistochemical methods. Of 54 dye-filled myenteric neurons (n = 22), 45 were uni-axonal and eight were multi-axonal. There was a significant bias toward recordings from large neural somata. The close association between morphology and electrophysiology (long after-hyperpolarizations and fast EPSPs) seen in mice and guinea pigs did not hold for human myenteric neuron recordings. No slow EPSPs were recorded; however, disruption to the myenteric plexus during dissection may have led the proportion of cells receiving synaptic potentials to be underestimated. Neurons immunoreactive for nitric oxide synthase were more excitable than non-immunoreactive neurons. Distinctive grooves were observed on the serosal and/or mucosal faces of myenteric neurons in 3D reconstructions. These had varicose axons running through them and may represent a preferential site of synaptic inputs.

Conclusions: Human enteric neurons share many features with laboratory animals, but the combinations of features in individual cells appear more variable.