Electrical characteristics and responses to jejunal distension of neurons in Remak's juxta-jejunal ganglia of the domestic fowl

Remak's nerve is a ganglionated nerve trunk found only in birds that runs parallel to the gut from the duodenal–jejunal junction to the cloaca. We report the first electrophysiological characterization of these neurons and their responses to gut distension. A segment of chicken jejunum with attached Remak's nerve was pinned in an electrophysiological chamber. Neurons in Remak's ganglia were impaled with microelectrodes. The adjacent segment of gut was distended with fluid. One hundred and thirty neurons were characterized into three electrophysiological classes: (i) tonic neurons (74 %) fired action potentials spontaneously (frequency 3.5 Hz) and continuously (up to 40 Hz) throughout a depolarizing current pulse; (ii) AD neurons (22 %) fired a brief burst of action potentials (1–10), which were followed by a prolonged after-depolarization (AD) of duration 2.8 ± 0.3 s; and (iii) phasic neurons (4 %) fired an initial burst of action potentials followed by an after-hyperpolarization (duration, 520.0 ± 32.0 ms). Tetrodotoxin (1 μM) abolished action potentials in tonic and AD neurons as well as the after-depolarization. Spontaneous fast excitatory postsynaptic potentials (FEPSPs) occurred in all classes of neurons; they were not observed, however, in ganglia isolated from the jejunum. Intracellular injection of biocytin revealed that neurons could be characterized into four morphological classes. Tonic neurons, which had long and extensive dendritic trees, were Remak's Type I, II and IV neurons. AD neurons also comprised Remak's type II neurons. Phasic neurons were Remak's Type III neurons. Most neurons had axons that projected orally along Remak's nerve. Distension of the jejunum evoked FEPSPs and action potentials in tonic neurons, and repetitive bursts of action potentials (1–4) followed by an after-depolarization in AD neurons. All responses to distension were blocked by hexamethonium (300 μM) and tetrodotoxin (1 μM). In conclusion, neurons in Remak's juxta-jejunal nerve appear to regulate gut motility. Three distinct electrophysiological classes of neurons were observed, all of which appear to be activated by distension sensitive cholinergic intestinofugal neurons in the jejunum.