ELECTRICAL CHARACTERISTICS AND RESPONSES TO JEJUNAL DISTENSION OF NEURONS IN REMAKS JUXTA-JEJUNAL GANGLIA OF THE DOMESTIC-FOWL

1. Remak's nerve is a ganglionated nerve trunk found only in birds tha t runs parallel to the gut from the duodenal-jejunal junction to the c loaca. We report the first electrophysiological characterization of th ese neurons and their responses to gut distension. 2. A segment of chi cken jejunum with attached Remak's nerve was pinned in an electrophysi ological chamber. Neurons in Remak's ganglia were impaled with microel ectrodes. The adjacent segment of gut was distended with fluid. 3. One hundred and thirty neurons were characterized into three electrophysi ological classes: (i)tonic neurons (74%) fired action potentials spont aneously (frequency 3.5 Hz) and continuously (up to 40 Hz) throughout a depolarizing current pulse; (ii) AD neurons (22%) fired a brief burs t of action potentials (1-10), which were followed by a prolonged afte rdepolarization (AD) of duration 2.8 +/- 0.3 s; and (iii) phasic neuro ns (4%) fired an initial burst of action potentials followed by an aft er-hyperpolarization (duration, 520.0 +/- 32.0 ms). Tetrodotoxin (1 mu M) abolished action potentials in tonic and AD neurons as well as the after-depolarization. 4. Spontaneous fast excitatory postsynaptic pot entials (FEPSPs) occurred in all classes of neurons; they were not obs erved, however, in ganglia isolated from the jejunum. 5. Intracellular injection of biocytin revealed that neurons could be characterized in to four morphological classes. Tonic neurons, which had long and exten sive dendritic trees, were Remak's Type I, II and IV neurons. AD neuro ns 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. 6. Distension of the jejunum evoked FEPSPs and action p otentials in tonic neurons, and repetitive bursts of action potentials (1-4) followed by an after-depolarization in AD neurons. All response s to distension were blocked by hexamethonium (300 mu M) and tetrodoto xin(1 mu M). 7. In conclusion, neurons in Remak's juxta-jejunal nerve appear to regulate gut motility. Three distinct electrophysiological c lasses of neurons were observed, all of which appear to be activated b y distension sensitive cholinergic intestinofugal neurons in the jejun um.