LONG ABORAL PROJECTIONS OF DOGIEL TYPE-II, AH NEURONS WITHIN THE MYENTERIC PLEXUS OF THE GUINEA-PIG SMALL-INTESTINE

Enteric AH neurons, with multipolar Dogiel type II morphology, project around the circumference of the intestine to myenteric ganglia, the s ubmucosa and mucosa, Using retrograde labeling in vitro, intracellular recording, dye filling and immunohistochemistry, the projections of t hese neurons along the intestine were studied, When the retrograde tra cer, Dil, was applied to the myenteric plexus, labeled nerve cell bodi es were located up to 111 mm orally but only 13 mm aborally, demonstra ting a marked difference in the lengths of projections up and down the small intestine, Of labeled nerve cell bodies located 2-110 mm orally , 43% had Dogiel type II morphology and of these, 70% were immunoreact ive for calbindin, a calcium binding protein exclusive to Dogiel type II neurons, Intracellular filling with neurobiotin revealed several lo ng circumferentially directed nerve fibers and short, filamentous dend rites; thus these were ''dendritic'' Dogiel type II neurons. This clas s accounts for approximately 3-4% of all myenteric neurons, and about 10% of all Dogiel type Il neurons, Intracellular recordings revealed A H cell characteristics, with long afterhyperpolarizations following th eir action potentials, pronounced slow excitatory synaptic inputs and a lack of fast excitatory synaptic inputs. Antidromic action potential s could be evoked from the Dil application site in some cells, confirm ing their aboral projection, This is the first account of a major abor al projection of AH/Dogiel type II neurons and suggests an important r ole in aborally directed reflexes in the intestine.